Ran into a weird problem.
the U100 LM833 was rail to rail shorted, and the regulators were blown up.
Replaced the regulators, and the LM833 with an NE5532 which is all i have.
High pass works, full range works, but NO lo pass at all.
I can see the low-signal on the outputs of the TL074 behind the FREQ pot.
However, U100 I have somewhat dirty audio signal on both op amp positive and negative inputs.
the negative inputs pin 2 and 5 are a +0.5v bias.
the positive inputs have no offset.
however BOTh op-amp outputs are -13vdc. hmmm.... strange....
any ideas?
the U100 LM833 was rail to rail shorted, and the regulators were blown up.
Replaced the regulators, and the LM833 with an NE5532 which is all i have.
High pass works, full range works, but NO lo pass at all.
I can see the low-signal on the outputs of the TL074 behind the FREQ pot.
However, U100 I have somewhat dirty audio signal on both op amp positive and negative inputs.
the negative inputs pin 2 and 5 are a +0.5v bias.
the positive inputs have no offset.
however BOTh op-amp outputs are -13vdc. hmmm.... strange....
any ideas?
It sounds like you have an open trace or possibly an open pot or switch.
The op-amp appears to be working correctly. If the inverting input voltage is greater than the non-inverting input voltage, the op-amp output will swing toward the negative supply rail. The gain (determined by circuit components, not the gain pot) determines how far it swings. Since the VCA (SIP IC, 2155?) is generally connected to the inverting input of the op-amp with no resistance, slight DC offset can cause very large swing.
Remove the VCA and connect a 1k resistor from it's input terminal to it's output terminals (the end pins are input and output). Does that eliminate the DC offset and allow the amp to produce audio when set to low pass?
The op-amp appears to be working correctly. If the inverting input voltage is greater than the non-inverting input voltage, the op-amp output will swing toward the negative supply rail. The gain (determined by circuit components, not the gain pot) determines how far it swings. Since the VCA (SIP IC, 2155?) is generally connected to the inverting input of the op-amp with no resistance, slight DC offset can cause very large swing.
Remove the VCA and connect a 1k resistor from it's input terminal to it's output terminals (the end pins are input and output). Does that eliminate the DC offset and allow the amp to produce audio when set to low pass?
yes. both channels have output.
but when i flip over to low, the gains inverse. meaning when i turn up the left control, it brings up the right channel.
thats the weird part. Oh, about the meter, im using an old school fluke 8600A battery model with a fresh set of batteries.
Its not that accurate as the calibration is just a hair off.
but when i flip over to low, the gains inverse. meaning when i turn up the left control, it brings up the right channel.
thats the weird part. Oh, about the meter, im using an old school fluke 8600A battery model with a fresh set of batteries.
Its not that accurate as the calibration is just a hair off.
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