My first transistor overdrive / distortion

[duck_arse]

what is the problem with the volume pot wirings, as you hear it? generally speaking, all the tone and distortion stuff is done in front of the volume pot, and it just makes louder or less so right at the end, without affecting distortion amount.

[Banjan73]

The problem was, on the original schematics and the second one, that the volume control worked as a second distortion control at the same time as a volume control.
That means, to get the amount of distortion that I wanted, the volume had to be pretty high.
So, when testing the pedal at my marshall (with clean sound), when I kicked in the pedal it was waaay to much volume.
The original schematics had total wrong bias (as pointed out by Antonis), so when I tried to get maximum distortion out of stage 1, it started to oscillate (or something). Now when the bias is better, I have much more room for increasing the gain in stage 1 and to use stage 2 for adjusting the volume properly.
I have not tested the new setting yet, but it will come soon.

[Banjan73]

Oh. I needed two stages in the original schematics to get enough distortion. Now, hopefully, most of the distortion is created in stage 1 not in stage 2.

[antonis]

Oh. I needed two stages in the original schematics to get enough distortion. Now, hopefully, most of the distortion is created in stage 1 not in stage 2.

Why hopefully..??

I mean, is your intention for 2 stage total gain of 20 X 5 rather than 10 X 10, say..??

And if so, why (again)..?? 

[Banjan73]

Hopefully all the distortion now is created in stage 1. That means that I will have enough distortion at any volume level. Take a Boss DS-1 for instance. That pedal gives full distortion out even though the volume is at nearly zero.

[duck_arse]

Take a Boss DS-1 for instance. That pedal gives full distortion out even though the volume is at nearly zero.

find a DS-1 circuit diagram, see how the volume control is wired - and ignore the jfet switching and bjt buffering that follow it, as they don't affect the sound.

[Banjan73]

Good idea!

[Banjan73]

Shit!
First, the DS-1 circuit doesn't help much, since thats an OP-amp based thing, which is totally different from my common emitter thing.
The sound from the last configuration was non-existing (i might have built, accidentaly a noise gate😅), so I experimented a little bit with my breadboard directly in my amp.
It is not possible to get the amount of distortion I want from just one gainstage. I tried switching a lot of values for both collector resistor and the emitter resistor in stage 1. The value which works best (to get max distortion) is 12k and 1k. Higher and lower @#$%s up the sound.
I realize that I need two gainstages, and therefore I see now that I need one more stage for the volumecontrol. Thats a shit, because then it is back to the drawing board, ordering new PCB's and %&#@... Hehe. I will keep the 2n3904, because I really like the sound of those.
Well, anyway. More will come in a while. Will take some time, though..

[antonis]

OK.. Let's face it once more..

You CAN'T get more than 20 X Vcc Gain from a single CE amp.. (take my word for it.. - later we may discuss it..)

The above 20 X Vcc is extremely ideal, 'cause it doesn't count for neither input signal voltage attenuation nor Collector loading from next stage..
Also, doesn't count for Emitter bypass capasitor reactance..

Nevertheless, if you insist on single stage higher gain "conventional" CE, raising power supply voltage is one-way resource..
You should have in mind that more gain, by raising Vcc, may not result into more distortion, due to lager undistorted signal headroom..


P.S.
https://www.diystompboxes.com/smfforum/index.php?topic=122227.msg1152129#msg1152129

Delete C5, R8, R6, C4 & Tone pot, replace a single BJT for T1/T2 and make R2=120k

[Banjan73]

Nice.
This is why I do this, to learn
I take your word for the max gain of a single stage now (since this is also what I experienced).
Anyway, I will upgrade my schematics with a third stage for only contolling the volume. I've read somewhere that there is a limit for how many cascades one can hook up after each other, but I think (I hope) that his will work.
We'll see. I'll come back when I have some new info.

[Banjan73]

Hi.
It didn`t take that long time until I was back with another post here. Maybe I`m starting to get addicted to this forum?
I made an updated schematics based on the old one. Nevermind the values for collector and emitter resistors. They will be adjusted by ear and oscilloscope:)
The though here is the following:
Stage 1: Boost the signal enough (but not too much) so that stage 2 can be able to create enough (what I decide is enough) distortion. The thought here is that when gain is minimal, the pedal should be able to produce an almost clean sound.
Stage 2: Main distortion stage with gain (distortion) control.
Stage 3: For adjusting volume AND NOT DISTORTION!! Off course, I know that this stage is also an amplifier, so it will act as a booster (e.g. for breaking up a tube amplifier), but it shouldnt affect the distorion output of the pedal that much.
So, any thoughts regarding this schematics? 3 cascaded stages will be fine?

