Very nice!
I just tried the pre with some more efficient speakers, and the hum is way more noticeable. I’ve been listening to speakers that are about a 3ohm load (likely less), and under 80dB efficient. Put a pair of Coral Holey Baskets (in a Solo 103 enclosure) into my system, and the hum went up a lot.
Think I’m going to drag the Cornwalls out and set them up when I’m listening for hum…
I just tried the pre with some more efficient speakers, and the hum is way more noticeable. I’ve been listening to speakers that are about a 3ohm load (likely less), and under 80dB efficient. Put a pair of Coral Holey Baskets (in a Solo 103 enclosure) into my system, and the hum went up a lot.
Think I’m going to drag the Cornwalls out and set them up when I’m listening for hum…
As far as I can see it is an Aikido schematic. I was making an Aikido preamp long time ago, and it had too much voltage gain, so with that comes noise and hum. It was solved using negative feedback, the gain was adjusted to about 10db (3x). It sounds even better that way. I am currently using the Aikido cathode follower, no gain - no pain.
For the maximum PSRR (lowest hum), R10/R11 should be selected according to the tubes used. There are calculations and calculated values for many tubes at Broskie's website.
The B+ regulator seems to me to be some kind of improvisation, maybe that is the cause of the hum, and maybe it is due to the grounding of the device. R22 seems to be too large (1k5), the factory recommends 240ohm (if it is LM317). Instead of everything, I would put the TL783C and modify the connections a bit.
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