Woofer Amplifier

What makes a good low frequency amplifier?

I have biamped my system and at present am using an old computer speaker amplifier (cheap rubbish) for the bass (30 - 250Hz). I want to replace this temporary amplifier with a quality solid state item (diy ofcourse). So what about an amplifier makes it more suitable for driving a low frequency driver. The amplifier will be directly connected to the speaker terminals as I will be actively filtering the signal.

Thanks in advance

Dan
 
hi.

yes they did , many (all?) of them died before playing a single note :)

i havent heard of anybody that got a working amp out of the efforts.

"coolest amp" what does that mean , as i asume you dont mean the temperature , btw. the alexander amp is not very good in the lo freqs but quite good in the mid and high freqs....

bye k madsen - www.cadaudio.dk

ps. perhaps not the best amp to recommend to diy's ;)
 
I'm not sure if anyone has answered my queries so far?

What I was interested in was the characteristics of an amp that make it suitable to low frequency use. Some for example might be
- slew rate
- sn ratio
- output impedance
- power supply capacitance
etc. etc.

Can anyone help with this?

also tips on which DIY amps are suitable are welcome.

Dan
 
Dan,
A couple of things that occur to me:
--Large power supply
--Operating class is less important at low frequencies than mids and highs
--Some people feel that higher rates of feedback give more control at lower frequencies--this is open to debate, I'm just reporting the idea, not endorsing it
--If driving banks of MOSFETs, the gate capacitance is less important, since you aren't having to charge/discharge very quickly, hence the current drive capabilities of the front end or driver stage (depending on the design) are not as critical
--You can use a compensating cap to knock out anything over, say, 20-50kHz without fearing that you're going to induce audible phase shift in your chosen pass band. With this in mind, stability is easier to achieve.

Grey
 
ding said:
What I was interested in was the characteristics of an amp that make it suitable to low frequency use. Some for example might be
- slew rate
- sn ratio
- output impedance
- power supply capacitance
etc. etc.

I'm hardly an expert, but I'll take a stab.

Slew rate matters very much for full-range amps, but is completely irrelevant for a subwoofer amplifier. The crossover should roll off well before slew rate limiting becomes an issue. Any amp that exceeds 5 V/us will be plenty fast enough.

Signal-to-noise ratio is also not terribly important. Lower is better, of course, but because human hearing is much less sensitive to low frequencies, S/N is not as critical as it is in the frequencies above 1 KHz.

Output impedance (Z) is thought to be very important by some. Low Z improves the "damping factor." In practice, most any amp with modest amounts of negative feedback should have a sufficiently low Z. The resistance of your speaker cables will usually exceed the amp's output Z.

Power supply capacitance is good. More is better, and too much is just enough! The stiffer the power supply, the better the ability to knock out that deep bass.

How was that, gang?