Synthi-A must-have mods

Discussing some incredible modules that don't quite fit into the other forum categories.

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moog55
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Synthi-A must-have mods

Post by moog55 » Thu Jan 03, 2019 1:08 am

I've just received *the* email from Robin - "your name is up, do you still want the Synthi-A?" :)

He said I needed to decide my mods very soon. I know it can be a philosophical debate for many of the mods, but is there a short-list of must-have mods that everyone agrees on?

He hasn't emailed me the current list of mods yet. Hope to have the mods determined in the next week or so.

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Siren
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Post by Siren » Thu Jan 03, 2019 3:46 am

You will want to have slew on/off for the filter.
Syncable oscillators as well.

I think there is a magical amount of controls, a threshold that once you exceed it the instrument becomes cluttered and less intuitive to use.

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Post by Portabella » Thu Jan 03, 2019 4:39 am

Don't forget to want the GATE IN mod .. it's mandatory!
You will lose Mic input 2 but I never wanted more than one mic input.
Therefor you can trigger the envelope externaly

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Post by papz » Thu Jan 03, 2019 4:46 am

To me all mods are must-have, except the filter 4/5 poles whose effect is mostly just a move of the cutoff point. The filter slew/unslew is great for filter FM and percussive sounds.

Osc sync is great, so is the waveshape CV.

Buffers may be useful but I don't recommend buffering the whole matrix.
http://www.portabellabz.be/synthipcbs.html

Envelope times extension, inverter pins are useful too.

Many users enjoy my RVG/S&H mod, Robin installed it in several units, even in his own Synthi. I'm happy to ship the kit directly to him.
http://www.portabellabz.be/synthimods/rvg.html

These pages will give you more details :
http://www.portabellabz.be/synthimods/index.html
http://www.portabellabz.be/kits.html
http://www.hinton-instruments.co.uk/ems/emsmods.html
Last edited by papz on Thu Jan 03, 2019 6:09 am, edited 1 time in total.
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Post by construct09 » Thu Jan 03, 2019 6:08 am

I,d ask Robin if he will implement the push / pull knob mods like papz :hail: does :hihi:

You,ll need a KS too :mrgreen:

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Post by Portabella » Thu Jan 03, 2019 7:01 am

EDIT: overseen papz links for an overview over all mods :)

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Post by bsilverberg » Thu Jan 03, 2019 9:48 am

I find the Trapezoid polarity mod to be quite nice, highly recommended.

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Post by captnapalm » Thu Jan 03, 2019 10:37 am

Patchable inverter and osc sync are what I found I used the most.

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Post by skkatter » Thu Jan 03, 2019 10:58 am

Portabella wrote:Don't forget to want the GATE IN mod .. it's mandatory!
You will lose Mic input 2 but I never wanted more than one mic input.
Therefor you can trigger the envelope externaly
You don't need that if you get the Cinch Jones cable.

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Post by sanders » Thu Jan 03, 2019 10:45 pm

bsilverberg wrote:I find the Trapezoid polarity mod to be quite nice, highly recommended.
To me, env polarity is the most useful mod; I don't know if my envelope is out-of-spec having personally implemented the modification some time ago (as per Graham Hinton's switchable polarity mod), but I barely use the trapezoid in standard polarity since implementing this mod.
Someone can correct me here if I'm wrong about this-- but as I understand it, the "normal" Synthi polarity is actually negative. If you've ever used a synthesizer with reversible envelopes, you'll know the practical effect of a negative biased envelope. IMO, It can be awkward getting used to and difficult to assign sharp percussive enveloping. It's also very tricky using the negative envelope with external Gates.

After that, I'd say filter slew/unslew. In some ways this mod is necessary with the previous env polarity mod; the attack can be super slow and soft using the unmodded envelope-- the filter unslew gives the attack more bite; however, with the polarity reversal engaged, sometimes you'll want some slew on the filter to soften the attack "click".

I have a "slow" switch on Osc 1 and 3 that I use all the time, and a switch to sync Osc 2 to Osc 1. I use the sync much less for Osc-sync sounds and more for rhythmic synchronization.

I also have a switchable volt/per octave CV input on the front panel and a dedicated gate input; but you're probably just as well off using the accessory port.

If there's any mod I'd like to implement beyond these, it'd probably be Papz' S+H circuit. I don't have the KS Sequencer, so it'd be really nice to have some sort of internal pattern generator in order to make the Synthi that much more self contained. I find a S+H as good or better than a sequencer for many applications. That said, the Synthi is probably among the best designed synths when it comes to interfacing with other gear, and so it's not absolutely necessary having this internal controller.

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Post by papz » Fri Jan 04, 2019 4:48 am

The trapezoid output is bipolar (about -3V to +3V) and remains bipolar when inverted.

Normal
Image

Inverted
Image

In normal mode, the on time (horizontal line on the scope) is negative, but voltage controls on the Synthi are inverted : a positive voltage sent as is to an oscillator or to the filter makes its frequency lower, hence the inverting input amps used for external CV.
Last edited by papz on Sun Jan 06, 2019 8:42 pm, edited 1 time in total.
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Post by moog55 » Sun Jan 06, 2019 5:57 pm

Thanks for the great info, everyone. I'm still finalizing my list, but it'd getting there. Definitely going to go with Papz's S&H mod too.

