Class A biasing of opamps - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 23rd October 2002, 08:57 PM   #21
diyAudio Member
Join Date: Jan 2002
Location: Canberra, Australia
I'm planning to use the NE5534 (or replacement) in an MC phono stage hence the desire for low noise.

Eventually, I was planning (funds premitting) that it'll be upgraded to an AD797 or similar with mods where applicable to the circuitry,

As was said previously "pin compatible (sort of)"

At this point it's more in the prototype "will it work" kind of stage and hence I'm not planning of filling it with ultimate level chips and caps just yet.

The very first cheap metalfilm resistors and MKT polyester caps version actually sounds quite well, I was just wondering if the Class-A mod might also improve things.

It's a work in progress

  Reply With Quote
Old 23rd October 2002, 09:02 PM   #22
diyAudio Member
cocolino's Avatar
Join Date: May 2002
Location: Bavaria (south of veal sausage equator)
read over the datasheets, but I couldn't find the difference in the two (627 and 637). Anyone know?
Hello Brian:
difference between 627 and 637:
627: unity gain stable
637: stable in gain =>5
Hope this helps
  Reply With Quote
Old 23rd October 2002, 09:12 PM   #23
mlloyd1 is online now mlloyd1  United States
diyAudio Member
mlloyd1's Avatar
Join Date: Feb 2001
Location: Northern Iliinois
OPA627 has an internal compensation capacitor for unity gain stability.
Given 20 each? You have NICE friends These aren't cheap, thanks to the DI mfrg process.
Originally posted by BrianGT
I have a bunch of opa627 and opa637 that a friend gave me (20 of each). ..... I read over the datasheets, but I couldn't find the difference in the two (627 and 637). Anyone know?
  Reply With Quote
Old 23rd October 2002, 09:14 PM   #24
Electrons are yellow and more is better!
diyAudio Member
peranders's Avatar
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Originally posted by DrewP
I'm planning to use the NE5534 (or replacement) in an MC phono stage hence the desire for low noise.
If you plan to connect a "normal" MC pickup the NE5534 is way too noisy (OK a little bit too noisy). You should look for noise below 1 nV/sqr Hz. You can also use a preamp with a 2SK170 JFET. Check the Pearl phono amp.
/Per-Anders (my first name) or P-A as my friends call me
PA03 LM4780 amplifier group buy, SIGN UP HERE for the group buy 0 boards left. 118 paid.
  Reply With Quote
Old 23rd October 2002, 09:47 PM   #25
diyAudio Moderator Emeritus
jean-paul's Avatar
Join Date: Sep 2002
Location: Germany

OPA627 and OPA637 are probably the best you can get at the moment. 2134 you can't compare to these fantastic opamps.

OPA637 is faster and has a higher slewrate but is, as mentioned before, not unity gain stable.
It's only audio. Member of the non modular PCB design committee
  Reply With Quote
Old 23rd October 2002, 11:18 PM   #26
diyAudio Member
PhopsonNY's Avatar
Join Date: Feb 2002
Location: New York
Default Try the ad 8610 of ad8620

I am sure not all will agree, but I have had excellent success with the new AD opamps as replacements in my SCD player

I/V stage;
Replaced opa2604 with 2*ad8610s with broundog adaptor
(gave smoother mids, less grainy highs and deeper bass)

Mixamp stage (converting balanced signal to unbalanced)
Replaced opa2123 with ad8620
(got rid of upper bass hump and a more linear response)

Buffer/Servo stage (one half of dual opamp did both)
Replaced ad712 with ad8620
(gave a more dynamic response and greater transparency)

I then applied current loading (Biasing into class A) in succession with;
1. 1kOhm r - greater bass articulation
2. 1kohm r with CRD (1mA) - as above, but with smoother mids
3. 100ohm r with CRD/FET (1mA) - as #2, but slightly better
4. 1kohmr with cascoded JFET (1mA then 2mA) - much better than any other option - took a while to break in, but was very linear and articulate with very clean highs... any residual graininess totally eliminated.

I have not done a head to head with the opa627, but others at Head-fi and Headwize have carried out extensive comparisons and the majority consider the 8610/8620 to be much better.
Check out ppl's posts

One thing that comes out of their comparisons is that this is only worth it if the rest of your system is of high enough resolution to distinguish the difference.

Good luck with whatever you choose.
  Reply With Quote


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
biasing opamps in class a matjans Chip Amps 36 20th February 2013 02:16 PM
New class A biasing (with non-switching class AB overflow) Steven Solid State 34 24th March 2007 06:40 PM
low-biasing or high biasing in Class-AB amps Workhorse Solid State 124 18th October 2005 04:45 AM

New To Site? Need Help?

All times are GMT. The time now is 09:29 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2