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by Don T
Sun Apr 10, 2022 7:22 pm
Forum: Music Tech DIY
Topic: Korg Polysix Mystery
Replies: 27
Views: 1200

Re: Korg Polysix Mystery

Ah. Alright - right after I made my post, I started pulling the keybed apart. I tested continuity of the wiring harness and every point on the keybed circuit board. Since I had the membranes pulled, I cleaned those contacts and the gold plates (alcohol). Put it all back together and I’ll be damned ...
by Don T
Sat Apr 09, 2022 9:29 pm
Forum: Music Tech DIY
Topic: Korg Polysix Mystery
Replies: 27
Views: 1200

Re: Korg Polysix Mystery

So, after probing around for a bit on the 367 board and thinking about it some more, I decided to order a clone. Came in yesterday and dropped it in the Polysix - no change. Womp. Still no lights on the 366 voice board, so it's time to probe around that some more. And the key bed itself. Ok, at thi...
by Don T
Thu Apr 07, 2022 9:46 pm
Forum: Music Tech DIY
Topic: Buchla 158A Sine Saw Generator DIY
Replies: 28
Views: 3764

Re: Buchla 158A Sine Saw Generator DIY

Peake wrote: Thu Apr 07, 2022 7:59 pm Layout trumps schematic. A vintage module showed that resistor as being 4K7 (and also the missing transistor/resistor and the 0.0047uF cap value).

I've never figured out what the grey wire does; it's not on any vintage module I've seen!
Got a photo of it? (The vintage module I mean)
by Don T
Thu Apr 07, 2022 9:44 pm
Forum: 4U Format Modules + EMS
Topic: 216r edac power wiring
Replies: 4
Views: 220

Re: 216r edac power wiring

The 216 requires a +24V line, but the 216r has a DC/DC converter on board, so standard power connections should suffice. (Except for me, I screwed up the DC/DC converter by trying to sub the part, so I need to build a +24V power supply and run a line to it, which I have yet to do. (Yes, I'm not only...
by Don T
Sun Apr 03, 2022 6:54 pm
Forum: Music Tech DIY
Topic: Korg Polysix Mystery
Replies: 27
Views: 1200

Re: Korg Polysix Mystery

If you press a key 6 times, does the LED on each voice light up as they are triggered? Holy shit, thats RIGHT. I forgot about those voice leds. Indeed nothing is lighting up on the voice board (pretty sure its supposed those d11 resistor looking things at the bottom) Innnteresting. Hmmm Me thinks I...
by Don T
Sun Apr 03, 2022 2:51 pm
Forum: Music Tech DIY
Topic: Korg Polysix Mystery
Replies: 27
Views: 1200

Re: Korg Polysix Mystery

I'm guessing that if the CPU board is indeed fine, and there's no output, it's because the patches were never reloaded, and no one thought to press the "Manual" button and set up a patch on the front panel. If you press a key 6 times, does the LED on each voice light up as they are trigger...
by Don T
Thu Mar 10, 2022 4:40 pm
Forum: 4U Format Modules + EMS
Topic: Buchla 200 back in 4U as well !
Replies: 115
Views: 9172

Re: Buchla 200 back in 4U as well !

I wonder if those of us who did the research to find and correct some of Roman's mistakes, as well as coming up with part substitutions (I was the one that dug though pages of transistor substitutions and found the KC-811 and the 2N3806, among other things), will get a discount...
by Don T
Sun Feb 27, 2022 7:45 pm
Forum: Music Tech DIY
Topic: Mismatching VCF caps on purpose
Replies: 7
Views: 532

Re: Mismatching VCF caps on purpose

Off the top of my head, I would say look up the schematic for the filter in the TB-303, and then listen to a recording of it. Apparently the one smaller value cap was intended to be on the other end of the ladder, and is a design flaw that had desirable results.
by Don T
Fri Feb 25, 2022 5:07 pm
Forum: Music Tech DIY
Topic: How wide (in time) are samples in digital audio?
Replies: 31
Views: 1097

Re: How wide (in time) are samples in digital audio?

A couple thoughts: Grumble's photo may seem simplistic, but it is indeed accurate. The less coarse the stair-stepped DAC output (or ADC conversion), the more true the output to the original analog input (In theory anyway). As for the 24-bit DAC question, the output of a synth is far less complex tha...
by Don T
Fri Feb 18, 2022 8:55 pm
Forum: Music Tech DIY
Topic: Removing stubborn solder from inside through hole pad
Replies: 18
Views: 804

Re: Removing stubborn solder from inside through hole pad

If the hole is empty of solder, and a couple attempts have been made with the Hakko 808 and/or the big desolder pump, I will indeed take a drill bit slightly smaller than the hole, put it in a pin vise, and slowly drill the hole out by hand. I wouldn't dare do this with a motorized drilling tool.
by Don T
Fri Jan 28, 2022 8:16 pm
Forum: Music Tech DIY
Topic: What makes a "bad" power supply?
Replies: 2
Views: 286

Re: What makes a "bad" power supply?

