JFET RIAA Phono power supply - which batteries are best?

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mogliaa

mogliaa

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Joined 2009
bartola.co.uk/valves/
#1
All,
I’ve been enjoying my RIAA phono stage so far but with a cumbersome task of recharging my set of NiMH PP3 battery set regularly. My stage needs +/- 18V. (+25mA / -20mA) I’m using the NiMH set as it was recommended not to use the lead-acid batteries as they are noisy.

I’ve been exploring the LiFePO4, but these are expensive still. I was wondering whether a set of 12V+6V lead-acid batteries which you can get easily at a capacity of 7Ah could be bypassed by a proper capacitor to reduce noise. Has anyone tried this?

Other option that was suggested to me was using a LDO low noise regulator such as the LT3080. I would like to avoid going for an external power supply where possible and if there is a way of using high-capacity batteries, I’d rather do that.

Thanks for the suggestions
Ale
 
#2
So you need at least four lead acids... that is very messy for recharging.

As to noise, apart from when charging and perhaps for a short while afterwards I would have thought they were pretty quiet tbh. A capacitor in itself (I would imagine) wouldn't do much for noise because the internal resistance of the battery is so low anyway. You would need a series resistor to raise the impedance of the supply for a cap to be effective.

I really think noise is a non issue tbh.

Putting all your preconceptions aside... would you consider a DC-DC convertor and single lead acid battery. Are you using batteries to overcome hum and line noise ? A DC/DC still gives total ground isolation.

I just think four lead acids are to much hard work tbh with regard to charging. Also you need to regularly charge them fully for what is in effect "cyclic " use or they will deteriorate.
 
#3
Hi Mooly,
Yes, 4 batteries can be fidly. I was looking at the laptop type batteries. A Li-ion pack can be the option as they are +5Ah and could last a long time between charges this way.
Something like this:

12V 6800mAh Rechargeable Battery Pack for LED Light Strip CCTV Security Camera | eBay

Haven't found a supplier of these batteries. I believe they are 3.6V cells. Any ideas where to buy these cells/packs to build a 18V set?

I'm looking to run this with batteries given is an MC stage (+70dB gain) and with the current NiMH is very very quiet.

Thanks
Ale
 
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#6
Mooly said:
As to noise, apart from when charging and perhaps for a short while afterwards I would have thought they were pretty quiet tbh. A capacitor in itself (I would imagine) wouldn't do much for noise because the internal resistance of the battery is so low anyway.
Click to expand...

Battery impedance is high compared to most active regulators.

A fully recharged battery will have noise so low that you have to use cross-correlation techniques to measure it!

You'd probably be quite pleased with the performance of the Jung, Sjostrom or Linear Tech LT1963A/LT3015 regulators for the JFET pre.
 
#7
Hi,

Whilst +/- 18V is the max for most op-amps a phono
stage should run quite happily off +/- 9V on batteries,
and of course +/- 12V on batteries also.

Years back my NiCad battery powered preamp had
a wall wart, and an off / trickle charge / on switch.
4 pole 3 way to do all the proper switching.

rgds, sreten.
 
#8
Thanks for the input. I will give the lead-acid batteries a try. I've got the feedback that low capacity ones (i.e. 1.5Ah) are very quiet and reported very low noise in this application.
Unfortunately I need +18V due to my folded cascode JFET input requirements. I will try a set of 12V and 6V batteries.

@Jack. Thanks for your suggestion regarding the LT1963A/LT3015 low noise regulators. I will use them if I go for the DC regulated power supply option
Ale
 
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