I'm just finishing off a basic power supply for a computer style CD player to
use as a stand-alone CD player with my hi-fi. I've built it in a computer PS
box, and so far it consists of two 20VA trannies, configured with 6v and 12v
secondaries. I've mounted a 78S05 and a 78S12 on heat sinks about 1.75 ins
square bolted to the case, and have used a bridge rectifier (100v, 3A) and
4,700uf cap for each supply. Before I hook up the voltage regs, can anyone
suggest any preferred circuits, parts, part values etc for the purpose (cap
values before/after the regs etc, or other solutions)? I'm assuming this won't
run too hot but again, suggestions welcome. The 20VA trannie for the 12v supply
is a bit tight, but I just happened to have some. Andy

=== Andy Evans ===
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Audio, music and health pages and interesting links.

In article ,
Andy Evans wrote:
I'm just finishing off a basic power supply for a computer style CD
player to use as a stand-alone CD player with my hi-fi. I've built it in
a computer PS box, and so far it consists of two 20VA trannies,
configured with 6v and 12v secondaries. I've mounted a 78S05 and a 78S12
on heat sinks about 1.75 ins square bolted to the case, and have used a
bridge rectifier (100v, 3A) and 4,700uf cap for each supply. Before I
hook up the voltage regs, can anyone suggest any preferred circuits,
parts, part values etc for the purpose (cap values before/after the regs
etc, or other solutions)? I'm assuming this won't run too hot but again,
suggestions welcome. The 20VA trannie for the 12v supply is a bit tight,
but I just happened to have some. Andy

I'd normally use a 9 volt transformer for a 5 volt regulated supply using
a 7805 - although since the transformer is rather under run you might be
ok. But I think you'll have problems at 12 volts. I'd use 15 there.

4700µF should be fine for up to one amp. Add a 100nF ceramic disc in
parallel. On the output of the regulator, have a 10µF 100nF and a 1N4001
diode (cathode to negative) in parallel, to ground. Also another diode of
the same wired input to output of the reg, reverse biased, cathode to
output. The diodes just help protect things if you do something stupid
like me.

If checking the PS before use, remember to load it to at least 5mA.

--
*Someday, we'll look back on this, laugh nervously and change the subject

Dave Plowman London SW
To e-mail, change noise into sound.

Hello Dave - just a question here - the 5v supply is at 1A on the CD player,
and the 12v supply is at 1.5A. I'd like it to be a 'universal' PSU and another
CDP I have states:
5v - 1.4A
12v - 1.3A
Is this in accordance with your recommendations? Thanks, Andy




I'm just finishing off a basic power supply for a computer style CD
player to use as a stand-alone CD player with my hi-fi. I've built it in
a computer PS box, and so far it consists of two 20VA trannies,
configured with 6v and 12v secondaries. I've mounted a 78S05 and a 78S12
on heat sinks about 1.75 ins square bolted to the case, and have used a
bridge rectifier (100v, 3A) and 4,700uf cap for each supply. Before I
hook up the voltage regs, can anyone suggest any preferred circuits,
parts, part values etc for the purpose (cap values before/after the regs
etc, or other solutions)? I'm assuming this won't run too hot but again,
suggestions welcome. The 20VA trannie for the 12v supply is a bit tight,
but I just happened to have some. Andy

I'd normally use a 9 volt transformer for a 5 volt regulated supply using
a 7805 - although since the transformer is rather under run you might be
ok. But I think you'll have problems at 12 volts. I'd use 15 there.

4700µF should be fine for up to one amp. Add a 100nF ceramic disc in
parallel. On the output of the regulator, have a 10µF 100nF and a 1N4001
diode (cathode to negative) in parallel, to ground. Also another diode of
the same wired input to output of the reg, reverse biased, cathode to
output. The diodes just help protect things if you do something stupid
like me.

If checking the PS before use, remember to load it to at least 5mA.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

In article ,
Andy Evans wrote:
Hello Dave - just a question here - the 5v supply is at 1A on the CD
player, and the 12v supply is at 1.5A.

I'd like it to be a 'universal' PSU and another CDP I have states:

5v - 1.4A
12v - 1.3A

Ah - I didn't notice the 'S' in the regulator number. They're 2A?

