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SOHA II - Super SE Hybrid

post #1 of 707
Thread Starter 
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.
post #2 of 707
Sounds exciting. I am always on the lookout for a new build. Sign me up as a prototype volunteer.

Edit: And of course I will buy only an official board from the designer.
post #3 of 707
sounds delicious. can't wait to hear more.
post #4 of 707
That's pretty awesome Alex, can't wait to build this thing. When you're ready to look for prototypers, I'll definitely be interested
post #5 of 707
I can tell you all that this amp has been well thought out and has a really good layout. I am a fan of symmetry and form - no disappointment here and it is a very compact amp considering everything that has gone into it. The good news is that it is fairly straight forward to build and once I had everything in the correct place, it fired up as designed.

I am still working on small tweaks which we feel would be beneficial to the builder and although have had a preliminary listeing session or 2, I want to spend more time before I give a critical appraisal of its performance. I will say that it has enough bass which is well controlled to satisfy even the biggest basshead fans and overall impressions thus far are very very good.

Thanks to runeight for making this one happen ..dB
post #6 of 707
Thread Starter 
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.
post #7 of 707
the fun was all mine ..dB

A picture - I haven't taken any more with the board fully populated but in case some of you missed my teaser post in the build thread

post #8 of 707
post #9 of 707
Does the SOHA II still keep the original SOHA's goal of a low-cost hybrid amplifier in mind?

Or is it more akin to the Millet Max, with performance superseding cost?
post #10 of 707
Originally Posted by synaesthetic View Post
Or is it more akin to the Millet Max, with performance superseding cost?
I take it you are excluding the papaya oil-rice paper caps in this statement.

The SOHA II - Super SE retains simplicity in circuit design and optimizes all aspects to offer a high performance LOW VOLTAGE amplifier. It costs proportionally more because it has more components but in the grand scheme of things, it will still be relatively cheap to build. If you want creme of the crop, build a Stacker II as it is designed to squeeze every nuance out of the tube's performance , BUT be prepared to spend more money to get that performance and work with 300V. I believe SOHA II Super SE will get you 95+% of the way there, but I am not going to commit to that until I have spent more time with this amp and had time to "objectively" compare them. My Stacker is on a small trip to the NoCal meet (so enjoy Fallen) and I will be able to have a good listen when I get it back. Based on memory - this new amp is no slouch ..dB
post #11 of 707
Thread Starter 
Originally Posted by synaesthetic View Post
Does the SOHA II still keep the original SOHA's goal of a low-cost hybrid amplifier in mind?
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.
post #12 of 707
I'm glad I waited before building a SOHA, then. I still need more tools, as this recent failed PIMETA build has demonstrated. But once I'm set up adequately, I'll definitely give this amp some serious thought. <3
post #13 of 707
cant wait to build one! the soha has been my main amp for awhile.
Its got almost everything I wanted! delay built-in is pretty sweet.
Glad to hear 12au7 will still be compatible. In the picture there's two tubes. Do they need to be matched?
post #14 of 707
Thread Starter 
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.
post #15 of 707
Great job like always runeight and the amp looks fantastic dbel!
I can't say I'm thrilled about the MHM-styling of the board, but I've been looking forward to this for a while, and I'm definitely looking forward to building and listening <3
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