CMATMOD Brownie (BSIAB II) Low Volume

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Hey guys. I read through the whole debugging page, but I'm still completely lost. I'll get right to it: I'm not building my own BSIAB II, although I might if it turns out I somehow irreparably damaged the circuitboard on my Brownie. If I do have to rebuild it from scratch, I guess I'm in the right place.

I changed the transistors in my Brownie to NTE457's, the local electronics store equivalent of a 2N5457. I put these in Q4 and Q5.

It was working great. No problems and playing a lot over several days. Perfect.

Today, I had some sockets come in. I figured it'd make changing transistors easier...nope. I ended up taking them out, and soldering the transistors back in the normal way. I think I just clipped the legs off the sockets and soldered the legs of the transistors right onto those...I know, lazy.

I worried that I might've applied too much heat to the board while I was doing all this as I wasn't being quick or sharp with the soldering iron. However, I checked carefully and I do not have any solder bridges. The points on the back of the board are all clean. On the top of the board where the components are, there's probably more solder than there needs to be, but the joints are solid and there are no bridges either.

Now I'm having some issues. Very, very low volume. It seems barely at unity with all the knobs dimed.

I have no idea how to test transistors. But I tried. I just set my multimeter to Ohms, and found that testing the two outside legs of each transistor gave the same readings either way. I read that this is what they're supposed to do. The readings on all the transistors varied a lot, but on each one, it was the same reading whether I had the black or red probe on either of the outside legs of the transistor.

However, on Q4, in one direction I'm getting a really high reading, more than twice as high as all the other transistors (like 1200 ohms or something), and when I reverse it, it gives me a negative reading, around -300 ohms.

This is the only diagnostic criteria I have, if it can qualify as diagnostic criteria. The ONLY other mod I did was put a 100v .0010mf capacitor in place of where one of the .0022 capacitors used to be. I can't imagine that affected anything. I even tried clipping it just in case, but that proved to not affect anything.

I tried replacing the transistor, thinking maybe I just accidentally damaged that one. Put the old original transistor back in, it worked like a charm, and I thought I had it!

...until about 30 seconds into playing it, it started crackling a bit, and then the volume dropped. Back to the same very low volume it was at when I initially ran into the problem. And the reading on the transistor is doing the exact same thing (it was doing it before and after things went wrong again).

So...

1) Weird reading on Q4 transistor (others seem "normal" as far as I know)
2) Replacing the Q4 transistor worked, but only for a very short time before crackling/cutting out, and then finally settling at a very, very low volume.

It sounds okay with all the knobs dimed. So in a sense it still works. But obviously this is not how I want to use the pedal, and something is very wrong.

Any ideas?

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Scratch that...with the knobs dimed, it gradually started losing more and more volume. Went from being louder than unity to quieter than unity to fizzling out to almost nothing.

I'll repeat: only mods I attempted were changing the transistors, removing one tone cap and replacing one tone cap. No issues previously, but today ran into major problems.

Given that, is it possible I just fried the circuitboard somehow while trying to change the transistors? I looked at all the adjacent components and I didn't hit anything with the soldering iron except for a little fraying on the blue plastic of the trimpot where the iron hit it lightly. Transistors were working just fine for several days with zero issues, but attempting to put the sockets in today, removing them, then putting the transistor back in....was never the same after it.

I have a hard time believing I was so heavy handed with the iron that I fried the board, but is something like that possible?

I just got excited, re-touched every joint for the transistor, and it was working great...but then, AGAIN, after about 30 seconds, major volume drop, losing gain, fizzling out. And the transistor is still having that weird reading where it's negative resistance on one orientation, and really high resistance on the other orientation (black probe touching left leg in one case, black probe touching right leg in the other).

[PRR]

Welcome.

Don't "touch" joints. LOOK at them. SEE the solder has wetted both/all leads.

Since it was OK, and you tinkered, and now it is not-OK, odds are that you made a good joint bad "somehow". It happens. A lot.

[Slight Return]

Welcome.

Don't "touch" joints. LOOK at them. SEE the solder has wetted both/all leads.

Since it was OK, and you tinkered, and now it is not-OK, odds are that you made a good joint bad "somehow". It happens. A lot.

I'm gonna try wicking out all the solder so I can put the legs through the holes in the PCB and solder them properly. I didn't do that the first time and it was okay but maybe it'll help.

I'll redo it the best I can. If it'll help I'll put some pictures up of the solder job for any critique.

