Saturday, 27 September 2014

Synth Repairs


Analogue Systems RS-40 Noise, Sample and Hold, Osc


This came in as 'defective'. After a while it became obvious the noise output was not working. This was traced to an open-circuit LEVEL contol pot (10k lin) which was replaced. Still it didn't work as a sample and hold - i.e. I was expecting to see a stepped output from S\H OUT. Not having used the RS-40 before it took me a while to realise that the noise and clock signals are not normalled to the Sample and Hold circuit like the front panel markings suggest; the lines linking NOISE OUT to EXT SRC IN and INT CK OUT to EXT CK IN suggest to me these are linked in some way but no. 
RS-40
After looking at the jacks it was clear that these are not normalled (I'm not sure if this is the case with all RS-40s but this one looked clean and unmodified so I'm assuming it was factory standard). I used external patch leads and to link the noise and clock outs and ins and hey presto it worked. The first thing that I saw on the scope was at each sample point the sampled signal is present for what I guess is the duration of the sample pulse (about 0.2ms). When using the RS-40 to modulate a VCO I could not tell that the noise spikes were a problem, in fact it is probably above hearing range (at least mine). 
 
Noise spikes

However I didn't much like it and I didn't much like not having the noise and clock not normalled to the S/H circuit. I spoke to the owner and he agreed to have a couple of simple mods applied.

The noise and clock signals are present on the jack board close to where they would have to go for normalled connections. The switched contacts were connected to ground on both EXT SRC IN and EXT CK IN jacks by solder bridges. I removed the solder bridges and fitted links as can be seen here. This worked a treat allowing it to work without patching but still allowing external signals to be patched in if need be.

Solder removed from red arrows and links applied at yellow arrows
The noise spikes 'problem' although not audible was fixed by placing a 10nF cap across the S/H output amplifier's feedback resistor (27k) making it a low-pass filter with a cutoff of 590Hz. This got rid of the spikes without adding noticeable slew.

10nF capacitor

Spike free steps



Saturday, 13 September 2014

5 into 1 Analogue Systems to Doepfer Bus Adaptor/Expander

The new 5ASM2DB Analogue Systems Module to Doepfer A-100 Bus Adaptor/Expander is now in stock and available to order. 

NEWS UPDATE 25 Oct 14: SchneidersLaden have stock and can be ordered from their website at http://www.schneidersladen.de/en/manufacturer/synovatron.html. RhythmActive also have stock and can be ordered from their website at http://www.rhythmactive.com.au/

For DIY enthusiasts it is also available as a kit or as a bare PCB. 

The 5ASM2DB offers five Analogue Systems sockets on one small circuit board with low-current LED indicators to show that ±12V and +5V power is available. It comes with a ribbon cable to connect to the A-100 bus and four self-adhesive nylon PCB mounting pillars (you can of course use screwed in pillars so a drilling template will be provided).

If you have several Analogue Systems modules in a Euro rack then the 5ASM2DB could be a better alternative to using several ASM2DB Adaptors because it expands the bus and frees up A-100 Bus connectors for Euro modules; it costs roughly the same as three ASM2DB Adaptors. ASM2DB and DM2ASB Adaptors are still available.

5ASM2DB Adaptor/Expander
What you get with the 5ASM2DB Adaptor/Expander
What you get if you order the 5ASM2DB DIY Kit

Price info and ordering

For sales, support and combined shipping enquiries please contact synovatron@btinternet.com.  


The base price is without delivery and VAT.
The UK and EU prices include delivery and VAT @ 20%
The ROW price only includes delivery; VAT is not applicable. 
Model                                        Base            UK              EU                ROW
5ASM2DB Adaptor/Expander    23.00 GBP   30.06 GBP   32.58 GBP   27.45 GBP
5ASM2DB DIY Kit                      16.00 GBP   21.66 GBP   24.18 GBP   20.45 GBP
5ASM2DB Bare PCB                  Available from www.thonk.co.uk
UK delivery by Royal Mail First Class; elsewhere by Royal Mail International Standard.