Build a buchla 208 rev2

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ghostcode
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Post by ghostcode » Fri Jun 08, 2018 12:31 pm

papz wrote:Not sure what you mean by glitch but fine tweaking of the timmers on card 9, CO timbre and CO waveshape may help.

The former lowest frequency of CO is 55Hz, lower, instability might occur.
For a lower frequency range, a mod is detailed on Dave Brown's page.
It's not instability. It's almost as if a little bit of the edge of the square/spike is bleeding into the sine wave even when the pot for the wave shape is turned all the way to the sine side.

On the scope it looks fine, on headphones I can hear a little spike on every oscillation. If it was any other waveform, i wouldn't be able to hear it, but on a pure sine wave, it's noticeable.

The only way I can even see the spike on my scope is adjusting the wave shape or timbre trimmers and noticing a really small spike moving along the wave. When it's not moving, it's too small to see.

This only occurs on the sine wave output. I'm not sure if this is occurring on card 8 or 9. Honestly, the issue is so small, I wonder if all 208s sound like this. The best I can do for quieting this is to calibrate it so that these spikes occur closest to the transition from positive to negative on the waveform.

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papz
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Post by papz » Fri Jun 08, 2018 1:52 pm

Did you well select the 2N4399 on card 8 for a perfect sine ?
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Post by ghostcode » Fri Jun 08, 2018 2:52 pm

papz wrote:Did you well select the 2N4399 on card 8 for a perfect sine ?
I did, but i have one more with the specified IDSS i can throw in to test.

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Post by Ernst Bitter » Sat Jun 09, 2018 3:29 pm

papz wrote:Swap IC6 on card 2 just in case.

On the MB check continuity between
- the keyboard voltage in socket and the MO "trim" trimpot's left pin looking from the rear
- the trimpot's central pin and the top pin header of card 6
- the keyboard switch low pin and R57 (next to it) top leg
- the keyboard switch central pin and card 3's pin header 4 (+13.5V)
- R57's bottom leg and edge connector bottom row pin 24 and card7's top pin header

Also check R57 is well 390k.

Do you have keyboard CV via a program card with a 200k resistor in "MOD key" ?

Thank you very much so far!

Swapping IC didn´t help, but by the way I recognized that also the sequencer and the random also can´t be triggered by the Keyboard (but triggering Pulser and CO works fine) - so do they have a common trace which could lead me to another possible error source?

Anyway, I´ll check R57 an the continuity between the suggested points

Keyboard CV comes from a sputnik modular multi touch and I did the resistor mod with 240k on R56 to get 5v threshold...

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Post by papz » Sat Jun 09, 2018 3:52 pm

First of all, are your keyboard's and 208's grounds well interconnected ?

I have no experience with this keyboard but I'd remove the 240k resistor added in parallel with R56, it helps with a 218r but it shouldn't be needed with other sources.

Maybe with the extra 240k resistor the pulser trigger input "pumps" the signal and prevents other modules from receiving a sufficient trigger.

Anyway I rather add a 680k in parallel with R56 when I do this mod.
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Post by ghostcode » Sun Jun 10, 2018 1:34 pm

papz wrote:Did you well select the 2N4399 on card 8 for a perfect sine ?
Tried another 2n4339 in the specified range. Still there. I may have done a silly part substitution so, since I have another set of blue 208 boards, I’m going to have another go at the complex oscillator.

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Post by papz » Sun Jun 10, 2018 4:00 pm

Where do you monitor the sine with the scope ?
Since it doesn't seem to appear on the scope but you can hear it at the output, wouldn't it be just clipping ? :despair:

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Post by ghostcode » Sun Jun 10, 2018 4:32 pm

papz wrote:Where do you monitor the sine with the scope ?
Since it doesn't seem to appear on the scope but you can hear it at the output, wouldn't it be just clipping ? :despair:

Image
That’s what I thought until I compared it to my 259 sine output. I’ve been monitoring it from the two main output after mixing and LPGs. I’ll post a clip soon.

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Post by edwinm » Wed Jun 13, 2018 2:34 pm

ghostcode, is your glitch on the comp osc like the one in this pic?

Image

I had a long email conversation with Dave Brown about this, finally fixed it by replacing the 4066 with a 4016. Didn't make any sense but it worked. Hope this helps!

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Post by ghostcode » Thu Jun 14, 2018 2:27 pm

edwinm wrote:ghostcode, is your glitch on the comp osc like the one in this pic?
I had a long email conversation with Dave Brown about this, finally fixed it by replacing the 4066 with a 4016. Didn't make any sense but it worked. Hope this helps!
Very similar, just a lot smaller. If I remember correctly, I am already using a 4016 on the related card. I’ll check again.

