lm1875 fizzing away probelm - Page 15 - diyAudio
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View Poll Results: Was a good idea to use two lm1875 or a big stk chip
Use stk 8 27.59%
use lm1875 21 72.41%
Voters: 29. You may not vote on this poll

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Old 19th January 2013, 08:22 PM   #141
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
It sounds like a ground is missing; in the stereo input plug perhaps?
im using mono and pluging in one chanell at a time and the two grounds are hooked up toghrthrt
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Old 19th January 2013, 08:44 PM   #142
PetruV is offline PetruV  Romania
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Now botch chanels work just have to get another rca plug for my computer and an usb cable,volume controle being made from pc
Here it is ,looks like crap just like all of the stuff i have,but hey it works
From radio just one chanel is used
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Last edited by PetruV; 19th January 2013 at 08:47 PM.
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Old 19th January 2013, 09:21 PM   #143
blu_glo is offline blu_glo  England
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well if you leave an input unconnected you can expect it to pick up hum from the surroundings. You can make a special splitter to split one output from your radio into two outputs for testing stereo gear - it's as simple as two wires!! then you can connect both inputs to the same radio output and get a dual-mono signal from the stereo amplifier under test....
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Old 20th January 2013, 08:57 AM   #144
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
well if you leave an input unconnected you can expect it to pick up hum from the surroundings. You can make a special splitter to split one output from your radio into two outputs for testing stereo gear - it's as simple as two wires!! then you can connect both inputs to the same radio output and get a dual-mono signal from the stereo amplifier under test....
Hooked up to pc it now works but the gain is too high and it catches computer sounds
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Old 20th January 2013, 09:13 AM   #145
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Then you can put some low capacitance ceramic caps where they're needed :
to make a suitable low pass filter at the input of the amplifier. What about 1-2 KΩ and 500p/1nF ?
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Old 20th January 2013, 01:57 PM   #146
PetruV is offline PetruV  Romania
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Is this heatsink big enough for two lm1875,if its not then the have to endure the heat
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Old 20th January 2013, 02:31 PM   #147
blu_glo is offline blu_glo  England
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I can't quite figure the whole heatsink with the CD on top but it looks like a good start...
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Old 20th January 2013, 02:37 PM   #148
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by PetruV View Post
Hooked up to pc it now works but the gain is too high and it catches computer sounds
You will have to put an attenuator in the L and R inputs. Connect together a 10K and a 1K resistor. The input from computer sound card goes to free end of the 10K. The middle junction goes to the input of the chip. The bottom of the 1K should go to 0V. Do the same in the other channel.
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Old 20th January 2013, 04:04 PM   #149
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Default Fix the source not the amp.

Quote:
Originally Posted by PetruV View Post
Hooked up to pc it now works but the gain is too high and it catches computer sounds
I am afraid this is a common problem with most computers using most sound cards (Only seen one exception with a Pro sound card with balanced outputs did not have the same problem), my usual solution is to get an optical link from the computer to a cheap DAC form Ebay.

I personally hate the noises from computers, and even attenuated I still find them objectionable the external DAC issue has solved this for me every time I have tried.

Regards

Owen
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Old 20th January 2013, 04:22 PM   #150
blu_glo is offline blu_glo  England
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Owen - You *could* also use the TI PCM2706 etc USB chips to extract the digital audio directly from the computer bypassing the soundcard. These USB chips are supported natively by windows (i.e the driver is recognised by windows itself from -XP through to -8).

However, the chips are not easy for beginners and the audio output is 1V or so, and would still need to be scaled back for the TDA2822M......
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