Troubleshooting Krank Distortus Maximus - problems with transistor stage

[pahaahv]

I built the original Krank Distortus Maximus on breadboard and only had a slight punch coming through when I struck a chord. Checking the basic things like connections, wiring, values and polarities I found everything to be correct. Then I started probing around and trying through different stages of the build, so far I found that:
- I fed the signal into LM386 stage and it works well and already distorts rather nicely
- Tonestack works

The only thing that gives out a weaker gnarly signal than the guitar itself is the 2N5088 transistor stage.
I tried:
- rebuilding it to another space on breadboard to assure the connections are established - didn't fix it
- tried using different input/output capacitors, now when i increased the values of the capacitors, the input stage started letting more signal through, but I'd like to get the original circuit to work.

Right now I'm really focusing on the transistor stage and taking the output from the output capacitor.

Here's the schematic(s):
https://guitar-dreamer.blogspot.com/2017/03/krank-distortus-maximus-diy-and-mods.html?view=classic

What could be the issue? How could I make the input stage work?

PS. I tried the transistor in my fuzz build and it works fine. I tried a 2N3904 in the krank input stage and it doesn't work either.

[pahaahv]

I also wonder what the transistor voltages should be. (and how to measure them)

[duck_arse]

hello pahaahv, welcome to the forum.



please! be showing us some photos of that which you have built, we often see things you might have missed. also, your 'no volts' gives a clue that you have a wiring error somewhere, like a missing ground. what voltages do you read on the IC pins, please?

[pahaahv]

Let us focus only on the transistor stage.


I have built the IC and the transistor stage separately, and as I said the IC stage works well.
I can show you some pictures but it's quite hard to tell anything. As I already mentioned, I rebuilt the stage to a different location and I am still having the same issue.

[duck_arse]

did I just imagine you said no volts?

anyhoo. you need to measure the supply voltage on your board near the transistor. then measure the base voltage, the emitter voltage and the collector voltage. if your resistor values are correct, and the connections are correct, Ohm's Law will tell you what voltages to expect and where.

[GibsonGM]

Is your collector resistor actually 'at' the collector, or is it blocked by the output cap??  Caps block DC, therefore you'd have 0V there if this is the case. Can't see if you've bent it over in the pic.   Far right leg of transistor in the pic.


Nah, now I see, you have a different kind of R in there on the bottom side.  Check right there for voltage.

[PRR]

Welcome!

> Let us focus only on the transistor stage.

Does it have any Voltages in it?

We could suggest a range of voltages which may work. B=0.8V, E=0.2V, C=2V-7V. But the Actual voltages tell Actually what the stage is or isn't doing.

[willienillie]

It's obscured in the photo, but can you verify that the blue input wire is going to the right row to connect to the input cap?  It looks like it could be plugged into the top row, but I would expect no sound, or maybe an extremely weak, thin sound via capacitive coupling.  Everything else looks correct, except I can't make out the markings on the green collector resistor.

As a side note, I would've used 470k/47k on the base, because I have those common values on hand, and they would work the same.

[pahaahv]

So back here again. Procrastinating on my schoolwork I pulled out my dusty project and started fiddling around with stuff.

I googled some similar circuits and found a common emitter amplifier schematic from google. It was kinda similar to the preamp section of KDM, except the values for 100K resistor was 10x lower = 10K!

I took a 50K pot, inserted two lugs into where the 100K resistor should be, dialed it until it worked and measured resistance. Not hard to guess, I got 10K measured on the pot.

Why is there a 100K resistor in the schematic and why does it work for people is beyond me. I tried a bunch of transistors and none of them worked with the 100K value provided in the actual (verified?) diagram.

Of course you could raise the value of the 390R to make 100K work. I tried that too with a suitable pot, and indeed, it did work.

I don't know what to think of it. Right now I have it on vero, I hear some jittering in the background of the sound which I presume is some sort of oscillation. Will see what I can do about that.

[antonis]

Why is there a 100K resistor in the schematic and why does it work for people is beyond me. I tried a bunch of transistors and none of them worked with the 100K value provided in the actual (verified?) diagram

Just because with 100k Collector resistor, BJT is heavily saturated (bottomed..)

As Paul calculated above, VBase [9 x 43k/(470k + 43k)] and VEmitter [VBase - 0.6 ]  Collector current should be about 500μA hence voltage drop on Collector 100k resistor should be 50V!!
9V - 50V = - 41V.. but particular transistor CE amp Collector can't go negative (it can't even go all the way down to 200mV Emitter voltage) so it's permanently "stuck" at about half a volt or so..
(no signal amplification.. not even input signal amplitude maintened..)

P.S.
Additionally to  the above mentioned flaw, input impedance is about 27k (roughly estimated) and forms a high pass filter with 4.7nF cap of 1250Hz corner frequency, meaning that a signal of 125Hz will be amplified 20dB lees than a 1250Hz one..
(actually, amplfication factor should be the same but for a 10 times lower amplitude..)

[pahaahv]

Thanks for the answer.

As a person who knows very little about the calculations in electronics have to ask, what does that, what you explained, say about the original schematic though? Where is the flaw and why doesn't it work plug-and-play? Is it just the quirks of how components differ?

Let's say that I don't know if my approach to solving that problem is correct or should I stick to the original schematic and try to swap out something else until I'd get correct measurements and sound?

[antonis]

It's just a matter of elementary BJT bias calculation understanding..
(sorry but that's the naked truth..)

e.g.
You said: >Of course you could raise the value of the 390R to make 100K work. I tried that too with a suitable pot, and indeed, it did work.<
so you can realize that issue was Collector/Emitter resistor values ratio..
By altering actuall values (while maintaining the same ratio) you could realize that there are some BJT working acceptable margins..
(mostly in relation to working current value..)
Same for voltage divider bias resistors..
(you could also realize different bias points (Quiescent) by altering the value of one of divider resistors..)

P.S.
Of course, you can always use naughtily thrown items on a breadboard, knowing what you want but not knowing what you're actually doing..

[Carlos]

Hi everybody,
I opened my Krank Distortus Maximus yesterday and I can now verify that the value of the resistor at the collector of the transistor is 10K and NOT 100k. "10K" is even silkscreened under the resistor on the PCB.
The value 100k keeps popping up on many schematics, but it's wrong! The Krank Distortus Maximus is basically Aron Nelson's Smash Drive with a Sekova Power Booster in front of it. The Sekova Power Booster also has a 10K resistor at the collector.
So I suggest changing the resistor to 10K to get rid of your "problems with transistor stage"

[pahaahv]

Hi everybody,
I opened my Krank Distortus Maximus yesterday and I can now verify that the value of the resistor at the collector of the transistor is 10K and NOT 100k. "10K" is even silkscreened under the resistor on the PCB.
The value 100k keeps popping up on many schematics, but it's wrong! The Krank Distortus Maximus is basically Aron Nelson's Smash Drive with a Sekova Power Booster in front of it. The Sekova Power Booster also has a 10K resistor at the collector.
So I suggest changing the resistor to 10K to get rid of your "problems with transistor stage"

I was lurking here for old posts and man this just blows my mind
"Verified schematics" huh...

Thank you for going through with this. Anyway education wise, for me it was a good backwards engineering project. And a heads up for trusting what's on the net and what value "verified" has. I solved it in the way of adding a pot to suspicious stages and start playing around until it worked, since I am still not good with calculations. Ended up solving exactly the same thing.