When doing this test are the oscillators in a case or sitting on a bench?? If you remove them from the case and do this test, then it will confirm that the problem is in the power wiring and not in currents involving the case.
Richard Brewster
http://pugix.com
On 2/21/18 7:26 PM, Mike Burnham mikejburnham@...
[cgs_synth] wrote:
sorry I've asked some of these questions before.?
I read a lot?of Graham Hintons posts on the topic on Muff Wiggler and I am starting to get a better idea. I get confused with reading too much from people not so knowledgable and seeing all kinds of different?builds. I should try some mods myself and report back.
From: cgs_synth@yahoogroups.com <cgs_synth@yahoogroups.com> on behalf of Mike Burnham mikejburnham@... [cgs_synth] <cgs_synth@yahoogroups.com>
Sent: 21 February 2018 16:24:48
To: cgs_synth@yahoogroups.com
Subject: Re: [cgs_synth] Bleeding oscillators??Hi everyone
I am still having problems with oscillators intermodulating each other
I changed the power cables to the modules to 22AWG and it makes no difference!
So I changed the power supply and fat cables - still no difference!
Even with just 2 oscillators plugged in they affect each other. And connecting more causes worse intermodulation
I am not using screened cable - should I use it?
And on each module I have connected only one of the panel jack sleeves to PCB ground. The rest are connected through the metalwork. Should I connect the sleeves all to each other and then to PCB ground at one point? There are not many ground connections on the PCBs so I am limited a little
Thanks
From: Mike Burnham <mikejburnham@...>
Sent: 09 February 2018 21:44:05
To: cgs_synth@yahoogroups.com
Subject: Re: [cgs_synth] Bleeding oscillators?Thanks guys
well both the two types of VCOs are being affected equally.
Which probably points to a PSU or distribution problem. I must admit to harness these modules to the power I used some pretty crap wire. Thick sleeve thin strands. What is recommended as the best cable/wire to connect modules?
Can I post photos to this list - wil you see them?
Its weird because it has only just started bothering me. I built these cabinets 10 years ago at least and never really noticed these kind of problems before. Maybe I bought cheap power supply caps and they have dried out over time.
VCOS are driven by a Elby Designs PSU (LM723 if I remember right!) I am never sure how much current?each module draws. Recently I have built 2 more Routemaster power supplies. I have one for the modular Moog stuff and 3 for the other 3 cabinets. I'm sure thats enough right?
Theres no info anywhere to help when building power supplies. For example a CGS VCO - how much current does that use?
I built everything in an obsessive phase over about year. 4 cabinets of 16mu each. Loads of CGS stuff, EFM and modular Moog clones.
At the time I was obsessed with percussive and cross modulated hard sequences I did not really care about the purity of tones. Nowadays I am wanting to really do something structured and melodic with the system, including playing with a keyboard and note?purity is most important. Maybe thats why I am noticing this for the first time.
Its about time to spring clean the whole system which is what I am doing at the moment. Fixing bugs and modifying the modules for them to work exactly how I want them to.
From: cgs_synth@yahoogroups.com <cgs_synth@yahoogroups.com> on behalf of Dave Kendall davekendall@... [cgs_synth] <cgs_synth@yahoogroups.com>
Sent: 09 February 2018 20:35:14
To: cgs_synth@yahoogroups.com
Subject: Re: [cgs_synth] Bleeding oscillators??Agree with Richard Brewster that power should be looked at. . .As well as investigating the power supply, one easy thing you can do is to improve the power input conditioning of EFM VCOs.
If built as stock, they have only 100nF bypass caps on the power inputs. It?s possible in most cases to replace them with 10uF bypass caps in the same locations, and add 2.5mm - 5mm pitch 100nF ceramic bypass caps on the bottom in parallel.Be careful when removing the original 100nF caps - the PCB traces are quite thin and easily damaged.?In many cases, you have to pre-bend the 10uF caps? leads slightly near the base of the cap, so they fit outside the 0.156? 4-pin power connector. It?s a bit fiddly, but they won?t quite fit unless you do it - the bypass cap solder pads are a bit too close to the 0.156? connector for most electrolytic caps. It?s worth it, and relatively easy with a bit of care.?FWIW, I also added ferrite beads (the small hollow ones) around the + and - input wires right on the power cables right near the 0.156? 4-pin power connector housing. Heat-shrink them on to keep them in place. There's no room on the boards for extra ferrite beads.Some people add 100nF bypass caps to ICs on the board too. Wire them across ?+V and 0V, and -V and 0V. EFM boards don?t do this on any of the ones I have seen. ?Comparators and logic ICs are good candidates.?
The VCO4 D has bypass caps quite a long way from the input (IIRC, at the far end of the PCB! ), so it?s a bit harder to mod, but could use a bit of improvement. . . .VCO4E and VCO3D are easiest to work on. Don?t know about the others - early ones and 3500 and 4600 series etc.None of this is a magic fix, but it will improve noise immunity to some degree on the EFM modules.
Some modules radiate noise more than others on to the power rails. It may be worth temporarily removing some suspect modules to see if the problem lessens or changes.?Modules with lots of LEDs can be noisy, particularly those with older regular LEDs, not more modern super- and ultra-bright ones.Ken recommends powering some modules from their own ?dirty? supply for this very reason.
Post some more info on your power system, and good luck !?
?D.
On 9 Feb 2018, at 19:11, Richard Brewster pugix@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:
It is probably due to power issues. The first place to start?
troubleshooting is power distribution and the supply itself.? Can you?
give more information?? It could be as simple as that you are overtaxing?
the power supply.
Richard Brewster
http://pugix.com
On 2/9/18 10:23 AM, Mike Burnham?mikejburnham@...?[cgs_synth] wrote:
> All my oscillators in my Modular system to some extent bleed into each other and you can hear modulation when listening to pure waveforms.
> How can I avoid this or clean them up?
> I have 3 cgs VCOS and 3 EFM vcos
> I presume i need to use shielded cable to the outputs and have the shield grounded only at the pcb end?
>
> I suppose I should check to see if vcos are modulating through the PSU...
>
>
>
> Sent from my iPhone
>
> ------------------------------------
> Posted by: Mike Burnham <mikejburnham@...>
> ------------------------------------
>
> The CGS Modular Synth home page:?http://www.cgs.synth.net/
>
> ------------------------------------
>
> Yahoo Groups Links
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