Hi
I tend to agree with Brian on this, I hate switchers, not just because I
don't really understand them (yes I know the principles but they rarely
are as good as they are 'cracked up' to be). To make the HF radiation
low enough to make it usable for high quality audio you need so much
extra filtering you may as well have a half decent linear.
There are techniques to reduce dissipation of linear supplies and the
act of ensuring that the mains tapping is close to what you actually
have is one. Engineering the 'pass transistors' to allow very low
voltage differential across them is another. Using a 'standard' supply
rated for 15 to 28 Volts is wasteful when you want 17 or 18 Volts. There
is usually enough to be gained using the 12 - 15 Volt model and 'wind it
up' a bit unless you know your electricity supply dips really badly. Use
of an autotransformer or automated 'mains stabiliser' should be
considered in these situations.
Sorry I digress.
Shame the TL783 is rather expensive and not so easy to come by.
Matt S
Brian Roth wrote:
May I "wax philosophical" here?
Switching supplies:
1. Efficient...very low heat generation, and hence little amounts of
"input" power being turned into waste.
2. A "switcher" MUST use some sort of oscillator to "do the magic".
In audio applications, we hope that switching frequency is FAR above
the audible range...such as 100 kHz, so minimal "pollution" in the
audible range.
3. However, if a given audio system has multiple "switchers", and each
is operating close to the same frequency, then you end up with
"hetrodynes". Example: in theory, one "switcher" operates at 100 kHz,
and a nearby "switcher" operates at 90 kHz. A POSSIBLE difference
exists at 10 kHz! It would be a "whistle" sound....
I dunno if anyone here ever plays with AM radio, or shortwave radio,
BUT there is so much SCHMUTZ (aka...interference...) on all bands now.
Switchers!!!!!
Linear power supplies:
1. Much more heat. The underlying concept is about as "green" as
setting clothes irons on the ironing board! lol "Waste Heat" makes
it all work.
2. Essentially NO noise besides the inherent 60/50 Hz harmonics. OK
OK...maybe harmonics at 120/180/240....etc Hz series.
Reliability.
Switchers are inherently unreliable, and I speak from many years of
experience.
The circuits are very complicated. The manufacturers use the cheapest
parts. The idea is disposable...
Analog Stuff tends to last longer...as in LM-317 etc.
IMHO.
Bri
Brian Gibson wrote:
Hi,
I think the voltage regulator number you are trying to remember is
TL783.
Max input voltage up to 150V and output 125V max. at 700mA
Regards,
Brian G.
----- Original Message -----
*From:* eliya gwetta <mailto:[email protected]>
*To:* [email protected] <mailto:[email protected]>
*Sent:* Saturday, July 04, 2009 10:37 PM
*Subject:* Re: NEOTEK: Power for Series IIIc Pre's
Hi Matt,
Yes! I remembered the LM317 not being the right regulator for 48V, a
TL583 would be a drop in replacement or I would have to change other
components in the circuit as well?
On Sat, Jul 4, 2009 at 9:25 PM, Matt Syson
<[email protected] <mailto:[email protected]>>
wrote:
Hi
The JLM circuits are pretty much what you need so you could
either 'copy' the circuit and build it yourself or buy the kit.
I am not too impressed at using a LM317 for the phantom 48 rail,
they are only rated to 39 or 40 volt DIFFERENTIAL (input pin to
output pin) , meaning that if you short the output you stand a
good chance of 'blowing it up'. I presume the 47 Ohm resistor is
a lame way of trying not to 'kill' it, hardly a good engineering
solution.
You should substitute it for a TL583 (sorry this number won't
come to me, but there is a similarly packaged regulator that
handles 125 Volts).
Matt S
Donald Put wrote:
If you're up to making your own, there are numerous
PCBs/kits available for this type of project. They're set
up for dual voltages and 48VDC for the phantom power. Check
out JLM's offerings on his website:
http://www.jlmaudio.com/JLM%20Power%20Supply.htm
Cheers,
--
Don
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