Found it

[Alan0354]

OK, I am still trying to get the feel of sound with the design, but so far, I really feel the circuit has a lot more influence than the voltage. Seems like those are fine tune when you are there, not getting you there. As I said, I just did this experiment by increasing the resistor and drop the voltage, it just gave barely noticeable difference in sound and I can't even say it's better. I ended up keeping the higher voltage.

[eschertron]

I was playing around with the interactive tube data page at black magic amps Interactive Valve Data Sheets while trying to design a cold-clipping stage for a Champion 600 amp that I've been mutilating for some time now. I couldn't get the transfer function to look right until I lowered the B+ voltage to around 160vdc. That will require something like a 68k resistor for that power supply node. How does it sound? Maybe tomorrow I'll try the changes and see.

[daz]

OK, I am still trying to get the feel of sound with the design, but so far, I really feel the circuit has a lot more influence than the voltage. Seems like those are fine tune when you are there, not getting you there. As I said, I just did this experiment by increasing the resistor and drop the voltage, it just gave barely noticeable difference in sound and I can't even say it's better. I ended up keeping the higher voltage.

Maybe you aren't changing the voltage much, or maybe it wasn't high enough to cause it to be bad to begin with. Maybe your perception of changes isn't as sensitive as some others. There could be any number of reasons. But the difference in my amp from now to before i did this is not a subtle change. The amp's character has changed in most every way to one extent or another aside from the basic voice which remains basically the same.

[Alan0354]

Maybe you aren't changing the voltage much, or maybe it wasn't high enough to cause it to be bad to begin with. Maybe your perception of changes isn't as sensitive as some others. There could be any number of reasons. But the difference in my amp from now to before i did this is not a subtle change. The amp's character has changed in most every way to one extent or another aside from the basic voice which remains basically the same.

I changed 50V!!! I can make big sound change with just a 200pF feed forward compare to this. I did some major change on on the sound last night and I did the experiment again. Result was the same. When you are there, this is a final touch. It's not going to bring you there. I agree with Chuck that you might just happen to fix something by doing this and make a big conclusion out of it.

[daz]

I agree with Chuck that you might just happen to fix something by doing this and make a big conclusion out of it.

Well, you're wrong but you aren't here playing and tweaking my amp so theres no way for you to know what it did for mine. I think i may be slightly more in the know about MY amp than you, eh? By assuming that about my amp based on what it did in your amp is no different than telling someone they can't possibly like the taste of pizza because you don't like it.

[tedmich]

wasn't there some guitar guy who put a variac on a big fire breathing Marshall in the 70's and got some "colored" sound out of it by running lower voltage AC into it? Maybe I just dreamed it...

Does the lower voltage in the pre allow you to crank everything else more before your ear drums explode?

[Alan0354]

Not really. Variac mainly work on the power amp. I was one that did that on my Plexi in 1974 already. But result is not very good beyond certain point. I ended up designed a true power scaling exactly like London Power back in 1978 by isolating the preamp and filament using separate transformers and put the variac only on the power and PI stage. It worked beautifully.

I found higher preamp voltage gives more in your face sound where lower voltage gives a somewhat softer sound. Main thing I found that change the sound is controlling the frequency response of the stages, not by the voltage. Then use the voltage as the final touch to your taste.

[tedmich]

I concur, voltage is a pretty much secondary effect, some like "sag" and tube rectifiers but I tend to like my voltage like I like my pants: high up with plenty of "head room"

[Alan0354]

For the moment, I have it pretty high. But I have to get the basic sound first before I start messaging the voltage.

[Chuck H]

I'm going to back daz on this, though my tastes differ in what voltage sounds best. Going back twenty some years, before my 1959 RI Marshall had a master volume I never got to turn it up past about 2.5 volume. It always sounded spanky and hard enough at that low volume running stomp boxes. Once I installed the master volume, about the time I started modding amps, I took advantage of the ability to overdrive the pre master stages with a boost pedal and found the tone got too soggy. Bumping the preamp voltages did the trick. Tedmich has it right that it's an effect like sag. But it changes the feel in a way that's more profound than what I'd call a secondary effect. It becomes part of the core sound.

I'd say daz is in good company with the lower voltages. EVH used a stock Marshall (so, lowish preamp plate volts) cranked up and then lowered further with a Variac (bad idea). Point is, unless your really looking for a hard edge Marshalls are plenty spanky enough without increasing the preamp volts for most players. I do like 'em a little higher like Tedmich.

