Hi
My mivoc am120 plate amplifier died on me a few weeks back. It was still getting power but barely registering any coherent sounds from the driver apart from a loud hum. It was part of a kit with a Mivoc AWM 124 driver I bought it from lautsprechershop.de about 12 years ago or so. I have been really happy with my purchase although I have no way of measuring its performance against a shop bought one. I know that I have had the value from it but just hate the idea of scrapping it for a new one.
Anyway I decide to open the amp and, having a multimeter but no experience of performing much in the way of diagnostics, took it upon myself to start replacing the electrolytic capacitors on both the amplifier and the preamplifier boards because they were cheap and within the scope of my soldering capabilities. No joy. I'm thinking now buying one of these TDA7293 modules and hooking it up to the preamplifier on the existing heatsink as I am guessing - perhaps wrongly - that the fault is in the amplifier board. I would just like some advice on how I would marry up the two things. Here's a pcb schematic with the relevant wiring. The transformer outputs dual 32-0-32volts ac. Ideally I would like to use the existing white rca jack on the back of the woofer or if that doesnt work perhaps someone could recommend a premplifier board that I could incorporate onto the plate that would work with these voltages and the TDA7293. Thanks in advance for any suggestions.
My mivoc am120 plate amplifier died on me a few weeks back. It was still getting power but barely registering any coherent sounds from the driver apart from a loud hum. It was part of a kit with a Mivoc AWM 124 driver I bought it from lautsprechershop.de about 12 years ago or so. I have been really happy with my purchase although I have no way of measuring its performance against a shop bought one. I know that I have had the value from it but just hate the idea of scrapping it for a new one.
Anyway I decide to open the amp and, having a multimeter but no experience of performing much in the way of diagnostics, took it upon myself to start replacing the electrolytic capacitors on both the amplifier and the preamplifier boards because they were cheap and within the scope of my soldering capabilities. No joy. I'm thinking now buying one of these TDA7293 modules and hooking it up to the preamplifier on the existing heatsink as I am guessing - perhaps wrongly - that the fault is in the amplifier board. I would just like some advice on how I would marry up the two things. Here's a pcb schematic with the relevant wiring. The transformer outputs dual 32-0-32volts ac. Ideally I would like to use the existing white rca jack on the back of the woofer or if that doesnt work perhaps someone could recommend a premplifier board that I could incorporate onto the plate that would work with these voltages and the TDA7293. Thanks in advance for any suggestions.
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Start checking the pre-amp supply voltages +-15V
Check if there is a clean signal at the line out first in order to rule out the pre-amp.
32V rectified is 45V and too much for the TDA. Perhaps You can unwind some coils in order to get a lower Voltage for the power stage.
Check if there is a clean signal at the line out first in order to rule out the pre-amp.
32V rectified is 45V and too much for the TDA. Perhaps You can unwind some coils in order to get a lower Voltage for the power stage.
Thanks and sorry for not replying sooner. That makes sense and gives me somewhere to start at least. Disappointed to hear about the TDA7293 as it seemed ideal for replacing that section of the amp but it is a good opportunity for me to learn more about electronics as a hobbyist. I've probably spent more time and money on this than its worth but the steel plate the amplifier modules are mounted is pretty thick and heavy steel that seemed such a waste to throw away. Are there any modules I could buy off the shelf with my basic skills that could be retro fitted to it. Cheers.
Just a quick update that the +15 -15V are working so maybe the problem is in the preamp after all. I have noticed as well that as soon as I plug in the preamplifier board there is a sudden rasping/buzzing noise from the relay on the amplifier board. So maybe I need to check my soldering on the preamp board? Thanks.
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The relay is switching on the amp (connecting both supply rails) via the REM (remote) input from the preamp when sensing an incoming signal and switching it off when a temperature sensor reacts to high temperature, so something may be wrong there, causing the relay to oscillate.
Regarding replacing the Amp-board: There is a lot of functions included (and mixed) on the two boards, such as the ones described above, so it is difficult to substitute the amplifier section alone.
I am using an AM120 for quite a while now and would also try to repair it in case ...
Regarding replacing the Amp-board: There is a lot of functions included (and mixed) on the two boards, such as the ones described above, so it is difficult to substitute the amplifier section alone.
I am using an AM120 for quite a while now and would also try to repair it in case ...
Thanks for that. Very helpful. It all makes a bit more sense now. I think I might have located the problem. When I first took out the board to inspect it, I saw a brown stain on one of the white wirebound resistors and ignored it thinking that it was from glue or flux. Well when I plugged it all in again yesterday and the relay started buzzing, smoke began to emit from the area and the brown stain is much more defined now. I've ordered a couple of replacements so I will have one last attempt at fixing the problem.
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