Bearhug Debug

[Kipper4]

And I'm not getting any volume out of it. I thought it would give me a little boost for some reason.
The bypassed guitar is louder. Is this what was expected?

[midwayfair]

And I'm not getting any volume out of it. I thought it would give me a little boost for some reason.
The bypassed guitar is louder. Is this what was expected?

V1 isn't nearly as much boost as V2, but it'll still be about twice as loud (or more) as bypassed on lower compression settings.

Turn down the compression knob. Still not getting above unity?

Did you use 4.7K on Q1's drain, or 2.2K?

EDIT: I think it might help if you breadboard the first stage, the MOSFET booster part. You can use a 470R in place of Q3 (from the 47uF cap to ground).

[Kipper4]

Hi Jon
I used a 4k7 not the 2k2.
Just so I'm clear build the MOSFET booster that finishes after the 10nf and replace the q3 with a 470 to ground after the 47uf cap right.
Thanks

[bluebunny]

Here's the booster part:

  (Check out Jack's project page here - great little booster, btw!)

If you take out the 10nF that leads out to the MPSA18, then you're pretty much left with Jack's booster circuit, except that the gain control has been replaced by the 2N5457 JFET in Jon's circuit.  You could whip that out and replace temporarily with a small pot, just to check out the booster functionality.

[Kipper4]

I probed the booster section and im getting good signal at
the gate
the source
and initially the drain which quickly fade to practically no volume
i'm gonna whip out the 100pf and replace it and see if it make a differance.
the reason i say this is if i breach the grate drain connections i get a very loud signal and i suspect a poor qaulity 100pf
could this be it?

I'll build jacks booster later too just to try it. thanks Mark

[Kipper4]

Nope thats another fail.
This mosfet is going off bias very quickly.

[midwayfair]

I'll build jacks booster later too just to try it. thanks Mark

The reason I'm suggesting breadboarding it is because you've had the same problems twice now with two builds. Breadboarding it would allow you to remove and replace parts to determine (a) if something is wrong with some of your components or (b) if somehow a connection has been improperly made on both builds. If you breadboard the booster half and it works, then it's b. If you breadboard the booster half and it doesn't work, then it might be a.

Also, I'll PM you in a second.

[Kipper4]

i built jacks booster on a left over piece of perf and got pretty much the same results as found in the bearhug
ie a horrid buzzing while the mosfet settles then its a bit splatty which suggest to me its not biased right or the mosfet is blown.
The upside it doesnt loose volume or die on me but is unusable because it breaks up so badly.
I thought turn down the guitar signal. That didnt clean it up
turn down the gain pot. remained the same horrid break up just less volume.
i've got a few BS170s i havent tried yet (4) but they were all stored in the same bag so i suspect if ones bad then they all will be.
I'm getting closer
Thanks for all the help guys
Rich

[Kipper4]

i tried all the other BS170s and one sounds worse than the others but all seem to work despite the horrid buzz.
Sheesh this bosster has some serious gain.
Where too now guys any ideas?

[samhay]

Did you check the pin out? - BS170s and 2N700s are conveniently opposite to each other.

[Kipper4]

I cant think of a reason why the mosfet would become unbiased.

[samhay]

It sounds a bit like a cap charging and then causing a nuisance of itself. I don't think it will cause the symptoms you describe, but one other thing to try is the Zener - are you sure you have it the right way round?

You can test whether your MOSFETs are dead by making a very simple switch on a breadboard (it will work fine with 9V) -
https://www.google.co.uk/search?q=mosfet+led+switch&safe=off&client=firefox-a&hs=hs8&rls=org.mozilla:en-GB:official&source=lnms&tbm=isch&sa=X&ei=VkMSUurKAsbF7AbtzIHACw&ved=0CAcQ_AUoAQ&biw=1354&bih=890#facrc=_&imgdii=_&imgrc=1bJRXJSUZ9p2oM%3A%3BunMGhYRd5nLf2M%3Bhttp%253A%252F%252Fbrunningsoftware.co.uk%252FPictures%252FU-fig10.jpg%3Bhttp%253A%252F%252Fwww.edaboard.com%252Fthread244743.html%3B199%3B284

[Kipper4]

the zener has its cathode ( the end with the stripe on it IIRC) pointing to the gate

from source to gate

[bluebunny]

Did you check the pin out? - BS170s and 2N700s are conveniently opposite to each other.

If you build Jack's booster roughly following the topology of the schematic (9V "up", GDN "down), then a BS170 would "face" left, but a 2N7000 would face right.

I cant think of a reason why the mosfet would become unbiased.

Me neither.  Perhaps you need some anti-static bags for your MOSFETs?   

the zener has its cathode ( the end with the stripe on it IIRC) pointing to the gate

Yep, sounds right.  Sure it's a zener?  Daft question...   

Wanna see you fix this, mate.  I've built both, and both do their respective jobs brilliantly.  Hate to see you miss out!   

[Kipper4]

Did i make a booboo because i notice that the top left hand corner 10ufs cap anode  is not actually grounded in the layout

seen here

PDF: https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Bearhug%20layout.pdf

should i have made a connection between the two grounds between the switch 2 position and the uppermost  4148  diodes cathode?

[Kipper4]

When i zoom right in now i can see the white connection behind the resistor and 22k and the diode cathode brb.
Switches the iron on.

[bluebunny]

Good spot, Rich!  Yeah, you should be able to follow that white ground trace all the way from the top-left, across to the right, under the 22K (and forming one of the switch contacts), then down the right-hand side, before it heads west again (not forgetting the little return detour to the JFET).

[Kipper4]

Panic over it works a treat now and after only a few seconds trial i love it already.
Sorry guys my mistake.

[midwayfair]

Yay! It's working! But, um, I'm confused: What happened in the other layouts and the booster that your MOSFETs were distorting there? 

[Kipper4]

All the noise on start up is gone. It no longer sounds Dark and its got some serious squish if i want it.
Cracking design Jon
And guys Thanks for all the help over the last few days.
I dont like to be beaten.