Building the Meat Sphere

[add4]

Here's the follow up on this:
i'm still tracing the schematic: so far i noticed that :
- when i touch the positive leg of the led, the filter 'changes' and the led slightly lights up (barely seeable and it's an ultra bright blue led). so i guess the vactrols are sensitive to a voltage change around them, but the voltage doesn't change with normal use
- I traced the signal around the first half of the LM1458: if i touch the legs of the resistor and diode in the feedback loop, the filter triggers and i hear the music played through the pedal being filtered .. yay.
playing with that i noticed that sensitivity and attach pots seem to work correctly.

However i have questions about the decay pot:
on the schematic, is connected to the attack pot, and then to a 1.5K resistor to ground, with the middle lug of the pot being sent between the pot and the resistor. But i really don't see it happening on the pcb. is that normal? In fact, i have the impression that the 1.K5 resistor is placed BEFORE the decay pot, connected to 5 of the op amp, and that after that it goes to the outer lug of the decay pot, and that the other 2 pins of that pot are not connected to anything = ground plane? Right?
anyway, this seems to work when i use it so i'll make the hypothesis that it works...

the second half of the opamp circuit reacts well to probing, i can hear the filter change when it's probed, and it follows the schematic : pins 6 and 7 are connected. through the 330 k resistor, i go to the intensity pot which works very well, which goes to the direction up/down rotary switch.
3 lugs here : the upper one makes the same audio effect as when i touch pin 7 of the opamp. outer lug seems to be ground, inner lug makes a loud pop.. seems to be 9V.. everything ok so far.
It goes to the LEDs of the vactrols and indicator LED.. which doesn't light up ..
I don't really get what the problem is ...
voltage difference between the 2 legs of the indicator LED says 1.65V, isn't it enough to fire the LED up ? It's an ultra bright blue led, i googled the forward voltage of these it seems to be 2.8V, so it would be normal if it doesn't light up. The data sheet for the vactrols says 2.0 volts forward voltage.. so i guess if it have 1.65 volts, it's only normal that i don't have any filtering effect.
Maybe it's VERY opamp dependent? i tried with TL072 and the voltage between the LED lugs is 1.80, hearable change in the sound out of the circuit...

I just don't get why this voltage  between the LED lugs doesn't change with the envelope of the signal.... i guess it's the point, right? So if the voltage doesn't change it would mean theres a problem forward that i haven't found with all this process..
but i don't really know what more i could do.. do you have any advices? i'm a bit lost right now :s
...

Thanks in advance..
sorry for the long posts with all the details, but i hope someone can point out a problem i overlooked if i give all the details .. it's getting frustrating... and interesting to trace Taylor's pcb point to point

Looking forward to hear from you guys.. don't let me alone with this.. i'm only beginning :p

Peace,

Hello Taylor,
Here's an update on my debugging of thus build:
I'm playing music from my computer into the effect as i probe is, so i can hear what's happening with AC voltages and not be fooled by the cap thing
summary of symptoms:
I get bypassed sound and processed sound.
I can filter the sound with blend, intensity, colour, range, HP/BL/LP/ and UP/DOWN.
The filter is 'fixed' i can't hear any envelope following effect. it currently acts as a rather cool sounding fixed filter.
The LED does not ever light up (but does when i probe certain components, so it's wired correctly)
things not producing a hearable change in sound when tweaked: decay, attack, sensitivity, bandwidth (pretty much the entire circuit block around the LM1458)
reminder: until my tayda order is not here, i'm using a MC1458p instead of the LM1458.. pinout is the same... can't tell about the rest. changing that will be the first thing i do when i receive the right opamp.

