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That so depends...

68.212.129.197

Posted by A on April 14, 2005 at 11:38:23

In Reply to: Phase Inverters posted by BillyJack on April 13, 2005 at 20:39:55:

on what you need from the spiltter. The spilt-load type is a great performer but offers no gain and needs equal impedance on both outputs at all times so needs to be mated to a class A1 output stage that doesn't need a lot of drive such as pentodes/tetrodes.

The long tailed pair is better if you need to swing a lot of voltage but can be a bit harder to make outputs equal at all times. I tend to favor a cascode long tail pair commonly called a hedge type with a cathode CCS and a pot across the cathodes to adjust for equal outputs. This can be a "one stage" circuit that provides splitting and voltage gain at the same time. A negative voltage rail is needed to get the best. With enough voltage to work with it can drive most tubes.

The paraphase is rather out of style these days. The few older amps I listened to with them indicate they can do a better than average job in the 3D soundstage area. But frankly I personally wouldn't use them.

A transformer's main drawback is associated with cost. A good one isn't cheap and a poor one isn't near as good as a tube. IMHO, they are best used when they are needed. Sometimes for voltage reasons, sometimes for impedance reasons, sometimes to allow fixed bias without coupling caps, etc.

One option worth mentioning is to put the transformer in front of all tube stages where it need not be subjected to DC voltages/currents and use a hedge circuit after it. With both grids driven (normally one grid is grounded and the cathode driven) balance should be easier to achieve.

So, as usual in audio, there is no single best design. Instead it's about matching one part to the needs of the other parts and, of course, to your budget and abilities.

Russ

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