ANALOGUE WAVEFORM GENERATOR MODEL 25S

Buchla, Serge, Studio.h, Northern Light Modular, Keen Assoc., 1979, Vedic Scapes, etc. Banana systems
Be sure to look into MANUFACTURER SUB-FORA as well..

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solaranus
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by solaranus »

I have been troubleshooting mine for a few weeks now so I guess I can also report on my findings.

After finishing my build, and replacing every cmos ic once because before the first power up I was too excited and did not notice pin headers between pcbs 2 and 3 were not correctly aligned, everything seemed to work fine except MO was stuck at a certain frequency and could not be changed with pots, trimmers, fm or cv. It only responded to high-low switch. Even then, high frequency was still lower than lowest frequency of PO.

I checked every resistor value, tested every op-amp, swapped parts between two oscillators with no result. In the end, I started going thru every connection from pots to THAT chips, since problem had to lay somewhere inbetween. Good news was since it's a 259, it's the same circuit and there are schematics available. The redrawn schematic by Feedback Modules for their Two59 module was also helpful since original hand-drawn schematic might look overwhelming at the first sight.

Anyways, I noticed this:
Buchla_2590_1_200.jpg
Buchla_2590_1_200.jpg (34.83 KiB) Viewed 1527 times
This is the LM301, which I substituted with a TL071 and it worked for PO. That capacitor in the feedback path, C5 is 22pF for both oscillators in the original schematics. However with 25s, while PO has this 22 pF cap, MO has a 47n film cap in its place (C21 on PCB2). I replaced the film cap with a 22pF cap and it started working correctly. Now, I did not see any montion of this anywhere, maybe I missed it, or maybe it does not cause this problem with a LM301 but this is how I got mine to work.

Oh also, that electrolytic cap at FM input is other way around on the pcb.
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cafe-de-la-jungle
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by cafe-de-la-jungle »

Hi Guys,

Does anyone has any updates regarding the bom for the pcb v2.0? Just bought the pcb and panel for build and I was wondering if I should go ahead with the bom 1.0 or perhaps check with EMS. Have anyone build the 25s recently and have some insight into this?

Appreciate any help!
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solaranus
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by solaranus »

Another "late"discovery, changing R245 to 1k as described by Dave Brown also effects the range of the FM Offset trimmer and R244 (100k) needs to be reduced if one cannot get rid of the offset with the trimmer. I replaced it with a 33k resistor and also replaced the trimmer with a multiturn one and could dial in the exact voltage so the frequency of the CO is not affected when pitch modulation is selected and Index is by zero.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

cafe-de-la-jungle wrote: Mon Nov 16, 2020 7:50 am Hi Guys,

Does anyone has any updates regarding the bom for the pcb v2.0? Just bought the pcb and panel for build and I was wondering if I should go ahead with the bom 1.0 or perhaps check with EMS. Have anyone build the 25s recently and have some insight into this?

Appreciate any help!
Did you ever get an update to this? Just bought PCBs from EMS, I guess I should check with Shawn. It does not specify PCB revision.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

Bumping this thread. Turns out I'm getting V2 boards. Shawn really doesn't have any information. Anyone here who has built V2 care to comment? Any special considerations? Is the BOM accurate?
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

An update.... I confirmed from someone else who recently built that the BOM on EMS that is labelled v1 works for v2 as well. I'm almost done with mine and I will post the I've finished my build, but it all seems correct.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

I finished my build. It works as it should. I have a 259r from SAModular and, even without calibration, they sound very close to me. I'm super pleased to have this is such a small form factor. The only thing I think I will miss is having the dedicated keyboard inputs.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

solaranus wrote: Sat Jun 12, 2021 6:39 am Another "late"discovery, changing R245 to 1k as described by Dave Brown also effects the range of the FM Offset trimmer and R244 (100k) needs to be reduced if one cannot get rid of the offset with the trimmer. I replaced it with a 33k resistor and also replaced the trimmer with a multiturn one and could dial in the exact voltage so the frequency of the CO is not affected when pitch modulation is selected and Index is by zero.
I just came here to post this issue. I can confirm this value works great!!! Thanks so much!
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by CliffordMilk »

