GGG '70 boutique fuzz: what are the diodes for?

[Steben]

Stabilizing?
assymetric clipping?

[DougH]

Stabilizing?
assymetric clipping?

If it's FT70-based, that is. Got a schematic?

[jayp5150]

http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_b70.pdf

That one?

If so, I'm interested in the placement of D1. I know a lot of us have messed around with using a diode instead of the feedback resistor, but I've never seen one in series with the fb R; also, it's connected to the wiper of the gain pot.

I'm thinking this would allow a bit of a more usable lower range of the gain pot, but I'm not 100% on that. Or maybe a bit more touch responsiveness at lower gain settings (that's been my experience with a diode in that position, anyhow).

The Ge on the output would appear to be for assym. clipping.

[Steben]

As I looked at it I saw the feedback diode does two things:

1. creates short to ground at the input of Q1 for AC negative input swing (= clipper). Something similar hapens in the base-emitter diode of Q1 as well. It seems to me you have a parallel function of diodes, maybe leading to germanium tresholds (simulating input base-emitter cut-off in GE fuzz face)? Softening the silicon?

2. creates a short for low frequency signals (those that do not come through the elco cap) from emitter Q2 to base Q1, leading to massive negative feedback.
But I guess these freqs are too low to count?

[jayp5150]

As I looked at it I saw the feedback diode does two things:

1. creates short to ground at the input of Q1 for AC negative input swing (= clipper). Something similar hapens in the base-emitter diode of Q1 as well. It seems to me you have a parallel function of diodes, maybe leading to germanium tresholds (simulating input base-emitter cut-off in GE fuzz face)? Softening the silicon?

I thought with the positioning of that diode, there is no signal path TO ground from the Q1 base, as it cannot conduct in that direction.

I'll have to look into that more later. I have to go to work  (@ work, not you lol)

[Steben]

I thought with the positioning of that diode, there is no signal path TO ground from the Q1 base, as it cannot conduct in that direction.
I'll have to look into that more later. I have to go to work  (@ work, not you lol)

Why not? It cannot conduct positive in this circuit, but it does conduct negative signals. I guess it lowers a tad the base-emitter conduct leading to less collector current, pushing it a bit to at least less circuit gain.

[DougH]

As I looked at it I saw the feedback diode does two things:

I also see it as a mixture of feedback and shunt clipping. If it is the FT70 circuit (haven't compared them) it does sound nice as I've tried that on the breadboard before. The diodes add a pleasing smoothness to the sound.

[Steben]

As I looked at it I saw the feedback diode does two things:

I also see it as a mixture of feedback and shunt clipping. If it is the FT70 circuit (haven't compared them) it does sound nice as I've tried that on the breadboard before. The diodes add a pleasing smoothness to the sound.

Yes, I assumed it somewhat.
However, it definitely puts the DC drop from eQ2 to bQ1 at around 0.5-0.6v, which leads to restricted bias and possibly really lowers the conduct at Q1's base.