Bronx Cheer Not Cheering

[Jamforthelamb]

Hey Everyone.
I recently built a Bronx Cheer off of this layout...

I used all the called for components (I had to make a 22k resistor out of 2 10's and a 2.2), and doubled checked my diode orientation, and soldering. I'm not getting the cool envelope effects, only a bit of fuzz. Any idea what could be wrong ?

Thanks,
JFTL

[tcobretti]

If it sounds like a fuzz pedal but with no "bronx" weirdness, the first thing I would do is check the diodes to make sure they are lined up correctly.  Then I would verify with a Multimeter that all the traces are broken.  Then I would visually check all the strips on the veroboard to make sure there isn't solder bridging the gap.

When I have problems with vero, 90% of the time it's a problem with sloppy soldering.

Hope you like the pedal, I built mine from this layout and it is pretty cool.

[Jamforthelamb]

K,
I did all that, and everything still checks out good.
What else could it be ?

Thanks,
JFTL

[tcobretti]

Ok, the one other thing I can think of is to try turning your guitar down.  The circuit is extremely sensitive to input volumes, and seems to work best with the guitar's volume knob at about half way up.

If that doesn't work, I'd start running thru the debugging routine posted here:

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[trevize]

so if you use humbuckers or have non true bypass effects before the bronx cheer use a small audio transformer as in the original schematic

[Jamforthelamb]

Ok,
I ran a small audio transformer (not sure of the value) in front of it. No change.
I jumpered up a volume pot (hadn't used one before). No change.

So now I'm going by the debugging page.

I have checked the pinout for the MPSA13, and it is orientated correctly. Also I have it socketed so I have tried it both way. One way I get the fuzz with no envelope effects, the other way no sound.

The only substitution I've made is two 10k resistors, and a 2.2k, in series to for 22k resistor.

Here are my Vohm meter readings.

Q1
C: 1.6
B: 1.4
E: 0.0

I checked the diodes from left to right on the layout.

D1:
A: 1.5
K: 1.6

D2:
A: 1.6
K: 1.5

D3:
A: 1.6
K: 1.5

Thanks,
JFTL

[tcobretti]

I'll DMM mine tomorrow to compare voltages, but Q1 doesn't look right to me.

Also, the volume control I was suggesting you change is the one in your guitar.

[Jamforthelamb]

Ok, cool! I appreciate it!

Yeah, I know, I was just trying the volume pot to see if it changed anything at all. Changing the instrument volume didn't change anything either.

Thanks!
JFTL

[Tim Escobedo]

Most likely a simple mistake. I assume those little squares on the layout man the conductor trace is broken?

[Jamforthelamb]

Hey Tim,
Love all your circuits!

Yes, the traces are cut like shown in the layout.

Thanks,
JFTL

[tcobretti]

batt measures 9.4v

Q1
1.20
1.07
0.00

I also checked the diodes from L to R.  K=cathode A=anode

D1
A 1.06
K 1.2

D2
A 1.13
K 1.06

D3
A 1.2
K 1.13

I'd guess theres a problem between the battery and collector of Q1.

[Jamforthelamb]

OK,
I re-flowed all the solder joints for the resistor cluster I used to make the 22kohm resistor.
I also replaced the MPSA13 with a fresh one. The numbers pretty much match yours now, but I'm still not getting much "cheering". The only time I can get this to sound like it's working is running an old Casio Keyboard through it, into a little practice amp. I've tried a couple of different guitars to no avail.

Here are my new readings.

Batt: 9.1

Q1:
C: 1.2
B: 1.08
E: 0.0

D1:
A: 1.08
K: 1.2

D2:
A: 1.14
K: 1.08

D3:
A: 1.2
K: 1.13

Thanks,
JFTL

[tcobretti]

Well, I think the only thing left might be audio-probing it to check the signal path.

Have you tried it thru a different amp?

[Jamforthelamb]

I have run it through PC speakers, my PodXT with headphones, my roland digital recorder, and my little practice amp all with pretty much the same results.

[rocket]

I had the same problem but I used a different transistor (BC516 or 517), which might have less gain. I ended up adding one more diode/capacitor pair in series to the others and also making some capacitor values switchable - it cheers now.

[Jamforthelamb]

Well, I ended up throwing in the towel (for now), and re-using the board to make a 5th Gear Overdrive because it has a very simliar setup
.
Thanks for the tips though, I didn't breadboard this one to make sure I had it right before building, so I will likely breadboard it up with your suggestions before I have another go at it.

Thanks!
JFTL

[chemosis]

I had the same problem. I never got any envelope effects. just fuzz. I did it on a breadboard with no transformer.i didn't have a transformer and was told I didn't need one as long as my input volume was low enough

[garcho]

Hi there, wow, 13 years since the last post...

You don't need the transformer IF you're going directly from your pickups to the input of the Bronx Cheer. If you want to know why, there's plenty written about it, because it's somewhat the same phenomenon in other more well known fuzz pedals.

The diodes and caps to ground are key here, double, triple check everything there. This is a very simple circuit, as long as you give yourself room on the breadboard to make sure the feedback loop from collector to base is done right.

Did you mess with the switch at all?

I made my own version of the Bronx Cheer, the Scotch Bonnet: