file:///C:/Users/donlo/Downloads/hfe_jvc_rx-8010vbk_service(2).pdf
I'm converting this 5 channel AV receiver to a 4 channel bi-amp. It was brain dead (I have a stack of brain dead AV units). I already tested the amplifier boards and they all work. I already designed a control and protection circuit and it's installed and working. I have the power amplifier assembly on the bench now and I'm trying to finalize everything and I'm hung up on one feature of the original unit, which I'd like to either eliminate or integrate into my build.
Look at Page 34, board LVA1022-1. The circuit around Q811 and Q812 seems to control V+ to the differential input stages. It is associated with the 4/8 ohm switch. It looks like it drops V+ to 22 volts.
This doesn't make sense to me. The V+ is much higher than this (around 47 volts on 4 ohm setting). Is this a safety feature? Is it their way of limiting power output? Is this an anti-latchup feature?
I didn't test this feature because the unit was a zombie when I got it. I ripped most of the boards out and hotwired the rest and it works on 8 ohm setting. I didn't have the 4/8 ohm switch wired up but now I do (it controls relays on the power transformer board).
Can I rip this stuff out and replace it with a resistor like the V- diff supply? Do I need to scrub a few volts off to avoid latchup? I will probably leave it in the 4 ohm position (plenty of power) and drive 8 ohm speakers.
Thanks in advance for any ideas, advice, or comments.
I'm converting this 5 channel AV receiver to a 4 channel bi-amp. It was brain dead (I have a stack of brain dead AV units). I already tested the amplifier boards and they all work. I already designed a control and protection circuit and it's installed and working. I have the power amplifier assembly on the bench now and I'm trying to finalize everything and I'm hung up on one feature of the original unit, which I'd like to either eliminate or integrate into my build.
Look at Page 34, board LVA1022-1. The circuit around Q811 and Q812 seems to control V+ to the differential input stages. It is associated with the 4/8 ohm switch. It looks like it drops V+ to 22 volts.
This doesn't make sense to me. The V+ is much higher than this (around 47 volts on 4 ohm setting). Is this a safety feature? Is it their way of limiting power output? Is this an anti-latchup feature?
I didn't test this feature because the unit was a zombie when I got it. I ripped most of the boards out and hotwired the rest and it works on 8 ohm setting. I didn't have the 4/8 ohm switch wired up but now I do (it controls relays on the power transformer board).
Can I rip this stuff out and replace it with a resistor like the V- diff supply? Do I need to scrub a few volts off to avoid latchup? I will probably leave it in the 4 ohm position (plenty of power) and drive 8 ohm speakers.
Thanks in advance for any ideas, advice, or comments.
Here's Hi-Fi Engine link. JVC RX-8010V Audio Video Control Receiver Manual | HiFi Engine
The base of Q12 was driven by the microprocessor chip, connected to the "4-8 Ohm" port. No microprocessor controlled functions worked when I got the unit. It turned on and off, and did come out of protection, but that's it.
Thanks.
The base of Q12 was driven by the microprocessor chip, connected to the "4-8 Ohm" port. No microprocessor controlled functions worked when I got the unit. It turned on and off, and did come out of protection, but that's it.
Thanks.
Well thanks to all that looked. My inclination now is to leave that circuit on the board, finish up and power it up with the bulb limiter. I removed the protection circuit and I'm going to put a jumper in so the harness wire goes to my DC detect input on my protection circuit.
I made the harness up with the old harness. I reused the whole output relay and speaker output terminal board. It's driven by my control circuit and it's all working.
Interesting observation - when I first powered it up, offsets were high; a couple were around 60 mV. After ripping all extraneous boards out (that's most of them) and hotwiring it again, offsets were about half and the biggest was less than 30 mV. The original grounding scheme must have been convoluted; what little I bothered to reverse engineer was completely different from how I do it.
Maybe it will work better than original. I hope all this work was worth it. It was a learning experience for sure.
I made the harness up with the old harness. I reused the whole output relay and speaker output terminal board. It's driven by my control circuit and it's all working.
Interesting observation - when I first powered it up, offsets were high; a couple were around 60 mV. After ripping all extraneous boards out (that's most of them) and hotwiring it again, offsets were about half and the biggest was less than 30 mV. The original grounding scheme must have been convoluted; what little I bothered to reverse engineer was completely different from how I do it.
Maybe it will work better than original. I hope all this work was worth it. It was a learning experience for sure.
Almost all of them go brain dead after a few years. I haven't found one where the audio power amplifier section didn't work.
I don't get it. They cost so much money and usually don't last longer than five years. Then people go out and buy another one?
I troll the electronic dumpsters in rich communities. I've built five computers from them. My speaker enclosures came from them. I've pulled receivers and CD players from them that had nothing wrong with them.
These are new money communities. They send their kids to high school in new Maseratis. I couldn't afford to buy their trash.
I don't get it. They cost so much money and usually don't last longer than five years. Then people go out and buy another one?
I troll the electronic dumpsters in rich communities. I've built five computers from them. My speaker enclosures came from them. I've pulled receivers and CD players from them that had nothing wrong with them.
These are new money communities. They send their kids to high school in new Maseratis. I couldn't afford to buy their trash.
The permanent assembly is partially complete. No input or subsonic filter has been installed. The crossover hasn't even been finalized. But I wired up the power supply and control circuit harnesses and ran RCA jacks directly to the inputs.
I've been busy with other things and have put this off for about a month. But I did some testing last night. First I measured offsets. Now all offsets are around 15 mV. Then I measured power into dummy loads. On the 4 ohm setting the DC power supply is +/- 47 volts. I stopped measuring with 38 volts RMS into 8 ohms because my dummy loads ( a motley assortment of 8 ohm 10 watt resistors that I wire up for whatever test) are rated only 80 watts/channel. Dummy loads got real hot but amp modules didn't get that hot.
Then I hooked up two channels to my 8" two ways. These speakers are electronically equalized (+ 6 dB @ 60 Hz) so their equivalent efficiency derates to 82-83 dB/watt. This amplifier delivers the power necessary for these speakers to deliver the full bass extension they're capable of. My present amplifier is 40 watts/channel; enough for jazz to sound great at realistic levels but not enough for some music. It sounds great at low volumes too.
I put a lot of work into this and I'm not done. But now it seems like it was worthwhile.
I've been busy with other things and have put this off for about a month. But I did some testing last night. First I measured offsets. Now all offsets are around 15 mV. Then I measured power into dummy loads. On the 4 ohm setting the DC power supply is +/- 47 volts. I stopped measuring with 38 volts RMS into 8 ohms because my dummy loads ( a motley assortment of 8 ohm 10 watt resistors that I wire up for whatever test) are rated only 80 watts/channel. Dummy loads got real hot but amp modules didn't get that hot.
Then I hooked up two channels to my 8" two ways. These speakers are electronically equalized (+ 6 dB @ 60 Hz) so their equivalent efficiency derates to 82-83 dB/watt. This amplifier delivers the power necessary for these speakers to deliver the full bass extension they're capable of. My present amplifier is 40 watts/channel; enough for jazz to sound great at realistic levels but not enough for some music. It sounds great at low volumes too.
I put a lot of work into this and I'm not done. But now it seems like it was worthwhile.
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