# Nvx Jad800.4 modification thread



## bnae38

This is a continuation from this thread: http://www.diymobileaudio.com/forum...3785-my-take-nvx-jad-900-5-5-channel-amp.html

No results yet, this is going to take some time. Read on.. 

Essentials of lab consists of Prism Sound Dscope IIIA+, modified server power supply at 13.4v (good to 60+A) and 4ohm or 2 ohm switched non-inductive loads on large aluminium bar.


I got the two Jad800.4 from user forty5cal1911 packaged in a diaper box late this morning. Gave me a chance to tell the fedex guy, "uhh that's not what i ordered". Nice looking little amps, smaller than i thought.

Plan is to get a good amount of measurements on one of them, do the mods discussed (TI opa1642 in place of all 10 tl072 opamps, replace sixteen 10uf caps, and eight 22uf caps, all in the signal path with Elna Silmics), make sure things are functional, then compare. If i decide i want to check something else or forgot something (like lpf/hpf filter response.. oops) i can look at the 2nd amp and compare before modding it too.. 

So.. amp1. First thing i wanted to do was check my diy classD filter i recently made based on the AP aux-0025. I don't really own any class D amps and had been bothered by measurement problems when i have worked on them. Class-D carrier signal can swamp the pre-amps in the measurement equipment and corrupt measurements. Harmoics also alias back in the fft that aren't really there. The filter is a ultra-low distortion and linear response design that is nearly dead flat to 20k. After-which the roll-off is slight to about 90-100k afterwhich it's straight down. I cant remember all the details off the top of my head. 

With no signal on ch1 I was looking at this with no filter at full 192k spread.









Insert filter in line: 









Sweet moving on.. i already knew insertion loss was minimal and there were only a couple other side effects when using it (mostly minimal phase rotation).


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## bnae38

Ok at this point i ran a few power thdn sweeps to get a feel for it. Honestly distortion is quite good off the bat. 

I went to get a feel for phase response and got this.










Ook, i must have wired something backwards. All 4 channels were the same. Checked it all. Three times.. Ran a loopback external dscope analog in to out, checked out fine. Did everything but hook up another unit to verify things worked as expected (I'd played with this a week or so ago). Messaged Phil (forty5cal1911) wondering if he thought it might be so.

He found this after a bit(read below):
https://www.sonicelectronix.com/i40254_NVX-JAD800.4-Product-Reviews.html 
___________
Good amp
June 21, 2016
Its a solid built amp. Great construction and very cool looking. Sound quality is flat which I prefer and have a DSP to shape the sound. This is my second JAD800.4, The first had issues and was replaced promptly by Sonic's. I do have one issue that seems to be a labeling mistake. The speaker terminals appear to be flipped. The silk screening on the amp seems wrong. Its written -+ -+ but when I plug it into an oscilloscope I see +- -+. I hope Sonics can figure this out. I wouldn't mind a second NVX but I really want the terminal labeling to be fix. If I'm wrong, I wish they would have explained why both amps are outputting not as labeled. Its a big deal for an active system like mine. I put a lot of time and effort in with an oscilloscope on each wire and a spectrum mic I want my speaker polarity to be correct out the gate. I have flipped mine so they are right but I wish I didn't have to figure that all out on my own.
______________

Huh.. ok well, they f'd that up. The user in that review didn't seem to think he had flipped polarity on all channels, now that i read it closer... but that's what i've found. All 4 outputs are 180 out of phase with the input.

Suppose absolute phase being flipped isn't the end of the world if all the channels are the same; but something to note. Of course you can just hook up all speakers backwards 


So that's what i did, at least for these tests. Phase response below (i have the class D filter disconnected here).


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## bnae38

Frequency power response, not too shabby, don't expect it to change much when we make the changes. Gain full ccw, 3vrms input (about 30w).














Thdn sweeps 

Note, thdn sweeps in this thread will not be under resistive load because it will be more stress than I care to put on the amps.. Results will be better than if loaded but still gives us a good baseline for comparison.


Gain full ccw: Here are all 4 channels at 1khz swept up to about 1% thdn with a 4ohm load. Maximum input is about 7.5vrms before things start to fall apart.









Gain halfway up: At this point .5vrms is about as hard as you can drive the input. Sweep is about 10mv to .5v. Note lower output thdn is noticeably higher, this is mostly noise contribution with gain up.









Thdn frequency sweeps with gain ccw at 3vrms (about 30w output). See this a lot, things get worse then better, but have to keep in mind the harmonics are falling out of range (22khz software lpf) once we hit a certain point. Hoping we get some help from new opamps here...


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## bnae38

Couple more things i looked at were s/n and cmrr.

Signal to noise at 1w (all 4 channels were nearly identical, gains full ccw for test).

~8.5dbu at 1w









~-74dbu with no input. (150ohm load made no difference on input rca)









=about 82.5db snr




Cmrr, kinda spitballed this one, but at least we'll have something to compare to. Cmrr is an amplifiers ability to reject equal signals on the + and - at the input terminals. 

3vin, gain ccw. 22.9dbu with normal balanced input.









Input (dscope output) changed to balanced common mode (it puts out the exact same signal on both the + and - output terminals). 

-58.4dbu









Cmrr is the difference, 81.3 db.


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## bnae38

Ok.. time to mod this one.

Took out all bottom screws. Removed the end panels (sorry for lack of pics), disconnected the top plate led wiring, and slid the top panel out. Then removed the switch pcb for the input section, is attached through some wiring that pops right out. 

Here's amazons nice pic again..










Heatsink clips didn't let me down, total pita as expected even with a large allen wrench to carefully pry them loose. Need to make sure you don't knock anything over when they break loose. Popped fets etc loose from heatsink and the board lifted (didn't slide) right up and out.

Quite a bit of stuff on the bottom of the pcb actually, irs2092 drivers are there (wondered..).










Here's where I'm at currently.









