This vintage synth thing is way out of hand

[J. Dan]

This is a bit OT, but probably related in some of the things that are hard to put your finger on. Components change - even if it has the same part number and function, so even discrete analog circuits with the same parts can perform differently with modern components.

 

OT example. We have an industrial product that was first designed in 1989. It's just about the only think like it and we've been working on a modern replacement. The main reason for working towards a replacement is obsolescence of parts. But in the meantime, we've been getting failures on the old design and after investigating, it's due to "better" parts. Modern semiconductors are able to switch faster which is better for so,e circuits, but in an older design can cause problems, so we are starting to for instance where there should be a clean square wave, we get ringing every time it switches polarity resulting in noise which screws up the whole measurement. Theoretically the part is the same P/N and should do the same thing. These things are difficult to track down because power in one facility may trigger this issue but not in another facility. When we test at the factory we may not be able to replicate what's happening at the end user site.

 

Just thought I'd toss that out as an interesting side note.

[Al Coda]

... modern synths have caught up in sound.

 

At the end of the day it´s all matter of taste.

In fact, there´s no "better sound",- may it come from ancient sound sources or those designed using today´s technology.

 

It doesn´t matter if the filter of modern synth "A" doesn´t sound like vintage synth "B" and it won´t prevent a hit/ success.

When a tune sells big and is been done on a Kazoo,- that´s cool then !

When your tune is s##t and you used a ton of "holy grail" vintage gear,- who cares ?

 

So yes,- use what´s available today and be creative.

 

... They have also surpassed the vintage synths in reliability.

 

That´s not true.

All my vintage gear incl. what I sold, worked for a very long time and didn´t need much service.

I used only what worked and was reliable over decades.

I sold a lot,- Minimoogs, MOOG Taurus and Source, OB-8, Roland MC-202, MKS20, 70 and 80, D550, Yammi DX7, KX88, Fender Rhodes mkI, Rhodes mkII, Clavinet D6, ARP/Solina, Roland RS-??, Hohner String Melody and Yammi SS30 string machines, VOX organ and tons of stomp boxes, rackmount fx, amps and speakers .

They all worked when I sold ´em and I gigged w/ everything and there were transport several times a week for studiowork in the past.

You won´t get such jobs w/ unreliable gear,- never.

So it HAD to work and it did.

All these "tuning nightmare" and "gear failure" stories during gigs or studio sessions are almost unknown for me,- it didn´t happen that way.

The key is, protect and treat your gear well.

There were rare horror scenarios, but they were all caused by other reasons like roadie handling and power problems and not by unreliability of the piece of gear itself.

 

The only exception was the 1st Prophet 5 I bought which was a rev2 and up today I´m unsure about if ALL Prophet 5 rev2 were so unreliable or if it was only that one.

 

A.C.

[The Real MC]

I've recently been in more discussions focused on filter type, and know that the prophet used a very similar ladder (if not the same) to the Mini.

 

Nope. The filter ICs in the entire Prophet line - whether it was SSM, CEM, newer Curtis in the DSI - were OTA based filters not ladder filters.

 

The Minimoog ladder filter is a set of 1-pole discrete transistor pairs with the reactive element tied to the emitters, whose resistance is varied by the standing current at the bottom of the ladder. The capacitor combined with the variable resistance in the emitters forms the RC filter action. Stack four sets to form a 4-pole 24dB/oct VCF.

 

OTAs vary their output resistance with iABC, and the capacitor coupled to its output forms the 1-pole RC filter action. Chain four of them and you have a 4-pole 24dB/oct VCF.

 

Feedback architecture goes a long way to defining the resonant color of the filter's sound, and ladder vs OTA filters have vastly different feedback networks. There is no avoiding it.

 

Another contributing factor of a synth voice is the VCA. Until the late 1970s, VCAs were not high fidelity or low noise. They were easily overdriven and their distortion did give them that "vintage" sound. This is why early Oberheims and Moog sounded creamier than their later models. I'm not just talking the output VCA, there is also a VCA in the filter feedback loop that creates the resonance. If the synth is programmable, there will be many VCAs in the audio path.

