Why do IC opamps suck? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd May 2002, 05:30 PM   #1
diyAudio Member
 
MRehorst's Avatar
 
Join Date: May 2002
Default Why do IC opamps suck?

I have heard much derision of op-amps over the years and have yet to hear a detailed, technical analysis of what is wrong with them. Usually all I hear is "they sound bad", and some stuff about negative feedback, but no real technical analysis.

If they "sound" bad, there must be some identifiable deficiency in performance- either distortion, noise, frequency response, or dynamic response.

Can anyone in this forum steer me toward any good engineering-based analysis of discrete vs. integrated circuits and how measured peformance relates to perceived "sound"?

Thanks,

MR
  Reply With Quote
Old 23rd May 2002, 05:45 PM   #2
Banned
 
Join Date: Feb 2002
Location: Dallas,Texas
Thumbs up Not all op-amps suck.

Some people just feel that discreet designs have much more flexibiliy about what transistors to use, what topology to use, how much feedback ect. It is also more fun than just picking feedback resistors for op-amp design. If op amps are your cup tea there are dozens of very good ones. The question reminds of something I read once about one THE best opamp designers (I have listened to several of his opamp designs and they a very good) having a preamp made with discreet Jfets in his stereo at home. Kind of funny huh..... plenty of us roll your own types have used opamps, in all fairness I must admit that some opamps are quite good. Do a search on the forum.

http://www.dself.demon.co.uk/webbop/opamp.htm

http://www.passdiy.com/pdf/diyopamp.pdf

H.H.
  Reply With Quote
Old 23rd May 2002, 05:52 PM   #3
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Default Op-Amp Blues!

Well.

1) Insufficient bias in output stage for some applications and switches to class B. Sound better with a buffer attached so as not to load the output stage down.

2) Transient thermal distortion. Since the device is built on the same substrate when the output stage heats up it thermally modulates the other parts of the amp.

3) Output stage is usuall quasi-comp. problem of making matching p and n channel devices in the manufacturing process.

4) Istability problems and require some form of external compensation applied at the WRONG place. Compensated devices usually don't sound good.

5)Headroom limited by the rail voltage.

6)Duals usually have poor seperation detween devices


The list goes on but my main gripe is lack of control of the circuits operaing parameters.

Jam

P.S. Harry feel free to chime in at any time.....
  Reply With Quote
Old 23rd May 2002, 05:52 PM   #4
diyAudio Member
 
NU_NRG's Avatar
 
Join Date: Dec 2001
Location: Quebec, CANADA
Send a message via ICQ to NU_NRG
You might also be interested in viewing this website


-Simon
  Reply With Quote
Old 23rd May 2002, 07:34 PM   #5
diyAudio Member
 
MRehorst's Avatar
 
Join Date: May 2002
Default Re: Op-Amp Blues!

Quote:
Originally posted by jam
Well.

1) Insufficient bias in output stage for some applications and switches to class B. Sound better with a buffer attached so as not to load the output stage down.

>> Typical opamp output Z is <100 Ohms. What would you connect to it that would "load it down"? Almost all power amp inputs are >10K zin...

2) Transient thermal distortion. Since the device is built on the same substrate when the output stage heats up it thermally modulates the other parts of the amp.

>> I can see where this might be possible, but since the circuits tend to be differential gross thermal effects will tend to cancel. In a discrete design, you don't have the tight thermal coupling and THAT can lead to all sorts of problems.

3) Output stage is usuall quasi-comp. problem of making matching p and n channel devices in the manufacturing process.

>> OK, I know it isn't the philosophical ideal of mirror image
but what effect does that have on the sound?

4) Istability problems and require some form of external compensation applied at the WRONG place. Compensated devices usually don't sound good.

>> There's that "sound" word again. What characteristic of the sound is affected by this, and how do you attribute that particular effect to this particular "problem"?

5)Headroom limited by the rail voltage.

>> Very few audio system sources (CD players, tuners, tape decks, phono cartridges, etc.) exceed more than a few volts pk-pk. With 15V rails, most op-amps can swing 12-13Vpp out.

