I've heard that the quality of a feedback cap can influence sound quality quite a lot. Since the feedback cap in my circuit is large (47uF) film caps are out of the question.
What should I look for ?
Coupling cap spec like low leakage and low distortion, or low esr/esl spec like decoupling caps ? In a coupling situation a nonpolar low leakage elyt is often preferable to a high spec low esr cap like os-cons IMHO.
What should I look for ?
Coupling cap spec like low leakage and low distortion, or low esr/esl spec like decoupling caps ? In a coupling situation a nonpolar low leakage elyt is often preferable to a high spec low esr cap like os-cons IMHO.
Thank's for a quick reply. So a standard elyt cap, perhaps bypassed by a film cap, is what you recommend. In other words a silmilar setup to a signal coupling cap ? Some people find that specific caps like Elna for audio, Rubycon BG nonpolar etc make a difference. Anyone who has tried out different elyt caps in a feedback position ?
It may be all in my head, but feedback caps are the one place where I think I hear a difference. The key is up above- choose a large enough cap that no significant AC voltage appears across it. It can't have much effect if it's a short at all audio frequencies. Though they're great for bypassing and have very low esr, I don't like OS-Con caps in this location. IMO, NP electrolytic caps are undesirable as well. Go with a very high quality standard aluminum electrolytic, possibly protected from over voltage with a diode chain as Doug Self recommends. IMO, standard case sizes and higher voltages are also better than the ultraminiature ones.
The worst film cap is way better than the best electrolytic, though for the feedback values I use in power amps, I've never been able to shoehorn in enough film to do the job. Still, if you can do it, that's the way to go.
Question- with a jfet diff amp, why can't one scale up the feedback divider so the necessary cap is much smaller? That would seem to be a good reason to go jfet.
Question- with a jfet diff amp, why can't one scale up the feedback divider so the necessary cap is much smaller? That would seem to be a good reason to go jfet.
I can source "boutique" caps said to to good for audio signal coupling that would fit in my rather small power amp pcb with a lot of smd components. Either a Black Gate type C (C=coupling) or an Elna silmic, both 47uF 50V (high voltage rating for low tan delta). Neither is particularly expensive. There is a more expensive Black Gate type N (N=Nonpolar) but it is too big. Would you use anything else in this scenario?
Hi - thought I'd re-awaken this thread as I have a 47uF 63V MMK film cap. I was going to use it for the feedback capacitor in a Quad 606, but the folk at DaDa eletronics (Quad service/upgrade specialists) told me a non-polar cap should not be used in this position (C7).
Circuit diagram below:
http://www.dc-daylight.ltd.uk/Valve-Audio-Interest/Schematics/QUAD-606-service-data.pdf
I'm no expert so thought I'd double check opinion over here, as I've heard replacing eletrolytics is usually desirable in the feedback position?
Thanks,
- John
Circuit diagram below:
http://www.dc-daylight.ltd.uk/Valve-Audio-Interest/Schematics/QUAD-606-service-data.pdf
I'm no expert so thought I'd double check opinion over here, as I've heard replacing eletrolytics is usually desirable in the feedback position?
Thanks,
- John
In my amps I just use a standard 47uF electrolytic in the feedback chain just as most other designs do.
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