by EWBrown » Fri May 11, 2007 5:38 am
I was gonna run this White CF circuit on Tube CAD, to see what flay rod may be askew on the treadle (Old Monty Python reference).
The main bugaboo here will be that the output Z will be too high for most headphones, and lower frequency response will be diminished.
This may be a good place to experiment with a couple of those SPECO 7010 line matching trannies, Doc B uses these in a couple of the BH amp kits, and they work quite well. The 70Volt, 10W primary has taps that work out to 8K, 4K, 2K, 1K and 500 ohms (or 0.625, 1.25, 2.5, 5 and 10 Watts, respectively) , and the secondary is 4 and 8 ohms.
The main thing to remember with these particular trannies is that no DC voltage / current should be present on the winding, and another good tip is to wire them up as auto-transformers, connect the black "zero" wire of the primary to the 8 ohm tap of the secondary, and then the secondary's black "zero" lead connects to ground. This actually improves the overall freq response somewhat. Not too shabby, for $4 cheapo iron. It's definitely in the league witn Magnequest iron, but then the cost is about 2% of the MQ goods.
I know, the whole idea behind using the WCF circuit is to get away from using "iron", but I'd just mount the trannies in or on a separate small chassis, think of it as an "impedance adapter".
I've got a couple of spares of these SPECOs I can send you, if you want.
/ed b in NH
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