Debug BSIAB II Help needed!

[hilbi]

I'm debugging my bsiab II build now for a couple of days, found some errors, fixed it, but it still isn't working correctly. I get a distorted sound, but also quite some noise and sometimes oscillation if I maxize the drive.

The problem looks to be around Q5, I checked all the connections, resistors but can't find anything wrong, does anyone have an idea?


q1
g 0.0
s 0,3
d 5,3

q2
d 8,9
s 5,3
g 4,2

q3
g 0,0
s 0,1
d 4,3

q4
d 8,9
s 4,3
g 4,2

q5
g 0,0
s 0,6
d 2,0

Thanks in advance

[petemoore]

Q5 drain looks a little low...[isn't that a buffer Q / connected to V+ ?]

[hilbi]

I can adjust the drain of Q5 by adjusting the trimpot (R16) , but for now it doesnt change the voltages a lot, the Gate of Q5 stays 0V.

[hilbi]

no one any idea?

[hilbi]

GGG Read - My Readings
q1 - q1
g 0,0 - g 0.0
s 0,95 - s 0,3
d 4,5 - d 5,3
   
q2 - q2
d 8.0 - d 8,9
s 4,5 - s 5,3
g 3.8 - g 4,2
   
q3 - q3
g 0,3 - g 0,0
s 0,75 - s 0,1
d 4.3 - d 4,3
   
q4 - q4
d 8,0 - d 8,9
s 4,3 - s 4,3
g 3,8 - g 4,2
   
q5 - q5
g 0,5 - g 0,0
s 0,9 - s 0,6
d 3,4 - d 2,0 (depending on trimpot var from 0,0 to about 8,9V)

My power source gives out 9,5 V

My readings doesn't look to bad to me, Q1 and Q3 sources look a bit low to me, the gate of Q3 is zero and Q Q gate is zero.

I cannot find anymore wiring mistakes, is it possible that a component went bad?

Can anyone share his thought on the voltage readings,

Your help would be greatly appriciated.

[petemoore]

Well with the GGG Voltages as a reference, your's look not so bad !!!
 GGG's Q3 'n Q5 Gates are riding a little higher, not sure that matters because all your sources are higher than your gates...Q's 2 and 4 of course set bias for Q's 1 and 3, and appear to be doing so well enough.
 As far as I can see these two units Voltage points are at least close to being on the same par.

[hilbi]

thanks petemoore, i appriciate your help.

I linked to a mp3 file recording of my bsiabII, overall you can hear a lot of noise and at the end of the file you can hear some whoosing or something like that.


http://www.stennisonline.nl/audio/bsiab2hilbi.mp3

any ideas of what this can be?

[hilbi]

when i tested yesterday i also hear on sort of octave sound when i play single high notes, what can this be, or is this part of the other issues i have.

[Ed G.]

If it's noisy, something isn't right, because it's a very quiet circuit.
Is it noisy when your guitar's volume is all the way down? B/c if your guitar is not shielded/grounded right, the high gain of the circuit will amplify any noisy coming in through the guitar.

[hilbi]

Thanks for steppin in Ed.

it is noisy when the guitar volume is all the way down (fe compared to original RAT2)

But if you open the guitar volume it is even more noisier. also when you unplug the input cable, you get a lot of noise.

so something isn't right, any ideas?

[Ed G.]

I'm stumped at this point. I never experienced any octave effect. Either there's a bad component somewhere or something is of the wrong value. I'd double check all the values and see.
Is the circuit in a box? Are the input and output jacks grounded well?

[hilbi]

I found a wrong value, c3b was 0,022uF instead of 0,22uF, corrected this. Not sure what this does.


I also shielded the input wires to the board, this helped a bit.

It looks like the circuit is picking up a hum somewhere in the beginning and amplifies it true the whole board.

If I max everything (Gain, Volume) i also get a high pitched squeel (oscilation?)

I replaced the j201's, didn;t make a diffenrence.

Ed, the voltage readings i noted down earlier this thread are ok?

[hilbi]

Just did some audio probing on the circuit, the hum starts after the drain of Q1, any idea what this can be?

Is Q1 gone bad or is it something else?

[Ed G.]

I found a wrong value, c3b was 0,022uF instead of 0,22uF, corrected this. Not sure what this does.


I also shielded the input wires to the board, this helped a bit.

It looks like the circuit is picking up a hum somewhere in the beginning and amplifies it true the whole board.

If I max everything (Gain, Volume) i also get a high pitched squeel (oscilation?)

I replaced the j201's, didn;t make a diffenrence.

Ed, the voltage readings i noted down earlier this thread are ok?

The bsiab2 shouldn't have a problem with squealing or oscillation. The cap value shouldn't have made a drastic difference, it would have just thinned the sound out slightly.
I think JD has put some voltages on his site, where you got the schem from.
Is the barrel connection for the input jack grounded? If the barrel of the input jack isn't grounded it can make things very loud. Some let it ground out to the box, but others use a wire to make the connection just to make sure. Test this.

[bryantbr]

I've had that happen (high pitched squeel) on a Rangemaster from a bad solder joint on the pot.[/quote]

[hilbi]

I resoldered every solder joint on the board yesterday, that didn't make a difference, I didn't resolder the pots, wich I will do tonight (thanks bryantbr).

I checked against the JD voltages, and mine look quite similar. My readings doesn't look to bad to me, Q1 and Q3 sources look a bit low to me, the gate of Q3 is zero and Q Q gate is zero. (See earlier this thread for the complete comparing of my readings against JD's voltages)

The sleeve of the input jack is connected to the ground of the board, wich connects to the ground of the guitar and amp. The circuit is not (yet) in a case. So it isn't grounded to the case. Should it be grounded to somewhere else

Not 100% sure what you mean with barrel of the input jack.

Barrel is sleeve or ring?

I will work on it tonight and check the suggestions you did, thanks again for your help!

[Ed G.]

Barrel, sleeve, it's the same thing (to me)
Maybe it's noisy because it's not in a shielded box. It's high gain, and any extraneous noise that creeps in from anywhere will get amplified many times over.
But overall, it is a very quiet circuit, for the amount of gain it has.

[Benny]

hilbi,

I've noticed that a lot of high-gain circuits can be noisy when they're not in a box.  One thing that I've found works well while debugging is to take a pedal with a buffered bypass (i.e. a TS9, Boss pedal, etc.) and put it between your guitar and the circuit, in bypass mode.  I did this while debugging my BSIAB2 and it was dead quiet.  I can't give you a complete technical explanation, but I suspect that the low output impedance of the buffer is a factor.  Once you get the circuit working correctly it will probably sound fine when it's in a box.

Benny

PS Nice job with the BSIAB2 Ed, it sounds *GREAT*!!

[hilbi]

ok, good news, i resolderd the pots, the squeeling is gone now.

i put the bsiab2 in a hammond enclosure, still quite noisy. Per accident i stepped on the bsiab enclosure and it hit the side of my pedalboard, this side is made of a sort of iron and gone is the hum.

Any idea what this can be? is this sort of ground loop? how can this be fixed?

[hilbi]

the real nasty hum is gone now, it is still quite noisy (compared to rat2) but i keep hearing the "octave" effect on high notes, I don't hear this on fe my rat (my main compare pedal)

I recorded an mp3 of the effect, not sure if you can hear it, but i think i hear a lower octave or something, but maybe this is belonging to the bsiab, not sure about that.

http://www.stennisonline.nl/audio/bsiaboct.mp3