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Old 25th June 2003, 07:32 AM   #11
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Yo~! Guys...any one tried Mylar caps?? they are called polester caps as well...cheap though....
Yup. We know what are polyester caps. The perfect choice if you aim for cheap sound
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Old 25th June 2003, 07:56 AM   #12
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Hmm...meaning it would be good as well...for a cheapo one at least...I have built some tube amps..and I always use Mylar caps...better than those crappy wax paper caps I always see...and they melt when u apply solder near to their "ends"...I guss I will go with Mylar caps..I'm on a really limited budget here...just ordered for some LM3875TFs...insulated tabs...hehehe...I gonna kick a** (self-censoring)
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Old 25th June 2003, 09:02 AM   #13
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Well, there are many ways to kill the 3875 sound... Can't you at least manage a WIMA MKP4? I use no cap as preamp is either cap or transformer coupled.
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Old 25th June 2003, 10:01 AM   #14
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Where in Singapore would be the best place to get quality input caps?? I got the LM3875 free as a sample from National Semiconductors...resistors I plan to use 1% metal film and Panasonic alumninium electrolytics...any reason why not to go with RubyCon caps?? I heard they are bad...wonder why??
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Old 25th June 2003, 10:27 AM   #15
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Originally posted by Nuuk

(or nothing at all if there is no DC from the source).
Hi Nuuk.
Have you tested it?
I did.
With no DC from the source and no input cap, source playing, no input cap and measuring DC: as the music is playing, DC varies from a few mv to about 900 mv!
I wouldn't advise to use a GC with no input cap.

mdlover, good one, and a good first prototype.
But let me give you a suggestion: put the PSU caps closer to the chip, it has long pins, you can cut them.
P-P is definitely not for me, I do smaller and tighter with breadboard.
Try the LM3875, you'll have a surprize.
As a matter of fact, I'm doing things the other way around: first, the LM3875, then the LM3886 and yesterday I made a little board with two LM1875s.
My idea is to make what will probably be the smallest GC in the world.
Went to bed at 2 am, two resistors before finishing it.
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Old 25th June 2003, 11:03 AM   #16
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With no DC from the source and no input cap, source playing, no input cap and measuring DC: as the music is playing, DC varies from a few mv to about 900 mv!
Carlos

Do you realise the above does not actually make much sense? Whether the cap is in the source or in the amp, or there is some other way of blocking dc you get a pretty stable offset , whether music is playing or not. I have tested the variations of offset with temperature and they're very minor. How did you conduct your measurement?

cheers
peter
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Old 25th June 2003, 11:17 AM   #17
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Originally posted by analog_sa


Carlos

Do you realise the above does not actually make much sense? Whether the cap is in the source or in the amp, or there is some other way of blocking dc you get a pretty stable offset , whether music is playing or not. I have tested the variations of offset with temperature and they're very minor. How did you conduct your measurement?

cheers
peter

I had around 28 mv on one channel with the LM3886.
I wanted to try, and shorted the input cap with a wire.
DC was the same.
I pressed play on my portable MD player and measured as the music was playing.
And I measured huge variations in DC offset.
Test it and you'll see.
I think these chips really need an input cap, as normally bipolar devices do.
Maby the Fet-input OPAs don't.
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Old 25th June 2003, 12:36 PM   #18
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Hi Nuuk. Did you try it?
Hi Carlos, No, I wasn't saying that I used no DC blocking cap but several people on these forums have done away with one.

Your findings are interesting although I can't really understand why the DC offset should vary by so much! Like analog_sa, I would have thought that if you have a DC blocking cap somewhere in the line, it shouldn't make much difference where it is.

Could this be something to do with connecting to a portable device?
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Old 25th June 2003, 01:20 PM   #19
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Quote:
Originally posted by carlosfm



I had around 28 mv on one channel with the LM3886.
I wanted to try, and shorted the input cap with a wire.
DC was the same.
I pressed play on my portable MD player and measured as the music was playing.
And I measured huge variations in DC offset.
Test it and you'll see.
I think these chips really need an input cap, as normally bipolar devices do.
Maby the Fet-input OPAs don't.
Something wrong with your source. Some players pass DC when they in active mode. Normally the DC offset shouldn't go that high. I am also not using coupling cap and don't have any problem with excessive DC offset.
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Old 25th June 2003, 03:00 PM   #20
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For testing purposes I use the headphones output or my portable minidisc, as it allows me to control the volume.
Maby I should stop fiddling around and connect the line out to a pot and then to the amp modules while testing.

I have to test that again, because I it doesn't make any difference on the final DC, I will remove the input caps on my GC.
All my sources have output caps.
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