RJM Audio Sapphire Desktop Headphone Amplifier - Page 11 - 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 30th November 2013, 09:47 PM   #101
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
I finished up the front plate on my sapphire/J-Mo combo today. Nothing really changed inside the box except that I tweaked the shunt a little and mounted the heatsink for the shunt outside the box just for a little thermal management.

The chassis came from an old marantz cassette deck that had gone to the great tape tangle in the sky and the front is a bit of aformosia (I think). I like timber fronts on equipment. It still looks DIY but is very presentable and I find it easy to do. I can flick the source between the 2 headphone amps with a switch at the back. If having it at the back is an issue I can remount it at the front. But you can only listen to one set of cans at a time and my tendancy is to spend time with the k701 and then flick back to the HD650 for a while... so direct switching isn't all that big a deal I think.

One bad thing did happen - one of the gigawork pots was a bit gammy to start with, and when I tightened it up to the front plate it wouldn't work right at all. I think that there must be a cold joint in there somewhere as sometimes it would work if you squeezed it a certain way etc. Anyway, I stuck an alps rk27 in there until some new pots arrive from ebay. Not exactly the last word in transparency, but it will do for now.

Poor enough pic, but it gives the idea.

Fran
Attached Images
File Type: jpg IMAG0703_1.jpg (60.0 KB, 374 views)
  Reply With Quote
Old 1st December 2013, 10:59 PM   #102
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
That looks really nice Fran. Are you left handed? I have to say I prefer the volume control to the right of the headphone jack, so the cord doesn't block my hand as I adjust the volume.

The other thought I had was re. the selection switch. Really there's little need to have a switch. The line input can drive both volume pots full time, the only penalty is halving the input impedance seen by the source. If that's going to be acceptable you can just connect the input to both pots in parallel, bypassing the switch.

***

@stratus46

Thanks for the link. It's an interesting concept, and I've seen it (or variants) advertised in some few commercial circuits. I'm basically skeptical, based on the old audio axiom "there is no such thing as a free lunch". Adjusting the bias on the fly like that has got to have downsides, though -other than the complexity- they are not immediately obvious to me. I'll look into it though...

Generally speaking for a headphone amp there's no particular advantage to doing it as it is trivial (and costs little) to set the bias such that the output stage runs in class A under any realistic output. i.e. 100 mA or more if you decide that that's what you want. It's just a couple of watts.
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 8th December 2013, 08:16 AM   #103
diyAudio Member
 
jacques antoine's Avatar
 
Join Date: Jan 2013
Quote:
Originally Posted by rjm View Post
There will be 9 sets of boards available, and will do a limited edition kit if the interest is there.
Hi RJM,

I am interested in a pair of boards if you start a group ordering.
Cheers,

Jacques
  Reply With Quote
Old 8th December 2013, 11:41 PM   #104
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
Noted. I'll contact you when I get the boards.

Richard
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 15th December 2013, 12:45 PM   #105
Toaster is offline Toaster  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: South East England
I've yet to build my Sapphire kit Richard, so I'd be interested in the new boards for when I get around to it.
  Reply With Quote
Old 15th December 2013, 11:24 PM   #106
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
I can send you an upgrade pack. Drop me a line.
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 17th December 2013, 07:58 AM   #107
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
Version two up and running on the bench, transplanted into my original Sapphire chassis. As expected my simulation of the bias currents was a bit off. R9,10 should be reduced from the 10 ohms originally specified (giving 230 mA) to something around 6 ohms (100 mA predicted). At 5 ohms I'm getting 70+/-5 mA through the output transistors, stable.

Photos and listening impressions to follow.
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 17th December 2013, 10:14 PM   #108
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
Default Sapphire 14s to 20f upgrade

blog post
Attached Images
File Type: jpg DSC_3577 1000.jpg (398.6 KB, 211 views)
File Type: jpg DSC_3588 1000.jpg (311.2 KB, 204 views)
File Type: jpg DSC_3592 1000.jpg (388.8 KB, 194 views)
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 17th December 2013, 10:38 PM   #109
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Eagerly awaiting your sonic report Richard - those changes look like they could be easily enough done to earlier boards....


Fran
  Reply With Quote
Old 17th December 2013, 11:14 PM   #110
rjm is online now rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 101
Hi Fran, I was just about to email you on this subject. The downside of the transplant is the old version is no longer available for me to compare to, so I was planning on hitting you up for your evaluation of 14s1.

The circuit sounds a bit "gummy" for the first 2-3 days until the electrolytic capacitors shake themselves out. So my impressions of 20f will have to wait until the weekend.

While the 14s1 boards can be modified, it is not trivial: you'd have to cut traces on both the top and bottom of the boards, and wire resistors between pads to connect over the cut traces. If you are up for it I can show you what and where.
__________________
RJM Audio (phonoclone.com / G+)
  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
RJM Audio Sapphire Headphone Amplifier rev14a1 kit rjm Group Buys 12 12th December 2011 07:43 AM
RJM Audio Gainbloc Preamplifier Mk. I rjm Analog Line Level 11 7th September 2011 11:59 PM
Parts for RJM Audio/47 Labs Phoneclone jim rose Swap Meet 0 15th May 2011 06:55 PM
New Desktop Tube Amplifier, 6V6 SE Musik007 Twin Audio 11 6th October 2010 04:23 PM
FS: DIY Cavalli Audio Embedded Hybrid Headphone Amplifier sachi Swap Meet 4 19th May 2010 09:43 PM


New To Site? Need Help?

All times are GMT. The time now is 06:23 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