6)Duals usually have poor seperation detween devices

>> I routinely see specs of about 100 dB dropping to 60 dB at 20 kHz. How much more separation is necessary? If you gotta have better separation than that, use two of them, they're usually pretty cheap...

The list goes on but my main gripe is lack of control of the circuits operaing parameters.

Jam

P.S. Harry feel free to chime in at any time.....
  Reply With Quote
Old 23rd May 2002, 08:08 PM   #6
JoeBob is offline JoeBob  Canada
diyAudio Member
 
JoeBob's Avatar
 
Join Date: Nov 2001
Location: Montreal, Canada
Well, if you like them, good for you. I don't mind th sound of opamps, some designs with them sound really good. But they just aren't any fun. Like harry said picking a feedback resistor isn't any fun. Also with discrete designs you can change whatever you want and see how it affects the sound. With opamps you can't change anything, so you can't improve upon it in any way.
  Reply With Quote
Old 23rd May 2002, 08:18 PM   #7
Banned
 
Join Date: Feb 2002
Location: Dallas,Texas
Unhappy Engineers......

Man I have had these discussions over and over and over again.
Like I said if op-amps float your boat, go for it. I you want to do the work and go listen and build some discreet transistor circuits there are plenty links and references on the forum. I am a degreed BSEE and I don't get bogged down in the objective verses sujective debates anymore. After a few years of building and comparing different circuits you will form your own opinions and come by them honestly and the hard way which is the best way to learn. Check out the Borbely website since he is both a very technically astute engineer and also designs by listening. Psssst....... don't tell anyone but the two approaches are not mutually exclusive. Good audio designs are made to be listened to, not measured. The ear is the final arbitor......

http://www.borbelyaudio.com/

H.H.
  Reply With Quote
Old 24th May 2002, 02:40 AM   #8
diyAudio Member
 
Join Date: May 2001
In addition to all the points mentioned, maybe the bottom line is that IC op-amps are designed to be multi-application by design. Regardless of what it is, generally speaking, something that is designed to do multiple things, rarely does one thing especially well. Without getting too technical about the IC’s design, it basically means that the IC may have extra stages and components on the substrate that are superfluous to our needs. Many feel these “extras” detract from the ultimate possible performance.

Personally I’m over the “challenge” of designing, it’s just that I feel discrete components are able to do the job better for most applications in which we may otherwise use an IC op-amp.

Cheers,

Pete
  Reply With Quote
Old 24th May 2002, 05:33 AM   #9
diyAudio Member
 
Lisandro_P's Avatar
 
Join Date: Oct 2000
Location: Argentina
Send a message via ICQ to Lisandro_P
Opamps *DO NOT SUCK*... there're EXCELLENT opamps for audio, and if you use them well, they'll surely sound great. As JoeBob and Harry said, i tend to pick discrete circuits because they're more fun from the building/designing point of view. And tend to sound better, but this is only my opinion.

I want a discrete preamp for my next project (well... a preamp ) but the new preamp Rod Elliot proposed, using the burr brown chip looks yummy...
  Reply With Quote
Old 24th May 2002, 05:45 AM   #10
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Quote:
Originally posted by Pete Fleming
IC op-amps are designed to be multi-application by design.
Well, no, some op amps are specifically meant to amplify audio, e.g. OPA2134.
I remember Thagard's phono preamp design article in Audio Express, where he said it was very difficult to surpass op-amp quality using discrete components. I would bet that at this level of performance, the layout is critical and probably more important than the choice of discrete vs. opamp.
Having said all that, I agree that discrete is probably more fun. But if I have a little bit of room left in my preamp box and need a quick, high-quality headphone amp for my Senns, I'll throw in an opamp.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: Opamps Charlez Swap Meet 2 17th August 2008 10:45 AM
OPamps xaudiox Swap Meet 2 31st August 2006 02:40 AM
FS: Power Chip OpAmps and other OpAmps & D to A Converter dtm1962 Swap Meet 4 12th January 2006 10:07 PM
Opamps seiko_citizen Swap Meet 7 3rd May 2005 03:09 PM
blackouts suck :( dorkus The Lounge 7 18th August 2003 08:28 PM


New To Site? Need Help?

All times are GMT. The time now is 05:14 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2