Ampeg Scrambler not working, contains full debugging info

[Kain]

Hi all,

First post. Newbie here with problems with AMPEG SCRAMBLER.

Built on homemade protoboard, which is working ok. No switches.

1.What does it do, not do, and sound like?

Blend (full) Effect makes no sound at all until the input is very strong. Blend (low) clean signal.

2.Name of the circuit = Ampeg Scrambler

3.Source of the circuit (URL of schematic or project) = http://www.tonepad.com/project.asp?id=16

4.Any modifications to the circuit?  No

5.Any parts substitutions? If yes, list them.

R4 (2K2) 2 X 1K + 220

6.Positive ground to negative ground conversion? No

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 9.16

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 9.13
Voltage at the circuit board end of the black battery lead = 0.00

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1 (2N5306)
C = 9.13
B = 3.04 (problem?) R1 & R2 are 1M (brown-black-green)
E = 3.49

Q2 (2N3904)
C = 3.98
B = 0.91
E = 0.24

Q3
C = 9.13
B = 4.11
E = 3.59

Q4
C = 8.77
B = 4.09
E = 3.59


D1
A (anode, the non-band end) = 3.74
K (cathode, the banded end) = 4.11

D2
A = 4.08
K = 3.75

D3
A = 4.11
K = 4.10

D4
A = 4.11
K = 4.08

D5
A = 0.24
K = 0.13

Thank you for your help.

- Kain, Vasuri Kabala

[Kain]

A couple of pics of my mighty Vasuri-protoboard with the ampeg scrambler on it.

[Kain]

R1/R2 voltage divider is what I don't understand here. I took the resistors off the scrambler and tested like this:

+9.13V -+- R1 -+- R2 -+- 0V

Voltage across R2 is 3.04V. What am I doing wrong / not understanding here? Shouldn't it be 4.57V?

R1 & R2 are brown-black-green and measured to be both around 1M.

[Kain]

Uh, can we up this?

Please can anyone help me with my doom unit, just want to break all hell loose with it. Do you need more detailed pictures maybe?

And now as I am on it, I would like to thank everybody for all ideas and knowledge this forum is bringing to my humble house.

[Shepherd]

Check the pinout on the 2n5306 (if that is what you're using).  The pinout varies among manufacturers.

[Kain]

Thanks, doublechecked pintouts for all three 2N5306's again and everything seems to be ok.

Top view:

B C E
------
\    /
----

DMM gave about 1.2V on diodecheck (+) on B and (-) on C/E.

[Kain]

Transistors are like this on the protoboard

2N5306                 2N5306  2N5306
B C E                      B C E     E C B
-------         -----     -------     -----   
\ Q1 /        / Q2 \    \ Q3 /   / Q4 \
-----         -------     -----     -------
                 E B C
                 2N3904

[Shepherd]

What brand 2n5306 are you using?

http://pdf1.alldatasheet.com/datasheet-pdf/view/50032/FAIRCHILD/2N5306.html

[Kain]

From the Small Bear, marked

HT2N
5306

TO-98 package.

[glops]

I've had parts for a scrambler for over six months and decided to tackle it on the breadboard.  It didn't work at all.  I used the pin out from
fuzz central for the 5306.  After researching and finding out that 5306's have different pin outs I put the project in a bag for later use.  I search the internet for the pin out of the 5306's I have and couldn't find a match with the manufacturer.  I wanted  that sound but will go back to it in the future.  Went over to Bazz Fuss and circuit snippits for fun, and indeed, it is!

[Kain]

http://ampedals.blogspot.com/2008/02/tricerarocks.html

"After extensive troubleshooting, I got the clean stage working (with the blend rolled all the way to the clean signal, I was getting something), but the distorted signal was not coming through at all. After trying the recommended (MPSA-14) transistors in every combination I could think of, I tried some other transistors (5088's) and immediately the circuit worked! It was a huge relief. I think it sounds a little different than it's supposed to (perhaps not so much of an octave fuzz sound) but still a really far out, distorted stompbox."


I got exactly the same problem. Gotta test if this helps.

[glops]

Thanks, gonna try out some different transistors soon.

[gigimarga]

I've built this Ampeg Scrambler over 3 times (GGG's and Tonepad layouts) until it worked.
I made the same idiot mistake for 3 times: I didn't wired the Blend pot correctly (I wired it as a volume pot  )!!
As I can't find here any 2N5306, I used MPSA13 and BC517 and it works very well.

So, my advice: look very carefully at the wires of the Blend pot!

[Kain]

I changed all transistors with 5088's, but it was the same as with other transistors >> Blend 0 > clean // Blend 10 > no sound (without very hard strumming) = some biasing problem.

Gigimarga, do you mean you put third lug on the ground?

I think I have to start from the beginning and try to make it as clear as possible on the protoboard. I received ready to solder board from tonepad also, so I might try it on that too.

[gigimarga]

Gigimarga, do you mean you put third lug on the ground?

No, I wanted to say that you need to be very carefully NOT to wire the Blend pot as a volume pot: the lug 1 of it must to go at C3 and lug 3 must to go to C7! No wire from the Blend to the ground!

[Kain]

No, I wanted to say that you need to be very carefully NOT to wire the Blend pot as a volume pot: the lug 1 of it must to go at C3 and lug 3 must to go to C7! No wire from the Blend to the ground!

Yes, I understood. This is not the case on my scrambler tho.

[gigimarga]

No, I wanted to say that you need to be very carefully NOT to wire the Blend pot as a volume pot: the lug 1 of it must to go at C3 and lug 3 must to go to C7! No wire from the Blend to the ground!

Yes, I understood. This is not the case on my scrambler tho.

OK...good luck!
Anyway, you can try to use some MPSA13 or MPSA14 which have a more certain pinout or you may test the pinout of your 2N5306 in a simple booster as LPB (this is the way I do that).

[Kain]

Good idea, thank you sir.

[Kain]

you may test the pinout of your 2N5306 in a simple booster as LPB (this is the way I do that).

Tested all transistors in LPB and pinouts are correct (ECB).

[Kain]

Sry, had totally forgot this thread. Got an oscilloscope and there wasn't anything going on to the B of Q2 (that green jumper is connected to the wrong side of the notch). Added one jumper and KA-BOOM! Damn this thing is sick.