New Germanium DirtyBoost/Overdrive-use those russian transistors!-Dirty Boots OD

[rnfr]

the transistor markings are wrong on the initial correction.  this is a PNP circuit.  sorry for the mixup.  i'll read the rest of the posts later.  i'm at work right now.

[rnfr]

the new schem is correct sorry for the mixup-  guess i must've smoked too many "jazz cigarettes" back in the days-

to the best of my recollection-the diodes are correct.  i think i tried flipping them the other way, but wasn't too happy with the results.  right now i pulled it off the breadboard, because i was planning on boxing it up, maybe i'll throw it up again just to be sure  before i get out the iron.  i just hacked this thing together- really my first shot at designing a circuit.  never the less-  i am very happy with the sound.  it gives a great overdrive tone- much better than any diode clippers i've heard.  usually i have to do a lot of filtering to get clippers to sound decent.
i'd love to read the results of any real analysis that you do.

[rnfr]

I've spent a little time today looking at this circuit on a simulator...   I had to use Silicon trannies as I don't have any models for Ge transistors.

However, if the diodes are "reversed" -- i.e. like they are in the schematic, the sim. shows a working circuit if and only if the forward bias rating of the diode is less than the Vbe rating of the associated transistor...

With a silicon tranny, a schottky diode worked well -- produced a nice, distorted waveform with lots of gain.  The closer the forward bias got to the Vbe of the tranny, the more square-wave-like the output became, with less gain.

I need to think on this more, because obviously something is producing enough base current to turn on the transistor...

this would correlate with my findings as well- i tried a shottky and a silicon diode instead of the germanium.  the germanium sounds much smoother and less squared off, and more gain and distortion as well.   this seems like the opposite of what would usually happen with clippers-  more gain - more square.  but i guess that's an all together different animal.

[rnfr]

edited for too many %^&*tails.


cheers!

[rnfr]

i've been reminded that the internal resistors in GT313's go from E to B.   therefore you might want to increase the emitter resistors if you use normal germanium transistors.

[rnfr]

i'm still not sure i understand what the problem seems to be with the diodes.  each on is in a NFB loop.  how is this strange? 

[rnfr]

just wanted to update this with the latest version of the circuit.  if you have these, or any GT style russian transistors, i'd give this one a try.  it sounds great!

[solderman]

just wanted to update this with the latest version of the circuit.  if you have these, or any GT style russian transistors, i'd give this one a try.  it sounds great!

Hi
I really like this one it looks as if it wold sound OK but as allways I have to try and bread board this next week when I have a few minutes to spare.
- I am a little confused about the polarity here, isn't the C4 and C5 C8 caps oriented wrong if its a positive GND circut? (is C8 ment a 100uF DC filter cap and if C4 and C5 are ment as lo/hi pass filters isn't 10uF a bit big .01uF? insted) 
- Did you omit the gain switch for any particular reason?

//Solderman

[Isaiah]

The wiper attached to Ground on the 50K Bias pot looks like an error.

Looks pretty good otherwise - Shame I don't have any Russian GTs.

[rnfr]

sorry about the mistakes, here's the real stuff. it is indeed a positive ground circuit,  i omitted the gain switch because it seemed to be affecting bias, and i wanted to simplify it a bit.  C4,5 adjust the gain of each stage. the 470pF caps roll off the highs and control oscillation.  i found that grounding the bias pot reduced noise greatly.  i hope you  guys like it.  it really does what i want in an overdrive, and i tend to think most OD's sound kinda crappy.  i'm not too hip on diode clippers, but here the diodes really seem to add a nice compression to the circuit.  germanium diodes are key BTW.

[rnfr]

Shame I don't have any Russian GTs.

they're dirt cheap!

[danielzink]

Shame I don't have any Russian GTs.

they're dirt cheap!

I've got a handful of KT312 (npn, low gain) Russian transistors that I'd like to use up - could I reverse the polarized caps and wire the schematic as normal ?

Dan

[rnfr]

yes, you could try it, but i believe the KT's are silicon?   this circuit was really meant for germanium transistors.

[danielzink]

Are the GT's the 4 leg tansistors ?

Dan

[snap]

are that those aging transistors from a while back?

[rnfr]

Are the GT's the 4 leg tansistors ?

Dan

yeah, the fourth is attached to the case, and can go to ground, or just be clipped.  they also have an internal resistor from E to B which can give false gain readings.

[mat]

Are the GT's the 4 leg tansistors ?

Dan

yeah, the fourth is attached to the case, and can go to ground, or just be clipped.  they also have an internal resistor from E to B which can give false gain readings.

Do You think it gives too big or too small gain reading with R.G.'s gain/leakage tester ?

Do You know if other than GT313 ru-ge-transistors have the added resistor from E to B ?

Matti T.

[rnfr]

i think it shows a lower gain reading than what is actually there, and i think it's most of the "flying saucer" types that have the resistor.  308's, 311's, 313's.

[rnfr]

here is a verified vero layout for the Dirty Boots.
http://www.aronnelson.com/gallery/main.php/v/rnfr/VERO/DIRTYBOOTSV3_3VERO.png.html?g2_imageViewsIndex=1

[petemoore]

Do You think it gives too big or too small gain reading with R.G.'s gain/leakage tester ?
  Bound to reduce current, bein' a resistor and all...good question to ponder though.
  An alternative method might be to find a circuit where transistor gain matters over a wide range, or adjustable to allow more optimal trying out of different transistors...compare transistors.
  Or just get some various [knowable] gain 'regulars' to compare to in the shown circuit, check / diddle with bias/gain maybe, compare again.