[Alan0354]

I want to specify I never say high voltage is better. I just said do all the tweaking first before worrying about the +B. That is secondary effect. The voltage is not going to make or break the sound. Only when you are there, then tweak the voltage to get the last bit.

Actually in my case, I don't have enough output swing from the preamp because of the Marshall type preamp and I need every little volt swing. The voltage divider that I needed to set the filter is 10 times more important than the little improvement( if any) by lowering the voltage. So I have no choice but to raise the +B for the preamp to get the swing. That is 10 times more important than the little advantage of the softer sound of lower voltage.

As I kept repeating. The voltage is a touch up when you are there, not to get you there.

Like you said Chuck, you advised to change the voltage divider from using 470K to 220K. That make a day and night different even the divider is the same. It's the input Miller cap effect that drown the life of the sound using the 470K. I actually use a sweep generator the verify that. with the 470K, the -3dB is 7KHz. I get to 13KHz with the 220K. It might not sound important, but I believe the harmonics might down modulates down and make a difference to the sound. Those are the major things to look for, the filtering effect that change the sound of the whole amp. The voltage only affect the symmetric clipping and the rp. Those are secondary effect. You have to be there to see that. OP somehow get what he want and I am not going to say any more. But I truly believe he somehow hit the spot by doing that.

[daz]

You seem to miss the point over and over no matter what I or anyone else says. My voltages are NOT low ! They are *lower than before*. BEFORE they were higher than typical marshalls. I didn't lower them to get a soft sound, i lowered them because the sound was too hard with the voltages being HIGHER than a marshall, in some cases a lot higher. I'll leave it at that because if you don't understand now nothing i say will make you understand.

I want to specify I never say high voltage is better. I just said do all the tweaking first before worrying about the +B. That is secondary effect. The voltage is not going to make or break the sound. Only when you are there, then tweak the voltage to get the last bit.

Actually in my case, I don't have enough output swing from the preamp because of the Marshall type preamp and I need every little volt swing. The voltage divider that I needed to set the filter is 10 times more important than the little improvement( if any) by lowering the voltage. So I have no choice but to raise the +B for the preamp to get the swing. That is 10 times more important than the little advantage of the softer sound of lower voltage.

As I kept repeating. The voltage is a touch up when you are there, not to get you there.

Like you said Chuck, you advised to change the voltage divider from using 470K to 220K. That make a day and night different even the divider is the same. It's the input Miller cap effect that drown the life of the sound using the 470K. I actually use a sweep generator the verify that. with the 470K, the -3dB is 7KHz. I get to 13KHz with the 220K. It might not sound important, but I believe the harmonics might down modulates down and make a difference to the sound. Those are the major things to look for, the filtering effect that change the sound of the whole amp. The voltage only affect the symmetric clipping and the rp. Those are secondary effect. You have to be there to see that. OP somehow get what he want and I am not going to say any more. But I truly believe he somehow hit the spot by doing that.

[Alan0354]

Not that I don't understand, I don't agree with what you said completely.

As you said, it's your amp and I don't know your amp, so I am talking to other people at this point of time.

[isaac]

In mentioning preamp voltages, I had an amp that I custom built, custom circuit, but it was very direct bright and kinda hard to play, just didn't sound good. I looked at my voltages, and I actually fed my preamp and PI from the same filter cap, but I raised the value of that resistor to drop the voltage down some 50V, and the amp became warm and round, and totally different. I was very surprised, and I thought it sounded great. It still does.

[daz]

In mentioning preamp voltages, I had an amp that I custom built, custom circuit, but it was very direct bright and kinda hard to play, just didn't sound good. I looked at my voltages, and I actually fed my preamp and PI from the same filter cap, but I raised the value of that resistor to drop the voltage down some 50V, and the amp became warm and round, and totally different. I was very surprised, and I thought it sounded great. It still does.

Thats a good description of what mine sounds/feels like with 50v difference. In fact, it was indeed right about 50v that i dropped it.One way i KNOW i'm much happier with it is that the chassis has been back in the combo and all i have done to it since is play it ! I've had it like this before except that since i last have the voltages at this level, the preamp has been improved some. So i'd say this is the best it's been. Another thing i found since i did this, and it may seem odd since i did nothing to change the power section. But i guess because the preamp tone is more round full sounding, different power tubes which in the past i felt were lacking in bass and sterile now sound great. I use winged C el34's usually, but i have bought a set of the svetlanas which are far cheaper and found them thin in the low end every one of the 5 or 10 times i tried them. Now i tried them again and they sound perfectly full and thick ! In fact, i'm having a hard time deciding if i still like the winged C's more let alone MUCH more as in the past. Crazy...