Marsh headphone amp from Linear Audio

[31697B]

Richard,

Do you live in Cool, which would be pretty close to Auburn?

Jam

As a mater of fact, yes, it is the same place and I am back in Cool at this time.
(530) 885-6809


-Richard

 

[31697B]

It appears that Walt is shutting down his Blog, and all of the documents will eventually be available as archived PDF's. At this point though, the permissions seem to be wrong(and/or non existant) for the archived files on the "Site Pages".

Anyone interested might want to get what they can from his original blog here before its too late: Walt's Blog 2014 | Walt Jung's 2014 Blog and Info Archive

I received a letter from Walt a few weeks ago... he was disappointed that so few people were into DIY audio any more.... and so was going to consolidate everything and drop the blog.

-RM

 

[MrSlim]

I received a letter from Walt a few weeks ago... he was disappointed that so few people were into DIY audio any more.... and so was going to consolidate everything and drop the blog.

-RM

Is he consolidating it on DIY audio? I'm really suprised that he said that so few people were into DIY, hard to tell here.. Mind you a lot of cheap chinese hardware doesn't help.

 

[WaltJ]

Nonsense! just click on the links and see, as I just did

It appears that Walt is shutting down his Blog, and all of the documents will eventually be available as archived PDF's. At this point though, the permissions seem to be wrong(and/or non existant) for the archived files on the "Site Pages".

 

[Carl_Huff]

Walt,

Great to see you here!

But unless I am missing something, this is what I get when I on anything pointed to by your opening page ...

Forbidden

You don't have permission to access /PDFs/Walt's_Blog_2014_About_This_Blog.pdf on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

 

[sonidos]

Appears it was cached. I just got that page too and I went to his home page and clicked the link from there. Try that and it should work.

 

[MrSlim]

Walt, If I go to Waltjung.org and click through to the Archived "Sitepages" link I get the following on all of the PDF links:

Forbidden

You don't have permission to access /PDFs/Walt's_Blog_2014_Classic_Articles_Page.pdf on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

 

[WaltJ]

Pls try it again, starting from the home page (as noted in the signature line below), and click on Site Pages as indicated. Then click on whatever link you wish. They should all work.

I did see it work OK, then I also saw the 404 msg, etc.

However it seems to be all A-OK now. FWIW, this is what I am aiming for in terms of operation.

Walt, If I go to Waltjung.org and click through to the Archived "Sitepages" link I get the following on all of the PDF links:

Forbidden

You don't have permission to access /PDFs/Walt's_Blog_2014_Classic_Articles_Page.pdf on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

 

[Carl_Huff]

Pls try it again, starting from the home page (as noted in the signature line below), and click on Site Pages as indicated. Then click on whatever link you wish. They should all work.

Yes! It works this time. Thank you for making this available

 

[Bibio]

why is there links on a PDF? why not just put the links to the archives on the page. some pdf viewers dont let you click on links from within a PDF.

just sayin.

 

[MrSlim]

Yes! It works this time. Thank you for making this available

I concur..

 

[31697B]

There's a wealth of information on Walt's site. Highly recommended !
Something to make anyone's DIY project better.


-Richard Marsh

 

[31697B]

Here is a good art on matching bipolars:

View attachment trans match.pdf



THx-RNMarsh

 

[31697B]

It was mentioned before but if you do not like to do matching of transistors, you can buy a complete matched set of all transistors from Tech-DIY LLC. This takes a lot of the work/time out of the project. The output devices supplied are 2 each of the -649/669 types.

http://tech-diy.com/Store/MarshHeadphone.htm


THx-Richard

 

[31697B]

It was mentioned before but if you do not like to do matching of transistors, you can buy a complete matched set of all transistors from Tech-DIY LLC. This takes a lot of the work/time out of the project. The output devices supplied are 2 each of the -649/669 types.

Tech DIY Company Store


THx-Richard

Recently, I tried this package of matched transistors and tested it. The results are excellent: All harmonics were well below -100dB. depending on PS voltage and load, the harmonics were typically in the -110-130db areas. Again, using only 2 diode bias; two diode produce 100mA ouput current draw while 3 diodes will double that to 200mA idle in OPS.

So,you can use the matched semiconductor package from Tec-DIY LLC. without worry about the results not being as good. Plus, you can use +/-24vdc PS for greater load driving ability at very low distortion as the output devices are rated for higher voltage. However, the drivers (Vas stage) and OP stage will need greater heat sinking if you do.



THx-RNMarsh

 

[31697B]

Recently, I tried this package of matched transistors and tested it. The results are excellent: All harmonics were well below -100dB. Again, using only 2 diode bias; two diode produce 100mA output current draw;

0= -100dB and 10db/div






THx-RNMarsh

 

[31697B]

So, when do you need to use 3 diode bias string? Well, if your headphones are <100 Ohms, the thd will be higher with 2 diodes and <100 Ohms.
Use three diodes for <100 Ohm headphones to keep the thd at minimum.



THx-RNMarsh

 

[steve jones]

Any new builders to report how the Marsh Headphone turned out?

 

[ammel68]

Here is a good art on matching bipolars:

View attachment 552485



THx-RNMarsh

Nice article Mr. Marsh.

His test circuit matches by Vbe.
Should BJTs also be matched by Hfe, like for the input stage of an amplifier, for minimum offset or is Vbe the preferred way to match them?

Thanks...

 

[31697B]

yes, they should be matched for both ac and dc parameters... Hfe, Idss etc.

I most often use an Atlas tester and sometimes a 'scope curve tracer.


THx-Richard