 

Then there's the buffer systems used at the output of the ladder filter. Moog changed them over the years. The Minimoog wasn't perfect - the bipolar transistor buffers had an interaction with the ladder current that restricted its operation, but it sounded better than the JFET buffers on the prototype Model C (and I have played one). With each succeeding model, Moog was trying to improve the "technical specs" of the ladder filter without listening to the impact it was having on the sound. That's why many users complained that the "improved" synths didn't sound like a Minimoog. Imperfections can be a good thing, and while the Minimoog ladder filter wasn't perfect it sounded great.

 

So the inevitable result is the ladder filter is going to sound different from the OTA filter.

[Muad’Dib]

I know this may not be a vintage synth, but I had a used KORG MS-20 Mini, that died. After thinking it needed repair. It was originally owned by a Guitarist.

 

Had an Omni, that was dead when I bought it 20 years ago, Paid $250 for it, spent $250.00 on repairs and sold it partially working for $25.00 on eBay. My lesson, never buy a vintage synth again.

[Al Coda]

Nope. The filter ICs in the entire Prophet line - whether it was SSM, CEM, newer Curtis in the DSI - were OTA based filters not ladder filters.

 

...

 

So the inevitable result is the ladder filter is going to sound different from the OTA filter.

 

Thank you for this excellent explanation !

 

 

A.C.

[Moonglow]

I've recently been in more discussions focused on filter type, and know that the prophet used a very similar ladder (if not the same) to the Mini.

 

Nope. The filter ICs in the entire Prophet line - whether it was SSM, CEM, newer Curtis in the DSI - were OTA based filters not ladder filters.

 

The Minimoog ladder filter is a set of 1-pole discrete transistor pairs with the reactive element tied to the emitters, whose resistance is varied by the standing current at the bottom of the ladder. The capacitor combined with the variable resistance in the emitters forms the RC filter action. Stack four sets to form a 4-pole 24dB/oct VCF.

 

OTAs vary their output resistance with iABC, and the capacitor coupled to its output forms the 1-pole RC filter action. Chain four of them and you have a 4-pole 24dB/oct VCF.

 

Feedback architecture goes a long way to defining the resonant color of the filter's sound, and ladder vs OTA filters have vastly different feedback networks. There is no avoiding it.

 

Another contributing factor of a synth voice is the VCA. Until the late 1970s, VCAs were not high fidelity or low noise. They were easily overdriven and their distortion did give them that "vintage" sound. This is why early Oberheims and Moog sounded creamier than their later models. I'm not just talking the output VCA, there is also a VCA in the filter feedback loop that creates the resonance. If the synth is programmable, there will be many VCAs in the audio path.

 

Then there's the buffer systems used at the output of the ladder filter. Moog changed them over the years. The Minimoog wasn't perfect - the bipolar transistor buffers had an interaction with the ladder current that restricted its operation, but it sounded better than the JFET buffers on the prototype Model C (and I have played one). With each succeeding model, Moog was trying to improve the "technical specs" of the ladder filter without listening to the impact it was having on the sound. That's why many users complained that the "improved" synths didn't sound like a Minimoog. Imperfections can be a good thing, and while the Minimoog ladder filter wasn't perfect it sounded great.

 

So the inevitable result is the ladder filter is going to sound different from the OTA filter.

MC, I wouldnt know the difference between a ladder filter and a step-stool, but that was awesome.

 

Perhaps like EricBarker, when I first heard a lead on a Prophet-5 my initial thought was something like, That sounds like a Minimoog. This experience occurred in a nightclub, as an audience member, and I recall thinking that lead could have torn someones head off. Of course I have now come to appreciate the creamier sound of the Mini, but I wonder how much those type of differences among synths are dissolved into the random abyss of a live performance situation?

[David Emm]

Part of the rather male-oriented pleasure of synths is hoping one doesn't 'splode when you turn it on. Easily half of the vintage keys I've played were so lacking in some vital area that they were about as welcome as a dose of the syph. I love the hardware I've kept, of course, but there's much to be said for buying a couple of top-end models, just to get a decent keybed. I won't go there, because the topic is so elderly, all of its teeth are missing. I deeply appreciated CJ Vanston's comment about being called for many early gigs because he could make a Prophet-5 act as great harmonicas or french horns when few others were that savvy about it. The less hardware I've kept, the more adept I've become at making each piece sing properly. Only rare studios/schools, fringe collectors and Saudi princes will drop $20k on a vintage synth. Its like buying a Lamborghini; the sticker price is brawny enough, but wait until you see the insurance and repair bills!