New caps are installed at power amp inputs (16pcs of https://www.mouser.com/ProductDetai...v%2bZEstMxvIk6/CCXNvb4FJwpyao9Ino/zi4CA422kEY). They are large here.. and kind of a pita to get in. Crosstalk might not be wonderful with all the caps touching each other. 

Opamps have all been replaced with opa1642, nothing exciting there..

The 8 input caps are not placed yet. We planned to use these https://www.mouser.com/ProductDetai...FXu%2bleNsmjcKbC2hku8PdmrQxjd4X5AWu3xy%2bMA== but they are way too big. The stock 22uf 50v cheapo caps are 5mm diameter caps. We're going with these instead. Should be here in a few days. https://www.digikey.com/product-det...oem1MbFQ0blA5VDdheFNrUjJZWWxhbDhkNGxNTkl2RyJ9


Note that the glue you find on top of the caps is not easy to break loose, i decided to just cut all 6 out at once in the input sections. The two caps between the 4 input caps are 100u 25v, i had some panasonics i replaced them with.


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## forty5cal1911

Absolutely *STELLAR* documentation!

You are the man! Op-amp job looks great!!!

Gonna take some time this afternoon to thoroughly look through the measurements.

Measurements on the factory amp looks pretty good. Certainly looks like NVX has published honest data as they document this amp @ 140 x 4 @ 4 ohm 1% thd.


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## wr3nchmonkey

forty5cal1911 said:


> Absolutely *STELLAR* documentation!
> 
> You are the man! Op-amp job looks great!!!
> 
> Gonna take some time this afternoon to thoroughly look through the measurements.
> 
> Measurements on the factory amp looks pretty good. Certainly looks like NVX has published honest data as they document this amp @ 140 x 4 @ 4 ohm 1% thd.


This is pretty awesome

Sent from my SM-G920P using Tapatalk


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## DeltaB

bnae38 said:


> I went to get a feel for phase response and got this.


Wait until you test again without the TL072 before you go bonkers on phase. The TL072 can do and does phase inversion at even moderate levels.


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## bnae38

DeltaB said:


> Wait until you test again without the TL072 before you go bonkers on phase. The TL072 does phase inversion at even moderate levels.


My arc ks amps are full of them, they don't do this. 

Will admit I wondered if that was it though, I tried many different input voltages and always got the same results.


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## bnae38

Although.. it's a mix of ne5532 and tl072/4 in the arc..

True enough.. could be 

Is hard to believe they labeled the outputs wrong.


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## PPI_GUY

Sub'd. 
Very interested to see the results with these upgrades. 
Personally I kinda like the cosmetics of the Polk PA D version. BTW, the Polk PA D5000.5 claims to be 1 ohm stable on the sub channel. This doesn't seem to be the case for the NVX, PPI, etc. Any ideas what's going on with that?


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## bob01464

Great work!!!...Yea I ran into the same problem with Cap spacing on the 900.5


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## DeltaB

bob01464 said:


> Great work!!!...Yea I ran into the same problem with Cap spacing on the 900.5


That's why I said what I did concerning voltages. Since there is not enough room to use the very best caps for signal path, (poly film) then electrolytic's that are higher end specifically for audio usage, do tend to have larger bodies for a given voltage then you can find for other usage like voltage pull-up. It's why I gave pics of the ones I used in my 900.5


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## forty5cal1911

DeltaB said:


> That's why I said what I did concerning voltages. Since there is not enough room to use the very best caps for signal path, (poly film) then electrolytic's that are higher end specifically for audio usage, due tend to have larger bodies for a given voltage then you can find for other usage like voltage pull-up. It's why I gave pics of the ones I used in my 900.5


Even so, for the input caps those Silmic II 35v 22uF's at 8mm are a very tight fit between the 100uF 25v and the heatsink.

I wanted to stay with 50v even though with +-15v 35v caps should be safe. Given that we wanted to stay with the 5mm casing size the Nichicon KW was the best bet at that size and voltage.


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## DeltaB

forty5cal1911 said:


> Even so, for the input caps those Silmic II 35v 22uF's at 8mm are a very tight fit between the 100uF 25v and the heatsink.
> 
> I wanted to stay with 50v even though with +-15v 35v caps should be safe. Given that we wanted to stay with the 5mm casing size the Nichicon KW was the best bet at that size and voltage.


For signal path, even as low 16v could be used without fear of circuit failure. On the voltage rails as a pull-up, you want at least the rating of the voltage of that rail, and a little to spare. That's where the 80% rule is a safe bet. (rating 20% greater than rail)


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## bnae38

Fyi, thdn sweep clipping points on post3 are wrong, it is closer to 125w afterall. I had a resize/fit option checked, it stretched them to 175w.. sigh. Correct info coming in the next few days with amp1 results.

Happy turkey day!


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## bnae38

bnae38 said:


> Fyi, thdn sweep clipping points on post3 are wrong, it is closer to 125w afterall. I had a resize/fit option checked, it stretched them to 175w.. sigh. Correct info coming in the next few days with amp1 results.
> 
> Happy turkey day!


Disregard that lol.. one amp has +/-38.3v rails and the other +/-35v. 1st graphs are ok, amp one has the hotter supplies 

Also glad i'm not a total measurement tard.. wondered wth was going on.


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## bnae38

1st amp is done, same with most of the measurements.

Nothing too exciting or improved much upon unfortunately. Filter response seems to be a bit wonky with new amps (hpf/lpf), but only in that it flattens a bit instead of staying linear in rolloff. I'll post up pics after modding amp2 and getting all the info i need..

Gotta tidy up some other stuff and make GD sure the new opamps aren't oscillating . 

Things i do know: 

The outputs are wrong. Absolute polarity +/- are swapped. I'm sure of that at this point. 

Also seems to be some variation in the power amp rails unit to unit. Some may get a nice boost in power it seems . Fwiw, playing with that would mean playing with the big trafo, rewinding etc. Nothing to tread lightly with... thinking some units may have an extra (or 1 less) winding somewhere.

