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Old 6th March 2012, 06:44 AM   #21
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Looking at the circuit again, I noticed Nelson chose to put a 10uF for the power supply decoupling caps after the resistors. Any idea what type of cap it should be?

Thanks.

Oon
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Old 6th March 2012, 09:16 AM   #22
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Just checking the F2J shares the same power supply with the F1 right?

Oon
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Old 6th March 2012, 06:04 PM   #23
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Oon,

I'm using the same type used in the Zen 4 supply decoupling. Look at Digi-Key part EF1106. They are 10uF metalized polyester 100v

Power supplies for F1 and F2 are identical.

Cochleus
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Old 7th March 2012, 11:39 AM   #24
ianc13 is offline ianc13  United Kingdom
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Hi Oon,

With regards to your output cap have a look at this - only 63V (which is perfect in this circuit) but 470uF. It isn't cheap but at ~$30 but is maybe a 1/3 of the price of the 947c491k801cbms from Cornell Dubilier and would easily fit inside your chassis.

Audiocaps.co.uk - Arcotronics JSP

I don't know if they would ship out east, but you should be able to find other distributors closer to home.

Note: if you do decide to use audiocap.co.uk then they seem to be a good outfit - I ordered some capacitors and some clips from them, the clips were for different sized capacitors and they got in touch to make sure that I had not made a mistake when ordering which I thought was pretty good service.

It briefly passed my mind to use some of these in my F2J, but then I figured it would be ~$600 per channel for ~10000uF and then reality dawned
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Old 8th March 2012, 02:19 PM   #25
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Hi Ian,

Thanks for the tip. I think you made a small calculation error. The
One I was looking at was a bit cheaper.

For some reasons not clear to me this one is a lot cheaper than the rest.

Think will stick to this one. All for non audio reasons.

1) I want to have the dubious honour of being the first person on this forum to use a 1kg capacitor. Also with both channels, my cap will be heavier than my tranny. It's all about the bragging rights. Assuming nobody else have already beaten me to it. The capacitor is 4 inch in diameter and 5 inch long.

2} the other factor is, the jfets was developed for power inverters, so was this capacitor. So I thought it makes an ironic story... the pair working together...

3) On a different side of the matter. Using a much smaller capacitor does not reduce the bass response for the f2j. Since it is a current source the current will be the same on all parts of a series circuit. However the increase in impedance will reduce your maximum power output. It will be limited by your maximum voltage swing. The impedance of the cap will become significant at about 40Hz. So if you want to try it I believe the one 490uF you saw at the website will work. 2 might be better but 1 will be OK... In fact if you look up most op amp based low power single rail amplifier it is only about 1000 to 200 uF

Oon

Oon
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Old 8th March 2012, 04:07 PM   #26
ianc13 is offline ianc13  United Kingdom
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Sorry,

I thought the 947c491k801cbms was $114 each on Newark/Farnell/Element14.

The stacked foil works out about $30 each (the $600 was if I wanted 10000uF, i.e. 20 per channel!).

Ian
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Old 9th March 2012, 03:52 PM   #27
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Interesting. It shows up s $27 in my part of the world. Maybe it is locality dependent. I chose that particular one because it was instock in Singapore. Maybe if you had chosen one that was in the UK, it might be cheap on your side and expensive in mine...

Oon

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Old 9th March 2012, 06:34 PM   #28
ianc13 is offline ianc13  United Kingdom
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Wow $27 for 1KG of polypropylene capacitor, you can't argue with that, I shall be interested in your listening impressions when compete!
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Old 9th March 2012, 11:08 PM   #29
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Hey you can try it too. The one you suggested is of the same value. And it doesn't cost much. And as I have mentioned, in a current source amplifier unlike a voltage source amp, the current is identical everywhere in a series circuit. So there is no roll off in the bass like a normal voltage amp. Just a limitation in power output in the lower bass region....

Oon

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Old 10th March 2012, 02:00 AM   #30
JZatopa is offline JZatopa  United States
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Any chance someone can try their f2j with a traditional speaker and tell us a bit about how it sound?
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