Behringer System 55

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Re: Behringer System 55

Post by SkyWriter » Tue Sep 22, 2020 11:36 am

BowserB61 wrote:
Sun Sep 20, 2020 10:05 am
I thought it was very interesting how the 921 had very pronounced drift on the root frequency during warmup, but rock steady high frequency response, while the 921Bs had the opposite; very steady root frequency, but dramatically changing high frequency. So the 921 has solid scaling and easily compensated drift in tuning with temperature, whereas the 921B has sold tuning, but the scaling drifts with temperature in a way that can’t be compensated with the front panel controls. As many have already found, this makes the 921 the better choice for perfectly accurate playing.
Bowser, going through your notes here, I wasn't sure what you mean with the term "root frequency", and "high frequency". I want to make sure I understand exactly what you said before I perform some experiments. That way, I can confirm your readings, as well as extend the scope of data collection.

I noted that my 921B went about 23 cents sharp over the course of the early morning. I haven't changed any trimmers yet, so I can take factory measurements to for writing up any quick-start procedures.
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Re: Behringer System 55

Post by SkyWriter » Tue Sep 22, 2020 12:15 pm

Back to pots: **** who knows that logo? **** just noticed I got one in the shot.

Disassembled one of the troubling 05A105's - the true-log replacements - pointing out features in blue*:

Top: 2 o'clock wiper track; appears to be a non-uniformity in the spot where it gets icky hard to get a repeatable number. Also, that should be position where a 2-piece 5% taper would splice the resistive element.

905E7298-1578-4710-BDAA-1EC233A96062.jpeg

Here there's some similar aspect to the splice from a different angle, but harder to see. The features of note are the triple contact wiper and what is apparently ... carbon shedding? So early? Well, anyway there's your resistive gap as the wiper runs aground of the uncoated EOT's. Sort of hard to pick 280 over 300 here. Electrically there's no difference.

596ACF25-6B03-40D4-B1A9-A3CD586A92CA.jpeg

That's my critique for what it's worth. I can drag a whisker along the element to confirm, but I'm pretty confident there are issues there - whether I nailed them or missed completely :-) - I'll section a 'good' one, and we can kabitz this until the true-log come in next week and throw egg on my face. :roll: :hihi:

*-the 'other' red. :-)

N.B. This is really all good news to me. Behringer designs the product for cost conscience folks, but still provided an inexpensive path to correct the designs for the critical customers with above** average expectations. I couldn't ask for a better product. We get it cheap, use our noggins, everyone wins.

Remark on wiper: three wipers would assist in masking discontinuity traversing a splice cut in the element obliquely to the direction of travel. Also, nice modular construction! Two little drills and it separated nicely :-)

**-maybe even way above??
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Re: Behringer System 55

Post by SkyWriter » Tue Sep 22, 2020 3:56 pm

Popped open an ALPHA pot:

Note the ALPHA element in thinner, two electrical wipers, with non-electrical wiper as well.

This caught spectral highlights I could not catch on the ALPHA. Different coatings perhaps. ALPHA element looks more uniform. Need a microscope on it. There is some structure to the element prior to the EOT on the ALPHA. You can see light angles. Maybe a physical taper of the resistive element. We'll see...
C42012BB-4846-48AC-8771-D5564EB23161.jpeg
C82AF1FD-746F-4039-AD6D-BB3E8AB06556.jpeg
Nice modular construction - i could swap shafts if I could get pins to press-fit it back together. :-)

Here's a clean shot of the ALPHA. Very clean, uniform element.
145586B1-76D3-4972-9081-8E54B8760238.jpeg
Hmmm... the shininess of the BEHR part; are their any aqueous washes in these modern production lots? I would hate to think something gets inside. Yeah, idk. I try not to throw stones I don't understand. Anyone with recent Chinese low cost manufacturing? I don't have much relevant experience there.

Follow up on thermals: The thermocouple(s) will tell us how the system reaches thermal equilibrium vs when thermal gradients are creating local tuning variation. I did kind of stuff to qualify a optical disk library once, best to be as accurate as possible. If a lot of it turns out to be spit in the wind, let's at least use the good spit. :-)
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Re: Behringer System 55

Post by BowserB61 » Tue Sep 22, 2020 5:03 pm

SkyWriter wrote:
Tue Sep 22, 2020 11:36 am
Bowser, going through your notes here, I wasn't sure what you mean with the term "root frequency", and "high frequency". I want to make sure I understand exactly what you said before I perform some experiments. That way, I can confirm your readings, as well as extend the scope of data collection.

