They say you can never have enough VCAs...

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muleskinner
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They say you can never have enough VCAs...

Post by muleskinner » Fri Mar 20, 2020 6:12 pm

...but I'm finding you can never have enough buffered mults!
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Re: They say you can never have enough VCAs...

Post by starthief » Fri Mar 20, 2020 7:32 pm

I've never had any buffered mults or felt like I needed them :despair:
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Re: They say you can never have enough VCAs...

Post by muleskinner » Sat Mar 21, 2020 3:35 am

Really?

I'm wasn't really needing them so much when I was doing more 'standard' melodic sequencing driven from my Deluge but now I'm trying more generative stuff I'm finding I need them all the time - for triggers and modulation sources.

So they don't need to be pitch-accurate, but it seems most triggers cease to become a trigger for most purposes when they've been standard mult-ed more than x2, and other mod sources drop below the voltage range I need and/or become a PITA to re-balance once split.

Maybe I'm doing something wrong - I'm still fairly new to this, only a couple of years in...
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Re: They say you can never have enough VCAs...

Post by IEC » Sat Mar 21, 2020 6:58 am

i think a lot of people use stackable cales and/or passive splitters to save the hp/cost. myself i dont mind spending the $/space to have some mults about the place. sometimes i run out of long cables and the mult saves the day...

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Re: They say you can never have enough VCAs...

Post by huffnPuff » Sat Mar 21, 2020 7:27 am

muleskinner wrote:
Sat Mar 21, 2020 3:35 am
Really?

I'm wasn't really needing them so much when I was doing more 'standard' melodic sequencing driven from my Deluge but now I'm trying more generative stuff I'm finding I need them all the time - for triggers and modulation sources.

So they don't need to be pitch-accurate, but it seems most triggers cease to become a trigger for most purposes when they've been standard mult-ed more than x2, and other mod sources drop below the voltage range I need and/or become a PITA to re-balance once split.

Maybe I'm doing something wrong - I'm still fairly new to this, only a couple of years in...
You're not doing anything wrong. Whether you need a buffered mult depends on your patching style primarily, and the actual modules in use - some have more "robust" outputs than others.

I have 5 channels of buffered mults (in two modules / 10hp) in a 15u x 104hp system. And a lot more VCAs. And a bunch of mixers (with integrated VCAs and buffered outputs).
:mad: :mad: :despair: :mad: :mad: :mad:

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Re: They say you can never have enough VCAs...

Post by Arneb » Sat Mar 21, 2020 7:43 am

IEC wrote:
Sat Mar 21, 2020 6:58 am
i think a lot of people use stackable cales and/or passive splitters to save the hp/cost. myself i dont mind spending the $/space to have some mults about the place. sometimes i run out of long cables and the mult saves the day...
For me it's neither HP nor cost, but power connectors.

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Re: They say you can never have enough VCAs...

Post by starthief » Sat Mar 21, 2020 7:57 am

muleskinner wrote:
Sat Mar 21, 2020 3:35 am
So they don't need to be pitch-accurate, but it seems most triggers cease to become a trigger for most purposes when they've been standard mult-ed more than x2, and other mod sources drop below the voltage range I need and/or become a PITA to re-balance once split.

Maybe I'm doing something wrong - I'm still fairly new to this, only a couple of years in...
Nah, it's not you, it's the modules generally. Some modules have weird impedance issues, trigger signals that are weak or poorly shaped or extremely short, etc. Passive modules also sometimes need a helping hand (although oddly enough, a passive attenuator can sometimes fix issues with them).

Back when I was using MIDI-to-CV and wanted pitch to track well with multiple oscillators, it just happened that the CV.OCD's CV outputs could handle being multed a couple of times with no appreciable voltage drop. So I was lucky with that.

I don't think I have anything in my case now that's a problem, but I could always use Shades as a buffer (not a buffered mult) or Gozinta to boost weaker signals.
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Re: They say you can never have enough VCAs...

Post by windchill » Sat Mar 21, 2020 8:14 am

starthief wrote:
Fri Mar 20, 2020 7:32 pm
I've never had any buffered mults or felt like I needed them :despair:
How do you distribute a 1/v oct signal to multiple destinations without the tracking being off?

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Re: They say you can never have enough VCAs...

Post by starthief » Sat Mar 21, 2020 8:41 am

windchill wrote:
Sat Mar 21, 2020 8:14 am
How do you distribute a 1/v oct signal to multiple destinations without the tracking being off?
The music I'm making now tends to involve drone parts, with relatively minimal sequencing. It's rare that I mult any pitch signals to more than two modules, and never more than three.


Just as an experiment, I patched Monome Teletype into O'Tool+ and told Teletype to send 5V. O'Tool+ says it's sending 5.008V.

