So you think you got an excellent deal with your brand new "Renkforce MP-2000 power amplifier"?
(was McCrypt earlier, same pcb and stuff and components, namely a "raveland" pcb inside )
I own this amplifier and did some measures and looked at the internals
and came to some conclusions to this "2x 100W RMS/4ohm poweramp"
Mains fuse is rated at: 1,6A * 230v = 368w peak inrush, this is calculated rather high, but that's okay.
Transformator has around 120VA continous, and about 33VDC once rectified (volt times 4A fuse per rail: 132W peak DC).
Also, the main rectifier capacitors have a value of 4700uf 35V each.
Now, doing a quick calculation on the wattage with above information:
33VDC (23 AC volt * 1,4) max and 66W (per channel) = 2A output (matching the fuses)
With the class A/B amplifier (heat) loss (which is around 1/3) : 1,35A output per channel
With capacitor voltage loss (-10% on DC volts) multiplied by half of it is: 30VAC going to the speakers
Putting this in the right formula gives us a bit over 40w rms/channel (VAC * Ampere = Wattage)
This matches the relative small (for the 'rated' specs) passive heatsink nicely (around 20-25W heat per amplifier channel)
So, 100watts rms in 4ohm? nah, more like 40watts rms in 4ohm, stereo.
At 8 ohms speakers this might be about 20-30watts rms.
Now this might not sound like much, i bet it is enough for a medium sized living room when paired with some floorstanding speakers
Why? each doubling in volume to our ears requires 4x the power. (log scale)
A good example would be a car stereo: those are usually 10w / channel rms at 4ohm speakers, and still go pretty loud when needed.
Note: all these are my own measurements, and prove the RMS rating on these amplifiers is false.
This doesn't mean i hate it, i actually do like the amplifier for what it is designed for, amplifying with little to no distortion (thanks to the ST amplifier IC's).
It is currently offloading my home cinema receiver a little. however, please keep in mind that there is no speaker protection on board.
If something goes wrong inside the amp, you might fry your speakers as well.
Swapping out the main capacitors for 50V 6800UF variants, giving more stable power during peak powers, and bedtter voltage regulation overall.
Why: 35V doesn't have much headroom when you realize the DC voltage is 33V. Also, a power peak of +10% might kill those 35V caps within some time, as the stock design isn't designed for those power peaks.
Costs: some time and solder to swap the capacitors, and around 4€ for the 6800UF, 50VDC caps.
Don't believe the 100w rating on this amplifier series
For longetivity it is recommended to replace the main capacitors
I actually do like it's minimalist approach: less audio path interference (like component noise).
It's worth the money (€80) if you know how to do the decoupling cap upgrade.