Moon 505 - cutoff frequency calibration?

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levelhead3
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Moon 505 - cutoff frequency calibration?

Post by levelhead3 » Tue Jun 04, 2019 12:58 am

I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?

In low pass mode the filter really doesn't open up at all until 12:00 or so.

Adding a bit of CV brings the response more into the line of the rest of my filters, but without that the range is rather limited - and it makes LFO modulation less than useful as well.

JohnLRice

Re: Moon 505 - cutoff frequency calibration?

Post by JohnLRice » Tue Jun 04, 2019 1:30 am

levelhead3 wrote:I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?
Probably? Take a look at the back of yours, there are six trimmers labeled:
V/OCT
TUNE
REGADJ
REGOFS
OFFS1
OFFS2

I haven't tried adjusting any of these myself.

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hsosdrum
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Post by hsosdrum » Tue Jun 04, 2019 7:09 pm

Before you go fiddling about, try running your LFO modulation oscillator's output thru a Dotcom Q125 signal processor and then to the 505. That should give it more "oomph" when opening and closing the filter.

levelhead3
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Post by levelhead3 » Wed Jun 05, 2019 12:16 am

hsosdrum wrote:Before you go fiddling about, try running your LFO modulation oscillator's output thru a Dotcom Q125 signal processor and then to the 505. That should give it more "oomph" when opening and closing the filter.
The problem isn't the LFO's amplitude, it's that LFO's are bipolar - so they're driving the cutoff frequency down through half the waveform. As the cutoff frequency control dictates the center point for this modulation, it's a problem when through most of the control's travel the cutoff frequency is already lower than expected/desired.

Did that make any sense? It was a no-coffee day... :ripbanana:

levelhead3
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Re: Moon 505 - cutoff frequency calibration?

Post by levelhead3 » Wed Jun 05, 2019 12:23 am

JohnLRice wrote:
levelhead3 wrote:I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?
Probably? Take a look at the back of yours, there are six trimmers labeled:
V/OCT
TUNE
REGADJ
REGOFS
OFFS1
OFFS2

I haven't tried adjusting any of these myself.
Sounds like TUNE might be it. I will pull the module and take a peek.
Thanks John!

JohnLRice

Re: Moon 505 - cutoff frequency calibration?

Post by JohnLRice » Wed Jun 05, 2019 12:50 am

levelhead3 wrote:
JohnLRice wrote:
levelhead3 wrote:I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?
Probably? Take a look at the back of yours, there are six trimmers labeled:
V/OCT
TUNE
REGADJ
REGOFS
OFFS1
OFFS2

I haven't tried adjusting any of these myself.
Sounds like TUNE might be it. I will pull the module and take a peek.
Thanks John!
If you can before you make any changes mark the original position using a fine point Sharpie or what ever works so you can set it back to the way it was if needed. 8-)

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Rex Coil 7
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Post by Rex Coil 7 » Wed Jun 05, 2019 11:05 am

levelhead3 wrote:
hsosdrum wrote:Before you go fiddling about, try running your LFO modulation oscillator's output thru a Dotcom Q125 signal processor and then to the 505. That should give it more "oomph" when opening and closing the filter.
The problem isn't the LFO's amplitude, it's that LFO's are bipolar - so they're driving the cutoff frequency down through half the waveform. As the cutoff frequency control dictates the center point for this modulation, it's a problem when through most of the control's travel the cutoff frequency is already lower than expected/desired.

Did that make any sense? It was a no-coffee day... :ripbanana:
I do not own a Q125 but I believe you can adjust the input signal's offset with that module. You may then adjust the amplitude with the Q125 along with the offset ...

:despair:
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hsosdrum
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Post by hsosdrum » Wed Jun 05, 2019 4:14 pm

Rex Coil 7 wrote:
levelhead3 wrote:
hsosdrum wrote:Before you go fiddling about, try running your LFO modulation oscillator's output thru a Dotcom Q125 signal processor and then to the 505. That should give it more "oomph" when opening and closing the filter.
The problem isn't the LFO's amplitude, it's that LFO's are bipolar - so they're driving the cutoff frequency down through half the waveform. As the cutoff frequency control dictates the center point for this modulation, it's a problem when through most of the control's travel the cutoff frequency is already lower than expected/desired.

Did that make any sense? It was a no-coffee day... :ripbanana:
I do not own a Q125 but I believe you can adjust the input signal's offset with that module. You may then adjust the amplitude with the Q125 along with the offset ...

:despair:
What Rex said. The Q125 can add a -5V voltage offset. I'm currently using my 125s with EGs that output between 0V and+5V. The Q125's negative offset allows the EGs to close filters waaaaaaaaay more than they could when the EGs are connected directly to the filter's VC inputs.

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Dave Peck
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Post by Dave Peck » Wed Jun 05, 2019 5:06 pm

regardless of how an incoming CV signal gets processed, the complaint in the original comment is describing something that does not seem right at all. Turning the cutoff knob half-way up (to 12 o'clock') and there is still no audible effect of the filter opening?? That sounds like the filter is just not operating correctly.

Check it this way: patch pink noise or white noise into the filter. Set the filter to LOWPASS. Turn the resonance up pretty high, about 80%.

