Moog Sound Addiction

[Kevin Lightner]

Sweep... I haven't a clue what to call it. Jitter seemed best because that's what it looked like on a scope.

Solar, if your multimoog filter isn't opening as it should, it might be miscalibrated.
It should be almost exactly like your Micromoog.
They use the same boards (at least the ones with the filters anyways.)

One thing you might notice though- VCO A (pan to left) may have a bit more buzz or jitter than VCO B.
The B VCO in Multi's tends to be a bit purer.

[museslave]

museslave, you did not mention how hard you were driving the MF-101. As you probably know, the amount of MF-101 drive level will also change the character of the sound. Are you driving the MF-101 Level LED mostly in the green, yellow, or red for the sound that you like the most?

I did not mention that! I messed with it, a bit. The standard output level of the .com oscillators has the input in the red. In the red, with the drive all the way down, resonance all the way down, and the filter all the way open is where I was pleased with the warmth. I then experimented with lessening the output so it was in the yellow or the green, and still experienced the warmth I desired, but such settings possessed less.. um... buzz? crunch? But were still pleasing. The character afforded by drive was less important to me than the character merely provided by the filter.

[museslave]

A LOT of people complain about the Multimoog sounding thin. If Multimoogs and Micromoogs have the same filter, then I find that very surprising. My Micromoog, while not sounding like Mini, was still extremely broad, fat and warm. I have tons of proof, beginning with my YouTube Micromoog video... if anyone has any doubt. : )

[solarpanelasses]

Sweep... I haven't a clue what to call it. Jitter seemed best because that's what it looked like on a scope.

Solar, if your multimoog filter isn't opening as it should, it might be miscalibrated.
It should be almost exactly like your Micromoog.
They use the same boards (at least the ones with the filters anyways.)

One thing you might notice though- VCO A (pan to left) may have a bit more buzz or jitter than VCO B.
The B VCO in Multi's tends to be a bit purer.

Thanks for the info kevin, i just assumed it was how the filter was since my micro does the same thing, guess i need to get both worked on!

And yes VCO A is jittery as heck, I actually need it calibrated because its starting to actually drift these days. I need to do some research where to get them worked on, I didnt like the service I got last time (deltronics in chicago).


muselave, hopefully I will be able to agree with you very soon if my filter does start acting like mr. lighter said it should, because with my moogerfooger it sounds very nice, hopefully even better when I get to use my micro and multi's actual filters.

im very excited.

[Kevin Lightner]

You guys sound like you have good ears.

The Micromoog was designed to *intentionally* overdrive the filter a bit.
It's explained in the service manual as the designers not caring much about increased harmonic distortion since it was a one oscillator instrument.
But it was intentional.

The Multimoog added a second and third board that contained an additional VCO (and aftertouch, etc.)
They routed both VCOs in a different way and with less distortion.
Had they run both VCOs hot, they would have increased intermodulation distortion, which wouldn't have sounded very pleasing.
So they're the same basic VCOs, same filter, but different drive levels.

Multimoogs suffer from two chronic VCO problems. (tech stuff coming);-)

One problem is that Moog riveted a ground terminal in the back that contains AC filtering caps.
This rivet can come loose and create noise and little pops through out the system.
Tapping around the AC inlet jack can identify when the unit's closed, but I usually solder a wire to ground when I'm inside.

VCO A is often buzzy because that oscillator is broken up over two boards.
Wires connect between them and to the rest of the synth.
Because the Multimoog uses a 50khz signal to generate aftertouch signals on one of the same boards, bleedthru can occur.
Moog themselves cut a trace and added a shielded wire, but it's not enough.
To eliminate the buzz, I've done this to the lower added board...

Lift shielded traces (cut) from C12 to R45, R46 & CR6 (RG-174 single Gnd shield)
Lift shielded traces (cut) from A2 pin3 to connector P2-4 (RG-174 single Gnd shield)
Float Q2, P3-2 (usually shielded already) & R5 (2.2K)
Add a direct Gnd from P1-2 to IC1 pin 14.

It's also recommended the boards be very clean and if possible, the IC sockets eliminated.
The trimmers and aftertouch often need lots of attention too.
Maybe this info will help some techs.

[electrical_engineer_gEEk]

It's also recommended the boards be very clean and if possible, the IC sockets eliminated.

Wow! they have IC sockets on that synth? That's interesting, do you know of any other moogs that have all socketed ICs? neither of mine have them.

[eric coleridge]

i just assumed it was how the filter was since my micro does the same thing, guess i need to get both worked on!

Solar,

This is how my Multi's filter performed too--and I've read this complaint from a lot of people. So I think your Multi might be "fine."

