komrade boost

[pinkjimiphoton]

so i set out to debug the liberal komrade with boost pedal i abandoned about 6 months ago, and got it working.
i'd made some mistakes on the vero and pulled it, and was determined to make it work, and did.

couldn't get the boost to work tho... i'd tried making a pnp version of the omega boost dino turned me on to for the suzy q project, but it didn't work.

since i'd fixed the fuzz, i was determined to make the boost part of the vero work, too... so i looked at simple boosts, and tried a few on my breadboard.. and after messing with something a little more normal looking, i yanked a couple resistors to try a different voltage divider going to the base of the transistor.. and WANGO... suddenly what i was looking for was there in spades.

when all's said and done, the simplest booster i think i've seen,  7 components, not counting switches/jacks/wiring.

present for you, the komrade boost (boost from the liberal komrade II that i just finished).

why komrade? cuz it's 3 russian mn165/b whatever pnp germaniums in it. hfe 120, tho it didn't seem to matter.

assuming leakage comes into play... tried 12 of these transistors randomly outta a bag full, and a quick twist of the trim pot and every one sounded great.

goes from a nice cleanish boost to a nice crunchy overdrive. try one on your breadboard, i think you'll be pleasantly surprised.

the optional switch lets ya go from a treble boost to a mid boost, which i liked. i did try it as a footswitch, and liked it enough to keep it... switching from the .001 to .022 gives a real nice boost on top of the other boost.

sounds great with the liberal komrade fuzzface driving it. they're on one board, in one box.
i tried RG's juggler to swap the boost and fuzz, but there was no comparison, the boost needed the fuzz first in this case, tho the other way gave a really creepy trent reznorish overloaded broken fuzz that was real thin, almost an octave, that "swelled" and "overloaded" in a kinda cool way... but not cool enough to keep.

anyways... nice booster. check it out and let me know what ya think...



so... who's circuit did i recreate? it's simple as hell, but man, it sounds really sweet!

[PRR]

Just for fun: short R1. Can you trim it into operation?

I'm thinking that with this "no bias" circuit, R1 C4 do "nothing" and are just a waste of solder.

[pinkjimiphoton]

nope, distinctly audible difference with/without the cap. more highs/gain.

you could definitely ground the emitter directly tho and probably it would work, but i'm thinking leakage is responsible for it biasing up.

i know it looks like... "wha?" but it works. try it. it's a nice little boost with a nice crunch when it's pegged.

speaking of pegged, you could almost eliminate the trimmer, too.

just an accidental discovery on the breadboard, trying to fix/adapt a slightly different boost that wasn't working in the circuit i was trying to graft it in to.

you can literally plug it in in about 30 seconds and have it running. i'm building one right now point to point inside one of them little hammond boxes (about half the width of a distortion +.

[pinkjimiphoton]

here's a vero with filtering/polarity protection:



here's the micro sized one for them little hammond boxes (tho i think i'm going p2p)



i know it looks stupid, but it sounds pretty freekin' good.

it's almost like a tube circuit. the 1m pot gives a load, the audio passes thru a cap to the base, the emitter is bypassed with a huge cap to get some highs and gain back (and stabilize the transistor) and then a cap to block dc off the collector. dial in the voltage that works. wango.

will try it with some other transistors beside the mn16b or whatever they are, i can't read cyrillic.

[haveyouseenhim]

What? You aren't going to call it the 'Roossian Traktor'? 

[Tony Forestiere]

What? You aren't going to call it the 'Roossian Traktor'? 

I was waiting. You didn't disappoint. 

[pinkjimiphoton]

actually i was gonna call it the socialist bastard (that even liberals would like stomping on) but i thought SOMEBody may take offense...again...

komrad boost cuz it's the booster from the LIBERAL KOMRADE (or soviet transistor fuzzface) with boost.

i just built ANOTHER one. tried it without the e resistor, just the cap. didn't work. tried it with just the resistor...worked but was muddy.

the pair together it's a real nice boost with some grit sounds alot like .....dare i says it??

TOOBZE.

hear me no und believe me later, this thing will

*PUMP*

you up   

seriously... try it. may take all of 5 minutes. gonna try making an npn one too.

[PRR]

> distinctly audible difference with/without the cap

Read what I wrote. "Short R1" (thus shorting *both* *both* R1 and C4).

Of course with R1 and with-out C4 will be different.

> without the e resistor, just the cap. didn't work.

Obviously. (NO current flows.)

