PSU optically decoupled?

Archived from groups: rec.audio.pro (More info?)

Hi,

Just idlin' & remembering a description of a preamp I saw in a Hi-Fi
magazine sometime in the late 80's/early 90's...:

The PSU was *optically* decoupled from the main curcuit: the
transformer secondary was rectified & smoothed & then lit up an
incandescent bulb that shone on a selenium cell that then powered the
preamp.

Is this a valid/useful/interesting technique? -

eg - For reducing hum (and other unwanted interactions) between the
PSU & the main circuitry?

And/Or:

- resolving decoupling/earthing issues with other externally-connected
components eg record decks etc?

Or was it just a 'snake-oil' marketing thang?

Archived from groups: rec.audio.pro (More info?)

On 26 Aug 2004 19:44:58 -0400, kludge@panix.com (Scott Dorsey) wrote:
>gmc <gmc@intlog.demon.co.uk> wrote:
>>Just idlin' & remembering a description of a preamp I saw in a Hi-Fi
>>magazine sometime in the late 80's/early 90's...:
>>
>>The PSU was *optically* decoupled from the main curcuit: the
>>transformer secondary was rectified & smoothed & then lit up an
>>incandescent bulb that shone on a selenium cell that then powered the
>>preamp.
>>
>>Is this a valid/useful/interesting technique? -
>
>It is interesting. I am not sure it is valid or useful. It is certainly
>not very efficient. It does decouple the input electrically, but then a
>transformer does that very well. It does not have any low pass action;
>selenium cells are pretty fast to response (and silicon solar cells are
>really fast... also way more efficient). It's also going to be a pain to
>get high voltages this way.
>
>>eg - For reducing hum (and other unwanted interactions) between the
>>PSU & the main circuitry?
>
>Won't reduce hum a bit. Silicon cells are used for optical sound pickups
>on projectors... they reproduce 20 KHz just fine, let alone 60 Hz. (Sadly
>the optics and source tracks don't reproduce 20 KHz so well...)
>
>>- resolving decoupling/earthing issues with other externally-connected
>>components eg record decks etc?
>
>It will do this, just as well as a power transformer will. Transformers are
>pretty damn ingenious things when you think about it.
>
>>Or was it just a 'snake-oil' marketing thang?
>
>Audiophiles like to try out strange things that don't make much sense. Now
>and then, they actually hit upon something that is a significant improvement
>even though it may look silly. I don't think this is one, though.

Hear what you say, Scott -

Also, maybe it *was* a silicon cell (rather than selenium) - from what
I remember from the pix in the magazine, it might have been a thin
square - perhaps umm.. 1/2" square, with a black, shiny front face(??)

I can't remember if any secondary smoothing/LP filtering (ie in the
preamp) was mentioned in the text, but I guess the
designers/marketeers would have got that covered :-)

ISTR The bulb was a standard 'LES' one - umm.. 6V?

--

Although I'm not a Audiophile-head/HiFi buff by any means, I've gotta
say that that one stuck in my mind - apart from anything else, I kinda
like the poetry of a thing being powered off its own little Sun :-)


>--scott
>--
>"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

gmc wrote:

> Hi,
>
> Just idlin' & remembering a description of a preamp I saw in a Hi-Fi
> magazine sometime in the late 80's/early 90's...:
>
> The PSU was *optically* decoupled from the main curcuit: the
> transformer secondary was rectified & smoothed & then lit up an
> incandescent bulb that shone on a selenium

Correction to silicon photocell noted

> cell that then powered the preamp.
>
> Is this a valid/useful/interesting technique? -

It's very inefficient for one.

It's entertaining for sure < giggle / boggle ! >.


> eg - For reducing hum (and other unwanted interactions) between the
> PSU & the main circuitry?
>
> And/Or:
>
> - resolving decoupling/earthing issues with other externally-connected
> components eg record decks etc?

All of those issues can be resolved very adequately by simple competent
design.


