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The Alison Project
Joined: Jul 21, 2006
Posts: 187
Location: Canada
Audio files: 2
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 Posted: Thu Aug 16, 2007 5:12 am Post subject:
Mankato Issue |
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I just finished my first Mankato and I have one slight problem. When using as a LFO when the Coarse pot is from 0-30% my output at +6dB increases in frequency no matter what way the LFO was currently going, one it hits top frequency (I guess) is stays put, I get the exact opposite from the +24dB output, it goes low and stays low.
This is with the Fine tune pot at approx 50%, any ideas????
This is a Rev 2 board. |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Thu Aug 16, 2007 12:28 pm Post subject:
Re: Mankato Issue
Subject description: Possible causes |
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| The Alison Project wrote: | I just finished my first Mankato and I have one slight problem. When using as a LFO when the Coarse pot is from 0-30% my output at +6dB increases in frequency no matter what way the LFO was currently going, one it hits top frequency (I guess) is stays put, I get the exact opposite from the +24dB output, it goes low and stays low.
This is with the Fine tune pot at approx 50%, any ideas????
This is a Rev 2 board. |
Hey Chris,
Let me make sure I understand the problem: You have a Mankato acting as an LFO controlling the pitch of a VCO. The Mankato is oscillating when the Coarse control is above 30% or so, but when you drop it lower than that, the pitch of the VCO goes up (or down, depending on what Mankato output you're using) and stays there. Am I right?
If so, my first guess is that the Resonance trimmer is set too high (higher resistance = less feedback = Mankato less likely to oscillate). I've had this happen where the filter will oscillate just fine at higher frequencies, but stops oscillating at low freq. A slight tweak of the trimmer should get you going.
If that doesn't cure the problem, then I would:
1 - Check the components in the CV summer (R42a, b, c, d; R37; R38; R39; R41; D1; C15) to make sure they're the right value. Double check D1 to make sure it's oriented correctly.
2 - Swap a new TL072 for U5.
3 - Make sure any parts in sockets are seated firmly in the socket.
4 - Make sure you have V- at one end of the Coarse pot, and V+ at the other, and that the voltage at the wiper changes in a nice linear fashion as you rotate the pot.
Most likely, the problem is with the Resonance trim, but let me know if none of this helps. As a side note, you might want to change R42d (the 1V/OCT CV input resistor) to 200K, and R43 (the V/OCT trimmer) to 1K. This will make setting the response to 1 v/oct much easier. |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Thu Aug 16, 2007 12:32 pm Post subject:
Mankato Issue
Subject description: Knew I forgot something |
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Geez, I forgot to sign off from that last message!
Tim (a day without parenthesis is like a day without punctuation) Servo |
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The Alison Project
Joined: Jul 21, 2006
Posts: 187
Location: Canada
Audio files: 2
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| Posted: Thu Aug 16, 2007 12:38 pm Post subject:
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Yeah I havent touched the trims yet, after I sent the message I went to sleep cause I was up a bit later having Mankato fun.... I will try that.
Note: my 42d is 200k and 1v/oct trim is 1K
thanks, sorry if it was just the trims, may have jumped the gun on this one |
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janvanvolt
Joined: Nov 24, 2005
Posts: 285
Location: Mainz, Germany
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| Posted: Wed Aug 29, 2007 6:58 pm Post subject:
Re: Mankato Issue |
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Hi!
I'll also have some issues (after finishing the soldering today).
The VCF does not react to any FM input.
i only get a very "quiet" output signal when IN pot is fully turned CW, turning CCW get it quieter. Reversing connection 1 and 3 i get a loud signal all the times.
Reso works. So down to two issues: - no CV control and output signal (or is it input) problem.
thanks for any ideas. i'll appreciate any help. |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Wed Aug 29, 2007 8:43 pm Post subject:
Re: Mankato Issue
Subject description: Thing to check |
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| unit-sound wrote: | Hi!
I'll also have some issues (after finishing the soldering today).
The VCF does not react to any FM input.
i only get a very "quiet" output signal when IN pot is fully turned CW, turning CCW get it quieter. Reversing connection 1 and 3 i get a loud signal all the times.