[pinkjimiphoton]

ah, gotcha. brain dead. i did do that originally, grounded the emitter. then i tried a few small value e resistors, from 47r to 4.7k, just randomly stuffing stuff in.
tried the bypass cap, cuz i've found it to work well in some other projects.

this was how it was when i was experimenting, with a 3.3k  (2.2k honestly was about the same) and a 22u cap when i pulled the voltage divider resistors out, i think it was 510k-.47k+ (being a pnp circuit) when i noticed it worked and sounded better than the booster i was playing with.

it was a total accident. so i did ground the emitter originally...

i'd assume it would make the gain go up and the bias point change on the transistor's sweet spot.

i checked the voltage... with a 9v 1 spot, i was getting -8.33v on the emitter, reading 0v (tho it would go up slighly to maybe .30-.40v) on the base and .1v on the collector.

i don't know what i did or how i did it, you know me, i am a hack not an ee, all i know is it works and sounds pretty good. maybe it's an active version of the black ice? i dunno.. it boosts a little, and sounds very sweet.

i will try shorting the emitter tomorrow. i suspect you could probably wire this b+ to e and b- to c and it would work.

what the hell did i do?

video is uploading, this program gets worse and worse so just listen and don't watch or it will make ya crazy. sync? what's that?

here's pics




the black blobular at the top is the transistor, it's a metal hat type and the base is connected to the case so i had to wrap it in black goo tape.

smallest thing i've ever built.



in the video (to come) you can hear this same circuit in the liberal komrade boost, too..

in this case, i used a 4.7n input cap, in the one in the video, first boost is a 1n input cap, second boost is a .022u in parallel with it. too high, and it gets unstable and motorboats.
if i had a bit more chops at using such a small box, i would have added another switch to change the input cap. .0047 just seemed like a good range. for this.

next one will be slightly bigger, and probably with the second footswitch for a different boost. it's nice to use it to overdrive your amp a bit, then wallop it with the bigger cap.. big sustain, very creamy.

anyways... back shortly.... yawwwwwwwwwwwwwwwwwwwwn  

edit: here ya goes....

one stupid pedal trick.....

[pinkjimiphoton]

an explanation of why it works? maybe?

i was good til the math started.

it appears the bias is fixed by the two resistances, kinda like a self-biasing triode stage (which is what it really reminds me of) and in this method, beta/hfe doesn't need to be accounted for...

interesting. at least i thiMk that's what this linky says:

http://www.electronics-tutorials.ws/amplifier/amp_2.html

i mean with a simple triode, you need a load (1m pot) feeding the input cap to the grid (think base) the cathode has a smallish resistance to ground bypassed by a fairly large electro (think emitter) and you need a resistance feeding the tube's plate, and block  the dc output with a coupling cap (think collector).

i think that kid ryan from strickland amplification was run outta here a few months ago for posting something similar. 

all i can tell ya is here's a schematic, here's a layout , here's video/audio proof..... it does indeed work and sound pretty good.

[petey twofinger]

how does this compare to say a stratoblaster or an lpb-1 ? as far as output / grit etc ...

i did watch the video , but ...

thanks again for sharing !

[dwmorrin]

Jimi, I threw this on my breadboard and checked it out.
I got it rocking with a very leaky (465µA on the GEO tester) NKT275.  Gain derived from GEO test: 76.
Lots of gain.  With a 100mV p-p sine wave @ 660Hz, I got 7.9V p-p out.  Asymmetrical distorted awesomeness out.
I upped the input cap to 100n for myself.  It was much lower gain with the 1n.
Trimmer set to 27k for max signal output.
Voltages:
-V = -9.0V
Vc= -4.0
Vb= -0.657V
Ve= -0.576V

Then I tried a not leaky (44µA) NTK275 with a GEO derived gain of 86.
Not as great.  Only got a clunky boost with trimmer maxed to 100k.
Input same as above, output 6.48V p-p, distorted, but less awesome.
Voltages:
-V= -9.0V
Vc= -5.55V
Vb= 0.174V
Ve= 0.121V

Tried a real leaky one and a not leaky one to see if that was the trick, and I think my results are confirming this so far... maybe others will try too.
Did you happen to measure the leakage of your transistors?

The nice sounding, leaky, circuit is a simultaneously pleasant and edgy overdrive.  Definitely has a cool '60s overdrive/booster vibe.

For my transistors, beta/hfe is definitely ruling the day... I monitored the collector voltage while touching the transistor, and I got some serious mV movement, and holding my iron near it really sent it running.

You've no fixed bias resistors, so that's not it.  And I got better results from a real leaker, so I'm leaning hard towards this is a "leakage current bias" circuit. 
Real curious now what the leakage and gains are on your transistors.

