First Pedal PCB Build: The Muffin

Big Monk

Well-known member
I'm going to use this thread to document my build on the Muffin board.

I'm using the schematic values from Kit Rae's site for the Version 2 Violet Ram's Head 1972 #5 unit:

1973#5.PNG

I have a whole stash of Amperex A115 transistors that I bought from Small Bear in the hopes they actually delivered around the gain bucket Steve showed. I wanted to use them for Axis Face Silicon Fuzz units. Turns out his hFE bucket was low for some reason. Most of them were over 150, with a distinct gathering around 175-200. Not so great for what I bought them for but good for the more traditional Silicon Fuzz Face and, as it turns out, this project. I decided to go with Kit Rae's site again where he singles out 2 exceptional Violet Ram's Head units with all 4 transistors in the 160-200 hFE range:

Qs.PNG
I ended up picking a fairly matched set of A115 units:

Q1, Q2, Q3 = 171 hFE
Q4 = 164 hFE

I had some 1N456 diodes left over from my Ampeg Scrambler parts so I grabbed 4 of those centered around a Vf of 756 mV. Nothing special other than they look really cool.

The last thing I am working on right now is the tonestack. I'm going for more of a Gilmour thing here and plan on using this by itself but also EQ'd by a Vick Audio Overdriver. My little Single Ended EL84 amp is fantastic for my home playing and the Drive control I installed gives me a broad range from clean to semi-dirty to full out crunch. It has a reasonable amount of mid-range content when driven so I don't want to do anything crazy with the tonestack except to flatten out the mid-scoop a touch.

So, I went to the Duncan TSC:

Tonestack 1.PNG

In the form you see in the schematic, there is a -12.5 dB mid scoop at around 1kHz when the tone control is at 50%. I wanted to bump this up a bit but not quite flatten it out as I have a somewhat mids-forward amp and ways to adjust the mids should I need to. I'm still not certain how I'll end up configuring it, but I'll likely just pick an appropriate value for C9 and call it a day.

Here are the TSC charts for C9 = 6.8 nF and 8.2 nF, respectively:

Tonestack 2.PNG Tonestack 3.PNG

The mid-scoop at 50% Tone goes up to -8.3 dB and -9.4 dB respectively.

Lastly, here is the mockup with controls and mechanicals attached to the Tayda Ball Silver enclosure:

BMP1.jpg
BMP2.jpg

Should find some time this week to get everything wired up.
 
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let me know where you end up on the tone control values, I've been messing with these myself quite a bit lately
 
let me know where you end up on the tone control values, I've been messing with these myself quite a bit lately

I think I'm simply going to play with C9. It seems to have the most effect on the mid-scoop. With 39k resistors in R5 and R8, changing C9 shifts the mid-scoop up towards flatness at 50%.

My gut says I'll go with 0.0068 uf there. That reduces the mid-scoop from -11.4 (ish) dB to around -8.3 dB. I don't want to flatten it too much given my amplifier and the fact that I play a Les Paul much of the time as well.
 
I've been going with lower values of that, like 3.3nF and 2.7nF

I originally started messing with these based on the Elk Sustainar which had like 390pF, but it sounded very bad lol

I know the R and C values form low and high pass filters, but I don't understand what effect changing the cap vs changing the resistor has
 
I've been going with lower values of that, like 3.3nF and 2.7nF

What I am thinking of doing is having my "scoop reducer" cap value on a switch. This way I can "deepen" the scoop when playing my Les Paul and make it less shallow with my Strat.
I know the R and C values form low and high pass filters, but I don't understand what effect changing the cap vs changing the resistor has

I'm not an expert either on the BMP tone control. As a general rule, tweaking C9 up will raise the mid-scoop toward flatness, while tweaking C8 down will do the opposite. Tweaking either R5 or R8 down seems to deepen the mid-scoop.

Have you used the Duncan Tone Stack Calculator before?
 
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to add, as a guitarist I've generally come to dislike the left half of the tone knob and so I've pushed the low pass filter up towards 1000 Hz (smaller R and C values) to get useable sounds from the full turn of the knob

no mud or flabbiness here
 
I have not, I've been basing my decisions based off info from this page:


I'd recommend the Duncan TSC:


It lets you see how how the component changes the frequency response.

When you look at the mid control on the Hoof, you can see that it actually makes the scoop much deeper at it's minimum, as the pot is in series with a very small resistor. At the maximum value of the mid control it's just a touch under flat at 50%
 
So, I decided to drill a small hole where I had room inside near the switch:

ACBFAE1A-CB25-4B70-B6E8-97E4298E01DA.jpeg

My logic is simply to switch the C9 to compensate for when I go between my Les Paul and Strat.

