Firstly, you must always have heatsinks fully attached because the FET's run at such high current in this design. They will get sizzling hot in seconds without and that may well damage them.
I would say that the voltages you measure under those conditions may not be reliable because the FET may.
The voltage between Q1 Drain and Q2 Source should be around 900 millivolts. That voltage appears across the 0.47 and 0.68 ohm resistors and allows us to calculate the current.
Connect your meter to the two arrowed points and you should read about 0.9 volts.
I would say that the voltages you measure under those conditions may not be reliable because the FET may.
The voltage between Q1 Drain and Q2 Source should be around 900 millivolts. That voltage appears across the 0.47 and 0.68 ohm resistors and allows us to calculate the current.
Connect your meter to the two arrowed points and you should read about 0.9 volts.
Attachments
Sorry again for so many posts. I'm going to try and attach a diagram of how i tested the mosfets. Thanks again for your help!
An externally hosted image should be here but it was not working when we last tested it.
Attachments
If you have never had heatsinks attached then I would say that it probably would have worked correctly had they been.
I think you should replace the FET's now tbh as they may well be impaired or damaged due to excess heat. They got even when bolted to the heatsink.
You mentioned you had around 5 volts between Drain and Source of the two FET's. If so then that suggests the the 0.47 and 0.68 ohm resistors are high in value... again damage that could have occurred due to running the FET's without heatsinks.
Check those resistors are OK.
0.83 volts sounds OK. That means a current of 1.44 amps is flowing (assuming those resistors are OK) and that is correct.
So working with it as it stands now you should also have approx 12 volts between ground and the midpoint (the output coupling cap... see my diagram above).
If all that is OK then it should all be working.
So working with it as it stands now you should also have approx 12 volts between ground and the midpoint (the output coupling cap... see my diagram above).
If all that is OK then it should all be working.
Yes, I'm using the Mean Well PSU supplied with the kit.
The plink sound is coming from the ACA itself, not the speakers.
Its heard about 10 seconds after hearing the capacitor charging sound from the speakers.
May remove the top cover plate to try to identify the source of the sound.
Otherwise no other issues.
A vast improvement over the Version 1.5
Thank you for the assist.
The plink sound is coming from the ACA itself, not the speakers.
Its heard about 10 seconds after hearing the capacitor charging sound from the speakers.
May remove the top cover plate to try to identify the source of the sound.
Otherwise no other issues.
A vast improvement over the Version 1.5
Thank you for the assist.
Well there is a lot of heat generated instantly by the FET's and so the mounting of those would be the first place to look. If they were not attached to the heatsink they would sizzle water in just a couple of seconds.
You may well find just moving it around and/or opening it up stops the noise... it has that kind of 'feel' about it from what you describe.
You may well find just moving it around and/or opening it up stops the noise... it has that kind of 'feel' about it from what you describe.
Pulled the amp from the system. Removed the top plate. Checked for any loose components. Found none. Everything snug. Powered up; no plink sound. Repeated half dozen times. No plink sound. Returned amp to system, running with cover off. No plink sound. Next will try with cover simply resting on top. Then will screw down cover. Thought I might use lock washers to secure top cover, allowing for some small amount of movement.
Thanks again for your help
Thanks again for your help
It will be fine. As mentioned, I think it has to be heat from the FET's given that it happens in seconds. It may even be the board creaking/moving in response to the heat.
I wouldn't disturb the FET's but you could always loosen and retighten any other chassis screws when the amp is really hot. That might set things in a minutely different position should it prove troublesome to pin down.
I wouldn't disturb the FET's but you could always loosen and retighten any other chassis screws when the amp is really hot. That might set things in a minutely different position should it prove troublesome to pin down.
My ACA chassis makes a noise every now and again, too, and it could very well be described as a plink. It's most likely to do it within 30 minutes of turning it on and will happen occasionally after that. Or not. It's pretty random.
I've toyed with loosening up some of the case screws a bit but it's never really seemed worth fussing with. Curious to hear how you make out with the issue.
I had the same thing happen to the first 1.6 I built. It appeared to be expansion of the chassis due to thermals. I'd left things a little loose
when squaring things up after the build and I guess I didn't really
tighten things enough. I snugged the chassis up tighter and I haven't
heard it since. A good way to determine if the issue is the chassis or your speaker is to disconnect the speaker and put an 8ohm power resistor across
the outputs and then listen for the noises. Similarly if you think the issue is the SMPS, try another one. Eliminate the variables and hone in on the root of the problem.
BTW one way to avoid that annoying cap charge whining at startup is to use a linear supply. The smaller SMPS wall warts don't have the umph to push through the uncharged cap and have to try a few times (repeatedly tripping their overload/limit function). The ones I now use push right through the cap and are ready to listen to in a few seconds including the bigger Meanwell SMPSs I am using (6amps @ 24vdc).
--Tom