SEX as preamp? Running out of steam on speakers.

[Grainger49]

I had a hard time with Klipsch Forte's and SET's. My Fostex 206 in a passive radiator box is currently my fave speaker with the SEX amp. I think you could get good volume out of them in a large room.

Amen, Brother!

There are a lot of good single driver/horns out there.  You just haven't found them.  

I am composing a long return PM and should be finished later.  But, a properly designed single driver with a sub )and a super tweeter if you are old like me, and I don't think that is the case) can be extremely satisfying!

[Grainger49]

If you want a high efficiency, full range speaker then check out this kit:

Rob, beautiful pictures.  I will check them out later.  There should be a lot of examples of good systems out there and you have supplied an excellent example.

[Dr. Toobz]

Thanks for the responses! Maybe I will look into the single-driver thing again, if I can find somebody to make me cabinets (or buy the wood pre-cut). Perhaps the limited exposure I had with a friend's Fostex speakers was not indicative of the genre overall. I'm thinking that if I go with something "whizzer-less" (like the sigma variants) and use a supertweeter for 10kHz and up, maybe that will give me the sensitivity I need, plus a warm, present sound while not compromising on the top end.

I'm not very old, being in my early thirties - so my hearing still seems to be good to about 15 or 16kHz at normal listening levels. Anything above is definitely gone - I used to be able to hear up to 19 or 20kHz well into my twenties, but my hearing is starting to get worse. Whizzers always have sounded weird to me, though I suspect it won't be long (10  or 15 years, perhaps) before they sound like supertweeters!

[Dr. Toobz]

Well, I recently came to an interesting realization when digging out my old Marantz SS amp and hooking up some of my Klipsch speakers. The S.E.X. amp's 2W output doesn't seem to be the problem, and perhaps the high Z-out isn't either. Listening carefully, I noticed that the S.E.X. bass frequencies (really, anything from 100Hz downward) are what is "running out of steam" at 50-100% volume, which is causing my speakers to sound thin and tipped-up in the higher midrange and treble. Mid and high frequencies are LOUD at 2W, even on a pair of 92dB speakers I have (due to the wood floors, probably). It's the lower stuff that sounds feeble, which causes me to want to turn up the volume knob.

While my old Marantz (1060b) claims a damping factor of 20, I think the fact that it seems pretty flat down to 20 or 30Hz is what balances out the sound more so than any improvement from better woofer control. If impedance matching were the sole issue, I'd be getting boomy, flabby bass, not a reduction in anything below 80 or 90Hz. I seem to recall Doc saying that the Specos start to roll off around 100Hz and hit their -3dB point around 50Hz (and I think that was at 1W output, not the core-saturating, pot-all-the-way-open levels I tried).

In short, I now understand why the MQ upgrade is so recommended! It sounds like better irons and coupling caps may balance out the sound on my current speakers, requiring less volume. I'm therefore going to invest there first before throwing out my current speakers (or demoting the S.E.X. to pre-amp status). It's funny how much you learn by going through this process - I didn't understand how C4S boards could possibly improve the stock S.E.X. until installing them, and up to now, I never bothered to think about the limitations of cheap OPT's at lower frequencies.

[Paul Birkeland]

Your realization is quite correct.  The Speco transformers work very nicely in the circuit, and some steps have been taken to really squeeze every inch possible out of them, but in the end they don't quite have the primary inductance to really grab the low notes like a higher priced transformer.  Whenever the Stereomour transformers are finalized, it is possible that they will go in the SEX amp in place of the Specos, in which case the bottom end ought to improve quite a bit on loudspeakers.  Until then, the MQ upgrade is a great way to go!

[Paul Joppa]

Just thought I's mention, it's the plate choke as well. Stock is about 30 henries, or 3.75 henries per kOhm of output transformer impedance. The Stereomour iron will be 35 or 40 henries - nearly 5.0 H/k. The MQ choke is 50H, 6.25H/k.

The Speco is an interesting study in what you can get. At saturation the maximum inductance is achieved, which is about 100 henries. This happens at 40Hz, 2 watts (30 Hz 1 watt, 20Hz 0.5 watt). At 1v out (1/8 watt) inductance is still quite large, 30-50 henries, and bass is extended to -3dB at 27Hz. At small signals its inductance is around 10 henries and the bass extension suffers. So it has pretty good bass at moderate levels with most of the music, with some loss of bass at very small signals and some distortion of the deep bass when near saturation.

My limited measurements indicate the Speco is built on ordinary silicon steel. The MQ is not only larger, it uses grain-oriented silicon steel and should be good for at least another octave of bass before saturation, with no significant falloff for small signal levels.