# Mid-Power Amplifier Test



## Nemesis87 (6 mo ago)

As I continue the build for my VW Golf Alltrack, I’ve somehow acquired a lot of amplifiers that I want to try out. I originally started with two but ended up with around 9 or 10.

The test is going to be fairly straight forward, with the main goal being to determine the real world differences between each amp at normal music listening levels.

I haven’t quite figured out how I’m going to run the source but I know I’ll be using my Windows laptop with REW and a calibrated mic.

The speakers are Illusion Audio L6 components, passive, bi-amped, with the woofers in the lower part of the doors and the tweeters in the a-pillars. That should keep things fairly consistent but maybe I’ll trying active, through the DSP later.

The plan is to set each amplifier with the same SPL output reading using pink noise or sine waves (200hz and 3,500hz) OR set each amplifier to the same output voltage (15 to 20v) with the speakers connected. Then take measurements at the low and high range that REW will accept. Ideally the graphs will be the same, only offset, but we’ll see if a slight increase in demand does anything.

All the amps are roughly 75 to 100 watts rms, are class AB (except for 2) and should be each company’s own design. Some are supposed to be the best of their kind, others just basic stuff. 

*Still looking for an ARC 4100SE and a similar Mosconi.*


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## Nemesis87 (6 mo ago)

The Setup:

Source - Lenovo L580 Laptop -> NuForce uDAC-2 -> Helix DSP.3
Baseline Amplifier - TRU Tungsten 4RS-HV
Speakers - Illusion Audio L6, passive, bi-amped.

Measurement mic - Dayton Audio U-MM6
DMM - Fluke 325
RTA - Phonic PAA3
Oscilloscope - DSO Nano v3.

Real-World Signal Path:
Apple iPhone XS
Apple Lightning to USB cable
VW Golf Alltrack HU (Model XX?, eq flat, position centred)
VW MOST150 cable
NavTV ZenV (jumper settings…)

*Output 1* (FL) - to amp input channel *1 - Left Tweeter*
*Output 2* (FR) - to amp input channel *3 - Right Tweeter*
*Output 3* (FL) - to amp input channel *2 - Left Woofer*
*Output 4* (FR) - to amp input channel *4 - Right Woofer*
4 Channel Amp, crossovers set to FULL
*FL / Channel 1* Output - Left passive: *Tweeter IN
FR / Channel 2* Output - Left passive: *Woofer IN
RL / Channel 3* Output - Right passive: *Tweeter IN
RR / Channel 4* Output - Right passive: *Woofer IN*.

Test Method:

Play music at *NORMAL* listening level. Switch to pink noise and measure amplifier input and output voltage and SPL.
Play music at *LOUD* listening level. Switch to pink noise and measure amplifier input and output voltage and SPL.


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## Nemesis87 (6 mo ago)

The Contenders:

Arc Audio XDi 1200.6
6 x 150, Class D, xx A

Brax X2400
4 x 100, Class AB, 100 A

DLS Reference RA50
4 x 70, Class AB

Euphoria FX 90.4
4 x 90, Class AB, X A

Ground Zero GZUA 6.200SQ-Plus
4 x 110, Class AB, Adjustable Bias

Helix G FOUR
4 x 80, Class AB, 60 A

MMats HiFi-6150D (Class D)
4 x 150, Class D, ‘Best Components’

MMats SQ4100
4 x 100, Class AB, 30 A!?

Mosconi Zero 4
2 x 100 + 2 x 210, Class AB, 150 A

Rockford Fosgate Punch P600X4
4 x ‘75’, Class AB, PEQ, 100 A

TRU Technology Tungsten T4RS-HV
4 x 100, Class AB, High-Voltage, 60 A

Wildcard
Similar power, ‘budget’ brand.


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## Nemesis87 (6 mo ago)

Just a quick note on measurements before we get to some data. I think some people might get confused when they read a spec. giving the accuracy of a particular measurement device and are quick to dismiss data that fall within that range.