[pinkjimiphoton]

petey, not as loud as a stratoblaster or lpb 1.... just a nice sounding subtle boost, probably about 6-10db when cranked. unity gain is about 3:00 on the boost, above that ya just get a nice clearish crunchy very 60's ish sounding boost.

you no like?

or is it the damn video? i've tried all kindsa stuff, i can't get the damn thing to sync up. guess i'll just point it at the pedal from now on...lol

[pinkjimiphoton]

Jimi, I threw this on my breadboard and checked it out.
I got it rocking with a very leaky (465µA on the GEO tester) NKT275.  Gain derived from GEO test: 76.
Lots of gain.  With a 100mV p-p sine wave @ 660Hz, I got 7.9V p-p out.  Asymmetrical distorted awesomeness out.
I upped the input cap to 100n for myself.  It was much lower gain with the 1n.
Trimmer set to 27k for max signal output.
Voltages:
-V = -9.0V
Vc= -4.0
Vb= -0.657V
Ve= -0.576V

Then I tried a not leaky (44µA) NTK275 with a GEO derived gain of 86.
Not as great.  Only got a clunky boost with trimmer maxed to 100k.
Input same as above, output 6.48V p-p, distorted, but less awesome.
Voltages:
-V= -9.0V
Vc= -5.55V
Vb= 0.174V
Ve= 0.121V

Tried a real leaky one and a not leaky one to see if that was the trick, and I think my results are confirming this so far... maybe others will try too.
Did you happen to measure the leakage of your transistors?

The nice sounding, leaky, circuit is a simultaneously pleasant and edgy overdrive.  Definitely has a cool '60s overdrive/booster vibe.

For my transistors, beta/hfe is definitely ruling the day... I monitored the collector voltage while touching the transistor, and I got some serious mV movement, and holding my iron near it really sent it running.

You've no fixed bias resistors, so that's not it.  And I got better results from a real leaker, so I'm leaning hard towards this is a "leakage current bias" circuit. 
Real curious now what the leakage and gains are on your transistors.

hey dave,
thanks for trying this and posting your findings. i didn't test for leakage, i still haven't gotten around to building rg's tester...

i generally just socket stuff and if it sounds good, it is.
when i originally built this, i used the 100n input cap, and it is WAY louder and WAY more wooly.... too much for me. i wanted a nice cleanish boost to push a fuzz with, so went with the 1n cap.... i kick in a 22n cap for a gain boost and it works really well.

i think from what i'd read earlier, a common emitter  circuit self biases kinda like cathode bias in a tube triode circuit.

i mean... literally.... this is the same as a simple tube stage...  pot is the grid load, input cap to grid (base) power to anode thru a 100k resistor (collector) with output taken thru a blocking cap,  and a cathode (emitter) biased by feedback from an rc network.

leakage defineately accounts, but pretty much every ge pnp i've tried yet seems to work.

i'm thinking an input cap like joe's easy face is the way to go... pan between 1n and 100n to get the perfect amount of grit.

weird circuit!! i held my iron near the little one, no appreciable diff.

i think it's just like a tube... on a tube, if there's signal present at the grid, it opens the valve and lets the tube amplify.

dave, did you try shorting acxross the e resistor as paul suggested? i haven't had a chance, ground's a little shaky here at the moment for me to be making noise..

i bet it is a combination of leakage and the self-biasing of the circuit, as explained here:

http://www.electronics-tutorials.ws/amplifier/amp_2.html

tho in their example, they too show a voltage divider to set the gain, i think...  i really don't understand this stuff, this is pretty much just a happy accident.

thanks for trying it for me!!

[petey twofinger]

 no , not that .

it seems like you most always set your amp a little dirty , i have always set my amp tones clean ... so determining how much grit the circuit produces is tough .

i got this decca guitar with a gold foil for ten bucks and its a good player . i was thinking onboard stratoblaster / lpb1 / npn v2 which i have been wanting to try but no vero yet .  i have one of those commie transistors , i think . (thanks !!)

i tired out a bunch of this stuff and ended up using the npn a lot .it sounds great and uses parts i have .  i was thinking trim pot , bypass switch , some sort of rechargable battery and then  add a small jack somewhere to recharge  . maybe some sort of coin cells , like you were sayin .  

it would be important that i could get clean though .

[dwmorrin]

Shorting emitter to ground, as suggested by Paul, and I liked it even better!
Trimmer set to maximum output:
-V= -9.0V
Vc = -4.3V
Vb= -0.093V
Ve= 0V

I think I'll just leave the 3k3 and 22µ out for now.

