No O-scope measurements.
Based on previous amplifier builds and assumption, seems to be mains hum.
When jumpers are removed and used as a dedicated power amplifier hum reduces to almost inaudible.
Based on previous amplifier builds and assumption, seems to be mains hum.
When jumpers are removed and used as a dedicated power amplifier hum reduces to almost inaudible.
I wonder if the mains wiring inside the amplifer - on the right side of the photo, yellow, red and orange wires would be useful to replace with shielded ones?
Just as a precaution.
I also have a +/- 60V adjustable power supply but disconnecting the rectifier wirings (the transformer has two secondary windings) in order to provide external power (at two voltages) is a bit more than I would like to do as first step.
The photo is from the amplifier in its initial condition (the red Wima caps are from a previous technician).
Just as a precaution.
I also have a +/- 60V adjustable power supply but disconnecting the rectifier wirings (the transformer has two secondary windings) in order to provide external power (at two voltages) is a bit more than I would like to do as first step.
The photo is from the amplifier in its initial condition (the red Wima caps are from a previous technician).
Saturday tuned into Sunday but batter late than never...
Warmed up the gear, yes noise is still visible:
Should I use digital scopes?
Tried it out:
Picoscope:
Owon XDS2102:
Back to Tektronix then, vannot make much out from the digital ones.
Left (upper channel) probe tip against my finger to capture ambient noise, right channel (lower) on speaker output.
Signals in opposite phase with slight shift?
Next to check- power lines (as Hugo recommended)....
Warmed up the gear, yes noise is still visible:
Should I use digital scopes?
Tried it out:
Picoscope:
Owon XDS2102:
Back to Tektronix then, vannot make much out from the digital ones.
Left (upper channel) probe tip against my finger to capture ambient noise, right channel (lower) on speaker output.
Signals in opposite phase with slight shift?
Next to check- power lines (as Hugo recommended)....
OK, B+ and B- on power amplifier pins 29 and 30 - nominal value should be 50V, DMM shows +50,4V and -50,7V.
AC wise there seems to be ca 50mV P2P pulsation on both rails:
Should I look at the rectifier?
AC wise there seems to be ca 50mV P2P pulsation on both rails:
Should I look at the rectifier?
48V regulated rails (pins 16/17 and 22/23):
Measured values (DMM) +49,2V and -49,7V.
Looks clean on Picoscope
and also on Tektronix.
Measured values (DMM) +49,2V and -49,7V.
Looks clean on Picoscope
and also on Tektronix.
+35V (regulated) on pins 19/20 is also clean (as +/-48V).
Will check also the arriving (from power supply board) power on other boards but I would doubt if the wiring would cause any difference.
Will check also the arriving (from power supply board) power on other boards but I would doubt if the wiring would cause any difference.
Another set of voltages +/-24V (on control amplifier pins).
Measures +24,1V and -25,1V, clean on scope.
Next step - B+ and B- recifier or start shorting the signal path step by step starting from power amplifier input selector towards signal inpot sockets?
Measures +24,1V and -25,1V, clean on scope.
Next step - B+ and B- recifier or start shorting the signal path step by step starting from power amplifier input selector towards signal inpot sockets?
Post #26:
What is the vertical scale on the Tektronix?
The noise measured with the picoscope looks decent to me, +/- 0.062mVPP.
Hard to understand that there is so much difference between Tektronix and picoscope.
The Owon I don't get... 🙂
Other posts:
Voltages all look OK, the sawtooth is strange, never saw that on rails for the power amp.
I'll look at the schematic and let you know.
Hugo
What is the vertical scale on the Tektronix?
The noise measured with the picoscope looks decent to me, +/- 0.062mVPP.
Hard to understand that there is so much difference between Tektronix and picoscope.
The Owon I don't get... 🙂
Other posts:
Voltages all look OK, the sawtooth is strange, never saw that on rails for the power amp.
I'll look at the schematic and let you know.
Hugo
Nah, looks like normal ripple from unregulated supply. At 50mV p2p it's not to shabby/bad at all.
Since hum is 50Hz I'd be looking before rectification.
I would conclude, looking at the noise figure from the picoscope that this amp is pretty OK.
I got the impression the Tektronix is fooling you. (Open case?)
Hugo
I got the impression the Tektronix is fooling you. (Open case?)
Hugo
I kind of do not right now buy this 😉
I will do some signal path grounding and see what shows up.
Brief update - I started shorting the signal path wires to ground and reached a spot where noise does not disappear.
Basically located at "two short cable flights with switch contacts between them upstream from Normal/separated switch".
I will do some more testing/eliminating and then post photos and more detailed results.
Another challenge has been to take photos of the slowly passing signal on scope screen with a mobile phone camera (max "shutter speed" only 1 second does not capture two channels too nicely on one photo)...
Basically located at "two short cable flights with switch contacts between them upstream from Normal/separated switch".
I will do some more testing/eliminating and then post photos and more detailed results.
Another challenge has been to take photos of the slowly passing signal on scope screen with a mobile phone camera (max "shutter speed" only 1 second does not capture two channels too nicely on one photo)...
Midweek update:
I think I nailed something...
Now it is this:
and now it is that:
, and no soldering involved.
More to follow on Saturday...
And seems that my Tektronix is earning its wages 😉
I think I nailed something...
Now it is this:
and now it is that:
, and no soldering involved.
More to follow on Saturday...
And seems that my Tektronix is earning its wages 😉