BSIAB II noise (hum, hiss)

[nooneknows]

Hi,
I've just built a BSIAB2 , it works, the sound is awesome (although a bit too bright), but the circuit is really really noisy, much more than I expected.
I knew it could be a bit noisy but I didn't expect it so much, anyway this is a picture of my build:



I could shorten a bit the wires but I don't think I can go very far.
I' don't see ground loops as far as I can observe, there is just one ground wire and it goes to the input jack.

Any idea about? I was thinking about filtering a bit the output, I would trade some highs for a quiter pedal since it's very bright by itself but I'm wondering if anyone already does it and how.

thank you

[PRR]

> circuit is really really noisy

What kind of "noise"? Hiss? Hum? Buzz? Whine? Wine? Intergalactic? Woodpeckers?

Does it change when you stick your finger near?

[nooneknows]

A bit of hum but mostly hiss, like the one from very high gain circuits not shielded.
In my pedalboard supply I have separated grounds, no other pedals hums and hisses like this, I have a Catalinbread Formula 55 and an original Timmy in the same pedalboard but they are both dead quiet.

edit: to complete the picture, Q5 drain is at 3.4V with a 9V supply, all fets are 2n5457

[PRR]

http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf

Looks like a ^HIGH gain design, but I have never tried one.

[Elijah-Baley]

I built the BSIAB II (four knobs), I don't have it anymore, but I can't say it's too bright. Instead, I'd say, that it became a bit dark at high gain setting. Indeed I added a three way "bright switch" to change one of the last two 2.2nF (it's a common mod) with smaller cap or no cap and make it brighter.

[willienillie]

Looking at the GGG schematic there is a big electro filter cap, if you are getting high-pitched noise from your power supply, a 100n ceramic in parallel with that should help some.  You could tack one on the back of the board, wouldn't hurt.  Other than that, most hiss I've encoutered has been from active components.  Your JFETs are socketed, do you have any extras to sub out?

[iainpunk]

like Willie Nillie said, its possibly one of the Jfets that's particularly noisy.
also, dat output impedance tho.... maybe add a simple Jfet buffer?

cheers, Iain

[duck_arse]

complaints about humming pedals are not permitted while one of the jacks is missing a ground connection [other that the unreliable case]. add the ground wire to the right hand jack and test again, please.

[nooneknows]

complaints about humming pedals are not permitted while one of the jacks is missing a ground connection [other that the unreliable case]. add the ground wire to the right hand jack and test again, please.

the ground is already connected via the input jack ground, the box is made of alluminium, tester read 0 ohm, connecting another wire makes a ground loop.

[iainpunk]

complaints about humming pedals are not permitted while one of the jacks is missing a ground connection [other that the unreliable case]. add the ground wire to the right hand jack and test again, please.

the ground is already connected via the input jack ground, the box is made of alluminium, tester read 0 ohm, connecting another wire makes a ground loop.

just give it a try, having a loop can always be cut away again. (also, you should never expect the enclosure to cleanly ground a jack, i always isolate the out jack with some shrink tube)

cheers, Iain

[GGBB]

Mine is a bit noisy like you've described but not excessively so for high-gain. Definitely bright however - I ended up using the Wampler Pinnacle's tonestack which helped tame the highs. (Pinnacle is a modded BSIAB2.)

[antonis]

the ground is already connected via the input jack ground, the box is made of alluminium, tester read 0 ohm, connecting another wire makes a ground loop.

Some mA current run through 5cm (less than 2") wire (0.053 Ohm/m) makes nothing audible/measurable.. 

P.S.
I'm pretty sure duck_arse is aware enough of your particular build ground connections, so his suggestion might worth a try..

[anotherjim]

Thing is for future reliability. Cast alloy and plated steel are not good friends and nuts work lose. Small area, audio frequencies, both parts doing the same job -  there is negligible ground loop potential by adding a wire. 

Thin & hissy sometimes means that at some point along the circuit path, there is a high resistance contact at a place where the impedance is high. With FET's there are high impedance points into every gate. A bad contact looks like a small pF value capacitor which a weakened signal can pass through but its mostly treble.

With a double-sided PCB, there is always the chance of through-plating being missed from a hole or two. With those polybox caps, you can't see if solder has flowed through the hole via the plating. You could try "chopsticking", that is tapping parts to find a bad joint while listening for clicks or thumps.

[bluebunny]

Thing is for future reliability. Cast alloy and plated steel are not good friends and nuts work lose. Small area, audio frequencies, both parts doing the same job -  there is negligible ground loop potential by adding a wire. 

Wisdom.   

[nooneknows]

[
just give it a try, having a loop can always be cut away again. (also, you should never expect the enclosure to cleanly ground a jack, i always isolate the out jack with some shrink tube)

cheers, Iain

Tried it, although I was skeptical, no differences in noise, it didn't decrease neither increased.

[nooneknows]

ok, thank you all: I shortened every wire where possible, tried the ground connection on the output jack as suggested by duck_arse, redone almost every solder to be sure, I also changed every transistor (I had other 2n5457s), the hum and hiss are exactly the same, even using a 9V batter, I came to the conclusion that it's  this type of circuit being noisy to my standards.

I'll try something like the pinnacle tone section as suggested as extrema ratio

thank you

[antonis]

Although PCB might not allow it, place 100 - 150 pF Miller caps (between Drain & Gate) starting from Q5 and going back to Q3 and Q1..
(I've never done it for a JFET "μ amp" but you have nothing to loose..)