4uF Coupling Cap Suggestions for this CCS stage

[riotubes]

I'd appreciate some suggestions for 4uF coupling caps for a dac stage (and a source to buy if possible).

I'm nearly finished building an output stage that is a discrete design by John Swenson based on Gary Pimm's CCS boards used as a current mirror. I did not build the follower shown on the right side of the schematic linked below.

I don't want to spend a fortune but want to do justice to this circuit and have read posts by others who say one can really hear the difference in various caps with this type of design.

http://db.audioasylum.com/cgi/m.mpl?...ohn+swenson&r=

[SY]

Here's a better idea: increase the impedance of the load, then use smaller caps. At 1u, a load of 100k will give you a sub-2Hz corner frequency, and it will be a lot easier to find a high quality 1u cap. My personal recommendation is Wima FKP, but there's lots of good alternatives.

Don't take the audiophile testimonials too seriously, you'll spend less and get just as good a sound. There's a lot of misunderstanding and hype surrounding caps; the reality is that if you avoid the worst, you'll be fine.

[riotubes]

Thanks for suggesting this alternative SY!

I use a Transformer Volume Control (Stevens & Billington TX-102). Here's what S&B says about input impedance....

"The input impedance of the TX-102 is strongly dependent upon the load impedance and selected attenuation. The worst-case input impedance occurs with no attenuation selected, in this case the input impedance will equal the load impedance plus the copper losses for the unity gain connection/version. As the TX-102 should not be used with loads lower than 10kOhm the use of a 2.2uF or larger coupling capacitor in equipment preceding the TX-102 should suffice in all conditions unless the device is operated with the split primaries in parallel."

I use 2 amps from time to time:
- 300B SET with input impedance = 100K ohm
- First Watt F3 with input impedance = 10K ohm

My current Dac stage has 2.2uF coupling capacitors on the output and the volume level on both amps is sufficient.

Please educate me:

- I was thinking that the circuit required this 4uF value, but I am gathering that it is only the equipment downstream that should determine the value?

- The S&B specs state that if the load impedance is 10K ohm (i.e. my F3) then I need 2.2uF. But you suggest that for my 100k ohm load (300B SET) I can get away with just 1uF. The goal here is to set the cap value to realize a sub-2Hz corner frequency? Can you describe what this means in laymen terms?

Thanks!