Scrambler problem - few possibilities

[Drake120]

Of course I found some topics about Scrambler here, but my main problem is that I don't have a voltmeter... But I made some "research" in the circuit, and that's what I found:

Bypass works - there's a clean signal when the stompbox is bypassed
When I turn the Blend pot all the way down (so there should be only clean signal) AND TOUCH THE SOLDER JOINTS OF Q1, there's a clean signal... when I don't touch the Q1 or turn the blend pot up, the signal disappears
I've tested the circuit with audio probe - signal is everywhere (I mean, there's a hum wherever I touch the traces)

I don't know if I'm right with the grounding - I soldered the sleeves of input and output to the trace which has two "GND" points on the end of it. I'm using tonepad's layout. I read somewhere, that the C3 on the layout isn't properly orientated. But not everyone has submitted that.. how do I orientate the C3? Next: I'm using the millenium bypass 2, and the LED is always on. I've read about it, but could it be also the matter of a mistake on the board? Or is it just a broken BS170? My last question - I made a clipping diodes switch - I used a DPDT switch to switch D1 and D2 (between stock and germanium). I wired it like that:


But, I don't know if it is a proper way to switch between polarized units. if it isn't and it could affect my Scrambler, just tell me and I will remove the switch and leave only the stock ones. Don't ask why I wanted to have germanium diodes in here

Hope my long explanation will be enough for you to help me. Thanks,

JS

[GibsonGM]

Hi Drake,
Diode switch SEEMS right (but maybe a little cumbersome, no big deal tho).  You say when you audio probe you get hum?   Are you applying an input signal like a CD or radio, or someone strumming your guitar?  You shouldn't get hum, and if you do while there's signal present, experience says you might have grounding problem.  The audio probe is used to find the 1st occurrence of a problem, and narrow down the problem to that section, so start at the input cap and work from there...

You need to get a DMM, even a cheap $20 one is better than none!   Without voltages, it's very hard to suggest what may be wrong. 

The touching Q1 suggests to me it's mis-biased, in backwards or something (again, need voltages there).  Check the pinout again to be sure it's in correctly.

Hope this gives you some ideas!  Try to get a meter...
~mike

Orienting C3 would be that if the cap is polarized, the "+" end goes to the end of higher potential, with "-" facing towards the lower potential (or ground).   If you're using a nonpolarized cap (NP), it doesn't matter. 

I'd remove the Mil Bypass until you get the ckt debugged, just makes things more complicated. 

[Drake120]

Today I will obtain a voltmeter.

But I have one more question: can anyone look at the datasheet of BC517? I used it instead MPSA14. Did they have the same pinouts? I was looking at the datasheets for a long time and I can't recognise which side is the flat one and which side is the rounded one at these pictures. Maybe that's my problem.

And I have exactly THE SAME problem with Small Stone - works bypassed, no sound when effect is on, and the LED lights all the time. I'll remove the mil today to see what happens without it.

And I know what does "polarized" mean I just don't know if the C3 at this layout: http://tonepad.com/getFile.asp?id=31 is well orientated. But even if it wasn't, it still has to work (just a loud pop when bypassing), so it's not my main problem now.

Thanks,
JS

[Drake120]

OK, so... obviously, I mounted transistors in a wrong way... So now, it works! It's a very nice overdrive, but:

- in this position (I don't know which diodes work in this position):

the signal is choppy, ends after about 2 seconds or even less
- it's not the almighty Scrambler! Even in the "working" diode switch position, it's a powerful overdrive, but nothing more. No octaves. Blend pot only turns the volume down, Texture adds gain (or lessens it)... I took some measurements:

Q1
C:9.29
B:3,20
E:3,15

Q2
C:4,50
B:0,30
E:0,30

Q3
C:9,60
B:4,56
E:3,60

Q4 pretty much the same as Q3

Diodes (Csil-cathode of a silicon diode, Ager - anode of the germanium etc.)

D1
Csil:4,20
Cger:4,41
A:4,45

D2
C:4,40
Asil:4,40
Ager:3,90

D3 (only silicon)
C:4,20
A:4,30

D4 (only silicon)
C:4,28
A:4,30

D5 (only silicon)
C:1
A:0,39

As you can see, I made a switch that changes only D1 and D2, D3, D4 and D5 remains stock (silicon) all the time. Maybe that's a mistake?

Hope that clears up anything,
JS

[Drake120]

bump

[hellwood]

Q2 has a problem w/ the base/emitter

[Drake120]

OK. I still didn't manage to catch any spare time to sit and try something... Probably I'll do sth tomorrow. But I reminded myself of something I wanted to ask - in fact, my measurements can be unspecific, because in fact the value of voltage was changing all the time. Of course, the differences were not big, max about 0,60V for a specific place. I'm sure I checked it for DC. Is it caused by the fact I don't have alligator clips so I was minimally moving the test end of multimeter all the time?

And anyone can tell which diodes are on in the position I drawn in my last post? I don't know if the toggle switches work "symmetrical" or not.

