Serge PCO/NTO - stronger sync mod?

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cycad73
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Serge PCO/NTO - stronger sync mod?

Post by cycad73 » Tue Mar 14, 2017 11:24 am

I have a panel (Oakland-era) with two PCO's, they have much stronger sync than the standard NTO/PCO -- basically similar to Roland "weak" sync on sys. 100, locking mostly to octaves, fifths. This is not a hard sync, but an extremely fast locking of the PLL. I find this much more useful than the standard sync.

Anyone knows who did this mod? or has documentation (such as replace this component with this...) I would like to have this for all PCO/NTO -- or even better some kind of variable sync setting controlled by a switch.

Thanks!

Permette
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Post by Permette » Sun Mar 19, 2017 7:34 am

Agree with you.

I found my PCO sync a bit weak also. I often run through a comparator before getting into the sync and it works harder.

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cycad73
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Post by cycad73 » Sun Mar 19, 2017 5:21 pm

Well gladly the weak sync can be "fixed", as the case with this one panel which has a more Roland style soft sync

just interested if someone has documented the mod (schematics etc)
is it as simple as replacing one resistor value with another?

also interested, how far can the sync be pushed, can it ever become a hard sync?

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cygmu
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Post by cygmu » Mon Mar 20, 2017 8:54 am

I thought the PCO sync was a hard sync. A sharp edged waveform into the sync input causes the ramp to reset to zero. Isn't that what hard sync means? I don't think there is any PLL circuitry in a PCO or NTO. Could be wrong though.

cycad73
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Post by cycad73 » Mon Mar 20, 2017 10:52 am

cygmu wrote:I thought the PCO sync was a hard sync. A sharp edged waveform into the sync input causes the ramp to reset to zero. Isn't that what hard sync means? I don't think there is any PLL circuitry in a PCO or NTO. Could be wrong though.
It's definitely soft sync. PCO will lock on to some rational multiple of the master osc frequency, with occasionally some slight buzziness. It's just more musically useful if the ratios are limited to those having small denominators, something like 5/4 instead of 121/117. A weaker sync gives more often the latter situation.

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dksynth
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Post by dksynth » Thu Sep 26, 2019 11:39 am

someone mentioned this to me yesterday so I started taking a look at the sync on the PCO vs the Roland system 100M.

I think you could add an optional hard/soft sync relatively easily to a PCO ... both the system 100M and the PCO have sync in the same spot changing the reference level of the reset comparator.

Image

You'd be adding the circuitry in red and connecting it to the the same point the Sync jack is currently connected to on a PCO.

I don't have one to try this on but if anyone takes a shot at it would love to know if it works!

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Post by syncretism » Thu Sep 26, 2019 12:42 pm

cycad73 wrote: It's definitely soft sync. PCO will lock on to some rational multiple of the master osc frequency, with occasionally some slight buzziness. It's just more musically useful if the ratios are limited to those having small denominators, something like 5/4 instead of 121/117. A weaker sync gives more often the latter situation.
Is this something that can be approximated by a VCO driving a slope generator for subharmonic generation, and syncing the VCO to that slope generator?

cycad73
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Post by cycad73 » Fri Sep 27, 2019 11:42 pm

the mods are most certainly done by Kevin, and they consist of making the sync like that of the 1973 oscillators, which i have now. so anyone who has schematics of both (I guess they're out, since there are clones) can tell what was done. it may be just changing a few components.

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Post by bitone » Mon Sep 30, 2019 9:38 am

cycad73 wrote:the mods are most certainly done by Kevin, and they consist of making the sync like that of the 1973 oscillators, which i have now. so anyone who has schematics of both (I guess they're out, since there are clones) can tell what was done. it may be just changing a few components.
yes was just about to comment the same - on older panels sent to Kevin Fortune for any reason, module repair, calibration, etc. if there are PCO's present he usually changes the sync to a harder sync - he did this on my old oakland panel and I'm happy he did! Sounds great, if anyone can figure out whats involved with this I would be curious as well.

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dksynth
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Post by dksynth » Mon Sep 30, 2019 10:25 am

cycad73 wrote:the mods are most certainly done by Kevin, and they consist of making the sync like that of the 1973 oscillators, which i have now. so anyone who has schematics of both (I guess they're out, since there are clones) can tell what was done. it may be just changing a few components.
you are referring to the 73 VCO as seen in the 73-75 board set?

If you just want a harder sync on the PCO I think you'd be reducing the value of R19 / 22k which is the resistor that the sync jack/point D is attached to. On the 73 oscillator it is a 22k to ground followed by a 10nF and 4k7 in series to the sync point. On the PCO is a 22k in series with a 220nF. If you reduced those to 4k7 and 10nF respectively you should get a much stronger sync.

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cygmu
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Post by cygmu » Mon Sep 30, 2019 12:17 pm

I would try increasing the value of R15 -- the 2k2 that goes from the comparator pin 3 to the reference voltage -- so that the sync signal is attenuated less.

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dksynth
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Post by dksynth » Tue Oct 01, 2019 11:37 am

cygmu wrote:I would try increasing the value of R15 -- the 2k2 that goes from the comparator pin 3 to the reference voltage -- so that the sync signal is attenuated less.
Good catch! Totally missed how low that value was... would definitely try that first!

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