Lowering plate resistor to lower gain w/o affecting tone/harmonics etc

[12AX7]

I like the way this sounds after a number of changes i made recently but the one thing i can't seem to do w/o affecting the tone and feel is to eliminate what is for my tastes excessive gain. Tried split loads, lowering master value, (w/parallel R) higher cathode value on V2A, tried a 68k where u now see 220k at V2A. Then i tried lowering the plate R at V1B to 50k by paralleling a resistor which put the gain in a good range but affected the tone and feel some.  If i were to do it permanently I'd use a 56k. Question is, if i were to lower gain that way permanently using a 56k plate R, is there a cathode R and cap combo i could change to that would retain the same feel and tone while only lowering gain?

[kagliostro]

Have you tried various option with split load ?

That (the split load resistor) is a method that usually performs well


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You can put a minimum value resistor and a pot and take the signal from the wiper of the pot, then try options turning the shaft of the pot till you find the right split valute

ATTENTION doing that, position an INSULATED knob on the shaft and use rubber glove, turn the shaft when the amp Is OFF or in STANDBY

BE CAREFUL PS capacitors can have a residuale charge

Franco

[pdf64]

Yes, 2 options that should have little effect on valve operating points are to split the 100k anode load resistor, or to split the 220k grid leak resistor.
For an example of the former, see the 6G3 deluxe 2nd stage https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_6g3.pdf

[shooter]

I always go the easy route
put an AU7 in v1 and or V2, since they are low gain tube, you get less gain 
if V2 is your happy spot for using an AU look at Merlins example of a properly configured DCCF

[ac427v]

I find a 12AY7 in V1 to be my favorite tube to lower gain without creating unwanted tonal changes. I use that in a 6V6 plexi with great results. The Y version was used in the tweed bassman--that's good enough for me

[pdf64]

The preamp design is a hot rodded 2204, so it will have a lot of gain.
If it’s too much, why not revert to a standard 2204 preamp gain structure?
ie 2nd stage cathode to 10k unbypassed.

[12AX7]

The preamp design is a hot rodded 2204, so it will have a lot of gain.
If it’s too much, why not revert to a standard 2204 preamp gain structure?
ie 2nd stage cathode to 10k unbypassed.

Yeah, as a matter of fact i have and the difference was nite and day as gain goes. WAY too little. I couldn't even get a classic rock degree of gain all the way up. Not to mention all the complexity was gone. I'm not looking for low gain, just less. A 50k plate on V1B was about right but the tone changed enough to make me post this in hopes of a better solution. The split grid leak u mentioned sounded like a good idea, but then i had a 220k grid stopper there before and when i lost that and put the 10k thats there now just to be safe the tone was worlds better. Seems like big grid stoppers never sound good to me. Using that split load would be doing the same, or am i missing something?Come to think of it, i HAD it configured as a split grid leak before. 68Kto ground and 220k grid stopper with cap between them if thats the kind of thing u mean. Thats what i wanted to get away from. With only a 220k grid leak and no grid stopper it just sounds and feels worlds different/better. On a side note. using a split there, one R is considered a grid stopper and one a grid leak because the coupling cap is between them, correct?

[shooter]

when you split load, I believe you change the "headroom" characteristics, there will be less clean before hitting compression
throw an AY or AU in V1, no solder, no hard thinking, simply to see if that's the right direction you're looking for.
otherwise
use a scope, look at the signal as it progresses to the speaker and actually see where things get off track for you

[12AX7]

when you split load, I believe you change the "headroom" characteristics, there will be less clean before hitting compression
throw an AY or AU in V1, no solder, no hard thinking, simply to see if that's the right direction you're looking for.
otherwise
use a scope, look at the signal as it progresses to the speaker and actually see where things get off track for you

All i have is a u, but won't that drop the signal level so much the amp will lose volume? I think those are 80% lower gain which i think will be overkill. Thats the other thing i have been fighting....it's too low for band use w/o cranking it which then overdrives too much. Been looking for a higher sensitivity speaker because of that. I'll try it tho, what the heck.Also, wouldn't headroom be if you RAISE the plate load, not lower it?

[12AX7]

12AU7 actually worked pretty well, but as i thought the drive was too little. it could be great in a band context depending on how much the 6V6's are adding to the amount of OD, but i'm not sure. i will take it with me next time out tho. I think what i will do now is try a split load again and put 2 coupling caps on a switch on the AC side and switch between them so if i find i don't like it next time out with band i can switch back. This time a 68k from the plate so there will be a bit more gain but maybe less change in tone or feel.

