PPIMV ?

[Buschman]

There is so much internet info that it is hard to make heads or tails from it.
Have any of you tried one in your Express with any success? Which circuit? Rich Mod-Larry-Collins. I tries the #3 from the Trainwreck pages & it does not work well. I am not looking for bedroom volume here. I am also not looking for a crunch monster. There are times when knocking 5 or 10 db off without turning the amp down would be desirable.

[HeeBGB]

Have you tried an Airbrake attenuator? That's pretty transparent and knock 5db's off (I think) easy!

[CaseyJones]

Master volumes are for pussies!

Good God y'all, they make as much sense as restrictor plates. For those of you unfamiliar with the concept NASCAR came up with a plate to be mounted under the carburetor to makes things "equal" between the original Chrysler Hemi and everyone else back in the '70s. We've been stuck with them ever since.

Build the amp smaller and beat it harder. Nuthin' compares to the majesty and splendor of a cranked 'Wreck which is why you want to crank it to begin with, right? Well you can have a big dog on a short leash or a small dog on no leash. Gimme a Jack Russel, pound for pound they're as tough as a pit bull.

[skyboltone]

There is so much internet info that it is hard to make heads or tails from it.
Have any of you tried one in your Express with any success? Which circuit? Rich Mod-Larry-Collins. I tries the #3 from the Trainwreck pages & it does not work well. I am not looking for bedroom volume here. I am also not looking for a crunch monster. There are times when knocking 5 or 10 db off without turning the amp down would be desirable.

Hey Buschman. The TW designs are just not suited to MV IMHO. Turn everything to 12 oclock and dial back the guitar volume. If it's too loud, throw a blanket over it or hand out earplugs. One of these days I'm gonna build one with 6CA5's. It'll have about 3 watts. Too much for the bedroom but probably just right for a small club. If you want a MV they are better suited to amps with pre amp distortion than amps that get the mojo out of the power tubes.

[CaseyJones]

Yeah, what Sky said. If God... I mean Ken Fischer (who BTW knows God personally now I hear) intended Trainwrecks to have master volumes he would have put 'em in there to begin with.

[Firestorm]

Yep. A 'wreck with a master volume ain''t a 'wreck anymore. There are a couple of places in the circuit you could tweak to "clean up" the sound, but nowhere you can reduce the power output without A) screwing up the sound or B) doing something major like cutting B+ (and then, you'd have to reset the cap and resistor values on just about everything.)
Try Greg's (HeeBGB) Airbrake suggestion (or Sky's blanket idea )

[RHGraham]

What about the PowerScale circuit, it's definately not the same as a typical mastervolume between the pre and the poweramp, I've heard two amps now with PS and I was quite impressed by how they worked and didn't colour the sound when they were rolled back, I can't see any reason this wouldn't work on a TW design.

[Firestorm]

Power scaling might be worth a try. The only place it might have a negative impact is on V2, which is set up to produce a moderate amount of gain, but a pretty narrow output swing (permitting a little bit of clipping). Power scaling could shift the bias point enough to change that. Maybe a subtle adjustment to Rk would extend the range where V2 does more or less what it's supposed to. Interesting.
Oh--since you'll also reduce gain in the rest of the preamp and the PI, there may be more tweaking to do.

[UR12]

Power scaling might be worth a try. The only place it might have a negative impact is on V2, which is set up to produce a moderate amount of gain, but a pretty narrow output swing (permitting a little bit of clipping). Power scaling could shift the bias point enough to change that. Maybe a subtle adjustment to Rk would extend the range where V2 does more or less what it's supposed to. Interesting.
Oh--since you'll also reduce gain in the rest of the preamp and the PI, there may be more tweaking to do.

I am in the middle of power scaling errr ughhh regulating the voltage on a Liverpool style amp that I have converted over to fixed bias. Not what I would call the best method of testing but that's all I have at the moment. If you regulate the voltages down on the whole amp across the board you should be able to keep the gain structure of the amp in tact. In other words, since the amp is set up for the power tubes to distort first, if you turn down the drive to the power tubes as you turn down the voltage to the power tubes everything in theory should stay the same down to a point below a couple of watts.

On another note, while I don't think a MV sounds all that great in a TW (For the same reasons sited above). Ken did include information in the Trainwreck pages on how to add a PPIMV mod to other amps so he must not have been totally against the idea in other amps.

