Subwoofer amp

What would you do to modify a bipolor amp to be better suited to drive a subwoofer.Even if it meant sacraficing the upper frequencies.
There are several things that you can do, all of these with increased complexity as you go further down the line. The first thing to do is to make sure that the amp has adequate AC coming into it. This means a good connection to a heavy AC circuit via the use of a heavy gauge low inductance power cord.

The second thing to do would be to install snubber capacitors across the rectifiers. This will reduce the amount of noise coming in from the outside AC lines and reduce the internal noise as generated by the rectifiers themselves. On poorer designs, this may actually make the unit sound "leaner". That's because the output of the amp is actually passing the second, third, fourth, etc.. harmonic of the AC line. This would mean "extra" output at 120, 180, 240 Hz that wasn't on the recording. As i've mentioned before, most units have very poor power supply designs and that's why the differences in power cords are audible.

The third thing is to increase power supply reserve i.e. increased filter capacitance. This will provide both more dynamic bass and better definition. The power supply on most amps will suffer from noticeable voltage sag on sustained low frequency passages. By minimizing this, bass will not only hit harder, it will offer more control and less "roundness". 100,000 uF's worth of filter capacitance should be considered minimum for a good sized amp.

The next most logical thing is to check the gauge of the wires / conductive path from the output devices to the board and / or the binding posts. Since you aren't concerned with anything but sheer "grunt" here, skin effect and other problems associated with lower grade, heavier gauge wires aren't really a factor here. As such, use something that will pass as much current as possible without being difficult to work with.

The fifth thing would be to place smaller yet sizable caps right at the point where the rails feed the output devices. This provides more "punch" and improved transient response under heavy loads. Something along the lines of 4700 uF devices or a couple of 2200 uF's in parallel across each rail should be plenty. If the amp isn't running in single ended mode, you'll have to pay special attention to polarity here. Some caps will appear to be going into the ciruit "backwards", but that is normal.

Depending on how brave you are, bypass the fuses in all but the most pertinent areas. If you have a tendency to blow fuses on the amp prior to attempting any mods, this probably isn't recommended. If you have never popped a fuse, have at it. Just remember, you've reduced the "idiot proof" devices in the amp, so one mistake could be a lot more costly than just replacing a fuse. Most amps have WAY too many fuses in them and the sonics suffer from this.

Most all of the recommendations above benefit the entire frequency range, not just the bass. Having said that, the one about using heavier gauge wire from the output devices and back "might" be detrimental to high frequency performance. This would depend on the actual wire used and how it was implimented.

Hope this helps... Sean