Building the Meat Sphere

[charmonder]

- 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!

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

Is it kind of the sound like a sewage drain gargling water?(but on mars of course!) if we're talking about the same wobbley sound, I'm about 99% sure that  its that the guitar signal is getting clipped on its way to the envelope, even though it doesnt sound clipped in the filter's audio path. so there's nothing wrong with the circuit, its just too much signal. sometimes this is a desired effect, like the roland funny cat.  if you've included the effect loop a good solution is to use a limiter (or compressor on limiter setting)

you can substitute limiter for compressor, or maybe soft clipping distortion/OD, but limiter will be the best at preserving dynamics without putting wobble on chords. probably a good simple pedal for this situation is mxr dynacomp. maybe if theres a simple limiter circuit it would actually do wonders in place of the "bandwidth" control, I don't really get much use out of the band width maybe its helpful on bass

the only problem though is that now the "clean" side of the blend knob exports the limiter sound, where as itd probably be more useful if it exported the sound of the fx chain going into return the jack. which seems like an easy mod, BUT you'll need a buffer for these two signals to actually mix. I haven't actually done this mod YET so beware that it might not work(seems like it should though! so first get a buffer circuit, then take another lead from the return jack, wire it to the buffer input, then use a lead from the buffer output to replace the first lug of the blend pot. I think this should improve the blend knob in normal guitar--->meatball-->amp situations.

but then again the lack of buffers in the circuitry has its charm.

[charmonder]

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.

somewhat agree,  but I find in bandpass mode intensity usually has to be very low for me to even hear anything

- 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.

yes! I have the same difficulty so its possible theres anything wrong with your circuits. unless you can never get one of those two positions to work. hundreds of times now Ive been convinced that UP mode was not working, its like the "sweet spots" for a knob are only relative to other knobs, and then ALL these relationships change when switching between UP or DOWN mode. and even that change depends on what signal is going into the box. /cathy.

- the LED still doesn't light up too .. I might definitely have a problem with the up/down switch !

the LED is tricky! I never figured it out, for the one of my meatspheres where the LED seems to work, it never works for any of the good filter settings!

- 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

this takes the highs out of the signal going to the envelope, like rolling back the guitar tone knob. when you find a good setting overall, try switching between Half and Full, you should notice that the filter responds to the bassier notes better in Half mode. you might also use Half mode to get smoother attack shapes.

[add4]

very interesting .. thanks .
i'm still trying to find a way to make the envelope work before boxing it ..

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.

somewhat agree,  but I find in bandpass mode intensity usually has to be very low for me to even hear anything

- 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.

yes! I have the same difficulty so its possible theres anything wrong with your circuits. unless you can never get one of those two positions to work. hundreds of times now Ive been convinced that UP mode was not working, its like the "sweet spots" for a knob are only relative to other knobs, and then ALL these relationships change when switching between UP or DOWN mode. and even that change depends on what signal is going into the box. /cathy.

- the LED still doesn't light up too .. I might definitely have a problem with the up/down switch !

the LED is tricky! I never figured it out, for the one of my meatspheres where the LED seems to work, it never works for any of the good filter settings!

- 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

this takes the highs out of the signal going to the envelope, like rolling back the guitar tone knob. when you find a good setting overall, try switching between Half and Full, you should notice that the filter responds to the bassier notes better in Half mode. you might also use Half mode to get smoother attack shapes.

[WhenBoredomPeaks]

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.

I swapped the 10u cap with a 100uf one. It made the decay slower but did not affected the attack. Someone told me on an other forum that i should use a 500k pot for the attack pot instead of the stock 5k pot.

[daverdave]

Increasing the pot will stop the evelope triggering as the higher resistance will allow only a tiny current to pass, there's hardly any current there anyhow.

It's not a circuit that can achieve long attack times really, the losses you'll incure by increasing the attack pot just will mean a more useless travel on the pot.

There are other types of follower circuits that can acheive slower attack times, but are generally more complex.

[WhenBoredomPeaks]

Increasing the pot will stop the evelope triggering as the higher resistance will allow only a tiny current to pass, there's hardly any current there anyhow.

It's not a circuit that can achieve long attack times really, the losses you'll incure by increasing the attack pot just will mean a more useless travel on the pot.

There are other types of follower circuits that can acheive slower attack times, but are generally more complex.

Ok, i am actually thinking about going back to the stock cap because i've found some cases where consecutive fast notes couldn't "retrigger" the envelope follower. (even on the fastest decay setting)
Btw i've sent some synths through the pedal and it worked pretty good with the different volume ADSR settings i used on the synths.
Sadly now i want a standalone ADSR generator which can be retriggered by my pic attack and i would use that to control the brightness of the LEDs in the vactrols of the pedal.

[giantrobot]

Hey guys! I just finished the Meatsphere and it sound pretty awesome but I have a wee problem. For some reason when I turn the Up/Down switch to up position my LED turns off. Sup wit dat? I'm new to DIY so excuse my noobishness

[LaceSensor]

the led is an indicator of the envelope "position"

in up, its off, then gets brighter the more the evelope is "opened" (becoming more trebley) ie by picking harder
in down, its on, meaning fully "open" , then goes off, representing the filter "closing" (becoming more bassy) when you pick

hope that helps. Its normal.

