Need advice

[yunger]

The thing that amazes me is with all the tricks people have come up with over the years, It seems no one ever figured out a way to implement a volume control that is tonally linear. Adding this tube allowed me to get it much better, but it's still a ways from where i hoped it would be. I had it very close a few times, but when i did some other thing wasn't right.

i think that's why the suggestion to buffer the pot came in. then you set a fixed amount of treble cut to your liking.

another thing to try is scrapping the 4th gain stage (and using that new tube for a reverb), go back to the 1M master volume as before, followed by a (value unknown) capacitor to ground. at the right value, it wouldn't cut highs when the master is low but would start cutting as you start cranking it up(volume). just a thought.

[daz]

i think that's why the suggestion to buffer the pot came in. then you set a fixed amount of treble cut to your liking.

Might be worth a shot. Can anyone point me to schematic showing how to implement this? I haven't got a clue.

[daz]

As I mentioned in my earlier post, the best arrangement is probably going to be replacing the resistor to ground in your voltage divider with a lower value pot; It will act like your current MV from 0 to the "sweet spot" that you set at maximum. This arrangement will also give you additional headroom in the extra tube stage as you turn the volume down.

At this point i'm really questioning the benefit if any of the extra tube after complimenting this in place of my MV. I had it set up like this first...treble pot out>trimmer setup as a typical volume pot>new tube>your MV idea>PI. Then after a lot of experimentation i swapped the treble out from the new tube right to your MV at the PI input bypassing the new tube altogether. So basically i'm back to the way the amp has always been except for the MV being a 10k signal to ground shunt pot with a trimmer in front of it to set the overall gain level. This seems to be possibly as good as the extra tube as far as low to high volume linearity tone wise, but the basic tone is better. I liked the change in tone from the extra tube at first, but the more i played it the more I began to notice it wasn't as focused, and major thing with me. So this MV idea of yours seems like the better solution. Why don't others use this idea? I haven't seen it anywhere but it seems to work well, and with that trimmer in place i can really tweak it. Anyways, further playing/testing is needed to be sure, and i'm still looking for more improvement in the tone change from low to high volume, as it's still not quite as good as i'd like.

EDIt: i think i know why others don't use this master. I believe I'm able to use it is due to one of the issues i have.....far too much signal. So a master like this won't render the signal to the PI too small. With the 10k ground shunt pot and a series trimmer from the tone stack i can adjust the overall output level and still have enough to drive it to high volume levels. maybe i'm wrong here since i don't have electronic theory they way you guys do, but thats all i can think of as to why others don't use it. Could it be that the excessive signal my amp produces in the preamp might have turned from a issue to a benefit?

[cbarrow7625]

Daz,

It sounds like you have a really great circuit that you are really happy with. If you are not planning on commercializing it, and there for introducing the unknowns of other people and situations, then just optimize the range for what works best for what YOU do. It sounds to me that you are SOOOOOOOOOOOOOO close to getting it what100% perfect that nothing else will do. It ain't possible, kid.

Count your blessings that you have something pretty awesome going on. I have a "tweaker" amp that has never stayed closed up for more than a free months at a time. I have then affliction too! Doesn't ever make it better. Just different. Until next time I decide it needs tweaks. You know what never seems to need those tweaks? Other peoples amps I try out at NAMM every year. I SWEAR they have special sauce and tricks I don't know........until I see them schematics later. Usually no crazy special sauce. What you are working on is WAY more special sauce than I usually see in schematics. We get so far into it that we can lose perspective on what we were trying to improve on in the first place. We get past that point (fairly quickly usually, right?) And set a new, tougher goal mid-stream. The 100% bug sets I , the cover never goes back on the amp and we obsess over what COULD be and lose perspective on how amazingly better then"compromised" design we have is so much better than our original goals.

Walk away for a couple weeks and turn it on at random one day after work. You'll be amazed at the awesome, consistent tone you achieved.

[daz]

Thats true for me too. That is, i can't stop screwing with it but it generally ends up different, not better. BUT, this time it HAS gotten better because it's the one problem area i have never spent any time on to speak of. And your idea for that master helped a lot, thank you. The issue however is still there to a smaller extent and doesn't show itself till a higher volume than before. But I'm not sure how much of the remaining bit of this issue is really an issue or just the combination of those things that tend to make tone change when loud, IE: munson curve, speaker, small fairly bright room, etc. So i will still always be searching to improve that. When cranked the high mids on up become hard and bright, the fluid squishy feeling mids are no longer fluid and squishy. And the tone just doesn't have the same focus. I know thats partially the things i mentioned, but i can't help but wonder just how much of that could be improved. I'm nearly there, and if i can find a way to retain what i like about the lower volume tone up to small stage volume i would probably not want to touch it again. The preamp is as good as i will ever get it i'm sure.

Daz,

It sounds like you have a really great circuit that you are really happy with. If you are not planning on commercializing it, and there for introducing the unknowns of other people and situations, then just optimize the range for what works best for what YOU do. It sounds to me that you are SOOOOOOOOOOOOOO close to getting it what100% perfect that nothing else will do. It ain't possible, kid.