[pdf64]

Yeah, as a matter of fact i have and the difference was nite and day as gain goes. WAY too little. I couldn't even get a classic rock degree of gain all the way up. Not to mention all the complexity was gone. I'm not looking for low gain, just less.

That’s strange, I think the 2204 is generally considered to have a medium gain overdrive preamp. Consider the possibility that there was an error in your implementation of the circuit.

Whatever, have you considered a halfway house in the 2nd stage cathode arrangement, eg somewhere between 10k unbypassed and 1k5 fully bypassed?
ie how does it sound with the 1k5 unbypassed?

…. With only a 220k grid leak and no grid stopper it just sounds and feels worlds different/better.  On a side note. using a split there, one R is considered a grid stopper and one a grid leak because the coupling cap is between them, correct?

Your post was such a dense body of text, containing queries based on descriptions of schematic arrangements, that I’m a bit stuck trying to get a clear picture.
When I referred to splitting the anode load resistor, it creates a potential divider. I meant a similar thing in regard of splitting the grid leak. Like a gain control but using 2 fixed resistors, one of which acts as the grid leak.
I suspect you’re getting mixed up with the terminology and function of stuff in the grid circuit.
Grid stoppers are unrelated to grid leaks and potential dividers (ie split grid leaks).

… it's too low for band use w/o cranking it which then overdrives too much. Been looking for a higher sensitivity speaker because of that….wouldn't headroom be if you RAISE the plate load, not lower it?

Are you thinking of the headroom of the preamp, or of the power amp? The context implies that of the power amp. But the point of an overdrive preamp is that there’s effectively negative headroom.

[12AX7]

Yeah, as a matter of fact i have and the difference was nite and day as gain goes. WAY too little. I couldn't even get a classic rock degree of gain all the way up. Not to mention all the complexity was gone. I'm not looking for low gain, just less.

That’s strange, I think the 2204 is generally considered to have a medium gain overdrive preamp. Consider the possibility that there was an error in your implementation of the circuit.

Whatever, have you considered a halfway house in the 2nd stage cathode arrangement, eg somewhere between 10k unbypassed and 1k5 fully bypassed?
ie how does it sound with the 1k5 unbypassed?

…. With only a 220k grid leak and no grid stopper it just sounds and feels worlds different/better.  On a side note. using a split there, one R is considered a grid stopper and one a grid leak because the coupling cap is between them, correct?

Your post was such a dense body of text, containing queries based on descriptions of schematic arrangements, that I’m a bit stuck trying to get a clear picture.
When I referred to splitting the anode load resistor, it creates a potential divider. I meant a similar thing in regard of splitting the grid leak. Like a gain control but using 2 fixed resistors, one of which acts as the grid leak.
I suspect you’re getting mixed up with the terminology and function of stuff in the grid circuit.
Grid stoppers are unrelated to grid leaks and potential dividers (ie split grid leaks).

… it's too low for band use w/o cranking it which then overdrives too much. Been looking for a higher sensitivity speaker because of that….wouldn't headroom be if you RAISE the plate load, not lower it?

Are you thinking of the headroom of the preamp, or of the power amp? The context implies that of the power amp. But the point of an overdrive preamp is that there’s effectively negative headroom.

No mistake...i removed the 1.5k/2.2uf altogether and replaced it with the 10k. Look at the schematic and if that seems like the way it is with a 10k in place of the 1.5k/2.2uf should leave me with enough gain for classic rock, then the only thing  can think of is our ideas of gain is different. Many classic rock tunes have more gain than that for their main rhythm tone. I think with the JCM the reason it's ok like that is a lot of people drive it with pedals and also when loud the output contributes. I also tried 5k and not much different. But no, i didn't bypass either but i thought the point of cold bias stages was not to bring the gain back that way but have a low gain stage. I suppose i could try that or even bypass it with a cap AND resistor in series. But then i'm into a lot of experimentation and on a area whete it sounds good right now and will surely change things as much but likely way more then a split anode.

As to what i meant about a split grid leak is that i already had it configured like that with a 68k to ground and a 220k at the grid with the coupling cap between the 2. First i removed the 220k and it sounded and in particular FELT a LOT better. Then i upped the 68k to 220k and gain it improved. So the last thing i wanna do is go back to that. A split anode gave much less of a change of tone.
What i said about a speaker is because at band levels the output overdrives too much and the preamp gain is too much also so i want more volume from a high SPL speaker to get the mast back down a notch or 2. It wouldn't take a lot to be ok. 

