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What is wrong with op-amps?
What is wrong with op-amps?
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Old 29th June 2010, 01:09 PM   #21
jean-paul is offline jean-paul  Netherlands
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There is a brand new ipod at my desk and it is winking at me for months now.
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Old 29th June 2010, 01:10 PM   #22
Sebastiaan is offline Sebastiaan  Netherlands
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Opamps, Tubes, FET's Transistors or an combination of all. I don't care. If it sounds good it is good!
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Old 29th June 2010, 01:19 PM   #23
jean-paul is offline jean-paul  Netherlands
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You forgot the ubiquitous :"and if it measures good" part...

Good sounding or pleasant sounding might as well be a good part distortion. The ears are good instruments but checking with measuring equipment is better.
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Old 29th June 2010, 01:55 PM   #24
Alan Frobisher is offline Alan Frobisher
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I concur with Mooly,had some great success with OPA604(single)/2604(dual).Operate with good headroom (rail voltage) and roll off the freq.response with a small cap.across the fb.resistor at 3-5 times required freq.
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Old 29th June 2010, 02:16 PM   #25
suntechnik is offline suntechnik  Russian Federation
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Quote:
Originally Posted by wahab View Post
musically speaking :
I am not a musian and apologizing the way I quoted the message in case it was done wrong. I assumed since the original message was above I can emphasis just a few words not repost everything again.

OK to be clear (sorry english is 2-nd foring language for me) my point is that studing high math I never heard that Fourier proved the odd harmonic sounds better then even. I could assume only that some guys were feeding different audio components with 1KHz test signal and while studying the spectrum coming out made an assumption later that AUDIBLY components having prevailing odd harmonics distortion as not as bad sounding as components having prevailing even harmonics distortion (at 1KHz). The validity of such statement might be considered at the following : "Tiramisu is a more delicious desert then an apple pie" or "NFB sounds bad".

However clean sounding device means 1KHz in ONLY 1KHz out. I would say Balanced / differential signal path has major impact here not tube vs transistor IMHO.
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Old 29th June 2010, 02:55 PM   #26
tiefbassuebertr is offline tiefbassuebertr  Germany
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Quote:
Originally Posted by jean-paul View Post
This is also the way I see it except that I would like to add OPA627 and LME49860 (a dual opamp) to the list of good devices. Since most of the commercial gear uses dual opamps the single versions are useless unless one wants to use pink cat adapter PCB's etc. which can make things worse.

As usual a non-technical opinion from me: in all cases where I replaced already tweaked opamp circuits (with even very good types) for an open loop discrete design with all its disadvantages it still sounded better. And no I did not listen to added distortion. The standard disadvantages with discrete circuits are :high offset/drift, channel differences etc. in a way larger magnitude than with opamps.

My experiences are with I/V converters in DACs and preamps. But it often is poor implementation of the opamps in question that defines the results. Proper decoupling the power supply lines is such an example where things go wrong.

Opamps are quite easy to work with when you know their limitations but a simple discrete circuit often sounds better but only so after a lot more work.

Despite all excellent explanations from true experts I simplified matters by avoiding designs around opamps as I think the feedback is what causes the disadvantages.

Yeah, "I think" is not the best of reasoning. And I too leave opamp circuits sometimes as they are and replace the devices for better types and decouple them as it is far less work than redesigning. The point is to think carefully especially with high speed high bandwidth opamps. An input filter around 100 khz can be a good remedy when it picks up high frequency signals.

BTW the original power supply of NAD PP-2 is an example of how not to do it !!
Regarded the OPA627 I can not understand why some count him as to the top class operational amps. The OPA604 and OPA134 I would prefer both for high gain stage (RIAA) and low gain stage (line).
In case of I/U converter there is a easy way to find out the sonic character of various op amps:
compare it to an easy resistor load like showed here :
Digi Scoop 1
until this day I haven't find out an OP Amp, that clearly outperform a simple resistor. For me is the best I/U converter that one from the Pass "D1" (very easy, but at my view very very hard to beat).

If more than one voltage gain stages is in the negative feedback loop, causes this the main disadvantages together with too low idle current in the power buffer stage. This means, not the feedback itself is the reason.

Mooly notice, that the OPA604/2604 sounds musical. Also one of my favorite. Additional the AD797 (Mr. Scott Wurzer's Design) and the OPA134/2134.

If you study the internal circuit, you will understand, why; only one voltage gain stage there is in the NFB loop and enough current through the last stage. This is for me fundamental for best sounding OP-Amps (and best sounding discrete line/power audio amps). Two gain stages in the NFB loop (still present by the most OP amp types) creates still high/odd order harmonics and thus harsh sound.

Interesting would be to know the internal topology from the LME series (and that one from newest TI/Analog Devices types). But I think, there is also only one voltage gain stage in the NFB loop - some guy's think, same basic topology than AD797.

BTW - I have compare some years ago two unity gain line preamp concepts, one with OPA627 and one with Andrea Ciuffoli's power follower in modified preamp line version (only 9V but 1A idle current). Unfortunately I haven't documentation of the measurement results. But it was to observe follow: At 1 KHz and 10 KHz much more better THD results by the OPA627. And by 100 KHz and 500 KHz and soundcheck clearly better results by the power follower ( OPA627 deliver sathtooth instead sine wave by 500 KHz). 2xIRF520 was in use by the power follower. Sonic quality was better in all respects by Ciuffoli's power follower. The used power amp here was a ZEN diy project and a tube power amp from VTL (see attachement). And the speakers at this time was a 2-way combination of PHL B17-1220 and Focal T120K (very high resolution loudspeakers);
have a look also to this this URL:
http://www.diyaudio.com/forums/pass-...g-phl1230.html
The also still present preamp VTL "Maximal" was in the perception between both, clearly better than the preamp with OPA627, clearly inferior to the power follower concept.
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Last edited by tiefbassuebertr; 29th June 2010 at 03:11 PM.
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Old 29th June 2010, 05:54 PM   #27
bob91343 is offline bob91343  United States
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TI has a new op amp line that looks great; I'm getting some. They are JFET input, very low bias and offset and static current, good bandwidth (11 MHz) and noise, and CHEAP. Intended for high end audio. OPA1641.
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Old 29th June 2010, 07:08 PM   #29
jean-paul is offline jean-paul  Netherlands
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Hi, just like CarlosFM did soem years ago I discovered OPA627 requires careful decoupling with an extra cap across the power pins. I still like it very much.

Testing at 500 kHz does not say much to me as I don't have any music that reaches such frequencies

AD797 is a difficult one to control/tame. I only use it in Flea power supplies.
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Old 29th June 2010, 07:51 PM   #30
MatchASM is offline MatchASM  Europe
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Quote:
Originally Posted by teemuk View Post
There are just awful alot of myths and erroneous beliefs that are reigning in the scene of audio electronics. The belief that discrete circuits for some mystical reason are better than integrated circuits is one of them.
There is nothing mystical about capacitive and inductive coupling of circuit nodes inside a standard IC package. They put a limit on the GBW that an opamp can have without becoming unstable. It's difficult to simulate accurately, that's all.

Discretes, if designed and executed well, don't have this limitation.
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