Damping factor can equate to less bass ?

[Nico Ras]

There is much more to a loudspeaker than its electrical impedance, it is a complex system that transform electrical energy to mechanical movement to acoustic energy.

Amplifier and power supply impedance makes a huge difference to what the system finally sounds like.

Ask yourself why more capacitors in the power supply or paralleling output devices provides for tighter control of the sound. Why does an amp with 1000 uF rail capacitor booms instead of thumps?

[moschfet]

In this context, I find the current drive technology very interesting.
Current-Driving of Loudspeakers

[JdAo]

Ok, but then (so I've read some more stuff about this and it seems that opinions vary but over a certain limit it's not that important) how do you explain that certain amplifiers with higher spec power supply and regulation seem to have less bass than lower df counterparts, is it the psu regulation ?

[DF96]

Originally Posted by Nico Ras

Ask yourself why more capacitors in the power supply or paralleling output devices provides for tighter control of the sound.

I prefer to ask myself: do more capacitors in the power supply or paralleling output devices provide for 'tighter control' of the sound?

[planet10]

I found the book quite interesting, i recommend it;

the discussion thread>

The Secret of Tube Amplifiers Revealed - and much more!

dave

[JdAo]

Ok, but then how do you explain that an amp with a beefier PSU and better capacitance reserves can sometimes seem to have less bass than one with a PSU with lower specs but less damping factor ? Is it the power supply regulation ? I allways read that having higher capacitance in the PSU gives better bass (then again, what is better...right ?)...

[system7]

Originally Posted by djk

Not likely.

I just checked this, and I think I am right. You see I used to have a SWEET and MUSICAL Radford STA25 valve amp, but it never gave the tight bass control that my transistor Pioneer SA-9100 did on big bass reflex speakers. Fiddling with the 4-8-16 ohm selectors didn't help much either, though I expect 4 ohm would have been tightest even if not the most efficient. But then, you tend to use sealed box or IB speakers with valves, and they are less affected by electrical damping.



IIRC, valves have an output impedance around 1K, and the transformer merely converts the 8 ohm loudspeaker load to be in this range. Voltage negative feedback plays a part, but is not really a game changer if you want good valve efficiency. Discussed in this diyAudio thread where they arrive at 3 ohms:
Typical output impedance for tube amps

A consequence of the different output impedance of a current amplifier like a valve amplifier, is that it dislikes driving open circuit. A transistor voltage amplifier dislikes short circuit.

[DF96]

Originally Posted by system7

A consequence of the different output impedance of a current amplifier like a valve amplifier, is that it dislikes driving open circuit.

No, nothing to do with output impedance. The issue is transformer parasitic inductance which can produce damagingly high voltages when unloaded.

The output impedance of a valve amp depends on the circuit. Pentode SE with no feedback has a high output impedance, higher than the loudspeaker load so DF can be less than 1. Triode or UL with feedback can have an impedance well below 1 ohm. An average figure is thus not very meaningful.

[system7]

Originally Posted by DF96

No, nothing to do with output impedance. The issue is transformer parasitic inductance which can produce damagingly high voltages when unloaded.

The output impedance of a valve amp depends on the circuit. Pentode SE with no feedback has a high output impedance, higher than the loudspeaker load so DF can be less than 1. Triode or UL with feedback can have an impedance well below 1 ohm. An average figure is thus not very meaningful.

I'm just a simple man, and I understood this explanation of why running valves with no speaker is VERY BAD!

OK now for running valve amps without a speaker. With no speaker plugged in there is, in the typically-wired amp, no load at all, which is an infinite impedance. Put an infinite value for R into V=IR, remembering that the bias and the potential in the amp will try to hold I constant, and have a think about it. What happens is that the valves make attempts to chuck out enough voltage to drive an infinite impedance. They can’t, of course, but they are high-voltage devices and they have a damn good try. The flash voltages they generate can be high enough to cause arcing inside your output transformer- and outside it too, spectacularly. Arcs can occur inside the valves too, and on the valve bases. Internal feedback from these events probably makes things even worse. Typically one or more valves go out, and there are fused turns in the output transformer, causing either no output or reduced, distorted output.

Pulling out valves, running without a speaker, and other output impedance matching issues Steve’s Amps

Though I fully accept that a high frequency oscillation might fry it too. I'd also agree output impedance will vary with tube design and feedback. You'd design speakers for valve setups to have quite a flat impedance for best result, I reckon.

[DF96]

That explanation is wrong, so 'understanding' it will lead you astray.