[sdiy] replacing a transformer, was:Re: (no subject)

Rutger Vlek rutgervlek at gmail.com
Wed Mar 8 16:07:04 CET 2017


Hi guys,

I did some measurements and found out both grounds of the 6 and 12VDC supply are connected (post rectifier) by one cable close to the expression pedal connector. And the 6V supply is really only for the lamp in the pedal, nothing else. I'd be tempted to remove the 6V supply entirely.

I also noticed that the shared DC grounds are connected to chassis parts as well, which made me feel a little uncomfortable about electrical safety. I'm not sure what the implications would be of converting the organ to a more modern protective earth scheme. Do you recommend it? Has anyone ever had problems with such old schemes?

Rutger



On 7 mrt 2017, at 14:19, Rutger Vlek wrote:

> Hm, I like that idea of simplifying the PSU and making the expression pedal more durable. I already learned the unit can't work without the pedal, there's no normally closed contact that substitutes for the pedal in connecting audio to the output socket. I'll check if the 6V is wired as the schematics suggest.
> 
> Rutger
> 
> On Tue, Mar 7, 2017 at 1:54 PM, Roman Sowa <modular at go2.pl> wrote:
> It looks like 6V is used only for the lamp in expression pedal that is used for photosensor.
> So replace it with good bright LED and skip the 6V part entirely.
> Or leave original lamp and fit inside the pedal any DC/DC converter to go down from 12 to 6V. But the lamp wil burn someday anyhow, so why not some slight upgrade now...
> 
> You should better confirm that by following the cables if it's really just the pedal lamp.
> 
> Roman
> 
> W dniu 2017-03-07 o 13:27, Rutger Vlek pisze:
> Good point Ingo!
> 
> Towards the end of the service manual
> (http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Yamaha-A-3-Service-Manual.pdf)
> the PSU schematic is displayed. There's a full PSU diagram, and an
> overview diagram. The latter shows a straight coupling between both DC
> grounds of the 12V and 6V lines, however the first diagram does not!
> Confusing, I'll measure this in the actual unit to be sure.
> 
> Assuming both grounds are connected, what you wrote is applicable here.
> So it means I'll have to start looking for a transformer with dual
> independent secondaries for 6.3V and 13V (or 12.6V). Anyone knows one?
> At least 7VA total.
> 
> Regards,
> 
> Rutger
> 
> 
> On Mon, Mar 6, 2017 at 6:06 PM, Ingo Debus <igg.debus at gmail.com
> <mailto:igg.debus at gmail.com>> wrote:
> 
> 
>     > Am 06.03.2017 um 14:00 schrieb Roman Sowa <modular at go2.pl
>     <mailto:modular at go2.pl>>:
>     >
>     >>
>     >> Is there any harm in using the centre tap for the 6.3V and the
>     end taps
>     >> for the 12.6V supply to the PSU? It means the coil between one
>     end and
>     >> centre tap gets a little more loading than the other side. The same
>     >
>     > No problem at all, just make sure that added load from 6V and 12V
>     circuits doesn't exceed current rating for that winding.
> 
>     Careful. This won’t work if the two secondary windings of the
>     original transformer are isolated from each other, and they are
>     feeding two bridge rectifiers, and on the DC side of the bridge
>     rectifiers the grounds are connected.
> 
>     With two half-wave rectifiers there’ll be no problem however.
> 
>     Ingo
>     _______________________________________________
>     Synth-diy mailing list
>     Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>     http://synth-diy.org/mailman/listinfo/synth-diy
>     <http://synth-diy.org/mailman/listinfo/synth-diy>
> 
> 
> 
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20170308/36860f9a/attachment.htm>


More information about the Synth-diy mailing list