Andy Armstrong, Soft Fuzz, in: Hobby Electronics, July 1983 🇬🇧

Free online ressources on guitars, amps, effects, guitar technique and more. Dedicated to the fond memory of its founder SPeter Davidoff.
Post Reply
User avatar
modman
a d m i n
Information
Posts: 4890
Joined: 19 Jun 2007, 16:57
Has thanked: 4394 times
Been thanked: 2131 times

Post by modman »

PDF:
Hobby-Electronics-1983-07-S-OCR Soft Fuzz.pdf
(315.91 KiB) Downloaded 254 times
----

Hobby-Electronics-1983-07-S-OCR Soft Fuzz 1.jpg
Hobby-Electronics-1983-07-S-OCR Soft Fuzz 2.jpg
Hobby-Electronics-1983-07-S-OCR Soft Fuzz 3.jpg
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

SoftFuzzLayout.JPG
Ready-to-print PDF-files:
SoftFuzzComponentSide.pdf
(21.46 KiB) Downloaded 83 times
SoftFuzzSolderSide.pdf
(4.58 KiB) Downloaded 77 times
Sprint-Layout6.0-file:
SoftFuzz.zip
(24.37 KiB) Downloaded 77 times

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

The value of R2 with 470 ohms was immediately suspicious to me, the circuit needed a high input level until the output signal began to clip, with 470 kiloohm then worked at lower levels.
Also, the frequency response showed that 470 Ohms must be the wrong value.
With 470 Kiloohms, the frequency response was then hi-fi and not suitable for guitar, there are still some things to improve.
R1 should have at least 560 kilohms I think that here also a digit "0" was forgotten in the value.
SoftFuzzFR.jpg

User avatar
Frank_NH
Solder Soldier
Information
Posts: 246
Joined: 12 Jun 2013, 14:18
Has thanked: 114 times
Been thanked: 152 times

Post by Frank_NH »

That seems right, Manfred. R2 is supplying the reference voltage for biasing IC1a, so 470K should be correct. The input resistor looks like an anti-pop resistor, so 1 meg would work there.

I'm curious to see what the soft clipping looks like. This is an unusual soft clipping feedback network which could potentially provide a more interesting distortion than the typical diode arrangement. I guess I should sim this in LTSpice too!

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

Frank_NH wrote: 31 May 2022, 16:17 That seems right, Manfred. R2 is supplying the reference voltage for biasing IC1a, so 470K should be correct. The input resistor looks like an anti-pop resistor, so 1 meg would work there.

I'm curious to see what the soft clipping looks like. This is an unusual soft clipping feedback network which could potentially provide a more interesting distortion than the typical diode arrangement. I guess I should sim this in LTSpice too!
SoftFuzzClippingCurves.jpg

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

SoftFuzzClippingCurves2.jpg

User avatar
mictester
Old Solderhand
Information
Posts: 2923
Joined: 11 Sep 2008, 20:29
my favorite amplifier: Mesa Boogie, Roost Sessionmaster, AC30
Completed builds: Hundreds! Mostly originals, a few clones and lots of modifications.
Location: Somewhat closer to Amsterdam than before!
Has thanked: 32 times
Been thanked: 844 times
Contact:

Post by mictester »

It's really worth listening carefully to this circuit. It's not really a "fuzz", it's far too smooth for that - it's a "tube-like" overdrive. If you add basic tone controls to the tail end of this, it will very effectively emulate a number of pedals. I've built (many times) a tweaked variant of this. The "zeners" in the feedback circuit come from a National Semiconductor data book from the 70s. The rest of the circuit (apart from the obvious mistakes) is pretty standard....

It's a worthwhile build, and you'll be pleasantly surprised by just how good it sounds - even on chords.
"Why is it humming?" "Because it doesn't know the words!"

Post Reply