Now, sweeping the cutoff knob SHOULD change the sound, going from a low rumble to bright unfiltered noise, and the change should be smoothly controlled by the cutoff knob - it should not be normal for the entire first half of the knob travel to have no effect on the cutoff frequency.

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diophantine
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Post by diophantine » Wed Jun 05, 2019 6:55 pm

I'll echo what Dave suggests as a test, but would like to add:

Are you using the dedicated Low-Pass Output, or the Mixed Output?

With the Mode pot CCW (Low-Pass Mode), do those outputs behave the same, or differently? (Turn the Mode Modulation pot CCW, too, just in case...)

JohnLRice

Post by JohnLRice » Wed Jun 05, 2019 10:49 pm

Note: I have two 505's here, a pre-productions prototype that was sent to me for testing and demoing and another one that I bought from Noisebug last year. I checked both today and they behave very differently! The prototype self resonates easily but can't fully cutoff the output when the frequency knob is fully counter clockwise, but the newer production one can't self resonate at all but does cut off the output, at least it can reduce a pink noise input to a slow sub sonic range.

I'll experiment with adjusting the trimmers on mine at some point but I'm wondering if the design of the circuit only allows for one or the other responses? :hmm: Something to keep in mind for folks trying to make adjustments.

levelhead3
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Post by levelhead3 » Thu Jun 06, 2019 1:49 am

Dave has the right of it, this has nothing to do with the processing of the CV inputs. Both the fixed and variable frequency control inputs work exactly as expected.

I mentioned CV in the original post only to point out that adding a +5v CV brought the response of the cutoff frequency control into the expected range - to highlight the fact that as-is it appears to be set way too low. Sorry if that confused the issue.

Also sorry I didn't make my originally testing methodology clearer - white noise into the signal input, no CV input, filter mode all the way counter clockwise, regeneration control set to 3:00 or higher, cutoff frequency control set all the way counter clockwise and then slowly raised - the cutoff frequency remains subsonic until 11:00 or so. There is no difference between the mixed and dedicated low pass outputs.

Every other low pass filter I have has a discernible frequency sweep throughout the cutoff frequency control's range.

JohnLRice

Re: Moon 505 - cutoff frequency calibration?

Post by JohnLRice » Fri Jun 07, 2019 7:07 am

levelhead3 wrote:
JohnLRice wrote:
levelhead3 wrote:I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?
Probably? Take a look at the back of yours, there are six trimmers labeled:
V/OCT
TUNE
REGADJ
REGOFS
OFFS1
OFFS2

I haven't tried adjusting any of these myself.
Sounds like TUNE might be it. I will pull the module and take a peek.
Thanks John!
Yes, it is indeed the Tune trim pot. (it's a 10 turn pot so not possible to mark it before changing but it's pretty easy to hear whats going on and the change is gradual). I played around with my newer factory production one which didn't seem to be doing a lot between 0 to 5 but it did cut off the output completely when fully counter clockwise. After adjusting it back and forth I settled on a setting where nothing really happens between 0 - 0.5 (although the output isn't completely cut off) on the low end and also no obvious effect between about 8.2 - 10 on the high end. I tried all of the other trimmers (except the 1v/oct) to try to determine what they affect but couldn't determine that they did anything. :hmm: :despair:

Here's a quick Instagram video for reference. I had the regen cranked all the way clockwise.


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Re: Moon 505 - cutoff frequency calibration?

Post by Thalassa » Fri Jun 07, 2019 10:25 am

JohnLRice wrote:no obvious effect between about 8.2 - 10 on the high end.

That might be that the filter is fully open and the resonance is going ultra-sonic. The best way to see it is to connect it to an oscilloscope and check if the resonance frequency is changing between 8,2 and 10

levelhead3
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Re: Moon 505 - cutoff frequency calibration?

Post by levelhead3 » Fri Jun 07, 2019 11:18 am

JohnLRice wrote:
levelhead3 wrote:
JohnLRice wrote:
levelhead3 wrote:I was wondering if there was any sort of calibration possible for the cutoff frequency control on the Moon 505?
Probably? Take a look at the back of yours, there are six trimmers labeled:
V/OCT
TUNE
REGADJ
REGOFS
OFFS1
OFFS2

I haven't tried adjusting any of these myself.
Sounds like TUNE might be it. I will pull the module and take a peek.
Thanks John!
Yes, it is indeed the Tune trim pot. (it's a 10 turn pot so not possible to mark it before changing but it's pretty easy to hear whats going on and the change is gradual). I played around with my newer factory production one which didn't seem to be doing a lot between 0 to 5 but it did cut off the output completely when fully counter clockwise. After adjusting it back and forth I settled on a setting where nothing really happens between 0 - 0.5 (although the output isn't completely cut off) on the low end and also no obvious effect between about 8.2 - 10 on the high end. I tried all of the other trimmers (except the 1v/oct) to try to determine what they affect but couldn't determine that they did anything. :hmm: :despair:

Here's a quick Instagram video for reference. I had the regen cranked all the way clockwise.

:hail:

Thanks John. I will check out the vid then take a crack at it this weekend and report back.

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