Envelope times; taper of the attack, decay and release sliders

[fanwander]

Hello et bonsoir!

I was always a little unsatisfied with the speed of the minibrutes envelopes and with the "feel" of the decay and release sliders - or more technically spoken: with the taper of the sliders for decay and release.

To reproduce what is bothering me in regards of the envelope speed do the following:
* Set the envelope speed to "fast".
* Set vca attack and decay to minimum. Set vca sustain and and release to maximum.
* Set filter attack, decay and release to minimum and sustain to maximum.
* Set cutoff to minimum and envelope amount to maximum.
* Start the arpeggiator with 16th notes 120~130 BPM (standard dance floor tempo).
* Now increase the vcf envelopes release time.
The useful range of the vcf envelopes releasetime fader will be between 0% and ~20%. Any value above 20% won't make a change. Same for the attack or decaytimes.

I think it does not make sense to have a "fast" setting for the envelope, which is not usable at 75% of its settings for a mid tempo dancefloor number. ( I don't want to think about up tempo Techno or even 176 BPM Drum'n'Base).

So I opened up the Minibrute (Tant pis! La garantie es perdu!) and found the capacitors C70 and C78 for the VCF envelope and C76 and C79 for the VCA envelope. Those have values of 1uF (C70 and C76) and 10uF (C78 and C79). As a test I replaced C70 by a 100nF capacitor - and whooopiee! I can use the whole range of the decay and release fader at a 120BPM  arpeggio. I think 220nF and 2.2uF would be optimized values.


Still I found that there is much change in the attack/decay/release-times at the lower 25% of the corresponding faders and only a little change at the upper 75%. That made me think that a wronge taper is used for these potentiometers. I desoldered one, and indeed there are lineare sliders used, where every synthesizer developer I know (and even Yves Usson) uses potentiometers with a logarithmic taper.

The B10k means: linear 10 kiloohms.

Can you tell me please which brand these sliders are? I would like to replace them with logarithmic ones.

kind regards (et a bonne soiree)

Florian Anwander

[stevism]

seems fine to me, definitely not worth voiding my warranty over

goodluck though

[coldwar1977]

Interesting read.
People are modding their machines to their personal taste, just like in the old days :-)

[Bruno@arturia]

That made me think that a wronge taper is used for these potentiometers. I desoldered one, and indeed there are linear sliders used, where every synthesizer developer I know (and even Yves Usson) uses potentiometers with a logarithmic taper.

I guess you unsoldered the filter release slider that is the only one being linear, all the others are log. Filter release uses a lin one because it's controlled with a volt per octave CV.

So unfortunately you won't have a better range by replacing sliders.

[fanwander]

I guess you unsoldered the filter release slider that is the only one being linear, all the others are log. Filter release uses a lin one because it's controlled with a volt per octave CV.

Hello Bruno,

Unfortunately this was definitely the Decay Slider. I already had measured it when it was still built in. If you want to, I can make further pictures, and check also the other sliders.  What values/laws should the four sliders of each envelope have?

Florian

[Bruno@arturia]

Unfortunately this was definitely the Decay Slider. I already had measured it when it was still built in. If you want to, I can make further pictures, and check also the other sliders.  What values/laws should the four sliders of each envelope have?

Ho! it's definitely not normal....

Value should be as follow:
VCA env:
A,D,R = 1Meg log
S: 10K log

Filter env:
A,D,R :1Meg log
S: 10K lin

please check the values I very interested


By the way, changing caps from 1uF to smaller values won't expand the range but shift it to faster value. But it's indeed a workaround to have more precision is short length.
But I'm not  sure what will happed at minimum setting tough, could be erratic under some conditions...

Let us know your results, and thanks for the investigations.

[Bruno@arturia]

can you please MP me your serial number too?

thanks again

[spinlud]

I have the same behavior on my minibrute. With envelope set to fast, the decay time slider is useful only from 0 to 30% of the range, upper values doesn't change the sound.

[fanwander]

can you please MP me your serial number too?

thanks again

Hello Bruno

now  a big big shame on me.      I managed it, to measure and desolder the wrong slider, and did not recognize it (ouuh ... comme c'est gênant). So everything is right with the decay fader. It is a 1MB log as it should be.

So I would have to change the proportion resistor/capacitor and increase the limiting resistor. I don't know whether the envelope is derived from http://yusynth.net/Modular/Commun/ADSR/ADSR-V2-sch.gif. But if it is, then I'd increase R13, R14, and R16 to 100k (yes, 100k!) and reduce C7 and C8 to 220nF and 2.2uF respectively (numbering form the yusynth schematic - not from the Minibrute).

Florian

[otherdreams]

So I would have to change the proportion resistor/capacitor and increase the limiting resistor. I don't know whether the envelope is derived from http://yusynth.net/Modular/Commun/ADSR/ADSR-V2-sch.gif. But if it is, then I'd increase R13, R14, and R16 to 100k (yes, 100k!) and reduce C7 and C8 to 220nF and 2.2uF respectively (numbering form the yusynth schematic - not from the Minibrute).

According to this post, you suggest these changes (with the correct Minibrute part #s):
ENV1
C70 1uf -> 220nf
C78 10uf -> 2.2uf
R247, 253, 258 - 100k

ENV2
C76 1uf -> 220nf
C79 10uf -> 2.2uf
R272, 274, 275 - 100k

Did you have a chance to try this arrangement?

Thank you for all of your excellent work!