diyAudio

diyAudio (http://www.diyaudio.com/forums/index.php)
-   Analogue Source (http://www.diyaudio.com/forums/analogue-source/)
-   -   Discrete phono stage, single supply. (http://www.diyaudio.com/forums/analogue-source/255309-discrete-phono-stage-single-supply.html)

nnx 26th April 2014 01:44 AM

Discrete phono stage, single supply.
 
2 Attachment(s)
In my search for a discrete phono-stage I fell over this old schematic on Paul Kemble's webpage.

It seems to originate from Wireless World, I wonder if anyone has built this one? The original is for dual 25V supply but I assume it will work for single supply too as shown on the second image.

There is no global feedback and bias is controlled by the voltage drop over 2 and 5 diodes respectively. A strange arrangement that needs to be modeled in spice and tested by experiment. The RIAA equalizer is of a passive type across the collector resistance of the first transistor.

If this works it may be an alternative to the Pacific-style jfet phono preamps, since it is based on standard bipolar transistors and not on difficult-to-obtain 2sk170's.

Please give your input and comments, thank you.

Link to schematic, at the middle of the page:http://www.angelfire.com/sd/paulkemble/sound4.html

DUG 26th April 2014 02:20 AM

2N5210 Max V 50V

I would keep away from the 50V end of things.

I would not load it too much with the next stage...but that is just me. :)

Otherwise looks neat.

paul kemble 26th April 2014 08:38 AM

DUG is right about the 50V but a friend who built the original was happy with it and I didn't see/hear any issues. One of the simplest and most compact solutions I found and used was the HA12017 (same web page) which, as I mentioned, was comparable to far more complex designs. Currently I'm still happy with a Technics design.

knutn 26th April 2014 10:35 AM

The first transistor has an emitter resistance of 22k. This is a very large value and equivalent to place a 20nV/sqHz noise generator on the input of the amplifier, ruining your signal to noise ratio.

Salas 26th April 2014 12:37 PM

Better look for Alex Nikitin's SRPP few BJTs circuits.

nnx 30th April 2014 12:10 PM

Thank you all for your comments! I don't have 2n5120 but 2SC1815, 2sc815 and 2N3904 are available.

My comments and questions:

@DUG: You are right, if I build it I will use 30 volts and not 50, maybe I need to scale the resistor networks in that case.

@Paul Kemble: Thank you for all the info on your page. I plan not to use opamps but only BJT's for this build. Which Technics design do you use?

@Knutn: Regarding emitter resistor noise, can you please show how to calculate? Would it help to scale the resistors down and increase the current?

@Salas: Alex Nikitin's srpp, do you refer to the Creek preamp? I had a look at it and it may well be an option, thank you for the tip.

From the first simulations in ltspice I believe some component values could be adjusted slightly....

x-pro 30th April 2014 12:50 PM

Quote:

Originally Posted by nnx (http://www.diyaudio.com/forums/analogue-source/255309-discrete-phono-stage-single-supply-post3910575.html#post3910575)
@Salas: Alex Nikitin's srpp, do you refer to the Creek preamp? I had a look at it and it may well be an option, thank you for the tip.

From the first simulations in ltspice I believe some component values could be adjusted slightly....

This "2010" version is designed for DIY and easier to build.

http://www.ant-audio.co.uk/Theory/Phono2010_v2.gif

The input JFETs should be a selected pair (J113 or BF244B may be used in that position). R4 value may need to be adjusted for the flattest LF response (using a reverse RIAA network on the input) - it somewhat depends on the BJTs used.

Cheers

Alex

knutn 30th April 2014 02:35 PM

Quote:

Originally Posted by nnx (http://www.diyaudio.com/forums/analogue-source/255309-discrete-phono-stage-single-supply-post3910575.html#post3910575)
Thank you all for your comments! I don't have 2n5120 but 2SC1815, 2sc815 and 2N3904 are available.

My comments and questions:

@Knutn: Regarding emitter resistor noise, can you please show how to calculate? Would it help to scale the resistors down and increase the current?

From the first simulations in ltspice I believe some component values could be adjusted slightly....

To be honest: I don't like the proposed amplifier. It would be much better to stick to for example the Salas amplifier (http://www.diyaudio.com/forums/analo...jfet-riaa.html). I don't think it is that difficult to get the transistors (2SK/LSK170).
And yes, generally it will help to scale down the resistor values, but it all depends on the equivalent noise current for the transistor chosen (but 2N5210 favours low collector current).

paul kemble 1st May 2014 08:11 AM

SU-V6 with EPC 205C mk3, SL-Q2 deck.

udok 2nd May 2014 08:42 AM

Quote:

Originally Posted by x-pro (http://www.diyaudio.com/forums/analogue-source/255309-discrete-phono-stage-single-supply-post3910612.html#post3910612)
This "2010" version is designed for DIY and easier to build.

http://www.ant-audio.co.uk/Theory/Phono2010_v2.gif

The input JFETs should be a selected pair (J113 or BF244B may be used in that position). R4 value may need to be adjusted for the flattest LF response (using a reverse RIAA network on the input) - it somewhat depends on the BJTs used.

Cheers

Alex

What is the advantage of using a FET input instead of a bipolar transistor?
Seems to me that the bipolar is a better choice as it has lower noise.

Any comments?


All times are GMT. The time now is 12:42 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio

Wiki