Crosstalk was a concern with the power amp dc blocking caps so near each other, but did some checking on that, all is well.. I'll post that stuff too.


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## wr3nchmonkey

So are you saying that all of this didn't really change anything after all?


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## bnae38

wr3nchmonkey said:


> So are you saying that all of this didn't really change anything after all?


Well i was skeptical all along , but lets not forget, point was to make sure we didnt fubar anything either with the changes... . From that angle, things are good.. (still need to check lpf/hpf response on amp2, could be a little bit "off")


For the measurements i did, that is correct though. No real gains in noise, distortion or overall phase performance. An amp is only as good as the sum of it's parts/design. Not just the pre-amps.

Now.. I'm not equipped to run effective slew rate tests... and this could be where it gets interesting. I already bought parts to do the mods too to my Arc amps. Honestly i was hoping for some measurable difference in the basic performance of the amp... but one of my real hangups with my current system is during busy passages, there is something that just irritates me, i cant quite put my finger on it. All is well during less complex parts of music, but when things get busy...  Guess part of me hopes faster opamps might help there.


I'll wrap up my measurements and post the things that make sense to post, but the next real step is listening. That's where Phil (forty5cal1911) takes over .


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## dcfis

Your arcs are bothering you during heavy passages?


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## bnae38

dcfis said:


> Your arcs are bothering you during heavy passages?


Yeah, could be the tune


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## bnae38

Ok finished up data collection. Long and short of it is nothing improved to speak of for the things i looked into, nothing broke.. basically not a whole lot of change for thdn over power, thdn over frequency, phase response, etc. Kind of frustrating for me lol.. figured something would improve, but on the flipside it's good to see nothing broke.

I'll post some pics just for completion, but much of what we see just lays on top of each other or changes are test stand variance/negligible. 

Freq response:









Phase response (outputs +/- flipped):









Phase response compared to an arc ks300.2, plug and play. Ie, i dont see how i can be off base that outputs are labled backwards .










Gain down Thdn power response at 1k before and after, basically tracked the same.










Ditto for gain mid.










Thdn over frequency at 3v (~30w). Some variation, nothing i really thought to look closer at.










Snr and Cmrr did not change to speak of as well.

Couple things i did on amp2 were crosstalk and filter response before and after.

Crosstalk before and after results, no real change. Drove all unused channels to clipping (.1-7.5vrms at 1k). Upper trace is actual output for a connected channel in to out. Crosstalk would be the difference, typically 80db. Did the same test for all 4 channels. The yellow trace is at 3v and a frequency sweep.









Filter response wasn't as wonky as i thought when i compared apples to apples (same amp before and after). Phase tracked fine for all filters, didn't post that.










Last thing is showing the output difference between the two amps i have here. With unit to unit rails varying as they do, the clip point will be different.


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## JCsAudio

Bnae38,

Thank you for taking the time and money to perform this objective testing. This is the kind of thing that these forums need and it’s been interesting to watch this thread. I’m wondering what those individuals might think that swore they heard a difference and then see this thread and these tests? 

Thank you again.


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## wr3nchmonkey

So then what are these results really telling us?
There really isnt a difference between a budget amp and a high end amp?

Or is it that upgrading pre amp components will not turn a budget amp into a high end amp?



Sent from my SM-G920P using Tapatalk


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## forty5cal1911

There you have it gentlemen.

While the opamps are an obvious technical upgrade, for the standard amplifier metric tests the 1642's have translated into no measurable performance increase.

I was willing to take the plunge and have Ben document this for the benefit of the community at large.

A few things to keep in mind here. There are areas that are clearly beyond the scope of what could and should be tested here. With Integrated Circuits in Amplifiers they can wildly swing how a particular amp recovers from clipping. This is an area we will see a benefit with a higher speed opamp and will most definitely be audible.

As you can see from the NVX factory measurements, they are good amps out of the box. They put out their rated power with acceptable noise floor. No big revelation there.

Let's all give a big *THANK YOU *to Ben (bnae38) for doing such a spectacular job putting this all together!

I know that in several instances he went back and Triple and Quadruple checked some things just to make sure he was giving us verified data.

:2thumbsup:

I will follow up with listening test results once I get the Amplifiers back in.


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## DeltaB

V8toilet said:


> Bnae38,
> 
> Thank you for taking the time and money to perform this objective testing. This is the kind of thing that these forums need and it’s been interesting to watch this thread. I’m wondering what those individuals might think that swore they heard a difference and then see this thread and these tests?
> 
> Thank you again.


A couple of things to keep in mind. One, since no changes were made to the MOSFET output stage, or the driver stage, it is no surprise that a single tone sweep wouldn't create anything but the same THD and power. You would have to change to GAN FET and reduce shoot through time in order to get any significant improvement in THD for the finals. That's just part of MOSFET based Class D. Concerning NVX's issue with improper phase designations on their board or end cap is beyond my control, nor is the equipment that Ben is using, or it's calibration state. My JAD900.5 is quite stable in a lissajous plot for phase, and doesn't represent the phase shift seen in his equipment. (I use a cal'ed Tectronics TDS320 and Fluke generator)

Any testing for improvements of the input circuit concerning S/N, floor or oscillations would have to be made not after the finals, but between the input circuit and the driver section. Since the finals have L/C filtering to eliminate the driver section Class D 400kHz tone, it would not make sense to be testing it after the finals.

Concerning listening tests, I own one. I know what I'm saying, whether you may agree or not. This ain't my first rodeo. And to think that input section improvements will give an amp more power, or make a Class D a Class A amp, would be like saying changing to high performance tires will make 200 more HP in the engine. However, driving my JAD900.5 at any moderate level there is simply put, a significant improvement in audio reproduction quality.