When i touch the pin 14 of the TL074, i hear a POP. this pop is also hearable at the via to the second layer: one of the diodes legs next to the TL074. I still have a sound at the other side of the via, and the same pop when i touch the + leg of the middle 10uF cap under the sensitivity pot. So far it seems to be ok since it follows the schematic (without the 10uF cap). From what i read of the schematic: the minus leg of the 10uF pot should then go to
- send
- left lug of sensitivity (near the center of the pcb)
If i touch these components: i hear the volume of the music lower, i guess i'm sucking voltages out of the effect. they seem connected all react the same way, so far so good.
Following the schematic: sensitivity controls the volume of the sound coming into the envelope section, so i should hear something if i probe the middle lug, and i do.
Signal then goes to the 4.7 k resistor which is i guess right under the 3 10uF caps under sensitivity. the lug on the outer side of the pcb which is connected to sensitivity lower the signal too.
The other leg of the 4.7 resistor doesn't produce anything hearable.. and it goes right to the middle lug of the bandwidth switch.. which doesn't work at all....
I tried reflowing the components, doesn't change anything. multimeter says the resistor is 4.7k so is the resistance between the outer lug of the resistance and the middle lug of bandwidth. With i turn bandwidth, it connect either to the lower pad which is connected to the circuit or to the other connected pad, with 4.7 resistance between it and middle lug of sensitivity. so i guess theres signal coming through the resistor (or through another path around the rest of the circuit??  But the changes of having 4.6k exactly seem very low to me) For this reason id say the soldering is ok. And i guess the problem lies ahead.

I'll continue this later. if anybody have an advice on what i have done so far, i'd be glad to follow any ideas

Thanks for pointing out that cap missing from the schematic. It's connected between pin 14 and the sensitivity pot.

Capacitors block DC voltages, so yes it's normal that there would be a DC voltage on what side and not the other side.

Again, IMO (having built probably 500 pedals and done a fair amount of debugging) audio probing gets to the heart of the matter much faster than voltages. If you have sound coming out of pin 14 but no sound at the center pad of the bandwidth switch, then that narrows it down to just a couple of components. Try reflowing all of those pads.

[JustinFun]

Thanks for the board Taylor!

I've built mine - very happy with the results so far but have 2 questions:

Can someone confirm the definitive switch positions for the 4 rotary switches? I'm assuming the following from the schematic
- Range 4 postitions
- Bandwidth 3 positions
- Up/Down 2 positions
- HP/BP/LP 3 positions

Secondly I'm having some trouble with powering the pedal. It's fine on battery, but when I connect it to a 9v power supply it craps out on me - just a very gated signal with no obvious effect. I've checked the wiring of the DC socket with a multimeter and it's fine - is the pedal particularly picky on voltage or current? I'm using the AMZ power supply (http://www.muzique.com/tech/power2.htm) and it's delivering just a shade under 9v (about 8.9).

[charmonder]

I built two of these meatspheres, I made two mods to the circuits that I think came out well, dont hold me accountable if this ends up breaking your circuits or if it doesn't go very well, im not sure the theory is behind these mods but they worked for me

the circuits points of interest:


1) you can take a lead from that yellow point on the intensity pot, then attach that to the center lug of a delay time pot on a delay pedal(works for three of my delay pedals in a row, probably works with a flanger's "manual" pot....)  this is loads of fun! im sure you can imagine if youve ever found yourself spinning delay time knob instead of playing guitar, but now you have your cake and eat it!

2)Instead of the blended output,(which I think doesn't come out very well, probably needs some signal buffers) I made three separate outputs from the highlighted points on the LPBPHP switch, this is so that the HP and LP signals can be combined on a mixer to get a notch filter also known as band stop(again you need to send it to a mixer, or through buffered pedals, to get them to combine well) so all in all theres 4 outputs, clean, hp, bp, lp,

with these outputs isolated, the blend pot and LP/BP/HP selector are no longer in use, allowing for THIS MOD:


3) disconnect the lead from the sensitivity pot(highlighted in the pic),
and connect it to the highlighted blend pot lead(dont disconnect the blend pot lead),

this changes the blend pot so that you can choose to have the envelope sensitivity read the filtered result not the unfiltered signal(but blending back to zero will have it read the unfiltered guitar as in the original), LPBPHP selector chooses which filter signal will go to the sensitivity.

its hard to say what this changes exactly about the effect but it certainly allows for new different sweeps, i find it very usable

now all the knobs and switches are working


4)haven't worked out the specifics but i think the next mod Im doing is an effect loop for the sensitivity portion, in addition to the stock effect loop for the filter portion... this would allow you to get the envelope to be following a guitar with some reverb on it, but then have the filter process the dry signal.

seems like this is easily done with an NC jack somewhere around the "send" part of the circuit, but I hope I don't have to cut a trace on the board(that gets ugly!).

[Taylor]

Interesting mods. Your delay thing will not work with all delays, but it's a cool use of the envelope.