[ksoper]

MC, I wouldnt know the difference between a ladder filter and a step-stool, but that was awesome.

 

My sentiments exactly. I truly admire those among us who know this stuff. I don't, but it never kept me getting sound out of a synth. You don't have to know how to cross-pollinate pine trees to write "War and Peace."

[TommyRude]

It appears there is a subculture of folks that prefer the older stuff, and will pay handsomely for it. The younger synths seem to be thinner, where the vintage, more seasoned and mature gear has a fatter, wetter sound. I think this more mature crop is called GILF? (Gear Id Like to Find)

[Nathanael_I]

I've made a conscious decision to avoid vintage synths. My one exception was to pick up a new Model-D from the recent run just because it does that "thing" - but it is brand-new.

 

Well-maintained examples of the big vintage synths definitely have that "sound". But my choice is more based on an aesthetic. Those synths were expensive - the best money could buy when new, and artists used them as best they could to find new sounds and new music.

 

I'm more interested in what is available today. What are the special instruments available now? What are they capable of? What sounds would they make now?

 

I am not trying to cop classic album tones, so there is also that - it isn't about nailing a sound for a cover band for me. If I was Hans Zimmer and scoring Bladerunner, I'd certainly use a CS-80 on the score - and he did!

 

The future certainly lies in digital instruments that go far beyond subtractive synthesis. We aren't fully there yet, but instruments like the Waldorf Quantum and PPG's Infinite Pro soft synth certain point part of the way - the Prophet X also, in its own way. There's a richness and complexity to the sounds these units make that just doesn't come from LFO's and the simple capabilities of an analog subtractive synth by itself. Modular is definitely where the mono-synth becomes unlimited, but for those of us that want to play keys, they have limits.

 

It's a great time to use synthesizers - pretty much everything is available for prices that are amazingly less than they used to be. That and I'm not 16 anymore and can afford stuff! That is also a good thing!

[Rally]

Forgive this post since it is not really relevant to the discussion, but Vangelis scored Blade Runner. Ahhh, Blade Runner 2049. . . my bad.

[RABid]

 

... They have also surpassed the vintage synths in reliability.

 

That´s not true.

All my vintage gear incl. what I sold, worked for a very long time and didn´t need much service.

I used only what worked and was reliable over decades.

I sold a lot,- Minimoogs, MOOG Taurus and Source, OB-8, Roland MC-202, MKS20, 70 and 80, D550, Yammi DX7, KX88, Fender Rhodes mkI, Rhodes mkII, Clavinet D6, ARP/Solina, Roland RS-??, Hohner String Melody and Yammi SS30 string machines, VOX organ and tons of stomp boxes, rackmount fx, amps and speakers .

They all worked when I sold ´em and I gigged w/ everything and there were transport several times a week for studiowork in the past.

You won´t get such jobs w/ unreliable gear,- never.

So it HAD to work and it did.

All these "tuning nightmare" and "gear failure" stories during gigs or studio sessions are almost unknown for me,- it didn´t happen that way.

The key is, protect and treat your gear well.

There were rare horror scenarios, but they were all caused by other reasons like roadie handling and power problems and not by unreliability of the piece of gear itself.

 

The only exception was the 1st Prophet 5 I bought which was a rev2 and up today I´m unsure about if ALL Prophet 5 rev2 were so unreliable or if it was only that one.

 

A.C.

 

This time it is my turn to say "That's not true."

 

I always took care of my analogs and never let a rodie move my gear unless I was at the other end of the case. My Model D always had problems with oscillator 2 dropping out of tune. That is a known design flaw. My MemoryMoog had lots of issues including tuning. The consensus in the industry was the product was pushed out too early and a lot of early users suffered. That synth taught me NOT to be first in line to buy a new product. Loved my Chroma and I was one of the lucky ones. Many people had lots of trouble with power supplies.

 

By the time the DX7 came out I was very willing to sacrifice sound for stability. Now I don't have to. I've never had a problem with any Access Virus and I have owned 4 over the years and still have two. My new DSI's don't sound as good as the original Prophet 5, but they seem to be rock solid and much easier to get serviced. That is why I would choose one over an original.

