Tube fuzz debug help

[jflam]

I just finished using the audio probe method of debugging craig anderton's tube sound fuzz, and this is what happened:

The signal coming out of pin 2 of the op-amp had a high level of sound, but a large hum accompanying it (this hum is what i'm trying to get rid of)..everything following that through to the output has that same problem.  

Everything else sounds good.

Does anyone have any ideas as to what can be the problem??

[brett]

Which circuit are you using?  The one in his book?
Is there a similar noise on the power supply rail?

[aron]

What are you powering it with?

If it's an adaptor, try a battery.

[jflam]

I am using the same design/parts found in the book...

I'm using a 9v battery replacement power supply (has the 9v power adapter, but plugs into the wall....

the power lead makes a hum, but it's about a third as loud...

[brett]

Hi.  You can get rid of that hum by adding a 100 ohm resistor in series with your 9V supply.  If there's any residual hum, increase the supply decoupling capacitor (usually 22uF or 47uF) to 470uF.  I find that a 100ohm resistor and a 470uF cap removed even the most horrible power supply noise.

[jflam]

there is already a 100 0hm resistor on the power rail as part of the circuit.  However, i don't know where to put the leads of the cap (before or after the resistor, and from power to ground, or some other arrangement)??

[gez]

there is already a 100 0hm resistor on the power rail as part of the circuit.  However, i don't know where to put the leads of the cap (before or after the resistor, and from power to ground, or some other arrangement)??

100 ohm resistor from V+ of power supply to Vdd pin of chip, and the cap from the Vdd pin to ground (-ve terminal of cap to ground).

[jflam]

I put the 470 uf cap just like you said and i still get hum....can you think of any other ideas.

I'm fairly new to this, but i've read a lot of information.  I've done four projects now, with the first three being abandoned after countless, frustrating hours of work yielding anon-functioning effects.  For the tube-sound fuzz effect: I did exactly what the book by anderton said and all I come up with is half-ass effect that hums so bad it makes me want to yack!

Is this what i get to look forward to with this hobby???  Does it get better??  I love working with my hands, and love electronics, but nothing i do works................

[gez]

I put the 470 uf cap just like you said and i still get hum....can you think of any other ideas

Is the wall-wart you're using one that you use with other effects and if so is it quiet when used with them?  Try it with a battery and see if it's any quieter, if not then filtering isn't going to help much, it's something else.

I did exactly what the book by anderton said and all I come up with is half-ass effect that hums so bad it makes me want to yack!

Does it sound/function like a normal distortion only it's noisy, or does the effect itself sound poor?  If it's the latter then perhaps you've wired things up wrongly, if the former then maybe using shielded wire might help (could be your layout - is this on a breadboard?).

Some people have reputably had problems with noisy chips though I’ve never experienced this, CMOS fuzz circuits tend to be exceptionally quiet.
The advice here would be simply to sub in another chip.

[gez]

Is this what i get to look forward to with this hobby???  Does it get better??  I love working with my hands, and love electronics, but nothing i do works................

Yes, it does get better so stick with it.  There's nothing like that feeling you get when something you've built works (eventually).  

Keep with this circuit for the moment, but maybe you should look at really simple boosters and stuff before tackling circuits like this, especially if you've had problems with your first three builds.

[jflam]

i've used a battery, it still hums...maybe even more....

i tried subbing in another chip, but it was still the same...

it sounds like it should...just with hum...

there's a switch between lead and rhythm, and when it is in the lead position, there's a fair amount of hum, and both pots work...

but in the rhythm position there is a lot of hum and only the volume pot has any effect on the circuit...the fuzz pot does nothing (at least nothing that i can tell).

I built it on a copperclad (used the pcb diagram in the book).

I used the audio probe and the hum starts right at pin 2....

[David]

Hey, this sounds familiar.  If your circuit's not in a metal box yet (or even if it is), connect the ground terminals of both the input and output jacks to the ground on your circuit board.  This is even more important on a breadboard.

[gez]

There's not a huge amount of gain when in Rhythm mode, but there should be SOME discernable difference as you turn the pot.  Are you sure you've got all connections to this pot wired up ok?

Is it in a box yet?  If all's well as far as connections etc, then using shielded wire is about the only thing I can suggest.

PS  I don't have the book.  Is the schematic you're using the same as the one linked from Schematics on this site?

[jflam]

the phone jacks are connected together, with one connected to the ground lug....

the fuzz pot is connected as so:

pin 15 out to 3rd post

3rd and 2nd post connected

post one connects with switch


I honestly can't see a problem....

[gez]

I honestly can't see a problem....

Unless you've wired up your switch incorrectly, neither can I.  

Try screened cable and stick it in a box?

[jflam]

this is the schematic found on this web-site....


can anyone tell me all the ways a pot can be wired up (ie-can they be different than 1-2-3 or 3-2-1 {eg-1-3-2})??

and is there such a thing as a 2M pot...and if there is can it be a problem for this circuit???  I ask because there is no 1m stamp on the pot...but there is a bunch of black ink lettering with 2m at the end....strange.

[gez]

and is there such a thing as a 2M pot...and if there is can it be a problem for this circuit???  I ask because there is no 1m stamp on the pot...but there is a bunch of black ink lettering with 2m at the end....strange.

You can get pots with values higher than 1M, though 2M2 seems to be more 'common' than 2M.  Measure it with a meter.  If if has a weird taper then this might account for the problem you had with it not doing much in rhythm mode.  You can check the taper with a meter too (though old log types tend to be better for doing this).

Try a 1M lin instead.  Wire it up as shown in the schematic - wiper to the outer lug connected to the output, other outer lug to switch.

Is this pot the cause of all the noise?  Who knows?!  How old is it?

[jflam]

This is a 2M pot...so i think....it measures 1.89M when hooked up to the DMM.   ..could this be my problem???

It's brand new...all the parts are brand new....

[gez]

This is a 2M pot...so i think....it measures 1.89M when hooked up to the DMM.   ..could this be my problem???

It's brand new...all the parts are brand new....

Yeah, it's 2M.  The 1.89M measurement is probably as a result of loading by the meter.

Is this your problem?  I doubt it, but who knows?!  Try temporarily replacing the pot with a 1M resistor, if the hum goes then there's your answer.  Are you using metal film resistors?

Are you sure all your ground connections are ok?

[jflam]

no...i have carbon....i've looked it over numerous times...i believe that the circuit is correct...