It is all Nelson's thoughts, he opened his garden for us and meanwhile we know many elements of his playground.
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Judging from the pictures, the K2013/J313 is labeled Q5 and Q6. The hockey-puck Q8. Assuming the SIT is Q7. This makes me think that the input jfets are cascoded.
I suppose these problems are the reason Nelson did not give free the link to the description and manual at FW.
Makes sense. The BA-3 is not very stable wrt offset and so to avoid the FE output cap plus ensure equal swing a little feedback perhaps makes sense.
I think there are caps involved. I suspect there is only enough feedback necessary to get the sound to have some authority but not enough to stabilize the offset completely. Having experimented with caps in the signal path, they are not enough of a detriment to the sound to offset the advantages that they bring. Plus, we see a big cap next to a film on the board which makes me think that is the speaker out.
Yes, of course output cap, no dual rail.
Moreover a cap between FE and OS is also necessary because the gate of the SIT must get the neg Vgs separated from the FE output.
Moreover a cap between FE and OS is also necessary because the gate of the SIT must get the neg Vgs separated from the FE output.