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Chip Amps Amplifiers based on integrated circuits

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Old 28th May 2004, 12:29 AM   #1
taloyd is offline taloyd  United States
diyAudio Member
Join Date: Apr 2004
Location: Los Angeles, CA, USA
Default values

Description Quantity
PCB containing board for 2 channels and power supply 1
LM3875T or LM3875TF 2
Aluminum Oxide insulator, along with insulated shoulder washer (only for T kits) 2
1500uF 50v Panasonic FC Capacitor 4
20k or 22k ohm Caddock MK132 resistor* (R2 and RNFB) 4
620 or 680 ohm resistor* (R3) 2
Caddock 220 ohm MK132 resistor (R1) 2
On Semiconductor MUR860 fast diodes 8
4.7uF 50v capacitors for power supply 2

I built the amp according to the instructions at BrianGT's site:


Values are on page 3.

The resistors aren't wired backwards...

There's definite gain when fed by the Discman. There's also gain when run through my living room CDP, just with a ridiculous amount of noise. And when fed directly from the output of a different CDP, it almost blew out the speakers, as it was putting out full power. So the gain is there, just not with my passive volume control. And the noise is there, just not with the discman.

thanks for all advice,

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Old 29th May 2004, 12:02 AM   #2
theChris is offline theChris
diyAudio Member
Join Date: Dec 2001
Location: SIUE, Illinois, USA
what noise when not used with discman? a hissing or crumbling sound, or a buzzing or humming sound? is music audible, or is the noise much higher then the audio?

as always, make sure there are no cold solder joints.
if only it could be used for good, not evil...
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Old 30th May 2004, 01:47 AM   #3
taloyd is offline taloyd  United States
diyAudio Member
Join Date: Apr 2004
Location: Los Angeles, CA, USA
Default noise


With the passive preamplifier, it's a hissing sound. With the active, it's a crumbling loud monstrous terrible noise...

I think I might resolder the boards... but I really don't think I did anything wrong. Or there any measurements I can take, voltage or resistance, that would help me find this?

thanks again,

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