Line Stage vs. Phase Inverter - 12A*7 - diyAudio
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 15th February 2013, 02:56 PM   #1
diyAudio Member
 
cogitech's Avatar
 
Join Date: Jan 2011
Location: Kamloops, BC
Default Line Stage vs. Phase Inverter - 12A*7

So, my amp came with 12AX7 as line stage and 12AU7 as phase inverter.

I have been reading a lot about different P-P amps and it seems that much more often than not, they are configured the other way around; 12AU7 as line stage and 12AX7 as phase inverters.

Can anyone guess why my amp seems to have these tubes reversed? Does it all just depend on the circuit design?

The power tubes are EL34, by the way.
  Reply With Quote
Old 15th February 2013, 03:10 PM   #2
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
Does it all just depend on the circuit design?
Yes, of course.
  Reply With Quote
Old 15th February 2013, 08:10 PM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
By 'line stage' do you mean voltage amplifier? They are not the same thing by any means.

Part of circuit design is to use the appropriate valve for the task. Two different designers can arrive at quite different but equally valid designs. These could even use the same valves but in a different order. On DIY sites people sometimes choose valves on the basis of fashion; this is easier than thinking.
  Reply With Quote
Old 15th February 2013, 08:29 PM   #4
diyAudio Member
 
cogitech's Avatar
 
Join Date: Jan 2011
Location: Kamloops, BC
Quote:
Originally Posted by DF96 View Post
By 'line stage' do you mean voltage amplifier? They are not the same thing by any means.
To be honest, I do not know what I mean.

What I know is that the 12AX7 is in the V1 position of my amp (and v5, for the other channel), closest to the line input. I have seen this referred to as the line stage, where the initial gain is applied to the input signal. It is a P-P amp, so it only follows that the V2 tube (12AU7) is a phase inverter.

It seems to me that I usually see 12AU7 used as the initial gain stage in other amp designs, and then 12AX7 used as a phase inverter.

I am just curious as to why the designer of my amp would have chosen to do this.
  Reply With Quote
Old 15th February 2013, 09:01 PM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The first stage in a power amp is normally the voltage amplifier. A line stage, if present, is normally a separate item. Nowadays there is little need for line stages, as modern digital sources have fairly high output voltages.

12AX7 has a stage gain around 50-80. 12AU7 around 10-15. Either can be used as a phase inverter/splitter. Depending on the circuit used, the PS/PI can have a gain slightly less than one or about half the gain of a normal voltage amplifier stage.

Guitar amps often start with 12AX7 as they need lots of gain so they can throw it away in clipping or passive tone controls. Hi-fi needs less gain.

Mullard popularised a long-tail pair phase splitter using the 12AX7/ECC83. Very linear and well-balanced, but may struggle to drive a heavy capacitive load such as a triode-connected output stage. 12AU7 can drive better, but has more distortion and poorer phase balance unless a CCS tail is used. Partly horses for courses; partly personal designer preference; partly fashion.
  Reply With Quote
Old 15th February 2013, 09:23 PM   #6
diyAudio Member
 
cogitech's Avatar
 
Join Date: Jan 2011
Location: Kamloops, BC
[Zoooom]

That was the sound of most of what you wrote going straight over my head.

However, I do appreciate you trying to help me

I am curious more than anything, and at least you have inspired me to continue learning!
  Reply With Quote
Old 15th February 2013, 09:50 PM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Broken record time: run right out and buy yourself a copy of "Valve Amplifiers." You'll be stunned at how much there is to learn and how straightforward it is to do so.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th February 2013, 10:09 PM   #8
diyAudio Member
 
cogitech's Avatar
 
Join Date: Jan 2011
Location: Kamloops, BC
Quote:
Originally Posted by SY View Post
Broken record time: run right out and buy yourself a copy of "Valve Amplifiers." You'll be stunned at how much there is to learn and how straightforward it is to do so.
Accessible to someone with virtually no electronics knowledge (and what little knowledge there is has been obtained by taking things apart, rather than building things)?

EDIT: Is it the M. Jones one? I found a PDF... Will see how it goes.

Last edited by cogitech; 15th February 2013 at 10:13 PM.
  Reply With Quote
Old 15th February 2013, 10:18 PM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
If it's a PDF, it's pirated and you're essentially stealing. No, make that "you are stealing." No "essentially" about it.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th February 2013, 10:23 PM   #10
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Quote:
Originally Posted by SY View Post
If it's a PDF, it's pirated and you're essentially stealing. No, make that "you are stealing." No "essentially" about it.
The 3rd edition has been available as a PDF for ages on (apparently?) legit sites. (so is Douglas Self's Design of Active Crossovers.)
  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
How to make a phase inverter? Fresh Analog Line Level 1 7th March 2012 07:57 AM
Phase inverter ThSpeakerDude88 Tubes / Valves 37 29th August 2007 03:15 PM
6C8G phase inverter engels Tubes / Valves 4 4th February 2007 06:01 PM
What is the purpose of phase inverter? RemoGaggi Digital Source 3 6th December 2006 05:09 PM
Mystery (to me) phase inverter? porkchop61 Tubes / Valves 17 6th October 2004 11:16 AM


New To Site? Need Help?

All times are GMT. The time now is 05:21 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