Gain mod on my amp

[giordydiver]

Hi guys, i need your help for my amp. I built my amp, very special tone but to much gain...to limit it i thing to change gain to from 1m to 500k. What do you thing about it? Any tone change?
Other could be a 2.2m resistor between wiper and ground...

I wait your advices...thanksq

[axeman]

What did you build

[giordydiver]

Is my project based on hot rodded jcm,
First stage 1.5k/680n, gain pot 1m
Second stage 10k/100n, voltage divider 470k/470k
Third stage 10k, voltage divider 470k/470k
Forth stage 820k/680n with 720p snubber cap
Very good sound but to much gain, i thing to change 1m to 500k to have less gain and more usable pot range, also it should reduce hiss(I known that for hi gain amp is better 500k than 1m, like soldano slo).
What do you thing about?

[axeman]

Convert to stock 800

[giordydiver]

I prefer this tone, than jcm...i want only decrease gain

[axeman]

Replace the 100k plate resistors 56k

[giordydiver]

Why don't change gain pot?

[d95err]

Changing the gain pot to 500k would probably not make much difference. I'd be more radical, e.g 100k, perhaps with a series resistor before it to reduce gain further.

Other things to try is removing the 100n on the second stage or the 680n on the last stage.

To reduce noise, use a snubber cap on the first stage.

[neikeel]

You could tap off more signal to ground with either of your voltage dividers between stages, try paralleling another 470k over one or both of the resistors going to ground, that will be temporary and you can tweak with different values to get where you want.

[giordydiver]

What about 500k gain pot? In term of noise and gain

[neikeel]

the shunt is easier to tweak

[giordydiver]

the shunt is easier to tweak

Sorry but in what sense?i dont understand(my english is not the best...sorry)

[neikeel]

Your voltage dividers at the moment are 470k signal and 470k to ground (bit like a 1M pot in the mid setting.

If you decrease the resistor to ground, i.e. add another 470k in parallel just by tacking it on temporarily you halve the resistance to ground and you get less signal passed to the next stage, it is easier to do than replacing a pot, but it is your time and effort to tweak so by all means have a try

[darkbluemurder]

Is my project based on hot rodded jcm,
First stage 1.5k/680n, gain pot 1m
Second stage 10k/100n, voltage divider 470k/470k
Third stage 10k, voltage divider 470k/470k
Forth stage 820k/680n with 720p snubber cap
Very good sound but to much gain, i thing to change 1m to 500k to have less gain and more usable pot range, also it should reduce hiss(I known that for hi gain amp is better 500k than 1m, like soldano slo).
What do you thing about?

Do you have anything before the 1m gain pot? If not I would insert a 470k resistor in parallel with 470pf cap and add a 220k resistor from the volume input to ground. That would reduce the gain especially in the bass and low midrange.

I also would take out the 680nf cathode cap on the fourth stage - too much gain IMHO with four gain stages. That would decrease the gain in the high and high midrange especially.

These two tweaks should be enough. If not you can also tweak the voltage dividers by changing the 470k resistor to ground for something lower, e.g. 220k.

Cheers Stephan

[giordydiver]

Is my project based on hot rodded jcm,
First stage 1.5k/680n, gain pot 1m
Second stage 10k/100n, voltage divider 470k/470k
Third stage 10k, voltage divider 470k/470k
Forth stage 820k/680n with 720p snubber cap
Very good sound but to much gain, i thing to change 1m to 500k to have less gain and more usable pot range, also it should reduce hiss(I known that for hi gain amp is better 500k than 1m, like soldano slo).
What do you thing about?

Do you have anything before the 1m gain pot? If not I would insert a 470k resistor in parallel with 470pf cap and add a 220k resistor from the volume input to ground. That would reduce the gain especially in the bass and low midrange.

I also would take out the 680nf cathode cap on the fourth stage - too much gain IMHO with four gain stages. That would decrease the gain in the high and high midrange especially.

These two tweaks should be enough. If not you can also tweak the voltage dividers by changing the 470k resistor to ground for something lower, e.g. 220k.

Cheers Stephan

hi, before 1m gain pot i have 470k/2200p.
I want try to change each to 470k/330k(10% less gain than 470k/470k)

To reduce bass response i want try to change first coupling cap to 4.7nF...
About 680n on 4th stage, i dont know, i don't want loose harmoncs, but to reduce high frequencies i think to decrease a bit preamp anodic voltage, for PI 320v(now 333v), for 4th and cathode follower 285v(now 298v) and for 1th 2th e 3th stage 270V(now 285V)..
what do you thing about?