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Sound lab mini mk2 vca ?
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ToriD



Joined: Mar 22, 2013
Posts: 12
Location: Usa

PostPosted: Fri Mar 22, 2013 7:06 am    Post subject: Sound lab mini mk2 vca ?
Subject description: Not sure if it works properly
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I don't understand how it operates but if I select the vco 1 with ad2 mod set to zero it produces sound if I turn the ad2 mod all the way up sound stops but when I play a note it will not decay fast even if the ad2 is set to zero

Could someone explain this the vca operations in depth. Thank you
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elmegil



Joined: Mar 20, 2012
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PostPosted: Fri Mar 22, 2013 8:23 am    Post subject: Reply with quote  Mark this post and the followings unread

According to the Block Diagram, VCO1 is only modulated by AD1, and VCO2 is modulated by AD2. Or do you mean the VCA which is modulated by AD2?

What do you mean by "makes sound", are you saying it's on continuously, or when you play a note?

It would help understand better if you explain all your settings through the sound chain --> what (if anything) is modulating the VCO, what are the mixer settings, what are the filter settings, what are the VCA settings? What is your keyboard source?

Normally when I'm troubleshooting one of these I take out as many variables as possible, for example, no keyboard should be attached, cutoff on the LPF should be set all the way up and the resonance all the way down, the VCA should be all the way open, the mixer should have only the VCO I'm testing all the way up and everything else all the way down, none of them being further modulated, and then make sure the VCO behaves as I expect. Then step through each of the components, does the mixer setting do what it should? Does the filter cutoff do what it should? Does modulating the filter cutoff do what it should? Does adjusting the resonance behave as I expect? Etc....
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ToriD



Joined: Mar 22, 2013
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PostPosted: Fri Mar 22, 2013 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
According to the Block Diagram, VCO1 is only modulated by AD1, and VCO2 is modulated by AD2. Or do you mean the VCA which is modulated by AD2?

What do you mean by "makes sound", are you saying it's on continuously, or when you play a note?

It would help understand better if you explain all your settings through the sound chain --> what (if anything) is modulating the VCO, what are the mixer settings, what are the filter settings, what are the VCA settings? What is your keyboard source?

Normally when I'm troubleshooting one of these I take out as many variables as possible, for example, no keyboard should be attached, cutoff on the LPF should be set all the way up and the resonance all the way down, the VCA should be all the way open, the mixer should have only the VCO I'm testing all the way up and everything else all the way down, none of them being further modulated, and then make sure the VCO behaves as I expect. Then step through each of the components, does the mixer setting do what it should? Does the filter cutoff do what it should? Does modulating the filter cutoff do what it should? Does adjusting the resonance behave as I expect? Etc....


Yes VCA modulated by ad2 what should this section do when working properly
Do you have any sound examples?

Ok so vco1 is all the way up kbd switch selected using midi to cv converter connected to an ipad for controll vco2 and white noise all the way off. Filter resonance and cut off any position (except, not the resonance all the way up, because of self oscillation) in the VCA section ad2 all the way down source mod knob turn any position selector switch set to vco1 not pressing any keys on the control source vco1 makes continuos sound then if I turn up the ad1 mod knob in the vca section vco1 stops making continuos sound until I press a key.
is this function correct? When a key is pressed on the control source it decays very slow no matter what I set ad2 at even if everything is all the way down.

Is there a step by step process to troubleshoot the whole device to ensure every thing is operating right

Thank you
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elmegil



Joined: Mar 20, 2012
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PostPosted: Fri Mar 22, 2013 11:45 am    Post subject: Reply with quote  Mark this post and the followings unread

It's a large device, so I'm not aware of any step by step procedure. It's mostly about following the logic.

I think having the keyboard in the mix is not good for this early testing.

I can make some sound samples this evening with my Soundlab (NOT a Mark II, but very similar).

