finding transformers ?
yann_...@my-deja.com
I'd like to have informations about finding audio transformers for my
DIY ESL project.
My cells are about 4"x42". There are two of these per speaker (not one
over the other, but to make a 1' large speaker). spacers are 1/8" thin.
I want to drive those cells with a 100W RMS transistor amplier. I use a
subwoofer for bass extension so that I don't need to go down to 100Hz
with my ELS...
Please let me know about the audio tansformers i should use, and maybe
about DC Bias...
thanks a lot
Yann
Sent via Deja.com http://www.deja.com/
Before you buy.
Barry Waldron
yann_...@my-deja.com wrote:
> Hi!
> I'd like to have informations about finding audio transformers for my
> DIY ESL project.
Thank you for letting me know about your post by E-mail, Yann.
Many years ago it was sometimes convenient to try audio output
transformers that were in our junk box of spare parts. It was also a
necessity to try and find a suitable and acceptable transformer from
all the ones available from each manufacturer. Not only could this be
an expensive undertaking, but with so many candidates to choose from, a
person might miss and not turn up the best device. Nowadays, very few
manufacturers are offering a selection of transformers for general
use.
In the early 1970s, Roger Sanders, spent a great deal of time and money
searching for a suitable transformer. He found that the Triad S-142a
was quite acceptable. It became the defacto standard among hobbyists
for nearly twenty years who were building speakers based upon the
published designs of Hermeyer, Sanders, and, Waldron.
Two years ago I began offering a much improved matching transformer.
The device was engineered and is custom made specifically for the
purpose of energizing electrostatic loudspeakers whose construction
is based upon our designs. Moreover, this greater level of performance
is available at a price slightly less than that of the Triad!
Information can be found on the Catalog page of my website:
http://www.jps.net/eslinfo
> My cells are about 4"x42". There are two of these per speaker (not one
> over the other, but to make a 1' large speaker). spacers are 1/8"
>thin.
If you have a choice, Yann, I would urge you to use spacers half that
thick. 1/16" or 0.0625" / 1.59mm. This size is more than adequate for
achieving your low end response; furthermore, the required operating
voltage will be considerably less. This translates directly into
greater sound pressure levels!
>I want to drive those cells with a 100W RMS transistor amplier. I use a
> subwoofer for bass extension so that I don't need to go down to 100Hz
> with my ELS.
Fs for a panel with these measurements is typically on the order of
90 Hz. It could be somewhat more or less depending upon the
diaphragm's tension. You will want to select a crossover frequency and
slope that will effectively remove the ESL at this frequency.
On the site's Associated Electronics page you will find a schematic for
a "full range" contour network. This circuit was designed with this
application in mind. It will permit an ESL to operate at or below Fs.
This makes it practical to use electrostats and subwoofer(s) with a
very low Xp.
> Please let me know about the audio tansformers i should use, and maybe
> about DC Bias...
Electrostats require a high voltage audio potential. Using a diaphragm
to stator spacing of 1/16", the required voltage is typically`in the
range of 2.5 KV. Working backwards, 2,500/50 (turns ratio)= 50 (an
amplifier's +/- power supply swing.) As a rule of thumb, a 100 w/p/c
amplifier is generally considered to be the minimum power required for
adequate output. Greater headroom is possible with an amp. of at least
150 w/p/c or more. It is for this reason that I do not recommend a gap
of 1/8".
If a person reading this is looking for an amplifier, it is important
to try and find a device that operates on the highest power supply
voltage possible. As mentioned, above, an amplifier's wattage is used
as a rule of thumb. Here is an extreme example for two one hundred
watt amplifiers: The first device has a power supply that swings 50
volts at 2 amperes. The second device has a power supply that delivers
2 volts at 50 amps. The first example will permit the electrostat to
play much louder because it produces much more voltage.
If your amplifier is a modern design and is stable at two ohms, it will
probably work just fine. For those audiophiles in need of an mplifier,
try and find a make/model that has a power supply capable of delivering
both high voltage as well as high current. Most products are
engineered to address the needs of conventional magnetic drivers. This
means that they produce lots of current in deference to the voltage.
While the ideal choice for an amplifier to energize ESLs is to have the
highest power supply voltage possible for a given wattage, it is also
very important to have plenty of current reserve. Voltage equates to
overall SPLs and headroom; current equates to transient attack. Given
enough of both, an impedance matching transformer can be made to seem
invisable.
There are several commercial products that work well with
electrostats. If a person wants the best possible performance, I offer
two suggestions: The Hafler DH-500 is often available on the used
marketplace for between $350 and $600. It is a superb amplifier for
this application. InnerSound, recently introduced the "ESL Amplifier",
a product specifically designed to energize full range and hybrid
ESLs. You can learn more about this remarkable amplifier by going to
the company's website: http://www.innersound.net
Power supplies___
These can be built following one of several schematics that have been
published in any number of electronics books. The usual circuit
configuration is to employ a voltage doubler (daisy chain) rectiier
that provides the required high voltage output. An assembled and
tested device providing output in 500 volt steps to -4KV is available
on the catalog page of my site.
The schematic for a regulated and fully adjustable switching supply is
available on the Associated Electronics page, courtesy of SDS Labs.
I hope this information is of help Got questions? Please do not
hesitate to ask or think it an imposition.
Cordially,
Barry
ESL Information eXchange
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