removing the volume pot

[mete]

I am using a preamp and since it has a volume control, I wonder if I can remove the volume pot on Crack. Can I directly connect the input to 12AU7 or do I need a resistor (like the volume pot is at max position) ? Is there a disadvantage of doing this or in other words is there a difference between half input level (from preamp) + max volume (fixed resistor) on Crack vs full input level + half volume on Crack ? Preamp output impedance is 75 ohms.

[Paul Birkeland]

I would leave the pot in the Crack, as you may find that it works better with your preamp if the volume pot is turned down rather substantially.

[mete]

OK, can you elaborate why it may work better ?

[Paul Joppa]

One risk is that you might end up with too much gain,leading to a hair-trigger volume control. try he connection with the Crack control all the way up and see.

[mete]

One risk is that you might end up with too much gain,leading to a hair-trigger volume control. try he connection with the Crack control all the way up and see.

Full preamp output (my sources are ~2Vrms and preamp is 1x gain) and full gain (without attenuation) on Crack will definitely be too much but what I mean is I can change the input level (to Crack) anyway from the preamp. Actually independent of my actual question (removing the volume pot question), the real question I ask is I think: is there a difference attenuating the signal at preamp vs. attenuating it on Crack (before the gain stages naturally) ? Lets say I am comfortable with 0.2V before the gain stages on Crack. I can attenuate 2Vrms source to 0.2Vrms on preamp (and keep Crack at max valume) or keep 2Vrms at some level at preamp output and attenuate it on Crack. Is there a difference between them ?

[Paul Joppa]

Yes, there is a difference. It has to do with the noise floor. If the preamp has an audible noise floor then you'd want to attenuate its output.

The ideal is to get each component to work at its best signal level, steering between noise floor and overload (distortion or clipping). That's complicated by the desire to get the primary volume control operating in its sweet spot, generally the top 2/3 of its range. The best compromise will change a bit if you use headphones of different voltage sensitivity.

Of course you may have no detectable problems, in which case you can substitute a resistor for the potentiometer as planned, no problem. That's why I suggested trying it before removing the control on the Crack.

[mete]

Yes, there is a difference. It has to do with the noise floor. If the preamp has an audible noise floor then you'd want to attenuate its output.

The ideal is to get each component to work at its best signal level, steering between noise floor and overload (distortion or clipping). That's complicated by the desire to get the primary volume control operating in its sweet spot, generally the top 2/3 of its range. The best compromise will change a bit if you use headphones of different voltage sensitivity.

Of course you may have no detectable problems, in which case you can substitute a resistor for the potentiometer as planned, no problem. That's why I suggested trying it before removing the control on the Crack.

Thanks Paul