Reso works. So down to two issues: - no CV control and output signal (or is it input) problem.
thanks for any ideas. i'll appreciate any help. |
Hey U.S.
Couple of things I'd check first:
V/Oct trimmer - set it to mid point. This shouldn't be a problem even if it was set to maximum resistance, but it's so easy to eliminate it as a potential source of trouble.
Connector wiring - double and triple check that. Hook up just one Audio input and one FM input and get those working first.
Component Values - Check everything there, and make sure D1 is oriented correctly.
Power supplies - check them (carefully) at the IC supply pins
U1 V+ at pin 4, V- at pin 11
U2 V+ at pin 16, V- at pin 9, Ground at pin 11
U3 V+ at pin 4, V- at pin 11
U4 V+ at pin 8, V- at pin 4
U5 V+ at pin 8, V- at pin 4
**************************************
If none of this helps, shout out again and we'll take it from there.
Tim (carefully) Servo |
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janvanvolt
Joined: Nov 24, 2005
Posts: 285
Location: Mainz, Germany
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Posted: Fri Aug 31, 2007 5:01 pm Post subject:
Re: Mankato Issue
Subject description: Thing to check |
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Hi Tim.
Results:
-D1 correctly wired.
-D2 /D3 is 1N4002 instead of 1N4001 (should not harm)
U1 V+ is 12V, V- is 0V
U2 V+ is 12.8, V- is -13.1
U3 V+ is 12V, V- (pin 11) is 0V, pin 12V is -13.1V
U4 V+ is 12.8V V- is -13.1
U5 V+ is 12.8V V- is -13.1
Tests:
SINE from VCO ..
COARSE/FINE in middle position
FM1 full CCW, RES full CW
When VCO into FM IN, i still hear it even when FM1 is CCW, gets more "modified" when turning CW wise.
When VCO in AUDIO IN, very quiet signal heard, but nothing really hearable.
Update: (02:39 CEST)
resoldered audio input.
when using the pot (B100K) with audio in, i get the "low signal", if i short the in/out part at the pcb, it works w/o any problem. i'll try another pot now.
Update: (03:47 CEST)
Problem fixed. one bad pot, and two cab cable connections (which you cannot see).
Need to finish the other jacks, but i'm done  |
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numbernone
Joined: Aug 16, 2006
Posts: 477
Location: new york city
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| Posted: Sat Sep 01, 2007 10:29 am Post subject:
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Wired up the first Mankato last night. This is as killer as promised, well worth the wait for sure. Couple questions... the coarse pot seems to sweep the full range from about 40%-90% of the rotation. Any lower goes waaay sub audio and disappears. Probably have to swap out a resistor? But I still cant figure out which one on my own...sniff sniff whimper.
Also, not EXACTLY sure what im looking for when tuning the res trimmer. I suppose the point at which it begins to self osc?? This is by ear mind you, I am still in the scopeless and hopeless class.
Anyhow, a total killer unit. Hats off to Thomas and Tim. Tonight I am gonna attempt some of the roundroom quad panning action, for which I have been waiting decades. |
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Thomas Henry
Joined: Mar 25, 2007
Posts: 298
Location: Southern Minnesota
Audio files: 2
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| Posted: Sat Sep 01, 2007 11:44 am Post subject:
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The Coarse pot is supposed to have a lot of range. This allows the unit to handle any combination of summed control signals (+5V types or 10Vpp types, or even inverted signals, in any combination). It's really no different than the usual Electronotes input stage on VCOs and VCFs.
Thomas Henry |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Sat Sep 01, 2007 11:57 am Post subject:
Mankato Issue
Subject description: Tuning, Resonance and other goodies |
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| numbernone wrote: | Wired up the first Mankato last night. This is as killer as promised, well worth the wait for sure. Couple questions... the coarse pot seems to sweep the full range from about 40%-90% of the rotation. Any lower goes waaay sub audio and disappears. Probably have to swap out a resistor? But I still cant figure out which one on my own...sniff sniff whimper.