[antonis]

You're still confused a bit..

3rd stage doesn't count for Volume adjusting, just because Volume pot follows this stage..!!

But let's start with more basic "notions"..

Volume simply corresponds to Voltage amplitude..

Distortion corresponds to difference between output theoretical Voltage amplitude & practically availiable one..

i.e. a CE amp fed with 9V single supply and biased at 4.5V can have an output Volume of 9Vpp.. Exhibiting a gain of 10 for an input signal of 1Vpp, results into a distortion of 1Vpp (10V due to gain minus 9V due to undistorted waveform..)
(expession totally out of technical terms but to get you into the point..)

That said, Volume pot could be placed before 3rd stage only if 3rd stage was a buffer..
(for impedance matching reasons which are beyond present discussion..)

As it is, 3rd stage plays the role of boosting 2nd stage output, resulting into additional 11db of gain hence adding more on 2nd stage distortion..

What I'm trying to tell you is that 3rd stage is completely useless from Volume setting point of view..
Just raise its value to 100k and connect it directly to C3..
(you'll "loose" about 10% of Q2 stage gain but you'll not even hear the difference..)

[antonis]

3rd stage only necessary in case of next effect/amp low input impedance impedance..

[Banjan73]

Hi.
Ok, I think I get your point regarding gain vs volume. It`s almost the same as when you crank up an old 100w plexi, you might get 150w out due to the clipping, right?
So, what you are saying here is that my third stage is unnecessary? I was actually thinking for a while that increasing the value of the volume pot might help (before I introduced the third stage). The point is to avoid to much current going from collector to ground, or what? I don`think I have a 100k pot laying around, but I DO have a 250k (think its an old guitar pot). Might that work?
What are your thoughts regarding the gain pot? Should it be at Q1 or Q2? I am thinking that if it is at Q2, it might be difficult to obtain a "clean" sound (low gain, high volume), but that depends on how much boost I am tuning in on Q1, or what?
The best would be, though, to keep the gain pot at Q1 because then I don`t need to reorder new PCBs.
P.S. I considered a buffer stage also for a while, but I am thinking that all pedals should have a high input impedance. If they don`t, it`s their fault, hehe..

[antonis]

It`s almost the same as when you crank up an old 100w plexi, you might get 150w out due to the clipping, right?

I'll pretend I didn't read that..

About gain pot: as closer to input stage as better it is but this is just theoretical..
"Clean" involves Gain value rather than setting it device placement..

[Banjan73]

I'll pretend I didn't read that..
[/quote]
Hehe :-)
Well. I`ll try with the 250k volume pot then. We`ll see what happens!

[Banjan73]

That worked!
Can`t understand why I didn`t do that earlier. Well, better blame it on someone else than myself, hehe
No, seriously. That 56k potmeter was just something I had in my drawer. I thought that 56k would be enough, but apparently not. 250k made it work like a dream. As Antonis says, I loe a little bit gain when volume is on very low, but I can live with that.
Now I have to order a couple of potmeters, solder a little bit and then we`ll see.
The circuit has pretty much gain now. Heres the schematics.

[duck_arse]

antonis - your Q3 bias might go a bit off without the decouple cap.

Can`t understand why I didn`t do that earlier. Well, better blame it on someone else than myself, hehe 

we can't understand, either. we'll just pretend we didn't read it. and, if you are losing gain while the volume is low, you are still doing it wrong, or not using the right descriptors. you don't mean you lose brightness/treble/top/sparkle when the volume is low, do you? that would mean you want a treble bleed cap as well.

[Gus]

Look for the Bee Baa and other circuits like that from the past.

A search of this site and other forums can give you ideas for gain stages in series and how to adjust them for the tone you want.

A good first search could be "joe davisson blackfire vulcan distortion schematic"

[Banjan73]

Hi.
To be honest, I tested the breadboard circuit on my amp at a very low volume because of this Corona thing. My whole family is at home, and they protest pretty quick if I crank up the volume as a wish I could, hehe.
I will listen a little more careful later, but I definetly still lose "something" at low volume. But as I said, I think I can live with that. I will also measure the new layout on a scope to see what it looks like.
Thanks for the tip for those other schematics. They look indeed pretty similiar to this one. A little bit strange with those diodes in the signal path though, but anyway.
When it comes to tuning the tone, I actually have some experience from ECG instrument building (low pass, high pass, notch, bandpass) and an earlier tube amp project.
The first (MK I?) exemplar of this pedal sounded maybe a little bit thin on my Marshall, but that is adjustable.