I wanted to know what happened to the Muffsy RIAA compliance if the capacitors were out of spec, and started with a plausible scenario where the capacitors were 3% below their stated values.
This time, lets see what happens if the capacitor values are extremely low. Let's say they're 10% below what it says on the capacitors. Like last time, the simulation goes from 20-20.000 Hz.
Clearly, the graph is a little more wiggly. But how bad is it? As it turns out, not too shabby at all.
The lowest deviation from the RIAA curve is -0.16 dB, which is all the way down at 20 Hz. The highest deviation is +0.55 dB, at around 19-20 kHz. Even though this could be read as if though the bass is lacking, notice that it is spot on again at 30 Hz.
What this simulation tells us is that you'll get a small boost in the bass and treble regions, an ever so slightly, very small loudness effect. Although this scenario isn't that probable, it could still happen as most of my measured capacitors are on the low side in the tolerance range.
So what happens if we take this to extreme levels? Pretty much more of the same. Below is a picture of the RIAA equalization circuit that is used in the Muffsy Phono Preamp.
These are the correct values:
- C1: 136nF (2x 68nF)
- C2: 47nF
What we're about to do is not at all recommended when building the Muffsy Phono Preamp. If you want this effect, you should use your amplifier's tone controls instead. Let's change C1 to 83nF (68nF +15nF) and C2 to 33nF:
The results of the -10% capacitor values are expressed even more. You will get a huge boost in both the bass and treble frequencies.
The level is -1 dB at 20 Hz and gets compliant at 45 Hz. It increases to +1.85 dB at 200 Hz, down to -0.2 dB at 1.5 kHz, before it goes up to +1.55 dB at 20 kHz.
You may very well find that you like this "loudness-RIAA", but it shouldn't be done in the phono stage. Nevertheless, this really illustrates what happens with extremely low capacitor values. Although it is way out of compliance, the result will be a fairly pleasant one.
For the next installment of these simulation, we'll look at what happens when the values are higher than what it says on the capacitors.