Also, not EXACTLY sure what im looking for when tuning the res trimmer. I suppose the point at which it begins to self osc?? This is by ear mind you, I am still in the scopeless and hopeless class.
Anyhow, a total killer unit. Hats off to Thomas and Tim. Tonight I am gonna attempt some of the roundroom quad panning action, for which I have been waiting decades. |
Hey Number,
Cool, I'm glad you like the TH-201. I'm extremely happy with how it has turned out. I love the way it sounds as a VCF, and it's also my favorite LFO (I'm now spoiled by it's range and find myself missing it in other LFO modules). As far as the range of the Coarse Tune, that's actually one of the best parts of the Mankato. You do have to be careful though, because the audio range is about the middle third of the pot's travel. If you're using the Mankato as a VCF, setting the Coarse Tune too low will result in no sound because the cutoff frequency is below audio range. This isn't something you have to worry about with most VCFs but as we know, the Mankato is... different.  The extended low range is why the Mankato can work as a slew limiter. A normal slew / glide circuit is basically a simple low pass filter, but set to work at sub-audio range. Most VCFs don't go low enough in frequency to really work as a glide circuit (and you have to have DC coupled inputs). Still, if you do want to limit the range of the Coarse Tune pot, change R37 (currently 150K). A higher value will reduce the range. BTW, R39 is currently a 3.3M and sets the Fine Tune range.
As far as the Resonance setting, what you want to do is set it high enough to allow oscillation when the Res pot is turned all the way up, but low enough to limit the distortion in the sine waves. The 6dB out is the most suceptable to the distortion, so monitor that one when you're setting the resonance. To make sure the Mankato is still oscillating at low frequencies, use it as an LFO to modulate the pitch of a VCO. Here's an excerpt of the info we send out now with the assembly docs:
******************
Trimming and adjustment is pretty simple. You'll want to set the
Resonance Trim first. Just turn the resonance pot up all the way, and
leave the freq pots set about to mid range. You should see a sine wave
at the outputs (if you're monitoring the outputs with a speaker, be
careful as the sine wave out is pretty hot). Look at (or listen to)
the 6dB output and adjust the Res Trim for the cleanest sine wave. If
you adjust the Res Trim too low, the sine wave starts to look really
nice and smooth, but the VCF won't sustain oscillation, especially at
lower frequencies. Because of this, you may need to do some tweaking
to get it to initially break into oscillation. Try setting the Res pot
and the Res Trim to their minimum resistance and "kick start" the VCF
with an audio input if you can't get it to initially oscillate. Give
the VCF a few seconds to start oscillating, again, this is especially
true if the Res Trim pot is set on the low side. The V/Oct trim is
self explanatory. Simply check the frequency and adjust for the best
tracking with a CV input to the unattenuated 1V/Oct FM input.
One item to always watch for on the Mankato: The frequency adjustment
has a VERY wide range. It is very easy to set the frequency so low
that nothing is heard when using it as a VCF. When using the Mankato
as an oscillator, too low will be below the range of hearing, and the
maximum frequency is about 22kHz! The "Audio Range" of the Coarse Tune pot is approximately from 10 o'clock to 2 o'clock. Also, you'll
probably end up setting the FM input attenuators lower than you would
on most VCFs, as the entire modulation range is (usually) more than
you want. Remember that the Mankato has a frequency range of about
2,000,000 : 1, so the low end is VERY low, and the high end is, well,
a heckuva lot higher than I can hear.
***********************
Hopefully this will help you get started. Give a shout if you're still having any troubles.
Tim (...different) Servo |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Sun Sep 02, 2007 12:30 pm Post subject:
Re: Mankato Issue
Subject description: Thing to check |
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| unit-sound wrote: | Hi Tim.
Results:
-D1 correctly wired.
-D2 /D3 is 1N4002 instead of 1N4001 (should not harm)
U1 V+ is 12V, V- is 0V
U2 V+ is 12.8, V- is -13.1
U3 V+ is 12V, V- (pin 11) is 0V, pin 12V is -13.1V
U4 V+ is 12.8V V- is -13.1
U5 V+ is 12.8V V- is -13.1
Tests:
SINE from VCO ..
