208p build thread (papz's PCBs)

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tele_player
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Re: 208p build thread (papz's PCBs)

Post by tele_player » Wed Mar 18, 2020 12:46 pm

Will the 208p board set fit correctly with a genuine BEMI 208 panel? I just noticed a panel on eBay, and I've been getting prepared to order boards.

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papz
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Re: 208p build thread (papz's PCBs)

Post by papz » Wed Mar 18, 2020 1:02 pm

No, the top holes for tinijax and banana sockets won't align properly (hence the 2 versions of the 208 Hub) and I wouldn't be surprised if some other holes don't fit the motherboard either.
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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Re: 208p build thread (papz's PCBs)

Post by tele_player » Wed Mar 18, 2020 1:51 pm

Thanks, I also figured that out by reading your FAQ.

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Chaotic
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Re: 208p build thread (papz's PCBs)

Post by Chaotic » Sat Mar 21, 2020 4:10 pm

papz wrote:
Sun Mar 15, 2020 7:23 pm
I select vactrols on test in the actual circuit they will be used in, but this requires to have some quantities.
To measure and match them, please refer to Dave Brown's how to on viewtopic.php?f=17&t=193690&p=2717652

The VTL5C3/2 dual vactrols reported bad for the LPGs are Xvive ones only. I use Excelitas VTL5C3/2 in my builds without any problem.
I agree with Papz here. I used xvive VTL5C3/2 when I built mine, but I was not satisfied. The tail was too short. So after a while I ordered ten VTL5C3 for matching. Now I have nice bongos :banana:

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Re: 208p build thread (papz's PCBs)

Post by Siri » Mon Mar 23, 2020 11:08 am

Chaotic wrote:
Sat Mar 21, 2020 4:10 pm
papz wrote:
Sun Mar 15, 2020 7:23 pm
I select vactrols on test in the actual circuit they will be used in, but this requires to have some quantities.
To measure and match them, please refer to Dave Brown's how to on viewtopic.php?f=17&t=193690&p=2717652

The VTL5C3/2 dual vactrols reported bad for the LPGs are Xvive ones only. I use Excelitas VTL5C3/2 in my builds without any problem.
I agree with Papz here. I used xvive VTL5C3/2 when I built mine, but I was not satisfied. The tail was too short. So after a while I ordered ten VTL5C3 for matching. Now I have nice bongos :banana:
This information is gold... I built mine with VTL5C3/2 too last summer and got not bongos...

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Re: 208p build thread (papz's PCBs)

Post by papz » Mon Mar 23, 2020 11:15 am

More details on viewtopic.php?t=222441
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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Re: 208p build thread (papz's PCBs)

Post by tele_player » Mon Mar 23, 2020 3:31 pm

When testing and matching vactrols, should response times be measured, in addition to current/resistance curves?

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papz
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Re: 208p build thread (papz's PCBs)

Post by papz » Mon Mar 23, 2020 10:00 pm

Ideally, yes, but even in a VTLSC3/2 they are not perfectly matched and it works fine, some tolerance is acceptable.
I select the LPG vactrols by ear in the actual circuit, but I'm lucky enough to have enough good VTL5C3/2's in my parts stock. ;)
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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Re: 208p build thread (papz's PCBs)

Post by nicdro » Sat Mar 28, 2020 6:41 am

HeYa! Hope you are all well!
My 208p has a problem with its timbre. It is fine in lower frequency range but in higher frequencies you hear both the oscillator not tracking and jumping around. I tend to say glitches but not really sure how to describe. Tried to adjust trimmer on card 9 and it helped but didn’t fix it totally. Any ideas? I’ve uploaded a sound clip:

https://boards.wetransfer.com/board/sy5 ... 0328085415

thanks!

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Re: 208p build thread (papz's PCBs)

Post by papz » Sat Mar 28, 2020 9:15 am

Adjusting card 9's trimpot only is not enough.
Let me quote the build notes, these are helpful and worth a good read. ;)
Card 9 : tracking of both CO oscillators together
This may be a tricky part and needs a proper balance between the CO timbre (TR4) and waveshape (TR7) trimpots on the MB and the one on card 9 to avoid spurious oscillation across the whole CO frequency and timbre range. Some oscillation might occur at specific points of the sliders course, try and adjust the 3 trimpots until you get proper performance, or one you can live with.

CO timbre
The timbre folding depends on vactrol VT1 on card 7. R3 attenuates the CV making a ground connection, increase its value will increase the number of foldings. There's no official number offoldings, some prefer more foldings, others prefer less, select R3 to best fit your own preference, keeping in mind that this may affect the tracking of both CO oscillators together.
If there are many foldings, glitches are more likely to happen, a lower value for R3 on board 7 should reduce the number of foldings and glitches.
On https://modularsynthesis.com/buchla/208/buchla_208.htm an oscilloscope shot shows the max timbre of an original 208 and is a good reference.
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.

nicdro
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Re: 208p build thread (papz's PCBs)

Post by nicdro » Sat Mar 28, 2020 3:11 pm

papz wrote:
Sat Mar 28, 2020 9:15 am
Adjusting card 9's trimpot only is not enough.
Let me quote the build notes, these are helpful and worth a good read. ;)
Card 9 : tracking of both CO oscillators together
This may be a tricky part and needs a proper balance between the CO timbre (TR4) and waveshape (TR7) trimpots on the MB and the one on card 9 to avoid spurious oscillation across the whole CO frequency and timbre range. Some oscillation might occur at specific points of the sliders course, try and adjust the 3 trimpots until you get proper performance, or one you can live with.

CO timbre
The timbre folding depends on vactrol VT1 on card 7. R3 attenuates the CV making a ground connection, increase its value will increase the number of foldings. There's no official number offoldings, some prefer more foldings, others prefer less, select R3 to best fit your own preference, keeping in mind that this may affect the tracking of both CO oscillators together.
If there are many foldings, glitches are more likely to happen, a lower value for R3 on board 7 should reduce the number of foldings and glitches.
On https://modularsynthesis.com/buchla/208/buchla_208.htm an oscilloscope shot shows the max timbre of an original 208 and is a good reference.
thanks! just read the timbre section and missed the tracking of both CO osc part. tho the trimmer werent enough i now have to change R3 and r46. thanks again!

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Re: 208p build thread (papz's PCBs)

Post by Karl71 » Mon Mar 30, 2020 4:37 pm

Hello, I just lost the A.M on my modultion setting. Its been working for quite some time. I noticed today that it Only F.Ms on both the A.M and F.M. Position. Can anybody suggest what ic to swap. Any advice would be appreciated. Thanks.

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Re: 208p build thread (papz's PCBs)

Post by papz » Mon Mar 30, 2020 4:50 pm

IC2 and IC1 on board 5 are good suspects.
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.

Karl71
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Re: 208p build thread (papz's PCBs)

Post by Karl71 » Tue Mar 31, 2020 2:33 am

Thanks Papz.

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Re: 208p build thread (papz's PCBs)

Post by Karl71 » Tue Mar 31, 2020 10:00 am

It was IC 1. One of the leg pins was folded under. I’m amazed it has worked as long it did.

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