SOHA II - Super SE Hybrid

Hello folks. I've had a few enquiries about the SOHA II. So here is an update.

The SOHA II is a vast improvement over the SOHA. You won't need any addtional buffers (such as the jisbos) because it already has a high current SE buffer built into it. And I already know about making buffers with a high Zi when loading tubes so you won't have to wait for another release to get this feature.

The front end no longer needs a plate CCS or a trimpot adjustment, but it will still maintain the correct plate voltage. It doesn't even use an opamp servo to do this.

The SOHA II will have the basic topology of the SOHA I with just a small coupling cap between the input stage and the buffer. It WILL NOT require a big output capacitor to interfere with the sound.

The SOHA II has an improved voltage doubler to create the B+ and like the SOHA I, it all runs from a single 15-0-15V/1A transformer.

But, better than the SOHA, the SOHA II Super SE will allow you to roll different tube types into the front end. Want to run 12au7s? No problem. Want to run 6922s, just flip the heater switch (or change the jumpers) and replace the tubes. Any set of triodes where two of them can run with 12.6V/300mA (series or parallel) will work without requiring any adjustments for voltage. 600mA can be supported with a bigger transformer and larger heatsinks.

The amp fits into a Hammond 1455T2201 (160mm x 220mm) enclosure. The extra room at the back of the box is for the tranformer and a DAC (if you want one). The amp board alone will fit into the shorter 1455T1602 hammond enclosure so that you can put the toroid in a walwart.

The amp also has a built-in e12 delay/offset unit. The board is 160mm x 115mm.

dBel84 has built the first proto on homemade boards. The amp works as designed.

I'll be looking for prototypers soon who are willing to build on the first commercial boards to test the fit and finish of the amp. If you're interested I think we may want about 5-10 prototypers.

So you can put your SOHA away with other amps that you've been building and try the next generation of hybrid amp from the guy who actually DESIGNED the original SOHA amplifier, the remake of the CKKIII amp (in collaboration with AMB), and the Bijou.

And I would like to thank dBel84 for ALL of the work he's done to get this amp built. NOTHING would have happened without his efforts to build this amp on a homemade PCB so that we could test it before committing to commercial boards.

Yes, but the SOHA II SSE/H expects to get excellent performance at reasonable cost. It will cost more than the SOHA, but it will have quite a few additional features (and fewer quirks) to go along with that additional cost.

The tubes don't need to be matched to each other. However, the operation of the input stage will be helped if the two triodes in each envelope are reasonably close. That is, no more than 20% difference in plate current for the same voltages. But, even if the tubes are more different than this, the front end will still work perfectly alright.

When I make the website available with an explanation of the design, you'll see why this is so.