[12AX7]

And after playing with the 12AU7 a while i think after all the gain is fine, but the lows are a bit fuzzy. But i may end up using it if i can get past that somehow. Definitely  possibility anyways.

[shooter]

lows are a bit fuzzy

How big is your cathode bypass cap?
I like to start at 10uF, then move up or down from there

[pdf64]

… i thought the point of cold bias stages was not to bring the gain back that way but have a low gain stage.

Common cathode circuit behaviour is that bypassed cathode will result in higher stage gain than an unbypassed cathode, all else being equal.
The cold bias affects the output waveform when overdriven.

I suppose i could try that or even bypass it with a cap AND resistor in series.
But then i'm into a lot of experimentation and on a area whete it sounds good right now and will surely change things as much but likely way more then a split anode.

Quicker to try it than to write about why not to?

As to what i meant about a split grid leak is that i already had it configured like that with a 68k to ground and a 220k at the grid with the coupling cap between the 2.

I can’t make sense of the above circuit description?

Below is a potential divider, what I was referring to with ‘splitting the grid leak resistor’ previously.

Neither R1 or R2 is a grid stopper.

What i said about a speaker is because at band levels the output overdrives too much and the preamp gain is too much also so i want more volume from a high SPL speaker to get the mast back down a notch or 2.

Altering a value of a preamp anode load resistor isn’t going to affect that. The preamp is being overdriven, so how could it?

[12AX7]

… i thought the point of cold bias stages was not to bring the gain back that way but have a low gain stage.

Common cathode circuit behaviour is that bypassed cathode will result in higher stage gain than an unbypassed cathode, all else being equal.
The cold bias affects the output waveform when overdriven.
That i understand and use it often.

I suppose i could try that or even bypass it with a cap AND resistor in series.
But then i'm into a lot of experimentation and on a area whete it sounds good right now and will surely change things as much but likely way more then a split anode.

Quicker to try it than to write about why not to? I finally did but it sounded very different in a way i don't like at all.

As to what i meant about a split grid leak is that i already had it configured like that with a 68k to ground and a 220k at the grid with the coupling cap between the 2.

I can’t make sense of the above circuit description? I was thinking the input of V2A where there is now a 10k grid stopper and 220k leak.

Below is a potential divider, what I was referring to with ‘splitting the grid leak resistor’ previously.

Neither R1 or R2 is a grid stopper. I have no understanding of where that part of the circuit is. I'm not an amp tech so i'm lost there

What i said about a speaker is because at band levels the output overdrives too much and the preamp gain is too much also so i want more volume from a high SPL speaker to get the mast back down a notch or 2.

Altering a value of a preamp anode load resistor isn’t going to affect that. The preamp is being overdriven, so how could it? It does lower gain in the preamp tho(have 100k/50k switchable at the moment and theres a notable gain drop) and what i'm saying is the whole reason i want to lower preamp gain (w/o changing the feel and sound) is because at band levels the power amp adds too much distortion unless i lower the preamp gain and at that point it's down far enough that it sounds and feels very different. The speaker i mentioned is to get more volume so i don't have to crank the master quite as high. But it's not going to be so much louder that the preamp will be fine as is because even a notch or 2 lower on the master will still be adding power amp OD even tho not as much. It's too hard to explain so i'll just leave it at that.

[12AX7]

lows are a bit fuzzy

How big is your cathode bypass cap?
I like to start at 10uF, then move up or down from there

Schematic is in 1st post.

[Esquirefreak]

One of my brownface based builds hits the phase inverter pretty hard, wich is cool, but whenever I need a little less drive I swap the first gain stage from 7025 to a 5751, to tame it a just a smudge. While 12au7 drastically reduces the gain, my experience is that in some amps they tend to be really bright.

/Max

[12AX7]

I believe i finally figured it out. I've done this before but it's been a few years. I simply lifted 1.5k/2.2up cathode at the cathode and and put a 820R in series. So the cap is across the 1.5k, not the 820R. It lowered the gain w/o really messing with the tone or feel. I will fine tune it by trying a couple other values, maybe 1, 1.2, 1.5k and see what gives the best gain level for me. Or if i have a 2k trimmer just out that in and dial it in perfectly. Best solution so far. I have an unused switch i can put it on too, or get a small 1k pot in series with the 820R or a 2k pot alone.

Is this something anyone has seen before in other schematics? Not being a tech I'm not sure how legit this idea is but if it works WTH.  I DID by the way try the cap over various resistors from 2.7k to 10k before i tried this idea but none worked well. Also tried the 1.5k with cap at ground end and another resistor in series with the cap. Not good either.