"Funky MF (Multimode Filter)" - LM13700 Multimode Envelope Filter

[orangetones]

Cliff,

Schematic is the one on the first page of this thread.  I'll try what you have mentioned though...

[frequencycentral]

That 10K resistor to ground from the release pot limits the release time - any shorter and weird stuff starts to happen. You could try making it a bigger value, or try dialling in a longer release. You shouldn't have to increase the value of the cap to ground that follows it.

I get a very loud popping when the filter engages.  Loud pop/click as the sound comes in, then it sounds fine.

Hmm, don't know why that should be. Is the effect acting as you would imagine it should other than this?

[orangetones]

It is not the release that is the issue (I am assuming that by release here we are talking about the decay).

I haven't had much chance to play around with it yet, but it seems to be doing its thing.  I couldn't really experiment becuase the loud surging at the beginning of every note was too loud and the wife was getting a little mad!

[frequencycentral]

........and the wife was getting a little mad!

There are a full set of voltages I posted a couple of pages back. You could check yours against them. Also, have a fiddle with the trimpot.

I only ever use this pedal with a distortion before it - you could try that and see what you get. It will kind of compress the signal, simplify the waveform, and make it more useable for the envelope follower to handle.

Good luck!

[orangetones]

Question (surprised it wasn't asked before), but do the voltages for the pin in your voltage posting match with the layout that I created?  i.e. are pins 1-3 that voltage divider on your tl062 voltages?, Are pins 1-3 on your LM324 the ones that connect to the diode and such?

I only ask because you probably didn't use the same parts of your opamp ICs for the same particular opamps in the circuit.  Right?

So again, do your pin readings match the pins on my posted layout?

[orangetones]

Here are the voltages that I have nebbed using a 12V regulator.  I will go over the circuit later on and see if I have built it wrongly on the breadboard.  There is always the possibility tha tI have made an incorrect connection in laying it out.

I have probably made a mistake, but Rick, is there any chance that there is an error in the schematic?  Seeing as that other fellow had trouble with my board layout that follows the schematic properly?

I am hoping to get this to work...  We'll see!

LM324
1   0.253
2   0.014
3   0.004
4   12.19
5   0.025
6   0.055
7   0.055
8   9.99
9   5.96
10   5.95
11   0.001
12   5.95
13   5.97
14   0.014

LM13700
1   0.522
2   0.331
3   6.08
4   6.25
5   0.15
6   0.001
7   0.14
8   2.061
9   1.923
10   0.002
11   12.19
12   0.002
13   5.91
14   6.08
15   0.004
16   0.522

NE5532
1   6.08
2   6.08
3   6.05
4   0.002
5   2.061
6   2.753
7   1.356
8   12.19

[orangetones]

Just another thought, I am using some Log taper pots, so mid point on them woudl be different from mid point on yours (assuming you used all linear as stated in the schematic.)

[frequencycentral]

Question (surprised it wasn't asked before), but do the voltages for the pin in your voltage posting match with the layout that I created?  i.e. are pins 1-3 that voltage divider on your tl062 voltages?, Are pins 1-3 on your LM324 the ones that connect to the diode and such?

I only ask because you probably didn't use the same parts of your opamp ICs for the same particular opamps in the circuit.  Right?

So again, do your pin readings match the pins on my posted layout?

I based my voltages on your layout - which required some detective work!

I built my pedal directly from the schematic itself, so any mistakes there would have translated to my build too.

As for you using log pots - you could dial them in so the resistance is equal both sides of the wiper.

Just looking at all those voltages, it's one hell of a debug. You also might like to refer to the original schematic that I base my design on: this circuit.

[orangetones]

Rick.  I agree, one heel of a debig.  I am going to trace the schematic again and go over the breadboard.  I might have something not connected properly.  I just got back from crosscountry skiing, so time for a shower and then a little circuitry!

I'll let you know if anything turns up...

[orangetones]

Updated Voltages.  I had one pot switched with another.  (1M where 100k should be and viceversa).  I set all the pots for equal resistance on either side and then measured the voltage again.  Still the same problem (loud popping when filter engages). and still different voltages.

Next step is to check the chips.  See if there is something wrong with them.  Try different ones from my stock.  Check some values too. 

If anyone has any thoughts on specific areas of this circuit to check over, let me know!

The filter sounds great when it engages, but that darn pop!  Just like a loud static discharge!

LM324
1   0.064
2   0.010
3   0.004
4   12.19
5   0.037
6   0.055
7   0.055
8   9.68
9   5.77
10   5.76
11   0
12   5.77
13   5.77
14   4.18

LM13700N
1   0.522
2   0.01
3   6.08
4   6.24
5   0
6   0
7   0
8   2.254
9   1.863
10   0.002
11   12.19
12   0.003
13   5.92
14   6.09
15   0.1
16   0.522

NE5532
1   6.09
2   6.09
3   6.06
4   0
5   2.254
6   2.949
7   1.353
8   12.19

[frequencycentral]

If anyone has any thoughts on specific areas of this circuit to check over, let me know!

The filter sounds great when it engages, but that darn pop!  Just like a loud static discharge!

