Author Topic: BIG Muff pi + 3 band EQ  (Read 465 times)

Digital Larry

BIG Muff pi + 3 band EQ
« on: January 24, 2021, 12:43:06 PM »
Wasn't I going to design an FV-1 board with a Teensy?  Yeah, well I thought about it and decided I might eventually do it, but I want to get back to trying to record some songs rather than invent things.  That said, I don't have a fuzz box of any sort and so have decided to build something like what's in the thread title.

I have a SparkFun ProtoPedal board.  https://www.sparkfun.com/products/13124

I'm using TinyCAD and VeeCAD to create the layout for this.  IME this is WAY better than improvising as I go or trying to do it on a breadboard first.  VeeCAD let me easily create the layout of the SparkFun board and update the netlist from the schematic as I go.  I like this part of the project as it's straight up puzzle solving. 

I only have the BMP circuitry on there at the moment but I think I will have enough room for the 3-band EQ based on a single op amp stage.

I'll publish my schematic once it's done and let you critique it.  I looked at some of the compendia of BMP schematics and notice that most of them are architecturally almost identical.  There is one variation where you take the clipping diodes off the second gain stage, which can be done with a simple SPST, which I think I will also do.

Digital Larry
DSP tinkerer and former transistor twister

antonis

Re: BIG Muff pi + 3 band EQ
« Reply #1 on: January 24, 2021, 02:53:14 PM »
I only have the BMP circuitry on there at the moment but I think I will have enough room for the 3-band EQ based on a single op amp stage.

You could use last recovery stage (just as used for original tonestack) instead of op-amp stage..
(way far from be considered "ideal" amp but it would worth a try..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Digital Larry

Re: BIG Muff pi + 3 band EQ
« Reply #2 on: January 25, 2021, 10:50:01 AM »
I only have the BMP circuitry on there at the moment but I think I will have enough room for the 3-band EQ based on a single op amp stage.

You could use last recovery stage (just as used for original tonestack) instead of op-amp stage..
(way far from be considered "ideal" amp but it would worth a try..)

Here's my VeeCAD layout.  I really like working in VeeCAD.  Nobody mentions it much but maybe there's some other Vero tool that everyone uses.




Here's my schematic in TinyCAD.  The ProtoPedal board has a MOSFET reverse polarity blocker built in so I will probably add a 47R/100 uF low pass right on that prior to heading to +9V on the main board.  Jacks and pots are not shown although I do have a 2-pin input.






Here's some design questions:
a) I'm not sure in advance of the P-P swing output from Q3 collector.  So I'm not sure if I should pad the input going to the equalizer.
b) Similarly I'm not sure now much to pad the output of the equalizer.  I can design in a couple resistors and then figure it out as I am building it.

Anyone notice anything missing?  I haven't put in part values and I will have to make sure that the parts, esp. the caps will fit in the footprints.  I can stand TH resistors on end which is why they fit into a variable amount of spaces, down to 2 0.1" apart.
« Last Edit: January 25, 2021, 11:19:00 AM by Digital Larry »
Digital Larry
DSP tinkerer and former transistor twister

Digital Larry

Re: BIG Muff pi + 3 band EQ
« Reply #3 on: January 25, 2021, 11:43:04 AM »
The design posted above has some obvious problems.  Points awarded for identifying them. 
« Last Edit: January 25, 2021, 12:47:49 PM by Digital Larry »
Digital Larry
DSP tinkerer and former transistor twister

Digital Larry

Re: BIG Muff pi + 3 band EQ
« Reply #4 on: January 25, 2021, 01:34:36 PM »
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« Last Edit: January 25, 2021, 02:17:51 PM by Digital Larry »
Digital Larry
DSP tinkerer and former transistor twister

antonis

Re: BIG Muff pi + 3 band EQ
« Reply #5 on: January 25, 2021, 03:20:23 PM »
Sustain pot is wired backwards..
(Lug 1 should go to GND)
Maybe with a stopper resistor in series..
« Last Edit: January 25, 2021, 03:26:02 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Digital Larry

Re: BIG Muff pi + 3 band EQ
« Reply #6 on: January 25, 2021, 04:56:48 PM »
Sustain pot is wired backwards..
(Lug 1 should go to GND)
Maybe with a stopper resistor in series..
I hadn't even thought about lug numbers!  ;D
There's still a bad problem somewhere....
Digital Larry
DSP tinkerer and former transistor twister

antonis

Re: BIG Muff pi + 3 band EQ
« Reply #7 on: January 25, 2021, 05:03:53 PM »
Move C14 before Sustain pot for crackle-free operation..

Add a big cap right after U1A output..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..