I thought I’d give this one a go. I’m wondering if anyone has a satisfactory build using Xvive vactrols. I really can’t justify buying them in large quantities for selection and have no Vactecs anymore.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by Sinamsis »

CliffordMilk wrote: Thu Dec 02, 2021 2:18 am I thought I’d give this one a go. I’m wondering if anyone has a satisfactory build using Xvive vactrols. I really can’t justify buying them in large quantities for selection and have no Vactecs anymore.
I used XVive on mine at least in one. Sounds fine to me, but I'm not picky. I will eventually send the two that I built to Dave Brown to see if he has any refinements he could recommend. He did a little resistor magic to perk up the shitty XVives I had in my 291r, and it sounds pretty decent now. My second 25s has really weak AM that I need to troubleshoot, but otherwise sounds pretty similar to the first I built. Honestly, I would be more worried about sourcing the necessary chips than the vactrols haha. To be very clear I am not a professional, I'm a paint by numbers sort of builder and generally have no clue WTF I'm doing. I just take my time, am incredibly thorough and have decent soldering skills.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by CliffordMilk »

That about sums me up too :) Thanks for the insights. I’ll roll the dice with Xvive. I do have a lot of J201s to select from to get a decent sine wave but will be riding my luck on the other ICs. Fortunately, my ears prefer more subtle wave folding.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by ModHiisi »

Does anyone know, is the Electric Music Store the only place to get the pcb/panel (actually, they're only stocking the pcb at the moment)..?
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by tarandfeathers »

PCBs have only ever been from EMS. There is an alternate panel here, with graphics to match 200 rather than 200e systems:

https://thebeast.co.uk/product/buchla-s ... l-reprint/

Out of stock but they're cut and printed to order so usually ship quickly, in my experience (I've had custom panels turned around in a couple of days from there).
Dunnington Audio - Various Buchla format accoutrements available
GitHub Repo - Open source Buchla format projects
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

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tarandfeathers wrote: Thu Dec 02, 2021 4:48 pm PCBs have only ever been from EMS. There is an alternate panel here, with graphics to match 200 rather than 200e systems:

https://thebeast.co.uk/product/buchla-s ... l-reprint/

Out of stock but they're cut and printed to order so usually ship quickly, in my experience (I've had custom panels turned around in a couple of days from there).
Hey thanks for the info! That's what I assumed but wasn't sure.

And that's good to know about The Beast, will be useful in the (near) future.

Little bit undecided if I just should go with the og version or this...
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by CliffordMilk »

Waiting for my PCBs to arrive and trying to glean the components from several sources. Could someone please tell me if the tall alpha pots from Thonk will fit this build?

https://www.thonk.co.uk/shop/alpha-9mm- ... -vertical/
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solaranus
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by solaranus »

CliffordMilk wrote: Fri Jan 14, 2022 2:56 pm Waiting for my PCBs to arrive and trying to glean the components from several sources. Could someone please tell me if the tall alpha pots from Thonk will fit this build?

https://www.thonk.co.uk/shop/alpha-9mm- ... -vertical/
I think normal alpha pots would be enough if you want to use rogan pots since you need 11mm spacers at most between the panel and the front pcb because of the push buttons.
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Re: ANALOGUE WAVEFORM GENERATOR MODEL 25S

Post by davebr »

Unrelated to the current discussion, I posted the modification I use for timbre. V2 added a timbre range pot but if this and timbre are adjusted just so you can burn the pots out. The timbre range is simply the R* which if adjusted to 0R puts -15V on the wiper of the timbre pot which can be adjusted towards 0R itself.

I've never really been happy with the timbre on the 25S. It seems to have too much range and degrades into square waves which aren't very pleasing like this.
25s_timbre.jpg
Timbre is created by wavefolding with a number of op-amps. The amount of folding is based on the amplitude of the input waveform which is set by a VCA consisting of Q10 and IC24. One can spend time selecting a Q10 to improve timbre, but you can accomplish the same by changing the value of the feedback resistor. I simply remove the timbre range pot, bend a lead over to form a variable resistor, set it to 33K, and replace R224. Then I adjust the maximum timbre until I get nice folds more along the line of a properly adjusted 259 like this.
25s_timbre_mod.jpg
Details are at the bottom of my 25S Analog Waveform Generator page in the Epilog.

Dave
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