Coupling capacitor cutover frequency

Do It Yourself
#1

Hi, I have a beautifully built Reisong A30 SET tube amp point to point which means easy to upgrade. Sounds incredible but I can’t sit too long without doing some kind of tinkering haah.

I wanted to do some capacitor rolling when something occurred to me. The coupling caps are 0.22uf at the manufacturer stated input impedance of 100Kohms the -3db cutoff point is 72Hz

So does this mean my amp will never be able to play music that goes as low as a pipe organ ? Even though my subwoofer and speakers can handle low frequencies?

Was thinking then that a higher capacitance would give me a lower cut off frequency for example 0.47uf would give me 33Hz.

I know the cut off frequency doesn’t mean anything below 72Hz is totally lost but what’s the margin ? Can it really handle very low frequency music and if not then would an upgrade to higher capacitance be better ?

#2

You are correct in thinking that doubling the value of the input capacitor would halve the -3dB frequency at the input, However you need to look at the characteristics of the output transformer, since that might be the limiting factor on the low frequencies the amp can reproduce.

It has been many years since I made such calculations, but my back-of-envelope working showed a much lower -3dB point for the values you gave.

2 Likes
#3

I believe it’s their own stock transformer primary impedance around 2500ohms output 4,8

Not sure what the frequency range is. I’ll need to email them to find out more specs

#4

Is it possible the cut off frequency of those parameters maybe 7.2 Hz rather than 72 Hz?

http://www.learningaboutelectronics.com/Articles/Cut-off-frequency-calculator.php#answer1

#5

Sorry I meant to say 7.23hz optimal low frequency response is 72Hz according to

https://www.v-cap.com/coupling-capacitor-calculator.php

If I add 0.47f the calculator gives
3.39Hz optimal low frequency response 33.8Hz