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Usable Power, SS Watts vs Tube Watts, and the First Watt??

E-Stat said:
I've been using an MC502MP in the garage system for four years. Wonderful midrange resolution and power output for the money.

Will never, however, replace the VTLs driving the stats having tried that. Top end transparency just isn't there and they don't seem to be happy driving a reactive load.
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I've seen you write that before, and I wonder if it's the VTL's reacting in ways you like to the 'stats or the bit of roll-off of the 502 in the top octave that you are hearing. Could be either, I suppose (or both). The 502 loses 1.3 dB at 20 KHz from its LP filter. That had no bearing on my choice of it--I know I can't hear that high any more. The Purifi has a higher switching frequency and the filter is higher, too. But they are more expensive and harder to get for a good price. Still cheaper than Benchmarks or other amps of similar quality.

Rick "seriously degraded hearing above 12 KHz" Denney
 
rothwellaudio said:
Are you sure the issue isn't simply the input sensitivity of the amp? Even a 1000 watt amp will appear to be "not very powerful" if it requires 5V at its input for full power output and is being driven from a preamp that will only put out 500mV max.
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Not sure. The little Fosi tube phono preamp that we’re using has three gain settings, and even the hottest doesn’t allow the 2.1 amp to drive these speakers even close to the published specs.

However, we’ve got a new revelation in this saga! I had ordered the 2.0 channel Fosi amp that was the sister of the 2.1 amp we were using. This 2 channel amp is much more capable of driving this pair of ADS L880. It’s very clear that the 2.1 channel Fosi was reserving half of its power for the passive sub channel. (It was advertised as a 50wpc + 100w passive sub. The 2 channel one is billed as 100 wpc.)

It’s nothing to write home about, but much better than the 2.1 version. We’ve got some volume, and then bass is more present.

Regardless, it’s just a placekeeper. I’m building an Akitika kit amp (~60wpc SS class AB). I’ll link the build thread later.
 
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Lancer X said:
...It’s very clear that the 2.1 channel Fosi was reserving half of its power for the passive sub channel. (It was advertised as a 50wpc + 100w passive sub. The 2 channel one is billed as 100 wpc.)

...
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The 50+100 amp was not "reserving" anything for the sub in the way you infer (witholding from the main speakers).

The "50W+100W" amp has two 3116 chips. One chip operates in stereo mode for 50W to the main speakers. The second chip is set up in parallel bridge mode for 100W to the sub.

The "100W" version of the amp also has two 3116 chips. But, in this unit, both chips are set up in parallel bridge, one for left channel and one for right channel.
 
whoaru99 said:
The 50+100 amp was not "reserving" anything for the sub in the way you infer (witholding from the main speakers).

The "50W+100W" amp has two 3116 chips. One chip operates in stereo mode for 50W to the main speakers. The second chip is set up in parallel bridge mode for 100W to the sub.

The "100W" version of the amp also has two 3116 chips. But, in this unit, both chips are set up in parallel bridge, one for left channel and one for right channel.
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Precisely. In other words, the design itself reserves half of its power for a passive sub. :p
 
I wonder if this amp is both "optimistically" rated, and because of the way Class D amps work, has a challenge driving a particular speaker load? No matter what a speaker's nominal impedance is, they can be lower than that when playing music. As opposed to test tones, into a fixed impedance?
 
NeilBEN said:
I wonder if this amp is both "optimistically" rated, and because of the way Class D amps work, has a challenge driving a particular speaker load? No matter what a speaker's nominal impedance is, they can be lower than that when playing music. As opposed to test tones, into a fixed impedance?
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Load sensitivity is not a specific ClassD weakness (or A/AB strength, for that matter). It’s all about implementation. Read the reviews of better Class D amps from Hypex and Purifi. They are all current-limited at 2 Ohms, but at high power. And within that envelope, their frequency response does not change.

Whether they will be perfect driving speakers like Wilson WATTs or Scintillas that dip lower than that, don’t know. And then there’s a question from above with respect to Hypex amps into purely capacitive loads. But that’s not relevant to most folks.

There are poir or inappropriate implementations in all topologies. Lots of Class A amps have high output impedance and therefore suffer significant changes in frequency response with speaker loads of incompatible impedances.

Rick “it’s about design” Denney
 
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