There is actually a fairly well documented modification you can do that is suppossed to correct the Multi/Micro filter performance. It's very simple, just soldering on a resistor to the filter section of the PCB board. However, I tried the modification on my Multi, and I wasn't happy with the outcome: Although the filter did start opening up much earlier on the knob, it also changed the tone quality of the filter in general (in my opinion, for the worse). I feel like it thinned out the sound of the Multi even more.


Incidentally, I've owned a Micro before as well as the Multi (neither of which I have now), and I always felt that the Micro had a bolder sound. This is perhaps counter intuitive, because the Multi has an additional oscillator, but it's the way I remember it. Which is'nt to say there's anything wrong with the Multi. I thought it was outstanding synth in many ways. But it wasn't right for me (which is funny because I wanted one for the longest time, finally found a mint condition speciment for only $400, and then sold it.).

I prefer the Mini to most every other synth, and I feel like most of the reason is because of the Oscillator's sound, not the filter. But it's difficult to clearly seperate the two.



I

[eric coleridge]

Luckily, though... I came up with a solution. My trusty MoogerFooger low pass, set all the way open, does its magic with those oscillators... it gives them that Moog Sound that is so desireable. Even just running the oscs through the Moogerfooger with resonance off and the filter all the way open... immediately, there is a desireable difference and I am much more happy with the patches I create. It's amazing. Perhaps a new Moog product would be Moogerfoogers in module form for dot com and MOTM, etc. modulars. : )

I also really love the Mini's oscillators, and have found a different solution as far as using their sound in my modular set-up:

I connected the mixer output from my Mini to the Mini's "Low" output (disconnected the output signal) so that I can patch the Mini's VCOs directly into my dot.com Variable State filter, or other modules, etc.

This way, I can use the Mini as a controller as well.

I also made the Osc sync mod thats on the Synthfool website. Osc sync sounds really great on the Mini and definitely adds alot of new textures to it's overall sound pallate. I'd really recommend this mod to anyone wanting osc sync for their Mini.
I haven't figured out a way to incorporate the switches onto the controll panel without drilling holes yet, so unfortunately the switches remain inside the enclosure for now. But they'll probably end up being push-pull pot switches as soon as I can find these type of components in the right values (for either the osc tuning pots or osc level pots).
I also need to figure out a non-invasive way to get individual CVs to Osc 2 and 3, in order to drive the sync effect-- if anyone has any ideas...

[Kevin Lightner]

Getting individual CVs to the VCOs is fairly easy, but you'll have to add a couple of resistors to the right side of the osc board.
(facing the components and assuming you have the older VCOs.)
This is where all CVs are summed in- pitch wheel, keyboard, mod, etc.
It can be done on a later board too, but you'll have to locate the points to add in voltages.

Please note that the envs in the mini don't have a lot of drive.
Attempting to drive the VCOs from them may be difficult.
When I did it, I added an opamp to buffer and offset the voltage.
I'd recommend testing whatever mods are to be done before drilling anything.
There is room between the selectors on VCO 1 to add switches, but I don't blame you for being hesitant to drill the panel.
I only do it when a client requests it.

[eric coleridge]

Please note that the envs in the mini don't have a lot of drive.
Attempting to drive the VCOs from them may be difficult.
When I did it, I added an opamp to buffer and offset the voltage.
I'd recommend testing whatever mods are to be done before drilling anything.
There is room between the selectors on VCO 1 to add switches, but I don't blame you for being hesitant to drill the panel.
I only do it when a client requests it.

Thanks for this info.

What I have been planning to do is add CV jacks for Osc 2 and 3 modulation, but the only way I can think of doing this(without drilling) is going through the accessory port and I haven't gotten around to sourcing these cinch-jones connectors yet. I don't want to drill any holes on the enclosure. I think about it from time to time, but always decide against it. I have a pretty low seriel number '73 Mini--which has been kept in really good shape up till now--and I feel like it's not fair to the person who has this Mini after me (after I die, I guess) to start drilling a bunch of holes in it. Which is also why the sync switches remain un-mounted.

Probably I should stop trying to turn my Mini into an Odyssey, but it's so much fun.
I love that sync mod on your site, and moreover, I've learned alot from all the resources you have up.

[Kevin Lightner]

How about this?

Even though you'd have to string the wires across the inside of the mini (shielded wire recommended), there *are* three unused pins on each accessory socket.
You can get the plugs all over- Mouser, Newark, etc and by several manufacturers, not just Cinch.
Part number is usually something like P-306.
About $3-4 each usually.

[eric coleridge]

How about this?

Even though you'd have to string the wires across the inside of the mini (shielded wire recommended), there *are* three unused pins on each accessory socket.
You can get the plugs all over- Mouser, Newark, etc and by several manufacturers, not just Cinch.
Part number is usually something like P-306.
About $3-4 each usually.

