Build a buchla 208 rev2

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Peake
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Post by Peake » Mon Oct 16, 2017 12:53 pm

Thank you folks, will apply today and report back in this post.
This is not the place I'd imagined it to be.

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Peake
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Post by Peake » Wed Oct 18, 2017 8:00 pm

After poking around on that topic I find that CO is in the correct range and I'm good leaving it there. :despair:

What IS up is nothing much going on in the Balanced Modulator. I have a previous 208 build here for mods and swapping the cards makes the current build work. All resistors are fine, all diodes are correct types and correctly oriented, caps are right, no solder bridges, all ICs are correct types and are oriented correctly, all Vactrols are oriented correctly. Now, I've used Xvive clones here, matched four for the BM per Don T's posts, using the red dot 5C1 clone types (the earlier, working build has matched original 5C1s). (One vactrol was reversed and correctly orienting it now sees the AM and FM working.) Unfortunately I've soldered all of the 4136 in place on this current build so swapping to test isn't as simple. I do have an oscilloscope if there are some points I could tap for confirmation of signal and voltage flow...

Also getting a slight dip in the CO sine wave when selecting Triangle, I think this has been mentioned before.
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Post by Don T » Thu Oct 19, 2017 10:23 am

Peake wrote:After poking around on that topic I find that CO is in the correct range and I'm good leaving it there. :despair:

What IS up is nothing much going on in the Balanced Modulator. I have a previous 208 build here for mods and swapping the cards makes the current build work. All resistors are fine, all diodes are correct types and correctly oriented, caps are right, no solder bridges, all ICs are correct types and are oriented correctly, all Vactrols are oriented correctly. Now, I've used Xvive clones here, matched four for the BM per Don T's posts, using the red dot 5C1 clone types (the earlier, working build has matched original 5C1s). (One vactrol was reversed and correctly orienting it now sees the AM and FM working.) Unfortunately I've soldered all of the 4136 in place on this current build so swapping to test isn't as simple. I do have an oscilloscope if there are some points I could tap for confirmation of signal and voltage flow...

Also getting a slight dip in the CO sine wave when selecting Triangle, I think this has been mentioned before.
I've found this problem while working on another 208 that had Xvive vactrols. I found out the problem was one vactrol not opening up enough, swapped it with another that turned out to open up too rapidly. The new one gave you the full range of change with only half the slider travel. Added a trimmer on the LED to mostly correct that issue.

At the moment, my 208 is back home, 350 miles away, and off the top of my had I cannot remember which vactrol it was I changed! I'll look over some photos later and try to remember which one it was.

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Peake
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Post by Peake » Thu Oct 19, 2017 11:41 am

Thank you. I've been told some places to test and will be doing so. I matched these from the initial "on" reading just like the 5C1 quad in the previous, good build.
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Post by Don T » Thu Oct 19, 2017 8:08 pm

Peake wrote:Thank you. I've been told some places to test and will be doing so. I matched these from the initial "on" reading just like the 5C1 quad in the previous, good build.
Try VT7, that's the one I swapped that took care of the ring modulation range. Apparently they have different slopes as the LED current changes.

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Post by Synesthesia » Sun Oct 29, 2017 12:40 pm

Hey guys,

I have 208 here - and the reverb is causing issues.

it was upside down, and now i am pretty sure the polarity of the send side is wrong. does anyone has a pic showing the black and blue cable and how it should be ?

i cant remember exactly where i double checked the info for mine ( which reverbs isnt working anymore ironically .... so better double checking )

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Post by davebr » Sun Oct 29, 2017 2:25 pm

Synesthesia wrote:Hey guys,

I have 208 here - and the reverb is causing issues.

it was upside down, and now i am pretty sure the polarity of the send side is wrong. does anyone has a pic showing the black and blue cable and how it should be ?

i cant remember exactly where i double checked the info for mine ( which reverbs isnt working anymore ironically .... so better double checking )
I don't think it really matters. There is really no relation to input phase and output phase. I have reversed the connections to test and really can't tell the difference. My 208 V1 page shows a good shot of the reverb and connectors.

Dave

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Post by sines » Mon Dec 04, 2017 11:11 am

80% of the way through my v2 208 build .. been sitting on unpopulated boards for a while and finally stuffing most it.

Questions:

1. Roman F told me I could use 1n4148 for all of the 1n457s. Any cards in particular were this would be a problem?
2. Can I use IN4733A [5.1V Zener Diode] for all of the occurrences of 1n5236 + 1n5228? Why / why not?
3. I have super tiny .01uf / 103 ceramic disc caps from Tayda [SKU A-550]. I also have monolithic .01uf / 103 caps 50V [SKU A1-1366]. And then some bigger, button / dime sized ceramic disc caps from Radio Shack or somewhere. Are all of these interchangeable? Why / why not?

There will probably be more questions, but this is where I'm at now. :) Haven't dealt with the µa726 yet, most likely going the Portabellaz route via SynthCube.

Thanks in advance!


Todd

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ImageImage

** and I need to add some solder to the 10k resistor in the lower left hand corner too. :)

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Post by boops » Mon Dec 04, 2017 2:10 pm

IMHO why ,you did not use sockets for your ics,it will be a nightmare to repair in the future ,economy?time is money :hmm:
FYI ,I ve got some ua726 in stock.
For the ceramics,you can use the same value,and above 25v ,of course .for audio path use good quality audio capacitor,film,polyester etc
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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Post by davebr » Mon Dec 04, 2017 2:37 pm

sines wrote:Questions:

1. Roman F told me I could use 1n4148 for all of the 1n457s. Any cards in particular were this would be a problem?
2. Can I use IN4733A [5.1V Zener Diode] for all of the occurrences of 1n5236 + 1n5228? Why / why not?

