Princeton Reverb clone treble cap leakage
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Stevem
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Re: Princeton Reverb clone treble cap leakage
I got to the point now that on repairs or mods with silver mica caps or ceramic types I pack silicone sealer around them to kill vibration induced microphonics.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Princeton Reverb clone treble cap leakage
Good practice seems to be to heatsink modern silver mica caps during soldering, eg put a crop clip on the legs.
Regarding ceramic caps, in this thread https://music-electronics-forum.com/sho ... hp?t=30756 Steve Conner mentions that those with a high-k dielctric tend to exhibit a significant voltage co-efficient, as well as the temperature co-efficient that I was aware of. Hence that can add distortion.
Of course in hifi, that would seem to preclude their use, but with guitar amps, where used appropriately they could be beneficial.
Dunno if the 250pF and 120pF ceramic caps we tend to see in BF preamps would use a high-k material, but the 1nF or 500pF at the input to the LTP may be a contender.
My understanding is that in modern times, high-k ceramic caps are primarily intended for use as power supply bypass, eg to keep the +and - supplies to op-amps very low impedance at high frequencies; as such, their exact value and hence their voltage and temperature coefficients aren't critical.
Regarding ceramic caps, in this thread https://music-electronics-forum.com/sho ... hp?t=30756 Steve Conner mentions that those with a high-k dielctric tend to exhibit a significant voltage co-efficient, as well as the temperature co-efficient that I was aware of. Hence that can add distortion.
Of course in hifi, that would seem to preclude their use, but with guitar amps, where used appropriately they could be beneficial.
Dunno if the 250pF and 120pF ceramic caps we tend to see in BF preamps would use a high-k material, but the 1nF or 500pF at the input to the LTP may be a contender.
My understanding is that in modern times, high-k ceramic caps are primarily intended for use as power supply bypass, eg to keep the +and - supplies to op-amps very low impedance at high frequencies; as such, their exact value and hence their voltage and temperature coefficients aren't critical.
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Re: Princeton Reverb clone treble cap leakage
yes at higher frequency the cap 'Q' becomes more important when passing audio signals. not all caps are designed for a high 'Q'.
Re: Princeton Reverb clone treble cap leakage
I'm not a fan of ceramic in the audio path and don't be confused by what looks like a ceramic disc capacitor. Fender used PAPER disc caps, not ceramic. These were made of paper and aluminum.
Marshall did use ceramic (500pf) pf caps for a brief time, treble bypass caps on the audio path of the Lead Channel (470K resistor junction, Bass and Lead Channels, red in color (see pic), and also in the Tone Stack) but I've seen more paper disc use. And then in 1998 (?) Marshall RI'd the Silver Jubilee Marshall using ceramic (small newer type yellow sausage shaped tubes) throughout the entire circuit path with horrible sonic results. I know this for a fact because I had the unique experience of rebuilding one (keeping the modern board) to original SJ specs while having both version in house. And bear in mind, the SJ had multi-gain paths within it, running the audio through many ceramic caps, not just a Treble cap or a Treble Bleed cap tied to a resistor. It was one of the most sterile amps I have ever played.
Marshall did use ceramic (500pf) pf caps for a brief time, treble bypass caps on the audio path of the Lead Channel (470K resistor junction, Bass and Lead Channels, red in color (see pic), and also in the Tone Stack) but I've seen more paper disc use. And then in 1998 (?) Marshall RI'd the Silver Jubilee Marshall using ceramic (small newer type yellow sausage shaped tubes) throughout the entire circuit path with horrible sonic results. I know this for a fact because I had the unique experience of rebuilding one (keeping the modern board) to original SJ specs while having both version in house. And bear in mind, the SJ had multi-gain paths within it, running the audio through many ceramic caps, not just a Treble cap or a Treble Bleed cap tied to a resistor. It was one of the most sterile amps I have ever played.
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