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Post by fluffybeard » Fri Jun 15, 2018 7:27 am

synthi wrote:OK, so I added a cable from the env switch for the the missing keyboard trigger at pulser:perfect working!
Now, the timbre:

It was weak, so first I added a 100K trimmer in parallel to the 15K resistor R46 to try different values and lower the resistance as pointd by Dave. Had some effect but not much... So then I changed r) from 27K to 82K as pointed by DonT. Better, but still about 3 folds with the timbre control travel.

So checking past comments I noticed a mesage from Dimitree telling about a diference in one resistor from the schematics and a real Easel and the 208R BOM, R3 would be 10K...
I`m not an expert but checking the schemos seem that R3 is part of a voltage divider that that goes to the led driver. A quick calculation shown that with R3@1.8K the voltage that goes in the the vactrol led would be lesss than half than the original 10K. So I redid all other mods and just put a 10K in R3.. Night and Day!!! this is a must!! now the timbre folds about 8 times, the simmetry is nice and I can calibrate the LF tracking better!
I think all of you must try that simple resistor change and enjoy the sound! I'm pretty sure its a roman BOM error

Also I had another minor problem, some kind of bleed that makes the pulser firing the sequencer even if the sequencer is in Key trig mode. There is a fix pointed by astroschnautzer, adding a 47pf cap on the switch itself. But before trying this fix, I just added decoupling caps to 3 ICs in the card#1 (IC3, 7 and 9). That cured the issue! so no need for the 47pf cap.
Now the only minor thing is that there are three leds switched on from the sequencer at power up, they goes as I trigger the sequencer and all works fine, maybe is "normal"???

Now time to enajoy the weasel!
Is this timbre-fix comfirmed? I had decent timbre without it but decided to try this out, and ended up with quite an aggressive timbre with too many folds for my poor old ears.

Btw, any good places too make add the missing pulser trace from the back? Removing the panel is tedious. :(

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Post by synthi » Fri Jun 15, 2018 9:08 am

Not a fix but bringing back the correct value for R3... I think you coud either select the vactrol or use lower resistance at R3 to tame the number of folds.
And yes!! the pulser switch missing trace is done from the back of the switches.

Good luck!
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Post by fluffybeard » Fri Jun 15, 2018 9:14 am

synthi wrote:Not a fix but bringing back the correct value for R3... I think you coud either select the vactrol or use lower resistance at R3 to tame the number of folds.
And yes!! the pulser switch missing trace is done from the back of the switches.

Good luck!
Thanks! I'll try something between 1.8k and 10k :)

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Post by synthi » Fri Jun 15, 2018 9:39 am

or a 10K trimmer! 8-)
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Post by sendepause » Tue Jun 26, 2018 7:39 am

Question!

Finished my 208, everything working except for the CO.
No sin out put, looks more like a clipped sin. Turning the wave select pot only does effect the sound from 0 to 2.

Trim pots, calibration results in nothing. Won't come near a sine whatever i do.

What i didn't do, and maybe i should, is using a well selected 2n4339, or at least i don't know if it's well selected.
What would be the outcome if the 2n4339 isn't in the range for the 208? Before i go and get another one and de-solder this one.
Could my problems be tracked backed to this? Or does is sounds familiar at all?

Here is a little video of the issue:

[video][/video]

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Post by davebr » Tue Jun 26, 2018 11:14 am

sendepause wrote:Question!

Finished my 208, everything working except for the CO.
No sin out put, looks more like a clipped sin. Turning the wave select pot only does effect the sound from 0 to 2.

Trim pots, calibration results in nothing. Won't come near a sine whatever i do.
There are two COs, one on card 8 and one on card 9. They have to be synchronized. Card 9 triangle is used for the sine and card 8 triangle and pulse are added to the sine to form the other waveshapes. Look at your triangle waveforms. The card 8 CO is on edge pin 15 and the card 9 CO is on card 8 edge pin 9. I suspect your card 9 CO is not a triangle. Also verify that they are indeed synchronized.

If both those look good then you likely have too much gain in the sine circuit on card 8. Recheck all the resistor values past the 2N4339.

Dave

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Post by sendepause » Wed Jun 27, 2018 2:24 am

davebr wrote: There are two COs, one on card 8 and one on card 9. They have to be synchronized. Card 9 triangle is used for the sine and card 8 triangle and pulse are added to the sine to form the other waveshapes. Look at your triangle waveforms. The card 8 CO is on edge pin 15 and the card 9 CO is on card 8 edge pin 9. I suspect your card 9 CO is not a triangle. Also verify that they are indeed synchronized.

