This 2A3 Push-pull amplifier, built in 2009, has proven itself to be an excellent performer. Compared with Single-Ended amps, I am happy about the additional watts and improved bass control.
The design of an amplifier is more important than parts quality – don’t waste $$ on expensive parts in a poor design.
However, I think it is worthwhile to spend some more time and $$ on this amp.
Firstly, we know that the Power Supply is very audible in amplifiers, especially Directly Heated Triode amplifiers.
1) Power Supply:
The first pi-filter capacitor (C1) has a large effect on the sound of an amp.
I was keen to change the existing electrolytic cap (F&T 47uF 500v) to an ‘aluminium film in oil’ type (33uF Obbligato Film Oil). This is a much larger capacitor however, see below…
The sound – not unexpectedly, was ‘bigger’, more ‘expansive’, with warmer-tone – but also with more resolution, more natural, less ‘distortion’. On the other hand, not as sharp-edged.
However, the ripple passing through the CLC filter increased – from 37mV to 58mV pk-pk. With my high sensitivity horn loudspeakers (~105dB/W), the ‘hum’ is audible.
So, after modelling using PSUD2 software, the 2nd filter cap (C2 – JJ 100uF) was increased to 330uF (F&T) – this should reduce ripple to ~16mV pk-pk…..
OK, the PSU/amp schematic now looks like this…..
2) Signal Capacitors:
The coupling caps C5 , C6, and the C7 phase-splitter ground decoupling cap, were originally Obbligato Copper caps (metallised polypropylene)…..
I had some Ampohm Tin Foil paper-in-oil versions. This type of cap is much larger than the metallised plastic film Obbligatos…..
The new coupling caps installed…
The sound – significantly better in all respects. Much more ‘presence’ and clarity, upper-midrange/treble detailing. Voice presence is very ‘alive’. ‘Soundstage’ scale seems increased, with ample ‘ambient decay’. Percussion is ‘meaty’, weighty and dynamic. More ‘power’ top to bottom.
The plate decoupling caps for the 6A6 phase-splitter and 76 input stages (C3 and C4) are Panasonic TSUP and ED types.
The Panasonics are good, but in the Linestage, I found the Panasonic TSUP to be more ‘mellow’, less hard-edged, less ‘rhythmic’ than the F&T caps.
I will try some more F&T electrolytics.
For me, dynamic ‘freedom’, un-restrained dynamics, is very important in order to sound like real, live music.
This is also one reason too, why I favour horn loudspeakers.
But that’s another story of course…. 🙂