Thanks,
(JD)^S

EDIT:
And one more: now it's time for you to laugh :] So, my other suspicion about what can be the problem is the wires I use... ATTENTION - I used the six small wires from the ethernet cable, since I thought they are simple conductors. Now I'm not so sure about it.

[Drake120]

OK. Finally, I managed to do something about it. I get rid of these ethernet wires, bought some 24 wire, resoldered some questionable joints... I also throw away the switch and the germanium diodes. And the only thing which improved, is that now Blend pot works. I've done a big research, so here's everything I found out:

1. MEASURING (as I said before, tha value was changing all the time, but that's probably because I don't have alligator clips)

Q1
C:9,5
B:3,2
E:3,6

Q2
C:4,5
B:0,5
E:0,3

Q3 and Q4
C:9,5
B:4,5
E:3,9

D1
C:3,9
A:4,1

D2 and D4
C:4,5
A:4,5

D3
C:4,5
A:3,9

D5
C:1
A:0,3

2. AUDIOPROBING
Q1 works fine. It sends clean signal to the Blend pot.
Q2: emitter: silence, base: silent overdrive, collector: LOUD overdrive
Q3 and Q4: emitter and base: overdrive, similar to this heard when "normal playing" (no audioprobing), collector: nothing

No octave at all, overdrive here sounds better than when plugged into amp normally. But I've searched and I found why...

Another interesting things:
At anode of D1 and cathode of D2 the signal is loud, there's no octave but very nice overdrive (it comes from Q2 collector). But at cathode of D1 and anode of D2, and both leads of D3 and D4, the signal is choppy, less loud, farty.

And... when I probed somewhere between Q4 and C7 (so it's a signal coming out of Q4's collector)... There's some octave that can be heard! Well, it's not the Scrambler I've heard, but that's something anyway...

3. Parts and sound when plugged "normally".

I used BC517's as Q1,Q3 and Q4 and 2N3904 as Q2. It sounds... well, it's a nice overdrive, but it's choppy, sometimes begin to fart. Texture pot turns volume up and down, and also changes the quality of the signal, Blend pot works well. Finally, one mod and one sub: I've read that someone used 100k instead of 10k for texture and that he had great results, I used 100k. But I don't think this may change the tone so much. I subbed a 10nF capacitor with a 1nF one, but only because I had no 10nFs. Can it spoil the sound?

Please, help me with it. There are so many cool pedals I want to build and I'm stuck a this one (Scrambler is cool anyway :])

Thanks,
(JD)^S

[JOHNO]

G'day drake. I just made one of these the other night. it seems you have a problem with Q1 and Q2. the emitter needs to be about .5 or .6v (a "diode drop") below the base for the transistor to work properly.
Here are my readings
      C      B     E
Q1 8.99 4.28 3.41
Q2 3.27 .94   .27
The rest of the voltages match (well almost). Im not saying my voltages are right but i do have a diode drop between base and emitter.I have a good octave effect but the gain is not that good. Im sure i have a problem with mine also but ill keep working on it.
BC517's seem to have the same pin out as mspa14's which is what i used. So double check youve got the trannies in correctly and check around Q1 and Q2 for shorts or bad soldering and the like. Good luck with it.

[Drake120]

Well, I sat to it again. Trannies are OK (well, I already resoldered them once). Maybe because of the values are changing all the time , my measurements were inaccurate. I measured everything once again, and Q2 has the "diode drop" indeed. But Q1, ALWAYS has base reading higher than emitter. It's about 0,4V different. I've also changed the cap to the proper value (10nF, ceramic) and now it doesn't fart. It's nice overdrive (maybe too trebly for me, but that's the Scrambler [if I got it work I will experiment with higher input cap values]), but still, no octave. I've heard octave only when I played open 1st string (the highest one). Then a very quiet octave could be heard, and it couldn't be controled by Texture pot.

I've also checked it for continuity, there's no connection where it shouldn't be.

That's driving me crazy :/

[JOHNO]

After listening to the sound clips over at ggg im convinced that my circuit is fine. The sound clips there sound a little farty too. Ill knock up a short video if youd like to hear it. I know this doesnt help you get yours going ,oh well.

[Drake120]

Well, I've already heard some samples, and mine sounds nothing like them. OK, the overdrive/fuzz is the same as Tone Frenzy samples, but the octave is REALLY hearable in the samples, which I can't say about my unit. Anyway, thanks for your concern

Anyone can help? Maybe it's the BC517 problem, they're kinda similar in characteristics to MPSA14's, but not the same. I don't know if the differences are big enough to "mute" the octave. It's weird, because the overall tone is the same but the octave...

(JD)^S

[Drake120]

Bump...

[Drake120]

Yeah! I got it to work properly. I just subbed the BC517's with BC550 and the octave finally is there :]

So my last problem with it is the LED staying always on. I installed a 1M resistor from board out to ground but it didn't help. Maybe my BS170 is dead, I will replace it later. Thanks for all your help!!!

(JD)^S