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Old 3rd March 2010, 02:59 PM   #1031
ss007 is offline ss007  United States
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Quote:
The "loud" effect may be due to clipping of some of the transients.
That could be due to asking the chipamp to drive low to medium sensitivity speakers
.

Just curious what sensitivity number would be considered low to medium? I'm building a pair of speakers with dayton Classic 8's. The sensitivity is around 88 db. I'm hoping a Audiosector classic LM3875 will match up OK.
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Old 3rd March 2010, 03:29 PM   #1032
AndrewT is offline AndrewT  Scotland
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I'm using 88dB sensitivity 8ohm speaker on a 3886. It plays low level and medium level nicely.
It becomes "loud" if the SPL is raised too high. It clips transients.
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Old 3rd March 2010, 04:03 PM   #1033
ss007 is offline ss007  United States
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Thanks Andrew!
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Old 7th March 2010, 03:06 AM   #1034
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Default Passive preamp

Hi everybody,

I just finish my second chipamp with the lm3875 kit. This time, I made a separated PS and a passive preamp. When the amp is connected with the preamp there's no noise, but when the cd is connected to the preamp I can hear a little buzz. But, when my ipod only is connected with the preamp there's no noise.

The preamp is made with an 20K pot and a grayhill switch for channel selection. To connect the amp with the preamp, I decided to try xlr 3 pins (not balanced) pins 2 and 3 for left and right signal and pin 1 for ground. The ground signal (xlr pin 1) at the amp is connected at ground star on a copper bar connecting the 2 boards. I don't know what is the problem.

1-Ground loop ?
2-My xlr setup ?
3-impedance matching ?

I will be glad to have some suggestions.
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Old 7th March 2010, 10:29 AM   #1035
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Quote:
Originally Posted by etoiledusoir View Post
Hi everybody,

I just finish my second chipamp with the lm3875 kit. This time, I made a separated PS and a passive preamp. When the amp is connected with the preamp there's no noise, but when the cd is connected to the preamp I can hear a little buzz. But, when my ipod only is connected with the preamp there's no noise.

The preamp is made with an 20K pot and a grayhill switch for channel selection. To connect the amp with the preamp, I decided to try xlr 3 pins (not balanced) pins 2 and 3 for left and right signal and pin 1 for ground. The ground signal (xlr pin 1) at the amp is connected at ground star on a copper bar connecting the 2 boards. I don't know what is the problem.

1-Ground loop ?
2-My xlr setup ?
3-impedance matching ?

I will be glad to have some suggestions.
Finally I resolve the problem (ground loop).I replug my cd player at another wall socket, and all hum is gone.
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Old 11th March 2010, 07:29 PM   #1036
Harolda is offline Harolda  Netherlands
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Attached you can see the progress of my gainclone with the LM4780 kits from Peter Daniel. The LM4780's will be bridged and are mounted on their heatsinks (left & right) with stips. Power supply star ground is on the heat sink.
The enclosure will be complete aluminium. The rest of the enclosure is being painted. But i did not find a solution yet for a nice front panel.

http://www.diyaudio.com/forums/attac...1&d=1268338696

http://www.diyaudio.com/forums/attac...1&d=1268338696

An identical second amp will be built. After that i will use them in an active setup.
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Old 18th March 2010, 02:16 AM   #1037
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Default LM4780 resistors value

Hi,
I want to know if the value(22k) for r1 and r2 in the lm4780 is critical. I want to use resistors I actually have in my bin and the nearest value I have now is 21.5K with 1% tolerance. Will it be ok to use 21.5K ?
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Old 18th March 2010, 02:28 AM   #1038
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The resistor values you have on hand are perfectly fine.
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Old 22nd March 2010, 10:03 AM   #1039
chuck55 is offline chuck55  United States
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Default Peak current of Gainclones

Has anyone ever measured the peak to peak current of the LM3875 / LM3886 / and LM4780 gainclones?

Thanks
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Old 22nd March 2010, 11:48 AM   #1040
AndrewT is offline AndrewT  Scotland
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I have not, the specification guarantees 7Apk when Tc=25degC.
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