Axe-FX III with Real cab vs. the Real thing

[tealtonerick]

Possibly. Hypex has much better damping specs. Never researched Purifi.

A lot of it is about transient energy storage. A tube amp stores a LOT of energy. Take a typical 100W tube amp like a Diezel. It will typically have 220uF of reservoir capacitance and a B+ of 450V. The energy stored is 22.3 Joules!!!

Now take a typical consumer Class-D "500W" power amp (actual continuous power about 100W). They usually have voltage rails around 50V and 680uF or so of capacitance. The energy stored (assuming bipolar supplies) is 1.7 Joules.

The tube amp has over 13 times the energy storage. So those palm mute transients are reproduced accurately. The Class-D amp runs out of gas.

For example, if your transient duration is, say, 100ms, and you're pushing a full 100W then the energy required is 10 Joules. The Class-D amp simply can't do it.

It's one of my pet peeves. People use cheap, low-end, consumer grade Class-D power amps and then make bold proclamations that the models don't sound as good as the real amp without understanding even a lick of the physics involved.

I put an Axe-Fx through a Crown X2 once and it Marty McFly'd me.

I am now having some very good success using a Purifi 1ET7040SA module coupled with the Micro Audio SMPS1k-PFCR2 power supply configured with +-70V rails and the output capacitor extension board as assembled for me by Dylan Launder of Buckeye Amps. This setup has a total reservoir capacitance of 44000uF and thus an the output energy capability of 215.6 Joules!... more than 9x the energy of the Diezel tube machine mentioned above.

The module's output impedance is spec'd at <0.65uOhms from 20 to 20kHz and with a 4Ohm load (which is what I happen to use), this results in a nominal damping factor of well over 6000, so basically only speaker cable limited. With this solution I have no trouble making the cabinet dance with palm muting transients via class-D. Just have to be careful with wielding the rated PEAK 420W at 0.1%THD to the speakers. On top of all that, the module output is just DEAD quiet as long as the input is.