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Old 1st December 2008, 10:39 AM   #31
Dan2 is offline Dan2  South Africa
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and this is what i have done...
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File Type: jpg la4570 dan's way.jpg (35.2 KB, 182 views)
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Old 6th November 2012, 05:58 PM   #32
vasko is offline vasko  Czech Republic
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Can someone tell me how to increase input impedance of LA4570 to 1Mohm?

I want to use guitar as source, guitar outputs are 10k impedance and guitar preamps are usually 470k - 1M input inpedance. Good ratio is 1:100.

This shematic says input inpedance is 30k. I guess input buffer stage with jfet or bipolar transistor, or to replace 82R at input with 1M?

This is circuit:

Click the image to open in full size.

Last edited by vasko; 6th November 2012 at 06:01 PM.
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Old 7th November 2012, 08:26 AM   #33
AndrewT is offline AndrewT  Scotland
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I can't read the schematic properly, but I think the input is connected to the -IN pin. This is always lower impedance.

Is this a headphone driver?
20mW output and 16ohms and Vccmax=5V

Have you bought this?
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Last edited by AndrewT; 7th November 2012 at 08:28 AM.
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Old 7th November 2012, 10:25 AM   #34
vasko is offline vasko  Czech Republic
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It's chip from old walkman, see page 2 of this thread.
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Old 7th November 2012, 10:40 AM   #35
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I think pins 2 & 15 are the +IN inputs, from the tape heads. The unlabeled caps I assume are part of the head assembly(?). Docs for this part are scarce, as are the chips themselves I'd imagine.
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Old 7th November 2012, 10:45 AM   #36
AndrewT is offline AndrewT  Scotland
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Throw it on the shelf until you learn how to use it as intended.
In the meantime buy a specific headphone driver chip.
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Old 14th November 2012, 05:43 PM   #37
vasko is offline vasko  Czech Republic
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If I choose to add one transistor input buffer with 1M input impedance, BJT is my only choice since Vcc is 3V?
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