I noted that my 921B went about 23 cents sharp over the course of the early morning. I haven't changed any trimmers yet, so I can take factory measurements to for writing up any quick-start procedures.
Yeah, I guess by root frequency I’m referring to the output with 0V CV input (640Hz) and by high frequency I’m talking about the output with +5V CV input (20.48kHz). To me, it seems like changes in the 0V data are reflected across all frequencies and can be fixed with the front panel tuning knob once it’s warmed up, and changes in the +5V data are more indicative of changes in scaling or tracking as it warms up.

KSS’s assumption is correct in that I left the input at 0V except when taking measurements. I routed the +5V and -2V to inputs on the CP3A-O and daisy-chained the CV inputs of the oscillators, skipping the 921A and ending at the 921. So each time I measured, I just used the routing switch to apply voltage long enough to take a reading. The idea of letting it warm up separately at each input voltage would be interesting because there was definitely some settling time each time the CV was switched. It would just take a really long time to measure it that way.

It may also be useful to know that 921B #3 in my data is not exactly at factory calibration. I started trying to calibrate it to track along with the 921, but realized it was far more tricky and dynamic than I expected because of the temperature sensitivity and tried to put it back as close as I could to the factory 921Bs before measuring everything at once.

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Re: Behringer System 55

Post by SynthBaron » Tue Sep 22, 2020 7:26 pm

Anyone measured the stability/tracking of the 904a yet?

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Re: Behringer System 55

Post by SkyWriter » Tue Sep 22, 2020 8:15 pm

SynthBaron wrote:
Tue Sep 22, 2020 7:26 pm
Anyone measured the stability/tracking of the 904a yet?
I haven't measured it. The original schematics did not implement much more than a simple adder to track CV. However, there are some critical component adjustment in the regen area. Which also happens to also have a C50K pot we have a replacement for - the other pot is blocked by the range caps. I'll have to pull it to be sure. I have not done an exhaustive comparison to the schematics, but there are discrepancies among the number and type of trimmers, and I can't resolve the TP's to the schem-o's.

It's late... Here's some dark pix for tonight. There are many of the very small (too small) 6 pin transistor packages, and few instances of the familiar 3 pin transistors.
D6AEAA25-0567-4FE0-B581-989413417B8F.jpeg
937B0891-B723-4E93-AAF7-569FC28643AB.jpeg

Update for 904A. It tracks badly. Hi-Q tracsk about +/- 400 cents. :-) welp, I have two, I'll try again tomorrow.
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Re: Behringer System 55

Post by SynthBaron » Tue Sep 22, 2020 11:30 pm

Thanks.

Yikes, makes me wonder if they production engineered this whole series more for the "Buchla" modular crowd than anything else...with such lax performance tolerances...

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Re: Behringer System 55

Post by SoLder » Sat Sep 26, 2020 1:31 pm

Got me two 960's and 3x962's . Was having some sequencing fun with the Model D , sounded great , thought "i know , i will try it with my Yamaha CS15 , i have an "s-to v trig coverter cable". All was going well , until. . . .
this morning , the CS15 has a strange problem with VCF1 , high pass works on half the keys, band pass sort of oddly, and low pass works on the reverse set of keys.
OHNO !
So i just looked at the input for the CS15 , it says +4V , but the 960 sequencer puts out 8V . . . .so maybe i put in too hot a signal ? but surely that would kill an oscillator not a filter?
Can anyone confirm this is the reason ? and if so what do i need to fix in the CS15 ?
all the other stuff in the CS15 works , the VCF2 is fine , i am worried i have killed VCF1 IC chip IG00156 .
ANYHOW , A HEADS UP TO ANY 960 USERS . . . . . .
HELP !

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Re: Behringer System 55

Post by SkyWriter » Sat Sep 26, 2020 1:57 pm

960 measured Vmax at +8.4 VDC in X4 mode. Although there are spikes between stages that rise to +11.0 VDC it'd only for < 5us.

Other than that, it's entirely a CS15 problem. Bummer. :-(

So, yeah, watch voltages. And don't stick spoons into live outlets. Use a fork instead! :-)

Just waiting on my last 921, and the pot's from Thonk. Then I'll start the soldering and posting directions if anyone wants to see how easy it is to do for themselves. I really liked what I saw with the decade box, so I believe the T1-3 timing will be as intended, as well as eliminating the timing gaps.
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Re: Behringer System 55

Post by SkyWriter » Sat Sep 26, 2020 2:01 pm

For anyone that's counting. Here are the issue's we've identified. Most are addressed already in some fashion on the thread waiting for some verification coming in the next couple of weeks as replacement parts arrive.

