Aguilar AG500 thoughts..

[seanm]

Now back to our AGUILAR AG500 program already in progress.

Nope, sorry more thread hi-jacking

And then I said: "I SUSPECT that they don't have the sag that an analog amp has. The switcher should compensate for heavy output current demands.

By switcher do you mean switching power supply or switching in class D amps? If it is the former, the iAMP does not have a switching power supply. Either way, could you expand on sag and how the switcher would help?

 

[Thunderfunk]

A Class-D amp (digital) is a switcher similar to a switching regulator power supply. The difference is that in a power supply the switcher is used to convert the wall voltage to a fixed DC supply voltage, whereas in a digital power amp, the output is variable. Take a 50KHz "slice" and it's either on or off. If it's on, it charges the output filter cap. If it's off, it doesn't. The speaker draws current out of the cap, while the cap averages the voltage of the pulses coming in to produce an "analog" output voltage. In a power supply the output voltage is tied to a reference, and the number of on pulses are adjusted to maintain the fixed output voltage. In a digital power amp the circuit must track the output speaker voltage to compensate for the load that's applied. That leads me to think that the amp would compensate for "sag" in the power supply. Thump a note on my amp and the power supply will sag, compressing the output signal, and "distorting" it. If this happened with a digital amp, wouldn't the amp see it as distortion and compensate? If you attach a 2-ohm load, it's going to draw more current out of the cap than a 4-ohm load, and the "switcher" will have to compensate with more "on" states charging the cap. And does the amp also compensate for changes in speaker impedance at different frequencies?

I don't know the answer to this, and it's why I asked the question. Are digital amps "stiff?" Is that bad?

 

[Mike Dimin]

A Class-D amp (digital) is a switcher similar to a switching regulator power supply. The difference is that in a power supply the switcher is used to convert the wall voltage to a fixed DC supply voltage, whereas in a digital power amp, the output is variable. Take a 50KHz "slice" and it's either on or off. If it's on, it charges the output filter cap. If it's off, it doesn't. The speaker draws current out of the cap, while the cap averages the voltage of the pulses coming in to produce an "analog" output voltage. In a power supply the output voltage is tied to a reference, and the number of on pulses are adjusted to maintain the fixed output voltage. In a digital power amp the circuit must track the output speaker voltage to compensate for the load that's applied. That leads me to think that the amp would compensate for "sag" in the power supply. Thump a note on my amp and the power supply will sag, compressing the output signal, and "distorting" it. If this happened with a digital amp, wouldn't the amp see it as distortion and compensate? If you attach a 2-ohm load, it's going to draw more current out of the cap than a 4-ohm load, and the "switcher" will have to compensate with more "on" states charging the cap. And does the amp also compensate for changes in speaker impedance at different frequencies?

I don't know the answer to this, and it's why I asked the question. Are digital amps "stiff?" Is that bad?

Dave,
I realize that this is the aggie thread and I am sorry that it got hijacked, but I just want to set the record straight, at least on the EA amps. Unfortunately, Dave, your expertise (as others here) gets warped by the those with their own intentions. Like I said, I am interested in Thunderunk and truly hope that you succeed. I really have a soft spot for the smaller companies, since they are the most responsive to the customer. I love to see each of them succeed, Thunderfunk as well as EA. Just a few things on the iamp to address your concerns about power supply:

The iamps have a digital amplifier but a linear power supply. The imaps linear power supply responds with voltage sag and compression just like tube amps. There are no pulse or smoothing transformers in the amplifier section. Pulse transformers are in switching power supplies, not in switching amplifiers. In speaking with Gary at EA, he agrees that switching power supplies will make an amp sound brittle if they are too tightly regulated; that is why EA uses conventional transformers. Also, you site, as an example, a sampling rate of 50KHz - I just wanted to let you know that the EA amps switch at up to 300KHz.

Mike