# SQ with LOC vs. aftermarket headunit



## Sub Sonic (Dec 17, 2014)

Ideally the aftermarket route would be best with headunits. However, with the newer cars it is very difficult or impossible to do them. So a common method is to do a loc post amp. Now you get all,kinds of issues like summing, eqing, bass roll off etc.

So my question is how much of a sound quality difference is there between a system with a loc vs a decent aftermarket unit?

Is the difference small? Does a factory headunit and a decent loc like a lc7i sound like crap compared to a aftermarket headunit?

The reason I am asking is that i will be having my system done by a shop in a few days. I can do the usual loc route but I have no idea how my system will sound. Might sound like crap? I dont know what the amp is doing to the signal. I Have never listened to a system with a loc. however, I would retain all factory features. The other option would be to do a nice aftermarket headunit,but lose all kinds of features of the car. I am willing to lose the features if it is worth it.

What do you think?


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## SQLnovice (Jul 22, 2014)

Subd. Thanks for starting this thread. I'm in your exact same situation.


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## Phil Indeblanc (May 27, 2015)

Well you lumped 2 things in one.

First off, not all car OEM HU come with amps and processing. Most often, only the premium stereo models do.

Mostly, the only features I know of that you lose and cannot replace is the adjustments that some HU have. Like when the doors lock, or the lights dim off, or the turn signal clicks count and so on. 

These are ALL adjustable with getting a OBD2 harness with the software for your make. 

VW/Audi has it for sure, and same with Toyota. I have used both. Some have amazing tools based on your car features, and others are more basic.
But if your car OEM HU has additional features that aftermarkets DONOT have, then it is a loss. Everything else would be a sound quality gain.

One thing I would lose if I took out my head unit is the ability for my texts to be read to me by the HU, so I just listen to my texts as they transfer to voice. I wish this was done in aftermarkets, as I find it very handy. Are you listening Alpine, Pioneer, Kenwood, JVC. (Does anyone else make head units worth looking at?)
You may have to look for it on ebay or Amazon as the brands donot want to have anything to do with it, and they rather you come to the dealership for any service.

But assuming that you will lose something and you decide to keep your oem HU. I first hand dont know yet, not until a week or two as I will have a 360.3 put in. But it will be the feed from oem HU that has no amp. (Which makes me want to ask....Is what I'm doing pointless?)


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## Niick (Jun 3, 2015)

Hi, your typical LOC, like the scosche LOC80, are total pieces of ****. I will soon post pics of measurements that I've made at work of what a LOC does to the signal passing thru it. It ain't pretty, as a result of the cheap little transformers located within them. The distortion gets worse as freq. decreases, at 40Hz, the sine wave is barely a sine wave anymore. With modern cars like you described, IF you need to use an interface between the factory head unit and the aftermarket amplifiers, then you should spend the money that you would normally spend on a HU, on an ACTIVE processor designed for this application. If you're even remotely concerned about sound quality, LOC should be no where in the discussion. The processor that we use most for this type of scenario is the Audio Control LC7i, and the Audison Bit 10. Of course, we also do a lot of Rockford 360.3's and Bit One's, but it's not absolutely necessary to spend that kind of money to achieve good results. Also, keep in mind that many quality amplifiers these days implement the proper type of input circuitry to allow you to directly input signals up to 8 Vrms or so. So, speaker level. Like the JL XD & HD amplifiers, or the Rockford punch and power series, basically, as long as it has differential (balanced) inputs, you can usually run a factory signal from your car straight into the RCA inputs. Just mind your input voltages. Of course, this doesn't help when you need signal summing, or equalization, or delay, but then that's what the processor is for. Basically, in place of a head unit, don't think LOC, think OEM interface processor.


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## Phil Indeblanc (May 27, 2015)

I like Niik's suggestion of doing it direct. I read this on another post he replied to, and he goes more into detail on how to tap into it, and keep that signal clean. Only part that is crutial is your amp. If you already have one, and it doesn't have the High volts inputs. You pretty much need an alternative.

