I had a question related to Class D


Hello all, I 'm testing TDA7498 100 watt class D amplifier. I had a question that relates to Class D. I'm thinking about buying a Class D solid state guitar amplifier, but I heard that Class D amps lose a lot of their power (more than Class A or A/B amps do) when they drive speakers above 4 ohms, and my speaker happens to be 8 ohms. Is this so? If it is, the high watts the amp manufacturer claims for the amp don't seem as impressive.

bryant11

The issue are not the amps but the power supplies feeding them. For some reason, class D manufactureres skimp on the PSUs.  If you get one with a powerful large toroidal unregulated PSU, they will not run out of steam. 

It seems odd to me that a manufacturer would post output specs at 10% THD. Who cares?

Why wouldn't they publish specs for a listenable THD?

My Parasound New Classic 200 Integrated uses Pascal D modules outputting 110 wpc with .05% THD @ 4 or 8 ohms.

They publish a 1% THD as well, but I don't care that if outputs 125 wpc at that THD level... it just tells me not to turn it up to 90-100% volume.

This D amp can get way louder than I'll ever need with 8 ohm, 87 dB speakers with the volume at 35-40%.  No power dropping off with 8ohm speakers. I'm guessing that story is from older D amps.

It seems odd to me that a manufacturer would post output specs at 10% THD. Who cares?

Why wouldn't they publish specs for a listenable THD?

The chips are not meant to be 'high end' FWIW. 100 watts is where the amp clips and at that point its making 10% distortion. So that is the spec they published.

but I heard that Class D amps lose a lot of their power (more than Class A or A/B amps do) when they drive speakers above 4 ohms, and my speaker happens to be 8 ohms. Is this so?

@bryant11 

No. Most solid state amps will make less power into higher impedances. So you have to look at the 8 Ohm rating to see how much power the amp makes into that impedance. Driving 16 Ohms will further cut the power in half... you see how this works? Its not a 'class D' thing.

IMO if you are planning to use this for guitar, you'll be better off with a tube guitar amp of about 25 Watts. I think you'll find that it plays just as loud but is a lot more musical.