Expanding the Class D Conversation: How Would You Characterize Their Differences?

@bartsw 

Good point.

There are plusses and minuses. Based on some research just now:

I realize there would be no coloration from active circuitry and the switching speed would be good because auditory memory is notoriously short.

There could be electrical challenges from the following issues:

• If there is any contact resistance and oxidation from relay contacts and rotary switches with low-impedance it could matter at the margins.
• More important, the when you switch between two amplifiers, the *inactive* amplifier’s output stage still presents an impedance to the speaker terminals. This can subtly load the active amp and cause issues, I’ve read. It’s likely the switchers address this in their design but I’d want to verify that. I don’t want both amps connected simultaneously even briefly.
• I’d be alert to grounding and hum loops if both amplifiers are connected and share a chassis ground through the switcher, especially with mixed solid-state/tube topologies.

As for the plusses and minuses from the audio/critical perspective:

Advantages:

• The switching speed advantage is decisive for level-matched comparisons and would allow focus on a specific attribute.
• Eliminates the "cable swap" time delay. The switcher removes that variable.

Disadvantages

• Rapid switching can prevent the kind of extended, immersive listening that reveals what an amplifier actually does to music over time — how it handles dynamic architecture across a whole movement, how fatigue accumulates or doesn’t, how your relationship to the music shift A switcher optimizes for *discrimination* at the cost of *acquaintance*. The experience of "listening for differences" is different from the experience of "listening to music."
• The inactive amp’s electrical presence is a genuine presence — not just electrically but sonically. The active amp is operating into a slightly different effective load than it would standalone. How much this matters depends on the specific output impedances and topologies. 

Overall: If I had a switcher I knew would be benign, I would use it as another way to compare, not a replacement for the way I compare now.

Thanks for the suggestion!

Great question.  I spent the weekend at Axpona listening to wonderful equipment.  As I traveled the various rooms I started to wonder, having heard so many amazing speakers, is there a difference that I am actually hearing with regard to this Class A/B and Class D question?  As I collated all the collected information in my head, I came to the conclusion there was/is something audibly different about these two classes of amplifiers.  Is it "musicality," "presence," or some other descriptive term. I do not know what to call it yet IMHO "it" was there as I preferred the Class A/B presentation as a whole. 

"@bartsw - @hilde45 passive switchers don’t add noise. Sometimes I truly think two amps sound different but they are not."

Old tip - avoid low quality switcher boxes. When helping friends shopping audio chain stores for amps and speakers, the first thing we’d do is listen, and then ask to remove all of the amp and speaker switcher boxes. Then direct connect all of it.  Immediately hearing differences, in some cases quite notable.

ime, results can vary, and notably so when mediocre quality switch boxes are used for amps or speakers. Having used both, and more so with mid-grade available parts, I’ve found both types to be impactful to the sound in several unexpected ways. 

A passive switcher adds extra wiring, extra switch contacts, longer signal path, and comes down to impedance, contact quality, layout and parts quality used.

Can add micro-resistance, contacts can oxidize over time, and smear low-level detail. Can cause slight loss of transparency, softened transients, and many times hearing reduced air in the sound overall. 

Check this more  - If an active preamp used has higher output impedance and two amps have lower input impedance, then adding a passive box can possibly alter frequency response slightly, dull highs, reduce dynamics, mess with imaging too.

In my prior tests with both type switch boxes, determined a mediocre switcher box will blur differences, especially things like midrange texture, harmonic density, and decay.  Low quality and poorly built switchers can also introduce grounding issues.

Ive found a direct cable swap, the most accurate, and while painful to do, but can be more definitive. I would rarely do it for comparisons if the switch boxes were designed and built with extremely high quality parts, and still then - probably not. 

@swaudiofan 

As I collated all the collected information in my head, I came to the conclusion there was/is something audibly different about these two classes of amplifiers. 

This is a great observation. I, myself, would feel hindered by changing rooms, changing components, level-matching, and other factors which would problematize the comparison. If you were able to hear differences and you think you could factor out all those changing variables, then you have come away with some genuine insight!

@hilde45  

The changing o the rooms was not really a factor as regardless of the volume being played, room acoustics, etc. there was just something (still unnamed) that was similar with all the Class A/B amps that I did not sense with the Class D's.  And I own a real good Class D.  Will definitely be looking into this more as when I left Chicago, I wondered if I am to consider making a change from D to A/B.