I'm really psyched most of this stuff appears easy to fix. Never though it would be this close to OG.

Behringer Moog System 55 Issues list
1) 911 T1-3 timing. Replace 05A105 with true-log B1M.
2) 911A Delay timing, 05A105 -> B1M
3) 961 B-column timing 05A105 -> B1M
4) 904A, 904B regeneration, replace C50K (reverse log 50K)
5) 923 HPF & LPF, replace C50K
6) 921 Sine and Triangle symmetry, adjust factory settings for Sub-audio.
7) 921 vs 921B AUX pulse polarity?
8) VCO Temperature compensation
9) 960 3rd row timing 0-2:2-10 non-mono-tenacity.
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Re: Behringer System 55

Post by KSS » Sat Sep 26, 2020 2:26 pm

Welcome to MW, SoLder!

Sorry you had to deal with that. That sucks. I'll dig up the CS15 docs and have a look. Meanwhile try to think of OTHER things that might have happened between the time all was working well and now. Sometimes it's easy to get fixed on a thing, and miss what else was going on. Like did you notice anything strange during the session? Was there bad weather in your area overnight? ANYthing else that could be the reason.. How long since you've used the CS15 with that input? Meaning before this session, when was the last time you externally fed CV/Gate into the Yamaho?. And for clarity, that *is* what yo did? CV-Gate from the 960 into the CS15's jacks for same?

Sorry if this reads poorly, I'm not meaning to imply anything. Have learned that often the thing I think it is,turns out not to be the thing. So am sharing that.

------
Had a quick look -before posting- at a page mangled PDF service notes for the CS15. Unfortunately the page breaks make for a *lot* of back and forth to connect the schematics.
To help me help you, can you verify exactly which patchcords went where? On quick glance it seems you'd have to blow an IC on the way to the filter -which would also affect the VCO- before the VCF itself would be hit. But I'd lkike to be sure of what you did and what you're seeing now. Since this may end up being more about a CS15 than the boog55, might want to copy your post to a new thread so we don't clutter this one with Yamaha talk.

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Re: Behringer System 55

Post by SoLder » Sat Sep 26, 2020 2:46 pm

KSS ,
you are also a font of knowledge,
no lightning here last night,
but
what i think i did was patch cv from a row of the 960 into the cv in on the cs15 , ( i may have also put it into the trigger( or gate) via the s-trig convertor cable.
I would love to think that maybe a switch needs cleaning on the CS15 , or a single item like a Capacitor or a diode has gone. But it does seem a coincidence that after hinesight of checking on the cs15 user manual , it says max 4volts in . and the 960 is 8v out . that gave me my first thought that indicated some damage has occurred as a result.
Patch cords would have come from the rows 1-3 of cv out , also the output of the gate from the 960 went to the input of the trigger , Yes , as you would expect , basic . (but at some point i may have put cv into gate and gate into cv) .
I totally hear what you are saying about something else getting burnt before the filter IC . ( the circuit layout is on the last page of the manual i think , stupidly ?) . I know of nowhere i can get IC1 (IC00156) even if thats what it was .
Thank you for your help , i am stunned you have pulled up the schematics !
How do i start a thread ? argh so many questions . .. .. .

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Re: Behringer System 55

Post by SkyWriter » Sat Sep 26, 2020 2:46 pm

Thanks KSS! I did not notice SoLder's first post. Where are my manners! :0)

@solder, can you post a scan of that schematic page? Or a pointer to it? NM. Found one. http://dl.lojinx.com/analoghell/YamahaC ... Manual.pdf

Input goes directly into KV input. At least the rails are +/- 18V, you didn't got above that. That would certainly stress that chip (going beyond chip VCC). I don't see how it caused partial problems as described. I suggest it's likely some thing else.
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Re: Behringer System 55

Post by SoLder » Sat Sep 26, 2020 3:09 pm

Yippee ! so as i understand Skywriter , only over 18Volts to a cv or gate input would fry something like IC ! phew . Is it possible the switch for VCF1 , HP,BP and low pass could be broken? it was crackly about a year ago, but been fine lately ( i continuity tested with a meter and all was good).
Being a newbie (actually an old timer) i'm not sure i can post a new thread ?
This help is amazing ! i am hoping its just a diode , capacitor or something basic .
The behaviour on the CS15 is odd , in the way that the top octave is useable and the filter controls like cutoff , lfo, eg and res all work ok,
but the lower octaves seem to be affected differently .
I thought the cs15 ran on +/- 15 volts , not 18 ?

