D.I.Y. "Duplex" 2sk369 jfet mm phono preamp

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Just wanted to present another option for a phono pre. It is a design by Carlos and can be seen at: diyhifi.org. It uses two 2sk369bl (or gr), one 2n1711, one bf393/side. I used 2sc1815 instead of bf393 due to sourcing problems.

It works well, and is low noise.

There are no pcb's or parts kits, but I did it ; if you can read a schematic, that should get you there.

I live in B.C. Canada, so all parts were sourced from Digikey, the 2sk369bl, 2sc1815 from B&D Enterprises, www.bdent.com, partsales@bdent.com.

The generic pcb came from RS(The Source), 11cmX 15cm. Aside from the design itself, which I take "0" credit for, sourcing the parts and part no.'s was a lot of work. This is where a kit shines!

If any one is interested, I have the digikey part no.'s that I used.

I did enquire regarding the Pass Pearl but decided to go with this one.

Cheers
doggy :)
 

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battery power

I have used battery power before, with an opamp phono stage it can go weeks to months before needing recharging.

This discrete design uses more power; it calls for 2 12v 4amp sla in series for24v dc; I used 2 12v 7amp sla. There is also 2x 10,000uf filter cap.s, bypassed w/100uf at the battery pack.

cheers
Thor[doggy]:)
 
Re: battery power

Originally posted by doggy This discrete design uses more power; it calls for 2 12v 4amp sla in series for24v dc; I used 2 12v 7amp sla. There is also 2x 10,000uf filter cap.s, bypassed w/100uf at the battery pack.

What benefits do the large filter caps provide? Do you have a schematic showing the battery circuit? - I'm having problems working out the grounding for mine.
 
power supply

This battery supply is part of the "duplex" schematic. A thread is started on diyhifi.org which will give you all the details. This is a design by carlosfm which is also referred to by Nuuk on his decibel dungeon site.

Maybe someone can comment on the application of large filter caps in battery supplies and what they do for filtering?

There is only one supply to serve 2 right , left circuits. The ground is attached to the negative ground plane or central ground wire as I did, and then on to the neg. at the bat. pack

cheers
Thor(doggy)
 

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The caps improve the slew response of the battery, and improve the sound to boot.

Dropping a 2 or 3 mH choke in the +, - and ground legs kills any chemistry noise in the supply too, and you can do that before the caps to ensure a silent supply.


Owen
 
I know this is an old thread (in fact 12 yo), but was tempted to show my implementation of this preamp.

An almost fully recycled effort, case and SMPS from old communications equipment, semiconductors - JFETs and BJTs old and recovered stock from other old projects, and also the power switch.
New parts are resistors, caps and connectors.

SMPS is followed by 2-stage PSU - passive RCRCRC filter and then Mosfet Cap multiplier with adjustable Vout.

VCC for 1st stage has additional Cx with a Zx450 and the 2nd one passively filtered.

The schematic is 99% as per Carlos', values are exactly as the original. The only difference is the gain of the 2nd stage is slightly higher, which makes the overall gain x136 or 2dB higher.
Calculated output is 0.68V.

Dead quiet, no hiss or hum. Connected to Amp Camp Amp (ACA) via B1 buffer so there is no scope for more volume at the moment. In the process of building a tube pre which will take care of this.

This is my second RIAA stage, 1st one was a variant of the Pacific pre which had a lot of noise issues.

Now the critical listening will begin, will report if there is any interest.

Some photos below.

Wish to thank Carlos Filipe for making the design available.
Obrigado Carlos.
 

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