[slashandburn]

I think your in the right place.    Good thing Paul got here first before I could say "reflow, reflow, reflow".   Follow his advice and use your eyes before you start hitting the problem areas with more heat.

If you can't see any obvious cold solder joints or shorts I'd hit it with an audio probe if you have one.   Cheap and easy to put one together and not much more of a ball ache to use than a multimeter.

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What a day!

I spent today removing the 3 transistors I plan on replacing, and thoroughly cleaning out the eyelets/through-holes. My new transistors (MPF102) have not arrived yet. I plan on using all MPF102's and running it at 18v, which means pulling the 3 J201's originally in Q3, Q4 and Q5.

What a nightmare. No matter what I tried, I couldn't seem to wick the solder out of the through-holes. I don't have any braid at the moment, but I do have plenty of stranded wire, so I just made my own. A little flux, stranded wire...it got all the excess off the PCB around the through-holes, but it couldn't get the solder out of the middle.

I even ran it through the holes carefully with some pliers while the solder was molten, and even that didn't manage to wick all the solder out. I would pull the wire out and the hole would still be plugged with solder.

I damaged one of the through-holes in an attempt to push a remnant leg of a transistor that I cut off...with a .030" guitar string. I used a bit too much force at the wrong angle, and off came part of the eyelet. The flanged part...about half of it. On the bottom of the PCB. The shaft going through the middle seems to be entirely in tact and on top where the transistor mounts it looks OK. But boy was I kicking myself after that. I pushed forward nonetheless.

I'm hoping that it will still function but if I have to repair that, I guess I'll have to learn that too. That was a bit of a forceful method, although it worked beautifully on the first 6 through-holes. I was gentler on those and only gently pushed the .030" string through the hole, and even found that with the addition of flux, the string was acting as a solder wick. When I got to Q3 I was overconfident, and that's when I damaged the eyelet. I pushed way too hard trying to force the string to eject the transistor leg remnant and residual solder plugging the hole, but I guess I was actually pushing on the flange of the eyelet. And off it came.

After all this? I had an epiphany. One that I wished I'd had earlier. A straw.

I simply heated up the through-hole/eyelets, one at a time, and forcefully blew through a straw when the solder was molten. Worked like a charm. Held the PCB up to good lighting, and could see light coming clear through all the through-holes. Finally.

The parts are so light, even if a long leg of a transistor/cap/etc. was left in the through-hole, I think this straw method would have worked just fine. I did check and made sure that no beads of solder that came off when I blew on the eyelets contacted anything else. It was such a trivial amount of solder that I could hardly find any of the pieces that blew off anyway. They were at the bottom of the metal case of the pedal.

So now I have open holes ready to accept my 3 new transistors that are on the way....I'm just hoping I don't have to replace the eyelet or do some other repair in order to get this thing to work.

The whole endeavor took well over several hours...and then I realized the power of the straw. I was about to go into the garage and try using compressed air, and then I was just like, "Wait a second..."

I'll have to look up how to make (and use) an audio probe. I have so much to learn.

I am determined to get this pedal working, though. Thanks for the replies, guys, and I will keep you posted on my progress. With any luck I'll be able to get this thing working and then record a video (with decent audio) demoing the mods to the pedal.

[slashandburn]

Good luck with it! A solder sucker would be a safer alternative to a straw. That molten solder you're blowing through the hole could go anywhere and cause shorts (or worse still, splashback in your face). 

An audio probe is basically half a guitar cable, solder a capacitor and Croc clip to one end and plug the other end into your amp. Croc clip to ground, use the cap to touch the pads on the pcb and listen. Follow the signal path and listen for where it gets weaker or lost altogether..   The hard bit is strumming the guitar while you do this. I tend to lay it in the floor and use my foot.

http://www.diystompboxes.com/wiki/index.php?title=Debugging

Section two on this page should have you covered if you go ahead and build one.

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Would you recommend any solder suckers in particular or does it not make a difference what brand/quality you get?

So...success! Kind of. The volume is sounding fine now. I put J113 transistors in place of all the old ones, except the Q1 and Q2 MPF102's. I have some MPF102's coming in the mail and I might try those now that I'm more confident in swapping parts.

Only thing is that when I have the gain turned all the way up, and a little less, it feeds back. It does this even when the guitar volume is completely rolled off.

Any ideas what that could be? I'm able to get rid of this "howling" by adjusting the bias with the internal trimpot. Just curious what that means, and if that's a normal occurrence.

