Wiring headphone jack and speaker outputs for different impedance taps?

[jrebman]

After hering how nicely the s.e.x. 2.1 worked with my Shure IEMs (in 32 ohm mode), I was wondering if it would be possible to wire the headphone jack for 32 ohms, and the speakers for 8?  I'm making the assumption that I would not use the impedance switching board, that there woul be no automatic speaker disconnect when the headphones are plugged in, and that bot the headphone jack and binding posts would be wired directly, but independently from the OPTs.

BTW, Paul, you were right, the 32 ohm configuration on the s.e.x. 2.1 is perfectly quiet on the IEMs.  That is a fine sounding transformer you came up with there!

-- Jim

 

[Paul Joppa]

In a word, no. The arrangement was chosen to minimize the increase in leakage inductance when using fewer turns, so the high frequency extension is not reduced on the lower-impedance taps. This limitation is one of the compromises I made among convenience, cost, and performance. At least it is possible now to get four different impedances, instead of the two in the earlier SEX amp, and with the switches you don't have to unsolder and resolder wires!

The best option for external control would be to move the switches to where they are accessible without flipping the amplifier over and exposing the wiring. These are low impedance wires at high signal levels, so there are fewer issues with shielding, routing, etc. Incidentally, it is possible to wire the SEX 2.1 for balanced outputs, though there are no holes for XLR connectors.

And thanks for the kind words about the sound. I've been pleasantly surprised with how my designs have come out. It was a great learning experience to try to come up with a decent sounding unit that is still affordable. Here's a side note for engineering geeks: the SEX and Stereomour OT-2 has bifilar windings for the secondaries; the Smack OT-3 is identical except the secondaries are single wire so there are twice as many turns, producing four times the impedance level.

 

[jrebman]

Thanks, Paul!

So, the balanced output option is interesting -- will that also work for speakers?  I wonder what advantage, if any that may have in terms of sonics.

I think one other thing that really struck me was just how good the stock kits sound -- I've mostly heard modified/upgraded BH gear and can see the benefits of some upgrades, but the stock kits are really much better sounding than I would have anticipated.

-- Jim

 

[Doc B]

Thanks, Paul!

So, the balanced output option is interesting -- will that also work for speakers?  I wonder what advantage, if any that may have in terms of sonics.

I think one other thing that really struck me was just how good the stock kits sound -- I've mostly heard modified/upgraded BH gear and can see the benefits of some upgrades, but the stock kits are really much better sounding than I would have anticipated.

-- Jim

Thanks Jim,

If some of you see me clenching my jaw at times when someone announces they bought the kit and plan to "fix" it by replacing half the parts with boutique parts without first listening to it with stock parts, now you know why. I'm going to play around with running some of the Paramounts in our speaker system balanced to see if it makes a difference. It certainly was an improvement running the Paramounts balanced into the K1000s, and I imagine balanced S.E.X. would give the same result. By the way, one person at the show owns K1000s and LCD-2s and after trying both on it she decided that the S.E.X. 2.1 was the amp she wanted. Having added the 32 ohm output to give some more voltage swing in V 2.1 really makes it work well with phones that have a rep for being a little difficult to match an amp to.

 

[jrebman]

Dan,

Yes, just sorry I didn't even think to try the HD-800s and lcd2s with the s.e.x. -- that really is an overchieving little amp, and I may just try experimenting with the IEMs and  balanced cable in balanced config too.

Good stuff!  And I'll be looking forward to your findings with balanced drive for room speakers.

-- Jim

 

[Doc B]

HD800s will sound fine with the S.E.X. too, though I actually prefer the Smack with those cans, for the greater resolution (which was unfortunately very difficult to discern with the noisy background at Can Jam). That will probably be my personal rig soon, unless I can get my experimental cans to work. Realized at the show that we really need to break down and buy some 800s for eval work.