Any DIY Amps for Subs?


2005-12-31 10:09 am
I've been using plate amplifiers in my projects, but I want more control over the features of the subwoofer amplifier as well as the shape of the "enclosure", etc.

How does one go about designing/building a subwoofer amplifier?

I'm lately a fan of Class D but and solid-state design would do.

Is a sub amp so simple as an regular amp with a low-pass crossover-style filter on the output? Or do they filter on the input?
There is a sub amp design in R Slone's Audiophile's Project Sourcebook, although he qualifies it by saying, "The only reason I specify it for subwoofer applications is because there is a "better" L-MOSFET design choice for general-purpose applications." [Ch 6, p 168]
And yes, filter the input.
The TDA7294 datasheet has the schematic in Figure 25 (Bridged Circuit). Says it will do 150 W into 8 Ohms with +/- 25V, or 170 W into 16 Ohms with +/-35V.

The TDA7293 datasheet does not show the schematic but mentions using it in a Bridged Circuit for a subwoofer. Says it will do 150 W into 8 Ohms with +/- 25V, or 200 W into 16 Ohms with +/-40V.

The TDA7295 datasheet has the schematic in Figure 18 (Bridged Circuit). Says it will do 100 W into 8 Ohms with +/- 22V or into 16 Ohms with +/-30V (100 Watts in both cases).

Each bridged circuit required two TDA devices.
If I was going to DIY a sub amp, I'd be inclined to use bridged and paralleled chipamps. They're about as cheap as decent power transistors alone. I wouldn't include a filter; that's the job of the active crossover or processor.

However, unless you have access to cheap surplus or salvaged parts, it can be more cost-effective to buy a used power amp. You can easily pick up a 400W into 4 ohms stereo amp for under $400, which comes with rather useful extras like protection circuits and resale value. With more luck or patience you'll find one for half that.

I think we overestimate how much power is really needed for subwoofers, perhaps because of the temptation to run them too loud. When I bothered to check sub levels using an SPL meter, it turned out I had them nearly 10 dB higher than the mains. Lately I've been running two subs off an amp that's a mere 40 watts per channel. That's still more than enough to hit levels over 105 dB at my chair and rattle the walls.