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Class D Switching Power Amplifiers and Power D/A conversion

Coupling caps.
Coupling caps.
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Old 26th February 2006, 08:38 PM   #1
Trebla is offline Trebla  United Kingdom
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Default Coupling caps.

My new coupling caps are too big to fit in the box with the amp. A bit of an oversight.
Has anyone experienced sound degradation when using caps mounted externally. I'm only talking about extending the leads to around four inches in length.
I really don't want to make a bigger box unless as a last resort.
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Old 28th February 2006, 08:54 PM   #2
Gorilla is offline Gorilla  United Kingdom
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If they are too big to fit in the box I guess you are talking about large electrolytic power supply smoothing capacitors. In my opinion they will already have a large series resistance and inductance so I would not think four inches or so of fat wire should make a difference.

See a thread on this forum (sorry dont have time right now to dig it up) on UCD snubberising (or snubberizing - not sure how to spell the plural) for a novel method of (and general information on) supply decoupling/bypassing.
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Old 28th February 2006, 10:47 PM   #3
Trebla is offline Trebla  United Kingdom
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I'm actually talking about large Obliggato film caps for input duties and a very small box, which i am reluctant to change because it matches the other two boxes which house the power supply and mains filter.
I suppose there's only one way to find out......
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Old 1st March 2006, 07:49 AM   #4
Pano is offline Pano  United States
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Coupling caps.
If you have the giant copper tube Obbs, you might try to ground the case. Should work as a nice shield. Havent tried it myself, tho...

Big caps can pick up hum and buzz, if you're not carefull. Usually not a problem inside the case. Bzzzzzzz......
Take the Speaker Voltage Test!
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Old 1st March 2006, 10:17 AM   #5
Bobken is offline Bobken  United Kingdom
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Hi Trebla,

Is it practical to use these caps on the 'outside', directly at the RCA sockets, perhaps.

If you were to solder a male RCA connector to one end of the caps and a female to the other, with a short wire bypass for the 'return' or ground side, you could merely plug this arrangement in at the end of the interconnects, to see what this will do to the sound.

It wouldn't really add any extra signal path wiring this way, except for the caps' leads which you are stuck with, anyway, and extending the ground return by an inch or two, shouldn't have much effect on things.

If this worked to your satisfaction, no doubt you could either ensure the arrangement was insulated and protected with some tape, or even install them in another small external box, perhaps.

I wouldn't worry about the shielding aspect, unless all your interconnects are already fully shielded and you have experienced problems of this nature in the past, but it is almost free to try out, and without any major 'surgery' being needed to the amps themselves. If and when fully satisfied with the results, it would doubtless be preferable to eliminate the extra connections, perhaps by soldering the caps directly to the ends of the chosen interconnects and tidying this up, but trying things out in this way initially, avoids any 'irreversible' decisions needing to be made before you are fully aware of the results.

Apart from very 'sensitive' MC head amps, I have not even enclosed most of my audio circuits for many years, mainly because they sound better this way, and it allows easy mods to be made at any time, as a bonus. Needless to say, I have not had any trouble with any RF breakthrough etc., or I wouldn't do things this way.

I hope this helps.
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Old 1st March 2006, 09:12 PM   #6
Trebla is offline Trebla  United Kingdom
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Thankyou Bob.

A bit of lateral thinking sometimes goes a long way.
Ill definitely give that a try.
All the caps I've tried so far have been mounted off the pcb without any problem, but these are much bigger and would need to have the extra length leads
Another way of doing it is to mount them horizontally above the pcb on some sort of support, so that half the caps protrude through the lid. This will either look quite cool or quite stupid but it would keep the leads relatively short. If i like them, I can always build another box when i've got the time.
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