[sdiy] ETI vocoder input amps

[Magnus Danielson]

From: Hallvard Tangeraas <northstar2010 at yahoo.no>
Subject: [sdiy] ETI vocoder input amps
Date: Thu, 25 Oct 2001 02:04:15 +0200

Hej Hallvard!

(This weeks lesson in Swedish - "Hej" means "Hi")

> A project of mine which has been waiting to get completed for many
> years is the ETI/Powertran vocoder.
> 
> I've got all the separate parts done except the input amplifiers. Quite
> ironic that such small and simple circuits are holding me back, but I
> can't for anything in the world get them to work. Then again I'm no
> electronics engineer either, just a guy who's handy with a soldering
> iron and likes buidling stuff..
> 
> Has anyone been able to complete this vocoder and can help out with the
> two input amps? Alternatively, totally new input amp circuits would
> have to be done to get the project completed.

Just to complete irony, I have exactly the same problem with mine!

Now, being known for at least finding the safe side of the soldering
iron, this is kind of embarasing, and especially saying it to this
audience (you *know* I can do better, don't you?). However, it is a
bit hard to debug it in its position and I have just never tried to
take them out and run them separate from the rest.

Just to annoy me even more, I have actually made one of them work, but
fail to duplicate this (which is *really* ironic, since they are
essentially identical).

For those that haven't looked up the schems, this is a 2-op-amp
curcuit with a handfull of resistors, caps, a pair of 1/4" jacks and a
pair of pots (level and simple EQ/Emphasis).

The design is kind of cheapish and bends some corners.

Also, the layout assumes you have a certain metallic support for the
pots, and uses that to jump ground. Also, it assumes certain behaivour
on the telejacks.

The layouts lack clear signal and component positions (oh, they did in
the article, but that was black on gray and that is just fuzzy for us now).

Now, these added aspects helps to bring in confusions.

I guess this is a proof that you can confuse people by simple means by
making a simple design sligthly obscure.

Now, I seem to slowly put up steam on repairing things (this evening
is devoted to debugging the PSU of a Synthi AKS) so maybe I get that
detail fixed eventually (I have several much more fun things to fix
before that) and actually get that vocoder trimmed up and put into its
place again (it has stood around here on the desk and on the floor for
a couple of years).

So, you where really not reading this, where you?

Cheers,
Magnus