Pedal Mule 20 - Prototype build

[SilverFox]

What's going on Gary? Just thought I'd stop by and see how the progress is going.

silverfox.

[gahult]

Corrected schematic pin out on V2a/V2b to 12AX7

NOT THE 6SL7 ON THE PEDAL MULE 30 THIS WAS DERIVED FROM.

[gahult]

Changed bright switch to parts and values supplied.

Gary

[gahult]

Schematic change "c"

Added B+ voltage readings.

Changed R11 back to original value of 1.2K as it really screwed with all aspects of the amp at 47K. Especially the voltages and operation of V2.

Gary

[SilverFox]

Have you gotten any tones out of the amp yet? Good, Bad, ?

silverfox.

[gahult]

Sounds pretty good for now, but need to do some tweaking and get rid of hiss.

Gary

[gahult]

I really need to adjust the date stamp on my camera.

Gary

[gahult]

I've started on the head cab now for a change of menu.

I drilled the mounting holes now to better see the positioning and ease of drilling with nothing in the way.

Gary

[DocJames]

How clean is this amp? Do you get a lot of headroom before break up?

[SilverFox]

Nice clean build. Congratulations,

silverfox.

[printer2]

Are R19 and R20 really 470k?

[gahult]

DocJames...The amp is clean, it does not breakup...very little if at all. I talked with MFowler (he has helped me on various aspects) and he mentioned that it is designed to be a clean amp.

SilverFox...Thank you. I will have a couple more pictures when done. Still doing some minor changes.

printer2.....OOP's good catch R19 and R20 are 470R not 470K. Either my eyesight or just a bad typo on my part. I will correct the schematic and post after tweaking. Thank you.

Gary

[RJ Guitars]

I've been distracted And locked away in my own little world... so i missed the startup of this thread. Great work Gary, i'm still studying it but will post some additional info when i get up to speed.

[gahult]

This is complete now except for getting it into the head cab.

That will be the last images I'll post when done.

The schematic is corrected and updated.

I need to get some sound clips to post....will do.

When this is kitted by rj he may offer it with a different OT (better sound and output taps to implement an impedance switch).

The images aren't the best, I'm a little shaky in my senior years, it is what it is, sorry.

Gary

[RJ Guitars]

Gary,

That is a great collection of documentation... thanks! This is almost exactly how I hoped the amp would turn out... you finished it long before I would have gotten it done.

I sent Gary this project because he was an experienced builder and was willing to take some time to put together a prototype that still needed some engineering work. I expected the Songwriter circuit would sound good as an octal amp since I got such a huge sound coming from the 30 watt PM-30 build. http://ampgarage.com/forum/viewtopic.php?t=26872 It seemed safe to believe that the PM-20 would sound similar but have an even smaller parts count. Seems like that is the case.

This was a collection of leftover parts from a few previous projects and I have a half dozen of these chassis and power transformers that I would be pleased to move along very reasonably to anyone who has an inclination to put together one for them selves.

Great job of building this amp. Looking forward to your field test results and any sound clips you can produce.

rj