Smoothing out a Pre-PI master volume setup

[dehughes]

SO, now that you all have put up with my whining and noob-ness regarding my gimptastic first build, I'm in the "tweak the master volume circuit" phase, which is much more fun than the "why the $#@$ doesn't my amp WORK?!" phase.

I'm running an AC30 12AX7 preamp (basically...) with a 250k pre-PI master volume pot, the usual .022uf Sozo tone caps, 100k slope resistor, a 47pf (close to 50, actually...) silver mica coupling cap off of the 12AX7 cathode into the treble pot, and from there out into both the EQ network and the master (to help keep things tasty at low volume levels). Essentially, it is just like the Top Hat King Royale preamp, as shown at this link:

http://www.schematicheaven.com/newamps/ ... royale.pdf

That's what I'm looking at. NOW, I know that these amps have to be opened up before things start sounding proper, but I'm wondering if there are any ways that I could smooth out and take some of the harsh out of high-gain, low power amp settings with this circuit. Maybe that's asking a square to be a circle, but I'm still newbified, so I figure I should ask. Any suggestions?

THANKS.

[Normster]

First of all, from one newbie to another, congrats for getting this far along.

I've never been successful at getting great tone a really low volume, but there are a few things that I've tried that help a little. Putting a 100k resistor between the master and the PI input seems to fatten things up a tiny bit. It's kind of like the "Loudness" switch on my old stereo. I've also been pleased with my Airbrake attenuator. Typically, I get the best low volume tone by using a combination of the master and the attenuator, but it's never as good as just opening the amp up.

Another approach might be low efficiency speakers. At low volume, my 50 watt Sammi's sound much better than the Tonespotter.

[dehughes]

First of all, from one newbie to another, congrats for getting this far along.

I've never been successful at getting great tone a really low volume, but there are a few things that I've tried that help a little. Putting a 100k resistor between the master and the PI input seems to fatten things up a tiny bit. It's kind of like the "Loudness" switch on my old stereo. I've also been pleased with my Airbrake attenuator. Typically, I get the best low volume tone by using a combination of the master and the attenuator, but it's never as good as just opening the amp up.

Another approach might be low efficiency speakers. At low volume, my 50 watt Sammi's sound much better than the Tonespotter.

NORMSTER. You inspired me to re-check my build and comparable amps.....it seems like I've omitted a 270k resistor in the MV circuit (at the end of one side of the PI) and that I have misplaced a 470k voltage divider resistor on the other side of the PI. DUH!!!!!!!!!!!!!!!!!!

NEWBIE MISTAKE!


THANKS MAN! I'll change that and post back tomorrow....

[skyboltone]

Oh how I love this place.

Lots of very talented but humble folks running around. Norm, you are one of the most prolific builders on here! You inspire me. I have never built a guitar amp in my life but I got mucho electronic experience and am in utter awe of the way folks here can follow the TONE thru the amp like its visible in red white and blue. I'm getting very close to the point where I start hooking up the wires and the wife is going away for 9 days starting tomorrow . I predict noise of some sort in the comming 9 days. Can't wait, hope it's not too bad to start.

Dan

[Normster]

Ah gosh fellas, ya got me blushin'.

BTW, here's my latest little adventure. Look familiar?

[Allynmey]

Very nice...I think I recognize that!

[philmanatee]

Sweet! Phil

[dehughes]

Norm, did you go and build yourself a Komet? Now now, that's just not fair.

LOOKS KILLER!!!

As for your 100k resistor between the MV and the PI input, were you implying that it was 100k from the PI input to ground, as a voltage divider with the MV? Or, did you mean that the MV went straight through the 100k into the PI?

[dehughes]

Well, I ran a 220k-ish resistor from the master volume side of the PI to ground, and that made a big difference. It made the MV side more manageable, or even-keeled....hard to describe, but it is a step in the right direction. I'll have to order some 270k resistors and see how that works...

THANKS!

[Normster]

Norm, did you go and build yourself a Komet? Now now, that's just not fair.

LOOKS KILLER!!!

As for your 100k resistor between the MV and the PI input, were you implying that it was 100k from the PI input to ground, as a voltage divider with the MV? Or, did you mean that the MV went straight through the 100k into the PI?

Well, let's call it Komet inspired.

I ran a 100k in series between the MV and the PI input, but that was on a non-reverb amp. I forgot that you had reverb so that particular little trick doesn't apply. However, it sounds like you've hit on the same concept by running a 220k to ground. Maybe try a 470k and see if it's moving closer or further away from your target tone. Also, try it a higher volumes to make sure you haven't compromised that tone.

[dehughes]

Well, let's call it Komet inspired.

I ran a 100k in series between the MV and the PI input, but that was on a non-reverb amp. I forgot that you had reverb so that particular little trick doesn't apply. However, it sounds like you've hit on the same concept by running a 220k to ground. Maybe try a 470k and see if it's moving closer or further away from your target tone. Also, try it a higher volumes to make sure you haven't compromised that tone.

Thanks man. I don't have reverb in this, actually. It is a two channel amp, with one side being an EF86 circuit a la the AC30/4 and the other side being a full-eq version of the AC30/6 12AX7 circuit. No reverb. No tremolo. Just plain tone. Sounds pretty good, actually. The 220k goes to ground off the left cap on the PI, and the MV connects between the resistor and the PI cap. I think it works out pretty well, at any and all settings. I'll try a larger resistor in there just for kicks, but I'm pretty close. Now if I can just get my Sozo caps for the Cut circuit I'll be done with this crazy thing...

[Darkbluemurder]

Since your amp does not have any global negative feedback a post PI master volume could work well. Matchless and Bad Cat use cross line master volumes.
The Sundown A-50 uses a combination of a Lead Channel Master and a post PI master volume (the "Governor" control). One of my Marshalls had such set up one time as well. It works well until about halfway down but then it starts to crap out. This is due to the feedback loop collapsing at too low volumes. That is why this set up works better in a non-feedback amp since there is nothing to collapse.
It appears to me it is probably the best to use all the controls to just slightly cut the volume and not radically. This also applies to any power attentuator use.

[Noel Grassy]

Normster that's another beauty! What iron did you use? Specifically the choke[looks correct] & the OI guess your working on the cab now