where to drop gain?

[daz]

No go. With V1B unbypassed it's mud like always. Thats even with a .68 on V2A, and blocking was happening still. This amp always requires .68uf bypassed both sides of V1 or it gets muddy. Always has no matter what i do with the rest of the amp. With a 470k/470k divider as in the schematic theres no blocking or anything. Just not as clear and bright as i'd like and gets lost in a mix to easily. With either side of V1 unbypassed it's horrible.

[soundguruman]

Try 33K or 68K resistor on the input.
Instead of 10K.
the 10K makes it sound muddy to me...

Well, there's really 2-3 factors...
first the pickup of the guitar.
"standard" would be (as we have observed) 1 volt peak to peak or less.
But on certain "high output" pickups, it might be triple that. (super distortion, etc...)
And so, the high output pickups are useless to me. To me, they all sound like mud.

It's not surprising that a "super distortion" pickup would sound like mud, on a high gain input stage.
after-all, the stage was probably designed for a standard pickup, 1 V PP or less.

And it's not surprising that an input stage may be modified, to help a high output pickup sound "good."

And it is not surprizing that high output PU will cause more oscillation, microphonic / ringing / buzz...

So, what is the PU that you are testing / judging it WITH???

[daz]

Try 33K or 68K resistor on the input.
Instead of 10K.
the 10K makes it sound muddy to me...

It's a 68k, i just missed that when i updated it.

[Chuck H]

I don't think telling someone what sort of Marshall mods have worked for someone else is applicable in daz's case. There are so many incarnations of the modded Marshall circuit that it's obvious no one likes the same one. The goal here, I think, is to help daz mod the amp to do what he says he wants it to. Right now that is to keep the gain and keep the tone but delete the blocking distortion.

Daz, try this:
On the 470k/470k divider jumper the series resistor and solder a 15k resistor parallel to the dropping resistor. So now you have just a 14.5k dropper (15k parallel with 470k) and no series resistor.
Now parallel your .022 coupling cap for that stage with another .022 cap. Or just replace it with a .047 cap.
Now tack in a 100k grid stop resistor to the grid this circuit feeds.

The alteration to the divider decreases circuit impedance considerably while maintaining the same gain level. The additional capacitance corrects the frequency that changed due to circuit alteration and the relative high value grid stop should be much more effective. This should significantly improve any blocking distortion problems.

[daz]

Chuck....note that with the 470/470 there it has zero blocking and sounds fab. Right now i have a 1M to simulate a cranked gain pot, and with that and the coupler going direct to the grid. THATS when i get blocking, not as the amp is in the schematic.

This thread was simply an idea i had that with no voltage divider i would have more brightness and the larger load along with it might give me a purer brighter tone. And it does. But i get blocking when the gain is turned up high. Not that i generally use it there at all, (usually have it around 1-2:00) but the idea that it does that is obviously not good.

[Chuck H]

Ok then... Follow me on this. Right now due to the high-ish circuit impedance that .022 coupling cap is passing WAY too much LF below the useful range for guitar amps. This, the high circuit impedance and the high gain are the causes of the blocking distortion. We want to keep the gain so we need to target the circuit impedance and eliminate the useless low end (keeping any useful low end of course).

If you change the 1M load to a 220k load you will only lose about 1dB of gain and you will reduce circuit impedance. Using a 220k dropper a .015 coupling cap should give you all of what you need and nothing you don't for LF. Do use a grid stop resistor but use the smallest value that gets the job done. Something like 100k should work.

[daz]

Ok then... Follow me on this. Right now due to the high-ish circuit impedance that .022 coupling cap is passing WAY too much LF below the useful range for guitar amps. This, the high circuit impedance and the high gain are the causes of the blocking distortion. We want to keep the gain so we need to target the circuit impedance and eliminate the useless low end (keeping any useful low end of course).

If you change the 1M load to a 220k load you will only lose about 1dB of gain and you will reduce circuit impedance. Using a 220k dropper a .015 coupling cap should give you all of what you need and nothing you don't for LF. Do use a grid stop resistor but use the smallest value that gets the job done. Something like 100k should work.

Well, this will have to wait, as now i am getting blocking after putting it back to how the schematic is. Obviously all this screwing around has caused a bad solder joint or something, so i will have to clean out all the old solder and redo the area. F***. Also, the 220k load will kill high end. I A/B'd 1M vs 470k and i heard a definite loss of clarity, so 220k....hmmmm.

Tired of this for now. I came down with a sore throat/cold the other day too so I'm pretty shot at the moment. Once i figure out where the problem is i'll try your idea tho. One question however....whay does marshall use .022's if what u say is the case? I do know when i tried .0047 on both sides of V1 in the past it always sounded too thin. Then again maybe now without the treble peaker after it....i dunno....cough, hack, ohhhhhhhhh. Only time in the last 3 or 4 years i took a long vacation for Xmas and wouldn't you know i get sick, which usually happens maybe once every 2 years. Geez...

[Chuck H]

Well, this will have to wait, as now i am getting blocking after putting it back to how the schematic is. Obviously all this screwing around has caused a bad solder joint or something, so i will have to clean out all the old solder and redo the area. F***. Also, the 220k load will kill high end. I A/B'd 1M vs 470k and i heard a definite loss of clarity, so 220k....hmmmm.

