new PP2A3 wrinkle

MagneQuest/Peerless Forum

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hey all,
ages ago, "jsn" of "boozhoundlabs" fame posted my schematic for a future PP2A3, which is at the link below.
Until today the amps were like the schematic, but without the EXO-173 autoformer. The sound was clear and lean, but despite that and its extremely low noise, I can't really recommend the topology, because it now seems like such an extremely inefficient use of resources.
So, having scribbled down the idea way back when, and seeing that the INGOT also has a resistive attenuator in parallel with an inductor winding, I thought I'd go ahead and try it.
Okay, so far so good, except that the noise is ten-fold, at 8mV at output. I measured 30mV at the first PS cap, 30mV at the second, 20mV at the top of the VR tubes, and 10mV at the shared output cathode (but about 200mV between the two output plates). So it doesn't seem like the PS ripple itself is too bad, though PSUD2 tells me I should replace the 30uF cap with a 100uF one. Maybe DC heaters for the first stage would help? Maybe parking the nickel OPT next to the PS choke isn't the best idea? Seems like it might just fit in front of the 2A3's, which would also make the OPT leads easier to connect to both the 2A3's and the binding posts.
I've got some 6H30's on order, to try "monkeying" the circuit, with the pair of choke+resistor loaded drivers drawing 40mA each from the output cathode, leaving about 20mA to drop through a pair of OB3's. I figure that reducing the PS draw from about 140mA to about 110mA and getting the output cathode heat above the chassis might be interesting.
Any suggestions on noise reductions or wild experimental possibilities would be welcome! --keto

http://boozhoundlabs.com/keto/ (Open in New Window)

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Topic - new PP2A3 wrinkle - keto 20:09:19 05/28/06 (12)

I think that schematic looks great - Ronnie Ericsson 13:14:06 05/30/06 (6)

Re: I think that schematic looks great - keto 21:54:26 05/30/06 (5)

Re: I think that schematic looks great, try an input transformer - j rodney 13:54:02 05/31/06 (4)

input transformer - keto 19:10:07 05/31/06 (3)

6H30 --- warning --- - gluca 10:27:18 06/02/06 (2)

new idea - keto 08:40:05 06/03/06 (0)

Re: 6H30 --- warning --- - keto 23:06:15 06/02/06 (0)

Re: new PP2A3 wrinkle - gluca 05:32:32 05/29/06 (4)

Re: new PP2A3 wrinkle - keto 08:39:48 05/29/06 (3)

Not me ... - gluca 10:31:26 05/29/06 (2)

oops - keto 12:32:00 05/29/06 (1)

Yes going for 10W... - gluca 13:16:49 05/29/06 (0)

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