Anyway, just in time for band practice! I'm not sure how I feel about the J113's yet. I am definitely a fan of clipping one .0022uF cap, and replacing the other one with a .0010uF. When I had MPF102's in Q1 and Q2, then NTE457's in Q4 and Q5, and a J201 in Q3, I quite liked the sound, and might end up going back to that.

I feel much better now that I'm not worried that I'll ruin the circuit board by experimenting (carefully).

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Scratch that....whole thing just cut out again. Not sure what happened. Seemed to be working fine. Sounded perfect. Then the volume dropped off again. And just standalone, it seems to be making an intermittent popping sound.

This time, it seemed to happen after kicking on a Fuzz Face. Could this possibly do anything to create issues, stacking pedals like that? I wouldn't think so...just seems I have the same issue as before, where the pedal is functioning fine for a while, then drops off.

Either way, that's the pattern...it works fine, everything sounds great and does what I'd expect it to do...then after a few minutes of being on, it just craps out. Loses all volume and gain and is about 5% as loud as it's supposed to be.

Any thoughts? I'll get around to making that audio probe as soon as I can. But if anyone has an idea what this kind of problem could be indicative of....just seems very strange.

Since I only messed around with the transistors I figure the problem has to be there...but I'm fearing that I damaged the board, as the solder job on the transistors looks perfectly fine to me. Can't understand what would cause it to work perfect for several minutes, but then splutter out seemingly out of nowhere. 

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All right guys! I didn't make an audio probe yet, but I used my multimeter to test the transistors, per the Debugging page recommendations.

I'm very new to all this, but I know transistors have Drain, Source, and Gate legs...and that *all* of them are supposed to have some kind of voltage.

I found that in Q2, Q3, and Q4, the topmost leg on each was reading out at 0 volts. I simply held the black probe from my multimeter on the ground tab of one of the jacks, and used the red probe to touch each leg of each transistor.

I went over the PCB and cleaned up any stray bits of solder. No solder was bridging anything, but I cleaned up any flecks on the PCB regardless.

I also put some electrical tape over each pot, as I suspected that they might be touching points on the PCB when the nuts are threaded on. They do seem very close to the PCB. So electrical tape to insulate them, just in case.

Then I re-flowed not only each of the offending legs reading 0.0 volts, but also the leads going to the jacks on the PCB. I forgot that I didn't know I could simply bend the pots out of the way to access the PCB to solder, and had tried to desolder the pots from the PCB. Only a couple spots looked a little anemic, but I added some more solder to those to fill them out.

Also, by fiddling around with the board so much, the wire for 9v power going to the PCB fell off, and so did one of the leads connecting the input jack and the PCB. I re-soldered those on generously and got as good and strong a joint as I could afford.

By some miracle, I tested again, and it worked.

Put a 9v battery in the clip and probed the transistors again. This time, *each and every leg* was getting a voltage reading. None of the legs on any of the transistors were reading out at 0 volts. Previously, when I was having the "fading out" volume and gain issue, I was getting wonky readings on some of the transistors. Now, while I have no idea what the voltage readings mean, I can see that each leg of each transistor has voltage.

I suppose that's a good thing

I was still getting a "howling" feeding back with the gain and treble all the way up. At first I adjusted the trimpot to re-bias, and that fixed it. I simply turned the trimpot with the guitar plugged in and the pedal on, and listened until the howling went away.

Then I had a thought. There are two .0022uF caps on the circuit. Why not try moving the .001uF cap to the other position? I remembered reading something where someone said that the .0010uF cap worked best on *one* of the two positions for those tone caps.

I don't understand it, but when I moved the .0010uF cap from one point on the PCB to the next, and left the other location empty...it worked perfectly. I was then able to re-bias with the trimpot and with the gain and tone all the way up, there was NO howling noise anywhere, no matter where I biased it.

I played for about 30 minutes just now. Stacked with OCD, and my Fuzz Face, and, *knock on wood*....no issues. Sounds AMAZING.

I've also decided that even though I have MPF102 transistors coming in, this project scared me too much! I will save those transistors for a potential BSIAB II build from scratch. I would love to make one of those myself, as these are great sounding pedals...and then I can try the mods shared by people in this community, without risking ruining my Brownie that I paid a good chunk of change for.

I'll play some more tomorrow. I hope it's safe to say that if my pedal works perfectly for a few hours of continuous running, it should be good to go. Maybe I can put a clip up of the mods I did and how they sound.

