Digital Amps vs Solid State Amps

Hi,

I've owned the Pass XA 100.5 mono amps for a little over a year, but recently sold them. I've also owned H2O Audio class D amps for a long time, and am currently using H2O mono amps to drive my Avalon speakers. So, I have compared both these amps directly with my speakers and have also listened to both amps extensively with the Magico V2 speakers. The verdict? They are both great when set up within the right system.

I think both the Pass and the H2O amps sound wonderful but in different ways, and my preference comes down to system matching. The Pass XA.5 amps have a full, warm sound with a glorious midrange and very smooth high frequencies, and sounded beautiful with the Avalons. However, the Pass amps don't have the control in the low end that class D amps generally exhibit.

The H2O mono amps don't flesh out the midrange as much as the Pass amps do, but they are still wonderfully liquid sounding through the midrange. They can be amazingly good sounding in the right system. I preferred them to the Pass when mated with the Magico V2.

Alan

Hello Alan,

While I myself own class D amplifiers (Spectron) and enjoy them immensely (with carerfully matched associate equipment) I absolutely diagree with your statement:

"...the Pass amps don't have the control in the low end that class D amps generally exhibit. "

What you observed is simply power matching of amplifier to the speakers it must drive (and control). If you would try Pass XA 200.5 or their more power power amp (if exists) you would write exactly opposite.

Hi Dob,

I respectfully disagree that the XA200.5 would control the bass of my speakers better than either the Spectron or the H2O.

I don't think the wattage of the amplifier is what determines its ability to control the low end of the speakers, as much as it is the overall topology of the design. While the higher line of the XA.5 series has more wattage and current available, you will notice that the damping ratio of the XA200.5 is exactly the same as the XA100.5, and I imagine that's due to the overall topology of the amplifier (its low loop feedback).

I've listened to other 100 watt amplifiers in my system, similar in power and current specifications to the Pass XA.5 series, that have controlled the bass far better than the Pass mono-blocks. So I think that if you use an amp designed with low or no negative feedback mated to a speaker with a difficult low frequency impedance load, the result will be comparatively loose bass control, no matter how much wattage the amp pushes out. If my speakers had a more friendly impedance load, I think the Pass would control the woofers to my satisfaction.

In contrast, an amp like such as Spectron or H2O has a much higher amount of loop feedback and a higher damping ratio, and that's probably what allows it to control the woofers of a low impedance bass load.

Alan

Alan - Digital amps most likely don't have higher amount of feedback since analog parameter - time (duty cycle) is more linear than class AB transistors. High damping comes from the fact that speaker is always connected between very low impedance points thru very low resistance Mosfets. Icepower uses full bridge (H-Bridge) of N-Channel Mosfets that keep speaker connected between GND and V+ - only direction changes.

Class AB amps in contrast have often very high gain before feedback is applied reaching 4000. Class A i better in that respect with gains as low as 200 and that's were I would place digital amps.

Hi Alan,

While I am glad the H2O are providing a very satisfying sound, I believe you would be please as Punch if you heard the XA160.5 or XA200.5 in your system. I do think the class D amps can provide a more realistically-priced and cool-running alternative to these monsters.

The XA200.5s provide bass that is simply natural and glorious in my system. The Pass bass exceeds a prior amp that had MUCH higher wattage and damping factor, which suggests to me that the topology is important and that Nelson got it right. My search is over, and I am relieved.