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## wr3nchmonkey

DeltaB said:


> Concerning listening tests, I own one. I know what I'm saying, whether you may agree or not. This ain't my first rodeo. And to think that input section improvements will give an amp more power, or make a Class D a Class A amp, would be like saying changing to high performance tires will make 200 more HP in the engine. However, driving my JAD900.5 at any moderate level there is simply put, a significant improvement in audio reproduction quality.


The one you own has these upgrades? and the sound is definitely improved?


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## DeltaB

forty5cal1911 said:


> There you have it gentlemen.
> 
> While the opamps are an obvious technical upgrade, for the standard amplifier metric tests the 1642's have translated into no measurable performance increase.
> 
> I was willing to take the plunge and have Ben document this for the benefit of the community at large.
> 
> A few things to keep in mind here. There are areas that are clearly beyond the scope of what could and should be tested here. With Integrated Circuits in Amplifiers they can wildly swing how a particular amp recovers from clipping. This is an area we will see a benefit with a higher speed opamp and will most definitely be audible.
> 
> As you can see from the NVX factory measurements, they are good amps out of the box. They put out their rated power with acceptable noise floor. No big revelation there.
> 
> Let's all give a big *THANK YOU *to Ben (bnae38) for doing such a spectacular job putting this all together!
> 
> I know that in several instances he went back and Triple and Quadruple checked some things just to make sure he was giving us verified data.
> 
> :2thumbsup:
> 
> I will follow up with listening test results once I get the Amplifiers back in.


+1 on this


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## DeltaB

wr3nchmonkey said:


> The one you own has these upgrades? and the sound is definitely improved?


I do not have the 800.4. Mine is the JAD900.5, and yes, pics were posted in the 900.5 thread. Ben's comment is correct, and I have said it as well, that sound will only be as good as the weakest link, (he said sum of it's parts) and this is true, but driven at modest levels where THD is around 0.02 (which is the best THD of the gate driver can produce) yes, it's improved. We'll let 45 get his back and installed and he can give us his own opinion.


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## wr3nchmonkey

Well I am looking forward to that. If there is even a small improvement than IMO it is worth the little money and I will be purchasing the 800.4 and get these upgrades done. Then all I will have left to do is purchase a standalone DSP and eventually upgrade my sub and I think I will have an all around pretty damn good sound system.


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## bnae38

DeltaB said:


> A couple of things to keep in mind. One, since no changes were made to the MOSFET output stage, or the driver stage, it is no surprise that a single tone sweep wouldn't create anything but the same THD and power. You would have to change to GAN FET and reduce shoot through time in order to get any significant improvement in THD for the finals. That's just part of MOSFET based Class D. Concerning NVX's issue with improper phase designations on their board or end cap is beyond my control, nor is the equipment that Ben is using, or it's calibration state. My JAD900.5 is quite stable in a lissajous plot for phase, and doesn't represent the phase shift seen in his equipment. (I use a cal'ed Tectronics)
> 
> Any testing for improvements of the input circuit concerning S/N, floor or oscillations would have to be made not after the finals, but between the input circuit and the driver section. Since the finals have L/C filtering to eliminate the driver section Class D 400kHz tone, it would not make sense to be testing it after the finals.
> 
> Concerning listening tests, I own one. I know what I'm saying, whether you may agree or not. This ain't my first rodeo. And to think that input section improvements will give an amp more power, or make a Class D a Class A amp, would be like saying changing to high performance tires will make 200 more HP in the engine. However, driving my JAD900.5 at any moderate level there is simply put, a significant improvement in audio reproduction quality.


Delta,

All the rest aside, please share your phase shift information. Interested to see what you have. The way the analyzer measures phase is by looking at the phase difference of input 1 and 2. Input 2 is looped back inside the analyzer from output1, and output 1 goes through the uut and back to input1.



Guess we should keep in mind, you have the 5 channel as well not the 4channel. I don't see a way the polarity can be correct as labeled on the 4ch, but if you're seeing a different slope as well.. (ie i see about 30deg at 10k) I'd be curious.

Ben


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## DeltaB

bnae38 said:


> Delta,
> 
> All the rest aside, please share your phase shift information. Interested to see what you have. The way the analyzer measures phase is by looking at the phase difference of input 1 and 2. Input 2 is looped back inside the analyzer from output1, and output 1 goes through the uut and back to input1.
> 
> Guess we should keep in mind, you have the 5 channel as well not the 4channel. I don't see a way the polarity can be correct as labeled on the 4ch, but if you're seeing a different slope as well.. (ie i see about 30deg at 10k) I'd be curious.
> 
> Ben


I don't use PC based scopes. I use a true oscilloscope (Tectronix TDS320) utilizing a lissajous for phase. Initial cal was +60 degrees to bring them concurrent. It was flat across the audible spectrum. Concerning the incorrect labeling by NVX, as long as relative phase is maintained across all the channels, then it isn't that big an issue I guess, however, you would have to do an impulse test to see if swapping the phase when it may appear to be correct, is actually correct or 1 full wave forward or behind. (360 out)


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## bnae38

DeltaB said:


> I don't use PC based scopes. I use a true oscilloscope (Tectronix TDS320) utilizing a lissajous for phase. Initial cal was +60 degrees to bring them concurrent. It was flat across the audible spectrum. Concerning the incorrect labeling by NVX, as long as relative phase is maintained across all the channels, then it isn't that big an issue I guess, however, you would have to do an impulse test to see if swapping the phase when it may appear to be correct, is actually correct or 1 full wave forward or behind. (360 out)


Flat 20-20k? You realize that's pretty unlikely right? I was testing under load as well, didn't think of that.


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## bnae38

Not sure how removing load would affect phase measurement, I'll have to take a look... 

Would think driving a load would be better representation of how amp would perform there.. but then it's not a perfect representation of a speaker load (just resistive).. plus 4ohm load at that analyzer input may screw with things I guess.

Guess I'm all for learning.. you're clearly all for telling me what I'm doing wrong lol, so feel free.

