[IN STOCK] L-1 MutantCure VCF -- Eurorack kit / module.

[L-1]

I made the new filter to replace the old Mutant VCF. Vactrol based 24dB LP HP.

All details please read on my site: http://l-1.su/MutantCureVCF.html


Module:





Kit:

[OlivierWah]

This one is really piece of art.

Very creamy, screamy resonance, a lot of character and insane harmonics at high resonance. And to finish a lot of possibilities with 1v/oct, 2 CV inputs + 1 CV to switch between modes.

Good work !

[L-1]

Thank you Oliver!

[derjip]

Hey, I'm currently building the Mutant Cure VCF. I had to switch to newer opamps, since OPA2604 are not available anymore. I decided to go with OPA1656 in cheap SOIC to DIP adapters (see attached photos). One question though: I could not find any instructions on how to calibrate the module with the trimmers. Did I miss that somewhere, or could you provide some insights?

Thanks a bunch,
Markus

[MoS-squared]

From Aleksei:
"Calibrating is standard - v/oct and offset."

[derjip]

Well okay that's what the silkscreen says
I can loosely think of (or google) a procedure how to calibrate V/Oct (get it into resonance and apply some voltage on 1 V/Oct input, measure output signal frequency, then add multiples of 1V and adjust the trimmer to get multiples of the frequencies and therefore - octaves).
I couldn't find anything about offset calibration, though. Also at Scott Stite's Website, the Mutant VCF design only has V/Oct but no offset trimmer.
If you could hint me to some useful resource, I'd be really grateful, since my search did not yield anything obvious. Sorry if I'm asking trivial stuff here, It's just that those topics are new to me and I'm a bit lost here.

[derjip]

Okay, in case somebody else might also need this, I finally found something here, which I guess makes a lot of sense and can easily be applied to the module:

V/oct adjust
01) Repeat steps for frequency calibration but reconnect the CV keyboard
02) Depress low C (0 volts)
03) Adjust initial frequency slider and fine tune slider for 200Hz
04) Depress C three octaves higher and adjust 1V OCT trimmer for 1600Hz
05) Repeat step 2-4 until low C remains at 200Hz and C3 remains at 1600Hz

Output offset
01) Monitor VCF output with oscilloscope
02) Initial frequency, fine tune, and resonance slider – left
03) All input sliders down
04) Adjust OUTPUT OFFSET for minimum DC output. Movement of the initial frequency slider should not cause more than 1V deflection

[L-1]

there is possible to trimm v/oct only approximately because of vactrols. Pitch flows a bit, so v/oct will be not precise.

You can just set frequency range from 16Hz to 16kHz and don't bother with v/oct.

[derjip]

Ok cool, good to know, thanks!

[muxbutter]

[deleted]

[muxbutter]

I decided to go with OPA1656 in cheap SOIC to DIP adapters (see attached photos).

How did the OPA1656 work out for you? I'm wary to buy OPA2604 from eBay...

Thanks in advance, take care!

[derjip]

I decided to go with OPA1656 in cheap SOIC to DIP adapters (see attached photos).

How did the OPA1656 work out for you? I'm wary to buy OPA2604 from eBay...

Thanks in advance, take care!

Sorry for the late reply. It works well and sounds really great. I don't have a reference to compare to though, can only say that it's one of my most favorite filter in my humble collection

[L-1]

Prices for OPA2604 on Ebay vary from less than $1 to $15 for one chip.

Probably all they are fake.

From the datasheet:
New circuit techniques and special laser trimming of dynamic
circuit performance yield very low harmonic distortion. The
result is an op amp with exceptional sound quality.

Do chinnese these technicues and laser trimming? Probably not. Ithink those OPA at Ebay are just repainted TL072.

Is possible to use some another dual opamp instead of OPA2604, and single opamp instead of OPA604. HiFi ones are preffered. It's a field for experiments.

[MoS-squared]

I'm wary to buy OPA2604 from eBay...

I've been using opa2134s for builds, but SynthCube also lists having the opa2604 in stock...oddly they show a picture of an opa2134...
https://synthcube.com/cart/index.php?ro ... ct_id=7527

[L-1]

This is OPA2134 I bought from official source.
As you can see a circle near first pin is not flat, it's like a track from a ball.

[fragletrollet]

I've used opa177 for 604 and lm4562 for 2604 with great success in my l1 mixers.

How does this compare to the old version, other than missing mode?

[fivesteppath]

I've used opa177 for 604 and lm4562 for 2604 with great success in my l1 mixers.

How does this compare to the old version, other than missing mode?

opa177 can be direct replacement for opa604? Maybe you used an adapter?
I see that pins 5 and 8 are switched between the two.

[fragletrollet]

Afaik pin8 on 604 isnt connected, like pin5 on 177. I've built a ton of discrete vintage opamps that have the same offset trim pin; never saw it connected to anything. Guessing it's used for trimming dc offset in critical applications (not audio), but I don't really have a clue. Yes it works as a direct substitute in the L-1 mixer, no adapter needed.

[muxbutter]

Synthcube had a great deal on a kit for this, so I put it together.

I love the unpredictable overtones coming out of this!

But, I've been having issues with the Resonance on HP mode making some clicking sounds when turning the RES pot around 7 through 8 with cuttof above 5---it moves down to between 6&7 at lower cut--off.
There is an ugly, slightly audible noise thumping when moving the resonance pot in these areas.

Seems like something to do with the vactrols in the resonance path struggling?

If this is normal behavior, please let me know--if not, it would be great if we could figure out the possible issue? Thanks.

Best

[muxbutter]

Thanks for everyone's responses about the chip substitutions, by the way!
I am looking forward to trying LM4562 in this filter.