I'm upgrading a nice phono preamp. It has inexpensive output coupling caps (some generic type). I'd like to play around to see if a premium or at least better than mass production inexpensive cap would improve things.
This unit has 2 30uF film caps coupling two 6922 tubes to the output to single ended RCA outs. That seems like such a massive size. Do I have some leeway in going down in capacitance? I don't like messing with a designers voicing but caps of that tolerance start getting huge when you buy better product.
This unit has 2 30uF film caps coupling two 6922 tubes to the output to single ended RCA outs. That seems like such a massive size. Do I have some leeway in going down in capacitance? I don't like messing with a designers voicing but caps of that tolerance start getting huge when you buy better product.
That all depends on the input impedance of the next stage, either a line level preamp or a power amp with volume control. If you use a tube preamp or power amp, most likely you can reduce it 10 folds, anything above 50KΩ. Again, check on the specs of the next stage.
Oh thank you directdriver!
I'm running the RCA outs from the phono tube preamp to a Vincent SA-T7 tube preamp with > 22 kOhm Input Impedance.
As an aside, my Vincent has tons of gain (not adjustable) and I run a low output moving coil and currently only need 47dB of gain on my phono pre as opposed to its higher setting of 62dB.
I'm running the RCA outs from the phono tube preamp to a Vincent SA-T7 tube preamp with > 22 kOhm Input Impedance.
As an aside, my Vincent has tons of gain (not adjustable) and I run a low output moving coil and currently only need 47dB of gain on my phono pre as opposed to its higher setting of 62dB.
A 22KΩ input impedance is pretty low for a tube preamp. (And it uses 8 tubes for a line stage?!) Must be a 25KΩ pot with a 220KΩ input resistor. Anyway, based on the calculator, if you used a 3uf cap coupled to a 22K load, you would have roll-off point at 2.4Hz. You can experiment with values from 1uf to 5uf to see what you like.