Headphones on Stereomour II

[aragorn723]

Hi,

I'm new to the Stereomour so please excuse the newbie question.  I see some people are running headphones with it, how do they connect?  Couldn't find anything in my search of the forum.

Dave

[fullheadofnothing]

I wrote up a how-to for a simple adapter on the blog a few years ago. The new version of the website software doesn't seem to allow linking to an individual post, but for now at least it's the first on the page: https://bottlehead.com/bottlehead-blog/

[aragorn723]

Cool, I found it.  Guessing this will drive a set of Grado sr125 headphones with no problem?  Would probably use the Stereomour with speakers more, but it's nice to know what the options are.

Dave

[Paul Birkeland]

It's hard to stuff more than about 2V into any Grado headphone I've seen before it gets unbearably loud.  That would be about 1/2W of the 3.5W available from the Stereomour.

I would suggest running the amp at 8 ohms and wiring in a pad between the speaker outs and the headphone jack, with perhaps a 6 ohm R2 and a 2 ohm R3 as shown in the drawing that's attached to this post.  Increasing R2 and decreasing R3 decreases available output but also reduces the noise floor.  Decreasing R2 and increasing R3 increases available output but also brings up the noise floor.  R2+R3 should roughly be equal to 8 ohms.  The effect of adding your headphone's impedance in parallel with R3 typically won't throw off the value enough to be all that important in the grand scheme of things. 

[aragorn723]

Looks simple enough.  Might be a nice sub box project.  Not sure I understand the horizontal lines above and below r2.  Aren't those redundant connections?

Would I have enough volume using the Stereomour into Def Tech Bp6b speakers?  I would use the Quickie to drive the Stereomour, and then into the speakers (they are 91db sensitivity).  My main source is a Turn audio orbit turntable with a Rega fono mini phono preamp.  The room is maybe 250 sqft, and I listen mostly at moderate levels.

Dave

[Paul Birkeland]

I don't know why those lines are there either, I would ignore them and not put them in.

[aragorn723]

How about the volume question?  I found this calculator:

http://myhometheater.homestead.com/splcalculator.html

It tells me that with 91 db speakers, 3.5 watts, speakers 7 get away, with speakers in a corner, the Stereomour will give me 98.9 db.  Sounds plenty loud.  I'm assuming this would be with a cd player that can put out 2 volts?  What kind of db would I get on the analog side with a Grado black cart and Rrga fono mini a2d mkii?

Dave

[Paul Birkeland]

That assumes you have enough signal voltage going into the amp to clip the amp.  IIRC, that is well under 2V to get the job done. 

If you knew the output voltage of the Grado black and the gain of the Rega Fono mini, then you would know the output voltage. 

[aragorn723]

Output voltage of the Grado Black is 5 mv.  Rega lists input sensitivity (not sure that's the same thing) as 5 mv for 500 mv output.  Sounds like I'm getting 500mv out?  How could I figure out the decibels from this?

Dave

[Paul Joppa]

It's not simple, unfortunately. CD player output is the instantaneous peak, which is (in traditional high-qiality recordings as made in the fifties and sixties) about 14dB greater than the peak loudness as measured with a sound level meter or a VU meter. Cartridges are measured at a needle velocity of 5cm/sec, which is approximately the peak meter loudness.

That 14dB difference is called headroom. In modern recordings, the headroom may be as low as 1dB or as great as 20dB, and the better cartridges will in fact handle 20dB above their rated 5cm/sec value, depending on the choices of the recording engineer and/or their marketing department.

Furthermore, SETs generally overload quite gracefully, and can tolerate as much as 6dB of clipping on instantaneous peaks before the distortion becomes obvious - depending on your individual sensitivity to distortion.

And room acoustics will result in a +/-6dB variation in loudness for the same speaker/amp combination for more-or-less conventional domestic listening rooms.

It's a jungle out there!

FWIW, most people listen at 82dB peak meter loudness, with a range of +/- 10dB or so.

[aragorn723]

Don't know if this helps, but I used a smartphone app today to measure my listening level.  Average spl was 70, with some peaks in the low 80s.  Think the Stereomour can hit an average spl of 70 with my vinyl setup?

Dave