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Old 11th March 2010, 07:45 PM   #1
rob1996 is offline rob1996  United States
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Default op-amps

Hi, I am a newbie at this site and would like to say hi to everyone. I have been reading posts here for a while and have found a lot of good information.
I am use a Hifidiy.net mini USB DAC for a small computer system. It is also a headphone amp but I am just using it as a DAC only to pass through to another amp. It has two exchangeable Op Amps that are (BB opa2134pa and BB opa2604ap) dual channel. I was thinking about swapping them out to a dual mono Op Amp set up. I was wondering if anyone had any suggestion on what Op Amps would be a good switch???
I have been told that the BB opa627ap is good or the AD797an is a good choice too. Any suggestions would be greatly appreciated
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Old 11th March 2010, 09:27 PM   #2
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Quote:
Originally Posted by rob1996 View Post
Hi, I am a newbie at this site and would like to say hi to everyone. I have been reading posts here for a while and have found a lot of good information.
I am use a Hifidiy.net mini USB DAC for a small computer system. It is also a headphone amp but I am just using it as a DAC only to pass through to another amp. It has two exchangeable Op Amps that are (BB opa2134pa and BB opa2604ap) dual channel. I was thinking about swapping them out to a dual mono Op Amp set up. I was wondering if anyone had any suggestion on what Op Amps would be a good switch???
I have been told that the BB opa627ap is good or the AD797an is a good choice too. Any suggestions would be greatly appreciated
I don't understand the willy-nilly swapping of opamps, particularly with high level signals. They either work correctly or not. OPA2134 is a fine amplifier with plenty of slew rate and current capacity and subbing with another adequate opamp seems a waste of time and money. For microphones or MC phono stages there will be a differences though primarily in noise levels. Swapping from a dual opamp to two single opamps involves cuts, jumpers and added circuitry. Certain configurations/ampliiers are more sensitive to stray capacitance than others. If it's "different", how can you tell what is from the amplifier change and what is from the wiring changes? Holistic audio?

If you DO go that route, a battery of tests to show the differences would be great but even more time thrown at it.

G
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Old 11th March 2010, 10:31 PM   #3
wwenze is offline wwenze  Singapore
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The fun of audio tweaking killed by the scientific method, ouch.

Circuits optimized for different components in this case op-amp may not give desired results with another op-amp, and while it will sound different, would you be able to tell if it's better or worse?

But counter-arguments to support op-amp rolling would be that the circuits are close to textbook circuits which could be used with any component, a cheaper part was used to save cost, and the designers probably designed according to their hearing (which many seem to take pride in - "extensive listening test") so their version of accurate is different from the end-user's.

Last edited by wwenze; 11th March 2010 at 10:33 PM.
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Old 12th March 2010, 02:11 AM   #4
qusp is offline qusp  Australia
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but if hes using as dac only, i'm not even sure they wil be in the signal path. perhaps one as a buffer or I/V
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Old 12th March 2010, 09:09 AM   #5
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Originally Posted by wwenze View Post
The fun of audio tweaking killed by the scientific method, ouch.

Circuits optimized for different components in this case op-amp may not give desired results with another op-amp, and while it will sound different, would you be able to tell if it's better or worse?

But counter-arguments to support op-amp rolling would be that the circuits are close to textbook circuits which could be used with any component, a cheaper part was used to save cost, and the designers probably designed according to their hearing (which many seem to take pride in - "extensive listening test") so their version of accurate is different from the end-user's.
I've done what you're suggesting in some old gear. My Phase Linear 1000 auto correlator used a 4136 as the input / output buffers. That amp is quite slow and I suspected slew rate limitations.The TL075 had the same pinout and much more speed so I subbed it into that unit. It was an improvement but we were dealing with limited performance.

I did the same thing in a Technics SH9010 parameteric equalizer originally equipped with 4558 opamps. Those are also quite slow and I changed them to TL072s in 1985 and changed THOSE out to OPA2132s in 1999. Is it better? Honestly I don't know but I 'feel' better about it. It is certainly working very well.

But in both my examples they were clearly marginal opamps by todays standards though they may have been the best available at design time. In the OPs case he's contemplating taking out a very good amplifier to put in a different very good amplifier.

G
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Old 12th March 2010, 07:24 PM   #6
rob1996 is offline rob1996  United States
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Thanks for your responses. Me being new to DIY Audio, I appreciate your time and knowledge. I feel the sound is good, but of course, the question is, what does better sound like?.
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Old 12th March 2010, 09:21 PM   #7
jstang is offline jstang  United States
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Last op amp upgrade I did was to LM4562na...from National. I liked them over the BB.... But get the actual National chips. they will cost more but sounded better to me.

Put sockets in and swap in different ICs till you find the ones you like.

JK
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Old 12th March 2010, 11:51 PM   #8
wwenze is offline wwenze  Singapore
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Originally Posted by rob1996 View Post
Thanks for your responses. Me being new to DIY Audio, I appreciate your time and knowledge. I feel the sound is good, but of course, the question is, “what does better sound like?”.
That is a very interesting question that has no right answer. What kind of sound do you want to shift your DAC towards?

AD797 is said to be analytical and bright, OPA627 BB-style laid-back but with more details.
AD8599 is like a 2-channel unity-gain stable version of the AD797, better suited for use in your DAC.
I like LM4562 too. It's like an all-purpose op-amp. And they cost $5 (used to cost <$3).
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Old 16th March 2010, 12:18 AM   #9
rob1996 is offline rob1996  United States
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Originally Posted by wwenze View Post
That is a very interesting question that has no right answer. What kind of sound do you want to shift your DAC towards?

AD797 is said to be analytical and bright, OPA627 BB-style laid-back but with more details.
AD8599 is like a 2-channel unity-gain stable version of the AD797, better suited for use in your DAC.
I like LM4562 too. It's like an all-purpose op-amp. And they cost $5 (used to cost <$3).
Im running my DAC to a small Meng tube amp, so a op-amp that is neutral with good detail to complement the amp would be more of what Im looking for. The sound right now is worm and detailed. But it is a little on the dark side. A little brighter sound might help it out??? I might pick up the AD8599 or LM4562 to try, no harm in that???
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Old 16th March 2010, 11:01 AM   #10
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I have swaped in my DAC's the opamps with LM4562 and there are great. Be carefull thou with cleaning the flux from the board below it before - it is sensitive to parasite/stray junk.

As for the "warm" sound - I think that is the tube amp, you cannot "fix" that with the opamp. Tubes just don't have the bandwidth needed to sound "crisp", sorry.
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