Go Back   Home > Forums > >

Headphone Systems Everything to do with Headphones

RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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
Old 25th November 2016, 09:03 AM   #1001
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
Two transformers 15W (2х12V, 0.55A) will be enough?

More than enough, sure.

Can I use a single transformer 40W (2x12V, 1.5A) and rectifier circuit in the picture?

Half wave rectifier. Not really ideal. Better to use full wave rectifier and power both boards from the common output.

I have DC voltage (0.015V and 0.01V) at amplifier output. It is within the norm?

Yep. This is excellent, actually.

OPA134PA has Offset Trim. This adjustment will work?

There is no need to trim, but yes, if you want to add the external components and connections needed, you can do it. There's some posts from disfunctionalshadow (I think it was) somewhere down in this thread where he does exactly this.

PS/aside: 1000 posts in the Sapphire amp thread? Wow. I guess I've been hammering away at this for that long, hey?
__________________
RJM Audio | phonoclone.com

Last edited by rjm; 25th November 2016 at 09:06 AM.
  Reply With Quote
Old 27th November 2016, 08:51 AM   #1002
Sarius is offline Sarius
diyAudio Member
 
Join Date: Nov 2016
rjm, thank you.
  Reply With Quote
Old 26th December 2016, 01:16 PM   #1003
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
Default Sapphire 4 [Unity H]

The next iteration of the Sapphire headphone amplifier is a part of Project Unity. It's going in a different direction than the Sapphire 3, and as such the older version will remain current for the foreseeable future.

Sapphire 4 aka Unity H drops the voltage regulator from the boards and replaces the op amp with a discrete current feedback amplifier. The parallel output transistors are replaced by a single pair of BD139/140 [Q19,20 in the schema below, which are modeled as BC327,327].

Boards will be unveiled shortly. For the moment, here's the basic circuit;
Attached Images
File Type: png unity H.png (73.0 KB, 566 views)
Attached Files
File Type: asc pre11 unity H.asc (5.7 KB, 10 views)
__________________
RJM Audio | phonoclone.com

Last edited by rjm; 26th December 2016 at 01:20 PM.
  Reply With Quote
Old 27th December 2016, 12:23 AM   #1004
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
Boards done.

The idea is the boards are dual-purpose. The headphone amp version changes a few resistors and uses the larger TO-126 transistor Q13H and Q14H with a small heatsink rather than TO-92 Q13,Q14. It runs at 50 mA bias.

The gain is adjustable by setting R2,R3. Gains from 3 dB to 20 dB should be do-able, and possibly 30 dB with a couple of tweaks. I'll do up a table in the BOM showing what values to use for the desired gain setting.

The voltage regulator is separate. This one should work nicely.
Attached Images
File Type: png pcb-unity-10b-brd.png (15.9 KB, 553 views)
File Type: png pcb-unity-10b-sch.png (19.6 KB, 556 views)
Attached Files
File Type: asc Unity 10a (H).asc (5.7 KB, 8 views)
__________________
RJM Audio | phonoclone.com

Last edited by rjm; 27th December 2016 at 12:25 AM.
  Reply With Quote
Old 27th December 2016, 02:09 AM   #1005
mlackey is offline mlackey  United States
diyAudio Member
 
Join Date: Mar 2013
Quote:
Originally Posted by rjm View Post
Boards done.
I'm in.

Any provision for upping the quiescent in the TO-126 pair? Would that require a bigger Q11-Q12 pair? If so, forget I asked.

Please post back when things are ready to go.
  Reply With Quote
Old 27th December 2016, 02:28 AM   #1006
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
How much do you need?

The ratio of R11/R17 controls the current multiple, so its just limited by the need to heatsink the transistors and supplying sufficient current to drive them. 100 mA or even 200 mA can be set just by changing a couple of resistors. Device dissipation climbs to 1 W and 2 W respectively. The output transistors can be folded back and screwed down to the chassis or metal block, either vertically or horizontally, for better cooling.
__________________
RJM Audio | phonoclone.com
  Reply With Quote
Old 27th December 2016, 03:45 AM   #1007
mlackey is offline mlackey  United States
diyAudio Member
 
Join Date: Mar 2013
Quote:
Originally Posted by rjm View Post
How much do you need?
How much do I need? Probably no more than the design calls for. How much do I want? Well, now...

It "would be nice" would be to run the output stage in class A. Based on what I've read the consensus seems to be 100ma, give or take. I'm not quite sure how that is arrived at, and (as with all things) is open for discussion. My head tells me that because of the low voltage/current involved in a headphone amp an AB output stage probably stays in class A most of the time, but my heart says not just no but heck no, give me pure class A all the time. To keep ying and yang balanced, I'd say class A if it's reasonable.
  Reply With Quote
Old 27th December 2016, 04:26 AM   #1008
rjm is offline rjm  Japan
Richard Murdey
diyAudio Member
 
rjm's Avatar
 
Join Date: May 2004
Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
At the specified 50 mA the output stage is expected to remain in class A with a considerable margin of safety.

But it all depends on how sensitive the headphones are, what the impedance is, and how loud you want to go.

For your info, my design specification for this is 15 mW minimum class A output 16-300 ohms. This requires a minimum bias current of 28 mA and voltage rails of +/- 6 V and will bring a set of headphones with a typical sensitivity of 95 mW/dB to at least 107 dB. For 60 ohm headphones the output stage delivers 60 mW and 112 dB.

I'd recommend proving to yourself you actually do use more before making changes, you might be surprised to learn you never actually crack 1 mW.
Attached Images
File Type: png power estimate.png (71.2 KB, 532 views)
__________________
RJM Audio | phonoclone.com

Last edited by rjm; 27th December 2016 at 04:42 AM.
  Reply With Quote
Old 27th December 2016, 05:21 AM   #1009
mlackey is offline mlackey  United States
diyAudio Member
 
Join Date: Mar 2013
Quote:
Originally Posted by rjm View Post
For your info, my design specification for this is 15 mW minimum class A output 16-300 ohms. This requires a minimum bias current of 28 mA and voltage rails of +/- 6 V and will bring a set of headphones with a typical sensitivity of 95 mW/dB to at least 107 dB. For 60 ohm headphones the output stage delivers 60 mW and 112 dB
My favorites are Denon D2000s, 25R, 106dB/mW, 1800mW max input. With 15mW min across 16-300R seems like plenty to drive 25R well over 106dB, and I'm not interested in that. At all.

I think I've created much ado about nothing.
  Reply With Quote
Old 27th December 2016, 05:24 AM   #1010
Luke is offline Luke
diyAudio Member
 
Join Date: Sep 2001
Hi i like my sapphire 3, tempted to try this. Would jfets work in front end?
  Reply With Quote

Reply


RJM Audio Sapphire Desktop Headphone AmplifierHide this!Advertise here!
Thread Tools

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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
RJM Audio Sapphire Headphone Amplifier rev14a1 kit rjm Group Buys 17 10th February 2021 09:38 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 06:52 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki