My daughter, Genevieve, enjoys music and audio so some time ago I gave her a pair of Aurum Cantus speakers with a very nice ribbon tweeter.
These have separate terminals on the back, suitable for biwiring or passive biamping. Initially I had also given her some generic Chi-Fi Class D monoblock power amps, but I’d always kept an eye out for something better.
I was also gratified to read that the thrust would be large and the sense of surging strong.
I learned about these amps reading this diyAudio thread and saw that the OP had substituted an Audio Note copper foil/mylar capacitor for the supplied WIMA type as coupling capacitor to good effect.
I reverted to the 0.22uF capacitance for the AN cap, which would lower the ‘knee’ of the bass response (that I never thought of as significant because of the intended biamping).
With the modifications complete I put in the tubes (Psvane Cossor 300B, Psvane UK series 6SN7, Shanguang 574P rectifiers) and hooked it all up in the guest bedroom.
I thought I would break them in full spectrum and then biamp later. The speakers crossover at 2.2kHz.
Well, I love how they sound so much that I’ve abandoned the planned biamping. Combined with an SVS Classic 1000 sub taking over at 120 Hz these little 8 watt 300B’s were plenty loud enough for recreational listening in a medium room. And the mids were too sweet to go back to the Class Ds.
The other gear pictured is a Doge 8 CD player on top, my old Holo Audio Spring I and a VTL Maximal preamp (2 x ECC801s Telefunken). Using a Chromecast Audio for streaming to the DAC through 48k Toslink. This will be replaced by a Holo Audio Red in due course.
The output terminals are very busy, being biwired with spades to the speakers and a hi-level input to the sub from banana plugs. I didn’t get a biwired harness, so it’s two sets of spades and a banana plug on each terminal. Ugly and awkward, but doable. The speakers are 8 ohm and the hi level connection to the sub draws virtually no current.
Good fun, inexpensive and a nice upgrade for Genevieve.
Note that opening these amps voids the warranty and tube amps contain lethal voltages even after switched off until power capacitors discharge (about 20 minutes). In my case I am such a chicken that I did the mod before the amps had ever been turned on.
Sounds interesting, but does it sound like they describe on their site?
…the power is large, the sound is transparent and full, the thrust is large, and the sense of surging is strong.
For just a few pence more they could have put a high value bleed resistor across the HT to ground to remove the high voltage safely and slowly after switch off. How many hours are the power tubes rated for?
I can’t find any ‘official’ rating. Google AI says 2,000 - 3,000 hours for the Psvane Cossor 300B but I have no idea where it is getting that figure. The Original WE 300B were renowned for lifespans of 40,000+ hours.
The most likely tube to fail is the rectifier, so I have a spare pair of those. I think it was Steve Deckert from Decware who said ‘If you buy a lamp with one bulb, you’re going to spend some time in the dark.’
Edit: That figure of 2-3k hours seems absurdly low and may even be an hallucination. I think a lot varies with operating conditions, particularly start up, which can adversely affect tube life. One of the benefits of the tube rectifier is a softer start up.