If there is a metal meter rule, that has cm and mm gradations along it’s length, with an accuracy given as 2 mm, it means that under a given set of parameters and over its intended operating range, the measurement made with it can only be accurate (absolute) to within 2 mm. Reading 783 mm can be anywhere between 781 and 785 mm (absolute). What it DOES NOT mean is that if I measure something as 585, turn around and measure 585 again that one measurement can actually be 583 and the other 587. No, they are in fact the same. This information is given so you know there is some deviation when comparing measurements at different times and under different circumstances or across devices.

Have you ever wondered why a set of digital callipers, that claims to be accurate to 0.1 mm even bothers to read to 0.05 mm? It’s because the absolute measurement has that degree of accuracy, over the entirety of its intended operating range, and not that each measurement taken with it could be off by 0.1 mm. This seems to confuse people more than I thought so hopefully it makes more sense now.

This is exactly why for this amplifier test I’m going to be running all the amplifiers at the same time, under the same conditions, AND THEN compare their results. Had the tests been carried out over a period of days, or even at different times throughout the day, the results might not be useful, or only as useful as tolerances allow. But instead, by keeping as many variables as constant as possible, this should give some good insight as to what the actual differences between these amplifiers are.

At their core, they are nothing more than a well organised series of different, known materials in contact with each other, with electricity flowing through them.

Results:


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## abbispa (Feb 24, 2015)

Results?


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## Nemesis87 (6 mo ago)

abbispa said:


> Results?


Still waiting on some more stuff to arrive; amps speakers, connectors.

Any particular amp or performance metric you’re interested in?


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## abbispa (Feb 24, 2015)

All of them, and could possibly send a few your way.
I love the idea of empirical data.


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## clange2485 (Dec 10, 2020)

This sounds awesome! I’m no expert but why not use the PC as the controlled testing source for everything and i know you mentioned before trying to keep the electrical system in check so maybe clamp it and check each amp individually as well. I’m sure some are more efficient then others and might be something you factor in down the road. Also the rew measurements are a great idea but I’m thinking your ears are going to be the ultimate judge.


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## Nemesis87 (6 mo ago)

abbispa said:


> All of them, and could possibly send a few your way.
> I love the idea of empirical data.


That would be awesome! I’ve pretty much had to buy all these amps (except the Wildcard) just to see what they sound like. If you have any that might fall into this category, I’d love to throw them in. Sending you a PM.


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## Nemesis87 (6 mo ago)

clange2485 said:


> This sounds awesome! I’m no expert but why not use the PC as the controlled testing source for everything and i know you mentioned before trying to keep the electrical system in check so maybe clamp it and check each amp individually as well. I’m sure some are more efficient then others and might be something you factor in down the road. Also the rew measurements are a great idea but I’m thinking your ears are going to be the ultimate judge.


The PC will be the source for the tones, pink noise, sweeps etc., but I wasn’t sure if I was going to plug the computer straight into each amp, or pass it through something else first.

I do plan to get voltage and current readings for whatever standard signals I choose to test with. Should be able to get some real-world listening-level efficiency data like you mentioned. That’s also why I made note of the required fuse amperage beside each amplifier. Even though they are all supposed to be putting out similar power, current draw is all over the place. The Brax was drawing almost twice the current as the GZUA with all 6 channels on high bias mode!


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## Nemesis87 (6 mo ago)

clange2485 said:


> This sounds awesome! I’m no expert but why not use the PC as the controlled testing source for everything and i know you mentioned before trying to keep the electrical system in check so maybe clamp it and check each amp individually as well. I’m sure some are more efficient then others and might be something you factor in down the road. Also the rew measurements are a great idea but I’m thinking your ears are going to be the ultimate judge.


I might add something, like the TRU line driver or Audiocontrol EQX, just to get the PC output voltage on par with what a typical head unit might put out, that way I don’t have to rely on unnecessarily high amps gains to make up for the laptop’s weak signal.

Edit: I literally just figured this out and now realised why I was unsure about the method. Thanks for asking! Hahaha


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## hurrication (Dec 19, 2011)

So you're re-creating the Richard Clark amp challenge? AFAIK, nobody has actually successfully passed his challenge yet and it's been almost 2 decades.


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## Nemesis87 (6 mo ago)

Not really. I ended up with a bunch of amps and wanted to see what measurable differences there were, if any. I’m sure the Richard Clark set up is well designed and tuned to negate any difference between amp topologies. I’m more looking at “What happens if I swap this amp for this amp?” under real-world conditions.