The 10K resistor between the unity gain buffer and pins 1/16 of the 13700 is a critical value. The three resistors in that ara set the initial frequency of the filter. If that 10K is any lower you will have problems. Raise it and you will raise the initial frequency of the filter. You might try increasing the value a little - try 15K maybe. Also, play with the trimmer, mine is set halfway around at teh moment.

A little earlier in this thread Mark Hammer suggested a cap in series just before the range control - that might be a good idea, and maybe something I should experiment with on mine.

[orangetones]

Rick,

I have checked everything,  even changed out the chips.  Checked the values, tried that 10k/15 thing.

Here is what I can see as the problem.  This damn popping!  It is like there is a gate or a threshold which I must pass before the filter takes effect, but once I have broken through, so to speak, I can play softly and get the funky sounds, as long as I don't let the envelope close fully (or else I have ot pick hard to get back into that envelope).

You see?

Does this make any sense?  Any thoughts on this? 

I kind of wondered if you driving this with a distortion or something avoided this problem.  How does yours sound when driving it clean?  Then again, you would probably notice the pop!

Maybe I will PM Mark Hammer for his thoughts incase he isn't reading this thread.

[frequencycentral]

Here is what I can see as the problem.  This damn popping!  It is like there is a gate or a threshold which I must pass before the filter takes effect, but once I have broken through, so to speak, I can play softly and get the funky sounds, as long as I don't let the envelope close fully (or else I have ot pick hard to get back into that envelope).

I get it. Mine doesn't do that. If you're getting 'funk' then the filter is working well. It would seem to be a problem with the envelope follower. Did you try it with a distortion before it yet?

Maybe I will PM Mark Hammer for his thoughts incase he isn't reading this thread.

That's a good idea - I can breadboard/build this stuff but I don't fully understand the hows and whys. I have no doubt that the envelope follower could be improved by someone like Mark who understands what's going on.

[Cliff Schecht]

The envelope follower you used is a standard approach to the problem. I think that Oranges problem lies either in an incorrect value or maybe a miswire somewhere. I just ran some simulations on the circuit and it does its job as it should. I'd recommend for Orange to double check values first (although I'm sure you have) and maybe try increasing the "attack" resistor value to 100k or larger to see if that slows down his dV/dt (change in voltage over time) enough to prevent the popping. Anything under a few milliseconds and you're going to hear that audible "click/pop" at the output every time you hit the strings hard.

Frequency: It always helps to understand the circuits you design with, but it's obvious that you aren't all that lost. Understanding op-amp design is really not that hard once you understand a few limitations, and even those LM13700 OTA's aren't hard once you understand how a transconductance amplifier works. TBH, everything in your schematic is pretty dang standard and so explaining the circuit isn't as hard as you think. If you want, I can break it down for you in more detail than you'll care to know .

[orangetones]

I am going to triple check this later tonight.  As for changing the attack resistor value.  Do you mean the 47k attack pot? or some other fixed value resistor?

[Mark Hammer]

Got your note orange.  Your faith may be a little misplaced in this instance.  I'm reckoning Steve Giles is your man, but I will offer one suggestion: consider popping the NE5532 out and sticking a TL062 in, since that is what was originally used.  I'm also wondering if the resonance is too high.

[orangetones]

Mark,

The NE5532 is only in the output buffer (I am assuming that's a buffer!) and the voltage divider.  I have a tl081 in there right now though.

I retraced the schematic and redid the breadboard layout.  My 10k resistors measure about 9.75.  Maybe this circuit is really finicky with values?

[orangetones]

Rick, I am wondering which of the opamps in the schematic you used the tl062 and the lm324 for?  Is it possible that having the TL062 performing the function of a specific part of the circuit has something to do with the problem?

[Cliff Schecht]

I am going to triple check this later tonight.  As for changing the attack resistor value.  Do you mean the 47k attack pot? or some other fixed value resistor?

Yup. You can try making this pot value much larger, or put in different resistor values instead (like 100k, 470k, 1meg, etc..) and see if it helps anything out. You could have a bad pot in there, which would explain why you have so much attack that your filter pops. If that pot can't get over something like 100 ohms then you're most likely going to hear that pop.

I wonder if Rick'sbuild will pop if he turns the attack pot all the way counter-clockwise (or whichever way takes the pot to 0 ohms). Let us know by plucking the crap out of some strings!

[puretube]

If anyone has any thoughts on specific areas of this circuit to check over, let me know!

The filter sounds great when it engages, but that darn pop!  Just like a loud static discharge!

The 10K resistor between the unity gain buffer and pins 1/16 of the 13700 is a critical value. The three resistors in that ara set the initial frequency of the filter. If that 10K is any lower you will have problems. Raise it and you will raise the initial frequency of the filter. You might try increasing the value a little - try 15K maybe. Also, play with the trimmer, mine is set halfway around at teh moment.

A little earlier in this thread Mark Hammer suggested a cap in series just before the range control - that might be a good idea, and maybe something I should experiment with on mine.

I`d implement the voltage divider at the input-side of the buffer... (but keep the 10k where it is!)

and remember, that any voltage applied to the 10k must exceed 2 diode-drops, before any current flows into pins 1/16...