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How Can I Trim the Waveshapes on my BEMI Easel?
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author How Can I Trim the Waveshapes on my BEMI Easel?
CliffordMilk
I noticed my waveshapes are way off on the Triangle, Square and Saw waves when the Timbre pot on the CO is fully clockwise. The MO could also do with a tweak.

Could someone please point out which trimmers I should adjust?

Also, if there's an internal high frequency tracking trimmer, I think I need to give that a spin too.
search64
You should check out the notes on how to trim a 208r/p clone. I suspect the inside of a BEMI easel is a sort of surface mount adaptation from the original, so the trimmers should also correspond.

I just built a clone myself and still need to trim, but know what you are getting into. A lot of these trimmers interact with one another, so it's a bit of a task to get the waveshapes right, as well as the tracking together of both oscillators, and you can get spurious oscillations as well. Nothing that can't be fixed, but just know this before you get into it.

Notes on trimming here:
https://modularsynthesis.com/roman/buchla208v2/208spss.htm
Drillionaire
What part of the circuit are you observing the waveforms from? They're not going to look "normal" if you're looking at the waveform coming out of the panel or 1/4" outputs.
CliffordMilk
Thanks very much for these replies. I was taking it from the panel. As I understood it, with the CO waveform switch in the square position, the timbre slider fully down and the pot fully clockwise, I would see something like a square wave on the scope. Instead, I get the following:



Is this normal for an Easel?
search64
Is this with the LPG in VCA mode? If so I think the CO waveshape trimmer might help with the symmetry.
CliffordMilk
I am in VCA mode. I’m now a little confused as to what I should be seeing from the panel outs.
Umcorps
I can check mine and post images from the panel outputs later today if it helps any.

But apart from the sine, the wave shapes on mine also bear precious little relationship to the ones suggested by the panel silkscreen.

I might have been naive but I've always assumed that was part of what made the Easel sound like it does. hmmm.....
CliffordMilk
I would definitely be interested in seeing how the CO waves from other (Buchla/BEMI) Easels look. I have nothing to use as reference.
Umcorps
OK. Here you go. These are the basic waveforms on my BEMI Easel for both oscillators.

https://www.dropbox.com/s/e0o87v00nu6c7ot/Easel%20waveforms.pdf?dl=0

As you can see, the only shapes that come close to the description are the sine and the tri.

Would be interesting to see the raw wave shapes made by the Arturia software version of th Easel as it sounds quite authentic in some of the demos I've seen. Wonder how wonky they are?
CliffordMilk
Thanks for that. Very different from mine but equally deviant smile I'll ask the folks at Buchla if there is any kind of standard in this respect.
Phalanxe
Just FYI, I noticed the same thing on my BEMI Easel a couple months back. Here are my CO waveshapes:





I reached out to Buchla and got this response, but I haven't had a chance to actually make any adjustments, so not sure how close to a perfect waveshape you can actually get:

"If this is the Complex OSC if so it looks like the Timbre section is to high. You can adjust this with the trim pot on card 9B. Also on card 8B there is a trim pot for a sine wave adjustment."
search64
After having trimmed the waveshapes on my clone I can honestly say this is not normal. I didn’t make screenhots of my scope, bit they’re pretty close to the scope shots from this original Easel:
https://modularsynthesis.com/buchla/208/buchla_208.htm

Looking at Buchla’s response, the trimmers are the same ones.
CliffordMilk
OK - I've been in touch with Buchla and have now been sent the scope images from a newly factory calibrated 208, along with images of the front panel.

It took me a while, but now I'm back to where I was before I started messing with it smile

From here on in, I think I'll just use my ears.
ArguZ
Half of the images show a front panel
CliffordMilk
Yes - He included those to show the correct slider positions for calibration. They are pretty much the same apart from the waveform switch position.
search64
That still looks kind of bad tbh.
CliffordMilk
I guess it’s the sound that matters. It sounds great.
synthi
having both , a BEMI easel and a 208R v2 I can say both are very diferent sonically, specially in the square waveform.
You can see he BEMI easel waveforms don´t resemble the original easel waveforms (scope shots posted earlier in this thread) but the 208R does. The square wave of the BEMI lacks the harmonics and loudness of the original or R versions.
But what always keep me off using the wavesahape in live use s the fact that the sine have a lower amplitude that the other waveforms (as you can see in the scope photos by BEMI) so when you try to go from sine to other waveform it doesn´t do it smottly because there is a BIG step in volume, so big that you need to compensate at the LPG output for not distort the output stage. Oddly, this behaviour (a big fault IMO) is also in the software version by arturia.
Of course the vintage easels or 208Rs don´t do that, the volume for the waveshapes remain constant so you can smoothly use or automate the parameter without that big jumps in volume and presence across the waveshape range...
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