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RE: Modern opamps and output capacitors

Posted by madisonears (A) on August 5, 2018 at 18:09:05

In Reply to: Modern opamps and output capacitors posted by KanedaK on August 5, 2018 at 10:00:51:

An amplifier that is DC coupled should never have any DC at its input. An amplifier that is AC coupled can have DC at its input.

Many opamps, new design or not, have DC at their output. Yes, you must measure to know with certainty the amount in your circuit.

If you use crappy output/input caps, you'll have crappy but safe sound. If you use decent caps, you can tune the sound to your liking and still be safe. If you remove one stage of caps, you'll still be mostly safe and might get better sound, depending on the caps. If you remove all caps, you might get better sound but not be safe.

Instead of removing caps, you could lightly solder, or physically attach with a crimp, a piece of wire across the cap leads, shorting the cap. Saves risk of damage to pads/parts. You could then power the amp with xover attached but without speakers attached and measure DC at the amp output. That way you'll know exactly what your speakers will see.

Be aware that there are upstream elements, such as noisy volume controls or switches, that can occasionally generate DC, and the results with no caps in the circuit could be very ugly. If you remove all coupling caps from the xovers and amps, you should consider installing "guardian" caps in front of your tweeters. Because you would need a large value of decent caps to avoid messing up FR (the knee they create should be at least two octaves lower than the xover freq), you'll possibly spend more money on them than you would on decent coupling caps.

My amplifiers have Jupiter copper foil/wax input caps. I like the sound more with them in circuit. Capacitors are not always poison to good sound, and people get pretty silly about avoiding them.

Peace,
Tom E
berate is 8 and benign is 9

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