In which case you'd be better with 6800µF reservoir caps. Everything else
should be ok.

A quick glance at the spec shows a minimum input voltage under load of 8
volts for 5, and 15 for 12.

I expect Jim will be along with a more sophisticated PS arrangement
shortly ;-)

--
*I was once a millionaire but my mom gave away my baseball cards

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

In which case you'd be better with 6800µF reservoir caps. Everything else
should be ok.

6800uF ? to run a PC CDROM drive?

Holy moly! most small PC SMPSUs use about 480uF tops.

why not use a small PC PSU anyway?

6800uF ? to run a PC CDROM drive?

My mate Chris Found (Beard audio) suggested 10,000uF. Like Bill Beard, he likes
large caps.

Holy moly! most small PC SMPSUs use about 480uF tops.why not use a small PC
PSU anyway?
I am - there's a good sound in there somewhere, but I can't get rid of a really
steely treble. Tone is OK and detail is good. Therefore I want to use a much
better PSU. And also bolt the mech down onto a really chunky slab of alu. (like
the Flat Fish if you've seen one)

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Andy Evans wrote:

I am - there's a good sound in there somewhere, but I can't get rid of a really
steely treble. Tone is OK and detail is good.

The treble is 'steely' and yet the tone is good... OK.

Therefore I want to use a much better PSU.

Why? the rest of the CDROM wont have been designed with any care wrt
noise on the audio outs.

And also bolt the mech down onto a really chunky slab of alu. (like
the Flat Fish if you've seen one)

What makes you think that will make any difference?

In article ,
Ian Molton wrote:
In which case you'd be better with 6800µF reservoir caps. Everything
else should be ok.

6800uF ? to run a PC CDROM drive?

Well, 6800 is the 'standard' for two amps. And Andy said it was to be a
universal PS - not just for this particular app.

--
*If you tell the truth, you don't have to remember anything.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:


I expect Jim will be along with a more sophisticated PS arrangement
shortly ;-)

Not really. :-) I have tended to design PSUs on a more 'specific' basis.
Thus I have some preferred topologies, but wouldn't comment too much on
component values, etc, without knowing more about the details. Not made a
PSU for the purpose Andy describes, so can't comment in detail beyond saying
that what you/he have discussed looks fine to me.

FWIW I *do* have a prefered topology, aimed at low noise/ripple rather than
being a rigidly predefined voltage. Also ensures a slow start-up and
decline when turned on/off which is important in some applications.

http://www.st-and.demon.co.uk/Audio/700/700page5.html

If you look at the above page it shows an example of the form of PSU
that I tend to use when low noise is desired. For the example shown
the required voltage was around 20Vdc and the output current around
100mA. I tend to avoid feedback or ICs in such supplies as my
experience (perhaps now out-of-date) was that these tended to
either give more noise, or risk unintented HF instabilities under
some conditions of use.

If interested in the above, you would probably wish to fiddle with
some of the component types and values. :-)

Above said, I can't say that the design I've used would be 'better'
than what you have already tried, but offer the above in case
it is of interest.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

The treble is 'steely' and yet the tone is good... OK.

what if I said "the reproduction of timbre seems good with the exception of a
steely ring in the treble which I hope to remove by a better PSU, non
switchmode."?

the rest of the CDROM wont have been designed with any care wrt noise on the
audio outs.

I'm reasoning that if the tonal reproduction is good (as above) then the player
must be doing something right, and indeed better than my Pioneer CDP which is
my current alternative.

And also bolt the mech down onto a really chunky slab of alu. (like
the Flat Fish if you've seen one)
What makes you think that will make any difference?

I'm working on the assumption that the designer of the Flat Fish, who I talked
to at the Heathrow show, has a good reason for bolting his mech down to a solid
slab of alu. Plus others have suggested it, plus if you look at Levinson gear
which ain't shabby, it's all built with substantial alu extrusions. Plus I'm
guessing that in the inverse side of it, the flimsy pressed steel chassis
)which you can bend through at least a cm) is not doing much to improve the
sound of the Pioneer. Plus by putting different damping materials on the
Pioneer base it seems to alter the tonality so I'm working on the theory that
resonances in the structure of CDPs affect the digital output. None of this may
be 'proof' but it all adds up to a lot of probability, and enough to warrant a
build.








=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.