mcmeat problem

[jmasciswannabe]

Been workin on this one and can't seem to find the problem. I am getting filtered sound, but no envelope. Like a fixed wah sound. Switch 1 isnt doing anything as well as no discernable difference with the attack decay and intensity. Looking at the schem this points to the stuff surrounding the lm1458. The light does come on. Can anyone give me some hints or some voltage or audio probe points to check to further narrow down the problem? Switch 2 works. I want to get this sucker working SOOO bad, and I know I am close.

Thanks
Ian

[jmasciswannabe]

sorry, here's the link:

http://home.planet.nl/~joep.remkes/mcmeat.pdf

[jmasciswannabe]

sorry, here's the link:

http://home.planet.nl/~joep.remkes/mcmeat.pdf

[Mark Hammer]

Well, the first thing youhave to do is verify that the envelope follower has something to work with.  Sooooo, stick your guitar plug into the input jack, stick your DMM probe on the wiper of the sensitivity pot, and with your meter set for something that will let you see AC voltages in the 50-150mv range, strum away.  The Sens pot should be up full, but you can also verify the functioning of the pot by varying its position a bit.

If the signal seems to find its way to the follower side of the pot, then you want to make sure it finds its way to the IC2 side of both C5 and C6.

If you can verify that IC2 has a viable audio signal to boost and rectify, then you will want to measure the AC output of IC2, and the AC voltage at the junctionof D4 and R7.

Okay, now verify that there is a viable envelope signal by measuring the AC voltage on pin 7 of IC2.

If all of that checks out, then it would suggest that somehow that envelope signal is not translating into LED illumination, either because you've oriented your optoisolator wrong, or because you've damaged it somehow.

Provide some feeback on all of these tests, and we';; take it from there.

Incidentally, has the PCB layout been verified?

[markusw]

At the beginning I too had troubles getting a sound from this box until I realised that the wiring was OK, I just did'nt dial in the proper settings to make it working.

If I got it right, the LED flashes when you hit the strings?

SW1: if you turn it to "off" does the blinking stop??

If you turn the intensity pot does the external LED get brighter/dimmer?

Colour pot: to get a reasonable sound you have to turn it nearly to 100% (90-95%). If you want to have a linear response of the coulour pot (which makes the thing much easier to use IMHO) simply connect pin 2 and 3 of the pot with a wire.

One hint regarding the attack and decay pots. As a starting point turn the attack pot to 0 and the decay pot to about 50%, (if the attack is too high the filter does'nt start sweeping) Put the filter in up mode, lp or bp , range pot lowest or one higher. Then increase the sensitivity while playing. Then you should be able to see the LED flashing and hear the filter sweep.

To get the filter working in down mode you may have to increase the decay (and ensure that the attack is at/close to 0, depending on the output of your guitar).

Good luck,

Markus

Edit: oops..too late.

[jmasciswannabe]

First, thanks guys!! Second, I should have mentioned that the light does not flash or blink, its just either on or off.

Mark - always a relief to see your name ....i set my dmm for 200m and got a reading of 5.6 when the light is on off the wiper of the pot. All three lugs actually showed that. Got 1.97 volts after both c5 and c6....2.12 on pin 1 of the 1458....1.71 between d4 and r7....2.03 on pin 7 of the 1458....

while strumming the guitar i get no change in the value off the middle lug while the light is on, it just stays around 5.6 (dmm at 200m)

i don't know if the pcb has been verified or not. I know that there haven't been a lot of builds, and just learned that moos was still trying to get his up and running right.

markusw - intensity does not make light brighter, i thought that i probably didn't have the settings right either, but I believe it is more than that, especially now that i realize it should be blinking as the envelope opens or closes

what i learned: dark to bright makes the envelope go one way bright to dark the other, hence the up and down...that's right, i didn't know that :oops:

what i don't get: how the voltage is controlled to to make the envelope.

[hank reynolds 3rd]

my mcmeat had a similar problem (no triggering ,just a static filter sound) until i realised i had wired the att, decay and intensity pots wired in reverse....
hope this helps, as its the daddy of mutron type filters!!

Sam

[hank reynolds 3rd]

PS: I tried red and green leds ( iread somewhere that the original meatball uses home made optocouplers...) and the green ones seem to be spot on....

[jmasciswannabe]

Ya the wiring is a little tricky.  But I have gone over it many times. It's the reverse of the diagrams on this site right?:

http://pisotones.com/Meatball/psst/meatball-psst.html

I was listening to Beck's Midnight Vultures and decideed that no matter what I must get this circuit working  

Thanks for the advice,  I will go over the wiring AGAIN just to make sure.

[hank reynolds 3rd]

i also had to make sure the 3pdt was wired right (i used a 4pdt,but it works the same)...I´ll try and find the time to see how mines wired up...
I´ve just moved to barcelona and all my stuff (the unboxed pedals) are in jiffy bags, and i´m pretty sure some got f"%ked in transit...

It´s something in the envelope generator/detector tho,i´m pretty sure...maybe a new 1458??

Cheers

Sam

[jmasciswannabe]

I have tried two different ones....i will check the wiring on the 3dpt, too. Ya if you run across it and see the wiring let me know! I hope this thred will clear up any confusion on the wiring of the mcmeat.

