I am sort of settling on a simple design for my HPA, but I'm sort of trying to perhaps shoot myself in the foot by complicating things.
I'm happy with the design for a simple headphone amp with a 12au7 and three paralleled ecc99s OTL each channel for low impedance headphones. More than enough power.
However I'm sort of trying to hedge my bets in the longer term for adjusting the design for a push pull backend with a LTP phase spitter and possibly a cascode - which I don't think the 12au7 seem that happy about compared to 6sn7s. The front end is simply consumer line in, so I'm designing for 3.16V transients.
I don't have experience with both valves so I'm sort of overanalysing it all, over complicating etc.
So sonically I like clarity, neutral-warm (all my solid state runs biased into class A, including the CD player output stage). I like subtle, but by musical tastes cover opera, operatic metal through to electronica, with a lot of female vocal soul (thinking Nina and others).
I've heard reports of the 12au7 being noisy, non-linear etc.. and 6sn7 being the jack of all trades being able to drive more but more boomy/airy... all really surjective and none of those reports really say what the tube was shoe-horned into.
I see for example Jadis use 12au7 with ax7 driver.. so it can't be all that bad if you don't expect the 12au7 to drive by itself.
So do I:
a) stay simple - 12au7 -> 3x ecc99s , 150V supply rail for everything
b) accept a little complexity - 6sn7 -> 3x ecc99s, same design but slightly complicate with 320V supply rail and a 150V.
I'm happy with the design for a simple headphone amp with a 12au7 and three paralleled ecc99s OTL each channel for low impedance headphones. More than enough power.
However I'm sort of trying to hedge my bets in the longer term for adjusting the design for a push pull backend with a LTP phase spitter and possibly a cascode - which I don't think the 12au7 seem that happy about compared to 6sn7s. The front end is simply consumer line in, so I'm designing for 3.16V transients.
I don't have experience with both valves so I'm sort of overanalysing it all, over complicating etc.
So sonically I like clarity, neutral-warm (all my solid state runs biased into class A, including the CD player output stage). I like subtle, but by musical tastes cover opera, operatic metal through to electronica, with a lot of female vocal soul (thinking Nina and others).
I've heard reports of the 12au7 being noisy, non-linear etc.. and 6sn7 being the jack of all trades being able to drive more but more boomy/airy... all really surjective and none of those reports really say what the tube was shoe-horned into.
I see for example Jadis use 12au7 with ax7 driver.. so it can't be all that bad if you don't expect the 12au7 to drive by itself.
So do I:
a) stay simple - 12au7 -> 3x ecc99s , 150V supply rail for everything
b) accept a little complexity - 6sn7 -> 3x ecc99s, same design but slightly complicate with 320V supply rail and a 150V.
If the extra heater current needed is present, simply substituting 12BH7s for 12AU7s will get you better linearity.
Why this much complication! Any of the high gm triode/triode connected pentodes loaded with suitable OPT for HP duty will do it nicely.
Hi Eli, thank you for that suggestion - initial sim results are very very good.