A push-pull tube design and Single-ended class A designs


Hello,

Between a push-pull tube design and Single-ended class A designs amp, is Single-ened class A better in sound quality, why?

Regards,
Eddy
eddy1

Showing 3 responses by atmasphere

Its not that simple!!

SETs work really well if you have a speaker efficient enough to really take advantage of their strengths. If you don't, you are wasting the money invested in the amp! SETs should be used such that only about 20% of their total power is invoked at any time during your listening session. If you use more power than that, the distortion gets high enough that the amp will be pretty distorted on musical transients. The kind of distortion present (higher ordered harmonics) is used by the human ear brain system to calculate the volume or loudness of the sound (Loudness Cue). So the result is that the loudness cues will ride on the transients, causing the amp to sound very 'dynamic'. This is why you hear tales about how SETs are so dynamic for their otherwise low power. Its distortion masquerading as dynamics.

Essentially when describing dynamics, you can replace the word with 'distortion' and not change the meaning of the conversation.

OTOH, at lower power levels the distortion becomes unmeasurable, quite unlike that of most push-pull amps. This is the source of that 'inner detail' for which SETs are so lauded.

Push-pull amps do better at higher power levels (having less distortion), and so sound smoother when you push the system harder. In addition, they often have more power and wider bandwidth, which means you can run less efficient speakers that might have more bass response (typically the kind of speakers you need to work with 90% of all SETs need to be over 100db 1 watt/1 meter for best results- this means they won't be playing that bottom octave and may be missing some of the octave above that as well).

We've not described the effects of loop feedback, which is a conversation on its own, but many P-P amps have it while most SETs do not. Feedback can cause the amp to sound brighter due to bifurcation of existing distortion into higher orders, which the ear treats simultaneously as brightness and harshness.

If the Push-Pull amp is designed properly (no feedback and no separate phase splitter circuit), the distortion will also decrease with power to unmeasurable, but IME these types of Push-Pull amps are rare. However if that quality is present its sort of like get your cake and eat it too- you have the advantages of SET (good lower level detail) without the power or bandwidth limitations. 
Based on the specs of the speaker an SET is out of the question!! You would want a speaker that is at least 10db more efficient with most SETs made. The recommended minimum power is 40 watts, which is a **very very** large amount of power for an SET!

The best SETs seem to make no more than about 7-10 watts; the turly best of them make considerably less (the less power they make, the better the bandwidth, but as you can see the greater efficiency is needed in the loudspeaker).
Generally speaking, if you want to explore what SETs really have to offer, higher efficiency loudspeakers of easy impedance (8-16 ohms) are preferred.

A great speaker would be the Classic Audio Loudspeakers Hartsfield reproduction. Its about 105 db and very wide range for that efficiency!

If you are on more of a budget I would consider a full-range loudspeaker like a Lowther or PHY in an open-back cabinet or baffle.