Hello,
I have a "problem" with the VU meter on the KA801 amplifier. When I turn on an amp VU meter needle on the right (sometimes on both) channel jumps a little before the speaker relay engages. I know that is not a serious problem, but it is irritating. Aside from this problem, the VU meter works well. There is a TA7318P driver.
I check voltages, there is no input voltage before relay click. But there is voltage on output when I turn on the amp (before relay click), the left channel jumps to 7mv and then to 4mv. Right channel jumps to 13mv and then falls down to 4mv. This causes a jump on the VU meter.
When speakers are disconnected it jumps more. I have no clue how the speakers can affect when the relay is not engaged.
Can be something wrong with ta7318P ? Thanks a lot
I have a "problem" with the VU meter on the KA801 amplifier. When I turn on an amp VU meter needle on the right (sometimes on both) channel jumps a little before the speaker relay engages. I know that is not a serious problem, but it is irritating. Aside from this problem, the VU meter works well. There is a TA7318P driver.
I check voltages, there is no input voltage before relay click. But there is voltage on output when I turn on the amp (before relay click), the left channel jumps to 7mv and then to 4mv. Right channel jumps to 13mv and then falls down to 4mv. This causes a jump on the VU meter.
When speakers are disconnected it jumps more. I have no clue how the speakers can affect when the relay is not engaged.
Can be something wrong with ta7318P ? Thanks a lot
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When the speaker relay is not closed the speaker outputs are floating and so can pick up all kinds of stray interference. A DVM will not reliably show what all that interference is but in any case its a non issue.
As long as the DC offset of the amp is OK as measured before the relay then you have nothing to worry over.
The only way to stop the meter showing this random floating voltage would be for the manufacturer to include a muting circuit for the VU meter which would not be cost effective.
As long as the DC offset of the amp is OK as measured before the relay then you have nothing to worry over.
The only way to stop the meter showing this random floating voltage would be for the manufacturer to include a muting circuit for the VU meter which would not be cost effective.
Thanks a lot for your response. Yes, but as I remember it didn't do it before recap. C35 cap has a huge 25ohm ESR, C34 has 5ohm ESR. Also 0.47uf caps in the input line have much bigger ESR than actual WIMAs.
When I turn it on with DBT needles stay down.
Do you think that ESR has some role ? Should I try it with old caps or add some resistance ? Thank you
When I turn it on with DBT needles stay down.
Do you think that ESR has some role ? Should I try it with old caps or add some resistance ? Thank you
It possible I suppose as time constants always play a part in anything like this but I still don't think you have a problem.
You could try linking the left hand ends of C15 and C16 to ground to short any input signal to the chip and see whether that alters the behaviour. That eliminates anything at the input causing a problem.
I really think you are looking for something that isn't an issue though. The meter circuit is almost certain to show some kind of transient pulse at power on imo. If you have altered any values of caps on things like the rails then that can alter the rate of rise of a rail and also cause unexpected behaviour... but I really don't see an issue here.
You could try linking the left hand ends of C15 and C16 to ground to short any input signal to the chip and see whether that alters the behaviour. That eliminates anything at the input causing a problem.
I really think you are looking for something that isn't an issue though. The meter circuit is almost certain to show some kind of transient pulse at power on imo. If you have altered any values of caps on things like the rails then that can alter the rate of rise of a rail and also cause unexpected behaviour... but I really don't see an issue here.
There is no quick fix for it because there isn't really a fault 
You could add either a DPDT relay with perhaps the coil also driven from the speaker relay circuit and use the relay to apply a short to ground at the inputs (or even just to open the meter movement connection) to stop it registering at power on... all experimental though.
You could add either a DPDT relay with perhaps the coil also driven from the speaker relay circuit and use the relay to apply a short to ground at the inputs (or even just to open the meter movement connection) to stop it registering at power on... all experimental though.