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Old 25th May 2007, 04:42 AM   #11
NIC1138 is offline NIC1138  Brazil
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Quote:
Originally posted by lineup

Here's a schematic of
the original Germanium transistor version of the Dallas-Arbiter Fuzz Face:
lineup, that's precisely the boy I've been studying... The curves on my last post represent this circuit working (with similar resistor values ).

What happens is that the first transistor is simply a linear amplifier, and the second one clips the signal, either because the transistor gets saturated, or cut, or both, getting out of the active region.

This is quite different from what I heard many times, people stating that older distortions were more "smooth", and newer circuits are more "harsh". How can the saturation and cutting of any transistor, including germanium, not be harsh!?...

I'm trying to study exactly why germanium might make a difference... I'm finding out that this circuit clips "hard", so the only difference must be internal capacitances and input / output impedances, something like this... The lower Vbe should men it would be easied to make the first transistor get reverse-polarized, but this doesn't make a difference, because the same result appears when we just saturate the second transistor.
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Old 25th May 2007, 04:49 AM   #12
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Quote:
Originally posted by Minion
Another interesting thing would be to also test Germainum and Silicon Diodes in Clipping stages, as Many Bipolar Transistor based Distortion curcuits will use Diodes to clip the signal and create that overdrive sound,

Others will use a fet and drive it into clipping to get Distortion or even some use a fet to overdrive a Mosfet.......There are many ways to use Transistors to create anything from a simple Boost up to a killer over the Top distortion......


Yes, my next step is a diode distortion!... The fun part is that the op-amps with diodes will turn out to be a more "smooth" distortion than the one with germanium transistors! I'm considering using germanium diodes, not because of how they might sound, but just because I think they might make the cicuit better somehow..... let's see

I've been looking for a mosfet overdrive too... Now this is one I believe will produce the so much advertized "smooth distortion"!!... Do you happen to have a schematic for this?
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Old 26th May 2007, 08:10 PM   #13
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Be careful with those... GErmanium devices tend to run away VERY easily. The hotter they get the more I they draw until kapow!

Mark
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Old 26th May 2007, 09:15 PM   #14
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Germanium sounds great, all else being equal. And even when you have to use transformers! I know from experience. I have working examples.
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Old 26th May 2007, 10:15 PM   #15
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Hi NIC1138

RS still sells germanium, I think. Typically only AC128, AC127 (not a real NPN complement, AC176 was "exact"), AD161, AD162 and AD149.

So it should still be possible to get these if anyone wants to see how things were done!

AC128 was the pro-electron version of the OC81 as far as I can recall, and the OC81 was widely used in tranny radios, as was the AC128.

I have a feeling one of ST's old plants might still be making them, but this must be about the only place in the world, unless they are NOS.

ONe reason germanium might have sounded reasonable was that using transformer outputs required lower overall feedback - and less chance of transient/slew overloading. On the other hand overall distortion levels were around 1%, not exactly your average SOA today

cheers
John
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Old 26th May 2007, 11:01 PM   #16
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Quote:
Originally posted by john_ellis

Hi NIC1138

RS still sells germanium, I think.
------------------------

So it should still be possible to get these
if anyone wants to see how things were done!
------------------------

I have a feeling one of ST's old plants might still be making them,
but this must be about the only place in the world, unless they are NOS.
------------------------

One reason germanium might have sounded reasonable
was that using transformer outputs required lower overall feedback
- and less chance of transient/slew overloading.
On the other hand overall distortion levels were around 1%, not exactly your average SOA today

cheers
John

Very good info - for us interested in germanium.

Nice with something different, for a change, to explore in diyAudio.
When we, in some day and moment, feel fed up
by bothering with those same old silicon and mosfet devices.

thanks to you, john ellis
from your
lineup
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Old 28th May 2007, 09:39 AM   #17
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Germanium sound great...and they have amazing power bandwight ( cca 10 kHz ! )... Do you meat it seriously, John ?
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Old 28th May 2007, 09:55 AM   #18
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Old 28th May 2007, 12:52 PM   #19
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Default Exageration..... 10 Megahertz is too low Pavel!



They sound great....if we forget the noise they made.

But you are rigth about the ones dedicate to audio ranges.

ahahahah!

Carlos
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Old 28th May 2007, 04:38 PM   #20
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Default low bandwidth

Low bandwidth is one aspect of germanium that I tought might be responsible for the "better" sound... Perhaps the old germanium fuzz faces had fiterings in the transistors that the silicon versions don't, so a non-modified silicon version would sound different, and more harsh perhaps...

People tend to say that the AC128 is "leaky". So I was wondering... wouldn't it be possible to simulate all these effects simply by putting small capacitors in parallel to the B-E junctions, and resistors in parallell to C-E?...

The problem is, I couldn't even reproduce these effects with my pair of AC188s...

___

What about distortion in big-swing class-A amplifiers? Does anybody have experience with that? How do I make MORE distortion with low power?...

That's how people use to say that the first distortion circtuits were born... But I can't find yet an old circuit that doesn't work only with clipping... I could only find "smooth distortion" in modern op-amp based circuits, and MOS... (an of course, perhaps in real, large amplifiers, but not in a stomp box... )

I was trying to simulate a two-stage amplifier... Input around 10-200 mV (That's what I measured on my guitar). I changed the parameters (gain and DC current), trying to maximize the distortion, but I never reached the ultimate distortion! Just a little bit distorted... I couldn[ t figure out yet how to design how much distortion I want. and how much would be the maximum...
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