Build Your Own Clone Message Board

Hi!

I'll create a thread for this problem itself...

I just tried changing the 820 and 150 Ohm resistors with 100 Ohm ones, changed the 3.3k with a 33k and changed the 4 transistors with 2N2222A's.

I had a real hard time getting the old parts out. Got the explanation from CallMeRog. But I'm not a complete noob at soldering and modding anymore. Have build 2 pedals and modded 5 pedals without problems.

Anyway, I switched the parts and then plugged in the pedal to check it. There's sound, but it's quite low! Even with volume at 100% the sound isn't that high. The pedal isn't longer a fuzzy distortion it's a mild fuzzy overdrive!

What went wrong?

I didn't use transistor sockets. I soldered the transistors straight onto the PCB. Should I try to get 4 new 2N2222A transistors? And how can I test if a transistor is good?

I don't have any pictures of the PCB. If you want some I can try and make some tomorrow.

Please help!

if the transistors are germanim there is a chance you overheated them. I dunno how to test them though.

2N2222A's aren't germanium, but silicon. So I don't think that I fried them. I just got one or more bad ones I think. I'll order some more.

or...it could be a poor connection to one or more of the transistor legs. take a look down there, maybe do some re-flowing of solder connections. Don't know what those value replacements do though.

will do. But they looked good to me. But I'll take a look tomorrow when I'm home again.

could you have damaged the board with excessive heat?
my dmm has a trans checker on it you can check around for a dmm with one i used to have a cheap dmm with a trans checker there once was a thread on how to test trans look for that.

I don't think that I damaged the board. I haven't applied more heat than usual when soldering/desoldering.

I happened to have had a similar problem with a Large Beaver that I built. After a bit of probing and DMM testing I found that I had a bad solder connection from the volume potentiometer to the board. I disordered the connection and then re-soldered and then it worked great.

I’m not sure this is the problem you are having but I thought I would share.

Good luck...

That's not my problem as the pedal worked fine before the mod.

But I'll try and resolder the connections when I have the time for it. If that doesn't help I'll change the transistors for 4 new ones.

Just talked to some guys about my problem.

They all say that there's no wrong connection or bad transistors. It's simply because this type of transistor (the 2N2222A) is a very low amplifier (hfe between 50 and 325). The standard 2N5088 has more gain (hfe between 300 and 900).

So I don't get why this mod should make it better. In my world (and my source (who builds and repairs pedals, amps, guitars etc for a living!)) the mod actually reduces the Large Beaver to an overdrive instead of a distortion/fuzz.

Any comments?

I don't know that transistor gain plays a huge role in the BMP circuit. One of my Cherry Pie builds used ~535 hFE 2N5089s and another used ~310 hFE 2N5133s. Sure, measuring gain with a DMM can be problematic, but that's another thread. In any case, the approximate gain and output volume of both are very close. The character of the distortion is different, but that's to be expected and what I was hoping for with these builds.

With two back-to-back gain stages, I wouldn't expect this circuit to sound much like an overdrive, unless the Sustain knob is way down, and even then this seems to happen in only the choicest BMPs.

I suppose if you had a really low-gain transistor in there, you might get the results you're experiencing. Replacing the 2N2222As with sockets and then comparing the 5088s and 2222s would confirm this if you don't have a transistor socket on your DMM.

From R.G., one of the sources I saved when researching this circuit...

"Many if not most discrete transistor circuits are deliberately designed to make the specific transistor gain not matter by using feedback. This is in fact true with the Big Muff circuit. The input and output stages of the Big Muff are simple transistor gain stages and they do not contribute to the distortion unless they are badly, badly misbiased. The two distortion stages are set up as simple feedback clipping stages - in effect, operational amplifiers with diode clipping around them. They're imperfect opamps, true, but the overall effect is to mask the characteristics of the transistor stage in favor of showing off the characteristics of the diodes and caps in the feedback path."

Let me check some voltages on a couple of mine and I'll post back.

Use your DMM to check the voltage at the collectors of each transistor. With the flat-side of the silk-screened transistor graphic facing you, the collector is on the right. See if you're getting around 4.5v. If necessary, you could adjust the values of the resistors on the collectors to get to approximately 4.5v (never tried that myself - just a tip from the web).

If replacing the transistors with sockets and installing other transistors doesn't at least make the pedal work normally, you likely have a problem with one of the modded resistors - maybe a cold joint. If it does work normally, then it sounds like a transistor problem.

DMMs that can check transistors are pretty cheap, less than 10$US. I tend to buy a batch of several transistors, then weed out the bad ones using a DMM. That won't tell you if they're noisy, but it will tell you if one has abnormally low gain.

[EDIT] I forgot to add that if you did NOT add the 82K resistor from the base of Q2 to ground, don't expect to see 4.5v on Q2's collector. It'll actually be in the ~1.25v territory. I have no idea why EH left off this resistor in the 2nd schematic.

I'm having the exact same problem.. I started the pedal off this way and socketed the transistors (metal can 2N2222A's, tab facing the flat side of the outline) and at first it bypassed and the led lit but when switched on there was no sound.. I realized I had accidentally put in a pair of 8.2k's where the 82k's go, I corrected that and now it works but I'm not getting much volume or gain at all.. sounds like a low gain overdrive pedal at this point which is not what I was expecting after owning a bunch of different BMP's over the years. I have a few transistors from a green Sovtek BMP that I was going to toss out.. I'm not sure if the parts survived being removed from the old pcb. Would it be safe to try putting those in right now or would I have to adjust the resistors? also is there a good chance they would've survived being removed from the old pcb? could I have damaged something while having the wrong resistors in?

I talked to Jay and his worked well right away with this mod.. so I'm concerned I got a bad batch of 2N's, I've retouched every solder joint and have triple checked every component on the board.. all are correct at this point and I have no idea how to proceed

Yes, you can put in the other transistors no problem, and you shouldn't need to change anything else. They should have survived fine if the removal was done with care. Offhand, I don't see how the incorrect 8.2Ks could damage anything. Since you socketed the 2N2222As, why not test them?

thanks.. I just put the other ones in and there's a big difference in volume and the gain is definitely there though I'm not sure it's quite as much as the green muff those transistors came from. My guitar is in for repair and I had to use my bass so that could be throwing me off a bit here.

I'm pretty new to all of this so I'm not really sure how to properly measure the transistors.. I did a quick check yesterday with it set at 20v's DCV and got a bit over 4v's on one of the legs, nothing on the other and a very low amount on the third. If anyone can tell me if that's the way to do it or if not where I should set the MM and which leg is which I'll report back with the results for both sets of transistors

I got some advice to flip the 2N2222A's around and it worked! it's really loud, much louder and way more fuzz than with the transistors from the green muff.. I assume those would have to be biased with this circuit. Downside is it's pretty noisy at high levels but I can live with that

have you tried this yet andefeldt?

Haven't tried flipping them around.

I'll get some sockets and install them first. Then I'll try flipping transistors etc.

But why should they be flipped? They are still NPN transistors.

I've installed them like this:

The 2N5088's where installed with the flat side of the transistor parallel to the flat side of the drawing on the PCB. The 2N2222A's where installed with that little "tip on the can" down towards the parallel side of the drawing of the PCB. Isn't that how they're supposed to be installed? I just looked at the layout of the legs on the transistors and compared that with the orientation.

here's the link I was given for them.. http://aph.huji.ac.il/Microelectronic/E ... n2222a.pdf

I now have the tabs facing where the rounded part of a plastic transistor would go and the pedal now works

Just installed the transistors the other way around and now it works!

Only thing now is that I got more noise than before.

But thanks for the tip daydreamdelay!