Been experimenting with one of these - https://www.ebay.co.uk/itm/265099568381 - it actually sounds pretty reasonable.
A big part of the appeal was it should work with a wide range of PSUs and doesn't need a dual rail supply, I was hoping to power this and a cheap class D amp off the same PSU - I was thinking a generic 18v laptop supply to keep costs down.
I've found that it's hum free with my bench PSU but that it has a slight hum with the laptop supply. Initially I thought this was power supply noise, but using the laptop supply I tried running a wire from ground on the phono board to the (mains earthed) case of the bench supply - the hum went away.
The turntable I'm using is not earthed to the mains either, so with the laptop supply earth is floating.
Any ideas on how to get this working quietly without a mains earth? I wonder if a similar switch mode power supply with a 3 pin (earthed) mains would behave differently?
A big part of the appeal was it should work with a wide range of PSUs and doesn't need a dual rail supply, I was hoping to power this and a cheap class D amp off the same PSU - I was thinking a generic 18v laptop supply to keep costs down.
I've found that it's hum free with my bench PSU but that it has a slight hum with the laptop supply. Initially I thought this was power supply noise, but using the laptop supply I tried running a wire from ground on the phono board to the (mains earthed) case of the bench supply - the hum went away.
The turntable I'm using is not earthed to the mains either, so with the laptop supply earth is floating.
Any ideas on how to get this working quietly without a mains earth? I wonder if a similar switch mode power supply with a 3 pin (earthed) mains would behave differently?
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Most turntables have a ground (GND) terminal or a captive ground wire that you would connect to the GND terminal on the preamp.
It may also be necessary to connect the preamp GND to a screw on the main amplifier's metal chassis that will act as a GND terminal.
If you've already tried that without success, tell us about the turntable and amplifier you are using to test the RIAA preamp.
It may also be necessary to connect the preamp GND to a screw on the main amplifier's metal chassis that will act as a GND terminal.
If you've already tried that without success, tell us about the turntable and amplifier you are using to test the RIAA preamp.
Earth leakage from the smps in the laptop supply. Put it on a linear supply and proper 3 pin earthed chassis.
Yes.
Currently testing the phono board with one of these: https://www.ebay.co.uk/itm/186733669961
Turntable is a generic NEC direct drive.
I am not using a metal case, so have connected the turntable ground to the specified grounding point on the phono board, as well as trying other ground points within the system. Any point I have tried works equally to remove the bulk of the hum, and operation is quiet with the bench supply, but with the smps i still get a small residual hum unless I run a second wire to a proper mains earth.
Yes, considered this but it somewhat defeats the object of the project as a decent linear supply is either expensive or relatively involved to build. Any way around it?
Had a quick google, this page seems to help explain what is occurring:
https://electronics.stackexchange.c...-earth-leakage-compared-to-regular-ac-dc-smps
The second diagram seems to indicate that adding an additional dc-dc converter would reduce the leakage. Not sure if this would be practical in my setup.
I had already considered whether one of these might solve the issue - any thoughts?
https://cpc.farnell.com/ideal-power/44atm036t-p180/psu-desktop-18v-2a-36w-c14-medical/dp/PW04993?st=Medical 18v power
https://electronics.stackexchange.c...-earth-leakage-compared-to-regular-ac-dc-smps
The second diagram seems to indicate that adding an additional dc-dc converter would reduce the leakage. Not sure if this would be practical in my setup.
I had already considered whether one of these might solve the issue - any thoughts?
https://cpc.farnell.com/ideal-power/44atm036t-p180/psu-desktop-18v-2a-36w-c14-medical/dp/PW04993?st=Medical 18v power
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Use an older wall wart. Criteria: has some weight to it (200 grams or so) and two prongs, ungrounded. Pretty much every device of 10-20 years age came with one, check the required voltage though.
Would probably work for the phono stage, but ideally looking for a solution involving a single power supply for the preamp and power amp - ideally close to 20v and a supplying decent amount of current (at least 2 amps). Hard to find a wall wart with those specs.
Another option is to test different Laptop supplies - I assume a grounded one with 3 prongs would be the best choice then.
A 40W wall wart is pretty uncomming, unfortunately.
A 40W wall wart is pretty uncomming, unfortunately.
@ blue tom, a single rail raw dc psu should be easy enough. What voltage does it need?
I’ve found a couple of earthed laptop supplies to try - odd sizes of DC plugs and life getting in the way are delaying testing of these.
@Simon1972 I’d like to have a go at building a PSU at some point but the thinking with this project was to avoid dealing with mains voltages, and because of that I chose pre-made boards needing only single rail supplies. If I was DIYing a PSU it might open up a few more possibilities in terms of the rest of the amplifier.
Let’s see if it works with any of the PSUs I have here already. 🙂
@Simon1972 I’d like to have a go at building a PSU at some point but the thinking with this project was to avoid dealing with mains voltages, and because of that I chose pre-made boards needing only single rail supplies. If I was DIYing a PSU it might open up a few more possibilities in terms of the rest of the amplifier.
Let’s see if it works with any of the PSUs I have here already. 🙂
This did the trick. Found an old Asus supply with a 3 pin mains cable. The power lead is shielded and -ve is tied to earth. Sounds great now.