I just build 2 of this circuit on a prototyping board, the one with the holes pre drilled, but instead of 21x gain, I used 11x, 33K as Rf and 3.3K as Ri and a ceramic 100nF capacitor in parallel with +Vcc and -Vcc.
I'm using a record player with a RIAA preamp, still on breadboard, and the gain of such preamp is about 100x @ 1Khz. which means about 500mV overall. Sometimes both channels work, but most of the times just one works, and there is a hum on the other speaker being fed with the not working channel, probably 60Hz. When one of the channels ist not working, the postive supply voltage drops upon not feeding the power amp with the signal comming from the preamp on the working channel, it drops from 23V to about 17.5. The negative supply doesn't change. Any sugestion on what could be the problem?
Additional info: As I'm trying to build a 4 channel amplifier, both LM1876 shows the same issue. I also jerry rigged grounded the whole system using a bike spoke and it does make a difference, when it's not grounded the 60Hz noise is stronger. I also tested the RIAA preamp, change the channels into the LM1876 and both channels of the preamp are working, the issue seems to be on the power amp.
I'm using a record player with a RIAA preamp, still on breadboard, and the gain of such preamp is about 100x @ 1Khz. which means about 500mV overall. Sometimes both channels work, but most of the times just one works, and there is a hum on the other speaker being fed with the not working channel, probably 60Hz. When one of the channels ist not working, the postive supply voltage drops upon not feeding the power amp with the signal comming from the preamp on the working channel, it drops from 23V to about 17.5. The negative supply doesn't change. Any sugestion on what could be the problem?
Additional info: As I'm trying to build a 4 channel amplifier, both LM1876 shows the same issue. I also jerry rigged grounded the whole system using a bike spoke and it does make a difference, when it's not grounded the 60Hz noise is stronger. I also tested the RIAA preamp, change the channels into the LM1876 and both channels of the preamp are working, the issue seems to be on the power amp.
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That is, indeed, a good point the datasheet says they, both, require 2-2.5v in order to be active, and voltages less than 0.8V are considered the low state. In my circuit the 8 pins, stand by and mute from each channel aren't connected to anything, should I ground them in order to make sure there is 0V?
Your schematic is missing a DC Return on the signal input. Add a 33k to ground @ the jack. The input termination should be the same value as the feedback to maintain DC OFFSET. You are missing the way your are handling the "MUTE, & STANDBY's"
Duke
Duke
Like the image above? But instead of the potentioemter a 33k resistor to ground? And, I did ground the mute and stand by pins and there is still a non working channel.
