Topping PA5 Review (Amplifier)

[proplayer69]

Please read the tech note on PFFB carefully, Ti states the THD improvement is max 5 db with pffb. So it is not only PFFB!

You're right, it's not only the PFFB that makes the PA5 a huge improvement in THD. The PA5 and Topping's latest designs use an active phase compensator in the feedback loop that compensates for the reduced loop gain at higher frequencies and the phase shift created by the LC filter. By doing so, they can increase the negative feedback significantly without compromising stability and still maintain a healthy phase margin even with inductor slightly saturating. I bet you all know the theory behind this feedback and compensation thing but i just say it just in case someone don't know. Sorry for bad english, im from east, far from western english

 

[capslock]

Thank you for that explanation. I always suspected the PA5 used a composite approach but that was denied in this thread:

TPA325x composite amp

So the TPA325x series of chip amps came out about a decade ago, yes really that long! My datasheets for the TPA3251D2 are dated June 2015 and that's where we happen to be now only 10 years later, so, happy birthday TPA325x series. :Present: Over the years I've seen it mentioned a couple of...

www.diyaudio.com

When you say active, does it mean there is an op-amp in the feedback loop?

Is there any documentation about the feedback loop? I looked at gamerpaddy's reverse engineered schematic of the potted module but of course, without knowning the schematic of the main PCB, one cannot understand the full circuit and feedback/compensation strategy.

Part of the reason why some 325x amps (PA5, 3e AF5, Wiim Vibelink) are so much better than standard PFFB amps is their gain structure. They shifted some of the gain needed to the preamp stage. But that is just the flip side of the coin of saying the achieved more feedback around the 325x.

 

[NTK]

If Topping implemented its patent in the PA5, it is a composite design.

CN216959816U - High-fidelity D class audio amplifier circuit - Google Patents

The utility model provides a high-fidelity D-class audio amplification circuit which comprises a filter circuit, a D-class power amplifier and a low-pass filter, wherein the filter circuit is electrically connected with the D-class power amplifier, the D-class power amplifier is electrically...

patents.google.com