gain pot question

[12AX7]

if i put a 220k resistor in parallel with a 1M resistor the result is 180k. Question is, when putting a 220k across a 1M gain pot, given that the wiper is variable and the pot isn't a simple variable resistor, does this give you the same exact thing as using a 180k pot or are there other considerations? I ask because i did this to reduce gain and it works, but i can't help but wonder if i am missing something tonally with the pots ground reference now being 180k instead of 1M.

[HotBluePlates]

No, not really.

Plus, the lowered resistance to ground represents a heavier load to the previous stage, and actually kills some of the gain available from that previous stage.

Why the desire to parallel a 1M audio pot with a resistor?

[12AX7]

Well, i wanted to reduce gain but the way the circuit doesn't really have a place to put a voltage divider, at least not that sounde good. An other things i've tried like a split plate load seemed to change the tone too much.
When you say "no, not really", are you saying it's NOT the same as using a 180k pot?

[HotBluePlates]

It is somewhat the same, but only when the pot is full up. This specific technique is all about faking a linear pot into a log taper.

What is the circuit in question?

Ways to lower gain:
1. Add a resistor to the top of the 1M pot, to set an upper limit on the output available. It seems you tried this already. Does not change the gain of the stage itself, only the output signal level.

2. Use a split plate-load, which also reduces output signal. Does not change the gain of the stage itself, only the output signal level.

3. Use a smaller valued resistor/pot in place of the 1M. This reduces the gain of the previous stage by loading.

4. Remove cathode bypass cap of the previous stage (if present). Will reduce an average stage's gain by 1/2.

5. Change plate and/or cathode resistor values to achieve less gain and/or less output and/or more/less output before distortion. Requires an analysis of the original stage values to determine how to alter the values to arrive at the desired result.

6. Change plate and/or supply voltage. Will change output signal strength, possibly also output before distortion and/or nature of distortion. How to change depends on specific original circuit and desired result.

7. Change the tube to a lower-mu tube. May require additional changes to plate/cathode resistors to arrive at a suitably-performing stage.

8. Add NFB to the stage. Different from local NFB due to an unbypassed cathode resistor. Requires addition of a cap and resistor, possibly an addition of/change to a series grid resistor. Gain can range from 1 to full normal stage gain.

9. Any combination of several of these techniques.

And there are other ways as well.

Are you trying to reduce the output signal of the stage to prevent/limit overdriving of the subsequent stage, reduce the distortion within the preceeding stage, or ???

[12AX7]

I've tried most of those, but in #1 do you mean in series with the wiper? If so, that would be a grid stopper and i lowered one there to brighten the tone.
So far i have found nothing works w/o changing the tone, even when with each method I turn the gain up to match where i usually keep it. (treble bleed partially responsible 4 that) I guess it's just part and parcel of lower gain. This is nit picking tho because i'm pretty happy with it as is. Just wondered if doing this was in some was detrimental and i would later start noticing it.

[HotBluePlates]

... in #1 do you mean in series with the wiper? ...

No. Between the coupling cap from the previous stage and the "input" to the pot (the ungrounded outer lug). This creates a fixed voltage divider when the pot is full up.

In other words, it is like a volume pot which you can't turn above "8" (or any upper limit you choose, based on the pot, pot taper and resistor values).

[The_Gaz]

You can also add a voltage divider directly after the pot, and if the series resistor darkens the tone too much,  you can add a bright cap across. The bright cap can be used with HBP's method as well if the tone becomes too dark.

[12AX7]

I do have a resistor at the pot's input, but  i have a 390pf across it. In fact, that 220k on the pot was part of a voltage divider i had between the 470k/390pf network and the pot. But i was looking at it and thinking the network's resistor and the one after it were both part of the divider and therefore rather large. So i removed the one at the input lug. It went like this...470k/390pf>330k>input lug, then a 220k across the pot. I was thinking of it like this...the RK network was there to add the bit of high end sweetness, the 330k and 220k were a voltage divider before the pot. So i had that high pass filter, a voltage divider, then the gain pot. So 2 voltage dividers in succession. I looked at the 470k/390pf as a seperate thing till i realized the 470k and the 330k after it were basically making the voltage divider a 800k/220k divider with  that cap passing 470k of the 800k series resistance. I realize that was probably confusing, but i hope it can be understood.

As for a divider AFTER the pot, thats something i haven't tried so i'll give it a go. I just hate slopping up this board which is why i ask questions first before trying in hopes of getting an answer that will make me realize whether it's worth reflowing the solder joints again or not. But i'll give that a shot since i don't have to flow any turrets top do that. I'll let u know how that goes. Thanks.

[HotBluePlates]

It went like this...470k/390pf>330k>input lug, then a 220k across the pot. I was thinking of it like this...the RK network was there to add the bit of high end sweetness, the 330k and 220k were a voltage divider before the pot. So i had that high pass filter, a voltage divider, then the gain pot. So 2 voltage dividers in succession. I looked at the 470k/390pf as a seperate thing till i realized the 470k and the 330k after it were basically making the voltage divider a 800k/220k divider with  that cap passing 470k of the 800k series resistance.

There's GOT to be an easier way.

Honestly, I can barely follow what's going on there, and why it has to be so complicated.

What is the circuit, and the desired result?

[12AX7]

No matter. It's actually very simple but hard to clearly explain. But i tried the suggestion of a divider after the pot and that worked great. However, it also made me realize that the way it is just seems to be the best amount of gain for the sake of the tone. It just seems to be the way it sounds best so i'll leave it as is. Like i said before, it's nit picking because it's good as is.