Thanks for the help, guys. I do have a DS-1 lying around that is broken, and while I've been learning, I might as well try to fix that one while I'm at it. I'm keen on making an audio probe and seeing if I can build up some experience with working on guitar effect PCBs.

Thanks again! 3AM over here and I can finally sleep now that my Brownie is working :p My Fulltone OCD isn't the only OCD in my house right now....lol.

[bluebunny]

Put a 9v battery in the clip and probed the transistors again.

Does the famous debugging thread not say to connect a battery?  The clue is in asking for the battery voltage right at the beginning.  No volts in = no volts out. 

I suppose that's a good thing

"A learning opportunity."  Initiation complete. 

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Idk why I mentioned the 9v battery like that...I did use one from the beginning, otherwise no current! I followed the instructions from the very beginning, starting with testing the battery to make sure it had some juice in it, then snapped it onto the battery clip in the pedal and started testing the transistor leads.

I'm feeling great after getting the Brownie up and running. I like it a lot more with the lower gain transistors. I do have a broken DS-1 pedal that my friend left over here that might turn into a little project. It is not working at all. Someone plugged an 18v power supply into it and it fried it. Blew the diode which I'm assuming is there to protect the board from exactly what happened to it.

An audio probe seems like the perfect tool for the broken DS-1. I'm excited to get one going and see if I can figure out what's wrong with that thing, and get it working again.

It would be nice to be able to learn on something that I don't care about. I have a lot invested in the Brownie and especially it being a brand new pedal for me, the stress of having it not functioning was a bit much for me to deal with.

But man! What a harrowing experience. I guess the areas that were originally getting 0 volts were just cold solder joints. Maybe I just did them too quickly for fear of causing damage. Dabbing a little flux on each terminal and then holding the iron against them for several seconds seems to have woken things up.

I did not touch Q1 and Q2 to my knowledge, but since Q2 was getting 0 volts on one leg as well, I decided to re-flow the joint there too, just in case. And it did look like it could use it.

Amazing how many issues a simple cold joint can cause.

Initiation complete indeed

[duck_arse]

it be a bit late now to ask, but can you please post at least a link to the circuit you are working from/to, the board layout as well, if you like, and some photos of the board you have built, including the off-board parts? besides we just like to look, there might be "some things" that we can see might help you on your next build.

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I guess not too late...played again today and it's blatty and weird sounding. Horrible.

I get home to try it out, and now it is not working at all. All it's doing is very loud crackling when I turn the pedal on, and no other sound at all. Kill me -__-

http://guitarpedalbuilders.blogspot.com/2012/06/bsiab-2-ii-brown-sound-in-box-2.html

There's the schematic...as I understand the CMATMOD Brownie is a licensed BSIAB II. So the schematic should be the same. FYI, I have *no* idea, not even a tiny one, about how to read a schematic. I've got a ton of homework to do with that.

I changed transistors Q3, Q4, and Q5, replacing them (for the time being) with J113's instead of J201's that were originally in there. I also put a .0010uF cap in place of the original .0022uF cap. You can see it in the picture below...it's the green capacitor, the only green one on the board. It looks quite out of place :p

My only intention was to change those transistors and then the cap, that's it...so I'm still running into problems and not sure why.

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Update. Hopefully this info will be helpful for anyone who can potentially help me with saving this pedal.

http://www.generalguitargadgets.com/pdf/ggg_bsiab2_instruct.pdf

According to that picture, the BSIAB II should have about the following voltages:

Q1:

Gate.......0v
Source....0.95v
Drain......4.5v

Q2:

Gate.......3.8v
Source....4.5v
Drain......8.0v

Q3:

Gate.......0.3v
Source....0.75v
Drain......4.3v

Q4:

Gate.......3.8v
Source....4.3v
Drain......8.0v

Q5:

Gate.......0.5v
Source....0.9v
Drain......3.4v

I just hooked a 9v battery up to my pedal, put a jack in the input, turned it on, and tested each transistor with my multimeter. Black probe went on the ground from the jack, and used the red on each individual leg of the transistor. Hopefully I'm doing this right. My 9v battery is reading out at 7.7v. I am running the pedal for playing use with an 18 volt isolated power supply, FWIW. Here's what I got:


Q1:

Gate.......0v
Source....2.01v
Drain......5.08v

Q2:

Gate.......2.26v
Source....5.06v
Drain......6.7v

Q3:

Gate.......0.1v
Source....0.99v
Drain......4.11v

Q4:

Gate.......2.2v
Source....4.1v
Drain......6.66v

Q5:

Gate.......0.1v
Source....0.81v
Drain......0.85v

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Made an audio probe just now. I assemble and wind my own custom pickups, and I had an old extra one lying around, so I had a thought:

Just wire the pickup directly to a Switchcraft jack, and play music on my phone next to the pickup to get consistent audio while I'm free to probe with the other hand. I had two spare Switchcraft jacks hanging around so I just wired everything to those and plugged the jacks right in.

