Low noise HT - non BG!

[James D]

In response to comments for a non BG version of the low noise psu I knocked this version up. Changes are to replace the RC stage with an LC stage since standard caps in the PSU are noisier than chokes and so hide its self noise. The choke is snubbed by two 100nF caps connected to ground from each end of the choke. The big electrolytic is bypassed with a nice PP cap and the output cap is a nice PP of about 10uF. This a nice quiet supply and is the one I use in guitar amps. Again note the balanced power connection on the mains side - it really does make a difference as long as the earth is clean.

ciao

James

[Paul Barker]

James, surely for the balanced connection on the input you first require an isolating transformer, since neutral and cpc are joined at the sub station by placing one at the centre tap of a transformer and the other at the oposite pole to phase, you are effectively shorting out half of the winding.

Apart from that lubberly as my local late night eating house owner would say.

(My work mate and I went at 11pm for our fist meal of the day once, he said, "why you work so late, you been doing gubby job?")

For those who don't know in the east coast a guvy job is out of hours work for cash that your boss doesn't know about.

You know the British Gas fitter doing jobs on the side (for which by the way he isn't corgi registered and not insured and he can't gas work notify so you can't get a certificate of compliance with the building regs <which all good solicitors will now be asking for in house sales>from him).

[IslandPink]

Looked v. useful when I saw it at the weekend James. I was going to print it off this morning but forgot I wouldn't be able to see it !

More comments soon .
Mark

[Andrew]

Originally Posted by Paul Barker

James, surely for the balanced connection on the input you first require an isolating transformer, since neutral and cpc are joined at the sub station by placing one at the centre tap of a transformer and the other at the oposite pole to phase, you are effectively shorting out half of the winding.

Yes, James, I'm struggling with this one as well, mains is essentially single ended, as Pauls says, balanced mains needs a TX, like those big yellow boxes on building sites around the country.

cheers,

-- Andrew

[James D]

Absolutely right chaps! Sorry, I screwed up. Mea culpa!!!

My audio mains ring and my test bench (portable) both have isolation transformers and I tend to forget that I have them in circuit! So my situation isn't typical and normally you would need an isolation trannie in front of the psu trannie. I'll upload a modified drawing and the reference documents on balanced power when I have more time online.

Again - sorry for the incorrect diagram above.

James

[dave dove]

working on this to supply 200V@20mA
struggling to get the shunt working
have tried 6n1p with 100R to sink @22mA
but nothing goes down there at all
may have read curves wrong
may try both halves @11mA
unsure about the grid bit
have used 2uf and 1m grid leak
is this ok?

it has to be small noval to fit casing
was going to use both halves 6n6p
but it won't fit under the roof

dave

[James D]

Quick check on the curves I have shows you need to use both halves in parallel and set cathode resistor to between 220R to 270R. Bypass should be at around 680uF

For the grid cap with a 1M grid resistor the cap should be around 680nF so your 2uF is fine.

I can't find accurate curves for Va 200V and Ia 22mA for a single section

ciao

James

[dave dove]

cheers james

page 3 top left:

http://www.mif.pg.gda.pl/homepages/f...112/6/6N1P.pdf

tallies with yours too
will try again later

later:

but of course
the reason it ain't conducting
is 'cos the heaters can't get enough
600mA see.... way too juicy

i've got some 63/ol2 somewhere
they should work fine
and sink enough current
also
forgot that R and C formed high pass filter
and that i could have worked it out myself ;-)

dave

[dave dove]

well james

i built it at last
but so far it's very noisy
here's what i did:

4x4007 > 0.68uf > 20H > 47uf > shunt reg > 20uf PP
i've bypassed 'lytic with 2uf

shunt reg:
HT = 200V
6/30L2 set to sink 8mA a side = 16mA

took me ages to figure oscillation
1K grid stoppers sorted it

phono stage draws @ 12 - 14mA

hums like a good 'un

i could increase 1st and 2nd caps
it is star earthed
any ideas?

dave

[James D]

It is best when star earthed as the shunt needs a solid earth reference to 'push' against.

Would you disconnected the cathode bypass and see if the humm increases or decreases. This will tell us how the shunt is working or not.

I should have mentioned gris stoppers and anode stoppers for some tubes - particularly high Gm tubes and I guess a parallel 6N1P counts as high Gm.

I was wondering in the shower this morning if you wouldn't be better served by a series reg followed by shunt reg using one side of the 6N1P for each in your application. The straight shunt is very low noise but its mains ripple rejection isn't as high as a series reg would acheive... maybe for an RIAA stage we need both...

James

James