[ottopit]

Hi,

Having a bit of trouble with this build... no effect and weak signal, to make matters worse I ended up burning up the plated area where the positive leg of the LED goes because my iron was too hot. My question is can I add the jump to the +9V on the board or is there something more specific it needs to go like close to one of the Vactrol? Sorry for the total beginner questions not that great at following(or understanding) the schematic yet.

     

[Taylor]

The LED gets switched to different spots by the up/down switch, so you can't just connect to 9v or ground, but you can follow where the traces go pretty easily on the board.

The POS pad goes to the RLED right pad, the other goes to the negative LED legs of the optocouplers. Just verify visually where it's connected and you can run a wire to whichever pad got burned up.

[ottopit]

Just to add to the above. If looking at the schematic and tracing the audio path so it would go in-> 470n cap-> pin 12 of the TL074->pin 14

then, this is where I get confused, does it break of and go through send -> sensitivity 10k -> SW1 bandwidth (3) ->no connection, 470n or 22n -> LM1458 pin 2 than 3  etc..  Not sure if Im on the right track here and when it goes through send is the only time its hitting the LM1458?

[ottopit]

The LED gets switched to different spots by the up/down switch, so you can't just connect to 9v or ground, but you can follow where the traces go pretty easily on the board.

The POS pad goes to the RLED right pad, the other goes to the negative LED legs of the optocouplers. Just verify visually where it's connected and you can run a wire to whichever pad got burned up.

Thanks Taylor, I ordered another pcb from you today 'cause I'm Jones'n for this effect so figure I might divide and conquer I guess I wasn't looking close enough because I assumed the path to the rled was just negative only.

Probably a really dumb question but would it make a difference for my volume issues if there was no LED connected? I know the Vactrols have I guess use it to indicate the level of envelope from what I've read above, but should it completely kill the signal. Just wondering how much importance it has if I just jumper it for now to focus on the lack of volume and effect, I never could get it to light before I ended up burning the pad anyway. 

[Taylor]

The LED just lights up to show the envelope action, so if you don't need it just leave it out and do not jumper it. It won't affect the sound or functioning of the pedal at all besides having no LED to look at.

[DavidM]

Hi all,
Have a question that has been asked before to no reply. What is the purpose of those diodes in antiparallel at the very beginning?.

Thanks,

David

[ottopit]

When I probe this with an audio probe, the sound is the right level from input to the first 1.5k resistor but from the other side of the resistor to anything else in the audio path the sound is really faint I have to crank my amp to hear it, I tested for continuity on that 1.5k and it was fine but I'll reflow or replace it anyway.
Just wondering if anyone has ever probed this audio path can you confirm if the level is supposed to drop that quickly(or at all) and maybe where in the circuit it would get loud again. 

[ottopit]

Okay after careful examination of the parts I installed on the board it looks like I put a 1.8 Ohm resistor in place of
the 1M8 resistor    maybe that explains why the sound drops so significantly after the 1.5k resistor since thats the next component after (God I hope so!) I'll try to source some from my local electronics shop. 

[slacker]

Have a question that has been asked before to no reply. What is the purpose of those diodes in antiparallel at the very beginning?.

The diodes are to protect the opamp inputs, these can be damaged if something causes the voltage on them to be different by more than a certain amount. It's drawn with the diodes between the output and + input, but as the output is connected directly to the - input, the diodes are also connected between the two inputs.  The diodes mean the two inputs can never be different by more than 0.6 volts. I don't really understand this and I'm not sure what it protects against. In normal use the diodes don't do anything.

Google "opamp differential input protection" if you want some more information, or someone here who knows what they're talking about might be able to provide a better explanation.

[Taylor]

Okay after careful examination of the parts I installed on the board it looks like I put a 1.8 Ohm resistor in place of
the 1M8 resistor    maybe that explains why the sound drops so significantly after the 1.5k resistor since thats the next component after (God I hope so!) I'll try to source some from my local electronics shop. 

Ah, yes that'll definitely do it! Those resistors form a voltage divider, and with those values you're nearly muting the sound. Glad you found the source of the issue.

[DavidM]

Thanks for your reply, Slacker. So better to leave them there.

OT: Still owe you my progress on the dry output for the EchoBase. Will let you know when I am done.

Best,

Dave

[ottopit]

Cool repacing the 1M8  solved my audio issues, I had some other external factors that stopped the effect from happening but for now I have it up and running! Man its cool!
So glad to have it working I've been playing with it for hours (taking a break right now but will be back at it, heheh)

The other issues I had, were that I had a problem with the send /return jacks, something was shorting out or not wired quite right, so I just wired the send to return for now;The other problem or at least I suspect  was using my AMZ power supply I built, during which I used an L7812cp instead of the 7809cp regulator for more headroom and I guess was feeding it too much voltage and was getting little to no effect  I then put it in my "sag"output on AMZ that was giving out around 6 volts or so and this thing sprang to life in a very good way! I then put it in my Power Pedal with around 9 volts or so and the effect was there but not as good as  the Sag output.

I guess I will continue on and get the send/return jacks going, then hopefully get the Led running, try the Moog mod and the Colour mod which is what I'll probably do next.I really learned quite a bit from this experience...shout out to Taylor for getting this on a killer board.

Next up after this will be a Ugly Face, then maybe Taylor's Tap Tremolo and then eventually the Skyripper...man I'm getting %^&*y now!