There has been some interest lately in the EHHA Rev A amp. As many of the know the original EHHA is available from Glass Jar Audio and information about it it on the Cavalli Audio website.
Rev A is designed to simplify the build while improving the amp.
Things that are the same in the two amps:
1. Still uses 6GM8s
2. Sill runs the tubes from the 30V rails.
3. Still has mosfet or bjt outputs
4. Can still be configured for ranges of OL and CL gains (or equivalently NFB)
5. Still runs at 100mA bias with plenty of power
6. Is still DC coupled front to back. No coupling caps
Things that are different:
1. Diff amp CCS is now a CRD for simplicity
2. Each board has built-in, linear regulated rails. That is, each board is a complete amp.
3. All you need are one 30-0-30/400mA transformer and one 6.3V/1A transformer (or a DC heater supply)
4. Sigma22 is not required in this version
5. No more trimpot on the diff amp
6. EF drivers for the O/P stage increase bandwidth
One prototype has been built. The amp works very well, but it has not, so far, been tested over multiple builds by different people. Please remember this sentence as the discussion proceeds.
I can post a schematic if you all are interested in going further and even the current board design.