COARSE/FINE in middle position
FM1 full CCW, RES full CW
When VCO into FM IN, i still hear it even when FM1 is CCW, gets more "modified" when turning CW wise.
When VCO in AUDIO IN, very quiet signal heard, but nothing really hearable.
Update: (02:39 CEST)
resoldered audio input.
when using the pot (B100K) with audio in, i get the "low signal", if i short the in/out part at the pcb, it works w/o any problem. i'll try another pot now.
Update: (03:47 CEST)
Problem fixed. one bad pot, and two cab cable connections (which you cannot see).
Need to finish the other jacks, but i'm done |
Wow, a bad POT? Now that's one you don't hear every day. I'm very glad you got it sorted out though. I still worry a little bit about V- on IC1 sitting at 0 volts. That really should be the same negative voltage you have on the other chips. Make sure that is all sorted out, and it sounds like you're ready to rock!
Tim (built like a rock... a short, round rock) Servo |
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The Alison Project
Joined: Jul 21, 2006
Posts: 187
Location: Canada
Audio files: 2
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| Posted: Mon Sep 03, 2007 7:57 pm Post subject:
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Alright, so I double checked all the parts played with the Res trim and nothing fixed it, so I put it aside...
I built my second one, all parts from the parts list. (the first one i used diff versions opamps I had on hand) this time I used the specified ones, and it does exactly the same thing when using it as a LFO...
How are people wiring up the 1V/oct jack, I just took my jack directly the the SW pad at the end of the CV Inputs.
Same time everything else works great and I am having tons o fun with this VCF. |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Fri Sep 07, 2007 12:09 pm Post subject:
Mankato Issue
Subject description: Fixa the no worka |
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| The Alison Project wrote: | Alright, so I double checked all the parts played with the Res trim and nothing fixed it, so I put it aside...
I built my second one, all parts from the parts list. (the first one i used diff versions opamps I had on hand) this time I used the specified ones, and it does exactly the same thing when using it as a LFO...
How are people wiring up the 1V/oct jack, I just took my jack directly the the SW pad at the end of the CV Inputs.
Same time everything else works great and I am having tons o fun with this VCF. |
Hey AP,
The 1v/oct jack is normally meant to be used with a switching jack. Starting with the PCB connector, pin 1 goes to the "signal" lug, pin 2 goes to the "ground" lug, and pin 3 goes to the "switched" lug. If you're not using a switched jack, just use pins 1 and 2. Perhaps this input isn't wired correctly? A little info: There's a connector on the right hand side of the PCB just below the DC power input that is meant to take a 1v/oct input from a distribution board. The CV In pin on that connector goes to pin 3 of the 1v/oct jack connector and then through the switching jack.
Let me know if you're still having problems and I'll see what else I can think of. I'm really swamped right now, preparing for AH Cali this Sunday, so I apologize in advance if I can't get a reply out until next week. Thanks!
Tim (last-minute thrash session) Servo |
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Tim Servo
Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
Audio files: 11
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Posted: Mon Oct 29, 2007 6:21 pm Post subject:
Re: Mankato Issue
Subject description: Frequency range |
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| The Alison Project wrote: | I just finished my first Mankato and I have one slight problem. When using as a LFO when the Coarse pot is from 0-30% my output at +6dB increases in frequency no matter what way the LFO was currently going, one it hits top frequency (I guess) is stays put, I get the exact opposite from the +24dB output, it goes low and stays low.
This is with the Fine tune pot at approx 50%, any ideas????
This is a Rev 2 board. |
Hey Chris,
Is this still an issue? I realize it's been a while, but I've just tweaked a few part values and I get a more usable range from the Coarse Tune pot now. I changed R37 to 220K and R38 to 402K. This makes the Audio Range a bit wider, and gives me oscillation with the Coarse pot anywhere from "1" to "10." It will still stop oscillating if I turn Coarse all the down below 1, but that little extra bit of range can be useful when working with several summed CV sources. Details and a new parts list are in the "Mankato Builds" topic. Let me know how your Mankati are working out.
Tim (whippin' the Mankati into shape) Servo |
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