Thanks in advance!

Todd
I see no reason why a 1N4148 and a 1N457 are not interchangeable. They look different.

The 1N5236 is a 7.5V zener and is used to lower the operating voltage of IC1, IC2, and IC3 on card 5 to +/-7.5V. Your substitution of a 5.1V zener would change the operating voltages to +/-9.9V, resulting in a power supply total of 19.8V. The CD4016 is spec'd at an absolute maximum of 18V with the TI spec'd at 20V. Not a good idea.

The 1N5228 is used on cards 3, 4, 10, and 11 in a variety of applications. A 5.1V zener will change the operation of these circuits. You may or may not like the result. I'm not going to take the time to figure out what the change is, but the EG, Pulser, and LPGs operation will change.

These zeners with these voltages were selected for a reason.

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Post by sines » Mon Dec 04, 2017 2:44 pm

ok — got it; proceeding with order of correct Zener diodes! Thanks guys.

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Peake
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Post by Peake » Mon Dec 04, 2017 4:54 pm

I believe Roman has updated the BOM to use modern ceramic caps instead of the enormous vintage versions, some of which may have become discontinued.
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sines
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Post by sines » Mon Dec 04, 2017 5:41 pm

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These are Tayda .01uf 50V multilayer monolithic caps.. should work, right?

https://www.taydaelectronics.com/0-01uf ... citor.html

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Post by dsf » Thu Dec 07, 2017 3:11 am

Yes those work without a problem. I'd use sockets too, mainly because all the documented trouble with CMOS for example, i ended up having to swap a bunch of ICs during troubleshooting, gladly i used sockets...

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Post by keninverse » Thu Dec 14, 2017 11:51 am

Perhaps this is a failure on my understanding...
Transposing sequenced oscillator should be simple as patching something like a 218 preset out to the same oscillator that's being sequenced correct? When I do this I get nothing except when drop the voltage on the preset to a millivolt and it then only transposes down. Am I missing something here? Now if the "keyboard in/out" is "in" and I use the 218 it seems to work but not when patched directly.

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Post by papz » Thu Dec 14, 2017 5:43 pm

You can split a CV output to different inputs by simply stacking cables but mixing different CV outputs to a single input this way doesn't work because of impedance.

To achieve this, a CV mixer is needed. The ToolBox offers one. 8-)
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Post by keninverse » Thu Dec 14, 2017 6:14 pm

That's what I was thinking so I tried it with the on board inverter which didn't seem to work. Are you stocked up on toolboxes?

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Post by papz » Thu Dec 14, 2017 6:25 pm

The onboard inverter won't work either for this.
A real mixer with individual input for each CV is needed.

The ToolBox is currently sold out, PCBs will be available again in January.
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Post by dsf » Sat Dec 16, 2017 6:09 am

When i thought my 208 was fully finished... I have a big volume difference between triangle and square-Saw in my MO, Triangle being much lower than the other too, i didn't care much, but being honest it bugs me. Guess this is vactrol involved, but is anyone else experiencing this? I used Vactec, but i honestly didn't match much either for Gate or MO CO...

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Post by papz » Sat Dec 16, 2017 8:56 am

This difference is normal, a triangle wave usually sounds softer because it doesn't have much overtones.
You'll notice a similar volume difference in other synths' oscillators as well.
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
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Post by J3RK » Sat Dec 16, 2017 12:52 pm

Are you referring to the apparent audible volume, or did you put it on a scope and measure it to be lower. As Papz said, it will sound quieter than the other waves due to harmonic content of the various waveforms.

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Post by dsf » Mon Dec 18, 2017 5:45 am

Yes I'm aware triangle has less harmonics and therefore is perceived lower in volume, but it seems more than expected, it also affects in a different matter the modulation index, but it might be just like that. Will check amplitude on the scope later, though to be honest I don't want to keep opening this thing

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Post by Synesthesia » Tue Dec 19, 2017 3:54 am

I am having trouble calibratin the CO on a rev 2 at 1.2V per octave.

I decreased Card 7 R14 from 120K to 75K qs advised -
but i am still off. http://modularsynthesis.com/roman/buchl ... 08spss.htm

I am using a 218 as voltage source, and trying to tune using TR8. Anything else i should look at ?

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Post by boops » Tue Dec 19, 2017 5:04 am

There is 2 trimmers to tune a vco in a 208 rev2 ,Not only one


Synesthesia wrote:I am having trouble calibratin the CO on a rev 2 at 1.2V per octave.

I decreased Card 7 R14 from 120K to 75K qs advised -
but i am still off. http://modularsynthesis.com/roman/buchl ... 08spss.htm

I am using a 218 as voltage source, and trying to tune using TR8. Anything else i should look at ?
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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Post by dsf » Tue Dec 19, 2017 6:25 am

What Boops said, i might add, in my experience not every build is the same, so i0d just attach a 100k pot to trim to your desire scaling, take the pot out, measure and find the closest resistor to the value.
That being sai, i went thru all tunings, and to be honest i really think the easel was thought for 2v tuning, everything makes more sense on that scale, the sequencer is much more accurate and playable etc... not only me saying that BTW. I just reajusted my gtcv pulse converter for 2v to play out with other gear.
Synesthesia wrote:I am having trouble calibratin the CO on a rev 2 at 1.2V per octave.

I decreased Card 7 R14 from 120K to 75K qs advised -
but i am still off. http://modularsynthesis.com/roman/buchl ... 08spss.htm

I am using a 218 as voltage source, and trying to tune using TR8. Anything else i should look at ?

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