bsiab 2 hum

jimmyandrex · January 03, 2014, 01:41:18 PM

I built a bsiab2 years ago but I have never used it as there is unacceptable 50hz hum. I can accept hiss but not hum. The other od/distortion on the board which i have built are not that noisy eg ocd, muff, screamer, octavia etc. Is this normal for the bsiab2. I'm wondering if I have made some earth loop gaff -I can't see one unless there some thing odd on the circuit board. I would like to use it as its got a great sound (although normally I use the ocd all the time anyway and forget the rest)

PRR · January 03, 2014, 10:52:48 PM

> unacceptable 50hz hum

With battery?

jimmyandrex · January 04, 2014, 11:29:24 AM

a)It's exactly the same whether powered by PSU or battery.

b)Adjusting the trim does not alter the hum level

c) There are no hum loops - if checked

d) If adjust any of my other devices to extreme distortion the hum level is a great deal lower than the bsiab on moderate overdrive.

e) I have checked all components on the board and grounding they appear correct

Kipper4 · January 04, 2014, 12:07:52 PM

Probably best to take a look here

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

And come back buddy

jimmyandrex · January 04, 2014, 12:26:08 PM

The pedal works fine but is hum noise usual with this build?

Morocotopo · January 04, 2014, 02:55:43 PM

My BSIAB 2 hums also, more so than other pedals. It´s quite high gain, so some noise is unavoidable, but I have wondered at times if it needs more power filtering, more bass filtering, or some other measure to limit hum.

jimmyandrex · January 04, 2014, 05:31:50 PM

may be you can't have your cake and eat it !

pinkjimiphoton · January 04, 2014, 07:32:43 PM

in my experience, when a build does that, there's a ground somewhere that's not connected. literally every single time so far.

J0K3RX · January 04, 2014, 09:19:33 PM

Does it hum with the volume knob all the way down on your guitar or does it keep humming? I would assume that it keeps humming...

What schematic did you use? There are a few variants floating around...

jimmyandrex · January 05, 2014, 05:32:16 AM

It ceases to hum with the volume on the guitar turned right down (same for all guitars so its not a guitar fault )
The board came from General GG revision 2005 May 22 by JD Sleep.

J0K3RX · January 05, 2014, 06:04:17 AM

Quote from: jimmyandrex on January 05, 2014, 05:32:16 AM
It ceases to hum with the volume on the guitar turned right down (same for all guitars so its not a guitar fault )
The board came from General GG revision 2005 May 22 by JD Sleep.

I was asking because that is about the exact same thing I was getting with my Black Forest builds... I finally got it down to normal levels (no hum).

Try raising the source resistance of Q1 and Q3 and see if that starts to lower the hum noise. Mine are both at about 2k

I would start lower than that and work my way up until the noise goes away...

We really need voltages to attempt to properly diagnose.

jimmyandrex · January 05, 2014, 01:59:38 PM

Here are the voltages

G S D

Q1 0 0.46 5.7

Q2 4.2 5.7 8.95

Q3 0 0.1 4.58

Q4 4.26 4.58 8.95

Q5 0 0.6 4 J201

0 0.8 4 2N5457 ( swopped - trimmer adjusted to 4v on drain)

PRR · January 05, 2014, 03:13:10 PM

If battery power, *closed* metal box, every ground good..... it can't hum.

jimmyandrex · January 05, 2014, 05:26:05 PM

Regarding the voltage readings I have posted - both Q3 and Q5 show "0v" on the gate is that right? according to the voltage chart I have seen Q3 should be 0.3v and should be Q5 0.5v

PRR · January 05, 2014, 06:43:17 PM

There are many re-drawings of this circuit, and they don't all number the transistors the same.

Three of the Gates will be "zero" volts (much less than 100mV) and two will be at half the battery voltage.

IAC... bad bias is usually no sound, not hum.

jimmyandrex · January 06, 2014, 07:25:26 AM

There's something about this which is confusing me:
The input socket tip is not grounded when the jackplug is withdrawn as i disconnected that connection it when debugging for some reason (they the plastic sockets). It does not hum in this situation almost silent. However when i plug the input jack plug in the circuit seems to greatly amplyfing any noise coming through guitar cable/guitar but much more so than any of the the other pedals and more so than you would expect from the gain levels. With the input disconnected and not grounded no hum/noise would indicate that there isn't a technical problem with the pedal but this could be an inherently noisy design maybe?

amz-fx · January 06, 2014, 08:03:52 AM

Quote from: jimmyandrex on January 06, 2014, 07:25:26 AM
There's something about this which is confusing me:
The input socket tip is not grounded when the jackplug is withdrawn as i disconnected that connection it when debugging for some reason (they the plastic sockets). It does not hum in this situation almost silent. However when i plug the input jack plug in the circuit seems to greatly amplyfing any noise coming through guitar cable/guitar but much more so than any of the the other pedals and more so than you would expect from the gain levels. With the input disconnected and not grounded no hum/noise would indicate that there isn't a technical problem with the pedal but this could be an inherently noisy design maybe?

There is a lot of gain in the BSIAB. It may be that you are playing/testing in a noisy environment, and the high gain of the pedal is amplifying noise that is already present.

1. Are you playing single coil pickups?

2. Are you close to your computer monitor?

3. Does the room have fluorescent lights, including CFL bulbs?

4. Is there a dimmer on any of the lights in the room?

Any of these items can possibly present a noise problem, especially with high gain. I have a brand new Tele that cannot be used with high gain in my studio, unless I turn off the overhead fluorescent lights. Even then there is some slight residual hum that the pickups are sensing.

I would also check the cables to make sure that they are in top shape and that there is good continuity. A meter set to read Ohms can be used to test the signal and ground of each cable.

Best regards, Jack

jimmyandrex · January 06, 2014, 10:24:53 AM

Well yes to 1, 2 and3 (no to 4).

but the other pedals aren't affected to the same extent

I always switch the fluorescent lights in the garage below off as they are as noisy as f**k - then "somebody" comes along and switches them on again, to use the washing machine!

BTW cable are fine

jsleep · January 06, 2014, 04:36:13 PM

It's the noisiest pedal I have, but I still have it on my pedal board. If you have a single coil guitar, it's gonna be worse than humbucker. It's not hum, it's high gain noise. JFETs are extremely variable and unpredictable out of the box. You might have better results with noise with selected JFETs. I've recently had complaints of bad JFETs causing oscillation, which is a reality for sure. Why do we use JFETs for distortion? We oughta know better by now I guess, but like GE transistors, they can just sound SO good sometimes, maybe it's worth the trouble.

JD

jimmyandrex · January 07, 2014, 07:46:38 AM

"You might have better results with noise with selected JFETs" are talking about transistor noise here eg hiss not amplified extraneous noise from the input - hum. I tested for gain, they were all fairly consistent no probs with oscillation, i think they are a good batch. I do use single coils, the hum varies with orientation.
Its seems from what you are saying, is that my pedal performance is as expected, which is something I am trying to ascertain. Maybe the gain/bias of the first stage be adjustable?

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bsiab 2 hum