bearhug compressor problem

[1878]

Hello Peeps.

Just finished a Bearhug Compressor build from 1776. Lovely PCB, clear instructions etc... I have 2 problems though. Firstly, it works only as a boost, no compression. Secondly, I can't get bypass ?!?!

Regarding the bypass problem, I've tried a couple of switches & jacks. Same with each. Complete cut of signal.

Regarding the no compression, I changed the 2.2k to a 4.7k as I'm a single coil type of guy. Still no change.

I've taken some voltages on the off chance that someone could see a glaring problem.

9.3v going in.

BS170

S: 0
G: 0
D: 5.4

MPSA18

C: 6.6
B: 0.7
E: 0.2

2N5457

G: -0.3
S: 0
D: 0

Any help would be greatly appreciate.

Thanks.

[mth5044]

Posting a link to your project so we have an idea what you're talking about is helpful.

http://1776effects.com/wp-content/uploads/2015/03/Bear-Hug-V2-1.pdf

No bypass sounds like a wiring problem, could you post pictures of how you're doing it?

[1878]

No probs...

I don't have an image account anywhere at the moment but it's wired exactly like this...

http://fuzzcentral.ssguitar.com/faq/switchwiringnpn.gif

I wired it this way on a 3PDT initially, then a DPDT minus the LED.

[GGBB]

No probs...

I don't have an image account anywhere at the moment but it's wired exactly like this...

http://fuzzcentral.ssguitar.com/faq/switchwiringnpn.gif

I wired it this way on a 3PDT initially, then a DPDT minus the LED.

If you wired it exactly that way, and didn't make any mistakes, you would have bypass, unless the switch is defective. If the switch is not defective, then you made a mistake. Usually someone about now would ask you to post big sharp close-up images of your work so that we can try to spot any problems, but seeing as you don't have an image hosting account, all I can suggest is go over what you've done very carefully and check that that switch isn't defective. Or get an image hosting account.

[1878]

Just checked again & it's wired as the diagram. It's getting a bit late here & I'm in work for 6.00 a.m, but I'll register with an image host tomorrow & post some pics.

[1878]

One problem solved. Just quickly wired it up to a large DPDT toggle switch & it worked in bypass !! I then rewired the 3PDT & again, no bypass.

I have 2 dodgy switches.

[Transmogrifox]

Either that or you have the 3PDT switch rotated 90 degrees from the layout.  It's easy to get confused with these because the matrix of solder lugs makes a square that looks the same either way you rotate it.

Try rotating it 90 degrees and solder per layout and I would be willing to bet it works.

[1878]

Hastily taken photo from early this morning. Everything SEEMS ok. Transistors are in the right place, electrolytic caps in the right way.

Definitely dodgy switches. Tried them on a working pedal.

Thanks.

[midwayfair]

Your BS170 gate is getting 0V. Does that change when you turn the trimpot? If it doesn't, reflow your solder joints on all parts connected to the gate and to Vb (including the trimpot).

Also, put the 4.7K back to 2.2K. There should be no need to change that resistor in the new version, as the trimpot allows you to adjust the gate/drain voltage.

[1878]

Thanks for the reply Jon. I've reflowed all solder joints. Whilst doing so, I realised the 22k resistor was the wrong value !?!? I replaced it with the correct value & I have different readings on the transistors.

9.3v going in

BS170

S: 3.18
G: 0.53
D: 5.3

MPSA18

C: 7.5
B: 0.7
E: 0.2

2N5457

G: 1.46
S: 0
D: 0.13

Unfortunately, it still doesn't compress. The boost still works, but the 1k comp pot & the switch do nothing. I have a feeling it's something really simple but it's eluding me at present.

Thanks again.

[midwayfair]

Again, does your trimpot change the gate value when you turn it? It's a MOSFET, not a FET; your gate should not be near ground, it should be almost equal to or just below the drain voltage.

If you can get the gate voltage closer to 5V with your drain voltage staying close to the same, then you can start worrying about the compression circuit. You can test it by audio probing the collector of Q2, and then using your multimeter to check if there's voltage appearing on the JFET's gate when you play a chord on the guitar and the compression knob is turned up. You can then measure the resistance across the FET (gate to ground) to see if the resistance climbs to a few kiloOhms.

[samhay]

The gate is held up by a 10M resistor, which will be seriously loaded down by just about any DMM. I wouldn't be too worried about the gate voltage if the circuit passes / amplifies signal cleanly.

OP - any chance you have a bad J-FET (where did you get it from)?

[midwayfair]

The gate is held up by a 10M resistor, which will be seriously loaded down by just about any DMM.

Well, then he can bias by ear, but my cheapo multimeter with 10M impedance has no trouble measuring 5V on the gate of a perfectly functional Bearhug PCB I have on my desk. I still need to know if changing his trimpot has any effect, because if it doesn't, then his dry path isn't working and it's pointless to speculate about what might be wrong on the envelope side.

[samhay]

I wondered that too, but the OP does say that "it works only as a boost" and the drain voltage looks reasonable.

[1878]

Right. Just managed to get a bit of time without my 3 y.o boy asking, 'Are you making noise Daddy ?? Can I help ??'

The gate of the BS170 ranges from 0v to 0.75v fully clockwise.

Strange thing happened though. I plugged the power supply in and it started smoking. Didn't see exactly where it was coming from, but it looked like the pair of 1N914's. I plugged my guitar in & it works as before. Boost no compression. I can't see any discolouration on any of the components or board under a magnifying glass, but it smells a bit iffy.

[mth5044]

Check to see if your pots are still functional as they can sometimes release some magic gas.