Fwiw, if it wasn't obvious by now, I wouldn't have made the thread if I knew I wouldn't see any real changes. That would be stupid.... I figured noise would improve at a minimum.

On that note, it wasn't to rub anything in your face delta....


I have all the parts to mod my 6 channel, and have already started removing crap I want gone, all pots and switches. Going to hard set gain, and have no mechanical parts.. New opamps, silmic caps, then disconnect what's left in the crossovers..

I hope to hear a real difference after the upgrades, even though I probably won't measure any net gains.


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## DeltaB

bnae38 said:


> Flat 20-20k? You realize that's pretty unlikely right? I was testing under load as well, didn't think of that.


When you want to determine phase shift for a given circuit like an op-amp in the input buffer, you don't place the probe on the output of the finals. The same holds true for other measurements like insuring oscillations are not present.

http://www.ti.com/lit/an/slyt087/slyt087.pdf


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## bnae38

DeltaB said:


> When you want to determine phase shift for a given circuit like an op-amp in the input buffer, you don't place the probe on the output of the finals. The same holds true for other measurements like insuring oscillations are not present.
> 
> http://www.ti.com/lit/an/slyt087/slyt087.pdf



How does that apply to real world use of the product?? We're talking phase relationship input to output.


I understand only making changes to the pre-amps wont necessarily make things better in the grand scheme of things, but measuring half the circuit is pointless in this case..


Yes, i probed the outputs of most opamps in circuit for oscillations, obviously not at the output terminals.


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## DeltaB

bnae38 said:


> How does that apply to real world use of the product?? We're talking phase relationship input to output.
> 
> I understand only making changes to the pre-amps wont necessarily make things better in the grand scheme of things, but measuring half the circuit is pointless in this case..
> 
> Yes, i probed the outputs of most opamps in circuit for oscillations, obviously not at the output terminals.


If you want to do a complete redesign, start with GaN-FET. You will have to get out of MOSFET in Class D to rival Class A or AB2. If you want to leverage these advantages in Class AB2, it is much easier than Class D, (by using the right output devices and bias) and will equally benefit from input upgrades, given modern op-amp design.

Each element brings to the table it's own strengths and weakness. Obviously, discreet input sections driven at Class A will provide the best audio quality for the driver section. This is one of the circuit designs that was at it's apex in the middle to late 70's in some of the finest Class A and AB2 designs. Mac's still use it in their automotive line of amps. But that can take up room and be much costlier than a single op-amp. Since we are utilizing op-amps to provide signal buffering, and what I've been saying all along, (as well as TI and many other engineers out there, which even you have cited) is that the TL072 is not your friend. From noise to overshoot to phase inversion to audio quality... the list goes on. JFET allows and brings with it high capacitance input, and doesn't exhibit some of the problems an engineer has to confront on bi-polar designs. In the end, it's about providing the most faithful, in-tact signal reproduction from it's input to the next stage of amplification. And this is certainly audible. I'm sorry you didn't take time to A/B listen test when you had 2 identical amps, and one already done. But, it is what it is.


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## forty5cal1911

Received the Amplifiers yesterday and got them put in last night. Didn't do any real listening but physically hooked everything up in reverse polarity. I could immediately tell that the sub was out of phase with the front stage.

Doing some testing this morning.... so you'll have to wait for the full update.

I can also tell you this immediately, IASCA tracks 24 & 25 - noise tracks were dead silent at full volume, whereas they were not before. They had a very low volume noise previously. Now this could be due to some gain changes relative to pot position. I have the gains pots set at exact same level as prior. I will be putting the SMD DD-1 on it at some point to verify gain matching.

Just wanted to throw a quick update out there and will absolutely follow up with a comprehensive review.


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## bob01464

Look forward to your impressions. I got my 900.5 completed and confirmed everything works as advertised on my test bench but will not have the system done in the car for another month or so. So no critical listening till then for me.


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## DeltaB

forty5cal1911 said:


> Received the Amplifiers yesterday and got them put in last night. Didn't do any real listening but physically hooked everything up in reverse polarity. I could immediately tell that the sub was out of phase with the front stage.
> 
> Doing some testing this morning.... so you'll have to wait for the full update.
> 
> I can also tell you this immediately, IASCA tracks 24 & 25 - noise tracks were dead silent at full volume, whereas they were not before. They had a very low volume noise previously. Now this could be due to some gain changes relative to pot position. I have the gains pots set at exact same level as prior. I will be putting the SMD DD-1 on it at some point to verify gain matching.
> 
> Just wanted to throw a quick update out there and will absolutely follow up with a comprehensive review.


The most wonderful thing about reducing the noise floor, which is in fact part of S/N ratio, is when you have high dynamics (like the difference between quiet portions of a passage and high attack rates) in the complex content. It adds to the realism, especially when there is room acoustics like reverb and depth in the original track. It makes you want to go and listen to all of your old music again to hear the subtleties you didn't hear before.


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## forty5cal1911

First things first, my current set up:

NVX JAD800.4 - running tweets and midranges
NVX JAD800.4 - bridged to Midbasses (the unit that is putting out 175w per channel)
NVX JAD1200.1 - running Subwoofer

Signal is passed digital through the MOST bus to the Mobridge then digital to the Helix DSP.2 via toslink.

The first thing I did after getting everything hooked back up and gains set was to do a quick listen to make sure everything checked out. I could immediately tell the Sub was out of phase with the front stage. I popped into the DSP and knocked 180 deg off of the subwoofer phase control to compensate for the reversed (correct) polarity wiring. Honestly, when I was originally measuring the phase traces for the MB to Sub integration it should have prompted me to question why I had to have the Sub so far out to get them aligned.

Alright, now we're talking... everything sounding coherent again. Levels seemed pretty good and balanced still. Next, I ran a quick Impulse Response measurement @ 1K. Then inverted the polarity for that channel in the Helix and ran another IR measurement. I wanted to see why I didn't catch the inverted polarity system wide when aligning IR. Well... I incorrectly assumed that when hooked up in reversed polarity I should see the IR initial peak in the negative. That is not the case so I would not have been able to detect it via measurment.

Here's a shot of the IR comparison, you can clearly see that the reversed polarity (green trace) wave form is the same just (about) 180 degrees out of phase.










Ok cool. I'm satisfied.

Now on to the fun part some actual listening.

First thing I wanted to check was whether I could detect any improvement in noise. I used the new IASCA reference cd for this. Track 24 fades down and you attempt to keep the music at a comfortable level until you are at full volume. No noise at all on this one. Awesome! It did previously have low noise. The next track zero bit was dead silent as well at full volume. Beautiful that's an improvement for sure.

Some of the Albums & tracks I used for musical evaluation:

Steely Dan - Aja (Album)
Pentatonix - Pentatonix (Album)
Dave Matthews Band - Crash (Album)
Black Eyed Peas - the End (Album)
Norah Jones - the Fall (Album)
Phish - A Live One - Disk 1 (Album)

My next post will contain my impressions. *WARNING!* The following post will contain Subjective review information and opinion.


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## forty5cal1911

It should be noted here that I listen to my music pretty loud. Usually 60-80% on the Helix Master Volume control.

I should also note that I have always felt that the sound quality and detail from these amplifiers has been good.

My initial impression was that something does sound different. Hard to pinpoint what exactly. I got this impression as well the first night when I was function checking everything.

It's near impossible to determine what might be responsible for this. System wide phase change by 180 degrees should not be however a slight change in gain levels theorhetically could or a change in the clipping recovery of the new op amps. It's also possible that this is an example of confirmation or expectation bias. IDK

All of that being said, it does sound better. Not night and day better, but detectable.

The improvement is most noticeable during busy passages with a lot going on simultaneously.

From the DMB Crash album, two step and #41 were two tracks that I was a bit unhappy with at high volume as they've got a lot going on. This has improved with the new op amps.

Likewise for Phish & Steely Dan.

It is my opinion that indeed this upgrade has improved the performance of the amplifier. 

Is it worth it for someone else? No idea. I would encourage anyone looking to do the upgrade to critically listen and take notes prior to the swap. Our memory begins to forget musical material almost immediately.

Would I do it again? Absolutely

Ben did a top tier job on this! And again a big thanks goes out to him as well as DeltaB for stating his case and providing his first hand experience.


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## DeltaB

forty5cal1911 said:


> It should be noted here that I listen to my music pretty loud. Usually 60-80% on the Helix Master Volume control.
> 
> I should also note that I have always felt that the sound quality and detail from these amplifiers has been good.
> 
> My initial impression was that something does sound different. Hard to pinpoint what exactly. I got this impression as well the first night when I was function checking everything.
> 
> It's near impossible to determine what might be responsible for this. System wide phase change by 180 degrees should not be however a slight change in gain levels theorhetically could or a change in the clipping recovery of the new op amps. It's also possible that this is an example of confirmation or expectation bias. IDK
> 
> All of that being said, it does sound better. Not night and day better, but detectable.
> 
> The improvement is most noticeable during busy passages with a lot going on simultaneously.
> 
> From the DMB Crash album, two step and #41 were two tracks that I was a bit unhappy with at high volume as they've got a lot going on. This has improved with the new op amps.
> 
> Likewise for Phish & Steely Dan.
> 
> It is my opinion that indeed this upgrade has improved the performance of the amplifier.
> 
> Is it worth it for someone else? No idea. I would encourage anyone looking to do the upgrade to critically listen and take notes prior to the swap. Our memory begins to forget musical material almost immediately.
> 
> Would I do it again? Absolutely
> 
> Ben did a top tier job on this! And again a big thanks goes out to him as well as DeltaB for stating his case and providing his first hand experience.


You're certainly welcome. My best analogy to give as you get closer to real bit accurate reproduction, (and my home system is one of that caliber) it is like looking through a camera which is slightly out of focus, and the closer you get to being accurate, the sharper the image is as it comes into view. The ear and the brain are extremely sensitive to phase and the timing of accuracy. I'm saddened that your sub amp hasn't been done, because that is one area that would be improved more than just about anything by this upgrade. The muddiness goes away, and the attack which so much of music starts.


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## dcfis

So did you hook up the pos of your speakers to the neg of the amp our just hook them up as labeled?






forty5cal1911 said:


> First things first, my current set up:
> 
> NVX JAD800.4 - running tweets and midranges
> NVX JAD800.4 - bridged to Midbasses (the unit that is putting out 175w per channel)
> NVX JAD1200.1 - running Subwoofer
> 
> Signal is passed digital through the MOST bus to the Mobridge then digital to the Helix DSP.2 via toslink.
> 
> The first thing I did after getting everything hooked back up and gains set was to do a quick listen to make sure everything checked out. I could immediately tell the Sub was out of phase with the front stage. I popped into the DSP and knocked 180 deg off of the subwoofer phase control to compensate for the reversed (correct) polarity wiring. Honestly, when I was originally measuring the phase traces for the MB to Sub integration it should have prompted me to question why I had to have the Sub so far out to get them aligned.
> 
> Alright, now we're talking... everything sounding coherent again. Levels seemed pretty good and balanced still. Next, I ran a quick Impulse Response measurement @ 1K. Then inverted the polarity for that channel in the Helix and ran another IR measurement. I wanted to see why I didn't catch the inverted polarity system wide when aligning IR. Well... I incorrectly assumed that when hooked up in reversed polarity I should see the IR initial peak in the negative. That is not the case so I would not have been able to detect it via measurment.
> 
> Here's a shot of the IR comparison, you can clearly see that the reversed polarity (green trace) wave form is the same just (about) 180 degrees out of phase.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Ok cool. I'm satisfied.
> 
> Now on to the fun part some actual listening.
> 
> First thing I wanted to check was whether I could detect any improvement in noise. I used the new IASCA reference cd for this. Track 24 fades down and you attempt to keep the music at a comfortable level until you are at full volume. No noise at all on this one. Awesome! It did previously have low noise. The next track zero bit was dead silent as well at full volume. Beautiful that's an improvement for sure.
> 
> Some of the Albums & tracks I used for musical evaluation:
> 
> Steely Dan - Aja (Album)
> Pentatonix - Pentatonix (Album)
> Dave Matthews Band - Crash (Album)
> Black Eyed Peas - the End (Album)
> Norah Jones - the Fall (Album)
> Phish - A Live One - Disk 1 (Album)
> 
> My next post will contain my impressions. *WARNING!* The following post will contain Subjective review information and opinion.


