I have just built one of these headphone amps, works OK but some mains hum at high volume settings but this doesn't intrude at normal listening levels.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
You built the amp as a Class I (earthed) device. You may have some ground loops over the case in there. I would assume the PCB design did not take this into account.
And the obvious one, you didn't use shielded cables for the input.
(Temporarily take the board out and put in on a piece of cardboard or whatever to test #1.)
And the obvious one, you didn't use shielded cables for the input.
(Temporarily take the board out and put in on a piece of cardboard or whatever to test #1.)
Thanks for the tips 🙂 It was the earth, now totally silent even with unscreened cable on the input 😀
Does not need to be connected to earth, yellow green wire.
Only need to connect the power. Disconnect the line.
PCB through the screw and wire.
Normal HA-PRO connection. Signal to noise ratio is very good.
Well the answer is yes.......just
Although the AKG's took about 50 hours to come good.
I built this amp's case out of junk I had in my scrap metal pile. Its going to be a gift for my son. VU's are cool.😉
This amp sounds very good, for what its worth......very happy.
Although the AKG's took about 50 hours to come good.
I built this amp's case out of junk I had in my scrap metal pile. Its going to be a gift for my son. VU's are cool.😉
This amp sounds very good, for what its worth......very happy.
Attachments
i see that the board has a relay and some circuits for the relay.
what are the protection features?
delay start?
over-voltage?
loss of one power rail?
etc.
it is almost certainly OK.
but ultimately it depends on the voltage swing you need.
it goes roughly like this:
let's assume that 1.2 volts RMS is enough for the SPL (loudness) you want.
at 120 ohms the output current would be 10 ma and the output power would be 12 mw.
this is well below the board designer's claimed max current of 150 ma (at which point the opamps would still be considerably below their ratings for both current and power output).
Is the first stage inverting and the second stage non-inverting? So the output is inverting? Is that fine when powering a headphone? Sorry my knowledge is very limited 😀
Yes it is . It has a DC voltage protection , as well as delay function. Of course, I recommend switching above 275V104 a capacitor in parallel . Thus even better , you can eliminate off sparks, abnormal noise voltage generated .
If you turn off the power does not generate abnormal noise, then you can ignore it .
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