Fw: [sdiy] ETI vocoder input amps

[>>>marjan<<<]

> This is getting more and more confusing! Apparently I'm even confusing
> the corrected stuff with what I've done incorrectly in the past -I took
> a look at the circuit again and compared it with the assembled PCB, and
> I have indeed connected RV-2 like you explain here.
> I've corrected the PCB layout picture and uploaded it again which now
> shows (as far as I can see, if I haven't missed anything again) how my
> actual PCB is set up. I've also slightly changed how the leftmost pin
> of RV-1 is connected as that pin doesn't have a solder pad on the PCB
> to connect to and could easily lead to confusion:
> 
> http://home.c2i.net/w-392864/vocoder/new_revised/pcb_overview.gif

Obviously additional pads were for pot's stands, brackets or
whatever you call it (supports, short connecting all of them,
like in JH's arp phaser). One is missing, but I think
leftmost pcb corner should be missing (lines are there, you
added grey color), I think that square part in the corner
is sawn off. Otherwise there should be a pad.

> 
> >Line input is OK but rather unusual design. I'd add another
> >10k to ground from 4558's - pin.
> 
> But this isn't the reason why it's not functioning? It will just
> improve the design, just like Jurgen Haible says in a previous message,
> right?:
> 

That's right. Just a improvement. 

> >>BTW, do yourself a favor add a resistor from the wiper of RV1
> >>to GND. If the wiper temporarily looses contact, your inverting
> >>line amp has no GND reference for that time. 33k would be good.
> 

Sorry, I must've missed this mail. But, yes that was what
I meant.



> That's where the jack connectors go. The yellow on the left-hand side
> for SK1, and the light-green on the right-hand side for SK2.
> This is also pretty confusing as I've tried just about every
> combination I can think of and still don't get it working.
> After having figured out what's wrong with the actual circuit it's time
> to look at exactly how the jacks are to be connected, using the
> following diagram I've made of how the jacks work:
> 
> http://home.c2i.net/w-392864/vocoder/jack_pinout.gif

This was helpful. Just one note, following was relying on
assumption that jack input (hole) is towards pots (ie
"to down" on your pcb gif). Also I'm still not sure,
first I thought you don't need to mount jacks on pcb, but
now it seems they should be there. How, I mean pot are in 
there to (or they are off the pcb?). Do you mount pots
normal (up) and jacks down. To make myself clear, you're
looking on front panel. Jack are beneath or above
pots? To work correctly jack shoud go on upper (silkscreen)
pcb side (according to your jack gif).
So what they meant is whan you insert jack in line in (sk2)
front switch pair lifts feedback resistor from gnd and
your opamp becomes noninverting. Second pair (on the bottom
of jack, where tip goes), disconnect mic amp and now new
signal form line in feeds vr1 pot.
So to include your notification from the schematic,
connections are
yellow dots (sk1)
left up - A
right up - B
right down - gnd (this is first pair of switches, not used)

green dots (sk2)
left up - D
left down - B
right up - C
right down - A

upper dots are from switch pair at the bottom part of the jack
connector, lower dots are for switch pair at the front of the
jack where the input is


also don't forget to ground all jacks, the the metal sheet
around the input (sleeve part on the normal mono jacks)
as those are not on the pcb (but look the schematic).
sk2 will have contact without it, but sk1 won't (you should
connect plug gnd to somewhere right?)
 

> 
> At this point I feel like throwing the whole vocoder out the window or
> something. It's quite frustrating after having spent so many years of
> work apparently for nothing (so far at least).
> 

Well send it to me and you will never ever have to deal
with it ;) 
Really, I was that frustrated with my first larger digital
project - digital delay. I bought the pcb, bought all the
"strange" chips ("whatahell is ca3080?" :), put it together
for days, no beep, 10000000 times checked all the connections,
replaced the chips, so on. For months I've tried to get it
working but for no avail. Wrote to the mag where it was 
published, and to the author but no response. Later they
published some corrections. It didn't helped. I've kicked
in the box of Heinkel 162 Volksjager model. It was 1990. 
It's still in there. Sucker. I'll attack it with some
scope and patience one day. But that was a moment when
I almost left the electronics for good. Phew ;)




-- 



marjan


me    : Marjan Urekar
e-mail: urekar.m at eunet.yu
s-diy : http://surf.to/marjansystems
music : http://go.to/forcemajeure