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## forty5cal1911

dcfis said:


> So did you hook up the pos of your speakers to the neg of the amp our just hook them up as labeled?


Hooked them up reversed. IE positive speaker terminal to negative amplifier terminal and vice versa.


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## dcfis

Perfect, thanks!


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## dcfis

Huh, just hooked one up using the positive speaker to negative amp and after a quick listen seems to be out of phase. You think they might have marked them right on some?


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## bnae38

dcfis said:


> Huh, just hooked one up using the positive speaker to negative amp and after a quick listen seems to be out of phase. You think they might have marked them right on some?



Out of phase with what? 

Not sure, but i'd imagine they're all the same.


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## dcfis

How mines labeled. Does it match yours


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## dcfis

Specifically with my sub that was in phase with my mids. Also the image between the speakers sounded more l and r. Need to spend more time with it.


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## bnae38

dcfis said:


> Specifically with my sub that was in phase with my mids. Also the image between the speakers sounded more l and r. Need to spend more time with it.


Ah 10-4. Unsure how Phil's were labeled, doesn't look like i have pics.


Guess absolute phase is somewhat minor, just more of a surprise to me that these seemed reversed. Fwiw, i have my subs inverted and they sum best that way so need to keep in mind the big picture.

Best way to see if you hear a difference would be to try another amp in place with it's connections as it should and this one reversed (and see if they sum the same). I measured output phase 180 off vs my arc amps.


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## forty5cal1911

dcfis said:


> How mines labeled. Does it match yours


Yes that matches the labeling on mine. 

As Ben asked, out of phase in relation to what?

Sorry just saw your response dcfis. Yes your sub integration is going to be 180 deg off now that you've corrected the polarity on the front stage if it was perfect before. I had the same problem and it was the first thing I heard.


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## dcfis

I understand but it was a different amp. An xdi. It's pretty left and right sounding


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## bnae38

dcfis said:


> I understand but it was a different amp. An xdi. It's pretty left and right sounding


Xdi must be out of phase too. 

Hmm.. interesting.


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## forty5cal1911

dcfis said:


> I understand but it was a different amp. An xdi. It's pretty left and right sounding


What is your current setup?

If your front stage was previously wired up with the nvx according to the labeling, and your sub was wired on the xdi according to the labeling... and you had proper phase tracking between sub and midbass (or midrange). When you corrected the front stage by wiring in reverse you have shifted the phase by 180 degrees now. It's expected that the sub is not going to integrate properly now as it's phase rotation will need to be modified to get the phase tracing with your midbass aligned again.

Do you have Room Eq Wizard and a Mic? Are you using a DSP? If not simply reversing the sub polarity at the amplifier terminals will likely get you back in business.


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## bnae38

Oh I was thinking he tried an xdi 4ch.


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## forty5cal1911

bnae38 said:


> Oh I was thinking he tried an xdi 4ch.


Yeah I think you're right after re-reading that. That's why I added the question about his current setup.

I can 100% say that both of my 800.4's are labeled incorrectly. I would think that all those models would be the same but It's entirely possible they had it corrected at some point. Mine are 2015 & 16 manufacturing dates.

dcfis so you replaced a 4 channel xdi with the nvx and are trying to get it wired up properly?


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## dcfis

Ok I'm running a 2 way active from a dsp.2 to an xdi 4 channel. I replaced the xdi with the nvx 4 channel. I wired the nvx in reverse of the silk screening. So far the xdi is far more holographic between the speakers with pinpoint but small placement. The nvx is much more left and right sounding with diffuse placement.

I'll reverse the wires back or inverse on the dsp to see tomorrow. How do you check the manufacturing date?


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## forty5cal1911

dcfis said:


> Ok I'm running a 2 way active from a dsp.2 to an xdi 4 channel. I replaced the xdi with the nvx 4 channel. I wired the nvx in reverse of the silk screening. So far the xdi is far more holographic between the speakers with pinpoint but small placement. The nvx is much more left and right sounding with diffuse placement.
> 
> I'll reverse the wires back or inverse on the dsp to see tomorrow. How do you check the manufacturing date?


Manufacturing date should be on the bottom of the Amplifier.

It does sound like you've got something out of phase by your description. Have you modded your nvx or is it factory?

You can confirm correct polarity by running an impulse response measurement in REW.


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## dcfis

Thanks I'll pull up rew tomorrow. Mine is bone stock


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## dcfis

Mine is a nov 2016 manufacture


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## forty5cal1911

dcfis said:


> Mine is a nov 2016 manufacture


Mine from 2016 is a November manufacture as well.


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## dcfis

Well that seems to solve them changing anything


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## forty5cal1911

dcfis said:


> Well that seems to solve them changing anything


Yes I would say that almost certainly yours is reversed. You can confirm by running a measurement in REW (say a 1k sweep) and take a look at the Impulse tab. Correct polarity will have the peak that goes all the way to 100 at the top, reverse polarity will have the peek that goes all the way to 100 at the bottom. 