My low leakage transistor did not have the moving voltage issue, so your transistors may be low leakage.

With 4 resistors, and 2 caps, you can set up a triode, a BJT, or a FET up as an inverting gain stage, and the way the resistors work to create the amplification effect is largely the same.

That all external stuff to the actual device.  The actual operation of vacuum tube (triode), a semiconductor junction (BJT), or a conductive channel (FET) is quite different for each.

You're right, the 3k3 gives negative feedback, and so works to establish a stable voltage for the emitter and base terminals.  This is true for all the devices.  But it does not bias, or turn on, the transistor.
Just for fun, I stuck a 2N3906 in, and, guess what?  Nothing, as expected.  Collector was at -9, base and emitter both at 0. (With or without 3k3 and 22µ)

A self biasing tube has a resistor from grid to ground.  No such resistor here.

The only explanation I got for this transistor being alive is leakage current.  Prove me wrong Jimi!  And thanks for this circuit - still having fun with it!

it would be important that i could get clean though .

Mine is cleaning up nicely when rolling back on the guitar's volume.

[pinkjimiphoton]

Shorting emitter to ground, as suggested by Paul, and I liked it even better!
Trimmer set to maximum output:
-V= -9.0V
Vc = -4.3V
Vb= -0.093V
Ve= 0V

I think I'll just leave the 3k3 and 22µ out for now.

My low leakage transistor did not have the moving voltage issue, so your transistors may be low leakage.

With 4 resistors, and 2 caps, you can set up a triode, a BJT, or a FET up as an inverting gain stage, and the way the resistors work to create the amplification effect is largely the same.

That all external stuff to the actual device.  The actual operation of vacuum tube (triode), a semiconductor junction (BJT), or a conductive channel (FET) is quite different for each.

You're right, the 3k3 gives negative feedback, and so works to establish a stable voltage for the emitter and base terminals.  This is true for all the devices.  But it does not bias, or turn on, the transistor.
Just for fun, I stuck a 2N3906 in, and, guess what?  Nothing, as expected.  Collector was at -9, base and emitter both at 0. (With or without 3k3 and 22µ)

A self biasing tube has a resistor from grid to ground.  No such resistor here.

The only explanation I got for this transistor being alive is leakage current.  Prove me wrong Jimi!  And thanks for this circuit - still having fun with it!

it would be important that i could get clean though .

Mine is cleaning up nicely when rolling back on the guitar's volume.

dave, there is a resistor to grid from ground... the 1 meg pot. not thinking the 3.3k/22u biases it, i said it seemed to shift the bias point on the collector.

i'm thinking the input to the b is like a gate. put signal in, the transistor amplifies.

i will mess with it on the breadboard too, thanks for the info bro!

[dwmorrin]

The 1M pot is on the wrong side of the coupling caps to factor into biasing.

Breadboard the 4 transistor stuff you linked to... now remove the transistor.  Measure the voltage where the base should connect.  There's voltage, right?  R1 and R2 are strung between +V and 0V... no cap between them and the base.

Take your transistor out of the socket here.  What is the 1M pot contributing to the bias?  Where's the voltage?  Where's the beef?

[pinkjimiphoton]

cool, i understood that, thanks bro....

got it on the breadboard, gonna try some leaky ass ge's i have and see what happens... ones where reverse beta they have higher gain (that's another way to look for leakage i think)

it is a nifty little circuit, a cool way to clean up all the lower gain leaky stuff that would usually be waaaaay too hissy.

experimenting with maybe adding a 6 way switch to change caps from 1n to 100n.... but the switch is 60X the size of the circuit!

[PRR]

> this is the same as a simple tube stage...

Well, no.

We want a tube's Grid to be a little negative of Cathode. The simple way is to tie Grid to zero Volts (can be a huge resistor) and stand Cathode on a small resistor to drop some voltage.

That will NOT work with a BJT transistor. We must dribble current into the Base down from the Collector supply.

We dribble enough to bring the transistor "half on". Then signal swings it toward off and full-on.

The definition of "on" depends on the collector load. Which you have made variable.

Now, in your plan there is no "Base dribble" part. However "all" Germanium transistors leak significantly. A Base dribble is built-in.

Adjust the Collector resistor so the transistor is "half on" (1/3rd to 2/3rd on). You are surely trimming for 2V-7V at Collector. Even if you actually trim for good gain and output.

This will fail with a Silicon transistor. Their internal dribble is so small that even a 10 MEG Collector load may not bias-up.