Fuzz Face stuff you may already know...

[glesconz]

Hi, heres an interview with Roger Mayer talking about Germanium transistors, Hendrix, and Temperature...

http://digital.premierguitar.com/premierguitar/201008_1#pg69

Cheers,
Glenn

[amptramp]

Good article that says what I have been telling people all along: a design that depends on supply voltage, temperature, source impedance, load impedance and select-on-test parts for parameters that are a small segment of the usual production range is a bad design.  A fuzz face doesn't even have a power supply decoupling capacitor.  No wonder no two act alike and people have to build "deteriorating battery simulators" to make them work.

[ckyvick]

A fuzz face doesn't even have a power supply decoupling capacitor.  No wonder no two act alike and people have to build "deteriorating battery simulators" to make them work.

Isnt that because the stock ff has an 8.2k resistor instead of a trimpot which causes the pedal to be over(or usually wrongly) biased?

[amptramp]

Another good reason to use a different design.  A resistor which performs properly at one temperature is going to perform differently at another - if you are using germanium transistors, the leakage current will vary substantially with temperature.  A trimpot may be able to set the collector voltage at one temperature, but it would have to be readjusted when the temperature changes.  I noticed the article uses some of the same arguments that I have before - bringing a fuzz face in from a freezing van and setting up may give you unusable performance until the unit warms up.  Having seen the order of bands being changed to accommodate one band that arrived late, nobody wants to wait around for an effects pedal to return to ambient.  The article said Jimi Hendrix ran into that problem and that he had to pick from a number of fuzz face units to find one that was acceptable even at room temperature.

The lack of a decoupling capacitor is sometimes excused by people who say that the current in one stage increases while the current in the other decreases.  But these currents are unequal (and they must be for the effect to operate).

[m_charles]

so what's a good replacement? a silicone FF?

[azrael]

^google Axis Face, and check out that design. Sounds great.

[amptramp]

DougH reproduced the Axis Fuzz schematic in this thread in the lounge:

http://www.diystompboxes.com/smfforum/index.php?topic=86321.0



It uses silicon transistors so leakage is not an issue.  One transistor is PNP and the other is NPN as opposed to the Fuzz Face where both transistors are of the same gender.  Both stages have emitter resistance for stabilization of the operating point whereas the input stage on a Fuzz Face does not.  The Axis Fuzz has decoupling for the bias to the first transistor whereas the Fuzz Face has no decoupling, but neither unit has decoupling of the battery supply.  The Axis Fuzz also has an input capacitor to limit the RF sensitivity so that it will not act as a radio receiver.  Based on the schematic, it looks like the Axis Fuzz would have a bit better control of the operating point and therefore less temperature instability and less dependence on transistor gain, so it would be a little better in terms of usability, but the real test would be the sound - which do you like better?

[brett]

Hi

if you are using germanium transistors, the leakage current will vary substantially with temperature.

That's not exactly useful because it is literally true.   Confused?

Leakage current for Si transistors and Ge transistors (and others) varies a lot with temperature.  Except for low quality Ge devices it doesn't matter, because the leakage is low.  The answer - get good quality Ge or go Si.  IMO good quality Ge devices rip in FFs.  Try any of the later Japanese or Russian devices.  Basically, Ge devices from the US and Europe are leaky and gain is all over the place (if they aren't dead).  Try a 2SBanything or a GT308B.  Your life will change in a good way. 

[ckyvick]

so what's a good replacement? a silicone FF?

Make the silicon colorsound 1 knob fuzz, its by far my favorite fuzz face variant. The mkii bender is also good if you want something thicker/fuzzier

[mac]

Germs leaking less than 30ua, like some well-known Toshiba's (2sa49, 2sb54/56, etc) will probably bias at 8k2. And will deviate a lot less from the operating point with temperature changes.

mac

[zombiwoof]

The thing that I find interesting in this article is something he says that answers a question that many have asked, which is how did Hendrix get away with using his wah in front of the FF without the oscillation problems?.  I always figured that Mayer probably was aware of this problem and used some sort of buffer to make the fuzz work with the wah, and in this interview he admits this (although he says they did it in the studio, he doesn't say anything about what was done in a live setting).  There are concert recordings where Hendrix is using the wah into the fuzz, and he has the usual oscillation problems that we know about now, but I bet Mayer later put a buffer in Hendrix's wah, just like the wah buffers that are around now, to make it work better in that situation.  That interview is valuable for me just for that tidbit of info.

Al

[m_charles]

is there any real way to stabilize a germ's gain sensitivity to temp within the confines of a FuzzFace. I know there are other designs in FX that address this, but is it just not an option with the FF?

[ckyvick]

is there any real way to stabilize a germ's gain sensitivity to temp within the confines of a FuzzFace. I know there are other designs in FX that address this, but is it just not an option with the FF?

you can add a diode to prevent changes in sound due to temperature, i forget which transistor you put it across thou

[jasperoosthoek]

(Teaser alert) I'm working on a new design of the Fuzz Face using 2n3904 (!!!) transistors that hopefully sounds like the germanium fuzz. I hope to finish it today, if it works I'll post it with some sound clips for you guys to hear which one is the silicon and which one is the germanium fuzz.

[Greg_G]

It's the technical shortcomings of the Fuzz Face that make it sound and act the way it does.
..And a FF that's built with the right components and biased right sounds great, and reacts to playing technique like nothing else.

You can analyse it forever, but there's a reason players still love them after more than 4 decades.

[azrael]

DougH reproduced the Axis Fuzz schematic in this thread in the lounge:

http://www.diystompboxes.com/smfforum/index.php?topic=86321.0

Err....Not the Axis Fuzz I was thinking of.
http://fuzzcentral.ssguitar.com/axisface.php

[brett]

Hi'
Axis Fuzz = vintage RM circuit, while Axis Face = contemporary PB circuit.

I'm working on a new design of the Fuzz Face using 2n3904 (!!!) transistors that hopefully sounds like the germanium fuzz.

Piggybacking can wind a 2N3904 down to 560 or 100 hFE.  Search: piggyback
chers

[jasperoosthoek]

Hmm, I think I just re-invented the wheel! Here is my post of 5 minutes ago: http://www.diystompboxes.com/smfforum/index.php?topic=86374.0

[amptramp]

DougH reproduced the Axis Fuzz schematic in this thread in the lounge:

http://www.diystompboxes.com/smfforum/index.php?topic=86321.0

Err....Not the Axis Fuzz I was thinking of.
http://fuzzcentral.ssguitar.com/axisface.php

My mistake - sometimes it's hard to keep the 3874th version of a Fuzz Face separate from the 2865th version.

The Axis Face design at least addresses some of the issues with a Fuzz Face by adding a 100 uF decoupling capacitor and polarity protection.  It also adds a variable "smooth" control to allow variable input impedance and capacitance changes to reduce the bass.  Definitely going in the right direction.