A question for S.E.X.2.1 output transformer wiring

[jamestw]

I'm going to wire my S.E.X.2.1, the OT-2 output transformer can be configured for 4,8,16,32 ohm. I do not have a headphone so I will skip the headphone jack wiring and will connect output wires directly to binding posts (for speakers).

My question is, can I wire the 4-ohm and 8-ohm configurations on OT-2 at once ? As I have two sets of speakers one is 4-ohm impedance the other is 8-ohm, so when I want to change speakers, for example, I can just simply desolder 4-ohm wires from binding posts and solder 8-ohm wires on, no need to work on OT-2 again.

Is this possible ?

Thanks in advance.
james

[jrebman]

James,

BH will soon have a small PCB with switches on it that allows you to change the output impedance, plus single-ended or balanced modes.  They had this on the Smack and s.e.x. 2.1 at RMAF, and it's probably about to be released fairly soon.

HTH,

Jim

[Doc B.]

We have one brief manual ahead of that one in the schedule that we hope to get going on Thursday. So the manual for the switch board mod might happen in a couple of weeks.

[jrebman]

Dan,

Great -- didn't mean to back you into a corner, but I figured this was due oout soon.

Quick question, how many switchs and of what type does each board use?  DPDT? 4PDT? Something else?

Thanks,

Jim

[jamestw]

Oh, this is a great news to me, I'll wait for the switch board then
For now I can just wire output for a certain impedance, no problems.
Thanks guys...

james
 

[Paul Joppa]

Quick question, how many switches and of what type does each board use?  DPDT? 4PDT? Something else?

Each board has three identical DPDT slide switches. The terminals are spaced 0.10 inch, in a 3x2 matrix, hole diameter 0.035 inch - in case you want to substitute your own switches, or mount them somewhere more accessible. As it is designed, you have to shut the amp off, wait for the power supply to drain, then turn the amp over to get at them. They are not intended for frequent switching.

Two switches are used to set impedance (four combinations of settings). The third is wired as SPDT and switches between balanced and unbalanced.

In balanced mode, the two highest impedances have a grounded center tap, the lower impedances use a pair of resistors to derive a "center tap".

[jrebman]

Paul,

This is great -- with a pair of 4pdts (which I already have) and a dpdt, I think I can mount a plate to the back of the chassis (or somewhere) that will allow me easy external access.  I'd only do this on the s.e.x. because I'll use it with speakers and headphones, but the Smack and Stereomour I will just hardwire or leave set -- all my cans are 300 ohms, except the IEMs, which willl be used with the s.e.x. almost exclusively.

-- Jim

[Paul Joppa]

Electrically it won't hurt anything to switch with the amps running - tubes are very tolerant, especially if there is no feedback. Biologically though, you have one hand grounded holding the amp, and the other hand sticking into the innards with 400 volts running around - the path from hand to hand goes right through the heart - very bad idea.

You should ALWAYS unplug the IEC and set the amp into the base upside down so you can change the switches with one hand in your back pocket. The 2A3s in Stereomour are too tall for that, so you'll have to pull them first. If you wait five minutes so the tubes don't burn you, then the caps might be discharged too...

[Todd R]

Any updates on when this  switchable output impedance board will be ready? I sure could use one :-)