Marsh headphone amp from Linear Audio - Page 34 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

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 3rd July 2012, 08:25 PM   #331
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
@sonidos
I used 1W Panasonic ECG's for the BJT's (available from DigiKey), Vishay-Dale CMF60 for the gain and feedback resistors, and CMF55's for the rest (if the values matched.)
  Reply With Quote
Old 4th July 2012, 12:26 AM   #332
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Thanks for the breakdown on the resistors. Getting close to having my shopping list done. I got the jfets and next week I'll spend some time measuring and matching.
  Reply With Quote
Old 10th July 2012, 01:41 AM   #333
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Waiting for feedback from people who get this built and tell me how it sounds.
  Reply With Quote
Old 10th July 2012, 03:17 AM   #334
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Quote:
Originally Posted by RNMarsh View Post
Waiting for feedback from people who get this built and tell me how it sounds.
Ohh, it's coming!

I spent some time on vacation taking a closer look at the article and some of your comments intrigued me and I'll definitely have some questions. Some things you describe jibe with what one forum member (ex. Nat Semi) discussed with me in a few private emails.
  Reply With Quote
Old 10th July 2012, 05:03 PM   #335
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Default quote on page 32 of LA vol. 3

@RNMarsh

On page 32, I read the following:

"I also preferred the arrangement because the input and the feedback occurred in the same transistor - making the most direct correction."

Forum member audioman54 made a similar comment re. the Nat Semi LME chips (that would be Mark Brasfield who once worked on the LME chips). I had never given it any thought until I read his postings and the same comments in his personal correspondence with me. Many moons ago, I bought Walt Jung's book on audio op amps and read other articles where you see feedback and signal input are separate and so I always thought that's the best way. So your comment caught my eye because it is similar to what he told me.

Are the benefits measurable? Or one of those things where you can hear improvement? Can you expand a bit on this comment and your experience?

Last edited by sonidos; 10th July 2012 at 05:06 PM. Reason: clarification
  Reply With Quote
Old 10th July 2012, 06:38 PM   #336
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
My own work in this area dates back to the 1970's. I was developing toplogy similar to the now current-mode feedback amps at the time. I now call it a diamond amp configuration. It is very common now. I'll get some old schematics and old articles put up here, soon. But if you want the short story history - go to the Headphone amp article in Linear Audio. Too much to duplicate here. Anyway, it was WAY before IC makers started doing it this way and now have many variants.

Boy, I never thought I would be this old that i would be writing about audio history with myself in it. :-) I'll tell you all that if you spend every day and evening and weekends for twenty-five years studying, have no children (1) until late in life and are willing to keep doing this while your spouses (4) walk off.... and have access to the worlds largest technical library and great minds involved in research around you ---- you can far out distance mainstream. But it will cost you. So, I am willing to give what I know and can to help others take a shorter, easier path.

Last edited by RNMarsh; 10th July 2012 at 06:51 PM.
  Reply With Quote
Old 10th July 2012, 07:05 PM   #337
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Quote:
My own work in this area dates back to the 1970's... Anyway, it was WAY before IC makers started doing it this way...
kinda tough when Harris was selling CFA in early '70s, unless "WAY before" was months, weeks?

Walt Jung's History chapter in his (free, online) Op Amp Applications tome is worth reading

Google turns up a 1972 ref to HA2500 second source

many cirucit topologies were implemented in potted modules, hybrid circuits before semi processes allowed fully monolithic impelementaitons
  Reply With Quote
Old 10th July 2012, 07:27 PM   #338
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Quote:
Originally Posted by RNMarsh View Post
So, I am willing to give what I know and can to help others take a shorter, easier path.

Ha! 1 wife and 4 kids for me! That is why I am so farrrrrr behind. I won't catch up.

BTW, I have tried the approach recommended by audioman54 and was pleased that it worked. Your comment caught my eye, along with others in the article. So hopefully I'm not too pesky and receive a big bill from you in the mail. More questions to come. And thanks for the upcoming material.
  Reply With Quote
Old 10th July 2012, 08:20 PM   #339
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
@jcx -

Yes, Walt Jung has tons of great links and pdf's which I have read or skimmed. VERY valuable stuff.
  Reply With Quote
Old 10th July 2012, 08:51 PM   #340
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Default I missread Walt's history re HA-2500

I've poked thru a little more of the history - the HA-2500 is a conventional diff pair input amp

wikipedia credits CFA op amps as dating to 1980's patents - so Marsh could easily have anticipated those patents

but later in Walt's history he shows a 1937 tube amp "CFA" circuit

such series feedback amps became ubiquitous with single polarity input Q bjt amp circuits

I find it hard to believe no discrete bjt amp with complementary/offset cancelling front end was ever made in the prior 2+ decdes of discrete complementary Q availbilty before the fast complementary monolithic "CFA" op amps of the '80s

Last edited by jcx; 10th July 2012 at 08:53 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
FS: Meier Audio Corda Headphone Amp jtwrace Swap Meet 5 29th February 2012 11:34 AM
Histoically significant - Phase Linear audio pre-amp bobcul Swap Meet 0 21st February 2012 08:16 PM
Headphone amp with mixed-in telephone audio krfjr1965 Solid State 3 10th March 2010 03:50 PM


New To Site? Need Help?

All times are GMT. The time now is 08:50 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