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Old 7th July 2015, 01:33 PM   #1
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Default Need advice on Power supply

I have a small phono stage, that is a bit noisy.
I tried it direct with two 9V batteries, and it got better alot.
I am intending to power it up with five or six Li-Po rechargeable mobile phone batteries built into the the same enclosure.
The device has 24V DC wall charger type feeding into it, which goes into some smoothing and an LM317 regulator down to 20V.
The batteries (6 of them ) give 4.1V on full charge to 3.7V nominal.

here is the question:
should I keep the LM317 in circuit to get my steady 20V or should I not ?
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Old 7th July 2015, 02:00 PM   #2
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What kind of noise are you getting? Hum?

Lipos require a bit of sophistication in the charging (and protection against over discharge) or you are likely to set them on fire.
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Old 7th July 2015, 02:10 PM   #3
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Originally Posted by richie00boy View Post
What kind of noise are you getting? Hum?

Lipos require a bit of sophistication in the charging (and protection against over discharge) or you are likely to set them on fire.
No hum, background hash.
I should be able to charge them safely ( I got charger circuits).
i'll explain more, shall I.
Would the LM317 introduce any noise of its own, even if supplied by batteries?
if not, I can leave it in.
If it it does, I have to rearrange my circuit to work with 22V nominal.
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Old 7th July 2015, 02:12 PM   #4
DF96 is offline DF96  England
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You could leave NiCads on trickle charge quite safely for days. Modern rechargeable cells are more fussy, so fires or explosions are easier to produce. I would have thought that about the worse way to do it (unless you want explosions) is with a constant voltage charger. As a general rule, anything containing lithium needs to be handled with care.
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Old 7th July 2015, 02:16 PM   #5
AndrewT is offline AndrewT  Scotland
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one does not need light weight for a phone pre-amp.
That removes the ONLY advantage of lithium batteries.

Use sealed lead acid or nicad.
But a reasonably assembled lm317 will be quiet enough for most users.
Batteries may not give any improvement.
An ultra low noise PSU should improve the phono performance slightly.
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Old 7th July 2015, 02:17 PM   #6
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I am a little surprised you experienced a noise problem, usually it is hum. The LM317 should be fine to leave in circuit, when it can no longer regulate due to lack of headroom, the output just follows the input. You could always try it direct to batteries though.
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Old 7th July 2015, 03:05 PM   #7
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OK so far everybody is at fire risk assessment!
Let us assume I know what I am doing regarding safe handling and charging of my batteries.
the question remains,
1- does leaving the LM317 in circuit have any other benefits other than a constant voltage?
2- does leaving the LM317 in circuit have any disadvantages, noise or otherwise (compared to direct battery and a large cap.) ?
("should be OK for most users" is not helpful, if it was, I wouldn't have needed to open the device in the first place)

ofcourse I could try every scenario out, and discover it practically (the hard way),
but since I am lazy and value the opinions of most members here, I thought I ask!

Last edited by KenTajalli; 7th July 2015 at 03:07 PM.
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Old 7th July 2015, 03:11 PM   #8
infinia is offline infinia  United States
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Quote:
I have a small phono stage, that is a bit noisy.
you should concentrate on this original problem, as a new constant connected voltage battery charger may give the same problem plus added complexity or danger even.

what regulator circuit did you use originally? batteries are IMO a choice of portability or last resort.
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Last edited by infinia; 7th July 2015 at 03:20 PM.
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Old 7th July 2015, 03:18 PM   #9
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you should concentrate on this original problem, as a new constant connected voltage battery charger may give the same problem plus added complexity or danger even.
Let us assume I know what I am doing regarding safe handling and charging of my batteries.
what made you assume that I have my batteries "constant connected battery charger" ??
I charge them first, remove charger and then use the device on batteries only.
To my calculation I should get over 25 hours listening on one charge.
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Old 7th July 2015, 03:28 PM   #10
infinia is offline infinia  United States
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so do ever think you might be demanding answers to the wrong questions?
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