I asked this question a few days ago, from the replies, I was guided as that being the right way to go, so I was covniced I needed a DSP. Few hundred later, here I am waiting for that shipment  I wont have a LC7i to compare it to for you when installing, but if I can do something as a comparison, I would alos be interested in knowing.


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## Hugg727 (Sep 17, 2009)

Your best bet would be to test the signal coming out of the stock HU to see how much processing is going on. If it does then you really need a DSP to address that with EQ. Some DSP's like the Mosconi, you can EQ the input signal.

I have done several systems using a few of the Audiocontrol EQ/LOC products over the years. They are ok but there always seemed to have a high noise floor. I will never go this route again.

Unless your factory HU has features that you cant live without like NAV, BT etc, I would replace it with an aftermarket HU. 

Niick was spot on in his assessment above. It really comes down to budget.


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## wisnulie (May 24, 2015)

nice information
thanks all


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## oabeieo (Feb 22, 2015)

Whatever you do DONT SUM SIGINALS !!!! It sounds like complete A$$ !!!!! You hear the crosser phase shift on both sides of the active crossover and its mashed back to a single signal and you can't get rid of the phase shifts , so the system will sound phasey and you will NEVER get it to image or stage properly! I would use a full range signal out of rear channels and go into a DSP that accepts high level in , the LC7 is a piece of crap and sounds lousy , the dq61 isn't much better, the 360.3 is one of the best ones and the bit one is good as well there's a few others , I would take advantage of the aux in on one of those DSP units and maybe add a rca Bluetooth adaptor to the aux in and gain Bluetooth that way , there's some Bluetooth rca adaptors that have very good DACs and use better protocols than A2DP. Focal makes one that's good and there more than you can use your phone as a source or whatever you will use , if you have a Europe car that has MOST look at Mostbridge ,good luck high level in can sound ok if done correctly but it won't be as good as a clean low level signal , ever , also ver very few cars high level output can even do a clean flat or flattened signal without clipping or cut off on the highs or lows , please believe what I am telling you , it's 23 years of install experience and my shop does this every singe day to at least two cars a day , best of luck, I would just use you factory head strictly for navigation, phone calls , am talk radio , and that's about it and use the auxiliary on the DSP for everything else ,


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## Niick (Jun 3, 2015)

So, in response to signal summing, if, and I'm saying if, you are having phase issues due to the two signals not being aligned thru the overlap region, this IS something that can be measured, and this IS something that can be corrected. But, if you can't measure phase because you don't know how or have the equipment to do so, then phase issues will cause you problems. Remember, we sum signals ALL THE TIME!! Think of a 3 way speaker system, we're summing signals in the acoustical domain to reproduce the full range recording. And I correct for phase issues in the acoustical overlap region of speaker systems all the time. And measuring phase in the acoustical domain is way harder to do. So I say, adjusting phase in the electrical domain, is much easier.


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## Jepalan (Jun 27, 2013)

Sub Sonic said:


> Ideally the aftermarket route would be best with headunits. However, with the newer cars it is very difficult or impossible to do them. So a common method is to do a loc post amp. Now you get all,kinds of issues like summing, eqing, bass roll off etc.
> 
> So my question is how much of a sound quality difference is there between a system with a loc vs a decent aftermarket unit?
> 
> ...


OP - you have asked a lot of general questions here and you left out a few considerations. You can't discuss these questions in general terms and get a definitive answer because final quality depends on the specific make/model/year of car and which LOC or OEM processor you are using. Results can vary WIDELY.

So if you want an answer that matters for your specific situation, then at least tell us what make/model/year car you have.

Many OEM integrated systems can sound VERY good, but if the OEM headunit is a lousy signal source (low quality DAC, low dynamic range, high distortion, severe freq rolloff) then no amount of post processing is going to make it sound "SQ".


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## Niick (Jun 3, 2015)

I agree with Jepalan 100% on this. Better specifics would help.


