Function of R2 - 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 1st December 2010, 08:58 AM   #1
diyAudio Member
 
Join Date: Oct 2009
Location: Brunei
Default Function of R2

Hi,
Newbie alert:

I am planning on designing a anode follower as an output stage to my tda1541 dac. I was planning to use this topology, but was wondering about the purpose of R2, and how to calculate appropriate values. Is it a simple grid leak?

Click the image to open in full size.


Morgan Jones does really describe the anode follower (don't know why), so any help is appreciated.

Thanks
  Reply With Quote
Old 1st December 2010, 09:56 AM   #2
Gilgy is offline Gilgy  United Kingdom
diyAudio Member
 
Join Date: Oct 2009
R2 is there to provide negative feedback - good explanation here

Designing Single-Stage Inverting Feedback Amplifier
  Reply With Quote
Old 1st December 2010, 10:02 AM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
R2 is the feedback resistor. To a first approximation, voltage gain = -R2/R1 (like the inverting op-amp). In that circuit it is also arranged to be part of the grid leak via RL, but you could do it differently if you wanted.

R1 sets the input impedance - generally as low as possible for most current-output DACs. You could even try omitting R1, then you have a transimpedance stage (current in, voltage out). Input impedance would then be roughly R2/mu - which could still be too high for the DAC chip. Many circuits seem to get away with violating the DAC data sheet requirements - whether this is because DACs are more tolerant than their makers suggest, or people who fiddle with DACs are more tolerant of distortion than they realise I am not qualified to judge.
  Reply With Quote
Old 1st December 2010, 10:04 AM   #4
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
R2 is the feedback resistor wich sets the gain as being roughly (R1 + R2) / R1 providing that the gain you need is lower (says 1/20) than the Mu of the triode.
Output and input impedances decrease as much as this ratio is high so, without R1 (understand 0 ohms) the input impedance fall down and it's probably what your TDA1541 expects for good linearity.

Yves.
  Reply With Quote
Old 1st December 2010, 11:53 AM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Not (R1+R2)/R1, but roughly R2/R1 as I said - assuming sufficiently high open loop gain (equivalently, mu and appropriate load impedances).
  Reply With Quote
Old 1st December 2010, 01:37 PM   #6
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
In you, I trust
  Reply With Quote
Old 1st December 2010, 03:48 PM   #7
diyAudio Member
 
Miniwatt's Avatar
 
Join Date: Nov 2004
Location: Den Haag
Which tube are you using?
  Reply With Quote
Old 1st December 2010, 04:13 PM   #8
no gas is offline no gas  United States
diyAudio Member
 
Join Date: Jul 2010
Location: Los Angeles
And all this time I thought R2 was the little droid in Star Wars!
__________________
My stuff: MC30, MC225, MX110, PAS3, ST-70, RH-84, HK A224 and a lot of parts waiting for time.
  Reply With Quote
Old 1st December 2010, 04:49 PM   #9
diyAudio Member
 
Join Date: Oct 2009
Location: Brunei
I have some 6n16 submini's as well as some 6n2p's...

I will try to use 6n16 first, but havent done the calculations yet as to gain.
  Reply With Quote
Old 5th December 2010, 07:23 PM   #10
diyAudio Member
 
Join Date: Oct 2009
Location: Brunei
Allright, so I have done the math, but not sure of some things.
img31.gif

1. The value of R2 seems very high, and does not fit with your role of thump R1/R2=gain. I have calculated it using the formula on the aikenamps website (Rf = ( ((Ri+Ra-(Ri*A))*Acl)-Ra ) / (A-Acl).

I will use 2 parallel tda1541, so i/v converter of 28R is appropriate. That means I will be looking for A=12.4=Vout/Vin to get to 2Vpp on the output.


2. I was wondering about the 2mA 'DC' offset that the tda produces. In this setup, will that be present on the output? as there is no cap to block dc coming from the grid.

BTW the 6n16 datasheet is here

Thanks for the help!!

Last edited by studiostevus; 5th December 2010 at 07:36 PM.
  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
Bride of Zen r2 zei Pass Labs 0 4th July 2007 07:43 PM
OTL for Raven R2 ackcheng Tubes / Valves 4 8th July 2005 04:22 PM
OTL for Raven R2 ackcheng Multi-Way 0 3rd April 2005 03:47 PM
looking for driver for 2-way with Raven R2 BrianGT Multi-Way 2 14th January 2004 09:04 AM
Resistor R2 and Zen TikiGod Pass Labs 3 6th September 2002 04:37 AM


New To Site? Need Help?

All times are GMT. The time now is 02:11 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