volume padding and headphone use

[cpaul]

I've had a hair trigger volume pot with quickie as a linestage ever since I built her.  OK, not quite hair trigger, but it's very sensitive.  My problem is gain, of course, and I've played with input resistors and divider circuits with some success (but not a lot).  But now I'm adding an "output" transformer for a headphone output, and given the transformer I'm using, the headphone output is quite low even at full volume pot (no/little attenuation at the input).

So the issue is...when using Q as a linestage I need less gain.  But when using it as a headphone amp, I need more gain (or at least need NOT to reduce it).  So input attenuation will only worsen the headphone situation.  This got me thinking about padding the output at the RCAs.

Would this work?  Would it interact with the plate load and cause problems?   Note I'm using the PJCCS and the v.1 of quickie.

And if it could work well, how would I wire it?  As a voltage divider?  Let's say a 25k resistor at the output (AFTER the headphone output) connected to the RCA jack and 75k from there to ground.  Or maybe 25R and 75R???  And if I do this, will it affect the impedance interaction with my amps?  I've had some hum that I think may be related to the relatively low input impedance of my following amps (Marsh A200 at 50k and a gainclone at 20k I think) and my overall gain situation.  I also ask b/c one solution to my excessive gain was to pad the input of my amps, effectively increasing the amp input impedance.  So what's the difference between padding at the quickie output vs the amp input?  From an electrical perspective, they seem the same (ignoring the minor cable resistance and capacitance).

Thanks all.

[Paul Joppa]

The stock Q has a 4K plate resistor, which is replaced with a current source in the PJCCS. So you could load the Q with a 4K voltage divider and get the stock overload/distortion performance. Using a higher impedance divider would give in-between performance of the Q, but with increasing output impedance.

Without going into the math, a 12K divider or less would still never exceed the 4K output impedance of a PJCCS'd Q, no matter what attenuation was chosen. You can use a potentiometer as a divider, of course. Given all the above, I suggest a 10K potentiometer between the output capacitor and the output RCA jack as a reasonable compromise and an inexpensive experiment. The stock 2.2uF output capacitor is adequate.

[cpaul]

Thanks Paul.  Are you saying if I do that I'll get standard Quickie performance or just that distortion performance will be like distortion in a resistive plate-loaded Quickie?  I like the effect of the PJCCS and don't want to lose that sound quality, but I don't care how distortion is rendered (it's virtually never operating in that region anyway). 

Since I think I already have issues with output impedance with all of my amps, I'll have to test this and see what happens.  Anyway, thanks for your wisdom!