I then patched from O'Tool+'s passive mult to both Hertz Donut mk2 and E352 (tuned so they're in unison), using a Modular Addict stacking cable. O'Tool+ now reads 5.007V. 1/10 of a cent of pitch error over 5 octaves when multing a signal 3 ways is not bad at all and is 1/8 of Teletype's error. And audibly, the two VCOs wind up chorusing somewhat so their own tracking is a bit different from each other for reasons that have nothing to do with multing.

So then I tried it with Stages. Maxing a slider gave +7.997V. It's still +7.997V even after multing it to the two VCOs.
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Re: They say you can never have enough VCAs...

Post by DSC » Sat Mar 21, 2020 10:00 am

I use them as fast as I make them!

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Re: They say you can never have enough VCAs...

Post by muleskinner » Sat Mar 21, 2020 12:52 pm

This is all interesting reading, thanks!

It sounds like what I should do is get to know my modules better and identify the ones that do have impedance issues - it's likely I'm being overly paranoid and assuming certain things won't work without buffering when actually they'd maybe be ok.

I don't use stackables - I have a racked 4x4 passive mult as well as a couple of splitter cables. I prefer the splitters as you' re not tied to a particular length of cable.

I have a dream of a large mod matrix - big grid of buffered mults with an attenuator on each output. Maybe such a module exists...
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Re: They say you can never have enough VCAs...

Post by IEC » Sat Mar 21, 2020 5:18 pm

one issue i noticed when using passives was random feeedbacks would make my clock signal jump around and fck up my recordings. so its nice to have both options

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Re: They say you can never have enough VCAs...

Post by Pharmgrinder » Sat Mar 21, 2020 6:26 pm

windchill wrote:
Sat Mar 21, 2020 8:14 am
starthief wrote:
Fri Mar 20, 2020 7:32 pm
I've never had any buffered mults or felt like I needed them :despair:
How do you distribute a 1/v oct signal to multiple destinations without the tracking being off?
I turns out I just got done working through this problem in my rack. I thought any buffered mult will do it but they are not all of the same level of precision. I got the joranalog buff mult and it mostly solved the problem but then once everything is patched send a single note through and retune. Then everything should be all set to go as long as you don't push the oscillators beyond their tracking limits.

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Re: They say you can never have enough VCAs...

Post by Pharmgrinder » Sat Mar 21, 2020 6:31 pm

If you feel like you don't have enough buffered mults it really means you don't have enough modulation sources. :hihi:
Joking aside though I know what you mean. I feel like I am often running out of mults. I do think it depends on the type of patching you are doing. I do a lot of generative stuff too.

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Re: They say you can never have enough VCAs...

Post by luketeaford » Sat Mar 21, 2020 8:27 pm

starthief wrote:
Fri Mar 20, 2020 7:32 pm
I've never had any buffered mults or felt like I needed them :despair:
My sentiments exactly.

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Re: They say you can never have enough VCAs...

Post by thelowerrhythm » Fri Mar 27, 2020 3:20 pm

I heard that VCA tip right off the bat and started my system with 10. Then I got into extreme minimalism and hardly use them. :omg:
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Re: They say you can never have enough VCAs...

Post by Dave Peck » Fri Mar 27, 2020 3:53 pm

windchill wrote:
Sat Mar 21, 2020 8:14 am
starthief wrote:
Fri Mar 20, 2020 7:32 pm
I've never had any buffered mults or felt like I needed them :despair:
How do you distribute a 1/v oct signal to multiple destinations without the tracking being off?
Apparently a lot of it depends on the source of the 1V/oct signal. I use an Encore Expressionist and I usually have just one of the eight outputs passively mult'ed to eight oscs - six Dotcom Q106's, a MOTM Morphing Terrarium, and a Plaits macro osc. All eight of my oscs track very accurately over seven octaves, all from the same 1V/oct signal. I've heard that other midi to cv boxes often won't do this.

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Re: They say you can never have enough VCAs...

Post by Pelsea » Fri Mar 27, 2020 5:35 pm

OK, time for a bit of education--
The subjects for today are output impedance, input impedance and load.

The output impedance of a circuit refers to its ability to provide current. Because we are dealing with a constantly changing voltage, we specify output impedance in ohms, meaning the output will work properly if it is connected to a resistor of Rout ohms. (I'm going to stay with DC here, because the math of AC impedance gets a bit gnarly.) If we connect a resistor smaller than Rout to the circuit, the current demand is too high and the voltage will fall.

The input impedance of a circuit is a measure or how much current is required for the circuit to work. The input impedance of circuits is often determined by actual resistors such as the 10K potentiometers that are ubiquitous in Euro modules. It should be obvious that we want output impedance to be lower than the input impedance. (Huh? Yep, low resistance means high current. Current = V/R)

The load on a circuit is the effective impedance of everything connected to the output. Again just using R, the impedance of two parallel inputs is 1/(1/R + 1/R). If the two impedance are the same, the equivalent is one half that value. So when you start multing up inputs, the impedance goes down quickly (2 is 5k, 4 is 2.5k) increasing the load.