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## josby (May 8, 2011)

Hugg727 said:


> Your best bet would be to test the signal coming out of the stock HU to see how much processing is going on. If it does then you really need a DSP to address that with EQ.


Exactly. And there are some things no DSP can fix. Attached are two sweeps from the factory HU of my 2015 Accord LX - one at volume 9 (purple) and the other at volume 32 (green) (shifted to overlay each other). There's a bass boost happening at low volume that you can't disable, and no DSP can sense where your HU volume is set, much less apply different EQ curves based on that.


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## quality_sound (Dec 25, 2005)

Before we get too hung up on what 
MIGHT work, what kind of car are we talking about?


Sent from my iPhone using Tapatalk


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## subterFUSE (Sep 21, 2009)

Yup. Definitely is going to depend on the vehicle and the OEM system.


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## 14642 (May 19, 2008)

Niick is on the right track here. 

Summing through LOCs is the worst way to do this and it's akin to "just hooking **** up". It's favored by installers who don't yet understand audio fundamentals. Not all LOCs suck and sometimes a transformer in the signal line is the only way to get rid of noise.

EQ in the factory system that's designed to overcome road noise or to add a little bass at low frequencies isn't a disaster.

Summing is NOT straightforward unless you are able to make COMPLETE measurements of the output of the factory system and unless you have the tools required to sum and re-EQ effectively. Unfortunately, too may of the designers of aftermarket DSPs have no idea what's actually in the OEM processor. NONE of the DSPs except MS-8 (now discontinued) correct for factory time alignment. That can be an imaging nightmare. 

Depending on how the factory sub and front speakers are crossed over, summing the bass with the front can create a big hole in the midbass. 

The problem with summing using current processors is that the crossover and EQ in the factory amp is designed to overcome ACOUSTIC issues and when you remove the acoustic conditions by electrically connecting the outputs together, the crossovers are not symmetrical. The phase shifts that attend any change in frequency response cause frequency response anomalies and none of the currently available DSPs go far enough in correcting all of this.

It's unfortunate because ALL of them have enough processing power to do it, they just aren't configured with the tools that are necessary. You could use a couple of them. For example, you could use one PS8 to condition the inputs and one for acoustic tuning. For the first one, you'd connect the inputs to the outputs of the factory system, assign every channel direct to each of the outputs, EQ and delay the channels so that the outputs would sum correctly, sum them through symmetrical resistors (analog), feed the summed channels into a second processor and use it for acoustic tuning. 

So, it takes $2000 in processors to do the whole job CORRECTLY if the factory system includes delay and EQ. If you're just connecting to the output of a factory radio that doesn't include an outboard DSP amp, then just choose a processor that includes speaker level inputs. No LOC required. You may get lucky.


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## subterFUSE (Sep 21, 2009)

Andy Wehmeyer said:


> Summing is NOT straightforward unless you are able to make COMPLETE measurements of the output of the factory system and unless you have the tools required to sum and re-EQ effectively. Unfortunately, too may of the designers of aftermarket DSPs have no idea what's actually in the OEM processor. NONE of the DSPs except MS-8 (now discontinued) correct for factory time alignment. That can be an imaging nightmare.
> 
> Depending on how the factory sub and front speakers are crossed over, summing the bass with the front can create a big hole in the midbass.
> 
> The problem with summing using current processors is that the crossover and EQ in the factory amp is designed to overcome ACOUSTIC issues and when you remove the acoustic conditions by electrically connecting the outputs together, the crossovers are not symmetrical. The phase shifts that attend any change in frequency response cause frequency response anomalies and none of the currently available DSPs go far enough in correcting all of this.



That's really interesting. I wonder if the hole in the midbass is what explains this measurement I took when I had my BitOne connected to my Bose factory amp with high level inputs?

The below measurement was taken via REW. I ran the output from REW into my car's OEM head unit, and then measured the unprocessed output from the BitOne. 20Hz - 20kHz sine sweep.












Do you think that big dip at 200Hz is a summing issue like you describe above?


