Fw: [sdiy] ETI vocoder input amps

[jhaible at t-online.de]

IC1b is still wrong in the schematics:

Pin 5 must be the positive input, pin 6 the negative input.
The "+" and "-" symbols are *right* in the schemos, just the
pin numbers are wrong.

On the PCB, RV1 goes to pin 5, which is *right*. This
part should work.

So for IC1b, even when there's still an error in the schematics,
the PCB is ok.

For the other amps, schemos are ok (pin numbers, and overall
circuit as far as I can tell). So you just have to check if
the PCB is the same as the schemos. (Opamps look ok, too. But
I haven't ckecked all the passive components in the layout.)

The pots are both critical to set the DC bias for the opamps.
If the wiper looses contact, you loose the bias.


JH.





Hallvard Tangeraas schrieb:
> At 15:20 +0200  26.10.01, jhaible at t-online.de wrote:
> 
> 
> >> It's been a while, but I believe I looked over the 
> circuit schematics 
> >> and noticed these errors as well, but also saw that 
> the PCB itself 
> >was
> >> OK.
> 
> >I have *not* checked the layout, but:
> >
> >>  
> http://home.c2i.net/w-392864/vocoder/amp_schematic.gif 
> (schematic) 
> >
> >*This* drawing has the errors, and the handwritten pin 
> numbers at 
> >IC1b *confirm* the error there.
>  [..........]
> 
> I've looked through the circuit again and again, but I 
> still can't find 
> out what's wrong. With my limited electronics knowledge I 
> have however 
> figured out what you explained as being the errors in the 
> schematics 
> and fixed them.
> The PCB itself however looks OK, so why it doesn't work 
> is beyond me, 
> especially when Magnus Danielson has one of these which 
> does indeed 
> work.
> 
> I can see how hard it is to check out the PCB layout, so 
> I enlarged it 
> and have drawn the components again as well as marking 
> them. As I said 
> it looks OK to me.
> Here's the PCB layout (with components):
> 
> http://home.c2i.net/w-392864/vocoder/new_revised/pcb_ove
> rview.gif 
> 
> I haven't drawn in the where the jack connectors connect 
> (I have drawn 
> where on the PCB they connect, but not where these points 
> correspond to 
> on the jacks as I've tried several connections and none 
> of them worked). 
> 
> 
> ....and here's the schematic which should be OK now:
> 
> http://home.c2i.net/w-392864/vocoder/new_revised/correct
> ed_amp_schematic.gif 
> 
> 
> 
> Hallvard
> -- 
> Notator/Creator SL : <http://www.notator.org>
> Atari Launchpad    : <http://launchpad.atari.org>
> 
> 
>