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B*RT synthesizer (phutney clone)
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author B*RT synthesizer (phutney clone)
macsimski
Hi all.

I'm in the process of restoring a old vcs-3 clone but it is missing its matrix pins. after carefull measuring, i found that a 1.5mm pin fits snugly with a length of about 2cm. the brand of the matrix is sealectro. is this the same as the vcs-3 or synthi A?

the label on the matrix states:

Sealectro ltd.
walton road
Farlington, Portsmouth, Hants

part # C0035966
ref # 342903
serial # NI/168

It may be a obvious question, but as the search function is still broken, i've chosen to put up the question here.

Its a nice clone, completely in black with red decals and black red topped knobs. even the matrix is black. internally the synth lives on three boards like the vcs-3 but with a slight different layout. the matrix is broken out on the side to a multi connector so for testing i might just patch resistors up there. but before that, i still have to condition and test the capacitors in the power supply.
the bad producer
Sounds nice!

Sealectro matrixes were used in the Maplin 5600 (at least the 2 I've seen had them). AFAIK the VCS3 was Ghielmetti - I don't know that though, so hopefully someone else more knowledgeable will chime in!
Graham Hinton
macsimski wrote:

I'm in the process of restoring a old vcs-3 clone but it is missing its matrix pins. after carefull measuring, i found that a 1.5mm pin fits snugly with a length of about 2cm. the brand of the matrix is sealectro. is this the same as the vcs-3 or synthi A?


Yes. The only source of Sealectro pins now is EMS, unless some come up on eBay and that is very rare. They are like a miniature jack plug in construction and take a resistor lead through the centre of the pin.



the bad producer wrote:
Sealectro matrixes were used in the Maplin 5600 (at least the 2 I've seen had them). AFAIK the VCS3 was Ghielmetti


You are 180 degrees out of phase.
macsimski
it looks nice as well. :-)

here a pic:



so its about time to make some replacement pins then. :-)

I was discussing this with a mechanical engineering guy in the locksmith business and i think we can work something out. I will receive a pin for this one probably by Saturday. then i can take measurements to make a engineering drawing of them.

fortunately the whole matrix is broken out on a multiconnector on the side as well. :-)
macsimski


hmm. I find the measurments dubious. I think the thickest is 3mm and the others are thinner. this synth wants 1.5mm pins
Graham Hinton
macsimski wrote:
hmm. I find the measurments dubious.


You don't understand the measurements, they refer to the matrix grid pitch.
There are two different sizes of Ghielmetti matrix and one of Sealectro (not counting multiple layers) and none of the pins are interchangeable.

You won't be able to make component pins, when you realise what is involved the EMS and Ghielmetti prices will seem cheap.

The PDP8 makes a good support table, a novel change from a doorstop.
macsimski
Its alive!

after conditioning the big powercaps and replacing some other power caps, the machine actually produces sound.

https://vimeo.com/238941431

but there is a lot of work to do: potentiometers are very bad and need to be replaced/serviced, and i still need to test the filter and ringmodulator.

but there is a start.
macsimski
Graham Hinton wrote:
macsimski wrote:
hmm. I find the measurments dubious.


You don't understand the measurements, they refer to the matrix grid pitch.
There are two different sizes of Ghielmetti matrix and one of Sealectro (not counting multiple layers) and none of the pins are interchangeable.

You won't be able to make component pins, when you realise what is involved the EMS and Ghielmetti prices will seem cheap.

The PDP8 makes a good support table, a novel change from a doorstop.


ah. grid spacing. now i understand. the glue of my first test pin is curing while i rotate the pin in my left hand at the moment. i use superglue as a isolator band between the tip and ring as the shrink tubing was too thick. tomorrow i will get smaller shrink tubing. making the pin was actually not that difficult, but i have to improve the procedure a litle as this was my first test.

i started with brass tube of 1.6mm an 1.4 inner diameter. I cut off a 5mm part for the tip and soldered it to a 1mm rod. getting that in the center is one of the problems to solve. then i wound a small strip of paper around the remainder of the rod and saturated it with superglue. the i slided the tube around it leaving a gap of 6mm. after curing, the assembly is very sturdy (for a pin of 1.6mm that is)

i have not thought about the plastic cap yet, but i will think of something.

what resistor values are used for the pins? i seem to remeber there were three colors used.

(edit) found 2k7 somwhere on this forum and 68k for the high value...

ps. picures will follow as soon as the glue cured...
fuzzbass
macsimski wrote:
it looks nice as well. :-)

here a pic:



so its about time to make some replacement pins then. :-)

I was discussing this with a mechanical engineering guy in the locksmith business and i think we can work something out. I will receive a pin for this one probably by Saturday. then i can take measurements to make a engineering drawing of them.

fortunately the whole matrix is broken out on a multiconnector on the side as well. :-)


Nice PDP8!
macsimski
ok. superglue as a isolation band between the tip and the sleeve did not work out, but pla from my 3d printer and a hot air rework station works like a charm. maybe i just print the sleeves and fuse them in place with the hot air during assembly

[edit] here the pic I promised.




the isolation gap can be a lot smaller. i have a very narrow depth where both make contact. what is the length of the isolation part on a original pin?[/img]
Graham Hinton
macsimski wrote:

i started with brass tube of 1.6mm an 1.4 inner diameter. I cut off a 5mm part for the tip and soldered it to a 1mm rod. getting that in the center is one of the problems to solve. then i wound a small strip of paper around the remainder of the rod and saturated it with superglue. the i slided the tube around it leaving a gap of 6mm. after curing, the assembly is very sturdy (for a pin of 1.6mm that is)


You'll have to keep that brass polished, like old jackfield patchcords before Neutrik thought of plating them.

The most common Sealectro pins had a hollow inner tube and the resistor lead was taken through it and soldered at the tip. They did make some that were solid with a solder bucket in the body. Both types had a frame inside the body connected to the outer sleeve.

Quote:

what resistor values are used for the pins? i seem to remeber there were three colors used.


http://www.hinton-instruments.co.uk/ems/essential.html#pins

fuzzbass wrote:
Nice PDP8!


That's only the CPU, unless you like entering code in octal on the switches it requires a teletype, decWriter, decPack, decTape, etc. to make a system about as powerful as a low end PIC. Except you need a maintenance contract to keep it running...
My first computer was a PDP10.
Graham Hinton
macsimski wrote:
what is the length of the isolation part on a original pin?


About 2.5mm and the tip is about 3.0mm, but has a shape like jack plug tip which locates with the springs.
macsimski
Thanks for the link. Im now making the second pin with a little less space between the tip and sleeve. later on I want to plate the separate parts before assembly.



[/img]
the PDP8/f is actually part of a lab-8 setup with memory extension and 24K core. It has two serial cards atm and in the external box there are 2 12 port i/o and a 4chan dac. Would be a nice sequencer for the B*RT.

But I made a mistake during connecting it to the BA8 extension box and reversed one of the ribbon cables so -15 and +15 got on places not ment for non ttl voltages. so a lot of bus driver chips broke (N8235) and those are made of unobtanium. I'm in the process of making a small replacement pcb with some ttl logic emulating the part.
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