moderate cost - high damping factor - class D?

so, I don't claim to understand what much of this means - the moderate cost bit I understand - but I am given to believe that the speakers I am playing with would appreciate an amp with a high damping factor to get a grip on the bass

if I have it right, then in general class D have a big tick in this box

also, in the context of an on-all-day office system the efficiency is rather appealing

back to the moderate cost bit, the likes of Sony and Panasonic crop up in this field - but as far as I have seen only in the context of multi channel boxes

what's worth a look then?

 

Damping factor is the ratio of the speaker impedance to the amplifier output impedance. Thus, for any given amplifier, damping factor will be twice as high with an 8 ohm speaker than a 4 ohm speaker (on paper. In reality things change at both amplifier and speaker end as frequency changes).

Class D amplifiers do not necessarily have a low output impedance. In fact, a great many are pretty poor in this regard when compared with a good class AB design.

It becomes necessary to differentiate between open loop and closed loop designs. Open loop designs will have generally high output impedance. Designs with post-inductor feedback will have very good (low) output impedance.

 

The new Sony TA-FA1200ES looks interesting in this regard. One of the guys over on WigWam is trying one out currently:

http://www.hifiwigwam.com/forum1/12596.html

 

I'm curious as to how a 2x110W amplifier has a power consumption of only 100W...

 

The average signal level in music is much less than the peak signal level. The average power consumption will therefore be much less than the peak power output as peak power is only required for a small part of the time.

 

I understand that Chris... Usually the stated "Power consumption" number is the maximum, however. For example, my Rotel RA-971's state power consumption figure was 300W for a claimed 2x60W amp which I got over 2x100W out of in lab testing. That's in line with the expected ~65% full power efficiency for class AB.

If the sony's average power consumption is 100W, that's well over what a 2x110W class AB would be expected to draw.

Clearly there's not enough information about test conditions to draw conclusions on that. My comment was just a dig at the way many pieces of hifi, particularly cheaper AVRs are specified... eg "5x70W" where on the same page it says "Max power consumption 250W". The small print being, of course, that any one channel can achieve 70W in isolation, but the power supply won't feed all 5 that power at once, which in practice is largely irrelevant anyway.

Back on topic, no output impedance numbers are given. I don't know if the sonys are open or closed loop. Most digital input class D amplifiers are open loop.

 

and is output impedance a function of the specific implementation?

so, for example, a hypex module could appear in two different amps with different impedances?

 

I'm not familiar with the hypex module.

In an open-loop amplifier the output impedance will be dominated by the Rdson of the output FETs (both DC state and switching, the latter of which is hard to determine and not published in datasheets), and by the impedance in the audio band of the output inductor.

If the amplifier is bought as a totally self contained module (like D2Audio or ICEpower for example) then the FETs and inductors are within that and so different boxes using the same module will perform similarly.

 

hypex

very basic question: for output impedance what is low and what is high?

 

My advice would simply be, don't worry too much about damping factor. As long as it is reasonable (and most solid state amps are). If you get an amp with massively high damping factor, it can be thrown completely out the window by a few ft of extra speaker cable and the associated inductance, capacitance & resistance.

IME, the important thing for bass grip is a lot of power, that has no problem delivering current. Good watts need to be made of current and voltage, not just voltage

 

ah yes, watts...

when I was at school there were nice, neat relationships between power, current, voltage and resistance

some time later it appeared that, for instance, valve watts are different...

am just starting to get my head round 'available current' but there was a reason for choosing the mechanics over the electronics options all those years ago

 

The easy way to look at it is, if it has a fookin big transformer, it will be alright. If it claims 500watts and has a small light-weight transformer (unless it is switch-mode) it is probably mostly high voltage swing and little current.

 

FM DAD100Pro

The Flying Moles are worth looking at:
http://www.flyingmole.co.jp/new_en/products/new_product/dadm100pro/index.html

 

funny you should say that... (well vaguely, to me anyway)

Flying Mole was actually what I looked at first, but they're just too pricey for right now.
Turns out PMC aren't sole distributors any more - never did get around to finding out who else is bringing them in though.

 

Coda, they cost 106 000 JPY the pair including shipping. Add VAT, and the total is 544 GBP. Just click "Buy Now" and you'll have them in less than a week.