Here is the current link to Rod Elliot's page and the P3A amplifier.
You can note that in the input he uses a 100pF capacitor to ground.
https://sound-au.com/project3a.htm
What is interesting is that years ago when I downloaded the schematic the value of that same capacitor was 220pF. I still have that older schematic which has a value of 220pF.
Why such change?
I myself am currently thinking of what capacitors to put in this amp because I tested it with a square wave and got unpleasant output results, with a square input and a purely resistive output dummy load I got sawtooth looking output in my scope.
Some capacitor values were off so I will change them to spec, namely 100pF, what should I do with the input to ground cap? Follow the latest advice and use 100pF?
I am also thinking of using polypropylene caps , before I had ceramic.
Any advice from members is welcomed, thank you.
You can note that in the input he uses a 100pF capacitor to ground.
https://sound-au.com/project3a.htm
What is interesting is that years ago when I downloaded the schematic the value of that same capacitor was 220pF. I still have that older schematic which has a value of 220pF.
Why such change?
I myself am currently thinking of what capacitors to put in this amp because I tested it with a square wave and got unpleasant output results, with a square input and a purely resistive output dummy load I got sawtooth looking output in my scope.
Some capacitor values were off so I will change them to spec, namely 100pF, what should I do with the input to ground cap? Follow the latest advice and use 100pF?
I am also thinking of using polypropylene caps , before I had ceramic.
Any advice from members is welcomed, thank you.
That input filter corner is set at over 1MHz. The filter capacitor value is not critical.
If you have problems in the audio range, the input filter isn't the cause with those values.
You can use either ceramic COG/NPO, or extended foil film type, capacitors with short leads.
Maybe your scope probe was off calibration, check it on the scope's internal square wave .
If you have problems in the audio range, the input filter isn't the cause with those values.
You can use either ceramic COG/NPO, or extended foil film type, capacitors with short leads.
Maybe your scope probe was off calibration, check it on the scope's internal square wave .
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