Can someone confirm the definitive switch positions for the 4 rotary switches? I'm assuming the following from the schematic
- Range 4 postitions
- Bandwidth 3 positions
- Up/Down 2 positions
- HP/BP/LP 3 positions

Secondly I'm having some trouble with powering the pedal. It's fine on battery, but when I connect it to a 9v power supply it craps out on me - just a very gated signal with no obvious effect. I've checked the wiring of the DC socket with a multimeter and it's fine - is the pedal particularly picky on voltage or current? I'm using the AMZ power supply (http://www.muzique.com/tech/power2.htm) and it's delivering just a shade under 9v (about 8.9).

Your switches look right. The power thing seems weird. I don't see why this would be that sensitive about the power supply. I've just powered it with a 1-spot. You're sure that the voltages seen at the power pins of the opamps aren't different between battery andd supply power?

[add4]

Guys, i'd really like to have an input on this .. i'm short of ideas and still don't get any envelope.
I received my tayda order today .. i had LM1458 in the list. they sent me MC1458L instead.. i tried with that and it still doesn't work.
Earlier in this thread, Taylor mentions he was not getting any envelope with other opamps than LM1458, but he also says he think any 1458 would work ..
What could i do to track this problem further?
I think i'm not getting enough voltage at the output of the first envelope follower opamp. should i try to increase the 1.8 M resistance there to increase the gain and see it the envelope works?
I also planned to measure the voltage between the diodes and vactrols (led side) legs, to see if there are any voltage variations with the music.
that's the only things i can think of.. any help would be appreciated.
Thanks in advance

Here's the follow up on this:
i'm still tracing the schematic: so far i noticed that :
- when i touch the positive leg of the led, the filter 'changes' and the led slightly lights up (barely seeable and it's an ultra bright blue led). so i guess the vactrols are sensitive to a voltage change around them, but the voltage doesn't change with normal use
- I traced the signal around the first half of the LM1458: if i touch the legs of the resistor and diode in the feedback loop, the filter triggers and i hear the music played through the pedal being filtered .. yay.
playing with that i noticed that sensitivity and attach pots seem to work correctly.

However i have questions about the decay pot:
on the schematic, is connected to the attack pot, and then to a 1.5K resistor to ground, with the middle lug of the pot being sent between the pot and the resistor. But i really don't see it happening on the pcb. is that normal? In fact, i have the impression that the 1.K5 resistor is placed BEFORE the decay pot, connected to 5 of the op amp, and that after that it goes to the outer lug of the decay pot, and that the other 2 pins of that pot are not connected to anything = ground plane? Right?
anyway, this seems to work when i use it so i'll make the hypothesis that it works...

the second half of the opamp circuit reacts well to probing, i can hear the filter change when it's probed, and it follows the schematic : pins 6 and 7 are connected. through the 330 k resistor, i go to the intensity pot which works very well, which goes to the direction up/down rotary switch.
3 lugs here : the upper one makes the same audio effect as when i touch pin 7 of the opamp. outer lug seems to be ground, inner lug makes a loud pop.. seems to be 9V.. everything ok so far.
It goes to the LEDs of the vactrols and indicator LED.. which doesn't light up ..
I don't really get what the problem is ...
voltage difference between the 2 legs of the indicator LED says 1.65V, isn't it enough to fire the LED up ? It's an ultra bright blue led, i googled the forward voltage of these it seems to be 2.8V, so it would be normal if it doesn't light up. The data sheet for the vactrols says 2.0 volts forward voltage.. so i guess if it have 1.65 volts, it's only normal that i don't have any filtering effect.
Maybe it's VERY opamp dependent? i tried with TL072 and the voltage between the LED lugs is 1.80, hearable change in the sound out of the circuit...

I just don't get why this voltage  between the LED lugs doesn't change with the envelope of the signal.... i guess it's the point, right? So if the voltage doesn't change it would mean theres a problem forward that i haven't found with all this process..
but i don't really know what more i could do.. do you have any advices? i'm a bit lost right now :s
...

