New at runoffgroove.com: 22/7

[juansolo]

My chip is a Fairchild CD4049UBCN. I'm guessing the production number is PJ25AH. Bought the chip from Rapid, it's in their catalogue as unbranded, but what we got was a Fairchild.

Mine definitely isn't making the noise that John's is. Nothing like that at all.

[John Lyons]

The ICs I've used are:
Fairchild CD4049UBCN Batch P9948AK
Texas Instruments CD4049UBE Batch 3CE1H4K

Those are the only two types I have.
I tried a few from each type....

[stm]

Thanks for the info juansolo.

John, based on the info available on the chips, I think it is safe to assume that the chips are not the problem.
The kind of noise you have might be caused by some sort of oscillation. Possible causes for oscillation are:

1) Unused inputs not grounded or Vcc'ed (this should not be the problem since the layout takes care of unused inputs.)

2) Power supply quality and filtering.  The 470R and 100uF capacitor should filter the power supply adequately, however we should suspect these components until we prove they are OK.  Principal suspect would be the 100uF capacitor.  Things to do:

a. Check polarity as mounted in the PCB

b. Replace with a different cap, let's say a 10uF to 100uF WITH a 100nF ceramic or polyester capacitor in parallel.

c. Reduce the value of the 470R resistor, probably reduce it first to 100R, then just place a wire jumper, and see if the noise character changes.  These tests should be performed with a battery to eliminate the possibility of noise coming from a power adapter.

3) Layout issues.  This would not be the first time where the wires and the tracks layout give trouble.  This is a relatively high gain circuit and should be treated with some care.

a. In your layout the 1k resistor from the gain pot returns to GND sharing a common path with the power supply filter capacitor.  I'd suggest lifting the GND end of said 1k resistor and connecting to a different place far apart, let's say the GND of the 1M resistor in the tonestack.

b. The GND wires from the input/output jacks, as well as the volume pot and the power supply could be causing trouble.  I suggest changing the connections to see if there is some effect.  One thing to try would be a single GND point where all GND wires converge.  A suitable point would be the GND terminal on the PCB

The cause for the oscillation must lie somewhere along the lines described above.

Regards and good luck.

[Lurco]

Thanks for the info juansolo.

John, based on the info available on the chips, I think it is safe to assume that the chips are not the problem.
The kind of noise you have might be caused by some sort of oscillation. Possible causes for oscillation are:

1) Unused inputs not grounded or Vcc'ed (this should not be the problem since the layout takes care of unused inputs.)

2) Power supply quality and filtering.  The 470R and 100uF capacitor should filter the power supply adequately, however we should suspect these components until we prove they are OK.  Principal suspect would be the 100uF capacitor.  Things to do:

a. Check polarity as mounted in the PCB

b. Replace with a different cap, let's say a 10uF to 100uF WITH a 100nF ceramic or polyester capacitor in parallel.

c. Reduce the value of the 470R resistor, probably reduce it first to 100R, then just place a wire jumper, and see if the noise character changes.  These tests should be performed with a battery to eliminate the possibility of noise coming from a power adapter.

3) Layout issues.  This would not be the first time where the wires and the tracks layout give trouble.  This is a relatively high gain circuit and should be treated with some care.

a. In your layout the 1k resistor from the gain pot returns to GND sharing a common path with the power supply filter capacitor.  I'd suggest lifting the GND end of said 1k resistor and connecting to a different place far apart, let's say the GND of the 1M resistor in the tonestack.

b. The GND wires from the input/output jacks, as well as the volume pot and the power supply could be causing trouble.  I suggest changing the connections to see if there is some effect.  One thing to try would be a single GND point where all GND wires converge.  A suitable point would be the GND terminal on the PCB

The cause for the oscillation must lie somewhere along the lines described above.

Regards and good luck.

2) b. WITH a 100nF ceramic or polyester capacitor in parallel.
3) a.  I'd suggest lifting the GND end of said 1k resistor and connecting to a different place
b.  One thing to try would be a single GND point where all GND wires converge
i.e.: at the 100uF negative pin.

[John Lyons]

Doesn't that contradict what was said?
If the star ground point was the neg pin of the 100uf cap then
why should I remove the 1K from that point.

I understand that that point (100uf pin 1) is a high(er) current ground point but the board is small...
Moving the 1K to a point down the line near the tone section is closer to the end
of the circuit...won't that be a "dirtier" ground point...not sure that it maters much at
9v though...

Thanks for the Tips STM.
I'll try them out tonight.

EDIT:

Ok, tried everything above. still get the background noise, no change
The board has a single ground point that connects to the battery and in/out jacks.
Lowered the series power resistor, ceramic .1 across the (new) 100uf cap.
1k moved to the other side of the ground trace.

John

[azrael]

Kinda wanted to bump this, as I don't see it built often, but it's a very cool twist on the classic BMP.

Also, I made this layout:

Not verified yet, and actually a second of set of eyes to check for errors would be welcome.


John, did you ever alleviate your noise problem?

[stringsthings]

for your eyes only:  

http://www.diystompboxes.com/smfforum/index.php?topic=85661.0

one can never have enough pi !

[azrael]

oh yes, I saw yours. That was actually a big inspiration for mine, I wanted to compact it a lot more, wanted to fit it in like a 1590B or so.

[azrael]

Wanted to bump this, had a thought: For those having problems with noise, did you try grounding the unused inputs on the 4049?

[B Tremblay]

Wanted to bump this, had a thought: For those having problems with noise, did you try grounding the unused inputs on the 4049?

Hopefully they did, as there is a note on the schematic that those pins are to be grounded.

Did you have any noise issue with your layout?

[azrael]

Oh, never built it. I actually missed that note on layout, haha, so it's possible others did.