1. Dependability 2. Noise on power rails (a LPF does not always fix) 3. If switchmode, is it adequately shielded against emitting EMF noise? 4. How does it behave when a temporary overload occurs? 5. If switchmode, how does it behave if the input voltage drops too low for it? (Some will literally ex...
by Don T
Thu Jan 27, 2022 3:45 pm
Forum: 4U Format Modules + EMS
Topic: 216M
Replies: 1
Views: 254

Re: 216M

Guess I'd better start saving my money again...
by Don T
Tue Jan 25, 2022 4:13 pm
Forum: 4U Format Modules + EMS
Topic: 291M
Replies: 9
Views: 631

Re: 291M

shoegazer86 wrote: Tue Jan 25, 2022 11:17 am
Peake wrote: Tue Jan 25, 2022 10:57 am Someone with a vintage module should confirm or deny all of this.
It may be within the realm of possibility 8-)
Image
Excuse me while I pick my jaw up from the floor... :woah:
by Don T
Mon Jan 24, 2022 5:31 pm
Forum: 4U Format Modules + EMS
Topic: 291M
Replies: 9
Views: 631

Re: 291M

I'm hoping PCBs to go with this won't be too far behind
by Don T
Sun Jan 16, 2022 8:11 pm
Forum: Music Tech DIY
Topic: 1 transistor "passive" VCA-ish thingy
Replies: 47
Views: 12834

Re: 1 transistor "passive" VCA-ish thingy

Why not adapt this? (scroll down to JFET muting circuit):
https://sound-au.com/articles/muting.html
by Don T
Sun Jan 16, 2022 7:56 pm
Forum: General Gear
Topic: What would you pick as your"less is more" synth?
Replies: 101
Views: 4988

Re: What would you pick as your"less is more" synth?

SH-09. Wish I had never had to sell it
by Don T
Wed Jan 12, 2022 10:29 pm
Forum: Music Tech DIY
Topic: Electrostatic discharge to CMOS chips from handing
Replies: 4
Views: 214

Re: Electrostatic discharge to CMOS chips from handing

Most modern CMOS has input protection (but I still wouldn't mess around with rubber and silk and then pick one up. That said, once they are installed in a circuit there is very little (almost zero) chance of them being damaged.
by Don T
Sun Jan 09, 2022 12:19 pm
Forum: Music Tech DIY
Topic: Books on basic sound circuit design
Replies: 8
Views: 462

Re: Books on basic sound circuit design

Just reading some reviews on Art of Linear Electronics and it mentions you need a detailed understanding of things before digging into this book. Perhaps not a great beginners option then? Definitely for beginners, I think. There is little math involved, and it starts out by explaining how to read ...
by Don T
Sat Jan 08, 2022 4:39 pm
Forum: Music Tech DIY
Topic: Books on basic sound circuit design
Replies: 8
Views: 462

Re: Books on basic sound circuit design

If you want to know the "how" and "why" of what you're doing:



It tells you how every component works, and how they interact with each other.
by Don T
Fri Dec 31, 2021 4:06 pm
Forum: Music Tech DIY
Topic: Oberheim OB8 issues
Replies: 68
Views: 1409

Re: Oberheim OB8 issues

sounds like youre making good progress. are their leds for the transpose switches? do they light up like they should? im wondering if its an issue of the transpose switches being read incorrectly. is it both osc1 and osc2 on all voices that are off? if so, that sounds like the main processor is jus...
by Don T
Thu Dec 23, 2021 9:54 pm
Forum: Music Tech DIY
Topic: Oberheim OB8 issues
Replies: 68
Views: 1409

Re: Oberheim OB8 issues

If ANY of the CMOS chips (CD4xxx) have RCA logos on them, go ahead and replace them en masse to save yourself some time. Also, clean ALL the connectors!
by Don T
Thu Dec 23, 2021 9:51 pm
Forum: 4U Format Modules + EMS
Topic: MEMS 259
Replies: 10
Views: 1076

Re: MEMS 259

Hmm, maybe it's a good thing I haven't finished my 259r with the "Vintage" boards... Lucky!! I just finished my "vintage" 259r. Blood, sweat, and tears for sure, but at least it works! Well, I build an original, V.1 259r quite a few years ago, with all "vintage" parts....
by Don T
Wed Dec 22, 2021 10:17 pm
Forum: 4U Format Modules + EMS
Topic: MEMS 259
Replies: 10
Views: 1076

Re: MEMS 259

Hmm, maybe it's a good thing I haven't finished my 259r with the "Vintage" boards...
by Don T
Sun Dec 05, 2021 11:39 pm
Forum: Music Tech DIY
Topic: Tube amp repair
Replies: 21
Views: 584

Re: Tube amp repair

Wait, are the plates of the output tubes glowing??? If so, don't power it up again without checking the following: Every component in the bias circuit The resistance of the primaries (tube side) of the output transformer. Try to find someone else with one of these amps to compare measurements. Check...

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