Thanks in advance..
sorry for the long posts with all the details, but i hope someone can point out a problem i overlooked if i give all the details .. it's getting frustrating... and interesting to trace Taylor's pcb point to point

Looking forward to hear from you guys.. don't let me alone with this.. i'm only beginning :p

Peace,

Hello Taylor,
Here's an update on my debugging of thus build:
I'm playing music from my computer into the effect as i probe is, so i can hear what's happening with AC voltages and not be fooled by the cap thing
summary of symptoms:
I get bypassed sound and processed sound.
I can filter the sound with blend, intensity, colour, range, HP/BL/LP/ and UP/DOWN.
The filter is 'fixed' i can't hear any envelope following effect. it currently acts as a rather cool sounding fixed filter.
The LED does not ever light up (but does when i probe certain components, so it's wired correctly)
things not producing a hearable change in sound when tweaked: decay, attack, sensitivity, bandwidth (pretty much the entire circuit block around the LM1458)
reminder: until my tayda order is not here, i'm using a MC1458p instead of the LM1458.. pinout is the same... can't tell about the rest. changing that will be the first thing i do when i receive the right opamp.

When i touch the pin 14 of the TL074, i hear a POP. this pop is also hearable at the via to the second layer: one of the diodes legs next to the TL074. I still have a sound at the other side of the via, and the same pop when i touch the + leg of the middle 10uF cap under the sensitivity pot. So far it seems to be ok since it follows the schematic (without the 10uF cap). From what i read of the schematic: the minus leg of the 10uF pot should then go to
- send
- left lug of sensitivity (near the center of the pcb)
If i touch these components: i hear the volume of the music lower, i guess i'm sucking voltages out of the effect. they seem connected all react the same way, so far so good.
Following the schematic: sensitivity controls the volume of the sound coming into the envelope section, so i should hear something if i probe the middle lug, and i do.
Signal then goes to the 4.7 k resistor which is i guess right under the 3 10uF caps under sensitivity. the lug on the outer side of the pcb which is connected to sensitivity lower the signal too.
The other leg of the 4.7 resistor doesn't produce anything hearable.. and it goes right to the middle lug of the bandwidth switch.. which doesn't work at all....
I tried reflowing the components, doesn't change anything. multimeter says the resistor is 4.7k so is the resistance between the outer lug of the resistance and the middle lug of bandwidth. With i turn bandwidth, it connect either to the lower pad which is connected to the circuit or to the other connected pad, with 4.7 resistance between it and middle lug of sensitivity. so i guess theres signal coming through the resistor (or through another path around the rest of the circuit??  But the changes of having 4.6k exactly seem very low to me) For this reason id say the soldering is ok. And i guess the problem lies ahead.

I'll continue this later. if anybody have an advice on what i have done so far, i'd be glad to follow any ideas

Thanks for pointing out that cap missing from the schematic. It's connected between pin 14 and the sensitivity pot.

Capacitors block DC voltages, so yes it's normal that there would be a DC voltage on what side and not the other side.

Again, IMO (having built probably 500 pedals and done a fair amount of debugging) audio probing gets to the heart of the matter much faster than voltages. If you have sound coming out of pin 14 but no sound at the center pad of the bandwidth switch, then that narrows it down to just a couple of components. Try reflowing all of those pads.

[Taylor]

However i have questions about the decay pot:
on the schematic, is connected to the attack pot, and then to a 1.5K resistor to ground, with the middle lug of the pot being sent between the pot and the resistor. But i really don't see it happening on the pcb. is that normal? In fact, i have the impression that the 1.K5 resistor is placed BEFORE the decay pot, connected to 5 of the op amp,

Parts that are in series work no matter the order in which they're placed. It seems I reversed the order of these parts on the board but not in the schem, which I can see could be confusing, but in terms of the functioning of the circuit it's exactly the same.

Last I remember, you had no sound happening after the bandwidth switch. Did you ever get sound into the envelope sensing portion of the circuit? If you have it at one side of a part, but not on the other side of that part when sound should be there, either you have a bad solder joint, or the signal is being shorted somewhere accidentally, usually ground. Find the point where sound stops and reflow all joints, check for continuity to ground where there shouldn't be any, and try jumpering over parts that don't seem to be working to see if that changes things.

If you do have audio going into the 1458 but nothing coming out, then perhaps the opamp really is the culprit, but I think any 1458 should work.

