Help with Bearhug compressor

[ljudsystem]

Hi guys

I need help with Pattons Bearhug: It only acts as a clean boost and doesn't compress the signal. Here's a pic of my build:


I used this layout:




I used a 2n7000 instead of of a bs170 but I can't seem to get the drain voltage down to 5 -5.5 V with the trimpot all the way down my multimeter reads 6.5 v.

[duck_arse]

...... sorry, got confused by that layout, with un-named transistor placings. we will need circuit dia for your version and voltage measures on all transistors, supply, etc.

does the drain voltage vary with the pot trimming?

[ljudsystem]

Sorry, the only schematic I could find is the one in the build doc pdf.



Here are my voltages:

Q1 (2N7000): D 6.5 V
                     S 6.6 V
                     G 6.5 V

Q2 (MPSA18): C 10.7 v
                      B 0.8 V
                      E 260 mV

Q3 (2N5457) all zero V

Btw I skipped the decay switch as you can see.

[ljudsystem]

Sorry heres a link to the build doc:

https://cdn.shopify.com/s/files/1/0022/3952/9069/files/Bear-Hug-V2-1.pdf?16138734983046189115

[duck_arse]

what's your supply voltage? what is the comp pot set to in your measures? there is some kind of problem at the 2N7000, there should be some vastly different voltages there. look for a short somewhere thereabouts. does the trimpot voltage vary with rotation?

[ljudsystem]

I scraped the tracks again but I still have the same problem.

My supply is 9V.

When I turn the trimpot CCW the drain goes from ca 13 to 6.5 V while gate and supply go from 6.5 to 0v

[duck_arse]

erm - if your supply is 9V, how come your posted Q2 collector is at 10V? and the drain gets to 13V? am I reading wrong, or are you writing wrong?

don't worry measuring at the gate, your meter will load and mess up the reading. measure at the trimpot wiper is good enough.

is D1 right way around?

[ljudsystem]

Weird, I was using a Boss adapter that said 9V on the label but when i measured it it read 13V so there's your explenation.

I tried it with another adapter and now i get 5.5 V at the drain. The compression is very subtle though, I can't really tell if it's working or not.

[ljudsystem]

Yes, D1 is the facing in the right direction btw.

[duck_arse]

your D4 is backwards.

[duck_arse]

also, there's a 10nF cap next the 47R [grrrr - no id's] that appears to be a row or two low.

[ljudsystem]

Well, now I'm embarrassed  I thought I dubble checked everything. Ok, thanks for the help.

[duck_arse]

Well, now I'm embarrassed 

nevermind that, does it work?

[ljudsystem]

I'm gonna try fix it this weekend. Haven't had time yet, kids and work you know. I'll let you know if it works.

[ljudsystem]

Ok, I fixed the cap and the diode. With compress on full I get a nice clean compressed tone. but when I roll back on the compression knob I get broken sounding clipping. I tried adjusting the trimmer but that didn't do anything.

[duck_arse]

so, voltages etc. photos etc. what does the trimpot wiper voltage do, etc.

[satriale]

I have a bearhug that I have spent a lot of time with, both messing around and playing. I believe the circuit clips if the compression doesn't kick in hard or fast enough on somewhat larger input signals and is most noticeable on low compression levels. Anyways, I found that the clipping went away on mine with the drain of Q1 (I'm using the stock BS170) biased around 7-7.2 instead of 5.5. Midwayfair had told me that 5.5 should give me a symmetrical rectification but my particular BS170 seemed to want the drain around 7.

[duck_arse]

yeah, I kinda think aiming at "a voltage" is the wrong idea, you probably should just adjust the bias for best sound across the most settings. each mosfet will bias at some different point.

and welcome, satriale.

[ljudsystem]

ok, here are my voltages:

Q1 (2n7000): D 7V (trimpot goes from 4v to 8.5v)
                     G 1V
                     S 170mV

Q2 (Mpsa18)  C 7V
                     B 0.6V
                     E 30mV

(Q3 all zero)

[antonis]

First of all, check for Q3 proper legs-socket firm placing..

P.S.
Is there any particular reason for Q3 to be the only socketed transistor..??

edit:
If Q1 indeed is 2N7000, it's OK..
If it's BS170, it should be flipped 180^o..