I’m expecting to see and hear some differences between the amps, whether or not the instruments will show them, but your comment is making me consider taking wagers too. And even though an amplifier should have the least effect on the sonic differences between two systems that might mic equally flat on a FR plot, it will be interesting to see what they sound like and what I can measure.


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## Nemesis87 (6 mo ago)

hurrication said:


> So you're re-creating the Richard Clark amp challenge? AFAIK, nobody has actually successfully passed his challenge yet and it's been almost 2 decades.


How does one take this challenge?


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## hurrication (Dec 19, 2011)

Not sure how to participate in his challenge.

I understand what you're going for now and I think it should be an interesting experiment!


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## MrHarris (Feb 3, 2011)

Subscribed


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## Nemesis87 (6 mo ago)

MrHarris said:


> Subscribed


I should be finalising the testing procedure within the next week. Feel free to share any ideas or questions you might have.


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## knever3 (Mar 9, 2009)

There are two takeaways from this scenario. 

1. All amps set to the same output so equal playing field will result in a measured difference which to me means at measured output S/N, T.H.D, Damping Factor, Slew Rate, Distortion and Harmonics are plotted on a graph for each.

2. The one doing the test that is to gain (you in this instance) blindly chooses an amp that sounds the way YOU like, this is the subjective part. No one can argue with numbers plotted on a graph, but if you are satisfied with the results your time and effort are never in vain. 

Everyone would like the time and skills and equipment to achieve this goal, without the expense in changing out equipment and not having a fair test. There will be a HUGE discussion on this topic, but don't let anyone sway your personal preference. Your test will provide a lot of information to the group. 

I would love to do this, just no time with working and providing for my family. Good luck, can't wait for the results! There are so many different designs for Class D now. If anything, I hope your wildcard will include a Biketronics amp with the Hypex or Ncore tech to run with the ones you have. They are so underrated for the segment.


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## Nemesis87 (6 mo ago)

knever3 said:


> There are two takeaways from this scenario.
> 
> 1. All amps set to the same output so equal playing field will result in a measured difference which to me means at measured output S/N, T.H.D, Damping Factor, Slew Rate, Distortion and Harmonics are plotted on a graph for each.
> 
> ...


I’ve heard of that brand before but I don’t know what models would have that technology, they sound interesting. Could you point me in the right direction as to which model to look for and who might have one? Are they currently being made or at least serviced? 

Information about the Wildcard is mostly unknown to me. I might know the brand, but that’s about it. It’s an amp that someone is sending in just because they thought it might do well in the mix. I told them not to tell me anything about it so my listening will be as unbiased as possible. 

There’s also an amp in here that has conflicting information about it’s power output and it’s topology! I don’t actually want to know until after I listen to it and then measure it. Should be interesting. 

I can assure you, it’s highly unlikely that my personal preference will be swayed neither by graph nor another individual’s preference. That’s kind of the whole point of this. My ears will be the judge, for my system. My build will be using quite unorthodox components, but those are the things I like so I run them. 

I only know how to obtain Frequency Response and Distortion plots through REW. Do you know how I might go about obtaining some of the other data you mentioned, to be able to compare and present to others? I’ll also be making note of efficiency but I think that’s about it.


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## knever3 (Mar 9, 2009)

As for slew rate and damping factor, they are measurements that affect the control over the woofer. They are made usually at the terminals of the amplifier. Your woofers impedance will determine how the amplifier drives the load. Some amps like a higher ohm load, some lower, some are not affected by the changes in impedance (aka dynamic resistance), others drastically react to sudden changes in resistance. The behavior of the amp comes down to what they are driving. If you are doing this in a lab setting, (meaning if you are driving speakers that aren't to be used in your install) you are obscuring your results a bit. Most amps are okay if they are driven before clipping sets in, that's the whole point of the premise that "All amps sound the same" given they are of the same power and are not driven to clipping.

With that said, slew rate and damping factor are measured with some very expensive equipment and the information is nice for the results on paper, but not necessarily imperative to your end goal. Distortion can be measured and graphed on an Oscope along with noise. Harmonics are an awesome way to look at the sound signature of the amp, but it takes an expert to read the data and correlate it to what is heard. Harmonics are usually a deciding factor based on amp topology, tube single ended, or transistor. Transistor with feedback, meaning they take the output (before it leaves the amp) and recycle it and reprocess it again, changing the sound signature on the output. This part is a good explanation of the science behind why amps sound different.