If both those look good then you likely have too much gain in the sine circuit on card 8. Recheck all the resistor values past the 2N4339.

Dave
Hi Dave, in your infinite wisdom you were right: i have no triangle on card 9. It ust goes "high" on the scope...

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Post by sendepause » Wed Jun 27, 2018 3:17 am

davebr wrote: There are two COs, one on card 8 and one on card 9. They have to be synchronized. Card 9 triangle is used for the sine and card 8 triangle and pulse are added to the sine to form the other waveshapes. Look at your triangle waveforms. The card 8 CO is on edge pin 15 and the card 9 CO is on card 8 edge pin 9. I suspect your card 9 CO is not a triangle. Also verify that they are indeed synchronized.

Dave
replaced all ic's except for the mc846 and now i get a extremely "noisy" triangle.

sorry for the weird orientation...

Image

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Post by papz » Thu Jun 28, 2018 2:13 pm

ghostcode wrote:
edwinm wrote:ghostcode, is your glitch on the comp osc like the one in this pic?
I had a long email conversation with Dave Brown about this, finally fixed it by replacing the 4066 with a 4016. Didn't make any sense but it worked. Hope this helps!
Very similar, just a lot smaller. If I remember correctly, I am already using a 4016 on the related card. I’ll check again.
I'm finishing a 208 for a customer who asked for a stereo TRS 1/4" jack socket output.
Fully inserting a mono jack plug shorts the ring output channel to ground and causes a small level increase and a glitch in the sine wave at the tip output channel. This reminds me of your problem.
Does your glitch look like this ? If yes, you could check that an output channel is not shorted to ground.

Image
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Post by ghostcode » Mon Jul 02, 2018 11:37 am

papz wrote: I'm finishing a 208 for a customer who asked for a stereo TRS 1/4" jack socket output.
Fully inserting a mono jack plug shorts the ring output channel to ground and causes a small level increase and a glitch in the sine wave at the tip output channel. This reminds me of your problem.
Does your glitch look like this ? If yes, you could check that an output channel is not shorted to ground.
It's pretty similar. I'll check that out. I do know that I had one channel of my headphone output shorting to the boat when I first built it. I doubt that would have damaged anything, but I'll check around.

Thanks for the suggestion.

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Post by cleaninglady » Tue Jul 10, 2018 12:06 am

I have had my 208r built for a couple of years and have never really been happy with the calibration. I went back and checked all the various resistor value changes I had done on Card 6 and 7 and I am back to Dave's values for resistors in those Cards.

But no matter what I do, I can't get the CO frequency down to 100Hz initial frequency at at the bottom of the slider as per Dave's instructions.
(Key selected : C0)

I went through every single component on Card 7 today, systematically checking and components and I can confirm all components are correct.

The only changes from the BOM are R45 is 100K, R3 is 8.2k for Timbre and R14 is 75K as per Dave's recommendation.

Have checked and redone the MO as per the BOM resistors, it is totally off too.

Considering all is correct, can anyone point me somewhere else to look.

I'm totally stumped and don't know where to go next.

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Post by papz » Tue Jul 10, 2018 2:16 am

Did you well adjust the CO offset and CO range trimmers on the motherboard ?

Maybe you could try the calibration procedure in my buildnotes ? http://www.portabellabz.be/images/208/2 ... _final.pdf
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Post by cleaninglady » Tue Jul 10, 2018 7:24 pm

papz , yes it seems to be the trimmers are the hard part.

I got the MO sorted out ok late yesterday. There is a huge effect and a tiny sweet spot with the CO Range and Offset. Also, i have to be careful of the low frequency tracking and Timbre trimmers as they seem to have an effect on the quality of the calibration of the Range and Offset.

I'll try again later today. Will post again here.

:sb: :sb: :sb:

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Post by Wracked with Guilt » Fri Jul 13, 2018 10:59 am

Hi, it looks like the original link to Roman's BOM is dead. Would anyone be able to kindly send me a copy please? Thanks in advance :guinness:

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Post by tarandfeathers » Fri Jul 13, 2018 11:31 am

Wracked with Guilt wrote:Hi, it looks like the original link to Roman's BOM is dead. Would anyone be able to kindly send me a copy please? Thanks in advance :guinness:
https://electricmusicstore.com/blogs/bu ... -model-208

BOM links look like they are working to me...
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