SRPP decoupling cap vs. output transformer

[matejS]

Hi, all!

Currently I have a basic SRPP configuration with decoupling capacitor. Sound quality depends on this cap. I use 0,33uF (for Rload = 47k, load of preamplifier). I plan to upgrate to better cap (MCap Silver/Oil) 0,470uF.<br/>
What about using 5uF + 0,1uF in parallel?

Or even better, using an output transformer!? How much does that usually improves the sound? Of course, using a good quality OPT.

I did not manage to found any schematic of SRPP (preamp!) design of using OPT instead of decoupling capacitor Does anyone know how to do it?

Thanks,
Matej

[dsavitsk]

With an output transformer, you are still probably going to need a cap. Otherwise, the transformer primary will just be a short to ground. Its use is less as a better sounding cap, and more as a way to lower ouput impedance, or to eliminate ground loop issues.

[matejS]

Originally posted by dsavitsk
With an output transformer, you are still probably going to need a cap. Otherwise, the transformer primary will just be a short to ground. Its use is less as a better sounding cap, and more as a way to lower ouput impedance, or to eliminate ground loop issues.

Using C = 1/(2*pi*R*f) calucaltion and the value of power amp a value of the cap can be caluclated. For 100k input impedance of power amplifier and f = 2Hz: C = 0.8uF.

Commonly used is 0.470uF... but some (hi-end) use 5uF (or even more) + 0.1uF as bypass?

Can larger value hurt? (except $$$$)
Why to bypass?

- Matej

[dsavitsk]

Originally posted by matejS
Commonly used is 0.470uF... but some (hi-end) use 5uF (or even more) + 0.1uF as bypass?

Can larger value hurt? (except $$$$)

You need to remember that the resistor that usually connects the output of your preamp to ground is in || with the input of the next stage. So, if it is also 100K, then you need to use 50K in your formula.

Also, some power amps, especially solid state power amps, have a much lower input impedance than 100K. 10K is not uncommon.

Some people think that larger caps can degrade sound more than smaller ones.

Originally posted by matejS
Why to bypass?

An inexpensive large cap bypassed by a high quality small one can take on some of the characteristics of the small one and costs less.

[Rudolfs1972]

As I understand it, it is either OPT or SRPP.
If SRPP is retained, it will be a form of a parafeed, and, unless you wish to step up/down transformer, only benefit will be low DC resistance. And you will need high primary inductance (good OPT, as you said). Or use a choke instead?