[jjman]

I'm gonna try one in the "Express" I'm building soon. It's not a true "clone" so I'm not subject to the negative karma from a PPIMV right?

I read (here) that the Express OP tubes clip 1st, then the PI, then the 3rd stage. So I figure I could let the PI clip 1st, then the 3rd stage by using a PPIMV as an option. If it's useless I'll take it out and put something else on that dial. Like moving the presence control from the rear to the front.

If your "cloning" it's sacrilege !

[Buschman]

I've got other amps-18 watt-5e3 and they work great. The Exress has such a thick musical tone that I would like to use it more often. I can try an airbrake but a dual pot would be lots cheaper. Thanks for the input. let me know how the power scaling goes.

[Lonely Raven]

Master volumes are for pussies!

Good God y'all, they make as much sense as restrictor plates. For those of you unfamiliar with the concept NASCAR came up with a plate to be mounted under the carburetor to makes things "equal" between the original Chrysler Hemi and everyone else back in the '70s. We've been stuck with them ever since.

Build the amp smaller and beat it harder. Nuthin' compares to the majesty and splendor of a cranked 'Wreck which is why you want to crank it to begin with, right? Well you can have a big dog on a short leash or a small dog on no leash. Gimme a Jack Russel, pound for pound they're as tough as a pit bull.

OK, but with all this discussion of "if it's not built like an Express it's not an Express", then is a smaller Express like amp still an Express? Can it be made to sound like an Express on a smaller scale?

My Ceriatone is kicking my butt with how loud it is, and I'd love to simply "build something smaller", but is it the same, and honestly...I'm not sure how.

[Firestorm]

As long as everybody is in an experimenting mood, there's a few things I want try, but haven't yet.
1. Replace the 150K resistor on the V2 grid with a pot wired as a voltage divider. You can't usually find 150K pots, so maybe a 50K resistor to ground with a 100K pot on top of it. This would let you have full signal into V1a and V1b, but cut the signal hitting V2 and the PI and the output.
2. Instead of connecting the suppressor grids on the EL34s to ground, connect them to the bias supply (before the pot). Biased negatively, the suppressors will be much more effective at corralling stray electrons. KO'C says that Traynor did this and improved tube reliability, but it must have a sonic impact as well. (This only works on EL34s, not 6V6, etc.)
3. Change the 220K grid return resistors on the output tubes to 150K or even 100K. This cleans up Fender Deluxe Reverbs like magic. How would it impact a TW?
Any guinea pigs out there? Okay, I'll shut up now.

[UR12]

Firestorm

I have already tried #1 on your list. I used a 250k trim pot in my liverpool and dialed it in while my brother played through the amp. I ended up at about 100k (Pretty much in between the stock 68k and the 150k used in the Express). If you try and take it much above 150k-200k it starts getting rellly nasty sounding. You also need to look at the relationship between the .002 cap and the grid resistor as the form a rc filter tuned to about 440hz on the Express. Changing the value of the resistor may dictate a change in the cap value also to keep the amp voicing the same. We have had people try power scaling the output and PI section and the MV on the express and I don't remember anyone giving it rave reviews. Just my 2 cents, YMMV

BTW....Welcome to the forum Randal!

[Doug H]

(edited for brevity)

IMO, the best way to get less volume is to design a low power output stage to begin with. I've played with a bunch of different ideas using oddball output tubes and I think you could do a decent TW style amp at a lower wattage for more reasonable volume if you wanted to. I've experimented with a number of different PPIMV techniques and they all have limitations. In my latest amp I implemented a PPIMV (search for "power scaling for cheapskates" at ax84.com) that is a variable Rk in the PI. It biases the PI colder as you turn it down. This simultaneously lowers volume and increases PI distortion to compensate for the lack of PI driver. It's a cool parlor trick but I rarely use it. Most of the time I run the amp wide open.

I have built an attenuator too, but I don't like using it. Once you throttle the amp back like that it loses responsiveness due to lack of speaker air movement, bass response (google "Fletcher Munson"), etc. Plus I just can't wrap my head around the idea of building an amp that has to be attenuated just to use it. Why not design/build it for the proper wattage to begin with? (Makes too much sense, I know... )