Transformer versus RC coupling experiemnt
Posted: Sun Jun 12, 2005 2:41 pm
The PX25 amp as heard at the recent Yorkshire Boatanchor event had the first stage RC coupled. The valve is ML4, Holco resisto load 14k 1uF Mundorf Silver Gold cap, grid leak on px25 100k holco. Power supply for the amp is -r-c, driver stage takes power straight from same shunt regulated B+ as output stage. Marginal amount of hum but no distortion from this approach.
So to implement IT coupling I have to drop HT to driver, rather than use the resistors,which were previously anode loads and decoupling with a cap, and in keeping with Steves principles, I gathered all the small choakes I could to provide sufficient dc resistance and used an 0d3 for the volt drop.
so to recap the benefit of -r-c power supply is maintained, there is now no resistor on the anode of the ml4 or on the grid of the px25 so we have eliminated resistor sound issues, the coupling cap though the best I could afford is also now a non issue.
The result is that the soundstage has stepped forward to the level of the drivers. In my room the soundstage is always behind the speakers. Now the voices step forward. There is more clarity and improved base further.
These are just my own fairly ordinary IT's on ei120 layered manyfold and insulated after each pass of the winder, 1:1 something like 150h capable of 50ma (I wound them for the CF 211).
I suppose to sum it up in very few words, a film has been removed which was slightly obscuring and pushing back away from me the sounds.
Paul
So to implement IT coupling I have to drop HT to driver, rather than use the resistors,which were previously anode loads and decoupling with a cap, and in keeping with Steves principles, I gathered all the small choakes I could to provide sufficient dc resistance and used an 0d3 for the volt drop.
so to recap the benefit of -r-c power supply is maintained, there is now no resistor on the anode of the ml4 or on the grid of the px25 so we have eliminated resistor sound issues, the coupling cap though the best I could afford is also now a non issue.
The result is that the soundstage has stepped forward to the level of the drivers. In my room the soundstage is always behind the speakers. Now the voices step forward. There is more clarity and improved base further.
These are just my own fairly ordinary IT's on ei120 layered manyfold and insulated after each pass of the winder, 1:1 something like 150h capable of 50ma (I wound them for the CF 211).
I suppose to sum it up in very few words, a film has been removed which was slightly obscuring and pushing back away from me the sounds.
Paul