I'm finishing a power amp design which I will share later after prototyping. It's limited to 20 W into 8 Ohm. I have set a gain to 26 dB just because i't a very common value. Now I started to think isn't it too much? The amp will have a passive volume control attenuator at the front. As sources I have a USB DAC which can provide a full line level and even more and Phono Box E MM phono preamp which has 40 dB gain and its spec says 500mV (RMS?) of an output voltage for 5mV input. So it looks I'm about right as it will give full 20W at maximum volume. Any thoughts?
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You have it at 626mVRMS for full output. I wouldn't take it any lower. Maybe up to 774mV or even 1V.
26db is a gain = 20, if 500mV(Vp) is RMS, then the gain at the output of the amplifier will be 10V (Vp RMS), then the output power at an 8 ohm load will be 12.5 watts.
In case of passive volume control 26 dB of gain is even at the lowish side when using the phono preamp and wanting full volume (who really wants that?). It certainly is not too high, I would not change it.
The old issue of line level differences will show up as the phono preamp has the old standard 0.5Vrms and the USB DAC has the since many decades standardized 2Vrms output. You will notice level differences when switching sources. To overcome this the phono preamp could be upped to 1 or 2Vrms output. Or just put the volume louder 🙂 Lowering the output level of the DAC is walking backwards and then you'll have too low gain in both situations.
The old issue of line level differences will show up as the phono preamp has the old standard 0.5Vrms and the USB DAC has the since many decades standardized 2Vrms output. You will notice level differences when switching sources. To overcome this the phono preamp could be upped to 1 or 2Vrms output. Or just put the volume louder 🙂 Lowering the output level of the DAC is walking backwards and then you'll have too low gain in both situations.
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Allowing a headroom of 20dB above the 5 mVrms for the phono, I get an minimum amplifier gain of +28dB needed
to drive the power amp to clipping on peaks with the level control at maximum. So you're about right at 26dB.
to drive the power amp to clipping on peaks with the level control at maximum. So you're about right at 26dB.
It can't be both Vp and RMS at the same time and gain is not measured in volts.
No, it still be wrong. (1) Neither Vp nor Vpp is VRMS, which is the only V you should be concerned with here. (2) You mean 'output voltage', not 'output voltage gain'. Voltage is measured in, err, volts. Gain is a dimensionless ratio.
Output power is calculated from VRMS. Voltage gain is also calculated via VRMS. I can't tell what you put into Google Translate, but it must have contained something meaning 'output voltage gain' in the same sentence as '10V', which was wrong.
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What calculation? All I can see is a meaningless smorgasbord of terminology. When you make up your mind as to what units you're using, it might be possible to evaluate your arithmetic. At present it isn't.
that is, you surely see the obtained result in terms of output power and are just practicing the terminology?
now you are absolutely wrong.
now you are absolutely wrong.
There is nothing here for me to be wrong about. If you know P=V^2/R you don't need confirmation from me, but you do need to use the right units, and you haven't yet.
Everyone makes mistakes, and you are no exception.
to calculate the power, I take root mean square values, is it really not clear?
do you also go on being blind?
to calculate the power, I take root mean square values, is it really not clear?
do you also go on being blind?
No, it isn't clear at all. Not when you also talk about Vp and Vpp, and especially when you talk about two or all three of them being the same thing.