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It is currently 19 Jul 2019, 04:13

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PostPosted: 27 May 2019, 07:04 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
Hi everyone !

I’ve bought a pair of boards to build a dual mono phono stage bases on the "Le Pacific" circuit. Here’s a link to the ebay ad :

https://rover.ebay.com/rover/0/0/0?mpre ... 3730388614

The seller is from the toronto area and does it’s own designs, so it’s no chinese unknown circuit. (It looks a lot like the boozhound lab phono stage though...)

While i’m waiting for the boards to arrive, i’m starting to plan the power supply. I asked the seller for some recomendations regarding the power supply. Here’s his answer :

"Hi Gabriel,

General rule is: stay away from any 3pin regulators as LM78XX LM317, LM350 and so on, cause these are noisy.
Better results you will have with old, good uA723 / LM723, plus passing transistor.
By the way, my variant of the phono preamp has modified power section to improve filtering ripples and some noises from power supply.
I have a plans to design quiet power supply dedicated to phono preamp, unfortunately, right now I'm very busy with my day job.
Thanks and happy DIY-ing."

Btw, the boards need 18V to 24V.

Does anybody have experience with the LM723 regulator ? I looked at the specs and it’s clearly less noisy than a LM317, but a lot more complicated to me. I would like to know if it’s worth the trouble. My first idea was to use an external power supply in the style of a laptop charger, but couldn’t find one rated below 100mA, wich is the max current according to the seller. Could this kind of power supply be adequate considering the added filtration on the boards ? Could it be more appropriate to just use a 24V wall wart, and filter/regulate the supply inside the chassis on a third board ? I really want to stay away from batteries for this project.

Thanks in advance for your answers and your time !


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PostPosted: 27 May 2019, 16:54 
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Joined: 23 Feb 2017, 02:02
Posts: 497
The LM317 350 etc can be extreme low noise if you actually have a bypass capactiror on the adjust pin to ground
without this is nothing but a noise generator

If done properly all projects can work noisless


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PostPosted: 28 May 2019, 21:03 
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Joined: 04 Jun 2008, 20:59
Posts: 3987
Location: Arizona, USA
Hi, BTW that is true of all three terminal regulators I know of. The actual value of the capacitor will change the performance a bit. Small values (sometimes as low as 0.1uf) are often sufficient from a noise perspective and larger ones (up to about 10uf) will do even more with diminishing returns, but at the expense of regulation. They will slow the regulator performance down. In many of my designs I go for the larger values as low noise is more important than actual regulation speed.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


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PostPosted: 04 Jun 2019, 15:29 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
Thanks for your inputs. Since I wanted to be shure that I would get something silent enough without having to learn everything needed to build a good regulator circuit, I bought a regulated power supply kit on ebay. It is based on the power supply of a Studer 900 console and uses an mje15034 and TL072 op amp. It was the same price as the bhl power supply pcb alone, and has great support and reviews on diyaudio, so I decided to try it.

It is in fact two adjustable and regulated psu on the same board, one for each channel of the phono stage. I thought that it would make sense since the phono stage is a "dual mono"

Here’s a link to the ebay ad :
https://rover.ebay.com/rover/0/0/0?mpre ... 3801110585

Original studer electrical diagram :
https://www.diyaudio.com/forums/attachm ... der900-pdf

Original thread on diyaudio for those who are interested :
https://www.diyaudio.com/forums/attachm ... der900-pdf


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