Add headphone output to preamp

whitelabrat · 24th January 2008, 02:53 PM

I've currently got a pair of headphones rated for 250ohms. Nothing fancy (Koss Pro4aa). I'm wondering what changes are needed to add a headphone output to my preamp. Output caps such as those using in Morgan Jones' design?

http://headwize.com/projects/showfil...=cmoy5_prj.htm

I've attached a schematic of one channel of the preamp.

ErikdeBest · 24th January 2008, 07:01 PM

Hi

In theory, yes, add a large valued output cap parallel to C4 and you could use a headphone. The problem is distortion: although your headphones have a relatively high impedance, asking a 12AU7, even in CF, to drive it is asking for high distortion figures.

One possibility is to make a WCF of that output stage, just as in the project by Morgan Jones you linked to. But that's not that simple, as you would need another tube, which means another hole in the chassis, higher filament current...

What you could do is get rid of the second 12AX7 stage's that is, IMHO , superfluos anyway, and use the hole and filament current for another 12AU7 to make a WCF. And as you are at it, change the 12AU7's for E88CC's... But that is lot of reworking...

Good luck! Erik

AndreasS · 24th January 2008, 08:36 PM

Hello whitelabrat,

you can use this schematic for a headphone with little modifications:

Take the feedback path from the output of the CF, in the best way connect the cathode of V1B to a tap on R11 and omit C2, R7, R8 and R2 (a "ring of three").

Regards Andreas

24th January 2008, 07:01 PM	#2
ErikdeBest mostly thinkerer diyAudio Member Join Date: Mar 2003 Location: Zürich	Hi In theory, yes, add a large valued output cap parallel to C4 and you could use a headphone. The problem is distortion: although your headphones have a relatively high impedance, asking a 12AU7, even in CF, to drive it is asking for high distortion figures. One possibility is to make a WCF of that output stage, just as in the project by Morgan Jones you linked to. But that's not that simple, as you would need another tube, which means another hole in the chassis, higher filament current... What you could do is get rid of the second 12AX7 stage's that is, IMHO , superfluos anyway, and use the hole and filament current for another 12AU7 to make a WCF. And as you are at it, change the 12AU7's for E88CC's... But that is lot of reworking... Good luck! Erik __________________ my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Headphone amp circuit for preamp use.	marchel	Solid State	2	6th February 2008 11:11 PM
Jaycar Preamp as a headphone amp?	Fiat1	Headphone Systems	2	19th September 2005 07:23 AM
Headphone Output to GC amp	StalfoS	Headphone Systems	10	29th March 2005 01:08 PM
Passlabs preamp as headphone amp- need help	needtubes	Headphone Systems	3	16th February 2004 10:30 PM
What output Z for headphone amp?	jeffreyj	Headphone Systems	29	13th August 2003 11:28 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

24th January 2008, 08:36 PM	#3
AndreasS diyAudio Member Join Date: May 2005 Location: near Duesseldorf	Hello whitelabrat, you can use this schematic for a headphone with little modifications: Take the feedback path from the output of the CF, in the best way connect the cathode of V1B to a tap on R11 and omit C2, R7, R8 and R2 (a "ring of three"). Regards Andreas