Hi, this is my first project about madbeanpedals pcb.
Its a mangler with AC128, but i can set a good sound for the pedal, i tried different combination of resistors, but only get a sweet fuzz and when i turn the volume to the top, the sound dies. aso the fuzz knob does not work properlty. This what i did
1.-Resistors of Ac128 smallbear recomended.
2.-Resistors of Mangler
3.-Pictures are the actual situation smallbear recomended resistors.
Some idea to start troubleshoot?
i started with this pcb because it looks easy! and the reward is very gratefull. =)
These are the resistors:
R1 110k
R2 27k
R3 220
R4 480
Measure your voltages on each pin of both transistors and post those.
The resistor values don't help -- they bias each transistor individually, so we need to be able to see what's actually happening in your particular circuit.
Also, what is your fuzz knob *doing* that it isn't working properly?
And: Have you adjusted the trimpot to get 4.5v on the collector of Q2?
Sorry how do i measure the voltage on the pin of transistor?
I Tested the voltage with black lead to test hole an the red to ground. I cant adjust to 4.5
It only goes from 5.3 to 5.8 volts turning the trim at minium and maximum.
Quote from: isal on March 14, 2013, 09:13:00 PM
Sorry how do i measure the voltage on the pin of transistor?
I Tested the voltage with black lead to test hole an the red to ground. I cant adjust to 4.5
It only goes from 5.3 to 5.8 volts turning the trim at minium and maximum.
Post pics of both sides of the board.
The trimmer should take you from about 1v to over 6v. Something might be shorted or a solder bridge that's too small to see or something.
Here they are...
thanks!!..
You're gonna want to reflow those solder blobs on the bottom left of the board,and cut off any extra leads to the top of the solder you have left over for starters.
Another thing is to insulate or shorten the transistor legs. If any are touching that will cause problems.
And somebody correct me if I am wrong but I think the pots are wired in the wrong orientation (looks like you have both pots: lug 1 connected to pad 3, lug 3 connected to pad 1) that would be why the sound dies when you turn it all the way up. Just flip your pots around the other way so they lay over the pcb.
To measure the voltage you need a multimeter. There is a little pad (labeled "test") just to the left of the trim pot. Put one of the leads from the multi meter on that pad and the other lead to ground. Adjust the trim pot until you get a reading of 4.5 V, that's it.
3 points to start with.
1.- Reflow solder blobs and cut the extra
2.- Correct the pads of pot. (its not funny to desolder pots)
3.- Cut the transistor legs in order to avoid contact.
thanks tomorrow i will post the results!
Having the right tool can make things a whole lot easier. If you don't have one, you at least need a solder sucker. If you got the money you could step up to a desoldering station.
Ignore my advice to cut the legs, rather just strip some insulation off some wire and slip it over the legs. That will leave you some flexibility in positioning them in side your pedal enclosure.
So i tried to reflow all the solder joints, but sitll the same result.
so these are the current pictures. tested voltage 4.89 to 5.3 Turning the trimpot.
i have desoldering pump but i think i need desoldering braid.
Aren't AC128 NPN? It looks to me like you soldered everything up like its PNP.
Does anyone else agree?
IF THE ABOVE IS TRUE THEN:
reverse C1, C2, C4, as well as the Diode D1, and wire =9v (red) to the -9v pad and ground (black) to the ground pad.
AC128 are PNP .
Alright then, PNP it is. I'm out of ideas now. I hope you can get this figured out.
-Josh
for what it's worth, i built a Mangler and had no sound. the BOM calls for PNP GE in Q1 and Q2, so being extremely green at this, i ordered some off ebay as PNP GE. what i recieved was 2n1039. after reading in the forum, i discovered PNP GE could be several different part numbers. so i started trying different 2nx's and 2n5087's made it come to life! might be worth looking at....
LT
This doesn't particularly help, but those aren't AC128s. They are 3AX31Cs I believe (http://www.smallbearelec.com/servlet/Detail?no=680).
Still PNP though.