It's possible that whatever changed to cause blocking with the stock circuit had already changed by the time you tried the 1M vs. 470k load. Your perception of the difference may not even be real if the circuit was compromised. The difference should have been truly tiny. There would be a more audible difference between a 1M and a 220k, but still too small to get picky about it. No real difference in gain though. Still... Barreling into the third stage of a cascade preamp with a large coupling cap and a 1M load is blocking suicide. If you won't change the circuit and make a compromise there is no solution. The only other thing you can do is trim the useless LF from the circuit. The ideal capacitance will change with the load and with a 1M load a good coupling cap would be .0068uf. You could even try a .0047uf but that may start to trim audible LF.

[daz]

Ok, i'm gonna try this. But note that in the past i DID have it set up like that but not with a smaller cap because it always seemed thinner. But the reason i have a divider there is i had it set up like you're suggesting for years and switched to a divider because the tone was livlier and brighter that way. So i don't see how this will work unless i'm missing something as i picture how i had it in my mind. Anyways, i'm working on it now.

[Chuck H]

Like I said, the ideal cap value changes with the circuit. The same cap that sounds "right" but doesn't introduce useless LF with a 1M dropper would sacrifice audible LF with a 220k dropper. Conversely the right cap for a 220k dropper would introduce useless LF and compound the problem of blocking distortion that is already made worse by higher impedance and gain. All the circuit values are analogous to each other if you need to idealize. Which you often don't. But when difficult refinements present themselves it can help to pay attention to these things.

Hope you feel better soon.

[daz]

Ok Chuck, here are my findings. First, it wasn't a bad solder joint, it was a tube causing the blocking that was happening even when i went back to 470/470. I cleaned up all joints and when it still happened i had to think of what i have done and i remembered swapping V1 ans 3 (both tung sol RI) and i swapped them back which cured it. One more TS RI down the "tubes" it think, tho maybe it was just a bad connection at a pin socket i dunno. More head scratching crap to deal with.....never ends

Anyways, i tried your idea and I *think* I like it. I have to A/B it with the way i had it a few times, and it's not really a lot brighter or clearer. But it does seem to have a bit more jangle and liveliness. I have however like i said used this setup before with various values including these. And like i said i moved to a voltage divider because it seemed to be more janglier and livlier. But now it seems the opposite and guess thats due to the fact i wasn't using the treble peaker as before.

But it's definately is a good setup if not better than before. Also, i then tried it with the old .022 and there was no difference in mud or blocking, so thats another thing i have to consider. It seems fuller with .022 but more playing is needed to know. I feel this will probably cut better and if so that'll be the deciding factor. I'll keep ya updated. Thanks Chuck.

[daz]

Ahh, i realized you were talking about a larger cap than i thought. I used a .0047. When you said .047 i figured you just did a typo because .047 is larger than the .022 i already had. Now i see you mentioned a .015. I will try a .01. The .0047 is fine tho like i said it's a little thinner. But i have a new .01 i can use which is close enough.

[Chuck H]

You need to look back through my posts. I mentioned a lot of things that were systematically rejected, don't necessarily work together and all have different component values indicated. The exact value I specified will depend on which circuit you decided to try (or re-try). Your post has cap values from several circuits, not just one. And I'll point out again that the right value depends on the circuit. In other words, a .022uf cap doesn't always pass the same frequencies in every circuit it's used in. The circuit determines the knee frequency as much as the caps specified value does!

[daz]

You need to look back through my posts. I mentioned a lot of things that were systematically rejected, don't necessarily work together and all have different component values indicated. The exact value I specified will depend on which circuit you decided to try (or re-try). Your post has cap values from several circuits, not just one. And I'll point out again that the right value depends on the circuit. In other words, a .022uf cap doesn't always pass the same frequencies in every circuit it's used in. The circuit determines the knee frequency as much as the caps specified value does!

Yeah, i get that Chuck but it all gets confusing real quick. I lose track of all the changes and how they relate after a short time. I'm pretty happy right now with the changes i made tonite based on your suggestions. I may have misunderstood some of it, i dunno. Don't think so tho. anyways, every sat nite if i'm home, which at my age is most of the time, i crank some music and play along partly just for fun but mostly to see how any changes i made work in a mix. Thats what tells me how good the feel and freq curve of the current state the amp is in works. Tonite was the first time in a number of saturdays where i was very happy with the results. Manipulating the volume to vary the degree of clean/distortion was perfect, and they way it cut both clean and distorted was as good as ever with the feel and tone just right thru all ranges. really happy in that regard.

I've had it that good in the past, but i always enjoy it for a time then decide to F with it more to perfect some minor imperfection. I really hope i don't do that this time because it just plain works right now. Tone, feel, the way it fits perfectly in the mix, it's all there. But one thing i've found is this can happen and next sat nite it's the opposite. We shall see, tho i doubt is will change much. But for now i'm really happy with the changes enough to put the chassis back in the box for the first time in weeks. Not sure i did exactly what you suggested, but i bypassed the series R, made the ground R 220k, then added a 100k grid stopper and changed the coupler to .01. My playing really improves greatly when the amp is "right", and tonite i was able to play my best. Thanks for the suggestion Chuck.

[Chuck H]

Hey, I get an especially good tone on soggy days!!! Why? I dunno!?! It could be that the power grid is apt to a certain usage (I get a 7V to 12V drift on my outlets here). I haven't tested for that yet. It could be because the humidity in the air affects the sound waves and maybe even speaker cone activity!?! Who can ever tell about this sort of thing? The fact remains that you need a good amp that performs well in any circumstances! It will never be magic all of the time. A good amp is a good amp. On the best days (because of weather or your personal mood/state of mind) it's a great amp. When you get to that point it's time to play and try not to think about circuits. You've won!!! And achieved what you set out for in the first place. An amp that always performs and does something good. You'd think we could relax at that point and just play our guitars. But it never works out that way for long. The problems are in our heads, not in the amps.