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## 14642 (May 19, 2008)

^^^ Wow! That absolutely sucks. There are three big issues here. 

1. Yes, that hole at 200Hz is probably caused by two things--asymmetrical crossovers and delay on the front relative to the sub. 

2. The DSP did a ****ty job of level matching the high frequencies. 5kHs is 20db hotter than the rest! Geez...

3. The deep but narrow hole at 4500Hz look like a problem in correcting delay between a couple of summed channels. Looks like tweeter and midrange channels--do the tweeters have separate output channels from the factory amp? This appears to be the case because the error creates a comb filter--on deep and narrow dip followed by an additional dip at 9kHz. The other smaller dips in between are a bit of a mystery. They could be the result of some EQ applied in an attempt to correct the first dip at 4.5kHz.


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## 14642 (May 19, 2008)

Subterfuse, 

Are you certain of the polarity of the input connections?


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## Golden Ear (Oct 14, 2012)

Phil Indeblanc said:


> One thing I would lose if I took out my head unit is the ability for my texts to be read to me by the HU, so I just listen to my texts as they transfer to voice. I wish this was done in aftermarkets, as I find it very handy. Are you listening Alpine, Pioneer, Kenwood, JVC. (Does anyone else make head units worth looking at?)


I guess it depends on what kind of phone you have but my pioneer 4100nex does this with my iPhone in my Tahoe using Apple CarPlay.


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## Phil Indeblanc (May 27, 2015)

how do you get your Iphone to read you your texts? and can you auto-engages that when paired in cars BT, and disable that when disconnected, or is it a manual thing each time you hop in the car?


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## subterFUSE (Sep 21, 2009)

Andy Wehmeyer said:


> ^^^ Wow! That absolutely sucks. There are three big issues here.
> 
> 1. Yes, that hole at 200Hz is probably caused by two things--asymmetrical crossovers and delay on the front relative to the sub.


That makes a lot of sense, but I never thought about the OEM system having delay.



> 2. The DSP did a ****ty job of level matching the high frequencies. 5kHs is 20db hotter than the rest! Geez...


The image above was BEFORE applying the Audison De-Equalization.
Here is another image showing the before and after results of De-EQ.













> 3. The deep but narrow hole at 4500Hz look like a problem in correcting delay between a couple of summed channels. Looks like tweeter and midrange channels--do the tweeters have separate output channels from the factory amp? This appears to be the case because the error creates a comb filter--on deep and narrow dip followed by an additional dip at 9kHz. The other smaller dips in between are a bit of a mystery. They could be the result of some EQ applied in an attempt to correct the first dip at 4.5kHz.



I'm no longer using the high level inputs, but when these measurements were taken these were the outputs from the Bose amp that were used:

Front Tweeters L/R
Front Midrange L/R
Front Midbass L/R
Subwoofer

7 channel total required to sum together a full range signal.
The front midbass were crossed over rather high, which I confirmed when I ran a 40Hz test tone and the oscilloscope was dead flat.



It's no matter anymore since I went to the mObridge DA1 preamp.

Here's the signal coming out of the mObridge.











Obviously much better.


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## subterFUSE (Sep 21, 2009)

Andy Wehmeyer said:


> Subterfuse,
> 
> Are you certain of the polarity of the input connections?


Another good question.

I used the Audi Repair manual for my car to find all the wires out of the Bose amp. I wired everything according to the wire color code chart, so theoretically everything should have been in correct polarity. But I never actually tested the polarity coming out of the Bose amp.

In the future, I will make certain to always test polarity and delay on factory source outputs. I think both of those can be determined easily with REW.

Thanks for the suggestions! Really good info which I had never considered.


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## 14642 (May 19, 2008)

Cool. Thanks for the clarification. That's a big help as I begin work on a DSP.


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## 14642 (May 19, 2008)

Almost every OEM system that includes a trunk mounted amplifier includes delay. It's a very simple and very basic tuning tool. The factory amps include the same signal processors as aftermarket DSPs, why would an OEM system tuner not use that basic tool?

