• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

replacing cathode bypass cap. with shunt reference voltage chip

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MarcelvdG

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Joined 2003
If post 20 is an answer to posts 16...19, I don't understand the answer. It is unclear to me whether that 2 mV is RMS, peak or peak-peak and what part of it is noise. If it were 2 mV RMS noise, that would be terrible, even over a bandwidth of 100 MHz it would still be 200 nV/sqrt(Hz).
 
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978HK

Banned
Joined 2018
That is DC with 2mVAC p-p AC waveform without signal = noise. In context, and measured experience expect 7x without what was mentioned. Would I use a diode as bypass for a bias resistor? Got the right voltage drop? .. maybe, and I think it is one of those things - if it sounds better. Fortunately, I don't have that problem..

Just trying to help the OP.. try the above - was clearly apparent on my CRO. To the rest, kind regards.

HK
 
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MarcelvdG

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Anyway, there is a plot of the equivalent noise at the REF terminal in the TL431 datasheet. The white part is around 125 nV/sqrt(Hz), some 20 dB to 28 dB above the average A- and RIAA- weighted audio noise level you can obtain with a good optimally biased triode, so be a bit careful with it in low-noise stages. By the way, there is also an impedance plot showing that the impedance is nearly flat until 100 kHz at 10 mA cathode current.
 

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