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Old 6th September 2004, 02:28 PM   #1
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Default NE5534 Compensation Cap

Going to be doing a bit of experimentation, and I want to use an opamp with external compensation, such as the 5534.

So, is there another opamp suitable for audio with that pinout (yes, I need the same pinout as the 5534)? I've been searching, and so far come up empty-handed...

If not, the 5534 will probably be fine, but I'd love to expand my options here.
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Old 6th September 2004, 03:10 PM   #2
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You can just pick any good opamp, OPA134 is not too bad.
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Old 7th September 2004, 05:01 AM   #3
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I wish I could.

This opamp sits at the input of the amplifier section, and the whole driver+output stage is in the feedback loop. I believe that I will need the ability to adjust compensation in order to achieve stabiity in this amp, which is why I brought up the 5534 and (so far) only the 5534 seems to allows this external 'tweak'.

Just wanting to know if there are any others (that might be acceptable for audio).
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Old 7th September 2004, 06:20 AM   #4
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If you have the 22 pF attached and the opamp have a gain of 1 or near you can probably change the opamp but if it happens to be in a feedback of some kind it would help if you could get a schematics.
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Old 7th September 2004, 12:37 PM   #5
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Quote:
Originally posted by EchoWars


This opamp sits at the input of the amplifier section, and the whole driver+output stage is in the feedback loop. I believe that I will need the ability to adjust compensation in order to achieve stabiity in this amp,
Hi Echo

You can use a unity gain stable op amp and use a capacitor (5pF ...10 pF) between the output of the op amp and the input feedback node.

This way, you have feedback from the output of the amp in the audio frequencys and from the output of the Op amp in the Mhz region...This will increase stability...

Regards
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Old 8th September 2004, 01:38 AM   #6
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Quote:
Originally posted by peranders
If you have the 22 pF attached and the opamp have a gain of 1 or near you can probably change the opamp but if it happens to be in a feedback of some kind it would help if you could get a schematics.
I do have the schematics, and I have tried this on another identical amp some time ago with little luck (oscillated like crazy no matter what, and I gave up without battling too much),

The original opamp in this Philips AH578 amp is a RCA CA3100S. Very fast, but the amp I was working on then had a dead one, and I was having extreme trouble finding another one, so I was going to find a way to make a OPA604 or NE5534 work. Both oscillated, and in the midst of my frustration, I found a source for a CA3001 (for $20 ). I bought it, and called it a day.

Now I have another 578, and although the CA3001's in it are functional, memories of being beaten by the other amplifier linger, and I wanted to resume where I left off.

Tube_Dude, I may do this, but I was hoping to use existing traces and component holes. No biggie, and I can do it as you describe. But my question here was as much to see if the 5534 was the only opamp to offer the external compensation pins as to find a solution.

Thanks guys!!
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Old 2nd January 2006, 02:41 PM   #7
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Hello!

I have attached a simplified schematic of the NE5534 circuit.
I have put in a few values of components
that I have been able to find.

I think it can be interesting to compare this circuit to other amplifiers.

The NPN input differential stage, with offset adjust possibility,
drives a dual PNP stage, which is brought together by a mirror.
So far is like many other amplifiers.
But the last stages are all NPN based.

There are no less than 4 small capacitors, that helps amp to do better.
100pF, 40pF, 7pF and 12pF.
This last 12 pF is the internal compensation cap.
This is recommended to be parallelled with external 22 pF ( Pin5 - Pin8 )
when using NE5534 as a buffer. Gain = 1.
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File Type: png ne5534-2.png (9.9 KB, 977 views)
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Old 2nd January 2006, 02:51 PM   #8
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Quote:
Originally posted by lineup

The NPN input differential stage, with offset adjust possibility,
drives a dual PNP stage, which is brought together by a mirror.
So far is like many other amplifiers.
But the last stages are all NPN based.

There are no less than 4 small capacitors, that helps amp to do better.
100pF, 40pF, 7pF and 12pF.
This last 12 pF is the internal compensation cap.
This is recommended to be parallelled with external 22 pF ( Pin5 - Pin8 )
when using NE5534 as a buffer. Gain = 1. [/B]

Good PNPs are hard to make in ICs without fancy fab processes

The NE5534 was a masterpiece of nested feedback to get its distortion figure low.
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Old 2nd January 2006, 06:44 PM   #9
mikeks is offline mikeks  United Kingdom
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http://www.diyaudio.com/forums/showt...278#post221278
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Old 2nd January 2006, 10:37 PM   #10
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by EchoWars
I do have the schematics, and I have tried this on another identical amp some time ago with little luck (oscillated like crazy no matter what, and I gave up without battling too much),
The original opamp in this Philips AH578 amp is a RCA CA3100S.
Neither the NE5534 or OPA604 have the required gain-bandwidth product, I suspect they have used the CA3100 because of it's speed - it was never a cheap part. However... have a look at another one from the olden days: the LM318. This is just off the top of my head, I may be dead wrong here - the LM318 is slower (but not that much slower). A schematic of the circuit would help a lot. In general external compensation on OPamps is not standardized, although it may involve pin 1 and 8, often different connections are required with a different OPamp. Also, you may want to look at the single OPamps in general. If it is only the OPamp itself that is being compensated, you may get away with a higher GBW product amp that is internally compensated.
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