Curious...why a Si/Ge hybrid Fuzz Face?

[Nocaster Cat]

Wouldn't you still run into bias issues with the germanium in the Q2 position due to temperature? What's the upside of the hybrid setup? Thanks.

[joegagan]

in my experience, the hybrid style, using si in Q1 , ge in Q2 does go a long way in helping the temp stability issue. not perfect, but it helps.

i get a tighter, fuller low end, and probably less hiss. a slightly stronger fuzz while retaining good 'clean up' factor.
it also seems to play well with a pregain control allowing a nice OD type sound.
to me, it is the best of all worlds.

[Nocaster Cat]

Thank you sir!

[mac]

If you like maths there is a pdf file in my gallery about FF bias. When you solve the bias eqs you get that all thermal issues depends almost on Q1. This is because the emiter is grounded, and because any inestability come backs multiplied by Q2 through the 100k feedback resistor.

You can finger heat germs at Q1 and Q2, one at a time, and see the deviations from vcc/2 and compare the results.

If you use a BD233-5-7 or BD175 (sub class 6) which have low gain and a freq transition close to an AC128, 2-3mhz, you can have a good sounding and stable FF.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=41446

mac

[Nocaster Cat]

If you like maths there is a pdf file in my gallery about FF bias. When you solve the bias eqs you get that all thermal issues depends almost on Q1. This is because the emiter is grounded, and because any inestability come backs multiplied by Q2 through the 100k feedback resistor.

You can finger heat germs at Q1 and Q2, one at a time, and see the deviations from vcc/2 and compare the results.

If you use a BD233-5-7 or BD175 (sub class 6) which have low gain and a freq transition close to an AC128, 2-3mhz, you can have a good sounding and stable FF.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=41446

mac

Bookmarked for later reading, thanks!