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?

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

On 26 Aug 2004 19:44:58 -0400, (Scott Dorsey) wrote:
gmc 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."

On Thu, 26 Aug 2004 23:31:21 +0000, 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 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?

The geffel m300 mic does this to generate a voltage for the capsule from
the 48v phanton. I don't know if the mic electronics take their power the
same way.

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

Scott Dorsey wrote:

gmc 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.

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).

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.

Of course, a true audiophile will insist on a coating of phosphorous
because it gives a smoother sound...

- Logan

"Logan Shaw" wrote in message
...

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

Logan Shaw wrote:

Of course, a true audiophile will insist on a coating of phosphorous because
it gives a smoother sound...

Cue hilarious laughter !

Nice one.


Graham

Logan Shaw 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."

On Thu, 26 Aug 2004 19:44:58 -0400, Scott Dorsey wrote
(in article ):

gmc 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.


My brain hurts, but if I recall corrrectly, Gefell has some mics that use
optical coupling for their phantom supply.

Regards,

Ty Ford



-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at www.tyford.com

On Fri, 27 Aug 2004 02:33:57 +0100, Pooh Bear
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

gmc 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."

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" wrote in message ...
gmc 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."

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.

Also there is the problem of the 0.00001 hz hum.

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 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