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What level of "variability" between two Moog DFAM'
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author What level of "variability" between two Moog DFAM'
DruMunkey
Hi all...

I picked up a second DFAM. I understand that these are hand woven by Moog's monks, and that by their nature there will be some variability in sound, but I'm curious how much variability is "normal."

For instance... If I set up both of them with the patch cord-less "Big Bottom Bass" template, to get them to sound the same I need to have the VCA Decay knob about 5 degrees CCW more than other one, otherwise it doesn't sound as if the envelope closes between "notes" as cleanly as the other unit.

And in more playing around, I can get the two units to sound close to each other, but again, it seems there's a pretty significant amount of variation between the unit's knob positions.

I cool with this if this is pretty normal for units like this (I'm mostly been an Elektron or other DCO or VA user), but man, it REALLY makes you realize all the minute nitpicking on minor sound differences in the analog world is kinda pointless if there's that much variability at play.

Thanks all for your patience with this prob. noob question.
milkshake
DruMunkey wrote:
Hi all...

I picked up a second DFAM. I understand that these are hand woven by Moog's monks, and that by their nature there will be some variability in sound, but I'm curious how much variability is "normal."

For instance... If I set up both of them with the patch cord-less "Big Bottom Bass" template, to get them to sound the same I need to have the VCA Decay knob about 5 degrees CCW more than other one, otherwise it doesn't sound as if the envelope closes between "notes" as cleanly as the other unit.

And in more playing around, I can get the two units to sound close to each other, but again, it seems there's a pretty significant amount of variation between the unit's knob positions.

I cool with this if this is pretty normal for units like this (I'm mostly been an Elektron or other DCO or VA user), but man, it REALLY makes you realize all the minute nitpicking on minor sound differences in the analog world is kinda pointless if there's that much variability at play.

Thanks all for your patience with this prob. noob question.


I can't comment on the dfam.
But it is true that there can be quite a lot of difference between similar analogue equipment, as you have found out.

Perceptual testing, as you have done, is very very difficult. There are 2 reasons for that: 1 you can only test 1 difference at a specific time. And setting the knobs the same is not nearly enough, as you have found out. 2 Humans are very good at fooling themselves.
Lesson, of your not an expert on perceptual testing, trust the people who are: The scientists who publisch in peer reviewed papers. Learn what kind of distortions are audible at what levels.
Ignoring these people will cost you a lot of money.
TheDegenerateElite
Sounds perfectly normal.

I would bet that the actual "normal" value is likely somewhere in between the two units you have and not that one is significantly off.


All analog gear tends to have this sort of difference. It's in the component tolerances. It's exactly why people love analog gear to begin with, because it makes the synth into an instrument and not just a thing.

I've heard artists talk about stuff like Rolands that have a specific sound that they can't get from any other same model number unit. Same with Minis.


Most patch examples actually say somewhere that you will have to mess with the knobs to get the sound correct, as they won't match perfectly.
pulse_divider
I just pulled up some Alpha pots on Mouser and all the ones I looked at had a 20% tolerance. That means there can be up to 20% difference between the values of 2 of them.
mskala
pulse_divider wrote:
I just pulled up some Alpha pots on Mouser and all the ones I looked at had a 20% tolerance. That means there can be up to 20% difference between the values of 2 of them.


Depends on how they're being used in the circuit. That's the tolerance on the total track resistance. If the pots are being used as voltage dividers, then the total resistance doesn't really matter, rather the proportion to the left and right of the current wiper position, and that should be a lot better than 20% even on a 20% pot. The specification for this would be called "linearity" on the pot data sheet. However, if the pots are being used as variable resistors, then yes, you could see a 20% difference with 20% total-resistance pots.

Another significant issue is that the pots may be being used to trim out variations in other parts of the circuit, and so it's not only variation in the pots themselves that will show up in this kind of comparison.

If you want pot positions on a synth module front panel to be calibrated so that the same position equals the same setting on all individual modules of that type - like you might see on a piece of test equipment - you will pay extra for that. But you may be able to get a quick'n'dirty substitute for real calibration just by taking off the knob and reattaching it rotated a little, depending on how the knob is attached to the pot and whether it allows doing that.
Drakhe
pulse_divider wrote:
I just pulled up some Alpha pots on Mouser and all the ones I looked at had a 20% tolerance. That means there can be up to 20% difference between the values of 2 of them.


This... And two more words to add: calibration and analog ;-)

But yeah, the world tolerance is key. Not only for the pot's like mentioned in the quote, but every single component in an analog device (also the electronic ones) are subject to tolerance. It's all about the $$$. The smaller the tolerance (and therefore the more precise the component) the more it costs.
lisa
TheDegenerateElite wrote:
All analog gear tends to have this sort of difference. It's in the component tolerances. It's exactly why people love analog gear to begin with, because it makes the synth into an instrument and not just a thing.

Great point! I had this synth that I loved. It sounded great and I made some tracks with it that I was really proud of. My friend had the same synth and he brought it over one day. We did the same patch on both of them to enjoy the differances between them, as you do. To our shock and dismay they sounded about the same! eek! The synths that we loved and made our music with turned out to not even being instruments. Dead Banana Naturally we threw them away and has since then always tested synths in pairs before buying.
Dave Peck
mskala wrote:
you may be able to get a quick'n'dirty substitute for real calibration just by taking off the knob and reattaching it rotated a little, depending on how the knob is attached to the pot and whether it allows doing that.


When I read the OP, this was the first thing that occurred to me, which could account for the entire issue - the circuitry may match very well, but the knobs themselves may be oriented differently on the potentiometers.

There are different ways that knobs are attached to pots.

- They can have a "D" shaped hole in the center of the knob and fit onto a "D" shaped pot shaft, which means they only fit onto the pot shaft one way and cannot be installed at the wrong rotational angle.

- They can press onto a 'knurled' pot shaft, and this means they can be oriented at many different rotational angles.

- They can be attached to a ROUND pot shaft, using a small 'set screw' located on the SIDE of the knob. Loosening this screw allows you to rotate the knob relative to the pot and orient it any way you want.

So check the method used on this synth and if it is the second or third method, you can just re-orient the knob on the pot shaft so they are where you want them.
DruMunkey
pulse_divider wrote:
I just pulled up some Alpha pots on Mouser and all the ones I looked at had a 20% tolerance. That means there can be up to 20% difference between the values of 2 of them.


Gotcha.. That seems like a reasonable indication. On the DFAM it seems that the knobs control a pretty huge range, so 20% would be super audible.

I'm totally cool with the variability and it's the reason I like synths over samples. I mainly just wanted to make sure I wasn't chasing my tail on a bad unit.
Marizu
[quote="DruMunkey"]
pulse_divider wrote:
I mainly just wanted to make sure I wasn't chasing my tail on a bad unit.

If it sounds good, then it is good.
I can imagine that variations between units might make the difference between loving something and just liking something.
I built a DinSync Re303 and forgot to calibrate it, so I got the scope out and calibrated it as per instructions, but felt that it had lost a little 'something' in the process. Then I calibrated it by ear back in the direction that it had come from and I love it, now.
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