Hello everybody,
This is my first DIY amplifier project. I bought the Mauro Penasa MyRef Rev C kit Ver 1.4 from linuxguru. I populated all the components on the PCB (two monoblocks). I’m using a transformer Primary:0-230 Volt Secondary: 24-0-24 V/300 VA. I checked the transformer by connecting to the AC main and it is reading 23.5 and 23.6 respectively on the secondary.
After the full assembly I’m facing the following issues:
Channel 1: When I switch it on, first it makes the relay triggering sound and then after a couple of seconds it makes screeching sound intermittently, I checked for any loose connections, and did re-soldering, but the problem still persists. When I pause the source there is no screeching, but when I start again, it starts screeching intermittently.
Channel 2: When I switch it on, there is no relay triggering sound, but when I switch it off, exactly after 6 seconds I hear the relay triggered on and triggered off( two beeps) and I observed the LM3886 getting warm.
Please guide me on how to debug. what could be the problem?
I have attached the snaps.
Thanks in advance.
This is my first DIY amplifier project. I bought the Mauro Penasa MyRef Rev C kit Ver 1.4 from linuxguru. I populated all the components on the PCB (two monoblocks). I’m using a transformer Primary:0-230 Volt Secondary: 24-0-24 V/300 VA. I checked the transformer by connecting to the AC main and it is reading 23.5 and 23.6 respectively on the secondary.
After the full assembly I’m facing the following issues:
Channel 1: When I switch it on, first it makes the relay triggering sound and then after a couple of seconds it makes screeching sound intermittently, I checked for any loose connections, and did re-soldering, but the problem still persists. When I pause the source there is no screeching, but when I start again, it starts screeching intermittently.
Channel 2: When I switch it on, there is no relay triggering sound, but when I switch it off, exactly after 6 seconds I hear the relay triggered on and triggered off( two beeps) and I observed the LM3886 getting warm.
Please guide me on how to debug. what could be the problem?
I have attached the snaps.
Thanks in advance.
Attachments
hemanth - How confident are you that the correct resistor values are in specific locations? I thought I had checked everything with a VOM before mounting but twice found a K-value resistor where a value resistor should be. In one case that was preventing the relay from functioning. Otherwise, any other problems I had were born of cold solder joints.
Hi Bob,
I did verified them multiple times and even Siva(linuxguru) verified it and it seems to be fine.
Today I took help from Syed (who is one of the forum member) and he asked me to check the DC offset and the DC offset on the channel with no sound(delayed relay triggering) is 31.6V and on the channel with screeching sound is having a DC offset of 1.2V. According to him the Dc offset if too high(it should be <100mV). So I will talk to Siva on this to check if I can replace some of the components.
Thanks.
I did verified them multiple times and even Siva(linuxguru) verified it and it seems to be fine.
Today I took help from Syed (who is one of the forum member) and he asked me to check the DC offset and the DC offset on the channel with no sound(delayed relay triggering) is 31.6V and on the channel with screeching sound is having a DC offset of 1.2V. According to him the Dc offset if too high(it should be <100mV). So I will talk to Siva on this to check if I can replace some of the components.
Thanks.
having seen the pics you showed in post1, I cannot believe that Linux gave your assembly the OK.
The assembly is strewn with bad practice and errors.
That's why I said contact the seller. I think you have broken the amplifier sent to you.
I'm too lazy to look at pictures so i'll just comment on the data you gave us re DC offset - the one with 31 volts indicates that the amplifier is stuck the positive supply rail. This means that either the LM3886 itself is shorted, or something in the input or feedback path is shorted to the positive rail. Check DC voltages on pin 10 and pin 9 of the LM3886.
I have some insulation between the enclosure and the heat sink. As the assembly is not yet completed, I do have the thermal compound which needs to be used between the heat sink and LM3886.
Today I checked the DC voltage between the pin 4 and pin 7 on the LM 318 and it showed 24.3V, then i checked the DC voltage between the pin 9 and pin 10 on the LM3886, it showed 0.6mV. Are these values fine or something screwed up?
Today I checked the DC voltage between the pin 4 and pin 7 on the LM 318 and it showed 24.3V, then i checked the DC voltage between the pin 9 and pin 10 on the LM3886, it showed 0.6mV. Are these values fine or something screwed up?
I couldn't find any obvious error on the assembled *boards* only - didn't actually comment on the complete assembly. I am the supplier of the bare boards and components, and Hemanth did contact me, but my suggestions haven't yet been sufficient to locate the problem.
You don't need insulation, the LM3886TF Siva supplied are already insulated.
What you need is good thermal conductivity between the LM3886 and the heatsink, aka a flat, polished heatsink surface, thermal compound and a tight fastening.
Without that the LM3386's temperature will raise rapidly until it triggers the SPiKe protection...
I asked for pin 9 to ground and pin 10 to ground, not pin 9 to pin 10. Generally, all measurements are made respective to ground. If you get more than a few mV then there could be a short between one of the inputs and one of the supply rails (check with buzzer on your multimeter).
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