Noise - I hope this comes out okay, this is amp turned on then off (the clicks) and awaiting the solenoid to shut off to quiet
https://share.icloud.com/photos/0efzQA2b7LLEhc8JUc9wbzLpA
https://share.icloud.com/photos/0efzQA2b7LLEhc8JUc9wbzLpA
I tried a shorted RCA plug and some positive news (I think)
On with shorted RCA quietest so far, not silent and still a little too loud, just audible from the listening position, just. Then if you turn it off and listen it's totally silent so hopefully with some care, looking at grounding and shielding and perhaps running an external pre-amp it might be okay. I wonder where to look at for improved sheilding
On with shorted RCA quietest so far, not silent and still a little too loud, just audible from the listening position, just. Then if you turn it off and listen it's totally silent so hopefully with some care, looking at grounding and shielding and perhaps running an external pre-amp it might be okay. I wonder where to look at for improved sheilding
if it is silent the few seconds it runs on the electricity store in the psu caps it can be 2 things:
ripple of psu goes to output because bad ripple réfection of the amp module, then you have to filter more, CRC or CLC
stray field from toroidal, try rotate it or put it vertically
I had both in my first diy amp back in the 90s it was a standard toshiba schema, kit from malpin I think.
first was cured with regulated psu but small humm was still there. it went away after packing the toroidal in a steel box inside the amp case.... at that time didn't knew that mounting the toroid vertically could salve the problem.
since then I make apms with external psu box (toroid and bridge and first cap bank) the wires going from the psu box to amp box act as R in CRC filtering.
Oh thanks not yet I need to see if I can find one near that level. A Quick Look and only found a few single figure Ohm power resistors so I need to empty a few old crossover boxes and have a bigger rummage
Also consider where on the audio ground that you make the connection to the case earth. Connecting the ground of the input jack to earth is not the quietest method.
Case PE connection is the point to connect Audio GND to with the 10 … 100 Ohm 2W resistor. Why 2W?! Think about that 🙂 Use the standardised method with crimped M4 eyelet and serrated washer plus normal washer etc. A direct connection of Audio GND to PE likely creates more trouble than it will solve. Very likely when using several amplifiers.
Don’t touch or alter input RCA connectors.
Don’t touch or alter input RCA connectors.
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Interestingly with the RCA direct (no pot) and the shorting plug today it's not got a problem at all with the chassis earth to the mains. Then adding any RCA connection from 0V to the chassis with a resistor (I found a 33 Ohm) makes no difference. So perhaps something with the pot before and not anything else making this loud hum ? (I'll double check with no short plug later.
The residual noise when the input has been shorted is quite small but just enough to be annoying. I have tried placing some shielding in different places near the transformer but can't seem to hear any difference, I'll continue to experiment and try taking the transformed off the mount and move it a little
Here's the transformer in place. It has a metal shield under and to the side (RHS in image) over the heat sinks. I will try a bit more with the speaker out cable and sheilding neat the board. I might look at tidying the mains cable connections that link the fan, transformer and ultimately a pre amp if this sounds better
Any recommendations vs sheilding. I have a cover I had bent image below when completed this will be connected to the chassis with metal screws
The fan works great, so that's good....
The residual noise when the input has been shorted is quite small but just enough to be annoying. I have tried placing some shielding in different places near the transformer but can't seem to hear any difference, I'll continue to experiment and try taking the transformed off the mount and move it a little
Here's the transformer in place. It has a metal shield under and to the side (RHS in image) over the heat sinks. I will try a bit more with the speaker out cable and sheilding neat the board. I might look at tidying the mains cable connections that link the fan, transformer and ultimately a pre amp if this sounds better
Any recommendations vs sheilding. I have a cover I had bent image below when completed this will be connected to the chassis with metal screws
The fan works great, so that's good....
Loosen the mounting bolt on the toroid transformer and try rotating the transformer to find the orientation of minimum noise.
If you were connecting the RCA jack to chassis through a resistor, that is not a good place for that. Try the audio ground to chassis connection preferably at the power supply ground where it feeds the amplifier.
I'll have an experiment I have looked at the signal GND connections on the back of the amp plate
Light Blue smoothing caps 0v
Green transformer AC out 0v
Yellow signal in 0v
Dark blue Signal out 0v
Light Blue smoothing caps 0v
Green transformer AC out 0v
Yellow signal in 0v
Dark blue Signal out 0v
Yeah that is because they are connected to eachother 🙂
The PCB copper exactly in the middle of the 4 light blue circles is excellent for the resistor.
The person that built this device forgot essential washers at the TO3 transistors. The board also has flux debri. Sloppy work.
The PCB copper exactly in the middle of the 4 light blue circles is excellent for the resistor.
The person that built this device forgot essential washers at the TO3 transistors. The board also has flux debri. Sloppy work.
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I would place it after the last filter capacitor, which is the point of lowest ripple voltage. I think the input ground would be connected to that, so maybe in the wide area to the right of the yellow circle.
Too late to edit my prior post, but the article on the Elliot Sound Products website, https://sound-au.com/earthing.htm, has good info on where to connect earth and info on a safe ground loop breaker scheme. This is the same article that I mentioned in an earlier post.
Phew, not built by me
I did wonder if adding additional low impedance cable to the centre of the caps 0v might help reduce impedance ?
Maybe you could try the resistor? Diagnose and then determine the best solution? On second thought the suggestion to use the center is not most optimal with regards to charging currents (missed the center point with green circle), slightly left of the lower left light blue circle is best. If hum is lower but not gone GND to the RCA connectors could be done with a 10 Ohm resistor. There is an error in the grounding scheme of this device. It may not be built by you but you will be using it so correcting the sloppy errors it has seems logical. Or get rid of it and use silent well built stuff.
If you make a direct connection of Audio GND to PE please only do so in the power amplifier and definitely not in the devices connected to that amplifier (which is a factor one hardly can guarantee).
If you make a direct connection of Audio GND to PE please only do so in the power amplifier and definitely not in the devices connected to that amplifier (which is a factor one hardly can guarantee).
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The solution IMO is to isolate the central bolt of the toroidal from chassis, The proximity of the top cover is encouraging a shorted turn.
Looking at the picture of the bottom of the PCB, the dark blue circle is the signal out 0V. I guess this is the speaker ground. It looks like it is on the same trace as the power transformer 0V. I would move the speaker ground to a cleaner location as well.