 

 

I still have two fairly old analogs. A Moog Source with the known issue that makes the digital control weird out and start playing random notes, and an EML-400 that no longer scales correctly. I sold my Model D when I could not find a tech within 200 miles that could fix/replace the contact bar.

[Song80s]

I refuse to be outdone by these clever online resellers or faux collectors, etc.

 

I might sell my 7 yr old shipping box for my Kronos 88. I think its a collectible. Wonder if $250 is fair ? Local pickup only. Shipping is too much work

[The Real MC]

Thank you for this excellent explanation !

 

 

A.C.

 

MC, I wouldnt know the difference between a ladder filter and a step-stool, but that was awesome.

 

My sentiments exactly. I truly admire those among us who know this stuff. I don't, but it never kept me getting sound out of a synth. You don't have to know how to cross-pollinate pine trees to write "War and Peace."

 

That's one thing I appreciate about keyboard players - you're an open minded bunch.

 

Contrast with guitar discussion forums where guitar players read all sorts of myths and accept them as gospel. I used to be on those forums but I left because I tried to offer the truth but they refused to accept it. It wasn't because my pride was damaged - to those folks no explanation was possible.

 

KC, AH, and plenty of other keyboard/synth forums don't suffer from this, and that makes us cool

[Al Coda]

 

This time it is my turn to say "That's not true."

 

Aha ...

 

I always took care of my analogs and never let a rodie move my gear unless I was at the other end of the case.

 

Well, that might have been the mistake because in my case, my gear got sustained maintenance while touring.

When I said "roadie-handling" in my post above,- it was in the sense "stage-hands" moving the gear and did load in/out.

So, when these guys threw pieces around falling down the floor or such, damages were preprogrammed.

 

In opposite, my backline techs always were qualified crew members serving me well,- setting up the gear precisely, cleaning and tuning the gear and looking for failure once being set up and before I arrived.

So,- I was always happy not being on the other end of the case myself.

 

My Model D always had problems with oscillator 2 dropping out of tune. That is a known design flaw.

 

A design flaw, none of my Minimoog Ds introduced at all.

I have only one left,- but I power it up, give it about a quarter of an hr to warm up, tune it and it´s absolutely stable for several hrs,- at least in the studio.

After some hrs I recognize a slow and minimal drift downwards so I have to re-adjust the mastertune,- but OSC #1 and #2 in relation keep stable.

But this does NOT rule for OSC #3 which I use as LFO anyway most of the time.

 

Only extreme temperature changes make my Mini drift in some unusual way, hot sunlight p.ex..

I calibrate my Mini myself very careful and over a period of several hrs or a day in the same room, windows and doors closed.

That helped a lot and minimizes calibration procedures.

I wouldn´t use my Minimmog D when OSC #2 would ran out of tune always.

I had sold it then.

 

My MemoryMoog had lots of issues including tuning.

 

The Memorymoog is a special.

It was so well known for issues I didn´t buy one.

Everyone owning a Memorymoog or Memorymoog Plus complained and didn´t use it live,- so I was warned.

 

Surprisingly my MOOG Source worked better, but I didn´t keep it for long because I was not satisfied w/ it´s behaviour when trying to fine tune the OSC beating to that sweet spot where it sounds musical to me when doing that on my Minimoog D.

At least because the Source offered a preset system,- once a formerly stored preset was recalled, the OSC beating was too narrow or too wide.

Then, I sold it and it didn´t need much time and it crapped out completely for the new owner.

So it was just only luck on my side.

 

The others I bought were great.

Roland MKS80 never had an issue except it needed some autotune procedures during it´s 1st 45min after been powered up.

Fortunately it´s autotune cycle was, compared to other synths, extremely fast and could be requested over MIDI from my KX88 at that time.

I only had to do it when there wasn´t enough time for a 30min warmup.

The MKS70 worked flawlessly and didn´t need any service until I sold it in 2012.

The VFD display crapped out at the new owner were I helped finding the rare display-coil then.

 

OB-8 ... there was a single 6-leg chip in a socket w/ one of the legs bended invisibly.

Obviously it already happend during manufacturing.

Once found and replaced, it worked for ages.

 

Oberheim Xpander,- works ´til today,- even the rotaries and displays.

