Doepfer

Yes... what Peter said.

Regards,
Kevin

--- In Doepfer_a100@yahoogroups.com, "(i think you can figure that 
out)" <petergrenader@h...> wrote:
> This post might be a tad long.  I am responding to two 
> comments regarding vactrols:
> 
> A) Has Dieter ever fooled around with vactrols? 
> 
> Answer: TRUE (yes)
> 
> B) Vactrols are sonically unexciting.  
> 
> Answer: FALSE (no!!!!!)
> 
> I come from a point of confidence on both these as I have 
> discussed this with Dieter and as well I designed the circuit 
> modifications for the Cynthia Buchla Low Pass Gate module in 
> order to improve the response with non-Buchla voltage 
> configurations.  I also have about a billion hours clocked on 
> Buchla synthesizers.
> 
> Item A explained:
> 
> Yes, the Doepfer folks have looked into using vactrols.   Dieter 
> has even experimented with making his own.  This in itself ain't 
> all that hard, as a vactrol is nothing but an led and a photo 
> resistor positioned so the light path is pointing to the business 
> end of the photo resistor, and the whole mess potted into a 
> plastic enclosure so that ambient light does not effect the 
> resistor.  Usually this results in this 'thing' that has two led 
leads 
> sticking out of one end, and the resistor leads out the other.
> 
> How a vactrol works is the brighter the light, the lower the 
> resistance of the photo resistor.  There are few different types, 
> each having it's pwn characteristics: delcay time, on/off 
> resistance values, dual or single (some are confiugured as 
> pre-wired voltage dividers consisting of two photo sensitive 
> resistors in series).
> 
> So there's that.
> 
> B explained:
> 
> OK, I understand that this comment was an opinion and therefor, 
> completely acceptable.  But given that everyone is due their own 
> opinion, here is mine:
> 
> Vactrols are friggin'  wonderful in synthesis applications.
> 
> Will they give you the snap response of a non-vactrol circuit 
> equivelent?  NO.  Are they the best thing to have in a VCA which 
> (most engineers wil tell you) have to be fast to be good?  NO.
> 
> In analogy: Is the Wasp filter a good design?  NO.  It's a horrbile 
> design by engineering standards, it's a mistake - but that 
> mistake sounds good.
> 
> Such is the case with Vacs as well, although they were 
> intentionally introduced by Don for the purpose of noise 
isolation.  
> Remember, the Buchla signal level is just about line level. In 
> order for it to be heard, it has to be turned up like made and this 
> is where noise can cause you grief.  
> 
> Someone also mentioned they were in a Buch to keep the 
> control voltages isolated form the singal path, this is 99.9% true 
> in all cases accept (to my knowledge) the envelope detector in 
> which the control voltage generated from the external signal is 
> not isolated from the signal path electircally.
> 
> Remember, not only is the Buchla signals and controls 
> separated by two distinct patch cord systems, they run off of 
> completely different supply systems and different voltages in 
> some cases.  While the signal paths is fed with 15 volts, some 
> of the control modules are powered off of 24.
> 
> Let take the 292 Low Pass gate as an example.  It is, by nature 
> and due to the vactrols, slower than shit.  Most design engineers 
> would tell you that this makes for a very bad VCA design which 
> are supposed to be fast to be efficient. Due to the vactrol's 
> naturally slow decay time (35 MS), and the fact that the main 
> mode of operation of a 292 is a low pass filter, vactrols afford a 
> unique ringing of the low frequency spectra of a signal which 
> provides the percussive phrases with a lot of life.  I will post a 
> link by day's end of a comparison of the same signal gated by a 
> standard VCA and by a lowpass gate - you'll know what I am 
> talking about in a second.
> 
> Why is the decay so long in a vactrol?  It's the light.  Turn an 
led 
> on.  Watch it snap to attention.  No turn it off.  Ah-HA - it fades 
out 
> even if the signal going into it cuts instantly.
> 
> So no, in my opinion,  the while use of vactrols in analog 
> synthesizers provides a marketably different result than 
> functionally identical circuits not using them, they are no worse, 
> just different and in some cases, that makes for a pleasent 
> results.
> 
> VIVA LA DIFFERENCE!
> 
> Look for a posting with a link to sonic exmaples of the 292 in 
> action soon.
> 
> best,
> 
> Peter
> 
> 
> 
> 
> 
> 
> --- In Doepfer_a100@yahoogroups.com, "klamb000" 
> <lamb@c...> wrote:
> > Actually, I think it was said that the Buchla designs weren't as 
> > sonically pleasing as other designs.
> > 
> > And I also wonder if any vactrol modules are planned for next 
> year.
> > 
> > Regards,
> > Kevin
> > 
> > --- In Doepfer_a100@yahoogroups.com, "ethanzer0" 
> <ethanzer0@y...> 
> > wrote:
> > > A while back there was some discussion
> > > on vactrol based modules.  I believe
> > > the thoughts were that vactrols in the
> > > audio path are not that sonically exciting.
> > > Looking at buchla schematics I find that
> > > vactrols are used quite often to isolate
> > > the control path from the audio path 
> > > (optoisolator?) I understand the ultra-smooth
> > > response of vactrols make a modules response
> > > to CV something special.  I wonder if the
> > > design folks over at doepfer have considered 
> > > this?
> > > 
> > > Ethan