That's definitely what I'll eventually do.

I was thinking for a long time about either making a Voyager Vx-style breakout box, or a breakout panel for my custom modular. I thought about disconnecting the +-10 volt power pins on each port--which would give me 10 pins to work with (leaving the ground pins connected, of course). I was thinking of doing:

3 seperate VCO CV inputs
3 Osc audio outputs (tapped from their level pots)
3 PWM inputs
1 noise output (from the level pot)

However, I'm very much an amateur at electronics, and all my knowledge is specific to past projects I've done. So, I haven't been sure whether I need to take any special precautions with the disconnected 10 volt power lines. Not sure how they should be terminated/disconnected from the power supply-- and if this could have any side effects on the Mini's functioning. I wouldn't think that it would, but I'm not in the habit of taking any unneccesary chances with my prized and long sought after MiniMoog.

Maybe its safer to just appropriate the unused accessory port pins for my 3 VCO CV inputs and leave everything else as is?

[Mooger5]

I've previously documented jitter in Moog 901 vcos.
Additionally, Minimoogs have a small amount of AC that bleeds into the vcos and the vcos affect each other. This is all tone quality, not drift.
(note also that later Minis added more PSU filtering and have very slightly less of this quality.)

This is also very useful information, as I was thinking of beefing up the Rogue´s power supply, replacing the diodes and regulators with faster and less noisier parts and eventually replacing the 500ma wallwart with a heftier transformer.
Also, I´m going to order some Philips axial caps to replace the old electrolytics and was wondering if there would be any benefit in using caps made specifically for audio like Elnas, Wimas and Black Gates.
Did also a few experiences with different opamps (NE5534, JRC4558 and AD827) in the overdriving and output circuits, with mixed results: the Hi-Fi opamps sounded cleaner but the instrument didn´t cut through the mix as before and the character was lost. The JRC has the same gritty sound as the old 4558 but with a bassier response. I liked this one in the overdrive section. It´s a keeper

In 1981 the designer had to cope with available components and costs to keep the budget low, right? In principle there are better spec´ed parts today at a price the common diyer can afford. But now I have my doubts. If I do the upgrades, will my humble Rogue turn into a better sounding Moog or will the magic disappear, much as Museslave described?
I´m sure there must be a good compromise.

Regards

[Kevin Lightner]

Respectfully offered, you're always welcome to experiment on your own synth, but the more you know about the circuits and components, the more you'll avoid frustration.

You're correct in the assumption that there are better parts than in 1981.
But better is a variable term unless implemented correctly.
For example, it's possible to install a really high spec'd op-amp in a unit and wind up with more noise, radio reception, feedback, hum and other undesirable attributes.

A 741 opamp only has 1/2 a volt rise time.
Newer ones might be 30 or more.
Definitely there's faster opamps, but since that type of amp usually features a FET input and is wider bandwidth, it may cause problems when directly substituted.
Most circuits are designed around the constraints or features of specific opamps.
Change a part and the circuit may behave strangely or not at all.
Often things work, the tech puts the unit together, then later an issue is discovered.
One fellow brought me his modded 2600 and it received light dimmer noise very well.
I actually have a variac built into the wall for my shop's tracklights, but was able to reproduce his instrument's problem.

My personal view is that fidelity-wise you may make minor improvements, but none so much as to make the work worth doing when weighed against the risk of damage.

I don't think you'll see much results from using faster regulators or better caps in the unit. At least not vs the cost and risk of an accident.
You *might* see some improvements in noise or offset if key resistors are changed to metal film types.

I'd recommend carefully evaluating the synth you intend on modding first for areas you might consider low grade or compromised.
That is, if you hear hum from the unit, consider better filtering, better grounds and that sort of thing.
If it has a lot of noise even when not playing, you might consider redoing the output stage.
If an envelope amount slider outputs some voltage even when not triggered, you might consider a low offset opamp or installation of an offset trimmer.
Make the mod address the deficit.

If swapping opamps, sockets might help if installed, but be certain that the original amp does not use compensation capacitors. (LM301's do, for example.)

One area you might find useful and with great returns is the installation of a faster, higher input impedance amp in LFO circuits.
By changing the opamp and the timing capacitor, most basic LFOs can go into the audio range.
Simple one vco synths with an LFO modded like this can make a world of new FM sounds and it only takes a few parts.
Please note that without a range switch, an LFO speed control can span a huge range after such a mod.
Accurately adjusting the slider might be difficult.

Hope this helps in some way.

[thewaag]

First of all, I gotta tell you that I don't know an opamp from a pre-amp or a boat ramp.

I am just glad to see you back on this board occasionally Kevin. It is great that you can spend the time giving advise now and again.