[add4]

Hey Taylor, thanks for your help,
I did not had sound at the band witch switch because i did not input AC signal into it, as you said, the cap blocks the DC voltages so the probe does only a really small noise on the following pars  on my pcb. However, if i play music through the effect while i probe it, I have sound everywhere on the envelope circuit. While touching the envelope follower part with the probe, i can actually hear the envelope trigger when i touch them.
It's as if the envelope follower worked, but the sound from the input was not hot enough to trigger it. When i do that the LED does light up too , very lightly.

I reflowed every component of this part of the pcb, one by one...
Does it ring a bell for you?

However i have questions about the decay pot:
on the schematic, is connected to the attack pot, and then to a 1.5K resistor to ground, with the middle lug of the pot being sent between the pot and the resistor. But i really don't see it happening on the pcb. is that normal? In fact, i have the impression that the 1.K5 resistor is placed BEFORE the decay pot, connected to 5 of the op amp,

Parts that are in series work no matter the order in which they're placed. It seems I reversed the order of these parts on the board but not in the schem, which I can see could be confusing, but in terms of the functioning of the circuit it's exactly the same.

Last I remember, you had no sound happening after the bandwidth switch. Did you ever get sound into the envelope sensing portion of the circuit? If you have it at one side of a part, but not on the other side of that part when sound should be there, either you have a bad solder joint, or the signal is being shorted somewhere accidentally, usually ground. Find the point where sound stops and reflow all joints, check for continuity to ground where there shouldn't be any, and try jumpering over parts that don't seem to be working to see if that changes things.

If you do have audio going into the 1458 but nothing coming out, then perhaps the opamp really is the culprit, but I think any 1458 should work.

[Taylor]

Do you have the optocouplers in right? The side with the plus symbol is the LED side. The other side is the resistor. Make sure you have them in the right sides and that the positive side of the LED part is where the + symbol is.

If they're in right, then while playing sound into the pedal check if the resistance across the resistor side is changing with the input dynamics.

[add4]

Hello Taylor, thanks for your help ..
They seem to be places correctly: I have the VTL5C3 that you mentioned on the building list, so if they are placed correctly, the writing symbols over them are facing the PCB so the plus side of the led goes closer to the bandwith switch.

i measure 38.9k between the legs of the resistor side of the octocoupler. That value doesn't change at all with the input dynamics.
The voltage between the LED legs is 1.58 V and doesn't change at all with input dynamics too ..

I also tried to clip a direct lead from the 9v to the + side of the LED, with a 4.7k resistor between the two. the LED lights up, and the filter changes when the led gets enough voltage to light up. i tried playing with the controls while turning the led on and off intermittently: the attack, decay and intensity pots seem to be working. . can't hear anything change when the bandwith switch is being turned around though.. is it a normally big change or rather subtle?

so the octocoupler part seems to work ok.

So i guess the problem still ahead in the envelope part.. i rechecked the values of all resistors of this part of the circuit, just to be sure, they are ok.
If you have another suggestion/idea of something to check i'll gladly take it
Many thanks for your help on this Taylor!

Do you have the optocouplers in right? The side with the plus symbol is the LED side. The other side is the resistor. Make sure you have them in the right sides and that the positive side of the LED part is where the + symbol is.

If they're in right, then while playing sound into the pedal check if the resistance across the resistor side is changing with the input dynamics.

[digi2t]

I'm just wondering if someone can confirm that this project will work with an MC1458. I've had the same thing happen to me as add4, got MC1458's, instead of LM1458.

[Taylor]

In my next Mouser order I'll get some of the MC1458 and test them in my known-working board.

But, I'm looking at the datasheets for these chips, and if the equivalent schematics are to be believed, they are identical internally. It seems somewhat unlikely that they could be different enough to not work. But, since I believe the envelope detector is using the opamps near their limits of operation, perhaps chip tolerances are such that some units will work and others won't, even of the same exact part number. That would be pretty frustrating. I'll have to check it out.

It's also worth mentioning that this circuit is a little hard to use at first. Probably everybody tweaked the knobs and switches in every possible permutation before deciding it wasn't working, but I just thought I'd mention that. It's possible to set it in ways where it doesn't do much.

[karter2000]

I got my Meat Sphere done today, and while everything went together well my wet signal is very weak or quiet.  I get lots of dry or clean, but not much wet, even at 100% wet.  Has that happened to anyone before?