You're not alone. Apparently about three people developing products for the aftermarket actually know what's in an OEM system. God forbid anyone should actually measure one.


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## Golden Ear (Oct 14, 2012)

Phil Indeblanc said:


> how do you get your Iphone to read you your texts? and can you auto-engages that when paired in cars BT, and disable that when disconnected, or is it a manual thing each time you hop in the car?


Apple CarPlay uses Siri to read your texts and reply back hands-free. It's pretty sweet.


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## Niick (Jun 3, 2015)

Good quality transformers are one thing, the ones in your common LOC are quite another.....


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## bigjeep127 (May 12, 2013)

josby said:


> Exactly. And there are some things no DSP can fix. Attached are two sweeps from the factory HU of my 2015 Accord LX - one at volume 9 (purple) and the other at volume 32 (green) (shifted to overlay each other). There's a bass boost happening at low volume that you can't disable, and no DSP can sense where your HU volume is set, much less apply different EQ curves based on that.





Andy Wehmeyer said:


> Niick is on the right track here.
> 
> Summing through LOCs is the worst way to do this and it's akin to "just hooking **** up". It's favored by installers who don't yet understand audio fundamentals. Not all LOCs suck and sometimes a transformer in the signal line is the only way to get rid of noise.
> 
> ...





Niick said:


> Good quality transformers are one thing, the ones in your common LOC are quite another.....


So I've actually got the same car as Josby (2015 Accord Sport) and am dealing with the horrible HU (which I'm determined to keep using), I'm glad I saw this thread as I just ordered from MiniDSP and need a good LOC.

I just returned my MS-8 yesterday (it kept resetting) and didn't get another as I decided I just wanted/needed more control than it offered. No offense to Andy, the MS-8 is a great product and I've learned a ton reading his posts here, so a big thanks! I loved the way the MS-8 made my front stage sound but just didn't like the way it killed midbass when I added in the sub, and I got tired of re-calibrating and trying to get it right. This is all a learning experience too, so I'm excited to learn a little tuning.

Here is my build btw... http://www.diymobileaudio.com/forum...l-build-2015-accord-sport-pictures-fixed.html

My goal now is to get the cleanest signal possible to the MiniDSP's to avoid noise as I'm afraid it might be an issue as I do my best to correct for the bass rolloff. The last thing I want is for the LOC to kill even more low stuff. I came across this and think I may go this route, two transformers at $70 each isn't cheap but it's doable.

DIY Line Output Converter W/ DSP Module - Drive Accord Honda Forums

Am I on the right track or do you think it's a fools errand to try and mess with this HU? I'm not even going to get into the correction of the factory time delay (if there is any), this is my first time using a DSP. I need to do more reading to make sure I'm getting the right sized transformer to send the best signal to two MindDSP 2x4's, the guy above only had one (and I don't know how it turned out for him).

Anyone here have experience with these transformers? Again, I'm still new to all of this, but my intuition tells me I need to find out the voltage of the high level signal from my HU and then find the appropriately sized transformer to step it down to the optimal voltage for the MiniDSPs. He used 2 transformer for one DSP, but I think that if I have a higher output voltage from my transformer I can use a splitter to send enough signal to 2. I can even go balanced to the MiniDSP input to further mitigate noise though I may have the MiniDSP right next to the amp, not a long RCA run.


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## nl-fer (May 25, 2015)

I recently tried two transformer based LOCs to hookup my sub. first was an old photocan shaped model, a real classic. Freq response was just horribel, no subbass at all, just harmoniqs/ distortion in the midbass region. Replaced that with a new model, ACV Premium Loc, which claims low distortion. in the USA it is sold al NVX 150w/ch LOC. Response was better, now there was somr subbass, but it still distorted the signal. A 40hz test sine just sounded like a several notes played, Kylie Minoque's Slow realy turned the LOC mad, with alot of distortion and artifacts.