I had to replace two CEM 3372 ...

Now it´s 31 years old and it traveled all over europe and north africa,- suffering extreme heat and cold !!!

 

Loved my Chroma and I was one of the lucky ones. Many people had lots of trouble with power supplies.

 

Well, I think there ´s spread for standard factory models responsible for many issues users report.

I knew Chroma users suffering from voicecards falling out of their sockets during transport.

 

Products being released too early is common behaviour also today, especially when more or less complex software/firmware works inside or when it is a pure software product.

 

By the time the DX7 came out I was very willing to sacrifice sound for stability. Now I don't have to. I've never had a problem with any Access Virus and I have owned 4 over the years and still have two. My new DSI's don't sound as good as the original Prophet 5, but they seem to be rock solid and much easier to get serviced. That is why I would choose one over an original.

 

I´d never buy a original Prophet-5 used again !

I always bought NEW and I tested the gear in shops before I bought !

That might be the reason why my gear worked so good when I toured.

 

There were exceptions like the Minimoog D I bought used when one of my own got stolen.

Well, it was a early Minimoog D w/ a very nice grained wooden case.

It had a 4 digit serial number and I sold it soon because it really suffered from tuning instabilities.

Today most say these sound "warmer"...

Well, to each it´s own.

I always sacrificed sound for reliability and stability.

 

I sold my Model D when I could not find a tech within 200 miles that could fix/replace the contact bar.

 

I imagine making my Minimoog D keyless and play it over MIDI only in future and once the busbars and other keyboard related componets make problems.

 

 

A.C.

[ABECK]

I feel the same way about the fascination with Mellotrons (and the expensive digital re-creations). Having worked in a studio that had 2 Mellotrons at my disposal, I learned to hate those beasts. VERY temperamental and you often had to literally kick them to get sound to come out. Even a basic sampler 20+ years ago could cover the library nicely, but for some reason it's one of those Nostalgia things. I have no romantics yearnings to work with one of those again (neither does my back).

[The Real MC]

My Model D always had problems with oscillator 2 dropping out of tune. That is a known design flaw.

 

A design flaw, none of my Minimoog Ds introduced at all.

 

Depends on the Minimoog.

 

The design flaw was present in the middle period of oscillator boards, the one with the 3046 transistor array.

 

Minimoogs after serial 10175 had a newer oscillator board design that did not have the design flaw.

 

It was not uncommon for owners of older Minimoogs to upgrade their "flawed" oscillator board.

 

Only extreme temperature changes make my Mini drift in some unusual way, hot sunlight p.ex..

 

I did some modifications on my early RAM Minimoog to cure the tuning drift. It saw use at club gigs, I would tune it up at the beginning of the show and I never had to tune it again during the four hour gig. Not even the VCO detunings.

 

The Memorymoog is a special.

It was so well known for issues I didn´t buy one.

Everyone owning a Memorymoog or Memorymoog Plus complained and didn´t use it live,- so I was warned.

 

I'm one of the brave ones who gigs a Memorymoog, albeit it has been heavily hot-rodded to make the tuning and reliability far better.

 

I am now gigging an overhauled OBX.

 

Just about ANY polysynth made before 1984 needs a total overhaul. Memorymoog, Polymoog, Prophets, Oberheims, Roland, Yamaha, et al. I know tricks from my career in systems engineering to make old polysynths gig-worthy.

 

Surprisingly my MOOG Source worked better

 

There's a reason for that. The Memorymoog's Achilles Heel is its mass sea of interconnects. Many functions were split between multiple circuit boards and the stock interconnects were poor quality. Because the Source is much simpler, most of the important functions were on a single circuit board which drastically minimized the interconnects.

 

but I didn´t keep it for long because I was not satisfied w/ it´s behaviour when trying to fine tune the OSC beating to that sweet spot where it sounds musical to me when doing that on my Minimoog D.

 

At least because the Source offered a preset system,- once a formerly stored preset was recalled, the OSC beating was too narrow or too wide.

Then, I sold it and it didn´t need much time and it crapped out completely for the new owner.

So it was just only luck on my side.

 

The one you had must had been defective. Mine has real fine tuning.

 

Loved my Chroma and I was one of the lucky ones. Many people had lots of trouble with power supplies.