First thing I’ll do is decide on the depth of the mid-scoop (LP setting) then decide on a flatter setting (Strat Setting).
 
Awesome planning and preparation.

I tend to plan things in depth, but I'm nowhere as meticulous as you're being with this build — it's opening my mind up to thinking beyond the box (literally), I must reconsider the entire signal chain and all its influences.


I'm still planning my first Muff build, so this is very inspirational.
 
Awesome planning and preparation.

I tend to plan things in depth, but I'm nowhere as meticulous as you're being with this build — it's opening my mind up to thinking beyond the box (literally), I must reconsider the entire signal chain and all its influences.


I'm still planning my first Muff build, so this is very inspirational.

Thank you! I guess my thing is planning so I have no mistakes and also so I don’t regret component choices, etc. For me, I like to build things that far exceed what I could have bought and that occupy pride of place on my board.

I’m trying to accomplish a couple things:

1.) The Gilmour BMP Sound. I think the tweaks to the Violet Ram’s Head base will get me there. Also, I just purchased a Vick Audio Overdriver to use with it.

2.) A versatile BMP tone. I think with the mid-scoop switch, this will also be stellar with my Les Paul.
 
For versatility, why not 3 tones? C9a, C9, C9b

I really like how Aion uses an on-on-on DPDT where most would use an on-off-on.

The difference is with on-off-on you've got Flat-Scooped-Bumped in the switch positions.
Using the on-on-on, you get a logical (to me) Scooped-Flat-Bumped set of switch positions.


Any plans to build your own Colorsound PowerBooster?
 
For versatility, why not 3 tones? C9a, C9, C9b

I really like how Aion uses an on-on-on DPDT where most would use an on-off-on.

The difference is with on-off-on you've got Flat-Scooped-Bumped in the switch positions.
Using the on-on-on, you get a logical (to me) Scooped-Flat-Bumped set of switch positions.
I don’t think I need boosted mids. My modified single-ended EL84 is mid-forward and I can always EQ a mid bump on my 6 band if need be. I want it just under flat for my Strat and fully scooped for my Les Paul.

Plus I only have DPDT switches on hand! I do like your point though.
Any plans to build your own Colorsound PowerBooster?

Nope! Just splurged on a Vick Audio Overdriver. It can be powered with 9vDC or 18 vDC, which I have on my power supplies, so it’s essentially an Overdriver and Powerboost.
 
So, I think I have settled on tonestack values:

High and Low-pass Resistors = 33k
High-pass Cap = Switchable

0.0047 uf (Les Paul)

1627672183533.png

0.0082 uf (Strat)
1627672217794.png

Low-pass Cap = 0.01 uf
 

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I messed around with the tone stack calculator a bit yesterday

I still don't really understand what's actually happening because while the program may tell me one thing, my ears tell me another...for instance I seem to get more treble at the lowest setting on the tone knob vs at the middle position, something the graph cannot back up

I'm keeping my high pass cap (C10) at < 4nF and I will die on this hill 👀
 
I messed around with the tone stack calculator a bit yesterday

I still don't really understand what's actually happening because while the program may tell me one thing, my ears tell me another...for instance I seem to get more treble at the lowest setting on the tone knob vs at the middle position, something the graph cannot back up

I'm keeping my high pass cap (C10) at < 4nF and I will die on this hill 👀

Actually, I think what you are hearing is EXACTLY what the graph is showing you.

i don’t have it in front of me but on “10” you have a bump in highs and a roll off of lows. On the other hand, the tone control on “0” shows a steep roll off of highs.
 
I think what I'm hearing is actually more mids being brought in at 0 than at 5. Basically the middle setting on my latest big muff is the worst spot but everywhere else is fire
 
So, this is a first.

Got the circuit all wired up:

8184C283-C6E3-468B-A52F-9D3CE53FFAE8.jpeg F2171049-7621-4D10-B7F3-54FA6A66AD75.jpeg

The circuit works wonderfully. The mid-scoop switch worked like gangbusters.

But, the LED won’t light up. How’s that for the polar opposite of what you would have expected when you were a newbie? Perfectly functional circuit on the first try but no LED.

I checked the obvious: it’s oriented properly, I did a continuity check from power to switch, etc. I tried a different LED.

I guess I’ll have to remove the whole circuit from the enclosure and check my connections from the underside.

Anyone have any ideas?
 
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