info for ETI Maplin 4600 5600

[Ken Stone]

(here goes again. Lets see if it actually posts this time! Sorry if you've
seen it before.)

>since I am actually involved in costructing  an old ETI (Maplin) 4600
>analogue synthesizer (and some modules of the  ETI (Maplin) 5600 version),
>I would like to hear from someone already involved in such a construction
>some information/help about this system.

Me too.

>In particular, I am interested to know:
>1- overall impression about it;

The model I played around with was an 8 vco version, but with no operational
filters and no keyboard. Even so, it was fantastic to play with. I was
driving it off an ETI Sequencer. I have since played with one of the VCFs,
and it is pretty impressive. For a period I was using it as a LPF for a
subwoofer. Absolutely nothing above about 30hz was getting through it.

>2 - useful suggestions about, for example, the components and /or some
>entire modules need upgrading or replacing;

Depending on where you got your filter pcbs from, beware a track that has
gone missing off the artwork near the 4001(?). This was why the fiters in
the one I played with didn't work.

Add voltage control to the PWM part of the VCO. It's easy, but wasn't in the
original 4600. (I don't know about the Maplin one.) I think the Maplin one
also added sync, also a fairly simple mod.

>3 - how to find some "exotic" components such as chockes of 1 and 0.33
>henry and, more important, the matrix (4600 version) that permits
>inter-connections between modules.

The matrix? Who knows. you'd be better off using patch cords. Theoretically,
in the VCOs the 4416 can be replaced with a 4016 and a 4069, or perhaps a
4053 depending on if you are designing new pcb art, or using old. I've done
the 4016/4069 mod to one of my VCOs though so far I have not powered it up
to see if it works. Winding data for the chokes is supplied in the 4600
manual, and they are based on fairly common choke bodies (neosid?).

Just about any modern 4001 should work in the filters. No need to hunt for a
Solid State Scientific device.

>some one can suggest me the right way to connect modules of the same
>analogue synthesizer system?
>For CVs, it is OK a single cable?
>For Audio interconnection, a coaxial shielded cable is OK? do you suggest
>some particular impedance values? and, more important, to lower the overall
>noise and/or to avoid ground loops, it is better to use single or twisted
>pair shielded cables? do you suggest to grounding on both ends or just from
>the output module?

The one I played with used unshielded hookup wire as patch cords between
both audio and cv points. As such banana leads would be fine. Myself, I
prefer to use shielded cables and 1/8" jacks, keeping it compatible with my
Roland components (despite the linear/ 1V/oct differences). Grounding only 1
end of shielded cables within the modules seems to be fine. If you avoid
bunching all your wires into looms, you may even get away without using any
shielding at all. The 8 VCO unit used no shielding anywhere in it. I don't
remember it suffering from crosstalk, but I haven't seen that unit in a decade.


Cheers.

Ken
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                Ken Stone  sasami at blaze.net.au
                   ** Catgirl Paradise **
               <http://www.anime.net/~kens/>
         ** Australian Miniature Horses and ponies **
             <http://www.blaze.net.au/~sasami/>
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