EDIT: Ok, did some messing around, and obviously I have the send and return incorrectly hooked up.  I plugged a cable into the send and receive, and I didn't get signal with the cable in or out.  However, when I pulled the return plug out just slightly, the pedal seemed to work as it should.  I'm using a switching jack like in the build docs, and I'm pretty sure I've got things hooked up as per the diagram.

[add4]

Just a follow up on this .. so i plugged the effect again this morning, and thought i'd try tweaking all the knobs while playing music through it, and ..... it works!!
I haven't changed anything since last time i tweaked it .. i guess it was working but  the intensity, attach and decay switch weren't high enough to make it work properly ...
Thanks a million Taylor for taking the time to help me with this..
i also confirm that is does work with the MC1458, even if i don't know if it works correctly :-)
this pedal makes a LOT of wierd noises, it's actually not easy to dial in a straight - in your face envelope filter tone without tweaking it a bit.
List of questions i have and would have confirmed by other builders:
- I find that the intensity and color pots have to be kept very high to hear anything happening.
- I also think i might have some trouble with the up/down switch on of the positions clearly doesn't behave as well at the other with the switch all the way to the left it behaves as i imagine it should. when i turn it right, i get a very bassy sound, and no envelope again ... might have to check the connections there.
- the LED still doesn't light up too .. I might definitely have a problem with the up/down switch !
- the band witch switch does do ... something .. but i'm not really sure what with the moog mod it does some weird bubbling effects that are not happening in the other positions so it does work
- I get a kind of oscillating wobbling filter sound on some settings .. like the envelope triggers back and forth randomy when a chord rings.. does that sound normal?
i guess theres still things to tweak.. but this is already encouraging!

[WhenBoredomPeaks]

Just a follow up on this .. so i plugged the effect again this morning, and thought i'd try tweaking all the knobs while playing music through it, and ..... it works!!

- I get a kind of oscillating wobbling filter sound on some settings .. like the envelope triggers back and forth randomy when a chord rings.. does that sound normal?
i guess theres still things to tweak.. but this is already encouraging!

Glad to hear that it is working finally. When i first plugged my guitar into mine i thought that it is not working but then i strummed a chord hard enough to make the envelope work and it came to life.

Mine does that wobbly thing too with chords, i think it is because it can't track the signal well enough.

Here are some settings i've found somewhere on the net:

All settings have the trigger on Full and the filter at Low-Pass. The settings for the filter are Hi, Mid-Hi, Mid-Low, and Low (just to differentiate them).

Nice Autowah - Really liquidy and almost Bootsy-esque. I use this setting the most. If you're getting crazy peaks and it's making a lot of noise, try turning down the sensitivity first, and then the colour.

Sensitivity - Max
Attack - Min
Decay - 10 o'clock
colour - max
intensity - max
blend - max
trigger - UP
Filter - Mid-Hi

Mu-Tron Sound - You gotta adjust the Decay to taste on this one. It cops a pretty good Mu-Tron sound here though. Dynamics and how hard you hit and how you pluck the strings will really affect how this sounds.

Sensitivity - Max
Attack - Min
Decay - 12 o'clock to 1 o'clock
colour - max
intensity - max
blend - max
trigger - DOWN
filter - Mid-Hi

Nick Fyffe of Jamiroquai Tone - This is the setting he used on Jamiroquai's - A Funk Odyyssey (songs Little L and Main Vein) since he used a Meatball. It's kinda like a submarine funk sound.

Sensitivity - Max
Attack - Min
Decay - 1 o'clock to 2 o'clock
colour - max
intensity - 12 o'clcok
blend - * (there should be a * marking at about 1-2 o'clock, put the knob there)
trigger - DOWN
filter - Mid-Hi

Dubby Space Deep Filters - These are like the manual setting for the DOWN filter. Except a little deeper and spacyier.