Count your blessings that you have something pretty awesome going on. I have a "tweaker" amp that has never stayed closed up for more than a free months at a time. I have then affliction too! Doesn't ever make it better. Just different. Until next time I decide it needs tweaks. You know what never seems to need those tweaks? Other peoples amps I try out at NAMM every year. I SWEAR they have special sauce and tricks I don't know........until I see them schematics later. Usually no crazy special sauce. What you are working on is WAY more special sauce than I usually see in schematics. We get so far into it that we can lose perspective on what we were trying to improve on in the first place. We get past that point (fairly quickly usually, right?) And set a new, tougher goal mid-stream. The 100% bug sets I , the cover never goes back on the amp and we obsess over what COULD be and lose perspective on how amazingly better then"compromised" design we have is so much better than our original goals.

Walk away for a couple weeks and turn it on at random one day after work. You'll be amazed at the awesome, consistent tone you achieved.

[daz]

I have another question concerning the schematic below. The 10k pot is now a 25k which was needed to reach the volume i wanted at max. The 1M trimmer has been used like in the schematic and also i have tried it and am now using it as a 1M pot by grounding the unused lug.
This works great except one thing. the treble pot now does nothing from 0 to 1/2 way up. From there it works fairly normal. But noon to all the way down the tone stays the same and sounds like it normally does at i would say 9-10 o'clock. I can't look at the tone stack and the trimmer and master and wrap my head around it, so i'm asking if anyone knows why and also whether there is a fix you can think of. Please lets not get into the merits of lack thereof concerning this setup. I know it's unorthodox buIt really works great so i'd rather just concentrate on the treble issue. If thats not fixable i can live with it for the rest of the benefits this has brought. But if possible i'd like to see if the treble issue can be dealt with. Thanks.

[J M Fahey]

What taper did you use for the treble pot?
You need linear there.

[daz]

What taper did you use for the treble pot?
You need linear there.

It's not that. It only did this since i went to this master from the typical pre PI 1M master.

[J M Fahey]

Not what I asked.
Again: What taper did you use for the treble pot?

[daz]

Not what I asked.
Again: What taper did you use for the treble pot?

I can't remember, but it was the correct one. When i first built it i went by what the correct one used in jcm's and all the clones were using. If i recall it was linear. But it's absolutely what is used in the marshall it is closest to and what i believe is used it most all marshalls. It's however not 220k like they use obviously but 250k. I still fail to see why this matters since until this master change it worked completely normally. It's quite obviously due to the new master and what I'm asking is why that master caused this.

[Dave H]

It's quite obviously due to the new master and what I'm asking is why that master caused this.

It could be because the old master presented an almost constant impedance to the treble pot wiper but with the new one the impedance varies.

[J M Fahey]

^^^^ something like that.
Obviously the mod did something wrong, but we don't have the amp at hand to check that.

One big point, which has not been explained, is how was that 1M "trimmer" set .

And it makes all the difference in the World, since on most settings it loads down the Tone Control stack, big way, like Dave H suspects (and me too).

EDIT: so the short answer is: put a normal master there and it will work fine (since you claim it did so before).

[daz]

Thats not the answer. The question was why it does this and how to fix it while retaining the current master The whole point was is it possible to fix this and retain the current master section because this master works a lot better. There IS a trimmer there exactly as the original master was, (not like schematic) and then the 50k pot (yes, 50k not 25k as i mistakenly said) that acts as variable load master. If not, as i said originally i'll live with it because the benefit of the current master is more valuable than rectifying the treble issue.

Now that said, anyone have any ideas of how i could rectify the treble pot issue while keeping the current master and the volume? I will upload a corrected schematic in a few.

[daz]

Heres the updated schematic. Note that the trimmer now is grounded on one end making it exactly as the pre PI master was before i did this mod. there was too much signal into the PI and this is now used to cut that down, then the variable 50k load after that acts as master. Sounds a lot better like this in several ways, but if i could just figure out how to get that treble pots working more correctly.

[J M Fahey]

Note that the trimmer now is grounded on one end making it exactly as the pre PI master was before i did this mod. there was too much signal into the PI and this is now used to cut that down, then the variable 50k load after that acts as master.

No, no, no, how must I write it so you understand it is NOT "like before"?

Do you think circuit elements exist in a vacuum?

They are connected to other elements which interact.

Before, you had a 1M Log volume pot , connected to (calling legs a/b/c from top to bottom):

a to slider of 200K lin treble control.
b to tube grid (infinite impedance)
c to ground.

No matter where you set the volume control, the 200K treble pot (hence the tone control stack) is always loaded by 1M. ALWAYS.

Now with your mod:
the tone stack is loaded by 1M only if that trimmer is set to 0.
any other setting, the tone stack will see less than 1 M and its response will change.

I asked you many times what value the trimmer is set to, you never answered that important question.
As an example, if you set that trimmer to 5 , and itīs a linear taper one (whatīs normal in trimmers), the Tone Stack now sees 500K load-
If itīs in, say, 8, load is now 200K, 1/5 whatīs expected.
If itīs on 10 (where you might think itīs "doing nothing", since itīs set to "no attenuation") , load on the tone stack is a meager and absolutely wrong 50K ..... and that *if* the new "master" is set to 10, because otherwise it will be less .... even down to 0 ohms.

And you wonder why it now "reacts different"?