Second order harmonics are considered even harmonics, being even integer multiples of the fundamental frequency with the second multiple being the most prominent. Third order harmonics are considered odd harmonics, being odd integer multiples of the fundamental frequency with the third multiple being the most prominent. For audio purposes, the first harmonic is considered the fundamental frequency. This can be confusing, because in the RF world, the first harmonic is considered what musicians refer to as the second harmonic, or the first actual multiple of the fundamental frequency.

Even harmonics (i.e., second order harmonics) are considered to sound fat and warm, although they can be muddy and soft sounding as well. Odd harmonics (i.e., third order harmonics) are considered harsher and edgier sounding. A pure square wave gives only odd harmonics. A pure sawtooth wave gives both even and odd harmonics. A pure sine wave has no harmonics other than the fundamental.

Transistors and tubes produce both even and odd harmonics. There is a popular misconception that transistors produce odd harmonics and that tubes produce even harmonics. This simply is not true because both devices produce both types of harmonics. Transistors differ from tubes in the ratio of even to odd harmonics they produce, so it is true that tubes sound harmonically different than transistors.

The primary determinant of the prominence of even harmonic vs odd harmonics in both tube and transistor gear is the topology of the circuit. Single ended (i.e., SE) circuits without mitigating feedback produce an abundance of even harmonics, and produce odd harmonics as well. Push Pull (i.e., PP) circuits, on the other hand, naturally suppress even harmonics and leave the odd harmonics intact. Therefore, PP circuits, including differential amplifiers, tend to sound a harsher than SE circuits, assuming of course no use of feedback (FB). Once FB is introduced into the circuit, both even and odd harmonics are reduced under both PP and SE topologies.

An interesting musical fact is that the third harmonic is an Ionian Major Scale Fifth above the second harmonic, and playing in fifths is a technique commonly used my rock musicians. This factoid tells you that the best sounding guitar amp distortion subjectively needs both even and odd harmonics to sound good if you want the sound to emphasize fifths, meaning that the old idea that only even harmonics sound euphonic is purely a matter of taste when dealing with guitar amplifiers. In the case of recording preamps, even harmonics are preferred to odd harmonics, but most people would consider no harmonic distortion to be better yet, hence the extensive use of feedback within preamp circuits to remove both even and odd harmonic distortion. 

So, in a nutshell, amp topology isn't the sole deciding factor, it's not Class A/B vs. Class D, it's much more complicated than that. As for Class D, the output filtering and switching frequency circuits are what results in a good product. 


Biketronics is certainly making amps now, the only US made product that has a lifetime warranty, proudly made in Idaho. Their website isn't the best because they cater to the Harley Davidson crowd, not the DIY audio one. If you put out a wanted ad for someone to lend you an amp, surely someone will step up. They have crazy power for their size and have great control over a woofer, unlike the Alpine PDX I have used, at least the 1st gen. I wasn't a fan of the SQ at all on the sub.








BT4180 - 180 Watts RMS X 4


Replacement audio and lighting equipment for Harley Davidson Motorcycles




www.biketronics.com


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## dsw1204 (Mar 23, 2015)

Can’t wait to see the results!


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## gijoe (Mar 25, 2008)

OP, you said you already expect to hear differences, so that bias will be pretty much impossible to eliminate. Will you have someone switch the amps for you in a double blind manner? At an absolute minimum they need to be level matched to deliver the same output, even a couple dB's will sway you into thinking the louder amp is better. 

Doing this to obtain good, objective data can be helpful, I just hope you're a little more scientific about this. After going through all of this effort I would hate for your bias to skew the results.


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## Nemesis87 (6 mo ago)

Good point! I was actually going to make a note of my thoughts (bias?) about each amp before I did the test and see if anything changes after.

I don't think there's anyway for my bias to skew the actual measured data though. My amp preference yes, but whatever I record will be what's presented. It will be as controlled and scientific as possible (or as makes sense) and hopefully we'll all gain something useful from this.


