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Matrix Quattro amp: unboxing and initial impressions - Page 8

post #106 of 229
Quote:
Originally Posted by Loquah View Post
 

The 2604 is for the single-ended stage, the 604s are for balanced operation. They are essentially the same op-amps only the 2604 is a dual channel (stereo) chip versus the 604s which are single channel.

 

 

 

Does anyone have a schematic?

This doesn't sound right to me.

The amp can take either balanced or unbalanced inputs.

And it will drive either balanced or unbalanced outputs.

 

I'm guessing the OPA2604 is an input stage Op Amp configured to accept either balanced or single ended inputs which converts the signal to single ended which then drives the 4 OPA604 Op Amps which are for the 4 output amps:

Left Hot (or non-inverting)

Left Cold (or inverting)

Right Hot

Right Cold.

 

Call it an educated guess.

 

Single ended output is probably just the Left "Hot" and Right "Hot" amplifiers.

post #107 of 229
Quote:
Originally Posted by Yoyomama View Post
 

I know the op amps well, I just wasn't sure what part of the circuit the 2604 was in.  I personally can't stand how 604's sound.  I replaced them with ADA4000-1 and ADA4000-2 (2604).  Both of these chips are SMT so they need to be mounted on a BrownDog adapter board.  Its super easy and they work great no oscillation.  I also really liked the LME chips.  Those come in DIP chips so no need for the BrownDog board.  They had a really nice tight bottom end but overall felt a little scooped to me. 

 

Looks like the trim pots in the Matrix Quattro may be used to trim DC offset in the OPA604.

You can't do that with an ADA4000-1.

Just make sure you don't have too much DC offset at the headphone jacks.

post #108 of 229

I checked for oscillation and any DC.  All was good.  Very easy upgrade!


Edited by Yoyomama - 1/24/14 at 5:37pm
post #109 of 229
Quote:
Originally Posted by Yoyomama View Post
 

I check for oscillation and any DC.  All was good.  Very easy upgrade!

Great!

I'm sure most wouldn't or lack the equipment!

post #110 of 229
Quote:
Originally Posted by Chris J View Post

Does anyone have a schematic?
This doesn't sound right to me.
The amp can take either balanced or unbalanced inputs.
And it will drive either balanced or unbalanced outputs.

I'm guessing the OPA2604 is an input stage Op Amp configured to accept either balanced or single ended inputs which converts the signal to single ended which then drives the 4 OPA604 Op Amps which are for the 4 output amps:
Left Hot (or non-inverting)
Left Cold (or inverting)
Right Hot
Right Cold.

Call it an educated guess.

Single ended output is probably just the Left "Hot" and Right "Hot" amplifiers.

Interesting suggestion. I was going on project86's review, but would love to know if this is actually the case. Can anyone confirm?
post #111 of 229
So I plugged in unbalanced headphones after removing the left most of the 4 mono op amps and the left channel worked, but the right channel didn't. I'm guessing that confirms that all op amps are used in both modes with the dual amp used as a buffer.
post #112 of 229
Quote:
Originally Posted by Loquah View Post

So I plugged in unbalanced headphones after removing the left most of the 4 mono op amps and the left channel worked, but the right channel didn't. I'm guessing that confirms that all op amps are used in both modes with the dual amp used as a buffer.

Interesting.
Just to be sure, can you pull the Op Amps from the right side only and see if only the other jack works?

As a final test you could only pull the dual Op Amp and see what happens in either balanced input mode or SE input mode?

Lots of "homework" for you....tongue.gif
post #113 of 229

LOL

 

I pulled the dual op amp and balanced and unbalanced HPs still worked. I didn't have time to check the influence to the sound, but wonder if this allows some coloration in the same way the Audio-gd products do.

 

I also pulled the right most mono op amp and tried balanced HPs. The right most op amps do control the left channel as assumed, however, each op amp is responsible for one half of its channel's balanced signal so I still had sound in the left channel in balanced mode, but at very low volume.

post #114 of 229
Quote:
Originally Posted by Loquah View Post

LOL



 



I pulled the dual op amp and balanced and unbalanced HPs still worked. I didn't have time to check the influence to the sound, but wonder if this allows some coloration in the same way the Audio-gd products do.



 



I also pulled the right most mono op amp and tried balanced HPs. The right most op amps do control the left channel as assumed, however, each op amp is responsible for one half of its channel's balanced signal so I still had sound in the left channel in balanced mode, but at very low volume.


 



Weird.
Makes me wonder what the Dual Op Amp does?

Edit:
I had suspected that it was an Input buffer, used to convert the Balanced signal inputs into an SE signal for the SE outputs.
Edited by Chris J - 1/31/14 at 1:42pm
post #115 of 229

I think it is for the RCA inputs? 

post #116 of 229
Quote:
Originally Posted by Yoyomama View Post

I think it is for the RCA inputs? 


 



Maybe used to convert an SE input signal into a balanced output signal?
That makes sense.

This amp has a strange architecture.
If true, the balanced input to balanced output is a joke.
post #117 of 229
Quote:
Originally Posted by Loquah View Post

LOL



 



I pulled the dual op amp and balanced and unbalanced HPs still worked. I didn't have time to check the influence to the sound, but wonder if this allows some coloration in the same way the Audio-gd products do.



 



I also pulled the right most mono op amp and tried balanced HPs. The right most op amps do control the left channel as assumed, however, each op amp is responsible for one half of its channel's balanced signal so I still had sound in the left channel in balanced mode, but at very low volume.


 




Oooops.
I forgot to ask:
are you using the balanced input or the SE input?
post #118 of 229
Quote:
Originally Posted by Chris J View Post
 
Quote:
Originally Posted by Loquah View Post
 

LOL

 

 

 

I pulled the dual op amp and balanced and unbalanced HPs still worked. I didn't have time to check the influence to the sound, but wonder if this allows some coloration in the same way the Audio-gd products do.

 

 

 

I also pulled the right most mono op amp and tried balanced HPs. The right most op amps do control the left channel as assumed, however, each op amp is responsible for one half of its channel's balanced signal so I still had sound in the left channel in balanced mode, but at very low volume.

 




Oooops.
I forgot to ask:
are you using the balanced input or the SE input?

 

I'm using balanced so it is truly balanced. I'll test the RCA in without the dual op amp to see what it's doing.

post #119 of 229
Quote:
Originally Posted by Loquah View Post

 

I'm using balanced so it is truly balanced. I'll test the RCA in without the dual op amp to see what it's doing.

 



This sounds like a weird architecture.

Typically a balanced input signal should go into a differential receiver to reject noise, then go to the output stage.
I would have guessed that the dual Op Amp is used as a balanced input signal differential receiver.
It may go to the output stage as either a balanced signal or an SE signal, depending on how the output stage is set up.
post #120 of 229

The dual op amp seems to be purely for colouration of the sound. The amp works using XLR, RCA, balanced and unbalanced outputs even when the dual op amp is removed.

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