 

Well, I think there ´s spread for standard factory models responsible for many issues users report.

 

Early adopters usually take on some risk, but the Chroma was the exception. The ARP folks - now working for Rhodes - insisted on building the first 50 Chromas at their facility until CBS/Rhodes got their act together for a production line. Those first 50 were the best ones and are sought after.

 

I sold my Model D when I could not find a tech within 200 miles that could fix/replace the contact bar.

 

I imagine making my Minimoog D keyless and play it over MIDI only in future and once the busbars and other keyboard related componets make problems.

 

Studio Electronics used to do just that with their MIDIMoog/MIDIMini rackmounts.

[The Real MC]

I feel the same way about the fascination with Mellotrons (and the expensive digital re-creations). Having worked in a studio that had 2 Mellotrons at my disposal, I learned to hate those beasts. VERY temperamental and you often had to literally kick them to get sound to come out. Even a basic sampler 20+ years ago could cover the library nicely, but for some reason it's one of those Nostalgia things. I have no romantics yearnings to work with one of those again (neither does my back).

 

I like old stuff and am brave enough to take on restoration projects, but Mellotrons were never a good design and are just not worth the trouble. Just use a digital sampler.

[David Emm]

When bad keyboard players go to Hell, the devil points them at a lone Mellotron.

[RABid]

I tried everything with that Mini including a heater bar mounted to the back. Even during the last set of a 4 hour gig it would drop out at the worst time. The other issue I had was with the pitch bend wheel. It did not like to return to zero. A bend up would result in it being sharp. Pitch bend down and then returning to center would leave it flat. I had to learn to always end a bend up for tuning consistency. I do remember reading complaints about the lack of a dead zone in the middle to alleviate this problem. I'm not sure if this was an issue for most Mini's, or just some.

 

 

Luckily I don't have these problems with my Voyager.

[Doerfler]

Luckily I don't have these problems with my Voyager.

 

Nor do I.

[Al Coda]

 

The design flaw was present in the middle period of oscillator boards, the one with the 3046 transistor array.

 

Minimoogs after serial 10175 had a newer oscillator board design that did not have the design flaw.

 

Yup. Two out of three of my Minimoogs used the newer OSC boards.

 

It was not uncommon for owners of older Minimoogs to upgrade their "flawed" oscillator board.

 

Exactly.

That´s what I did w/ my 1st one.

The 2nd one already used the newer OSC board.

 

I know tricks from my career in systems engineering to make old polysynths gig-worthy.

 

That´s great !

B.t.w., I´d be interested in which mods you did for your Minimoog D.

 

... the Source ...

The one you had must had been defective.

 

Can be.

 

... the Chroma was the exception. The ARP folks - now working for Rhodes - insisted on building the first 50 Chromas at their facility ... Those first 50 were the best ones and are sought after.

 

Interesting info !

So, all the Chroma expanders aren´t the quality of that 1st 50 ARP Chromas ?

 

A.C.

[Al Coda]

The other issue I had was with the pitch bend wheel. It did not like to return to zero.

 

The dead-zone mod helped.

 

But there were also hardliners saying the dead-zone mod was for Sissies.

Well, in fact they prefered the original behaviour of the pitchwheel for doing more natural sounding vibrato instead using modwheel LFO amount.

Indeed that vibrato technique is much harder to realize when there is a dead-zone existing.

 

A.C.

[mate stubb]

 

Interesting info !

So, all the Chroma expanders aren´t the quality of that 1st 50 ARP Chromas ?

 

A.C.

 

I have owned several Chromas and a couple Chroma Expanders. All of the Chromas had power supply and voice card problems at some point. Both Expanders were trouble free, but that's probably a coincidence. Never saw an actual Arp Chroma in the flesh, but the people who worked at Arp like Phil Dodds certainly believed that the ones they hand built were best.

[The Real MC]

I tried everything with that Mini including a heater bar mounted to the back. Even during the last set of a 4 hour gig it would drop out at the worst time. The other issue I had was with the pitch bend wheel. It did not like to return to zero. A bend up would result in it being sharp. Pitch bend down and then returning to center would leave it flat. I had to learn to always end a bend up for tuning consistency. I do remember reading complaints about the lack of a dead zone in the middle to alleviate this problem. I'm not sure if this was an issue for most Mini's, or just some.

