Schaller - Fuzz (Germanium) [schematic]
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Manfred
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Thanks!
Here the redrawed schematic:
Here the redrawed schematic:
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Manfred
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I had already drawn the circuit diagram in one of the posts on this topic above with the SPlan7.0 Electrical CAD program from Abacom,
which I have been using for many years in the latest releases.
So I simply had to edit the schematic.
Did you measure the voltages on the transistor terminals and what was the value of the bias resistance during this measurement?
Last edited by Manfred on 30 Oct 2020, 03:12, edited 1 time in total.
the Voltage on Q2 Collector seems to be right for me at about 5,5V, but how statet, i adjust bias by ear.
the two bias Resistors are different, one goes down to 120R the other i can`t remember,but was signficantly different, will look tomorrow.
Also, i rebiased the two with AC151 Transistors, AC192 maybe will behave differently and of course of different working data.Didn`t want to desolder them and measure.
Can measure the Voltages also tomorrow for you,but you know,you only need the voltage on Q2 collector anyway in a direct coupled circuit.
the two bias Resistors are different, one goes down to 120R the other i can`t remember,but was signficantly different, will look tomorrow.
Also, i rebiased the two with AC151 Transistors, AC192 maybe will behave differently and of course of different working data.Didn`t want to desolder them and measure.
Can measure the Voltages also tomorrow for you,but you know,you only need the voltage on Q2 collector anyway in a direct coupled circuit.
Manfred wrote: ↑29 Oct 2020, 16:04I had already drawn the circuit diagram in one of the posts on this topic above with the SPlan7.0 Electrical CAD program from Abacom,
which I have been using for many years in the latest releases.
So I simply had to edit the schematic.
Did you measure the voltages on the transistor terminals and what was the value of the bias resistance during this measurement?
1. - is 5,78V at Collector Q2 and has a Bias Resistor of 270R
2.- is 6,5V " " " " " 150R
due to the increased current, compared to FF, the Circuit is more stable to temperature changes, but needs therefor higher gain Transistors (see the AC151 ones are AC151 VI, tey are in the range of 90 to150 hfe, but i think, they were very constant in upper range so about 150-shows the diy experience by ear.
BTW.: If you want build one by yourself or have the courage to solder on the original pcb, i ended up with putting in a 3,3K collector R instead the 1K and leave the Fuzz Pot as emitter R, so you have a more useful range of hfe downwards, but the Sound gets a little more mushy due the increased Z of Q2, getting a little bit more in FF Territory.
Thanks for all the info, Schoppo. I just breadboarded the circuit and tried the handful of AC151s I have. I got nice velcro fuzz. I tried biasing the circuit by increasing the resistance of Q2's collector. I went up to 5.6k but when I tried your method of adding a resistor in parallel to the pot/cap I liked the sound better! It retained for the original sound more.
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Manfred
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Hi Schoppo,
I have taken another look at the posts.
The value of the intensity potentiometer is in the schematic corrected by you with the Rbias addition 1 kOhm
but you wrote 500R.
Which value is correct?
elmenco wrote: ↑11 Feb 2021, 01:53 Thanks for all the info, Schoppo. I just breadboarded the circuit and tried the handful of AC151s I have. I got nice velcro fuzz. I tried biasing the circuit by increasing the resistance of Q2's collector. I went up to 5.6k but when I tried your method of adding a resistor in parallel to the pot/cap I liked the sound better! It retained for the original sound more.
Yes, me too. Like mentioned before in this thread, too rise the collector R raises Z (Impedanz) of Q2,whitch takes it more to FF Territory and Sound gets more undefined and mushy. Ilike this version much better by decreasing R emitter.
But see, it`s not paralleled to the Pot- it replaces the pot which is working as Re, the pot function is now only to adjust the Emitter Capaacitor to Ground or not.
So technically its paralleled to pot (or dialed in pot resistance) with C in series. I tried to parallel it to the pot only, but disliked the behaviour of the Fuzzcontrol.
Last edited by Schoppo on 20 Feb 2021, 21:23, edited 4 times in total.
Thats what we wrote some time ago about: 1K is standard, the 500R is a trimpot which i used, to correct bias in the Original Circuit with minimal desoldering (means, not to solder on original circuit board for biasing reasons), to keep it as Original as possible. I only got to desolder one point (1 pin on "Intensität" Pot), and put in an "corrected" Resistor.
I only use a 500R Trimpot (never went over 240R) to dial in the right biaspoint (by Ear)and then replace it with the nearest Standard R (E12 or E24 Series)
I`m very happy about all your interests
so btw, i got my third one by this time + 1 empty housing
on the next you can see the little blue Resistor on the pot. Pots are not original, the where dead. It was very hard to find some too fit in, because the housing is very thick, and most modern Pots are made to put in thin Tin Housings.
)I kept one Original all the way, because i own three and didn`t have to swap something in that also. But, I try to build one in this empty Housing as original as possible, including reppainting it with Hammerpaint
Some additional info:
I tried many different Ge Trnsistors, but none came only to the Neighbourhood of these AC151 in this Circuit. I´m normally not in this "swapping Trnsistors" in the same Circuit rather than adjusting the Circuit to fit my needs, but I like this Fuzz very much so it was worth it for me, to look for equivalents, to get the same Sound. In a surprising and very practical manner, i found, a Mix of a rather low gain Sillicon (so - around 150 HFE) and a warm sounding GE (in this Circuit- you can make GE allways make sounding harsh),comes nearest- no matter on which Position you set it-?????!!!??