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-   -   Question for CarlosFM & jean-paul (http://www.diyaudio.com/forums/solid-state/85474-question-carlosfm-jean-paul.html)

georgehifi 28th August 2006 07:55 AM

Question for CarlosFM & jean-paul
 
Just a question to you both, I notice you both advocate the use of .1uf MKT from + to - of opamps.
Can I ask what is the side effects if this cap is too big IE .4uf.
The reason I ask is that my active xover has 4 x quads and I put a .1 mkt at the + and - of each opamp and it is so smooth is it possible that the dynamics have been squashed becase in reality the supply is seeing not .1uf across it's + and- but in my case .4uf.
But then I also at the same time I did the .1uf caps, I changed the quads from TL074 's to AD713's maybe it's the that I need to get used too.

Cheers George

jean-paul 28th August 2006 08:30 AM

It's the change of opamps that changed the sound. Don't be afraid of using a 0.1 uF from + to - at each opamp: it should be done that way !

About advocating the caps: I am only using the cap from + to - with fast and sensitive opamps like OPA627/637 and the like. With bipolar opamps I do not hear a difference.


georgehifi 28th August 2006 09:49 AM

Thanks jean-paul, I also put the Panasonic FC 10uf X 50v at each rail to ground on each opamp. And my mistake it wasn't TL074's that I had before it was LF347's, and the AD713 has made the LF sound like a distorted mess up in the higher frequencies when the music becomes complex, if it was simple music the LF's were in control.
What is realy weird to see both on the scope, both gave perfect square waves at 100k with no overshoot, both flat out to 600k, both have very low dc offset the AD713 a little better (I have dc coupling from input to output) both are very low noise, they are basicaly indistingushable as far as the scope can see and it's a 400mhz Tektronic.
But the sound presentation is night and day, I have some you- beaut OPA4134UA smd here just waiting for the browndogs to arrive, I have a feeling they are really going to take some beating if all the hype is to be believed.

Cheers George

classd4sure 28th August 2006 10:43 AM

Quote:

Originally posted by jean-paul
It's the change of opamps that changed the sound. Don't be afraid of using a 0.1 uF from + to - at each opamp: it should be done that way !

About advocating the caps: I am only using the cap from + to - with fast and sensitive opamps like OPA627/637 and the like. With bipolar opamps I do not hear a difference.



Hi,

This is done for stability at RF?


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