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Modding a Schematic: hybrid-ish pedal -- help!

EricssonB

EricssonB

Apr 5, 2011
1,287
630
CO
#1
TB,

In my quest to occupy myself on a two-month night shift stint, I've found myself looking to do a mashup of two circuits I built two years ago.

The first (FBII) is a copy of an old MM two-band design. The frequency cutoffs are gorgeous and wonderfully voiced -- I love it. It doesn't boost the signal much, if at all, but that's okay. It fried itself a few months back, and I haven't gotten around to trying to fix it. Probably because I run it on a 12-15 VDC supply. Oops.

The second (FBIII) is a copy of somebody's copy of a 3-band Ray design. It pushes a hell of a signal, which helps the amp breakup and all of that. It's good in its own space, but doesn't zing like the FBII. Best part is that I have an extra board (the original prototype) sitting around!

I have a basic understanding of R/C filtering for directing hi/low-pass, but I can't compute how to pull the hi-pass from FBII and throw it into (the more complicated) FBIII grid. I would like to mod the existing FBIII design with the cutoff frequencies of the FBII.

Anybody?

FBII:
MusicManStingRay.jpg

FBIII:
FBIIISchem.jpg
 
#2
Breakdown of the R/C cutoffs, subject to edits:

TREB KNOB:
-- FBII seems to be a high-pass of 402.1 (220k R x 1n8 C, but that feels a bit low from miles away from my amp.)
-- Where would this go on FBIII? :chicken:

MID KNOB:
-- I will simply omit this from the final design. I left it out during testing, and it seems flat when it's left out. :cigar:

BASS KNAB:
-- Yeah I literally can't even. :help:
 
Last edited:
#3
Posted-this-at-a-bad-hour-when-the-night-creepers-are-out-but-still-need-some-guidance-meanwhile-I'm-gonna-see-what-that-LTSpice-program-is-all-about-because-it-sounded-cool-when-I-read-about-it-a-long-time-ago bump.
 
#4
Since only a small fraction of TB members do any DIY or circuit design, I think you'll always get more discussion and help from a dedicated DIY forum like diystompboxes.com. There's a huge concentration of knowledge there, and people are helpful.

Here's a cool applet for analog filter design. It's way simpler to dive into than Spice sims and you can tweak values in real time to see the effect they have on frequency response.

http://www.falstad.com/afilter/
 
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#5
Taylor Livingston said:
Since only a small fraction of TB members do any DIY or circuit design, I think you'll always get more discussion and help from a dedicated DIY forum like diystompboxes.com. There's a huge concentration of knowledge there, and people are helpful.

Here's a cool applet for analog filter design. It's way simpler to dive into than Spice sims and you can tweak values in real time to see the effect they have on frequency response.

http://www.falstad.com/afilter/
Click to expand...

This is pretty rad stuff. I've found a few comparable programs, and I'm trying to figure out which works best with me. Will post updates once I get the values plugged in.

Night shift and a complete rebuild of my PC and Windows environment... ugh. Maybe I can get that Java applet to open up at work, when I have nothing, but, time, to, kill.
 
#7
9iAbQvG.png

Here's some chicken scratch that'll serve as my notes for when I can get home in a few hours to run the simulation, since I can't get anything to work properly at work. This post is for me, not for you.

#VISIO
 
Last edited:
#10
Welp, went to go translate it to the board, but noticed a discrepancy on the Spice sim.

...didn't seem to make much difference, except perhaps a steeper slope on the low end. Whatever, Eric. Whatever. Circuit are stoopid.

3Am70Q6.png
 
#13
ybhwnX3.png


Both pedals read around +4-ishdB at 100Hz and seem to follow a similar curve, and the modded circuit has an inherent rumble filter in the design. I'm happy with this. I really have no idea what the phase discrepancies are though, and I'm not even sure if I care.

Gonna see if I can't boost the overall by a few dB. Why not. Let's give it some overhead.
 

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