Maestro FZ1: When it's cold I can't get no...

[M.Spencer]

...I can't get no good sounding fuzz tones! Hi forum, a friend asked me to build them a Maestro FZ1 for his 60s garage rock project. I used the Tagboardeffects layout (http://tagboardeffects.blogspot.com/2014/08/maestro-fz-1-fuzz-tone.html) with a 2k trimmer for Q2 collector. When my garage is warmed up to 65-70 degrees fahrenheit it sounds as it should; but when it's colder the FZ1 just sounds unpleasant (no sustain, lower volume than unity, the fuzz signal kind of ramps up and ramps down).

I can knock it into place with the trimmer, but it's less than ideal for the end user to have to open it up and adjust it by ear. What can I do to make this circuit more stable, and less dependent on temperature?


PNP germanium transistor specs
Q1 62 hFe, no leakage
Q2 70 hFe, 200 ma leakage
Q3 90 hFe, 400 ma leakage

Thank you!

[mozz]

Try swapping transistors around.

[iainpunk]

hey, welcome to the forum!

if you are powering it with an external power source, you could place a light bulb/low value resistor inside the enclosure to heat up everything... haha

but in general, Germanium fuzzes have temperature dependence, some more than others, but i haven't heard of Ge's without.
that's why Jimi Hendrix mainly used Silicon fuzz face, it sounded the same in Texas as in Alaska.
but it does sound slightly different than Ge fuzzes do, and they like a slightly different bias scheme.

also, were an international forum, Fahrenheit is only used in one country, please use Celsius or Kelvin, like the rest of the world. 

changing it to Si is an option, but it involves a bunch of extra resistors, and changes the character of the fuzz

cheers, Iain

[antonis]

A temperature servo bias mod should be an interesting market spot, shouldn't it..??

[kaycee]

Build him two, like taps - Hot & Cold.

[iainpunk]

A temperature servo bias mod should be an interesting market spot, shouldn't it..??

[M.Spencer]

if you are powering it with an external power source, you could place a light bulb/low value resistor inside the enclosure to heat up everything... haha

I like it! 
Wonder how much heat I could get out of an LED or two?  I'm using the 7660s chip for 9v to 3v conversion, there should be plenty of juice on tap.

Has the Benson Germanium fuzz been reverse engineered yet? Curious how they do it...

...
also, were an international forum, Fahrenheit is only used in one country, please use Celsius or Kelvin, like the rest of the world. 

Pardon me. 65° - 70° F translates to roughly 19 miles. 

I want to keep this pedal's tone as close to an original FZ1 as I can manage, so Si is off the table. But I do like the "cold one / hot one" suggestion.

[kaycee]

LED's don't generate any (significant) heat. Incandescent bulb is an option, although they are quickly becoming haram, but you'd need a thermostat of some kind, bi metallic strip?. If it is only one resistance you are needing to adjust then an external bias pot maybe?

19 miles. 

[PRR]

You don't need light. Resistor for heat.

[edvard]

Make that bias trimmer an external pot, maybe even put a low-profile knob on it and mount it to one side of the box so you don't have to get a new enclosure.  Mark the control for different ambient temperatures.  Easy-peasy and the only extra gear you'll need is a thermometer in your guitar case. 

Or heat the box with a small desk lamp loaded with an appliance bulb, the kind that's used for your oven light, they're still incandescent.

[M.Spencer]

You don't need light. Resistor for heat.

I'm considering moving the bias pot  outside the box with a low profile shaft as Edward suggests but the sweet spot between fizzy and farty is just so narrow...

Could you elaborate PRR? Is this just a matter of adding a low value resistor between 9v and ground and placing that near the transistors?

[antonis]

High value high wattage should be more effective..

P.S.
A pocket hairdryer should be more elegance remedy..

[kaycee]

Measure the range of resistance you need to hit the spot and get the smallest pot that will cover that range, that should make it easier to dial in.

[Phend]

These work in the coldest vermont winters. Put em under yer effect, and feet. Works up to 9 hrs.

[edvard]

High value high wattage should be more effective..

P.S.
A pocket hairdryer should be more elegance remedy..

Lower resistance = more current = more heat.  So, low value/high wattage but how much do you need to push a transistor over an ambient temperature threshold?  Shouldn't take much, but definitely should be powered by a separate power source.

Pocket hairdryer sounds... inconvenient.

[Phend]

Sorry for not explaining,  those heater packs used for winter are a small package that you "break" that causes a chemical reaction with the stuff inside. Thus producing heat. So no kidding, I am serious.  I understand that those in hotter climates would probably not know of such a thing. I bet PRR knows what they errrr.

[antonis]

Pocket hairdryer sounds... inconvenient.

If so, you're free to proceed to a X 2 per 10^oC (I'm not sure if it stands for Ge p-n junction) current estimation preprogrammed n-channel JFET working as variable resistor..

[kaycee]

Measure the range of resistance you need to hit the spot and get the smallest pot that will cover that range, that should make it easier to dial in.

Thinking on, a series resistor and small value bias pot should give you best fine control.

[Phend]

Just keep nitro away unless you want a model airplane engine sound, this may work.
Specifications:
Voltage: 1.3~1.5v
Heat rating: Medium Hot

[davent]

You don't need light. Resistor for heat.

I'm considering moving the bias pot  outside the box with a low profile shaft as Edward suggests but the sweet spot between fizzy and farty is just so narrow...

Could you elaborate PRR? Is this just a matter of adding a low value resistor between 9v and ground and placing that near the transistors?

Use a multi-turn pot or trimmer so the fine difference needed is spread out wide.
dave