> Or was it just a 'snake-oil' marketing thang?

I would say so. More of a gimmick really.

Graham

Archived from groups: rec.audio.pro (More info?)

"Logan Shaw" <lshaw-usenet@austin.rr.com> wrote in message
news:RhxXc.27201$Jn5.23976@fe1.texas.rr.com...

> Well, a light bulb's filament glows because it's hot, not because there
> is current flowing through it. As a result, the bulb will continue to
> glow when the current is removed, at least until it cools down. So
> there is low pass action because the filament doesn't instantly heat
> up and cool down with changes in current.

Right. However, it does heat up and cool down quickly enough that you can
read a strobe disc on a turntable with an incandescent light. Not as sharp
as a fluorescent or neon, but sharp enough to set the speed.

Peace,
Paul

Archived from groups: rec.audio.pro (More info?)

Logan Shaw <lshaw-usenet@austin.rr.com> wrote:
>Well, a light bulb's filament glows because it's hot, not because there
>is current flowing through it. As a result, the bulb will continue to
>glow when the current is removed, at least until it cools down. So
>there is low pass action because the filament doesn't instantly heat
>up and cool down with changes in current.

Yup. There's still a lot of residual hum at 60 Hz even from incandescent
lighting, though, as you'll note when you open up the sound head door on a
film projector with a worklight shining into it. Fluorescent lighting, of
course, is far worse. But the mass of the filament does provide a low pass
filter by staying hot between peaks, and the larger the filament mass, the
more effective this is.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

On Fri, 27 Aug 2004 02:33:57 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
>gmc wrote:
>
>> Hi,
>>
>> Just idlin' & remembering a description of a preamp I saw in a Hi-Fi
>> magazine sometime in the late 80's/early 90's...:
>>
>> The PSU was *optically* decoupled from the main curcuit: the
>> transformer secondary was rectified & smoothed & then lit up an
>> incandescent bulb that shone on a selenium
>
>Correction to silicon photocell noted
>
>> cell that then powered the preamp.
>>
>> Is this a valid/useful/interesting technique? -
>
>It's very inefficient for one.
>

Umm.. yeah but do we care about efficiency? - we're talking the order
of a few milliamps.

Having said that, if we go that route, the power-on LED would need its
own PSU...

"Get me marketing!" :-)

>It's entertaining for sure < giggle / boggle ! >.
>
>
>> eg - For reducing hum (and other unwanted interactions) between the
>> PSU & the main circuitry?
>>
>> And/Or:
>>
>> - resolving decoupling/earthing issues with other externally-connected
>> components eg record decks etc?
>
>All of those issues can be resolved very adequately by simple competent
>design.
>
>
>> Or was it just a 'snake-oil' marketing thang?
>
>I would say so. More of a gimmick really.
>
>Graham
>
>

Archived from groups: rec.audio.pro (More info?)

Why not just solar power the thing? No possibility of line noise then. Of course, most of us
audio people ain't too keen on sunlight.

--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
Payments preferred through Paypal.com
"Scott Dorsey" <kludge@panix.com> wrote in message news:cgommq$ebt$1@panix2.panix.com...
> gmc <gmc@intlog.demon.co.uk> wrote:
> >
> >Umm.. yeah but do we care about efficiency? - we're talking the order
> >of a few milliamps.
>
> Yes! The more current we dump into the thing, the more we can run it into
> class-A, the lower impedance internal lines we can use, the more input
> devices we can parallel! More current means lower noise and better linearity!
> More current is good! If it doesn't get warm, something is wrong.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

> On Sat, 28 Aug 2004 02:42:34 -0600, Stephen Sank wrote:
>
> > Why not just solar power the thing? No possibility of line noise then. Of
> > course, most of us
> > audio people ain't too keen on sunlight.


philicorda <philicorda@novocon.plig.org> wrote:
>
> Also there is the problem of the 0.00001 hz hum.


So you just need bigger filter capacitors. The kind made out of lead
and acid.


ulysses