RJM Audio Sapphire Desktop Headphone Amplifier - Page 8 - 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 21st March 2012, 01:14 AM   #71
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
This is a recent build from someone, not me. There are actually two different headphone amplifiers in the case, one of them is the Sapphire.

It's just such a nice example I felt I had to share.
Attached Images
File Type: jpg ron2.jpg (635.7 KB, 558 views)
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 6th May 2012, 01:34 AM   #72
diyAudio Member
 
dimkasta's Avatar
 
Join Date: May 2010
Location: Athens
Richard can the current Saphire version still be biased to act as a preamp?
Would you suggest such a test?
  Reply With Quote
Old 6th May 2012, 09:18 AM   #73
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
Yes, all you need to do is change the resistor values in the diamond buffer section to the ones listed in the B-board BOM. I can give you the details. You can leave off the heatsinks, they wont be needed.

The question lately occupying my mind is whether the circuit is sufficiently low noise.

My Sapphire amp, configured for headphones, has an input referred noise of 58 nV/sqrtHz. That's higher than the 8 nV/sqrtHz of the OPA134 op amp used in the input stage, so the diamond buffer is contributing to the output noise. Operating at reduced bias the output noise should be reduced, but even as-is it would be quiet enough as a high-quality pre-amplifier.
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 22nd May 2012, 11:48 PM   #74
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
Default Ceramic bypass capacitors

A significant improvement in sound quality can be obtained by bypassing the electrolytics near the diamond buffer with 0.1 uF ceramics. For more details, see my blog. It applies to both the B-board and Sapphire.

I will send caps to anyone who bought Sapphire (and B-board) boards/kits from me. Please contact me.

Not only does the top end become significantly less "edgy", but overall the background noise seems to be reduced. I had some trouble with RFI interference when I used my Sapphire with my desktop computer. That's gone now.

Why does it make such a difference? Well, I suppose the simple answer is that the diamond buffer has a bandwidth of 4 MHz or more, well in excess of the effective range of electrolytic capacitors. In principle there's no signal out there, but apparently it can pick up HF garbage which gets converted down to treble hash when not properly bypassed. I really not sure of the exact mechanics. I thought I would be safe by keeping the buffer out of the op amp feedback loop. Apparently I was wrong.
Attached Images
File Type: jpg DSC_1366 1280.jpg (288.6 KB, 422 views)
File Type: png pcb-sapphire-14s1-brd-bypass.png (37.8 KB, 376 views)
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 26th May 2012, 01:46 AM   #75
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
Yesterday I replaced a small SMT-based 24 position attenuator with this Takman 24 position attenuator. Both from eBay. The trick was the faceplate was predrilled for 1/4" while the new attnuator was a 3/8" unit. The lock pin is also further off center.

Some creative work at the drill press and the new attenuator is properly fixed to the faceplate, as shown. It's a bit stiff : the small, smooth volume not means it's hard to to turn, but the sound is excellent. I was not impressed with the SMT unit, though since it was all of $5 I suppose I can't complain too loudly. Muffled and dull. This Takman stack, I'm in love with.
Attached Images
File Type: jpg DSC_0179 1280.jpg (235.8 KB, 360 views)
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 30th May 2012, 12:23 PM   #76
kffern is offline kffern  Australia
diyAudio Member
 
Join Date: May 2006
Location: Perth
Send a message via Skype™ to kffern
Hi RJM,

The only thing about my Sapphire I'm not happy with is the volume control. I think I used the same pot as you did and can't find the right volume level. Its never just right and too big a change between clicks. I had planned on putting a LDR pot I finally had working, but by the time I installed it, it stopped working and fitting a seperate power supply was difficult in my case.

I'm looking for a new pot and spotted the Takman on ebay just a few days ago.
I'd like to know how it goes and would be interested in any cheapish alternatives. Have considered and Alps RK27 20K on ebay.

Thanks for the cap suggestion. I'll see if I have any in the stash you sent me or try and get some locally at RS supplies.

Regards,

kffern
  Reply With Quote
Old 31st May 2012, 03:04 AM   #77
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
Hi Kevan,

I have a several hundred bypass caps on hand, please let me know if you need a set.

After some thought, listening, and general messing about, I realized it is a good idea to also bypass the op amp socket, as shown below. Otherwise the op amp ends up "bypassed" by the caps near the transistors, a poor arrangement that degrades the sound.

With the five bypass caps in place, OPA134>NE5534, though the NE5534 is perfectly fine.

As for the volume control, with the HLLY case I had to do some surgery to get it to fit, and the switch is too stiff to be comfortable with the small radius of the volume knob. For the actual level control, though, it's great. I'm typically listening at position 10-12 (gain 12x, HD-600s), at those settings its 2dB per step, more than fine-grained enough for my needs anyway.
Attached Images
File Type: png pcb-sapphire-14s1-brd-bypass.png (40.6 KB, 304 views)
__________________
RJM Audio (phonoclone.com / G+)

Last edited by rjm; 31st May 2012 at 03:12 AM.
  Reply With Quote
Old 31st May 2012, 03:15 AM   #78
jtktam is offline jtktam  Canada
diyAudio Member
 
Join Date: Apr 2009
Location: Toronto, Ontario, Canada
Blog Entries: 17
richard,

can you post pictures of the opamp bypass?

-joe
__________________
our diyaudio forum - post your questions here
Audio Poutine - full web site coming soon
ODAC/O2 parts or assembled - Google spreadsheet
  Reply With Quote
Old 31st May 2012, 03:23 AM   #79
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
I'm kicking myself for not snapping a photo of it last night.

Pins of the socket stick out underneath the board right? I just soldered a cap across pin 4 and 7.

I "sketched" the arrangement in the doctored photo below.
Attached Images
File Type: jpg DSC_1366 1280 hack.jpg (310.0 KB, 136 views)
__________________
RJM Audio (phonoclone.com / G+)
  Reply With Quote
Old 8th June 2012, 05:21 AM   #80
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
Blog Entries: 98
Default The whole enchelada

A high res photo of my Sapphire after all the recent changes, for reference.
Attached Images
File Type: jpg DSC_1580 2k.jpg (719.4 KB, 171 views)
__________________
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 05:21 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