Attention Meatball cloners

[charbot]

Hi all,
I have a meatball clone that I built a few years ago.  It works wonderfully, except...when the settings are:   trigger -up
         filter- High   

there is a constant very high pitch squeal.  The frequency can be altered by the color and intensity pots and goes away when both are turned down half way.   

I used the joep layout with off board wiring.  the inside looks just as messy as the pics on the pisotone page. I also did the color pot mod.
Ive never seen a real Meatball or any other clones so I dont have anything to compare it to.   Has anyone else experienced this with their Mcmeat? 
Is this sound from from poor wiring/ interference,  slightly off component values, a side effect of the color mod?  its very quiet otherwise. 
any info is appreciated
thanks, charlie           

[Jarno]

What kind of opamps are you using? I am not familiar with the mods you mentioned, but when doing high resonance filters you can get problems with oscillation (which is probably what you are experiencing).

[MarcoMike]

no whine in my case... in mine I used a tl084 or 74, I don't remember... (not very helpful, I know)
but I can tell you I found really useful to add an inverting buffer after the LowPass section (actually you should do that as well after the HiPass, but I never really use it...). this way there is no volume weirdness while blending with the dry signal... really reccomended!!

[charbot]

Im using whatever was listed on the schematic.   TL074 and a 1458 i think.  I didnt try different opamps.
the color mod is simply connecting the 2nd and 3rd lug on the color pot.  No other wiring is altered. This adds a lot more range and function to the color pot.    Without the connection between lungs 2and 3, the color is very unresponsive, only has action in the last 1/3 of the pot. Its undetermined whether this is an "mod" or a correction of a mistake on the original meatball.
I may be wrong, but I believe I read that this was how the original meatball behaved.  there is a graph somewhere in the forum that  shows  how the modded color pot produces the expected the responce, while the unmodded pot graph is nearly flat and curves up slightly at the end.

anyway... thanks for the suggestion.  Do you think that its a tolerance issue?  Should  try different 1458's and TL074's,  trying to find the right "fit" or swap out for different models of opamps entirely?

MarcoMike, by volume wierdness, do you mean how the volume cuts when the blend is around50/50?

[MarcoMike]

yes! that's because in the filter opamps are wired as inverting, so LP and HP result invertedd an odd number of times... while the dry signal is non inverted. I decided to invert LP once again, because it's the one I use the most, together with BP... sonow they are all in phase and blend perfectly. but I just checked, no hi pitch sounds form mine in those settings... anyway, is it useful at all?! for me the first 2 lower settings are more than enough on guitar... I would rather add a lower one...

[charbot]

Oh, By the Way....looking through the forum I saw a lot of posts by builders who decided to not include the fx loop or pedal jacks....
to all future builders, I would most definately include the fx loop and at least pedal jack #2 (attaches to intensity).  The loop adds so much versitility to the effect and is the best spot for distiortion.   If you left it out, you dont know what you are missing.
Pedal jack # 2 is cool because with the trigger "off" and an expression pedal connected turns the meatball into a foot opperated  wah, with all of the meatball filter controls(right side of the effect.)
Dont have an expression pedal....?  Want a quick simple plug in proximity control?    check this out....
lovetone light jack cv controller]http://www.diystompboxes.com/smfforum/index.php?topic=81383.0]lovetone light jack cv controller  
I wouldnt pay the fifty bucks the ebay guy is asking but look like  it could be made in about 10 minutes with a cds and jack from radio Shack.    

[MarcoMike]

never buy things you know you can make yourself...

being a meatball lover myself (also with noodles) I tell you my experience: I omitted the external pedals you see on the schematic and added another one instead for sweep control: the standard one acting on intsnsity is not as effective as it should in my opinion, so I wired a pot like this: 1-R1-ground, 2-CV, 3-R2-V+. (R1 and R2 define min and max V). CV substitutes the normal CV when you plug the pedal. this way it really sweeps and you can use every kind of CV, as in modular synthesizers (I'm connecting my vanishing point here as well this way)
oh, CV is buffered with an opamp before going to the optocouplerse... just because I had one left...

then, one mod I found really useful was already discussed here somewhere and adds a setting on the LP HP BP knob, letting you have the unfiltered signal going through the loop and the blender but skipping the filter. this way you can use the pedals you put in the meatball's loop and blend them with the dry signal as well...  I don't remember which post was it, but if you'reinterested I can send you the schematic..

[charbot]

MarcoMike, do you have a schematic for your sweep control?  Is it still connect to the intensity pot? Are the resistors you mention, R1 and R2 on the board or is it 2 new resistors added? Sorry for all the questions.... interested and confused.

[MarcoMike]

2 more, sorry for the cheap explanation. i'll draw a schem...

EDIT: here you are, as usual hoping it's ok to post this way... (Joep you'll always be my hero!!)



the phase inversion is not shown, but it's just a buffer after LP (before the switch) and also the CV buffer is not there, and I think it's not even that important, I sust didn't want to use a super low value pot there in the pedal. with the buffer every pot should work, as very low current is passing and you don't have I*R voltage drops, but just the voltage divider.
the normal connection from IC2 to intns is interrupted when you insert the pedal jack

[charbot]

thanks Marcomike.
Are you using a battery powered volume pedal, or is a passive with the +9v being supplied by the meatball power line? Also, what is the value of the two resistors?

[MarcoMike]

the pedal is McMeat-powered and has 3 wires going to it. I don't remember about the resistors I used, but it will work even without... i think even at 9V vactrols won't get fried... and of course their values depend on which pot you chose and if you use a buffer or not for CV...

[charbot]

cool, so you used a stereo switching jack as the pedal out, and a stereo cable too, right? Adding buffers and improved pedal control sound like great mods on what is already my favorite pedal. Thanks for all of the info. 
Right now though, I just want to get rid of the high freq oscillation when the trigger is "up" and the filter is on "high."
Am I correct to assume that the oscillation may be ocurring in IC1 (TL074)?  Anyone have some  suggestions for replacement IC's?