One thing that seems strange about the setup as you have described it is that it sounds like you are using VCO1 both as the audio input AND as the modulation source. For initial testing, that switch should be "off". I'm assuming from the block diagram that it is an on-off-on SPDT switch, it should be in the off position and the attenuator/pot associated with that modulation should be all the way off, as you have done with the AD2 modulation. At this point, the Master Volume on the VCA should be the only thing controlling your signal--when it is off, the sound is off, and when it is on, the sound is at whatever level it is set to. No other input or knob twiddling should have any impact.

So then turn the AD2 modulation attenuator up. I believe it is right function for this to cut off the sound. I have not digested the schematic, but on the soundlab the AD EG puts out a negative voltage as its steady state.

Set the AD2 mode switch to gated. With the mod attenuator all up, press the AD2 manual gate and see if you get sound. I'm assuming the Attack pot is relatively fast, and the Release pot is relatively slow.

This sounds like the point where you have your (first Smile ) problem--if changing the release pot doesn't get you a different release time, that's definitely not right, and that's what it sounds like you're describing.

If you switch the mode to triggered, do the same test with the manual gate button, and see if changing the Release value changes the sound any. If you set the release too short, you may hear nothing or just a pop.

You might also try switching the short/long switch on AD2 to see if that makes any difference. The actual AD shape is set by caps C39 and C40, and even if there's something wrong with the decay pot wiring, switching the cap should change the behavior (how long it takes to decay).

If switching does change it, I'd be looking at the wiring of the Decay Pot and/or if the diode attached to it is wired backwards or something. (I originally cited R133 and D10, but then I realized those are the numbers for AD1, not AD2, I don't know those part designators...but the equivalent parts for AD2, not AD1).

Good luck, like I say I'll post some audio samples tonight after I've had a chance to play with my soundlab.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Fri Mar 22, 2013 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, I was going to use SoundCloud's nice comment feature to annotate my MP3, but unfortunately their new interface doesn't work right, so I can't put more than one comment on my own track.

So this is going to be commentary in order, but without any good time placement. Hopefully it makes sense.

Starts off with the AD connected, but the AD attenuator all the way down. I turn up the master volume, and you can hear that it's letting VCO1 through the VCA even though *its* master is also all the way down.

I then turn the AD attenuator up, which cuts off the VCA. This sounds like what you described and as I said I'm pretty sure it's normal.

I then turn the VCA master up and down a couple times just to make sure I can get the sound through it.

Then I hit the manual gate button (with the AD in gate mode). There's a short attack and a moderate length decay, and it stays loud while I'm pressing the button.

Then I switch to trigger mode and do the same thing, get a simple envelope, no hold while I'm pressing the button.

Then I connect VCO1 to the modulation input, and you hear it's making sound again.

I hit the manual gate while this is going on and you can hear it get loud again, but then it never goes to silence.

I disconnect VCO1, press the gate button a few more times, first time with a long decay, then twice with a short decay, then with a really long decay, and then with a really short decay.

And then it's done.

Hopefully this helps you get some idea what you ought to hear anyway.


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ToriD



Joined: Mar 22, 2013
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PostPosted: Sat Mar 23, 2013 11:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay so I'v astablished that the decay on the ad2 does not work but all the wiring is correct. Can't for the life of me figure out what the problem is
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elmegil



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PostPosted: Sun Mar 24, 2013 6:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I assume that means the attack works?

I'm still stuck on that diode, if it were backwards it could cause this, but I don't really see if you've checked it how that could be the problem.

You haven't mentioned whether switching between "short" and "long" has any effect.
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ToriD



Joined: Mar 22, 2013
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PostPosted: Sun Mar 24, 2013 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I assume that means the attack works?

I'm still stuck on that diode, if it were backwards it could cause this, but I don't really see if you've checked it how that could be the problem.

You haven't mentioned whether switching between "short" and "long" has any effect.


I checked the diodes and they are all facing the right way
The attack works fine the long and short switch seems to work properly

The only thing that come to mind is maybe the potentiometer is the wrong one but I would assume even a wrong one would do something?
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elmegil



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PostPosted: Sun Mar 24, 2013 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

yes, even a wrong one would do something. You actually connected the wiper though, right? If that weren't connected it would always be seeing the longest possible decay and the position of the wiper wouldn't matter, so the knob wouldn't do anything.
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ToriD



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PostPosted: Sun Mar 24, 2013 4:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
yes, even a wrong one would do something. You actually connected the wiper though, right? If that weren't connected it would always be seeing the longest possible decay and the position of the wiper wouldn't matter, so the knob wouldn't do anything.


