JohnH
Well-Known Member
hi @Jumping Jim , thanks for posting and Its so great that you can get your Dads old amp singing again.
Your case using an AC15 circuit is actually a very interesting reference point for our project. Vox AC circuits have no negative feedback, which makes them have very high real effective output impedances and they can be very sensitive to the impedances presented by the speakers, and in our case via the attenuator. With no NFB, bass resonance response and treble rise due to the interaction of speaker ad amp is maximised, accounting for the great touch response and bright sparkling tones of these amp designs. Most amps have some NFB, and give a different flatter response, but still with a lift. I tested and adjusted the attenuator design based on my two amps, one of which like Vox's, has EL84's with no NFB.
Our designs are able to adapt to these differences between different speakers and amps and let each amp and speaker develop its own real tone, adapting to the differences. Its a real 'Easter Egg' in the circuit design, unexpected when we first started but i think its why the attenuators have been found to work so well across many different amps and settings.
Your case using an AC15 circuit is actually a very interesting reference point for our project. Vox AC circuits have no negative feedback, which makes them have very high real effective output impedances and they can be very sensitive to the impedances presented by the speakers, and in our case via the attenuator. With no NFB, bass resonance response and treble rise due to the interaction of speaker ad amp is maximised, accounting for the great touch response and bright sparkling tones of these amp designs. Most amps have some NFB, and give a different flatter response, but still with a lift. I tested and adjusted the attenuator design based on my two amps, one of which like Vox's, has EL84's with no NFB.
Our designs are able to adapt to these differences between different speakers and amps and let each amp and speaker develop its own real tone, adapting to the differences. Its a real 'Easter Egg' in the circuit design, unexpected when we first started but i think its why the attenuators have been found to work so well across many different amps and settings.
. It worked successfully on first build. I’m getting 8.8 ohms across the 4/8 output jacks (and 9.3’ish on the 16 ohm jack, is that normal or did I make a mistake? I’d have thought it would be at 16). Anyway, it’s a blast to play and, for the first time, I was able to ‘dime’ my Carl’s Custom Amps 15-18W AC-15 homage (the V15). What a joy! 
