Here are the mono blocs that I used to drive these duplex.
Most of the credit goes to Paul Joppa who was cool enough to do this amp project with me. (I get banned everywhere, multiple times lol.)
(BB-proof 2A3) It is a direct-coupled 2A3 driven by a 6J5 I believe. The moniker was from the attempt to make a bullet proof direct coupled amp.
Some of the iron was custom wound by Hashimoto in Japan, some of it was stock Hshimoto parts. Tube rectified with a choke.
This system ruined everything else for me, which is why I haven't really done anything audio since then. Everything else is garbage except for what I can acquire in my hands. The audio hobby as it was, was torn away. I was left floating in space.
I'm not going to do much better than this for a 2 channel stereo. It was a very hyperbolic system.
Even though the speakers were ported, they were built extremely large as to push the group delay down to a lowest, more negligible frequency.
The large size was also to reclaim as much upper-low freq as possible from 604E, as these aren't "woofers" in the modern sense.
The result is very fast and tactile bass. Clear bass in the sense now like differences in fabric, is like you just discover new spices. Maybe you just got glasses.
You can feel fast transient spikes thump center off your upper chest, followed by an almost vacuum feeling in your lungs.
Bass became a large haunting entity as opposed to the localized burping boxes that I was used too. Bass has breath.
The are also pseudo-soffit mount to the walls. I had to put those "sides" on for internal volume, so that may add baffle diffraction I don't know.
Radar absorbing paint from a SR-71 blackbird was also applied to clean up the areas around the small signal wires. (This is a lie)
These were 5' tall, yet these 16 cu foot boxes took up less space on the floor than the 5cu foot boxes that the speakers originally came in.
You cannot and must not use DSP with stuff like this. You will hear it, even when EQ is set to flat. Go use DSP for your weddings and small concert.
Build your system FLAT as possible with your parts. Keep the parts minimum, every part has a compromise. No redundant mechanical-electro tone or volume controls. You can have a big switch.
At the time I was using FLAC with an optically linked DAC. This is not any kinda of statement against vinyl, it was and still is a pragmatic decision.
The amps I think were 2-3 watts each. Average listening levels with these speakers is around 0.25 watt. (Combined 104db/watt speakers)
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