Power supply.

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Daniel Quinn
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#1 Power supply.

Post by Daniel Quinn »

My new transformer as arrived. 300va 18v

The phono board needs 24 positive Volts on both inputs.

So im going to use the positive side of 2 bridge rectifier

Using my coke can caps of 33,000uf .

Do I use one cap feeding one positive rail and another cap for the other one or do I join the caps and attach both wires from the positive side.

Any other ways ?

And how do you measure impedenance with a multimeter
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pre65
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#2 Re: Power supply.

Post by pre65 »

Daniel Quinn wrote: Tue Dec 14, 2021 4:53 pm
And how do you measure impedenance with a multimeter
You can't as such Daniel, but if you measure the AC voltage and current with said multimeter then impedance is voltage divided by current, the answer in ohms.

In simple terms impedance is AC resistance.
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Nick
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#3 Re: Power supply.

Post by Nick »

I would use one bridge, and the two caps in parallel, then power both channels of the phono from the same point.

Re impedance, I would leave the answer as a simple you cant. To explain further would probably involve more than you need or want at the moment.

I think what Phil is telling you will measure the load that the phono board is applying to the supply not the source impedance of the supply.
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Daniel Quinn
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#4 Re: Power supply.

Post by Daniel Quinn »

Thanks gents , much obliged.

I used to trade legal knowledge for hifi knowledge with Richard , it made the relationship reciprocal .

But having relied on nurses to wipe my arse for 6 months I’m getting better at asking for help😉
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Nick
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#5 Re: Power supply.

Post by Nick »

Does the transformer you have have two 18v secondaries? If so there may be some theoretical advantage to using two separate bridge and caps supplies, but not a lot.

There may be some merit to transformer -> bridge -> cap -> CMC choke -> second cap -> load.

But of course that's adding filters :-)
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Daniel Quinn
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#6 Re: Power supply.

Post by Daniel Quinn »

Yes it got 2 18v secondaries.

‘some merit’ what deos this equate to ?
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Nick
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#7 Re: Power supply.

Post by Nick »

Daniel Quinn wrote: Tue Dec 14, 2021 7:18 pm Yes it got 2 18v secondaries.

‘some merit’ what deos this equate to ?
The CMC Choke will remove some HF noise, but I cant say if it will matter or not, hence its a theoretical suggestion.
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pre65
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#8 Re: Power supply.

Post by pre65 »

ESP do some interesting articles on hi-fi, and here is their one on linear power supplies.

Could be good bed-time reading.

https://sound-au.com/power-supplies.htm
The only thing necessary for the triumph of evil is for good men to do nothing.

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Daniel Quinn
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#9 Re: Power supply.

Post by Daniel Quinn »

the power supply is built.

started of with 2 bridge rectifiers but id obviously done something wrong as 1 of them blew up, wanting to see if it worked ,i changed to one rather than diagnose the fault

the dc voltage measured 26,1 which is higher than the expected 25.38, so 1,41 is only a rough guide? so i soldered 2 wires to the positive and one zero and left the negative supply as was.

it works :bounce: cant tell if its better than the regulator supply , will report back
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Nick
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#10 Re: Power supply.

Post by Nick »

so 1,41 is only a rough guide?
No, 1.414 is exact (to 3 DP its actually the square root of 2), but that does assume your mains is a sine wave. What will vary is the mains voltage and exact transformer winding ratio. The mains is probably the largest factor. Also the forward voltage of your bridge was a guess as was your transformer regulation.
left the negative supply as was.
I must have missed where you needed a plus and minus 25v, that seems a bit high for a common op amp, 25v seems about right for a single rail setup.
i changed to one rather than diagnose the fault
If it was me I would have wanted to know what I had done wrong so I don't do it again.
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#11 Re: Power supply.

Post by Daniel Quinn »

theres plenty of time to figure out the problem . there was a time were i would have messed up with it, till it was fixed , my near death experience as made me more sanquine .


the board takes 24v + on both sides and theres no op amps , its discrete.


note what you say re 1.44 , thats comforting to know . the world is full of people who ignore nuance because it makes things complicated , good to know in this instance theres certainty.
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Nick
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#12 Re: Power supply.

Post by Nick »

1.414
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IslandPink
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#13 Re: Power supply.

Post by IslandPink »

:)
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Daniel Quinn
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#14 Re: Power supply.

Post by Daniel Quinn »

Inadvertently I’ve discovered what I did wrong. The discrete stage was in competition with an op amp one. This - I discovered - had a power supply with 2 bridge rectifiers

What I had done is attach the ov leads to the bridge rectifier instead of the being directly attached to the caps and they went bang.
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Paul Barker
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#15 Re: Power supply.

Post by Paul Barker »

:shock:
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