Sensitivity - Max
Attack - Min
Decay - 9 o'clock to Max (the more the longer it will take to close the filter)
colour - Max (you might need to ease this back if you get a lot of intense peaks, bass or feedback)
intensity - max
blend - max
trigger - DOWN
filter - Mid-Low

edit: btw i think i gonna label my pots different than on the Meatball, colour=resonance, intensity=envelope depth, this way it makes more sense to me

[ringworm]

It sounds like this pcb has all the same quirks that the original Meatball had. I pitched in on an old thread in which the original pedal was cloned as people wanted to build it with on-board pots and switches.
It's here: http://www.diystompboxes.com/smfforum/index.php?topic=54508.0
It's worth a read for people trying to get used to playing this pedal and understanding what each control does (or doesn't do) It can take a few weeks to really get to grips with it. Leds not lighting, reverse sweep sounding odd, ripple (swirling noise), uselessness of the colour pot (when left unmodded, in fact even when modded I always left it at full) and weak filter activation were all symptomatic of the original Meatball pedal, never mind the many diy clones that were built. It's that sensitive to guitar output that I remember putting a new set of strings on mine even helped with triggering the filter, I also built the tonepad micro-amp project to put in front of it to get it really going.
I never got round to boxing it up but this pcb might twist my arm!

[WhenBoredomPeaks]

Where would you guys connect an external LFO to the circuit? I realized that i like the Meatball's filter sound than more than other filters i've made so i want to control it with an LFO instead of other filters.

I'd put it after the envelope detector but i am not exactly sure where is a good place for that on the PCB.

Sadly since this PCB have more layers i can't really follow it to match the schematics.

[daverdave]

If you want to drive the filter with an LFO instead of the envelope detector, just drive the optocouplers with an LFO instead.
Drive the LED side of the vatrols with the lfo, I'd say just before the up down switch, using an spst to switch in the lfo.

[WhenBoredomPeaks]

If you want to drive the filter with an LFO instead of the envelope detector, just drive the optocouplers with an LFO instead.
Drive the LED side of the vatrols with the lfo, I'd say just before the up down switch, using an spst to switch in the lfo.

Thanks!

Here is a mod in exchange for my next question:

If you want to make the filter easier to trigger, lower the 4K7 resistor connected to the Sensitivity pot. Alternatively raising the Sens pot's value can be useful too.
It is 1k in mine at the moment, you can go lower.
(when you crank the sens pot it forms 10k/4k7 voltage divider with that resistor, so ~1/3 of your guitar signal is still gets grounded but if you lower the resistors value down to like 1k you get only 1/10 loss.)

And the question: How to get more resonance out of the filter? I think changing the value of that 1k5 resistor connected to the colour pot can be the key. I wouldn't mind if the resonance could go up to oscillation. Maybe i should remove that 1k5 resistor to break the connection?

And a bonus question: (i will mod this all the way to Meat Sphere MKII )
If i want to achieve a slower filter attack response is it enough to raise the value of that 10uF electrolyte after the Attack pot?
(btw i am not sure if my attack pot does anything at all, i can hear what the decay does though)

[daverdave]

I've had a few beers, but 'll try and answer.

Lowering the 4.7k resistor increased the gain of the precision rectifier, but it's already pretty high. Opamps lose alot of gain at higher frequencies, so setting the gain for 1800 may not give you that exact gain, the amplified signal will be whatever frequency you've pumped into the recifier. I guess you're only interested in the fundamental to integrate but someone else probably can give a better idea of the flaws with this. I've open looped recifiers before to get maximum sensitivity, so the opamp acts like a comparator, works ok but you lose all sensitivity (well I did).

Just had a quick look in the ol' active filter cookbook by Don Lancaster (great book), as I see it, the colour pot is changing the damping by controling the amount of positive feedback fed back, the 1.5k resistor is limiting the voltage divider to a certain ratio above zero, I'm guessing changing it won't have a great affect but give it a shot, it's always worth a try. When I mess with sallen keys I always do a similar thing when using a volateg divider as a Q control. You could try and increase R20, which should give you more gain through the filter, only a bit, to 1.2k or somet. Might just oscillate like crazy or do nothing for whatever reason, more gain means more positive feedbvack and a higher Q value so it's worth a shot. I don't know the state variable filter thatn well.

As for longer attack times, increasing the 10u cap should give a slower attack as it will take longer to charge through the resistor, but I don't know how much. The reason for the attack not having much affect when the pot is turned up is for the current losses across the resistor I think. There are ways of getting a slower attack whilst maintaining the triggering, but they involve using more components, depends how many more parts you're willing to include.

Hiope this helps.

[electrosonic]

Sorry if it has been answered, but what is the purpose of the diodes in the feedback loop of the first stage?

Andrew.