@bonsai
Great resource. Thanks.
How does this apply to preamps and RIAA units, perhaps with signal and PSU connected via an umbilical?
If I have a preamp with, say, three inputs are you suggesting that I bunch all the jacks close together, bond all the grounds and then run a cap to the chassis? How does that connection work with the PSU grounding?
Great resource. Thanks.
How does this apply to preamps and RIAA units, perhaps with signal and PSU connected via an umbilical?
If I have a preamp with, say, three inputs are you suggesting that I bunch all the jacks close together, bond all the grounds and then run a cap to the chassis? How does that connection work with the PSU grounding?
Yes, Toroidy in Poland. Makes wiring a little neater as I don't necessarily need an extra terminal board. More of a style/neatness thing, not really a requirement.
Best,
Anand.
They are double insulated. If you look on the chassis, you will (probably) find the double insulated symbol which is a small square surrounded by a slightly larger one.
@Anand
Thanks Anand.
If you've gone XLR balanced then a lot of the problems associated with classic ground loops and cross channel ground loops are resolved since there is no low Z path to 0V on a balanced input so any induced noise currents in the signal wires (hot and cold) are negligible. (I have not done any DIY amps with balanced inputs, but my commercial stuff is all balanced).
Thanks Anand.
If you've gone XLR balanced then a lot of the problems associated with classic ground loops and cross channel ground loops are resolved since there is no low Z path to 0V on a balanced input so any induced noise currents in the signal wires (hot and cold) are negligible. (I have not done any DIY amps with balanced inputs, but my commercial stuff is all balanced).
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Awesome!!!
My entire system from the DAC to AMP is differential. I used to use a TAPX (balanced autoformer setup) but that’s gone too. Modern day dac analog output stages are really quite good! Honestly, the lack of noise (and maximum signal) makes music so much more enjoyable!
And I don’t spin vinyl anymore in the main system (on an Andover Spinbase, sure, but that isn’t serious). And I don’t have SE sources.
Still, the intellectual exercise in wrestling ground loops and hum is stimulating discussion and useful too.
Thank you!
Best,
Anand.
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I know what the double insulation means. But how do You compare it with the wires with single insulation fixed directly to the metal tabs?
How do you compare it with the uninsulated wires on the IEC mains socket?
I would never do it like this...
Sajti
As far as I understand it, air is an insulator. For a Class II appliance, you have to provide 6.4 mm between any live connection and any metal that can be touched by the user. So the exposed tabs on the IEC connector, while not pretty, are OK. The issue I have is the wire tie that holds the mains wiring to the chassis. I don't think the insulation of a single wire provides enough insulation to claim Class II. It looks like they tried to add some insulation (the black stuff) but it's in the wrong spot.
Tom
I went balanced years ago and haven't looked back.
Those who wish to add balanced outputs or inputs may find this handy: Universal Buffer – Neurochrome
Tom
I agree - I don’t do it like that either. Like a lot of things, the get out card in this case will be a notice on the rear of the amplifier that says ‘Do not open. No user serviceable parts inside. Refer to qualified technician’ or something similar.
The devil is in the detail in these things, but the takeaway point is if you are building DIY gear, make sure it’s grounded (earthed), stick to safe wiring practices etc. for example heat shrink bare connections (which is what I would have done in your picture you posted earlier).
I have one. Just assembled it this afternoon and need to box it up later tonight.
Neat board and highly recommended piece of simple test gear that will get you 90% of the way to building quiet amps.
I have one. Just assembled it this afternoon and need to box it up later tonight.
Neat board and highly recommended piece of simple test gear that will get you 90% of the way to building quiet amps.
Thank you much for the idea/circuit. I'll have fun building it and it to my audio bench tools.
Best,
Anand.
It’s hard to make a general recommendation without looking at the specific detail. Whatever approach you use, keep the ground and input signal (L and R) tightly bound together to minimize loop area.
The cap from the signal ground to the chassis is between 2 and 5 nF (disc ceramic or similar) and at RF shorts the interconnect cable screens to the chassis metalwork right at the input. This makes the source, the cable screen and the receiving gear a single enclosure at RF and stops a lot of RF getting inside the housing (where it gets into everything) since this type of noise is almost always common mode.
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I agree - I’m all balanced on commercial stuff, but many DIY amps (incl. mine) are not.
However, with care you can build very quiet unbalanced systems.
A ground lifter only helps with classic AC ground loops or in the mono bloc example shown in the first post, to break a cross channel ground loop. Normally, in a conventional stereo amp with a single shared supply and unbalanced inputs you would just use hum breaking resistors and pay careful attention to wiring. If you are getting hum with a balanced input , the noise mechanism is probably common impedance related, or if magnetic field related (you can test this by moving the transformer), it’s getting in later in the amplifier signal chain. So I would say no, you don’t need a ground lifter with balanced inputs.
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