 

Sounds very much like your Minimoog had a power supply problem. If the voltage rails aren't stable, neither will the tuning. The problem with the pitch wheel is a dead giveaway.

 

Luckily I don't have these problems with my Voyager.

 

Smart man.

 

I know tricks from my career in systems engineering to make old polysynths gig-worthy.

 

I´d be interested in which mods you did for your Minimoog D.

 

I have the 3046 VCO board and changes were done to power distribution, references, and CV processors - I was conscious about leaving the audio path alone. I referenced the front panel tuning pots off the local power rails of the VCO board, because those rails are on a Kelvin force/sense system but the tuning power are not - this causes CV errors IE tuning drift. The original 741 opamps have input offset error voltages that vary with temperature - while they are small, the CV processor does operate in the millivolt range which is in the error domain so I replaced the opamps with modern ones. I designed my own deadband for the pitch wheel and re-biased the CV processor circuits. I decreased the range of the trimpots - they were much wider than needed, if they are too wide just a miniscule bump can knock the trimpot wiper to a different spot and this causes drift. The old carbon comp resistors would change value just by touching them - you could hear the pitch change. Some onboard references were derived from a voltage divider - that causes tuning drift so I replaced them with a zener reference circuit.

 

I did all the changes sequentially and monitored the performance, so I know they work.

[J. Dan]

How much of a deadband was required on the pitch wheel?

[analogika]

My MemoryMoog had lots of issues including tuning. The consensus in the industry was the product was pushed out too early and a lot of early users suffered. That synth taught me NOT to be first in line to buy a new product.

Rudi Linhard fixed those issues on mine. What a beast.

 

A Moog Source with the known issue that makes the digital control weird out and start playing random notes,

Thats a five-minute fix.

 

The issue is that the power supply transistors are screwed to cooling arrays on the back panel, but theyre soldered into the main logic board, which is attached to the top panel. So every time you press a membrane button on the top panel, youre flexing that solder connection, and eventually it becomes intermittent, leading to random spikes and dropouts which will in turn trigger random notes.

 

The fix is to clip the transistors off the mainboard and bridge the connections with wire leads. Thats it.

[analogika]

How much of a deadband was required on the pitch wheel?

I dont have an answer for you, but my local tech recently refurbed one of my minis and explained that the official deadband fix from the moog factory service bulletins is insufficient, and that he designed an alternative.

 

I apologise for not offering any details. I oil my Hammond and can solder an obviously disconnected cable or something simple like the Crazy Source fix, and I tune my Wurli, Clavs and Rhodes, but beyond that, I hand these things off to people who know what theyre doing.

[Al Coda]

I have the 3046 VCO board and changes were done to power distribution, references, and CV processors - I was conscious about leaving the audio path alone. I referenced the front panel tuning pots off the local power rails of the VCO board, because those rails are on a Kelvin force/sense system but the tuning power are not - this causes CV errors IE tuning drift. The original 741 opamps have input offset error voltages that vary with temperature - while they are small, the CV processor does operate in the millivolt range which is in the error domain so I replaced the opamps with modern ones. I designed my own deadband for the pitch wheel and re-biased the CV processor circuits. I decreased the range of the trimpots - they were much wider than needed, if they are too wide just a miniscule bump can knock the trimpot wiper to a different spot and this causes drift. The old carbon comp resistors would change value just by touching them - you could hear the pitch change. Some onboard references were derived from a voltage divider - that causes tuning drift so I replaced them with a zener reference circuit.

 

I did all the changes sequentially and monitored the performance, so I know they work.

 

Thank you !

My Minimoog D S/N is beyond 10175,- so your mods might not be for mine.

But it´s very interesting info nonetheless !

When I knew all this late 80s already, I possibly still used the Mini I sold ´til today.

 

The dead band mod in my Minis weren´t original MOOG mods.

I also had a tech who did his own and IIRC, he said it was more comparable to the Prophet 5´s.

Can be I still have the schematics somewhere,- but never digitized.

I remember I got all when his biz changed.

 

 

A.C.

[Al Coda]

... my local tech recently refurbed one of my minis and explained that the official deadband fix from the moog factory service bulletins is insufficient, and that he designed an alternative.

 

Who´s that tech ?

 

 

A.C.