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Re: Behringer System 55

Post by SoLder » Sat Sep 26, 2020 3:16 pm

VCO 1 and 2 work fine through VCF2 , keys all play , track perfectly, so i am sure its not a keying problem,
I have a niggly feeling about the switch that was crackly last year , its odd that its the same switch area . Would a component in the VCF1 circuit exhibit different behaviour at certain keyboard trigger voltages that would result in this odd filter action two thirds of the way up the octaves? its almost as if the lower keys and associated voltages do not affect the filter to open it, but the higher keys do ? the top octave seems fine !
Could someone start a new thread on the cs15 to save clutter here ? i can pester you guys without clogging this thread up .

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Re: Behringer System 55

Post by SkyWriter » Sat Sep 26, 2020 4:43 pm

SoLder wrote:
Sat Sep 26, 2020 3:09 pm
Yippee ! so as i understand Skywriter , only over 18Volts to a cv or gate input would fry something like IC !
Well, no. Some over that (VCC) is bad news. Also I may have answered to quickly. Need to find more about that I/O*. Usually you don't hand easily susceptible products to customers. They tend to come right back that way.


But, I think at this point debugging should be another thread. If the next post doesn't slam dunk the answer that is :0)

*-I'll just update this post... the I/O i quickly looked at was a ket tracking input. When I looked for a rear panel I/O I could only find VCO in's. So... I would need to look at it more to confirm any speculative remarks I made. :-)
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Re: Behringer System 55

Post by SoLder » Sat Sep 26, 2020 5:44 pm

Thanks for the reply Skywriter, I think the gate(trigger) input max on the CS15 in the back of the user manual is over 8Volts , so that should be ok. But the CV in input is listed in the manual as max +4Volts .
Maybe the 960 sequencer has nothing to do with the CS15 problem , it could just be a coincidence. . . . .
I don't understand your comment "Need to find more about that I/O" . . . . . er , what does that mean ? in and out ? sorry to be simple. .
Im sure the 960 is doing what it should , but no idea why it would need to put out 8Volts (i thought eurorack was 5V). So i am concentrating on the CS15, the picture of the PCB on the last few pages of the service manual are hard to read , the schematic of the circuit diagram is easier, but for the life of me , i would not know why only the top few third of the keys work fine , but the bottom two thirds are "rendering the filter controls useless". I don't understand enough about how a likely component would fail. I know vintage caps fail, maybe i should replace them all? there are all kinds in that circuit , . . . im lost ?
many thanks for any advice .
how do i set up another thread ?

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Re: Behringer System 55

Post by KSS » Sat Sep 26, 2020 6:55 pm

I've still not got the CS15 manual re-arranged, but if you think about what you wrote, the filter is even more suspect.

Top KBD half=HP. Bottom half =Low pass. Middle weird = bandpass. Seems the filter may still be still working. At least partly. Key tracking is obviously not in effect. Sounds <-- Literally! like a static center frequency. Like what might happen if the chip got hit with too much voltage on that pin. Not out of the woods WRT maybe needing a new VCF chip. If the external vtrig got past the CV input op amp, it's a clear, clean straight shot to the filter chips CV input pin.
I'm currently suspecting you accidentally fed a gate into the ext. CV input. Mostly because -as SkyWriter wrote- I can't imagine Yamaha actually putting something out into the wild that would blow from 8V into a 4V spec input labeled *external*. I'd fire that engineer if so. But unfortunately that doesn't mean they didn't. And the spec does say 4V.

Kinda busy today but I'll try to get these service manual pages re-arranged and stitched together so the ext input and where it's going aren't at opposite ends of the Manual! There may be missing pages too. It's hard to say as the mnual appears to show one of two channels -whichg would be a normal kind of thing to do. But I may have missing pages.. K2,3,4 AIRC are the lines we're curious about.

Agree it needs to move to new thread. Just give it a try in the general modular section, Upper left corner, new topic.

edit: underlined somethng above to check. Did yo bump ormove a setting and forget it's been moved?