Now modern op amps have a very low output impedance, so they will happily drive many inputs. In fact, you can short them to ground with no damage. You don't need buffered mults for those. But in the not too distant past opamps would be blown if shorted, so prudent designers included a small resistor after the opamp to limit the load current. Since typical input impedances in those days was 100k, a 1k limiting resistor worked fine. However, there are designers out there who didn't get the memo, and they still use limiting resistors even with shortproof opamps. Connect that 1k output to a 2.5k load and you get a serious detuning. It's even audible if you combine four 100k inputs (typical for V/oct inputs) to make a 25k load.

Buffered mults give you separate low impedance outputs so they keep the CV unchanged.

Edited to clarify effect on pitch inputs.
Last edited by Pelsea on Sun Mar 29, 2020 2:08 am, edited 1 time in total.
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Re: They say you can never have enough VCAs...

Post by KSS » Sat Mar 28, 2020 9:47 pm

@Pelsea typo on 10K? Did you mean 100K?
Which ubiquitous Euro modules are using 10K inputs?

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Re: They say you can never have enough VCAs...

Post by Pelsea » Sun Mar 29, 2020 2:52 am

To be honest, I am most familiar with various kits I have built, where the pots range from 10k to 50k. I just grabbed 10k to keep the math simple. V/oct inputs don’t have pots of course, and 100k is still the typical impedance value. I edited the original post to clear that up. Mr. Hinton recently posted (On another thread) a detailed explanation of how loading by parallel 100k inputs translates into cents.
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Re: They say you can never have enough VCAs...

Post by muleskinner » Sun Mar 29, 2020 9:48 am

Thanks everyone who contributed here - it's been a bit of an education for me.

Just done some testing and it turns out (surprise, surprise) that I am indeed being paranoid and don't need buffered mults as much as I thought I did.

I measured the output from a bunch of my modules, both with a straight cable out and then with a cable that was passively mult-ed to two different sources as well. I tried the following outputs...

Pam's New Workout
Quadra envelope and expander EOC Out
Frap Tools 321 offset out
Micro Ornament and Crime CV Out (using an envelope from Piqued)
Maths envelope and EOC trigger out
SQ1 gate out
Deluge gate out

...out of all of these the only ones that dropped significantly were the SQ1 and Deluge. The Deluge gate output dropped from 5v to just over 4v and I suspect this is the route of my paranoia as it was the first thing I used to sequence my Eurorack modules. I'm guessing that just over 4v was probably just not enough to trigger whatever it was I was trying to trigger, hence I wrongly assumed passive mults equalled a large voltage drop.

The SQ1 dropped about 2v, but the gate output seems to be ridiculously (even potentially dangerously) high at a whopping 13.5v! It dropped to 11.5v, still way high enough to trigger anything in Euro-land.

As hinted at in one of the posts above, putting a source that droops through a module that's properly buffered means no more droop. So, rather than using a buffered mult I should be able to just pass the Deluge gate output through one of the channels in the Frap Tools 321 (as an example) and then use a passive mult.

The 321 and Maths seemed to be particularly stable in these very non-scientific tests.

Anyway, this has potentially saved me a few quid. Hopefully someone else may find it useful as well!
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Re: They say you can never have enough VCAs...

Post by shaun » Mon Mar 30, 2020 1:49 pm

Just wanted to say thank you as I did find this thread useful.

I no longer feel like a buffered mult is necessary in my case.

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Re: They say you can never have enough VCAs...

Post by wuff_miggler » Mon Mar 30, 2020 3:25 pm

Thank you for the explanation pelsea! Do you or any one else know if Doepfer use limiting resistors on output?
i dont know if passive mults will be ok for pitch CV just yet (my modules for first system are currently on order!)

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Re: They say you can never have enough VCAs...

Post by Pelsea » Mon Mar 30, 2020 5:02 pm

wuff_miggler wrote:
Mon Mar 30, 2020 3:25 pm
Thank you for the explanation pelsea! Do you or any one else know if Doepfer use limiting resistors on output?
i dont know if passive mults will be ok for pitch CV just yet (my modules for first system are currently on order!)
I don't know, but it's easy enough to test using a voltmeter with clipleads, an unused plug, and a 1k through wire resistor.
1. Remove the cover from the plug and insert it into the output you want to test.
2. Set the meter to Vdc and clip the leads to the plug- red on the center tab, and common on the shield (long) tab.
3. Note the voltage reading-- it should follow the output as you expect.
4. Hook one lead of the resistor to the center tab of the plug (there's usually a little hole).
5 Touch the shield with the other wire-- if the voltage changes, there is a limiting resistor.

I just tested a Doepfer LFO and it did not have a limiting resistor.
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Re: They say you can never have enough VCAs...

Post by wuff_miggler » Mon Mar 30, 2020 5:05 pm

Awesome! Will try when my modules arrive! Thanks pelsea :)

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