Pedal Mule 20 - Prototype build

[gahult]

I am about to start work on a project rj sent to me. I need to order a couple of parts but I'll will get going on the rest in the mean time.

Pictured is what rj had done when I got it.

I'll be posting up progress as I go.

Gary

[gahult]

Board is ready to mount in chassis.

[gahult]

Got some power supply and filament wiring done.

[SilverFox]

As I'll rebuild my pedal amp circuit at some point I'm following along on your build. Looks good so far.

silverfox.

[gahult]

I have taken it upon myself to update the schematic.
The changes I made:

EM 0740 and 125E xtfrs.
Choke info.
Bridge rectifier.
PS cap values.
Shunt jacks input and output.
R2,R5,R11 values.
Changed orientation (polarity) of C12.

Gary

[gahult]

A little more progress.

[SilverFox]

Okay, isn't the signal going to be a little weak without a second gain stage? What led to the decision to place the treble pot in the phase inverter? These are questions not criticisms.

Looking forward to the completed project.

silverfox.

[M Fowler]

That's a standard Vox AC30 treble cut control in the PI you can use different value caps and have a nice tone control.

[gahult]

Thank you Mark. i would not have had an answer to that as I am clueless.

Will be breaking off this to order parts, so I'll be back on me Rocket build for a bit.

Gary

[M Fowler]

SilverFox

Okay, isn't the signal going to be a little weak without a second gain stage?

It has a parallel first stage so the gain is increased more than normal and the fact that there is no tone stack makes up for the need to set the gain factor of this preamp any higher.

Mark

[SilverFox]

Just curious George here;

No feed back to the phase inverter? I've got a cut switch on mine and when I cut the FB out it gets Loud and Raw.

Did you leave out a feed back circuit on purpose?

Regards,

silverfox.

[gahult]

This is a design/prototype build from rj, hopefully he will break in here with some answers as to the whys and wherefores of the build.

Gary

[Zippy]

Just curious George here;

No feed back to the phase inverter? I've got a cut switch on mine and when I cut the FB out it gets Loud and Raw.

Did you leave out a feed back circuit on purpose?

Regards,

silverfox.

"... on mine": What amp are you referring to? After reading your comments, it seems you are working with a different circuit. An amp is the sum of its parts, what is "lacking" in one part of the circuit is compensated in another. Here the "lack" of gain in the front end is compensated by the omission of the feedback circuit. The EQ will be different as well.

[SilverFox]

Thanks all. Gary I'm about the same regarding technical knowledge. I've been reading lots and built some amps but in areas the inner workings are at some points mysterious. Hence the questions.

Zippy- The last amp I built was a JTM45 Pre with a Sunn Sceptre PA using, I believe a cathodyne phase inverter. Your answer is very informative as I hadn't made the connection between lower gain levels on the input and the advantage of no FB in the power amp section leading to higher gain.

What I like about this circuit is the simplicity that was suggested to me for a Pedal Amp but instead I chose the JTM model. While it has worked out well there are some bugs to clear up. As a result I'm very interested in the outcome of Gary's build.

Regards,

silverfox.

[Zippy]

Thanks for shedding some light on your context, Ag.

Some of these amps are a lil' off the beaten path, so you can't just pick out one detail, and assume that the results will be universal. On the other hand, making tweaks one at a time can be a great teaching/learning tool (even if they don't give the desired answer).