But luckily my amp has groundloop filters inside, i measured the rca input ground, it has over 100 ohm with amp ground, so i tried a cable with resistors in series and connected it to my amp. Although the resistors attenuade the signal voltage, the oem headunit still puts 6v dc bias on both the + anf - speaker output. The result: Low bass, undistorted, in time, articulate punchy bass.

so no LOCs for me anymore.

Does minidsp come in a differential input version? Can you hookup that with some resitors?


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## bigjeep127 (May 12, 2013)

nl-fer said:


> I recently tried two transformer based LOCs to hookup my sub. first was an old photocan shaped model, a real classic. Freq response was just horribel, no subbass at all, just harmoniqs/ distortion in the midbass region. Replaced that with a new model, ACV Premium Loc, which claims low distortion. in the USA it is sold al NVX 150w/ch LOC. Response was better, now there was somr subbass, but it still distorted the signal. A 40hz test sine just sounded like a several notes played, Kylie Minoque's Slow realy turned the LOC mad, with alot of distortion and artifacts.
> 
> But luckily my amp has groundloop filters inside, i measured the rca input ground, it has over 100 ohm with amp ground, so i tried a cable with resistors in series and connected it to my amp. Although the resistors attenuade the signal voltage, the oem headunit still puts 6v dc bias on both the + anf - speaker output. The result: Low bass, undistorted, in time, articulate punchy bass.
> 
> ...


I'm trying to understand what you did. So did you end up with a transformer followed by resistors? Or are the resistors after the store bought LOC?

I ordered the balanced MiniDSP 2x4's which allows for balanced or unbalanced input and output at 2V/4V unbalanced/balanced max.

Page 24 shows wiring options.

http://www.minidsp.com/images/documents/miniDSP Balanced 2x4 and Kit - User Manual v2.2.pdf


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## nl-fer (May 25, 2015)

I dumped the LOC's

Just some resistors in series.


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## t3sn4f2 (Jan 3, 2007)

Here's a DIY LOC using Jensen Transformers running into a mini-dsp. Courtesy of Minivanman.


DIY Line Output Converter W/ DSP Module


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## bigjeep127 (May 12, 2013)

t3sn4f2 said:


> Here's a DIY LOC using Jensen Transformers running into a mini-dsp. Courtesy of Minivanman.
> 
> 
> DIY Line Output Converter W/ DSP Module


Thanks, I saw that and it's my inspiration. What I need to figure out is if I can get away with just two transformers for two minidsp's (4 inputs). Could I split the wiring in parallel and have the voltage cut in half? I'm not sure if the minidsp will have a constant impedance. I guess another option is to use a LOC for one minidsp that is just running my front stage (nothing below 80hz) and use the transformers for the rear fill and sub (2.1 plugin on the minidsp).


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## t3sn4f2 (Jan 3, 2007)

bigjeep127 said:


> Thanks, I saw that and it's my inspiration. What I need to figure out is if I can get away with just two transformers for two minidsp's (4 inputs). Could I split the wiring in parallel and have the voltage cut in half? I'm not sure if the minidsp will have a constant impedance. I guess another option is to use a LOC for one minidsp that is just running my front stage (nothing below 80hz) and use the transformers for the rear fill and sub (2.1 plugin on the minidsp).


Oopps missed that you linked the thread already. 

I cant say for sure if you can split the outputs but i think it should work since the inputs are high impedance and wont affect voltage. Just speculating though, dont know enough to say for sure. 

Maybe you can link two minidsp digital and only then use one pair of inputs. I seem to recall that being posible, maybe with a minidigi.


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## bigjeep127 (May 12, 2013)

t3sn4f2 said:


> Oopps missed that you linked the thread already.
> 
> I cant say for sure if you can split the outputs but i think it should work since the inputs are high impedance and wont affect voltage. Just speculating though, dont know enough to say for sure.
> 
> Maybe you can link two minidsp digital and only then use one pair of inputs. I seem to recall that being posible, maybe with a minidigi.


I may look into that, sounds like I've got some options. I need to brush up on my electrical knowledge and maybe buy some equipment so I can do this right, it's been so long since school haha.


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