New member... Needing help with Ampeg Scrambler

[billdramp]

Hi everyone! This is my first post, and my first attempt at building a pedal, and guess what!? It doesnt work!

It is the Ampeg Scrambler clone from Tonepad

I have done all of the legwork to try and troubleshot this myself, and I believe I have finally given up... I hope some others with experience can give me some help.

I used the 2N5306, and the 2N5089's as per fuzzcentral.

Long story short... The pedal has sound but no distortion at all. 
It works in bypass mode as well, but sounds the same as when engaged.  One knob seems to control the volume, the other knob does nothing at all...

I have payed attention to the pinouts of the 2n5306's.  And tried changing them, with no change in sound.
I have tried audioprobing the circuit... I have clean signal all the way through, but it never gets distorted.

Here are some measurements.
Q1
C:8.92 B: 4.3 E: 3.4
Q2
C:1.78 B: .93 E : .33
Q3
C: 4.38 B: 8.91 E: 3.38
Q4
C: 4.41 B: 8.48 E: 3.38

Anyhelp is greatly appreciated!!
If I am making dumb mistakes, please let me know... As mentioned this is my first attempt. 

Cheers from Portland
Billy

[PRR]

> Q3
> C: 4.38 B: 8.91 E: 3.38
> Q4
> C: 4.41 B: 8.48 E: 3.38

Not right.

Should be more like:

Base-- a bit over 4V
Emitter-- a bit under 4V
Collector-- almost 9V

So it may be that you have B and C reversed, in your list or on the board.

Also note this PCB has 4 holes for 3 legs, perhaps to accomodate different pinouts.

[billdramp]

Here are some new measurements:

Here is the checklist to fill out:
1.What does it do, not do, and sound like?

Has clean signal, no distortion
2.Name of the circuit = Revolcador ampeg Scrambler clone
3.Source of the circuit (URL of schematic or project) = tonepad.com
4.Any modifications to the circuit? No
5.Any parts substitutions? If yes, list them. 2N5306's and 2N5089's
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? => 9.72
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 = 9.54
Voltage at the circuit board end of the black battery lead = 0

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
C = 9.56
B =.357
E =3.64

Q2
C=1.93
B=.96
E=.352

Q3
C=9.48
B=4.8
E=3.64

Q4
C=9.03
B=4.79
E=3.65

Dl
A (anode, the non-band end) =4.37 
K (cathode, the banded)=4.69

D2
A =4.69
K =4.78

Thanks for all suggestions!

Cheers. 

[PRR]

> Today at 08:36:14 PM   
> Q1
> C:8.92
> B: 4.3
> E: 3.4
>
> Today at 09:17:04 PM
> Q1
> C = 9.56
> B =.357
> E =3.64

How did Q1 Base change so much, and how is -any- signal getting past Q1?

> works in bypass mode as well, but sounds the same as when engaged.  One knob seems to control the volume, the other knob does nothing at all...

R8 may do little until the distorter works.

R16 should turn from pure (buffered) input to total octave-tone.

You say R16 turns from clean to nothing? Either not connected to distorter, or signal not getting into distorter.

Most shorts would show as bad DC voltages, so I would look for an open in a non-DC part. Like a missing or poor-solder C2 C4 C7.

A signal tracer would be handy to check if signal gets through Q2 D1 D2 Q3 Q4.

[billdramp]

PRR,

Perhaps Q1 changed so much because I changed batteries?  I wanted to start fresh when I redid the voltage readings... I will check the soldering around C2, C4, C7... I'm not sure if the wiring is correct on R16... I tried a few different ways, with no changes.  It seems alot of first time builders have had this problem with the Scrambler on the forum, however none of the posts I found had any positive conclusions...?

I will report back shortly.  Thanks for taking the time to offer me some advice.  I really appreciate it. 

Cheers.

Billy in Portland.

[billdramp]

Well... I checked all the caps, their polarities, and for any shorts and didn't see anything out of line... Anymore ideas?!

I thought building pedals would be a breeze after tube amps, but I am learning they are two different beasts entirely.  Its frustrating, but exciting at the same time.  Arggghhhh. 

[chromesphere]

I tend to give this advise when i see pedals not working threads, sorry to sound repetitive, but this is 99% of time the problem that i have.

Dont know if you have done this, but scratch around the tracks on the board with a sharp razor (not just the pads, everywhere).  Some solder bridges are so small, you cant see them with the naked eye.  Anything that looks dicey, give it a good scratch.  Also, if you see any pads that look like the solder joint is a bit NQR, reflow it.

Between solder bridges and cold solder joints, 99% of the problems i have are fixed.  Also check polarity of components (trans, caps, diodes, etc) and the values of all components on the board are correct.

I hope thats of some help to you, or leads you in the right direction.

Paul.

[billdramp]

Chromesphere... Thanks so much for the advice. Like I posted earlier... I'm brand new to this and am very likely to make mistakes, and I'm not too proud to admit it!

So... I reflowed all my joints and took an xacto to the traces.  The only difference I have noticed is that now NEITHER pot does ANYTHING to the signal.  Ugh. Hopefully I haven't made things worse!
Thanks again, and keep the ideas coming... I will try them all.

Billy.

[chromesphere]

Hi buildramp,

Sorry to hear things got worse...

I still suspect theres a bridge or dicey joint somewhere...if you have a magnifying glass or eyepiece go around the pads and check for bridges / dodgy solder joints.  Another thing i do is hold the board up to a bright window or a bright light (ceiling light for instance) so the board is backlight.  You can see the solder pads very clearly that way.

You can also quickly check the values of your resistors on this website (4 and 5 band).  Sometimes i accidentally put the wrong value in the wrong spot which creates all sorts of problems.  Hey, we're all human :-)

http://samengstrom.com/24614782/en/read/4_Band_Resistor_Color_Codes

When i started building pedals, i always thought, maybe one of these components isnt working properly?  I've built over 30 pedal now, and i can tell you, its very rare.  Infact i can only recall on 2 occasions a component failure: a CA3080 (old stock) in a small stone, and recently a MAX1044 which has a rep for being picky.  Every single other problem has been human error. Not sure why im telling you this...i suppose it may relate...

Good luck
Paul

[Derringer]

probably not your main problem, but there is an error on tonepad's pcb layout
C3 should be flipped so that its negative end faces the blend pot

good luck

[billdramp]

Ok guys... Update.  I went through and checked all of my resistor values and found that I had put in a 2.2M instead of a 2.2k  so I replaced that... And now I finally have some fuzz! BUT... it still doesn't sound quite right. It's fairly tame, and neither pot seems to do much.   
Any ideas where to look next? I'm enjoying this painful process for some reason, and can't wait to get it dialed in. 

Cheers, and thanks for the help everyone. 

Billy in Portland

[chromesphere]

Well thats some progress!

I still suspect a short / solder bridge or cold solder joint somewhere.  Also check the polarity of the caps and the pinout of the transistors you are using are correctly orientated on the board.

Another thing that can sometimes lead to more help, is providing macro photos of the the PCB board, both underneath and component layout ontop.  The clearer and closer, the better. Someone may spot an error.

Stick with it.  You will find the cause of the problems!

Paul.

[Tony Forestiere]

Now that you have the proper resistor value in place, new voltage readings are a must.