DAM fS 77 fuzz sound schematic d7c57ed577f8

D*A*M: Fuzz Sound FS-77, Tag Board Layout

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I couldn’t find a layout for the FS-77 anywhere, but I did find some photos online, so I decided to try and trace it back in November 2020.  I thought I had it, but when I looked at it again recently, I noticed the input didn’t look right.  The caps were the wrong way around for an input blend…  hmmm.  If it’s not an input blend, what is it?

So I went looking for more information, and recently someone was kind enough to share some photos with me (you’re a legend), which completed the picture – I was a bit lost without the additional photos, and had mistaken the blend pot for an input blend, which is not uncommon on D*A*M designs.


THE BONES OF THE FS-77

So what is the FS-77?  Like most Fuzz Sounds, it’s a Tone Bender MKIII with tweaks.  

  • The collector resistor on Q1 & Q2 is only 4k7, as opposed to 10k
  • 4.7uf input cap, with a 10n to ground
  • Usual 220pf cap across collector and case of Q1 is 47pf
  • Sonically the biggest change is the tone & blend controls, which are based on a Big Muff tone stack.  The blend is a kind of a mid-range control, based on the same idea as the AMZ presence control.  The blend pot changes the high-pass filter cut-off, which forms one half go the BMP tone stack.

D*A*M FS-77 FUZZ SOUND SCHEMATIC


D*A*M FS-77 FUZZ SOUND SCHEMATIC





ASSUMPTIONS

There are some component values that I’ve not seen, all other values have been seen on photos.

  • Fuzz, tone and volume have been assumed based on normal tone bender values used by D*A*M
  • Initially I had a 25k pot for blend, but after testing it, I’ve landed on 50k. Try some different values, maybe you prefer a 25k – the 50k just has a slightly wider range.   Being a BMP tone control, it’s easy enough to tune to your personal taste, even if the stock FS-77 values are a little unfamiliar.
  • The 220n between the tone and volume might be a different value – looks the same as the 220n on the board, and is large enough to not impact the frequency response after the tone control

TONE CONTROL

Despite being a BMP based tone control, they’re not even close to typical BMP values 

It does allow a mid hump, as well as a bit of a scoop on some settings.


Bass, low-pass filter

220k & 2.2n = 329hz


Treble, high-pass filter

25k pot:     10n cap & 1.5k – 26.5k = 600hz to 10.6khz sweep

50k pot:     10n cap & 1.5k – 51.5k = 300hz to 10.6khz sweep


LTspice – tone & blend swept in values from 1, 50 & 100% (50K blend pot)

ON THE BENCH 

It works…   it gives you some classics tone bender MKIII tones, and then some more modern sounds as a result of the tone control.  

The blend provides a nice sweep, and works well with the tone control.  There’s a lot of useable tones in there.  I prefer the 50k pot as you get more range.  

I ended up using a wider piece of tag board as I’m going for a landscape layout in the enclosure.


D*A*M FUZZ SOUND FS-77 – TAG BOARD LAYOUT

D*A*M FUZZ SOUND FS-77 - TAG BOARD LAYOUT







Note: NKT213 transistors also used

D*A*M FUZZ SOUND FS-77 – VIDEO DEMO

I believe this is the only video demo out there.  You get an idea of the sound, but the pedal stays on one setting throughout, so it doesn’t provide any ideas on the range.



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