Hey all,
Trying to build a mangler with ac128's and failing hard. Couldn't get a 20k trimmer but popped a 50k in there. Biases right to 4.5v and everything. looks like I'm all wired up proper too. plug it in and the led lights and it passes audio but the knobs do very little, no fuzz at all and the sound is akin to quiet icepicks.
nothing like functional.
any thoughts?
ZZ
are you positive you have the pins on the ac128's correct?
I believe the pins are correct.
Belief is not enough. You have to be positive. That's the first thing I would suspect too. Next would be no power to the transistors.
Jacob
there are no markings on them noting b e or c. that being said they only pass audio oriented one way.
also... tried two different pairs. the third pair is working wonderfully in my zombii.
hope that helps. again any assist would be great.
zz
I experienced the same kind of problem, along with a strong volume drop, when i put a 1n cap instead of a 100n in the signal path..
maybe check your cap values?
You're getting good advice from everyone (I'd put my money on add4's capacitor suggestion), but you'll get even better help if you can upload some high-resolution, in-focus, well-lit photos of your board.
isn't c3 supposed to be a 10n (what i used.) i'll check into it more this afternoon.
just rewired the pots... reflowed all solder joints. same issue. thin...no fuzz, huge volume drop but passes audio.
should i be switching c3 to 100n? i don't get it.
zz
When I troubleshoot fuzz face circuits I always put in silicon transistors first to make sure it isn't the transistors acting all weird. I am not sure what kind of stockpile you have but you could stick some 2N3906's in there just to take the finicky nature of germanium out of the equation. I've had a few really bad germaniums that sound just like you are describing.
did you socket the transistors or solder them? ge transistors are very easy to cook. is there any excessive noise? what package type are the transistors. the european black glass ones have a red dot to locate the collector. the metal can types from the us usually have a tab denoting the emitter.
Quote from: Zerstorte Zelle on March 23, 2012, 03:20:56 PM
just rewired the pots... reflowed all solder joints. same issue. thin...no fuzz, huge volume drop but passes audio.
should i be switching c3 to 100n? i don't get it.
No need to switch C3 to 100n. I think the point is just to confirm the 10n value of that component. And while you're at it, triple check the value of every component (especially C2, C3, R1, R3 and R4). Can't say it enough: photos help.
Here are two photos, best i could get with my phone. for what it's worth i just had it plugged in with a booster slamming it and it sounds like that helps but not nearly enough. also the knobs do little to nothing and only really sound like anything maxed out.
(http://farm8.staticflickr.com/7124/6862573016_d2780ab260_c.jpg)
(http://farm8.staticflickr.com/7212/7008689785_fb44589b3d_c.jpg)
Your electrolytics are backwards.
Jacob
yeah they are! that will ruin your day.
Ha! feeling super dumb about staring at that for the better portion of the day head scratching. however sounds the same. two sets of ac128s. It's not my first build but I'm stumped.
where next? i'm out of ideas here.
zz
So you have turned the electrolytics around? If you haven't you need to make sure the negative side goes to the round hole, and the positive side to the square hole.
Jacob
correct. i've flipped them. same sound two sets of ac128s. slightly more response from the pots but no fuzz just icepick thin and volume drop
Your voltages might help at this point.
Jacob
have you re-biased it since you switched the caps around the right way?
Have you tried pnp silicon's (2n3906, 2n2907,) in place of the germaniums? This will help rule out the transistors as your problem. They sell them (2n3906) at radioshack if you don't have any, and you don't feel like waiting to have them shipped to you.
I've rebiased several times also did pop in a pair of 2n3906s same issue.
If you have a multi-meter you could post some voltages, this would help greatly to see whats going on.
If your not sure how to test voltages...
Just set your meter to measure voltage (usually indicated by a DC or DCV symbol) and set it to the closest range to 9v (on mine it's 20v). Plug power into the circuit via adapter or battery, and put the red probe onto a leg of a transistor and the black probe to anything connected to ground on the board (or anything grounded offboard for that matter).
Do this for each leg of both transistors and write down the results, and while your at it, check to make sure your getting 9v to the "9v" pad on the board. (BTW, not trying to question your skills/ability, just saying in-case youv'e never been informed on how to test using a meter, because I had this problem for a while when I was starting out, and no one would be specific enough on exactly how to use the meter, but I do apologize if you already knew all of this).
Anyway, try that out and post your results.
Make sure your Fuzz pot is really a B1K and not a B1M or B100K, etc.
Kind of a stumper. Resistor values are correct. Caps have been turned around. Diode looks right. Transistors look to be put in the right way due to the way the leads are spread. Doesn't leave much else other than a proper positive ground supply and fully functioning transistors. ???
Is it possible that the electrolytics (specifically C2 and C4) could have been damaged before their orientation was corrected? I imagine with C2 out of the equation you'd probably get a much thinner sound with much less (and less adjustable) fuzz.
Hey All,
Really digging the all of the help around here. Hoping the trannies are fine. Out of town now but when I get back in I'll throw the meter on it.
I'm as stumped as you.
ZZ
SO...
I probed about with the mangler again today and after changing the electrolytics out for new ones it's alive and kicking. I suppose i fried the old ones good.
That being said I've wired up a 250kA pot in after the switch for an input trimmer and I'm wondering if it isn't the correct value. Would something like 500k be better for this?
The wiring goes... lug one from switch in lug two to pcb in lug 3 to ground.
Almost there with it.
Sweet!
ZZ
I used a 100kB pot for pregain in my mangler. Works very well.
I used a 50kb on mine. I am doing another right now and am going to try a 50kC. You can always experiment and see what works for ya. I have mostly heard of people using 25 to 100k though.
You think the 250k could be preventing the mangler from reaching full gain. i was watching some FF videos on youtube and mine doesn't quit fizz and sustain like the prod. models.
more of a fuzzy overdrive at max. Trannies blown out too?
tomorrow more meter work
zz
Sweet meats! After soldering the trannies in they were hot and not so exciting but now they are quite the pair ( pun intended )
mangler -> slow loris -> late 60's fender deluxe reverb is putting big grins on faces 'round here.
ZZ