Discrete phono preamp designs? - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th December 2007, 10:33 PM   #1
diyAudio Member
 
Join Date: Mar 2003
Location: Central NY
Default Discrete phono preamp designs?

I find myself in need of a phono preamp. I've looked around and it seems that I can find designs based on unobtainium components or designs based on opamps. Maybe I shouldn't be concerned about it, but I would like the first stage, at the least, to be discrete. Can anyone point me to designs that use readily available parts?

If not, anyone want to take a stab at designing one? Unfortunately, I'm not knowledgeable enough to do so on my own.

Whatever solution I settle on will need to work with average output moving coils (0.5 mv) and not be too expensive.

Thanks.
  Reply With Quote
Old 27th December 2007, 11:07 PM   #2
diyAudio Member
 
cromodora's Avatar
 
Join Date: Feb 2005
Location: Singapore
Default Lp797

First stage at least, discrete...

LP797
LP797 supply
About LP797

P.S. maybe this thread should be moved to the 'Analogue' section.
  Reply With Quote
Old 28th December 2007, 02:32 AM   #3
maxpou is offline maxpou  Canada
diyAudio Member
 
maxpou's Avatar
 
Join Date: Apr 2006
Location: Québec
Hi,
very easy to built. Maxpou
Attached Images
File Type: jpg pacificriaa-1.jpg (36.7 KB, 2680 views)
  Reply With Quote
Old 30th December 2007, 09:40 AM   #4
diyAudio Member
 
Join Date: Nov 2007
There's Norm Thagard's design in audioXpress, Jan-Feb 2001.

JFETs: 2SK389, 2SJ109
BJTs: LS352, LS312, MPS6523, MPS6521

I thought about building this design, but decided to go with an op-amp based one (ESP) for the sake of simplicity. I haven't done the research, but if the original parts aren't available, there's probably compatible ones with higher noise specs. Or with some redesign, it should be possible to adapt the concept for all-BJTs.

I too would like a discrete phono preamp, and I think have the knowledge to adapt/design one... But I have many unfinished projects as things stand.
  Reply With Quote
Old 30th December 2007, 01:16 PM   #5
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by maxpou
Hi,
very easy to built. Maxpou
I simmed it and it ain't pretty.
  Reply With Quote
Old 30th December 2007, 02:24 PM   #6
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
Hi

In the LP797 the hard to find duel J-fet appears to have both devices in parallel. Couldn't one just replace the pair with a single low noise J-fet and re-bias for that particular transistor?
__________________
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 30th December 2007, 02:53 PM   #7
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by CBS240
Hi

In the LP797 the hard to find duel J-fet appears to have both devices in parallel. Couldn't one just replace the pair with a single low noise J-fet and re-bias for that particular transistor?
You can use a matched SK170 pair -- mount in close proximity -- you can epoxy them together or use a tie-rap. I believe that Linear Systems will sell small quantities of the LSK389. The pair of '170's knocks the noise down (it is already very low).

The high gain JFET's also are somewhat high capacitance...

I don't particularly like the AD797's in this application.

Here's the Maison Pacific simmed with Linear Systems model for the LSK170 -- and some changes to the capacitor values. note that the deviation in the lower chart is +- 1dB -- this is only a sim, I haven't breadboarded the device yet.

Click the image to open in full size.
  Reply With Quote
Old 2nd January 2008, 12:17 AM   #8
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
the APT/holman preamp used a discrete phono pre, designed like a discrete opamp with an interesting twist..... the diff amp consisted of a JFET at the noninverting input, and a bipolar on the noninverting input. the 2 volt DC offset caused by this mismatch was blocked by a cap(the DC wouldn't have hurt anything, since it would be blocked by the rumble filter anyway). it was an excellent low noise RIAA pre.

i have a schematic of it, but i don't have it on this machine, so i'll upload it later.
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 2nd January 2008, 12:53 AM   #9
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Today, it would be best to stick with a fet diff pair. Fet noise is lower, today, and any advantage will be lost.
  Reply With Quote
Old 2nd January 2008, 02:28 AM   #10
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
John is right, that design was a cute way to save short money on parts but there's no magic in the asymetric input stage. TH has definately moved on to better thing$.

I found something funny trolling around this week, the microphone modding guys think the Japanese 2SK170's are bad compared to the LSK170's. The samples of LSK170's I evaluated met or exceeded every spec on the data sheet, but I still can't figure how either would stand out from the other in an appropriate circuit.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Where can I get a pcb for a discrete GC preamp? raypalmer Chip Amps 2 27th January 2009 11:45 AM
which discrete preamp ? sopapo Solid State 12 13th January 2006 09:11 PM
Pre-pre; phono; pre line ;device discrete (bjt/fet) o op. amplifier GIPIONE Solid State 8 18th December 2005 10:09 PM


New To Site? Need Help?

All times are GMT. The time now is 06:36 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2