Seems to be working very well and is extremely compact, and my other hand is free to probe while the music from my phone plays next to the pickup. It only has to be next to it, not on top of it.



I only had a .018uF cap lying around. I'll try to get a 0.1uF cap tomorrow.

I've been probing around, and this method does work, from what I can tell...but I don't know what I'm looking for. Should EVERY leg of EVERY single component on the board produce clear sound, just with different tones?

Because I have quite a few spots that sound either extremely distorted and messed up and awful, or are making no noise at all. Is the general idea to look at the schematic and simply follow the board from beginning to end, and your problem is indicated by the very first component that you find "failure" with?

I need to know what "failure" means to determine anything from this test. Some resistors I probed made it sound very good...very clear, clean, just like an amplified version of what my phone was playing. Other ones distort, as I'd expect, but other points make no noise at all, like some of the legs of the transistors.

The probe makes sense to me now. I'm quite happy with this method. I'd take a pic of the whole setup with the phone and all, but....I need my phone to take pictures.

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OK guys. Hopefully this will help. I really need help here and am at a huge loss. I edited this in Paint to highlight what I've traced with the probe so far, and where I ran into my first component that I think might not work.

TL;DR: I started probing at the Input. The first resistor legs both get audio and are the first connections after Input. One of these resistors gets no audio on one of the legs. That resistor is connected to a capacitor, and the capacitor is getting no audio signal either. The other resistor that works goes to Q1. That resistor and Q1 get audio on all legs. Q1 Drain connects to Q2 source. Q2 Gate and Source get audio. Q2 Drain has no signal. The transistors that Q2 Drain lead to also have no signal on any of their legs.

[Slowpoke101]

From your voltages;
Get a new 9V battery. Then have a very close look at Q5. You may have a short between the Source and the Drain legs of the transistor or that transistor is faulty.
It is possible that when you soldered it in some solder wicked up the legs and caused a short.

[Slight Return]

From your voltages;
Get a new 9V battery. Then have a very close look at Q5. You may have a short between the Source and the Drain legs of the transistor or that transistor is faulty.
It is possible that when you soldered it in some solder wicked up the legs and caused a short.

Image on the right is the old transistor. Soldered a new one in, and that one is on the left in the picture.

I just clipped the legs off the old one and soldered this one down, without cleaning the through-holes and inserting the new transistor. I tried my best to be careful not to solder too far up the legs or to bridge solder between them.

Checked with audio probe...nothing. Checked with voltmeter: same exact readings as before. Does anything look blatantly wrong with the way Q5 is soldered on? I know I left the legs quite long but I just wanted to see if a new transistor would change anything...apparently not.

From probing, I did discover issues earlier in the circuit. If the signal is getting cut off somehow very early in the circuit, namely at one of the first resistors after the Input, and at Q2, then naturally the later transistors will not be getting the full power they need, correct?

[Slowpoke101]

It looks to be soldered OK, no problems that I could see. However, is there a reason for using J113 FETs? The circuit is really intended to use J201 or 2N5457 types - if you can find real ones. Good ones are getting very rare.
From personal experience I found that the 2N5457 FETs work very well in the BSIAB II. The effect may not work very well with J113s.
Back to Q5 for a moment. The trimpot is initially used to set the Q5 Drain voltage to 4.5 volts, it is further adjusted for best sound when the effect is working. Generally set it to 4.5 volts and then forget about it. Measure the voltages on all 3 pins of the trimpot. One pin will be close to the voltage of the battery and the other two (which are connected) should be adjustable.
When probing with your audio probe you should find an amplified signal (which will distort the further along you go through the circuit) on Q1 Drain (Q2 Source), Q3 Drain (Q4 Source) and then Q5 Drain (greatly amplified compared to the input signal). The signal should then go off to the tone and volume circuits.
See what you find.

**EDIT: I really should mention that the 4.5 volt setting must be done with the battery (or power supply) running at 9 volts. It is meant to be set at half the supply voltage otherwise Q5 will not be biased correctly.