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From: bob urz on 20 Dec 2009 11:35
William Sommerwerck wrote:
> The following is unduly long -- especially as I want a short answer -- and
> is partly an excuse for bragging about an expensive luxury I own. But the
> question is serious, and the answer likely useful to many in this group.
>
> The most-common external power supply (wall wart, if you like) ever made is
> likely the Sony AC-E455D. This little black cube pumped out 4.5V at 500mA,
> to power hundreds of thousands of Discmans and other portable devices.
> They're so common that you can easily find them on eBay for a few bucks
> each.
>
> Jump to STAX. A few years back STAX introduced the SR-001 electrostatic
> earphone (not headphone) system. These little gems are driven by a tiny
> battery-operated amplifier/energizer that puts out 580V DC polarizing
> voltage (!!!) and about 300V of AC drive signal. They aren't cheap, but the
> sound justifies the price -- if you want really good sound when listening to
> portable equipment.
>
> http://www.audioreview.com/mfr/stax/headphones/sr-001-mk2-system/PRD_143823_2750crx.aspx
>
> Now, the amplifier/energizer is powered by two AA cells. But there's a jack
> on the back for 4.5V DC -- whose diameter and polarity just happen to match
> the AC-E455D's. Though STAX sells its own terribly overpriced power supply,
> one can't help but think that STAX was deliberately making the SR-001
> compatible with a very common AC adapter.
>
> Hang on, we're getting there...
>
> Sony also produced a switching version of the AC-E455D, which operates from
> 100V to 240V, and puts out 1000mA. Two years ago I bought a dozen of these
> on eBay for a buck apiece. As they were thinner and lighter than the
> "linear" version, they became the power supplies I carried with my Discman
> and STAX SR-001 system.
>
> The interesting thing (finally!) is that most of the switching supplies
> won't power the STAX energizer. The energizer's red "low voltage" light
> comes on, the energizer tries to turn on (briefly flashing the green "good
> voltage" light), but then drops back, and the cycle repeats, producing a
> "thump-thump-thump" in the earphones.
>
> Only one of the switching supplies I have will power the earphones -- and it
> often has to struggle a bit to get going.
>
> It's not an issue of voltage or current capacity, per se. What, exactly, is
> going on?
>
>

I would find it interesting that a supply of 1000ma would go into
current shutdown. If you had a peak hold DMM or some other way to
plot inrush current draw, it would be helpful to know what the device is
actually drawing peak. If it is an over current situation, maybe you can
get a NTC resistor to cut down the peak surge current. It might be
a challenge to find one with that low of rating.

on the flip side, if its shutting down from not enough load, you need
to put a small light bulb or such in parallel with the device for some
additional start up load.

bob
From: Jamie on 20 Dec 2009 17:07
William Sommerwerck wrote:

>>The STAX energiser obviously contains a high frequency
>>(supersonic at least ) inverter to generate the high DC voltage.
>>Betya anything it draws a heap of current when it first gets going.
>
>
>>Problem is, SMPSs usually have over-current protection which
>>typically shuts the supply down pronto -- then it may try to re-start
>>itself. Hence the hiccupping noise.
>
>
>>OTOH -- a battery supply or iron transformer supply can provide
>>brief bursts of high DC current that few small SMPSs can manage.
>
>
> That makes the most sense. Even with the supply that works, the red
> (low-voltage) light comes on for quite some time before the energizer
> switches to green, noticeably longer than batteries or the conventional
> power supply.
>
> Thanks for the info. I have to decide whether I want to accept things as
> they are (I use the headphones fairly often, and am not sure want to carry
> around a pile of rechargeable batteries), or modify the energizer with (say)
> a 10-ohm series resistor.
>
>
If you would like, use a power PNP transistor on the (+) output and bias
the base via the Hfe of the transistor to limit the max current of what
the supply can handle. The Collector would then be the output and the
Emitter to (+) of the power supply output. Base gets biased with
appropriate R to maybe just below the max current of the supply.

The beta will shift upward a bit when the transistor gets warm but
I don't think i'll matter after that..One could always place a Si diode
on top of the transistor to help clamp the bias voltage at the base to
stabilize it.

I've used simple PNP current limited circuits like that in many cases
to fix inrush currents on small circuits.

You can do this with a NPN if you want to float the (-) from the
collector.. Myself, I would go with the PNP..




From: Bob Larter on 23 Dec 2009 17:48
On 20/12/2009 8:04 AM, William Sommerwerck wrote:
> The interesting thing (finally!) is that most of the switching supplies
> won't power the STAX energizer. The energizer's red "low voltage" light
> comes on, the energizer tries to turn on (briefly flashing the green "good
> voltage" light), but then drops back, and the cycle repeats, producing a
> "thump-thump-thump" in the earphones.
>
> Only one of the switching supplies I have will power the earphones -- and it
> often has to struggle a bit to get going.
>
> It's not an issue of voltage or current capacity, per se. What, exactly, is
> going on?

My guess would be that the switcher is generating lots of hash, & it's
upsetting the oscillator in the phones. Try looking at the DC with a 'scope.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
From: Bob Larter on 23 Dec 2009 17:53
On 21/12/2009 12:38 AM, William Sommerwerck wrote:
>> Some switching supplies do no do well in the presence
>> of a RF field. Does the STAX emit this type of interference
>> through the power lead?
>
> The STAX energizer is an audio product, and it's unlikely any switching
> circuits in it operate above 50kHz or so.

Not so. See if you can guess how it generates the HV it needs for the
electrostatic field.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
From: mike on 27 Dec 2009 02:15
William Sommerwerck wrote:
>> I would find it interesting that a supply of 1000mA would go into
>> current shutdown. If you had a peak hold DMM or some other
>> way to plot inrush current draw, it would be helpful to know what
>> the device is actually drawing peak. If it is an over current situation,
>> maybe you can get a NTC resistor to cut down the peak surge
>> current. It might be a challenge to find one with that low of rating.
>
>> On the flip side, if its shutting down from not enough load, you need
>> to put a small light bulb or such in parallel with the device for some
>> additional start up load.
>
> I think is the issue is "too much" load. The power supply operates a
> Discman -- which draws 1/10 the current -- with no problem whatever. Ergo...
>
> I don't have a peak-hold meter. However, I did measure the battery current
> with a Fluke 87 -- it's around 180mA. But at the moment you connect the
> battery, the digital bar-graph display goes WHAM!, all the way to the right
> in a fraction of a second. I suspect the unit is drawing several times 180mA
> at turn-on.
>
> The AC adapter input is spec'd at 300mA -- presumably the maximum capacity
> required, rather than the average drawn.
>
> If I can find a matching plug/socket pair, I might experiment with small
> series resistors (1 to 5 ohms) to see what happens. At the moment, it's not
> a pressing issue.
>
>
You don't need a peak-hold meter.
You need a DC current probe and a dual-channel storage oscilloscope.
Conjecture is no substitute for measurement.
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