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I enjoy reviews and really appreciate all the work involved, but think that any review should start out with a simple generalised description of the circuitry of the component under review. I've read this entire thread, lots of adjectives and subjectivist impressions, but almost no technical information, My best guess is that we have a single ended two stage design, input transformer to handle either single ended or balanced inputs, a 6sn7 voltage amplifier with unspecified biasing, loading, and coupling. A transformer coupled Sophia PX-4 dht for output duty, again with unspecified biasing, operating points, etc. And finally, a seperate B+ supply of unspecified type. I'm a big fan of Pete's work, and a little technical information would really be appreciated. I'm sure it's a wonderful amp. But would like to know why.
Frank -
As an engineer, I would agree with you. But as a commercial product, is it really in Todd and my best interest to fully describe the circuit? Certainly this isn't done in mainstream high-end. I can't imaging the big boys giving any details of the circuitry...
I guess I am more worried about predujicing a potential customer, more than revealing any "secrets".
On the other hand, anybody can open the amp up and figure this out. And I suppose it is better to post the real information rather than allow people's guessing to influence others opinions!
So...
The Pinnacle is a 2-stage SE amp, using 6SN7 with LED bias as the first stage, capacitor-coupled (copper foil PIO) to the PX4, which uses conventional cathode bias (run at fairly low current and voltage) as the second stage. Transformer coupled input and outputs, with switches (inputs) and relays (outputs) to control balanced and unbalanced connections. Relays are used to switch the audio path, so the signal path is direct.
The HV power supply is SiC shottky rectified, RCRC filtered in the power supply box and another LC in the amp box. Isolated supplies are used for the two PX4 filaments, which use a somewhat complex combination of CCS in the PS box, and CM filtering and finally shunt regulation in the amp box. Another seperate regulated supply generates the 6.3V for the 6SN7 and 5V to supply the LEDs and relays.
Two delay circuits sequence the B+ and output mute relays. There are also protection circuits to prevent HV from being applied to the outputs, and also to kill any HV on the umbilical cable if either end is unplugged. (I've been designing equipment for almost 30 years (!) so I understand the regulatory safety requirements).
Hopefully that answers some questions - that's about as much detail as I think I should give!
Pete
how does the apex pinnacle sound with 307a tubes, vs the px4s shown at canjam? would you recommend one over the other, or is more just a personal choice/flavor sort of thing? could you describe the differences between the 307a amp and the apex pinnacle. the 307a is a fantastic amp, and the new one costs considerably more than it's expensive predecessor. i'm sure i'm not the only one wondering what accounts for the price differential.
