Pedal Mule 30 - Prototype build

[RJ Guitars]

You are making progress... as an amp becomes our own they always tend to drift toward the sound we want.

I looked into mine. First I played through it and all the controls worked just the way you might expect them to based on their labeling.
Bass = linear function with a good range
Treble = linear function with a good range
Bright = Added Brightness
Deep - Added Bottom end (this was not subtle)
Volume = goes from quiet to very loud (it does come on pretty sudden and gets loud quick!)

No weird hums or pops...

If you go back to KF's Songwriter, it was his intention to create each of the controls so that they minimally reduced the signal if you max the control out. Additionally he kept the leads very short which explains the bass control location in an unusual place. Komet has cleaned this up on their production models with a more tradition layout for the controls.

For the "Deep" switch, I simply bypass the .02 coupling cap with a resistor - thinking about that it might be better to use a bigger cap rather than a resistor but my own amp didn't suffer from that? This gets more of the low end back into the signal... I assume he had all the bass he wanted in his build but I wanted a little more??

So now I'd be curious if what I built matches the schematic I posted a long time ago. I'll add some pictures to help if anyone wants to critique or compare things. Also - let's look at what I have in archives for a schematic... I haven't been real active here for the past few years and it's possible the new and improved versions were not posted.

Looking at an old Songwriter schematic (I dunno if we are allowed to post those here. I know the guys at Komet were not so happy about that previously) I do see that he applied some negative feedback going into the phase inverter. Lemme know if that does any magic for you.

[Littlewyan]

With the deep switch you’re putting a .02uf capacitor in series with the 500pF/.1uF capacitors to give a bass cut and then bypassing it with a resistor to reduce its effectiveness. But I can’t see .02uF making much difference in series. Is that definitely the value you’re using? .002uF would be effective with a 500K volume pot, but .02uF wouldn't really be giving you any cut at 82Hz.

Edit: I also looked back at your notes and you mentioned using a .001uF capacitor here which would make more sense. You'd definitely notice a big change in bass with that value.

[Mark]

I noticed that C1 (cathode bypass cap on the first 12AX7 stage) is 1uF. In the past I worked on a Champ clone with a 1uF cathode bypass cap and I found that it limited bass response.

I found 5uf was a better value in this Champ style amp.

Could this be so in the pedal mule?

[Colossal]

I noticed that C1 (cathode bypass cap on the first 12AX7 stage) is 1uF. In the past I worked on a Champ clone with a 1uF cathode bypass cap and I found that it limited bass response.

I found 5uf was a better value in this Champ style amp.

Could this be so in the pedal mule?

Mark,

1uF on the input stage is the stock value on the Songwriter 30.

[freakshow__]

hey everyone...sorry I took so long to get back.....

So I think the hum and loud popping is the power at my apartment. I have a practice space in town that I brought this to and it doesn't hum AT ALL there. The pop at shut down is quite normal (small) too. So I "think" I have those issues solved.

as far as the controls being mild....

The treble (cut) control does work fine....I ended up reversing the leads so that it actually cuts CCW and not CW. It made more sense to me to do that.....I ended up putting a 100ohm resistor in series with it because if you turn it all the way to full cut, it makes some weird hissing and noise. The 100ohm in series stopped this.

The bass control works as well...the entire amp gets louder as you come close to full on CW. Is this normal? Bass increases but overall volume increases as well.

Bright switch works fine...pretty simple there. I went to a 500pF cap there.

now.......
The depth switch did not work at all. I currently have the switch setup as a NFB on/off instead. I used a 220K off the 16ohm tap, as is in the "songbird" schematic. It's kind of mild....doesn’t do much. I ended up with 33k as it made a noticeable difference. I may even try 22k. there is a ac30 schematic floating around where the guy used 33k/8ohm tap…..this works. the 220k/16ohm tap pretty much does nothing.

answers to questions...
I have everything grounded at a star by the largest filter cap with the exception of the incoming power...that has it's own dedicated ground lug. I tried to follow RJ's layout with the grounding since he had hum issues in the beginning.

The cathode resistor/cap is not glued to the chassis...it is screwed. I have glue there because I HATE things being loose on the chassis to vibrate over time. So I use E6000 glue to secure things to the chassis in various spots. The cap is glued to the chassis here in this case. I think I secured part of the resistor as well....but it is screwed to the chassis for sure.

Thanks everyone for the input so far, and thanks RJ for starting this thread years ago. It's a pretty fun build that you can get some easy personal "tweaks" to it seems.