Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 7th October 2008, 08:31 AM   #1
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
Default Yet Another Phono Stage Suggestions Thread

I have an old LP12 -- from 1974. A couple years ago I put a "nice" cartridge on it (some Clearaudio thing that cost too much), which broke after about a year of light use. So, after not listening to any of the gems in my record collection in a long time, I am now going to put a cheap cartridge on it, probably a Shure M97xE unless someone has a better $50 option. But I need a phonostage.

Any suggestions? I like the look of Thorsten's (12AX7 into 6922) and it seems simple enough, and I think I have all the parts necessary to build a cheapo version, but people seem to badmouth the 12ax7 for phono input duty. I have a really good stash of 6SL7's and 6SN7's that I am never going to use for anything else, so I wouldn't mind using them here. I also have several lifetime supplies of 6688's and 5879's so a pentode stage would not be out of the question.

Any particular circuit suggestions, or online tools for calculating RIAA curves? Also, this is going to have to push longish (15 foot) cables with a TVC on the other end. I do want to do tubes and stay away from opamps, but a mosfet follower on the output is an option. Cathode follower is probably fine as well, or a grounded cathode if rp is low enough.
  Reply With Quote
Old 7th October 2008, 10:07 AM   #2
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
My two pence:

http://www.dissident-audio.com/RIAA_PC900/Page.html

But build it larger than I've done, each channel dissipates near 10 Watts including heaters

Not to tell about regulators efficiency

Yves.
  Reply With Quote
Old 7th October 2008, 02:59 PM   #3
diyAudio Member
 
Join Date: Jul 2006
My understanding is that the 12AX7 is a bad front-end tube due to its high input capacitance. Given that what you're going for here is total gain, what's the problem with using a 6922 as your input tube and moving the 12AX7 behind it, where it won't load the cartridge excessively?
  Reply With Quote
Old 7th October 2008, 11:49 PM   #4
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Default Re: Yet Another Phono Stage Suggestions Thread

Quote:
Originally posted by dsavitsk
I have an old LP12 -- from 1974. A couple years ago I put a "nice" cartridge on it (some Clearaudio thing that cost too much), which broke after about a year of light use. So, after not listening to any of the gems in my record collection in a long time, I am now going to put a cheap cartridge on it, probably a Shure M97xE unless someone has a better $50 option. But I need a phonostage.

Any suggestions? I like the look of Thorsten's (12AX7 into 6922) and it seems simple enough, and I think I have all the parts necessary to build a cheapo version, but people seem to badmouth the 12ax7 for phono input duty. I have a really good stash of 6SL7's and 6SN7's that I am never going to use for anything else, so I wouldn't mind using them here. I also have several lifetime supplies of 6688's and 5879's so a pentode stage would not be out of the question.

Any particular circuit suggestions, or online tools for calculating RIAA curves? Also, this is going to have to push longish (15 foot) cables with a TVC on the other end. I do want to do tubes and stay away from opamps, but a mosfet follower on the output is an option. Cathode follower is probably fine as well, or a grounded cathode if rp is low enough.

Dude,

The objection to high mu/high RP types at a phono preamp's I/P is the potential for frequency response trouble, due to cartridge/Miller capacitance interaction. Some MM level carts. are fine working into an 'X7, while other carts. do poorly.

A variation on the RCA passive RIAA EQ theme should do the job for you. To make 100% certain that Miller capacitance is not an issue, use 6GK5s in the 1st gain block positions. Talk to your "neighbor", Jim McShane about 6GK5s.

KAB provides a passive RIAA EQ calculator. Look here.

Thorsten's design lacks the drive necessary for your situation. AAMOF, you have an especially difficult setup. Interconnect cables that are 15 feet long MUST be shielded. You need a phono preamp whose O/P impedance is LOW and whose drive current is HIGH, to deal with cable capacitance and the TVC. I suggest you use 6GK5 1st gain blocks, grid leak biased 6SL7 2nd gain blocks working into DC coupled 6SN7 cathode followers. The 'SN7 CFs have the "sock" needed to drive IRFBC20 source followers. Run the FETs at ID = 20 mA. Good bye to drive capability issues. Use a 9 V. Lithium battery in each channel to forward bias the gates. Since a high gate resistor value is not problematic, use a highly transparent PTFE dielectric coupling cap. of modest value between the 'SN7 and the FET. My guess is that a bypassed 10 μF. motor run cap. will be needed between the FET and the O/P RCA female.
__________________
Eli D.
  Reply With Quote
Old 8th October 2008, 12:16 AM   #5
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Never mind, sorry...

