Class-A power supply & 80V capacitors
I am excited about the SILICON CHIP 20W
Stereo Class-A Amplifier but I have a quick question. I have two beautiful and
new 33,000mF 80V electrolytic capacitors. Can I use them in the 20W Stereo
Class-A Amplifier power supply or is the rating 80V rating too high for the
capacitors to be effective? The capacitors have an ESR (equivalent series
resistance) of 5 milliohms. (L. L., via email).
You can certainly
use your 80V capacitors. In general, having a higher than specified voltage
rating is never a problem unless there is a limitation on physical size.
Getting The SC480 To Drive 2-Ohm Loads
Is it possible to add high-current output devices to make the
SC480 amplifier (SILICON CHIP, January & February 2003) stable into 2-ohm
loads? The power supply is no issue as I am using a 50kHz switcher for a car
amplifier.
I realise I would need to redo the PC board and make the high
current tracks a bit thicker. Could it work with ±40V rails and with three pairs
of MJL21193/4 (two less than the Studio 350) and something with more collector
current than the MJE340/350s to drive them? I’d really like to see an article on
how you draw the reactive load lines up when you design amplifiers.
I am currently using two of the April 1996 modules at home;
they’re great. (S. P., Carrum Downs, Vic).
In fact, just changing the output pairs
on the SC480 to MJL21193/4 should make it OK to drive 2-ohm loads. No other
changes should be necessary although we would prefer to see heavier copper
tracks for the main current paths.
You will also need to leave out the Polyswitch output
protection devices. Instead, we would recommend the Loudspeaker Protector from
the July 2007 issue.
For interest, you can plot the 2-ohm load line on the load-line graph for the
April 1996 modules and then take an approximation of the equivalent 1.4 +
j1.4-ohm reactive load line on the same graph to demonstrate that two pairs of
MJL21193/94 transistors should comfortably handle a 2-ohm load.
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