I found that it is the right pot.

Not sure what you mean by connect the wiper? I did not have to on any of the other pots.
It does seem to be stuck on the longest delay though

I did wire it properly I know that. I'v checked it several times
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elmegil



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PostPosted: Sun Mar 24, 2013 6:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

So what I meant:

a standard single pot has three terminals: Clockwise, Counterclockwise, and wiper. The wiper is the part that moves. In the AD circuit, the attack and decay pots are wired as rheostats, or variable resistors. The amount of resistance is what is supposed to determine the decay. Low resistance, fast decay, and vice versa.

Here's another thought; it's not common, but I could see perhaps the pot has something wrong with it. You might try hooking a small resistance in parallel with it, say a 100K resistor--from pin 1 to pin 2 per the circuit diagram, and see if THAT changes anything. If you get a faster decay then there is still something wrong with the pot. If you don't, and you're positive you have the pot wired correctly (sounds like you've checked it enough times Smile ) then the problem must lie elsewhere.

If you have a scope I think it might also be fruitful to look at the wiper (pin 2) of R157. Try disconnecting the wire that goes from there over to switch 4 to isolate *just* the ADEG and see if the oscilloscope behavior changes. That way you can tell if it's in the AD that your problem lies or if it's in what it connects to.

I'm assuming the connection from there to the banana is what you expect it to be....that wiper should only go to the switch and to the banana, not anywhere else.
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ToriD



Joined: Mar 22, 2013
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PostPosted: Sun Mar 24, 2013 9:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
So what I meant:

a standard single pot has three terminals: Clockwise, Counterclockwise, and wiper. The wiper is the part that moves. In the AD circuit, the attack and decay pots are wired as rheostats, or variable resistors. The amount of resistance is what is supposed to determine the decay. Low resistance, fast decay, and vice versa.

Here's another thought; it's not common, but I could see perhaps the pot has something wrong with it. You might try hooking a small resistance in parallel with it, say a 100K resistor--from pin 1 to pin 2 per the circuit diagram, and see if THAT changes anything. If you get a faster decay then there is still something wrong with the pot. If you don't, and you're positive you have the pot wired correctly (sounds like you've checked it enough times Smile ) then the problem must lie elsewhere.

If you have a scope I think it might also be fruitful to look at the wiper (pin 2) of R157. Try disconnecting the wire that goes from there over to switch 4 to isolate *just* the ADEG and see if the oscilloscope behavior changes. That way you can tell if it's in the AD that your problem lies or if it's in what it connects to.

I'm assuming the connection from there to the banana is what you expect it to be....that wiper should only go to the switch and to the banana, not anywhere else.


I'm slightly confused? The questionable pot is R152
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elmegil



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PostPosted: Sun Mar 24, 2013 10:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

R157 is the level output for AD2, and as such is the primary connection from AD2 to the rest of the world. The clockwise leg of the pot ( marked X63) is the only other outbound connection, and if you want to be 100% isolated, you should disconnect the wire that goes from there to R185 as well (blue in the wiring diagram).

Once you disconnect AD2 from all its possible connections, you can look to see if it still behaves the same way using a scope. If it does, you definitely need to be drilling down into the AD2 circuit. If suddenly it starts working, then your problem is somewhere in that wiring to R185 or outbound from the wiper of R157.

Honestly I do expect the problem is most likely in AD2 but there's only way to be sure, and it's best not to assume once the basic steps haven't resolved the problem.
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ToriD



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PostPosted: Mon Mar 25, 2013 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
R157 is the level output for AD2, and as such is the primary connection from AD2 to the rest of the world. The clockwise leg of the pot ( marked X63) is the only other outbound connection, and if you want to be 100% isolated, you should disconnect the wire that goes from there to R185 as well (blue in the wiring diagram).

