EHX Bassballs Clone Build - Help Needed! (Constant tone when engaged)

[steveyraff]

Howdy.

I made this:
http://tagboardeffects.blogspot.co.uk/2013/06/ehx-bassballs.html

Checked the layout, checked all solder points, values, wiring, looked for all solder bridges, etc etc.

Everything seems in order. I had zero optimism of this actually working, so I took extra care to make sure I was giving it my best shot.

The only thing I did differently, which may still be to blame, is I wanted to externally mount the trimmers as pots. I didn't have linear pots so I used A10K pots. I am not sure I got the wiring correct for these - can someone please confirm the correct pinout/numbering for these? ie - where each trimmer leg is supposed to go, I have a wire going from there to what potentiometer lug? Looking at the layout on the link I provided, I've tried going from where the top trimmer leg would be, to lug 1, then the middle to lug 2, and the bottom to lug 3. I've tried swapping 1 and 3 around and still no joy.

I get bypassed signal, but when I engage the pedal, I get a constant tone and can't hear my guitar. This tone either goes up or down in pitch depending on how I move the two trim pots. The response knob doesn't seem to do anything.

The only other thing I can think of which might be different, is that IC 1 and IC 2 are listed as 1458 and 4558. I was only able to find LM1458 and RC4558. Not sure that makes any difference?

Anyone any ideas?

All help muchos appreciated.
Cheers!

[vigilante397]

Pictures of your build? Voltages for the ICs and transistors?

It's a sweet circuit for sure, definitely worth debugging.

[idy]

You're correct about the trimmers. Top is 1, middle 2, bottom 3. That will be like the board shown. I did not compare to a schematic to make sure this won't result in "backwards" operation, but if the layout maker had wanted to reverse them he could have, right?

Audio probe.

[steveyraff]

Pictures of your build? Voltages for the ICs and transistors?

It's a sweet circuit for sure, definitely worth debugging.

Well, I've already the case finished for it - so I better get it debugged now lol. I will get this info for you tomorrow. Almost midnight here! It'd be great if I could figure this out though.

You're correct about the trimmers. Top is 1, middle 2, bottom 3. That will be like the board shown. I did not compare to a schematic to make sure this won't result in "backwards" operation, but if the layout maker had wanted to reverse them he could have, right?

Audio probe.

Yea, I mean, presuming I have them wired correctly - and the other way would have just made them operate in reverse - it shouldn't be what is causing it to not work. I'm just getting a constant drone that oscillates in pitch as I tweak the trimmers. Zero guitar signal coming though when engaged. 

[Mark Hammer]

The circuit provides two bandpass filters that are "tuned" by both the trimmers and changes in the effective resistance of the transistors,  Both filters are tuned to an audible frequency.  Theresonance or Q of each filter is set by the feedback resistance of each of the op-amp sections.  The higher the resistance, the higher the resonance.

All of which leads to my guess that the feedback on one of the filters is essentially open-loop.  That is, you either have no connection between one end of the 470k resistor bridging input and output on the op-amp, or else you've unintentially stuck in a ridiculously high value, like 4M7.  Either way, that would nudge the filter section towards oscillating...which is what you're hearing.

[steveyraff]

The circuit provides two bandpass filters that are "tuned" by both the trimmers and changes in the effective resistance of the transistors,  Both filters are tuned to an audible frequency.  Theresonance or Q of each filter is set by the feedback resistance of each of the op-amp sections.  The higher the resistance, the higher the resonance.

All of which leads to my guess that the feedback on one of the filters is essentially open-loop.  That is, you either have no connection between one end of the 470k resistor bridging input and output on the op-amp, or else you've unintentially stuck in a ridiculously high value, like 4M7.  Either way, that would nudge the filter section towards oscillating...which is what you're hearing.

Thanks Mark,

I'm not sure which 470k resistor you are talking about - but I checked them all and their values are all correct, and they seem to be soldered in correctly. When the pedal is on I am not hearing any of my guitar. There is just a constant oscillating drone, changing pitch depending on how I move the trimmers. I've re-checked it all 3 times over now.

[steveyraff]

VIDEO of behaviour:

http://vid597.photobucket.com/albums/tt52/steveyraff/20151204_142635_zps0lmrqd2q.mp4

[steveyraff]

IC 1 :
1= 4.4
2= 4.4
3= 4.4
4= 0.0
5= 0.0
6= 1.9
7= 1.9
8= 8.8

IC 2:
1= 4.4
2= 4.3
3= 4.4
4= 0.0
5= 4.4
6= 4.4
7= 4.3
8= 8.8

[steveyraff]

Any ideas ?

This thing is driving me nuts! 

[Kipper4]

Have you got a schematic that your working from Stevie?
I'm dubious about the 5,6,7 pin voltages

If I'm right I think Mark s talking about r12, r17 for the 470ks
How have you got t1,t2 set?
And how is the trimmer set on the output of the first op amp. I'm looking at the toppopiccio schematic.

http://guitarpedalbuilders.blogspot.co.uk/2013/01/ehx-bassballs-schematic.html
Hope this s ok.

[steveyraff]

Have you got a schematic that your working from Stevie?
I'm dubious about the 5,6,7 pin voltages

No Kipper - I'm really bad with schematics. I am just using the tagboard layout I linked in the original post. Do you think I should try changing that IC or something? Was hoping to not have to do that - but if it looks like its the problem, I'll have to. Let me know your thoughts - I appreciate the help,

Cheers.

[steveyraff]

Have you got a schematic that your working from Stevie?
I'm dubious about the 5,6,7 pin voltages

If I'm right I think Mark s talking about r12, r17 for the 470ks
How have you got t1,t2 set?
And how is the trimmer set on the output of the first op amp. I'm looking at the toppopiccio schematic.

http://guitarpedalbuilders.blogspot.co.uk/2013/01/ehx-bassballs-schematic.html
Hope this s ok.

By T1 and T2, do you mean both trimmers?

I've wired in 10K Audio pots instead of trimmers, so I can mount them externally. I've asked about this, and think I have them wired in with the correct orientations. Going by the vero layout I was using, the highest trim leg point, would be going to Lug 3 of the pot, then the middle to lug 2, and the lowest to lug 1.

I haven't them set in any particularly way. I've tried playing while tweaking the pots and setting them all ways I can come up with. Nothing is coming through except that noise you can hear in the video.

[Kipper4]

Your 470k in the vero are the lowest two .

[steveyraff]

Ive checked all resistors - and the 470k ones - they seem to be the correct value and soldered in correctly with no bridges etc.

[Kipper4]

Well at least the filter pots are working. Haha. Sorry I missed the video earlier.

The 10k pot is a kind of sensitivity control, by changing the resistance on the input of this Inverting stage. Changing that resistance controls the gain of the stage.

[vigilante397]

I'm dubious about the 5,6,7 pin voltages

Also. IC sockets save lives. The IC itself might be bad, but I would definitely trace the parts connected to those pins and make sure everything is right there.

[steveyraff]

Did you also notice in my video, when the trims are set in a certain way, there is silence, but a ticking noise?

[Kipper4]

Have you double checked your jumpers?
Maybe there's a crack in the board. Set your DMM to stun. Just kidding set it to beep when the probes are shorted.
Check when you bend the board like in the video.

[Kipper4]

Check your switch with the blue wires isn't shorted while your messing with the machine that goes beep.
😀

[Kipper4]

Sorry I thought the reason it went silent was because the filter was oscillating beyond my hearing.