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## knever3 (Mar 9, 2009)

Gain and Bias, the Puns just keep coming...


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## Nemesis87 (6 mo ago)

knever3 said:


> As for slew rate and damping factor, they are measurements that affect the control over the woofer. They are made usually at the terminals of the amplifier. Your woofers impedance will determine how the amplifier drives the load. Some amps like a higher ohm load, some lower, some are not affected by the changes in impedance (aka dynamic resistance), others drastically react to sudden changes in resistance. The behavior of the amp comes down to what they are driving. If you are doing this in a lab setting, (meaning if you are driving speakers that aren't to be used in your install) you are obscuring your results a bit. Most amps are okay if they are driven before clipping sets in, that's the whole point of the premise that "All amps sound the same" given they are of the same power and are not driven to clipping.
> 
> With that said, slew rate and damping factor are measured with some very expensive equipment and the information is nice for the results on paper, but not necessarily imperative to your end goal. Distortion can be measured and graphed on an Oscope along with noise. Harmonics are an awesome way to look at the sound signature of the amp, but it takes an expert to read the data and correlate it to what is heard. Harmonics are usually a deciding factor based on amp topology, tube single ended, or transistor. Transistor with feedback, meaning they take the output (before it leaves the amp) and recycle it and reprocess it again, changing the sound signature on the output. This part is a good explanation of the science behind why amps sound different.
> 
> ...


Very informative post. Thank you for the explanation. I have heard that about different types of harmonics/distortion (odd and even) being pleasing or not so pleasing, your post brings some clarity to that. The majority of the amps I’m testing are Class AB so it will be interesting to see if I prefer the sound of one over the other, and if there’s a measurable difference.

It’s funny that you mentioned fifths and rock, because a cello is probably my favourite instrument of all time to listen to, but I don’t really like the sound most guitar amps make.

Question about harmonics. If I pluck an open G string, on a cello, the fundamental should be 98 Hz, right? Would the first harmonic then be 196 Hz? And is that the same as the natural harmonic (light finger pressure half way up the string)? What would be the second?

For my personal preference regarding the amps, I think I’ll choose whichever amplifier best captures the correct balance of harmonics of actual musical instruments. Those seem most pleasing to my ears.

Another interesting thing I came across was the different Op amps TRU Technology uses in their equipment. Surely they must all reproduce sound a little differently? I meant to call them today to get their take on the differences and how they tailor them to achieve the particular sound they’re after.


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## knever3 (Mar 9, 2009)

I can't take credit for the informative post, I have cited another's work. I was writing my take on the harmonics topic as it relates to amplifier topology and solid state compared to tube and decided to solidify my thoughts and found a post that pretty much summed it up.

This is the article I grabbed.



https://gearspace.com/board/geekzone/734092-2-order-3-order-harmonic-distortion.html



As for the Cello, I agree the tone is pleasing. My son is actually picking it up!! My daughter and my wife play the piano so they are playing together.


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## Nemesis87 (6 mo ago)

Quick update:

The MMats SQ4100 arrived not well. Everything functions as it should but the output is distorted and follows the beat. Not sure what's wrong with it but it's on it's way to MMats to be serviced/updated, along with the 6150D. I just got the 6150D and haven't even hooked it up yet, but since I was sending 1 back to MMats, might as well send 2 for a check-up and possible upgrades. 

This is also part of the test, and primarily why I seek out amps/gear either made in the USA, or by a company that takes enough pride to manufacture their own products in house and has good representation here in my country. 

The Brax X2400 also arrived with an issue. It would go into protect mode if you tried adjusting the gain (up or down) of a channel that had a speaker connected to it. No speaker connected and it's fine. I have contacted MSC (Jason D I think) about sending it to them to have it looked at. Not quite as responsive as MMats (incredible service btw) but we'll see how the MSC experience plays out. I also have some Brax Matrix tweeters going to them and will post updates as i receive them.

If you're going to collect gear to look at or to brag about, fine, none of this might matter to you, but my gear has to function properly AND has to perform as good as, if not better than, advertised. I didn't give you a $50 bill disguised as a $100 bill, nor did I give you currency that will be obsolete or of no marketable value a year from now; so i expect the same from the products I exchange said currency for.


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