Once you disconnect AD2 from all its possible connections, you can look to see if it still behaves the same way using a scope. If it does, you definitely need to be drilling down into the AD2 circuit. If suddenly it starts working, then your problem is somewhere in that wiring to R185 or outbound from the wiper of R157.

Honestly I do expect the problem is most likely in AD2 but there's only way to be sure, and it's best not to assume once the basic steps haven't resolved the problem.


The only problem is all the wiring is very tight and getting a soldering iron in there is going to be tricky

I'm hope to find a less invasive approach
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ToriD



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PostPosted: Mon Mar 25, 2013 8:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay so some how I don't even know how the decay in ad2 works maybe just a matter of moving wires

I put a vm on the questionable pot and it measured up properly then examined all the wires thoroughly plugged it in and all of a sudden it works

Hopefully it stays functioning

My question now is. what does the mod knob in the VCA section set to vco1 supposed to sound like

On mine it has some effect but not much for instance if I set the two vco s to 0 and the filter resonance to 0 cut off up so basically only the vco1 mod knob is making sound it sounds like vco1 but at a much lower volume if the mod know is set to max it will make continuos sound regardless of ad2 setting. then if I turn up vco1 in the mixer section it pretty much over throws the mod knob in the VCA section and appear to have no to very minimal effect where as if I set it over to lfo mod it has a massive effect

Questions run rampant???
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elmegil



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PostPosted: Mon Mar 25, 2013 9:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

I hate when things fix themselves, because then I worry they'll be back. Good luck though, glad it's working.

ToriD wrote:

My question now is. what does the mod knob in the VCA section set to vco1 supposed to sound like

On mine it has some effect but not much for instance if I set the two vco s to 0 and the filter resonance to 0 cut off up so basically only the vco1 mod knob is making sound it sounds like vco1 but at a much lower volume if the mod know is set to max it will make continuos sound regardless of ad2 setting. then if I turn up vco1 in the mixer section it pretty much over throws the mod knob in the VCA section and appear to have no to very minimal effect where as if I set it over to lfo mod it has a massive effect

Questions run rampant???



The idea is that you're modulating the volume with an audio rate signal rather than the LFO rate signal. Don't send VCO1 to the mixer (turn down it's mixer knob) if you're doing this, or it will not be easy to tell what's going on.

It definitely will override AD2. Basically your VCA has two modulation signals which are mixed -- AD2 (at whatever level that knob is set to) and either VCO 1 or the LFO (at whatever level THAT knob is set to).

I would bring VCO 2 up all the way on the mixer, and/or some noise, VCO 1 all the way down on the mixer, and then turn up the modulation with the switch set to VCO 1, and vary the VCO 1 frequency. That should tell you if you're getting what you ought to. When it's very low frequency (for a VCO) it ought to sound like the LFO at a medium to high frequency....try fiddling with it though to be sure.

Oh yeah, that will only happen if you're using the same waveforms, so set them both to sawtooth to do that comparison.

I've attached the same with my soundlab, with just the square wave of VCO2 up on the mixer, modulating the VCA with VCO1, and then modulating the VCA with the LFO. The main difference is that the level from the LFO is higher, so it's a little louder. I also switched the LFO to the low low (rather than the high low Smile ) frequency range at the end.


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ToriD



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PostPosted: Tue Mar 26, 2013 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Elmegil

Your help has been very usefull!!
Thank you

The VCA seems to work properly, the main issue was I just didn't understand how it worked and I was trying to modulate vco 1 with vco 1 duh what was I thinking lol

All that's left know is the calibration process which may be a ways of since I do not own an oscilloscope. Nor do I know how to use one

I think I can still have fun with it in the mean time though

Thanks again
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elmegil



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PostPosted: Tue Mar 26, 2013 9:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Calibration can be done by ear, but you would still have to have a source of exact 1V step voltages. There's a pretty easy one to build at the music from outer space website, but I can see just playing without calibrating being a lot more fun Smile

Glad I could help.
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