Good day to all. I am a mature guy and have been in the electronics trade all my working life, I retired a number of years ago anywho I bought an XH-P901 pre amp board a couple of years ago and It has worked well up till recently it has now developed a fault. The sound is low and there is a lot of hum. I have changed the pair of NE5532P op amps and the electrolytic capacitors.
I would like to find a schematic circuit so I can investigate further.
I realise a lot of folks turn their noses up at this gear and I could buy a new board or in fact a better board for very little money but I like to tinker, it fills my time in 😴.
Thanks
I would like to find a schematic circuit so I can investigate further.
I realise a lot of folks turn their noses up at this gear and I could buy a new board or in fact a better board for very little money but I like to tinker, it fills my time in 😴.
Thanks
Opamps will not cause hum in themselves. There are really only two likely causes here.
1/ A genuine power supply fault but that isn't common on small low power stuff.
2/ A problem with a ground connection.
Has the preamp just failed like this in use or have you altered anything at all in the set up and connectivity of it?
1/ A genuine power supply fault but that isn't common on small low power stuff.
2/ A problem with a ground connection.
Has the preamp just failed like this in use or have you altered anything at all in the set up and connectivity of it?
Ta for your prompt reply and advise. I have to admit ,darn, I did tidy up the power supply wiring and changed the 12v supply lead, unfortunately, it had the positive and negative reversed, my eyes aren't so good these days, and blew up one of the op amps so I replaced both of them. I can't see any thing burnt out and would like to check the resistors etc and perhaps place a reverse supply protection in the circuit if I manage to repair it, just in cause seem silly person fits the supply the wrong way round.
Detail is everything you see 🙂 so the fault is man made 😉
You are going to have to look at the power supply and make sure that nothing is zapped there. An overcurrent situation could damage a regulator and let ripple through... so next question has to be what is the power supply?
You are going to have to look at the power supply and make sure that nothing is zapped there. An overcurrent situation could damage a regulator and let ripple through... so next question has to be what is the power supply?
Thanks for the advise, the power supply is a 12volt adapter and is working fine on other equipment, so I'm pretty sure somethings blown on the board.
Ah, I here an angel calling. My dinner must be ready. So I must obey and attend.
Thanks for your interest.
Ah, I here an angel calling. My dinner must be ready. So I must obey and attend.
Thanks for your interest.
Well... nothing on the board will generate hum as such. Hum is either picked up or introduced into the circuit. Could there be a low value 'ground break' resistor on the board that isolates the input ground from power supply ground. Typically this would be a few ohms and no more. Something like that might go open circuit with a reversed PSU.
Switch the thing OFF and check continuity from input grounds to output grounds and also to the power supply zero volt line.
I'm also going to say you could try the board with a 9v battery.
Switch the thing OFF and check continuity from input grounds to output grounds and also to the power supply zero volt line.
I'm also going to say you could try the board with a 9v battery.
That might not be conclusive proof if other equipment has onboard filtering and regulation. This preamp appears not to have that as it specifies a (presumed clean) 12 to 24 volt supply. I wouldn't bet against the power supply being faulty after a severe overload... but you need to prove it.
Thanks Mooly I believe you have solved my problem. Your mentioning the ground circuit, set me thinking and on close inspection 'a powerful magnifying glass' I discovered a terrible dry joint 😵 on the ground connector print through on the input plug which on cleaning up and soldering cleared the problem.
I'm a happy bunny again. 🐰
Thanks again. 🤓👍
