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Old 1st April 2008, 09:16 PM   #1
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Default Differential outputs as source for gainclone?

Hi,

Despite I'm not an expert in electronics, i got an idea about power opamps and differential outputs of a DAC chip.

Since my sound card's DAC chips (AKM AK4396) have direct out analog outputs (yes, this chips doing that) for each channel as L+, L- and R+,R-, I wonder that can we apply a power opamp to these output pins?

I'm using + pins as source directly from DAC pins for drive a non-inverting GC amp. And it sounds great already..

Is there any benefits of the differential output setup comparing with inverting or non-inverting setup?

I'm attaching a pic of LPF setup applied to DAC chip which may helps something about this issue.

Datasheet of AKM AK4396:
http://www.asahi-kasei.co.jp/akm/en/...k4396_f00e.pdf
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File Type: gif differential-outputs.gif (19.4 KB, 300 views)
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Old 1st April 2008, 09:55 PM   #2
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Default Re: Differential outputs as source for gainclone?

Quote:
Originally posted by terranigma
Since my sound card's DAC chips (AKM AK4396) have direct out analog outputs (yes, this chips doing that) for each channel as L+, L- and R+,R-, I wonder that can we apply a power opamp to these output pins?
Your sound card has what are known as balanced outputs. A power op amp configured as a differential amplifier or an instrumentation amplifier can accept balanced inputs.


Quote:
Originally posted by terranigma
Is there any benefits of the differential output setup comparing with inverting or non-inverting setup?
The main benefits of using balanced equipment are increased noise rejection and immunity to ground loops.
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Old 2nd April 2008, 12:02 PM   #3
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Default opa54x and LM chips

Thanks BWRX,

After some search following your explanations i found a member "Mad_K" was interested on this topology at this topic :

Gainclone with pseudo-balanced input?


He has used opa541 opamps in his works and it seems he has finalized his works with this picture.

I think that there is no critical reason for using a LM chip instead of OPA54x power opams. Is it right?

Any suggestions would be very appreciated...
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Old 2nd April 2008, 01:36 PM   #4
BWRX is offline BWRX  United States
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Default Re: opa54x and LM chips

Quote:
Originally posted by terranigma
I think that there is no critical reason for using a LM chip instead of OPA54x power opams. Is it right?
That is correct. You are free to use whatever brand chip you'd like. Keep in mind that the LM chips have a minimum gain requirement of 10V/V while the OPA chips are stable down to unity gain.

I also started a thread about a high power instrumentation amp here: Instrumentation Gainclone
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Old 2nd April 2008, 02:08 PM   #5
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Yes Brian, I saw your implementations after a little search also.. But I'm something nervous about using opamps before amplification. Is it possible to pull out them in your schematic?

I want to try Mad_K's schematic with LM1875. It is very simple. If you have any suggestion (resistor values for desired gain etc..) on his approach, i would be very pleased.

Thank you.
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Old 2nd April 2008, 02:17 PM   #6
BWRX is offline BWRX  United States
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Why would you be nervous about using op amps before the high power op amp? They serve an important purpose and if you use good op amps (LM4562, OPA2134, AD8620, etc.) there should be no problems.

Regardless, my schematic uses the LM3875 in a differential configuration, just like MadP's schematic with the OPA541. You can do away with the differential buffer (the dual op amp circuit) before the differential amp if you wish.
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Old 2nd April 2008, 05:57 PM   #7
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Quote:
Originally posted by BWRX
Why would you be nervous about using op amps before the high power op amp?
My diy approach aims fidelity to source as much as possible and simplicity. I believe in every element in signal path, especially active ones adds its own caharacter to the sound. I think, if it is possible without opamp, therefore no need of them so much.
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Old 2nd April 2008, 07:28 PM   #8
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I understand your logic and if you feel you don't need/want the op amp differential buffer then give the differential design a try. You could even incorporate the low pass filter into the amp, like is shown in the image in your first post of this thread.
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Old 4th April 2008, 05:56 AM   #9
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I was just thinking of doing a diff input to be driven from my Lex 12B. What do you think of this schematic? Bryston uses a straight op amp input so if it's good enough for them, etc.

The back end is basically the PA150 standard design out of the AN. Since the chips have a relatively low offset I thought I could use the offset null on the op amp to trim it down further.

As mentioned earlier I could use two with the inputs swapped for bridged mode as shown.

If they sound good enough I'll use them with the DCX-2496 for tri amped speakers

Any thoughts? Suggestions for improvements?
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