Buffer help needed - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 2nd April 2013, 04:28 AM   #1
diyAudio Member
 
Join Date: Mar 2013
Default Buffer help needed

Hi all.
I am fairly new to DIY audio, so please bear with me!

I have decided to tackle a preamp as my first design/project. The idea is to have a ladder-type step attenuator going into an opamp buffer. The attenuator, which I already have, is 10k. I'm planning on using a LM4562 opamp in the buffer.

Hifi setup is:
Arcam Alpha 7 CDP (Zout = 150R) -> preamp -> Rotel RB-1070 (Zin = 33k)
All cables are 65 ohm, 67pF coaxial.

I'm posting the schematic I've done for the buffer (one channel shown). I wonder if I could prevail upon your collective wisdom to answer a few questions.

1. Does the 47k input resistor interact with the attenuator in terms of Zin for the preamp as a whole?
2. Is the 100R output resistor necessary? I've basically included it because other schematics I've seen have something similar. I'm assuming it's there for drive current reasons. Opamp Iout is rated at 26mA into 600 ohms.
3. Should I use coupling caps on the outputs? Opamp offset voltage is 100uV max.
4. Is the buffer even necessary with the 10k attenuator?
Attached Images
File Type: jpg Buffer.jpg (115.5 KB, 62 views)
  Reply With Quote
Old 2nd April 2013, 09:48 AM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
A buffer is necessary if the capacitive load on the 10k attenuator results in impared HF performance.

The 100r on the output is a good addition.
The 100nF decoupling must be on pins 5 & 4. Are you pin numbers correct (8+ & 4-)? On a quick scan, I could not find the decoupling recommendation.

The sch is an inverting amplifier.
The gain is 47k/[47k+Rs] = 1 = +0dB if the Rs is zero. Added Rs give extra attenuation in addition to the attenuator.
The Zin is 47k // to cable capacitance.
The output offset will be much bigger than 100uVdc. This is because the input offset currents see different resistances @ the +IN (0r0) and -IN (47k//47k = 23k5) inputs. expect <1.6mVdc
__________________
regards Andrew T.
  Reply With Quote
Old 3rd April 2013, 01:05 AM   #3
diyAudio Member
 
Join Date: Mar 2013
Thanks AndrewT.

First of all - yes, I had the pin numbers screwed up. My bad!

Thanks for your reply. I've learned quite a bit from it. I'll have to go back to the drawing board I think - and read up some more on exactly how these opamp doodads work!
  Reply With Quote
Old 3rd April 2013, 01:49 AM   #4
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
There are a couple of good books on op-amp applications such as "Op amps for everyone" and sections in the audio electronics texts like Douglas Self's on Small Signal Audio Design. If you don't wan't to spend on books or rely on the device application notes, this download of Walt Jung's classic (or chapters from it) might suit you. Good reading!
ADI - Analog Dialogue | Op Amp Applications Handbook
__________________
regards
  Reply With Quote
Old 3rd April 2013, 02:21 AM   #5
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
TI's book is also online
http://www.ti.com/lit/an/slod006b/slod006b.pdf
__________________
regards
  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
ECC88 tube buffer NEEDED ! vmed_cha_gr Tubes / Valves 25 14th December 2011 04:01 PM
SONOS + DAC + 125ASX2 Icepower - buffer needed? Simes123 Class D 1 23rd October 2011 05:10 PM
is an input buffer needed for a sallen-key filter? oraz Solid State 2 12th May 2008 07:39 PM
A bass boosted preamp or buffer advice needed Dxvideo Chip Amps 12 27th June 2007 06:54 AM
Discrete X-over Buffer from LC Audio-URL needed Samuel Jayaraj Solid State 4 9th November 2002 07:59 AM


New To Site? Need Help?

All times are GMT. The time now is 10:48 PM.


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