Adding headphone out to SP-8

I recently built an sp8 in an oversized chassis, and I have some room inside and would like to add a headphone out.

I use 32 ohm grado headphones.


From what I have seen online, the sp8 has an output impedance of 3500 ohms (? not sure if this is correct).

Would this be as simple as getting a transformer to go from 3500 to 32 off of the main output? I am thinking I could install a switch on the front, and run the main out to the switch, one side of which would go to the main outs, the other side to the transformer and from there to the 1/4 inch stereo jack.

I have only picked out transformers for building amps, so I am not sure exactly what I would need to do this, or if it would sound good.

Is there a simple circuit I should look into? I thought about building a cmoy or something like that and installing it after the balance control with a switch similar to the above... I know this would give me hum problems because this circuit uses a virtual ground, and I havent had time to do the research to find out how to convert the circuit to normal ground. I am thinking of using the 12vdc line off of the sp8 transformer.

I know I could just build an external headphone amp kit, but that would be too easy now wouldn't it?

any ideas?

Here's a link to what I've been using for the last 9 years: http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=bender_prj.htm I built it as a stand alone unit, but if you have space you could build it into your preamp chassis. I use 300 ohm Sennheiser headphones, but I've also used it successfully with 32 ohm headphones. IMHO it's a great sounding headphone amplifier!

Best Regards,
Charlie

I've got a couple of small tube headphone amps I'd sell cheap if anyone is interested, PM me

Luddite wrote:Here's a link to what I've been using for the last 9 years: http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=bender_prj.htm I built it as a stand alone unit, but if you have space you could build it into your preamp chassis. I use 300 ohm Sennheiser headphones, but I've also used it successfully with 32 ohm headphones. IMHO it's a great sounding headphone amplifier!

Best Regards,
Charlie

I have a 16x16 chassis, so there is a good bit of room. Would putting an additional power transformer in the unit be asking for hum issues?


What is the impedance of the SP8 output?

I could also avoid that issue by tapping the output before the linestage to use with a headphone amp...

I would like to do this relatively cheaply, which is why I was looking into the cmoy type units

The tube one does look interesting



how many amps is the SP8 transformer able to handle on the B+ and heater taps?

if you've got a VTA SP8, contact me directly to answer your questions, if it's an Audio Research that's something else.
I can't tell from your "rockinrob86" if you bought it from me or someone else.
If it's one of my VTA SP8, the output impedance is 1000 ohms, and the power transformer may or may not have enough juice to run
an extra circuit, depending on which one(s) it has in it.
info@tubes4hifi.com

tubes4hifi wrote:if you've got a VTA SP8, contact me directly to answer your questions, if it's an Audio Research that's something else.
I can't tell from your "rockinrob86" if you bought it from me or someone else.
If it's one of my VTA SP8, the output impedance is 1000 ohms, and the power transformer may or may not have enough juice to run
an extra circuit, depending on which one(s) it has in it.
info@tubes4hifi.com

I'm the guy who recently bought the last SP8 board. I was trying to avoid bugging you too much through email

It is a great sounding unit btw, a significant step up in detail and all other metrics. The only downside is it makes the inadequacies of other things stand out, mostly my room, speaker placement, turntable set up and recordings.

The upside is my previous favorite, great sounding recordings sound significantly better!

I have been moving my speakers around some, and am about to go to town on my turntable's setup. I have Klipsch Chorus II speakers, and I think I had too much toe in, adjusting that helped greatly, lessening some treble sharpness and improving the bass.

Mine has the toroidal transformer you guys shipped with my board.

OK, so it's probably the 05T240, which doesn't have enough extra to power any other added circuits