Configure Stereomour for headphones?

[HF9]

How difficult would it be to configure the Stereomour for headphone duty? I was thinking particularly with a pair of 45s.

[Doc B.]

Physically it's not too challenging, you just add a headphone jack and wire it to the speaker outputs. However, the Stereomour uses AC heaters and at around 1mV of hum it may be too noisy for your taste (it was not intended to be used as a headphone amp and I have not tried it). PJs trick of adding 120 ohm resistors in series with the jack as used in the SEX amp might help reduce the hum in the Stereomour if it is not too intrusive to begin with, but you are going to have to try it with your headphones to be sure.

The Crack, SEX amp and Paramount are all quiet enough to use with headphones as-is. I use Paramounts with AKG K1000s and the DC heated filaments in those amps are very quiet.

[balancedtriode]

im very interested in being the test subject for this can some 1 please give me step by step instructions on how to do this?
thanks

[Doc B.]

I'm a pretty firm believer in the "give a man a fish" notion. ( you know - "Give a man a fish and you feed him for one day. Teach a man to fish and he'll be out on the boat every weekend getting trashed on Bud.")

So I'll give you the general stuff you need to know and I think you can probably take it from there.

A headphone jack is a stereo 1/4" phone jack. That has a tip, a ring, and a sleeve contact that correspond to the contacts on the TRS plug that goes into it, hence the common terminology of TRS. You can google TRS plug and see a zillion pics of this. The terminals will probably be labeled on the headphone jack you choose, but even if not you can figure the connections out - tip is at the tip, the ring is the middle contact and the sleeve is the one closest to the mounting nut. You connect the black (-) speaker binding posts from both channels to the sleeve terminal, aka "Common". The tip terminal connects to the left channel red (+) speaker binding post. The ring terminal connects to the right channel red (+) speaker binding post. If you want to try the 120 ohm resistors, they simply go one each between the left red post and the T terminal and the right red post and the R terminal.

You can either drill a hole, mount a chassis mount headphone jack and wire it to the binding posts under the chassis, or you could use an inline stereo headphone jack and connect wires to it that could connect to the binding posts like a regular speaker cable. If you do that it might be worth putting banana plugs on the ends of the wires for an easy connect and disconnect.

[Dr. Toobz]

Doc, is 1mV hum even that intrusive? I thought most amps available by other manufacturers were nowhere near that quiet. A hybrid tube/SS amp I had once featured a headphone jack and audible hum, which I would have guessed was well above a millivolt; more like 20mV! When the music played, you couldn't hear the hum, however.

The S.E.X. amp is quoted as having an 83dB SNR. What does that end up being in terms of mV of hum in the signal? (I can attest to the absolutely black background of the S.E.X. amp over cans and speakers). Perhaps the OP would be best looking at the S.E.X. amp first.

[Paul Joppa]

SEX runs around 0.3mV hum. You can get down to 2mV with a 2A3 on AC heaters usually, and a good old-stock 45 might get as low as 1mV.

[lolitsluis]

I was wondering if there had been any progress on adding a headphone jack to the stereomour

[sbelyo]

I have several pairs of 45's that were slated for a Tubelab SE.  I was going to build a headphone amp with it, but now I'm considering this amp instead.

This brings me to my question.  For that build I ordered custom OPT's with Headphone impeadences from Electra-Print.  They're 5K Primary @ 65ma 3W  Secondaries are 32, 120, 300, 400

would those OPT's work with the Stereomour for headphone use?

[Doc B.]

As you increase the impedance of the output taps the step down ratio of the transformer decreases, thus increasing the noise level in the headphone. This amp has AC heaters and is not intended as a headphone amp as it may not have a satisfactory noise floor in that application. Our transformers are designed for parallel feed and I don't know if the Electraprint model that you are speaking of is. I also don't know what size the transformer is so I don't know if it would fit. Jack would probably be the guy to ask if his transformer will work in our stuff.

We are looking into a transformer output headphone amp that would have multiple taps at higher impedances, but I can't say when that product will be ready. It would not be possible to adapt it to 45 tubes.

[sbelyo]

Thanks Doc...

The OPT's were single ended output.  I believe that's different than parallel feed.  I forgot about that part.

I know for sure they wouldn't fit, and it doesn't look they would work either.  I think I'll just sell them

[Paul Joppa]

FWIW, On the long-term radar I have an idea for a shunt regulated 45 amp with DC heaters, which could make a dandy little headphone amp.

[sbelyo]

That sounds good.  I think I'll hold onto the opt's and the tubes.  It'll be the better part of the year before I could build anything this big anyway

[Dr. Toobz]

I know this thread is old, but...

Still curious as to whether anybody has been brave enough to try the Stereomour with headphones (esp. those running 45 tubes vs. 2A3's). One thing that's honestly held me back from biting the bullet is that if I replace the SEX amp on my rack with a Stereomour, I lose the ability to listen to LP's with my headphones, or my Squeezebox, etc. My "main rig" definitely needs a headphone capability. Would 1mV of hum through a 5k-8 transformer with a 120 ohm series resistor really be that intrusive?

[Paul Joppa]

The reason that the SEX amp has DC on the heaters is that, even with indirectly-heated cathodes, there was too much hum for headphones using AC. Since this was to be our most affordable, entry level amp, we did not want to add the cost of DC heaters, but in the end decided that having the headphone capability was worth the added cost.

This was more than seven years ago, and I don't remember what the measured hum was, but it was pretty low. Just had to be lower for headphones. We did a lot of listening.

[Dr. Toobz]

The Crack uses AC heaters (albeit with IDHT tubes, just like the SEX). Is the lack of hum in that circuit due to the low output power (30mW?) in comparison to something like the SEX or Stereomour (2W or more)? The Crack is even quieter than my SEX amp over my HD650's.

Still hoping you guys will come out with the "ultimate" integrated amp: something that looks like the SEX amp, but with more inputs, a bit more power, and DHT's instead of dual triodes. If the Stereomour had DC heaters, that would be exactly the ticket, but I understand how that adds to the cost and complexity of the amp, not to mention that it poses additional engineering challenges with the power transformer, etc.