minimoog boards

[spuddo]

Hi All , i'm in need of a Filter board and PSU/Noise board. Anyone know where i might get these.
I've googled ebay and purchased VCO and Contour board , but no luck so far with the others.
Thanks in advance
Geoff

[torinkrell]

Hey - it sounds like you are trying to piece together a Minimoog by procuring boards and parts from a variety of sources! Has anyone successfully done this here?

[thealien666]

Not to my knowledge. And probably for good reason. The boards aren't the only complex circuitry inside a Mini. The front panel wiring of the knobs and switches is also quite an endeavour !

Not to mention that finding all the boards fully populated and in working condition will surely be a difficult task, and expensive. One has probably better odds of finding 2 broken Minis and making one good one out of those...

[armillary]

Judging from ebay prices, the days of Minimoogs being worth more parted out than whole is long past.

Micromoogs are a different story, I think.

[thealien666]

To spuddo: VCF board here

http://www.ebay.ca/itm/Minimoog-vcf-boa ... 352wt_1165

[Kevin Lightner]

Hey - it sounds like you are trying to piece together a Minimoog by procuring boards and parts from a variety of sources! Has anyone successfully done this here?

I would have guessed the same thing, but that's not the case.
Instead of "DIY artist building Minimoog", think "Minimoog owner, victim of tragedy."'

Sorry that I can't say more, but I just didn't want his intent assumed.

[thealien666]

While there's nothing wrong in wanting to build a Minimoog from the ground-up with separate parts, there is certainly something sad about having to restore one following a tragedy.

I sympathise with Geoff, and wish him to get back to having a fully working Minimoog soon.

Thanks for the clarification, Kevin.

[spuddo]

Hi All , thanks for your replies.
I'll not give up on the hunt and with your support i'll get Serial # 2530 back on board-----one day.
Alien 666----scary name , but thanks for the link. Anglian Art do not send to Australia--don't no what we did to upset him.
Kevin thanks for setting the record straight-----looking forward to receiving my Opto Keys , now i'll have an extra incentive to find the other bits.
Regards
Geoff

[Kevin Lightner]

Good luck, Geoff.

The only board I have here is an envelope board (board 2.)
A friend has various VCO boards available also.
But it appears you've already found these two above and I haven't any other resources.
I hope things work out best.

Also, you might find the character of the "new" Mini different than you recall.
Different era boards can do that.
I've modded newer vcf boards to sound like older ones, so I know it can be done, but expect that possibility.
Again, good luck!

[CZ Rider]

I've modded newer vcf boards to sound like older ones, so I know it can be done, but expect that possibility.

Curious about that reverse mod. In the service manual it is recommended that certain resistors be changed to "reduce intermodulation distortion".

Always wondered what reversing those resistors back to the old values would sound like? The R2 looks to be R701 in the old drawing, and the main output from the VCF. While R8 and R28 look to be R723 and R724 on the original drawing in the final (second) VCA. And R40 being the old R1310 from the main output of the A440. So the upgraded mod seems to reduce the volume of both the VCF and A440, while increasing a bit of gain on the final VCA to compensate. To add a bit of confusion, the values are a little different on the one board I have here where R2 is 82K, R8/R28 is 8.2 ohm, and R40 is 2.2K. This new combo was to be done on units below ser. 2000 to reduce this intermodulating distortion.
But isn't that intermodulation distortion a big part of the old 901/CP3 classic Moog tone?
Any info or insight on this reverse mod would be greatly appreciated. I have been tempted to try this myself, just to hear the difference.

[MC]

I know of no proof that IM is any contributer to classic tone, but my convention with vintage synthesizers is to leave the audio path as original as possible.

[CZ Rider]

I know of no proof that IM is any contributer to classic tone.

Depends on your definition of intermodulation distortion. On the 901 and CP3 combination, you get these moving distortions when the phase of the combined oscillators line up and cause peaks. These peaks inside the CP3 can go beyond the -6 volt rail causing clipping. This is what I would think intermodulation distortion would be refering to, but I could be wrong. Kind of a ripping sound. Too much is overkill, but just the right amount and you get a very animated interaction. Easy to get on the original R.A.Moog and very much a part of the sound.
The old 1971 schematics show different values than the one on my VCF board. So Moog made the changes to the original audio path on later Minimoogs.

[Kevin Lightner]

I know of no proof that IM is any contributer to classic tone, but my convention with vintage synthesizers is to leave the audio path as original as possible.

The issue here is that there's two "original" styles.
It depends on the rev mini one is at or attempting to be.

I don't like the later Moog suggestions where they change the A-440 level, but several of their filter and VCA changes are sound.
It just matters what sound you want.

[CZ Rider]

After studying the old scemstics, looks like Moog made a change in the filter/VCA circuit somewhere during the serials begining with 2000.
Here is a large scan showing the differences in the old and newer schematic. The red highlighted resistor was 47K on the early Minis, and changed to 82K on the newer ones. This is the main output from the VCF going to the VCA. So the older schematic shows a hotter signal passed to the VCA. The two green higlighted resistor pairs, 27 ohms on the older Minis was changed to 8.2 on later minis.

Not sure when these changes occured? The oldest VCF/VCA card I could find with he original values was labled 2498. So at the least the first 1500 Minis had these values for the VCF/VCA. There were a few other minor differences with the value of the A440 input and a 12K input resistor on the noise source, while later schematics show a value of 11K.


Seems like a simple enough mod to try. And both my 4000 series and 10,000 series Minimoogs have the newer values.
The 82K VCF input resistor is located near the top across from the "Blue Dot" selected ladder filter transistors. (Yellow arrow at 82K resistor)


The two 8.2 ohm resistors on the top left side of the board.


Not an expensive mod, the three resistors cost me about 3 cents. But if you pay top dollar this mod could cost as much a 3 dollars. Here are the removed newer values to be replaced with the original value resistors. Lead bender above for neatness.


All I have to do is solder in the old value components.


After re-installing the VCF/VCA board, the volume output was only slightly lower than before. But there seems to be more high-end harmonics present when all the oscillators are at 10. Easy to dial out with lower mixer volumes. Only a subtle change, but I like it!
Never really cared for the tone of the newer 10,000 series Mini with the newer oscillator card. But this inexpensive mod seems to change the tone just a little bit. I could always change this back, and only did it out of curiosity, to see if there was a difference. But I'll keep the mod, as is sounds slightly different in a good vintage Moog way.

[thealien666]

That is appalling ! Even sacrilegious ! Tinkering with a classic Minimoog D !

Nah, I'm only kidding. As long as you like the sound of a mod, and that's the most important thing, then anything goes...provided nothing is destroyed in the process.
Although I doubt very much anything could be destroyed by replacing some resistors... But I know a few people who could even mess this up !

Interesting experiment CZ Rider, thanks for sharing.