__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 8th October 2008, 04:37 AM   #6
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
Default Re: Re: Yet Another Phono Stage Suggestions Thread

Quote:
Originally posted by Eli Duttman
A variation on the RCA passive RIAA EQ theme should do the job for you. To make 100% certain that Miller capacitance is not an issue, use 6GK5s in the 1st gain block positions. Talk to your "neighbor", Jim McShane about 6GK5s.
Interesting, looks like a good tube to use here. Maybe these in conjunction with 6T4's for an all 7 pin project.


Quote:
Originally posted by Eli Duttman
KAB provides a passive RIAA EQ calculator. Look here.
Thanks. Very useful. R1 in the equation should be the resistor (R1') used in series with the Zo from the first stage?

Click the image to open in full size.
  Reply With Quote
Old 8th October 2008, 06:45 AM   #7
diyAudio Member
 
Join Date: Jun 2007
an excellent phono stage... I built it and sub'd ecc35 for the 5751's

You could also sub in 6SL7's for the 417a and 5751.

Is a Mu stage WE417a input and a Mu stage 5751 output with a passive RIAA eq in between.

There is no mistake in the schemo.... there is no grid stopper into the 417a..... designer says 417a is very happy without and one less resistor for the signal to pass through.

I used Allen Wrights SuperReg in the power supply

here's his PCB version with designers notes:

http://www.dddac.de/tp06.htm

here's the hardwaire version:

http://www.dddac.de/tp07.htm


JD
  Reply With Quote
Old 8th October 2008, 08:01 AM   #8
diyAudio Member
 
Join Date: Mar 2008
Default A1 gain ...

Quote:
Originally posted by dsavitsk
...
Thanks. Very useful. R1 in the equation should be the resistor (R1') used in series with the Zo from the first stage?

Click the image to open in full size.
Hi,
I am sure you don't want to know that A1 gain should exceed 40dB.

Kind regards,
Darius
  Reply With Quote
Old 8th October 2008, 04:18 PM   #9
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Default Re: Re: Re: Yet Another Phono Stage Suggestions Thread

Quote:
Originally posted by dsavitsk


<snip>

Thanks. Very useful. R1 in the equation should be the resistor (R1') used in series with the Zo from the first stage?

Click the image to open in full size.

Yes you need to include the preceding stage's rp in the total. Also to reduce sensitivity to variations in rp due to operating point, aging, and initial tube tolerances it is a good idea to make R1 several times larger than rp at minimum - with very low rp tubes you can make it much greater without exacting a huge noise penalty. Don't neglect the johnson noise generated by both the rp of the preceding tube and R1 - try to choose a high mu tube with a low rp for this reason. (Seems like triode connected 6688 might be good in this location as is the 5842/417A, or triode connected D3A or 7788.) FWIW I am a huge fan of the D3A in triode connection for this task.

All of my phono stages use this basic topology and the passive equalization is based on the work of Stanley Lipshitz (U of Ontario) who deserves to be mentioned when this eq network comes up.

I aim for as high mu as I can get in that first stage, and as few active stages overall that I can manage. (Just 2 currently) Gain in my first stage is about 37dB - not quite the 40dB that Darius recommends.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 8th October 2008, 05:01 PM   #10
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I cheat and use an input transformer, so my first stage gain is about 58dB. You need to do a few tricks to prevent overload...
__________________
"The way to deal with superstition is not to be polite to it, but to tackle it with all arms, and so rout it, cripple it, and make it forever infamous and ridiculous."- H. L. Mencken
  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
Phono stage for 12B4 amp [from previous thread] coffeedj Tubes / Valves 1 2nd April 2009 09:26 PM
DIY phono to replace roksan phono stage seroxatmad Analog Line Level 6 14th December 2008 05:46 PM
new phono stage or old preamp with phono? flohmann Analog Line Level 2 2nd October 2008 09:51 PM
Should I replace Scott 222C phono stage with Claret phono stage? Bing Yang Analogue Source 0 22nd August 2005 06:41 AM


New To Site? Need Help?

All times are GMT. The time now is 04:35 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