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Re: Behringer System 55

Post by SoLder » Sun Sep 27, 2020 2:19 am

Key tracking appears to be fine when i use VCF2 section, using either vco1 or vco2 . That works as it should ,meaning that the keyboard is still usable and all controls work if VCF1 is avoided.
I have compared IC1 legs to IC3 legs with a multimeter, (the fiter chips on vcf1 and 2), Not sure if keys needed to be depressed so i just did it in a resting state while the unit was on, the legs all read the same comparitably . For example the same pin read 15volts on both , 0.06 on another etc . . . I have started a new thread as "Yamaha CS15 repair from 960 " in the general modular section. Hopefully this will help others now too

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Solders CS15 thread

Post by SkyWriter » Sun Sep 27, 2020 7:55 am

For those in the future looking for that thread: https://www.muffwiggler.com/forum/view ... 4&t=238042
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Re: Behringer System 55

Post by mmckenzie » Sun Sep 27, 2020 9:47 am

I've recently acquired some of these most affordable modules, after having had a suppressed desire to own a Moog since 1971! Funnily enough my creative urges tend more to the Buchla thread of things, but we'll see how it goes.

My first slight disappointment was trying to use the 921 to slowly sweep some noise through the LPF. There is a bit of a discontinuity in the sine wave at low frequencies which causes a sudden step. I then discovered the existence of the original 991 Fixed Filter module described on

https://amsynths.co.uk/home/my-synths/s ... d-filters/

It has a switched HPF and LPF and an attenuator. After a little experimenting I realized I could easily replicate this module with a couple of extra positions in the LPF section to address the issue.

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Re: Behringer System 55

Post by SkyWriter » Sun Sep 27, 2020 10:02 am

mmckenzie wrote:
Sun Sep 27, 2020 9:47 am
I've recently acquired some of these most affordable modules, after having had a suppressed desire to own a Moog since 1971! Funnily enough my creative urges tend more to the Buchla thread of things, but we'll see how it goes.

My first slight disappointment was trying to use the 921 to slowly sweep some noise through the LPF. There is a bit of a discontinuity in the sine wave at low frequencies which causes a sudden step. I then discovered the existence of the original 991 Fixed Filter module described on

https://amsynths.co.uk/home/my-synths/s ... d-filters/

It has a switched HPF and LPF and an attenuator. After a little experimenting I realized I could easily replicate this module with a couple of extra positions in the LPF section to address the issue.
You can fix the sine and triangle sub-audio glitch on the 921. There are two trimmers I've mentioned in the thread to address this. You need to disassemble the module and need good eyesight, secure a suitable screw driver (#0), and even the cheapest scope can show you how you're doing if you don't trust your ears; I would use LF pitch modulation to listen how well you're doing. Should be able to hit it spot on. You might have to bounce between the two. I'm hoping to create directions to approx where it needs to go from (current? Initial? track lots???? ) factory calibration.

The Moog 991 filter function is provided by the B923 module, if you just want to filter it out to some extent. Of course, 923 also has addressible issues :-)
----------
I'm enjoying all those 5 911 & 911A fantasy's I've been harboring for decades :-)
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Re: Behringer System 55

Post by mmckenzie » Mon Sep 28, 2020 3:18 am

(5 x 911) Ha ha. Yes. I was fortunate to acquire my third 911 on eBay last night.

I've still not quite got the 911A to do what I expect. Can you take its output and feed it along with with another S-trig into a 911 or don't they OR together like that?

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Re: Behringer System 55

Post by KSS » Mon Sep 28, 2020 4:17 pm

Natural OR of S-trigs is one of their greatest strengths.

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Re: Behringer System 55

Post by SkyWriter » Mon Sep 28, 2020 5:09 pm

Fwiw, I replaced that 10us timing cap with a 2.2uf. As expected timing sped up by a factor of 4x. Ordinarily, a waste of time, but given the horrible pot, this makes some timing easier to hit now - like the point taper splice, and the EOT's. Now I can almost hit 5ms, instead of 20ms at the fastest. 0 is now 200us instead of 800us.

Found that the S + V trig 921 inputs are level sensitive rather than edge sensitive. While Trig is asserted the VCO output is forced to the clamping point, until trigger de-asserts. Then waveform begins. This presents problems synchronizing the waveform to the EG trigger to avoid random clicks and pops. So, it fatally distorts snappiness measurements :-( using the timing control on the 961 doesn't get short enough.

Ch1 is the envelope I was triggering (also used for clamping point trigger), and the CH2 is the triangle wave I was clamping. The level was the level at the clamping point. The width of the clamping level was equal to the trigger width - need to confirm this because, whilst I've seen it, I can't explain every picture.
2ED104DE-54CD-4440-8DF4-D32D3B65DAD6.jpeg
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