[Mark Hammer]

while strumming the guitar i get no change in the value off the middle lug while the light is on, it just stays around 5.6 (dmm at 200m)

That could likely be your problem right there, assuming everything is being measured right (that's 5,6mv AC, right?) .  Somehow no signal is finding its way to the gain stage that forms part of the envelope follower.

what i don't get: how the voltage is controlled to to make the envelope.

The audio signal that comes off the wiper of the Sens pot gets boosted a whole lot, and D3 and D4 make sure that what comes out of IC2 is an AC voltage that only goes in one direction, relative to ground, in contrast to a normal audio signal that would swing both ways from ground.  Then everything in between D4 and pin 5 of the 1458 adds selective amounts of lag so that the rise and fall of the single-sided audio signal can be altered.  THAT, my friend, is your envelope.  If there were no lag added, it would come and go so fast that it would be annoying.

Think of the LEDs in VTL1 and VTL2 as being status LED indicators.  Instead of staying on when you press a button, they only come on when you play loud enough.  R9, R10, R11, and VR5 are used to adjust the amount of current lighting up these LEDs, the same way you might choose a resistor value to provide proper illumination when you wire up a status LED to your 3PDT stompswitch.  The huge gain provided by IC2 is intended to transform your otherwise puny 150mv audio signal (which gets chopped in half by rectification via D4) into something big enough to light the LED up.  Keep in mind that you stick a 2.2k resistor between a 9v battery and a nonsuperbright LED to get a bit of illumination.  The combination of resistances between IC2 and the VTLs lets you stick almost 1.5k in there.  Clearly the audio signal needs to be goosed from its input level to something on the order of a few volts to be able to light up the LEDs enough to make the LDRs change value.

So, that's how it is supposed to work.  It seems to me that somehow, something is preventing IC2 from having anything to boost so as to be able to deliver that fluctuating voltage that lights up the LEDs and makes the filter sweep.[/b]

[jmasciswannabe]

Mark thanks for the info on how it works. You should have told me to read your article over at geofex! Great article, just found it! I need to read all of those, over and over, each time i reread i get a better understanding. As for the mcmeat, I am getting back to it this weekend. I am taking advice from the moose (thanks man!) and stepping away for a bit. Its probably best for the pedal, since last time I checked cursing it didn't fix it. I will let you know how it turns out!

Thanks Again Everyone!!
Ian

[Mark Hammer]

Both the biggest and smallest problems can often benefit from some time away, sometimes.

There's a psychologist at Harvard, who studies what you might call the cognitive basis of obsessive behaviour (http://www.wjh.harvard.edu/~wegner/).  Basically, it revolves around how thinking about something prevents one from considering other information.  His most "famous" work involved telling people NOT to think of a white bear.  Of course, as you'd expect, it tended to be ALL they could think about at that point.  A bit like when you try to remember someone's name, and you go "It starts with a B, and I know it's NOT Bill, but damned if I can remember it".  The name was really Richard, but once you got locked into B and Bill, you were done for.

Stepping away from problems allows you to cognitively "reset" and consider other avenues of solution rather than get glued to one.  That's why "sleeping on a problem" works.

[jmasciswannabe]

Would have been nice if I slept! I actually couldn't sleep last night because I kept thinking of pedals. I would actually see a circuit and think I would know the answer only to realize it wasn't the mcmeat circuit it was a small clone. THis isactually the third time it happened. I'm sure I am not the only one this happens to, at least I hope. I recently graduated with a psychology degree (still working at a musicstore) and remember going over that in my cognitive psychology class. Good stuff.

[Mark Hammer]

I recently graduated with a psychology degree (still working at a musicstore) and remember going over that in my cognitive psychology class. Good stuff.

You bet.  I'm lucky enough to have studied with Al Bregman, one of the real originals in the cognitive psychology of music perception.  http://www.psych.mcgill.ca/labs/auditory/laboratory.html

Understanding how people THINK about sound has helped me here immeasurably.  I hope, by extension, it helps others too.

[jmasciswannabe]

I started audioprobing to try to find where the signal wasn't getting in to the lm1458. Sensitivity pot was working! I got all the way up to d4 until I got no more sound. Unsoldered the end coming from r7, still nothing. That was about the time I realized that the input jack was not plugged in. Plugged up the jack. Then I started audioprobing again at the beginning and didnt get past the D1 end connecting to c4 and pin 13 on tlo74. I removed the tl074 and was able to get sound again up to c4. Any ideas? Hope everyone is ahaving a great memorial weekend!

Thanks
Ian

[toneman]

At D4, the signal is/shouldB a fullwaverectified(FWR) voltage.
this Voltage, drives the LEDs thru the buffer, IC2b.
"Sense" control is amount of signal going to FWR.
More signal, means more FWR voltage @ C7.
Voltage charges up C7 thru Attack, VR2;  
no signal , and Voltage discharges thru Decay, VR3.
FIRST, check signal @ blend/mix control wiper.
Input should equal output with Blend all the way "dry".
"Blend" is a mix of Filter Envelope & straight signal.
NEXT, (audio)signal  goes to input of filter, thru C17.
(from C4, thru Send & Return jacks, if used)
Do U have filter sound at output of Pin1, 7 & 8??(LP,BP,HP)
Got Mix knob all the way to filter??
Got pwr?  Got 1/2 pwr(Vref)?  Got milk??
tone