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Post by cheapmachines » Tue Jan 08, 2019 2:34 am

Had quite a few of the available mods done to mine and they're all useful to be honest... I'd say top of the pile are:

Papz S&H mod
Oscillator Sync
Oscillator Hi/Lo Switching
Filter Unslew
Prestopatch Socket (if you want to use the Digitania boxes or roll your own program cards)

Not a mod but get a few extra matrix pins. Also, don't overlook one or two green 68k attenuator pins (or get a few empty pins if you're good with a soldering iron) so you can have some different resistor ratings in there. Makes quite a difference to the sound and flow of the patches.

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Post by chriscarter » Mon Jan 21, 2019 2:33 am

cheapmachines wrote:Not a mod but get a few extra matrix pins. Also, don't overlook one or two green 68k attenuator pins (or get a few empty pins if you're good with a soldering iron) so you can have some different resistor ratings in there. Makes quite a difference to the sound and flow of the patches.
Agreed... that is a top tip .
:yay:

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Post by cheapmachines » Mon Jan 21, 2019 9:16 am

cheapmachines wrote:Also, don't overlook one or two green 68k attenuator pins (or get a few empty pins if you're good with a soldering iron) so you can have some different resistor ratings in there. Makes quite a difference to the sound and flow of the patches.
Few DIY jobs here for example - 10, 22 and 43k, an LDR and a photodiode pin

Image

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Post by mrfang » Tue Jan 22, 2019 3:27 am

Loving both the sample and hold mod and the variable oscillator sync on my newer Synthi.
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Post by dan_p » Tue Jan 22, 2019 5:24 am

Ahh, the photo diode pin is a great idea!! Nice one.
cheapmachines wrote:
cheapmachines wrote:Also, don't overlook one or two green 68k attenuator pins (or get a few empty pins if you're good with a soldering iron) so you can have some different resistor ratings in there. Makes quite a difference to the sound and flow of the patches.
Few DIY jobs here for example - 10, 22 and 43k, an LDR and a photodiode pin

Image
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Post by cheapmachines » Tue Jan 22, 2019 5:41 am

Cheers, think it was one of papz suggestions...

Just using an ordinary signal diode in a pin is interesting too as it'll rectify any bipolar signal.

For example, if you use it with the sine on Oscillator 1, the wave shape knob can act as a kind of switch as one half of the waveform is missing via the diode pin. Can also make some nice thinned out crackle / dust stuff when you use it with the noise generator.

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Post by papz » Tue Jan 22, 2019 6:01 am

2 LED pins with opposite polarities in a same column give interesting results too.

LED pins need a quite high voltage to let it pass the LED threshold, so it's good to have green 68k pins or other value to route the signal attenuated to other destinations.

Here's a video I did years ago with LED pins.

[video][/video]
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I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Post by jfloftin » Tue Jan 22, 2019 8:04 am

papz wrote:To me all mods are must-have, except the filter 4/5 poles whose effect is mostly just a move of the cutoff point. The filter slew/unslew is great for filter FM and percussive sounds.

Osc sync is great, so is the waveshape CV.

Buffers may be useful but I don't recommend buffering the whole matrix.
http://www.portabellabz.be/synthipcbs.html

Envelope times extension, inverter pins are useful too.

Many users enjoy my RVG/S&H mod, Robin installed it in several units, even in his own Synthi. I'm happy to ship the kit directly to him.
http://www.portabellabz.be/synthimods/rvg.html

These pages will give you more details :
http://www.portabellabz.be/synthimods/index.html
http://www.portabellabz.be/kits.html
http://www.hinton-instruments.co.uk/ems/emsmods.html
Yes to all the above!

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Post by jfloftin » Tue Jan 22, 2019 8:08 am

papz wrote:The trapezoid output is bipolar (about -3V to +3V) and remains bipolar when inverted.

Normal
Image

Inverted
Image

In normal mode, the on time (horizontal line on the scope) is negative, but voltage controls on the Synthi are inverted : a positive voltage sent as is to an oscillator or to the filter makes its frequency lower, hence the inverting input amps used for external CV.
Great pics!

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Post by chamomileshark » Tue Jan 29, 2019 9:34 am

As noted, most of the mods are useful - the only one I haven't found useful is the 18/24 db filter. Robin thinks it's useful but so far I haven't found so. Maybe it's because of the filter's odd topology but as again several other people have commented over the years it just seem to move the filter cutoff. I've got other filters that offer 24/18 db cutoffs and there I can hear a bigger difference so I don't think it's my hearing.
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Post by ARPMOOG » Sat Nov 23, 2019 7:59 am

Waving shaping is mandatory. I like to cross modulate them rhythmically
I have a AKS I had modded by Robin 20 years
ago and a early A stock. Ide like to send the A out for work but I
worry about it getting stolen in the mail with the current value and synth
revival.

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Post by pelican » Sat Nov 23, 2019 3:40 pm

What’s the difference between the portamento and glissando mods?
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Post by pelican » Fri Dec 13, 2019 10:19 pm

Anyone?
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