You can see this in my previous post with IR images.

http://www.diymobileaudio.com/forum/5176858-post42.html

Stage should not sound diffuse or pulled out to the edge of stage width. On mine for example staging and location are exact and focused. For example on the IASCA disc "Hollywood Love" track the vocalist is dead center with the bongos right of center, acoustic guitar far right and piano behind vocalist as the liner notes reflect.


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## dcfis

Ok I'll still need to do impulse but after adjusting the levels tweets low and right mb was low things are shaping up much better image wise with a bit bigger center image which I am digging. One thing though is I have a turn on pop both amps are turned on by the helix and I've never had it before. Any suggestions?


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## bnae38

dcfis said:


> Ok I'll still need to do impulse but after adjusting the levels tweets low and right mb was low things are shaping up much better image wise with a bit bigger center image which I am digging. One thing though is I have a turn on pop both amps are turned on by the helix and I've never had it before. Any suggestions?


Not sure, i havent had one in a car. 

Can try playing with the turn on/turn off delay settings on the helix (think that's a thing.. maybe i'm remembering the ps8)


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## wr3nchmonkey

So i ended up opening a box with one of these this morning. Is there anyone willing to do these modifications and for how much?

Sent from my SM-G920P using Tapatalk


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## bnae38

wr3nchmonkey said:


> So i ended up opening a box with one of these this morning. Is there anyone willing to do these modifications and for how much?
> 
> Sent from my SM-G920P using Tapatalk


I can. Send me a pm, can work out details. Prob plan on 60-70, plus parts and return shipping.


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## wr3nchmonkey

Well, my amp is being shipped over to Bnae can't wait to get it back. Not sure it really matters but I'll be happy to share my opinions once it's installed in my trunk. Pretty excited


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## Gump_Runner

wr3nchmonkey said:


> Well, my amp is being shipped over to Bnae can't wait to get it back. Not sure it really matters but I'll be happy to share my opinions once it's installed in my trunk. Pretty excited


Any updates?


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## wr3nchmonkey

Gump_Runner said:


> Any updates?


Yes, I apologize that I never followed up on this. I did ship my 800.4 to Bnae, he performed the modifications, and now this amp has been installed for several months.

Honestly, I am very happy with it. I am using this amp to power my Focal 165K2 drivers. One channel for each of the two tweeters, and one channel to each of the two midbass. Using the active crossover built into the amp. Excellent power to the midbass, I listen to a lot of different types of music and it seems to perform well in all cases. When listening to metal and hardcore stuff, the kick drum is tight and punchy, and the bass guitar is much more noticeable. The imaging also seems to be a bit more precise than it was before, but that could be just psychoacoustics. The biggest difference for me, is the clarity in music that is more complicated. I notice that there is less "mushiness" if you will, during a track that has multiple instruments playing at the same time.

Worth the time and money, In my opinion


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## Gump_Runner

wr3nchmonkey said:


> Yes, I apologize that I never followed up on this. I did ship my 800.4 to Bnae, he performed the modifications, and now this amp has been installed for several months.
> 
> Honestly, I am very happy with it. I am using this amp to power my Focal 165K2 drivers. One channel for each of the two tweeters, and one channel to each of the two midbass. Using the active crossover built into the amp. Excellent power to the midbass, I listen to a lot of different types of music and it seems to perform well in all cases. When listening to metal and hardcore stuff, the kick drum is tight and punchy, and the bass guitar is much more noticeable. The imaging also seems to be a bit more precise than it was before, but that could be just psychoacoustics. The biggest difference for me, is the clarity in music that is more complicated. I notice that there is less "mushiness" if you will, during a track that has multiple instruments playing at the same time.
> 
> Worth the time and money, In my opinion


Awesome! How much was everything total?


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## bnae38

Think i charged $125 all inclusive.

About $47/shipped in parts, and minus return shipping left me a little meat on the bone..


Pretty swamped at the moment with other projects, work and vaca coming up though


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## Tcheeks38

What exactly is everyone claiming is out of phase? Front from Rear or each right from each left output? If I have a sub on a separate amp does that mean my mids/highs share the same rel phase but are out of phase from my subs?


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## DeltaB

Tcheeks38 said:


> What exactly is everyone claiming is out of phase? Front from Rear or each right from each left output? If I have a sub on a separate amp does that mean my mids/highs share the same rel phase but are out of phase from my subs?


The silkscreen can be incorrect. Or, some don't pay attention that on some, like my JAD900.5 positive phase alternates from the upper to lower row of screws depending on channel/front-rear.


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## bnae38

Tcheeks38 said:


> What exactly is everyone claiming is out of phase? Front from Rear or each right from each left output? If I have a sub on a separate amp does that mean my mids/highs share the same rel phase but are out of phase from my subs?


The outputs are 180degrees out of phase in relation to inputs (at least as marked - can always just hook up speakers backwards). Not a big deal until you add another amp into the mix that does not invert, would need to keep this in mind when it comes to channels summing at XO etc.


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## forty5cal1911

These amps are still running strong for anyone who may be wondering.  Thanks again Ben!


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## bnae38

Glad to hear, thanks bud


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## bbfoto

forty5cal1911 said:


> These amps are still running strong for anyone who may be wondering.  Thanks again Ben!


NVX JAD 800.4 @ Sonic Electronix
The NVX JAD800.4 is currently $169.99 at Sonic...I believe that's 25% off. Not sure if they've always been this price?

Great deal nonetheless.


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## forty5cal1911

bbfoto said:


> NVX JAD 800.4 @ Sonic Electronix
> The NVX JAD800.4 is currently $169.99 at Sonic...I believe that's 25% off. Not sure if they've always been this price?
> 
> Great deal nonetheless.


Yes they were $199 when I bought mine. They're probably trying to get rid of old stock as I think all the JAD models have been discontinued and replaced with the VAD?


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## bnae38

Yeah I very nearly picked one up on Black Friday when they were $150. I have too many amps laying around already though .

Good price either way, think they are great little amps.


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