Seeking Quiet Class D Amp for High Sensitivity Horn Drivers

[drjlo]

I have the same problem as you did before. I was using the Heil AMT before and the efficiency on ESS is 94 dB IIRC and I use Behringer CX3400 as crossover to fed Icepower 1200AS2.
The 1200AS2 itself has 45uV un-weighted noise but I got quite noticeable hiss from the tweeter that's due to the 26dB gain that amplify CX3400's noise. Someone suggested me to get an signal attenuator before feeding into the 1200AS2 and it simply solved the problem.
Now I switched to the DCX464-16 and it has 112dB/W sensitivity. The source I'm using now is MOTU M4. With this combination I don't have hiss problem even at desktop monitor condition.
But it's just for testing. I don't need such high output for my compression driver.
Now I power my DCX with headphone amplifier and get enough volume.
Perhaps you can try the attenuator if the sound quality is already good for the original source.
Attenuator from Shure
The one I used before is very cheap just around $10 each.

How is the transparency of CX3400 and is the High-Frequency (HF) horn equalization for constant-directivity useful?

I have similar gear including 110+ dB CD/horns, AMT (Beyma TPL 150H 102dB), 1200AS2, GaN, etc and using active crossover.
When I had everything hooked up without preamp/volume pot/attenuator before the amps, I got pretty loud hiss audible from listening seat.
Inserting a preamp resolves a lot of the noise issues, but I do not need a preamp in the system with its own sound signatures, so I ended up placing EVS Ultimate Nude attenuators on the amp's input, which was a nice solution. Still, with CD/horn, I can still hear a little bit of hiss/noise if I get close to the horns but not at my listening seat.

 

[tombo56]

And if a good class D amp really has a noise floor that is ~45dB lower than an A/B amp, why isn't that making the headlines? I would have built my own amp in the beginning, if I knew it would be so much quieter!

If reason for considering class D is low noise in first place, there are DIY designs available here that hardly class D can compete with. Say, 10 W output and measured total unweighted noise from 3.5 uV to 5 uV max., depending on if build is very compact ,with transformers near amplifier’s PCB, or little more spacious. So, >120 dB SNR.

5 uV noise would produce power to 8Ω which is 115 dB below 1W.

 

[drjlo]

"there are DIY designs available here that hardly class D can compete with. Say, 10 W output and measured total unweighted noise from 3.5 uV to 5 uV max"

That would be really what I need for my horns, but which DIY design is that?

Fosi V3 monoblock Kickstarter is ending in 5 days, so placed an order...

 

[tombo56]

That would be really what I need for my horns, but which DIY design is that?

Well, this one:
https://www.diyaudio.com/community/...te-low-power-class-a-amplifier-my-way.404147/

 

[bwaslo]

How good are ICEpower units for low noise? Like ICEpower 125ASX2 and 50ASX2SE?

Those are available from parts express. They also have their own self-branded units? I'm sure they are competent amplifiers, but are they good for low noise in terms of high sensitifity drivers?

I've used that on a horn. Very quiet and good immunity to ground noise even run single ended input. The 200ASC is also good.

 

[yys310]

How is the transparency of CX3400 and is the High-Frequency (HF) horn equalization for constant-directivity useful?

I have similar gear including 110+ dB CD/horns, AMT (Beyma TPL 150H 102dB), 1200AS2, GaN, etc and using active crossover.
When I had everything hooked up without preamp/volume pot/attenuator before the amps, I got pretty loud hiss audible from listening seat.
Inserting a preamp resolves a lot of the noise issues, but I do not need a preamp in the system with its own sound signatures, so I ended up placing EVS Ultimate Nude attenuators on the amp's input, which was a nice solution. Still, with CD/horn, I can still hear a little bit of hiss/noise if I get close to the horns but not at my listening seat.

I haven't compare it with other solutions and I've sold my piece after switching to DSP crossover.
The noise floor of that is too high for me.

 

[mikessi]

So the plan. I need to get the quietest components and reduce the number of components, to reduce noise up stream from the amp. I think this means I'm buying the new MiniDSP HTx processor.

Once the new HTx is in the system, I expect the residual noise will drop dramatically.

The background noise of a miniDSP 4x10 HD is audible from >1m via 111 dB horn in my quiet studio (below 20 dBA ambient) when no music is playing. When the 4x10HD was removed from the circuit & the inputs of the Buckeye Hypex NC252MP 8-ch amp shorted, the hiss dropped down enough to be inaudible from more than a foot away -- ie, effectively silent. (A 2ch version of this amp was measured by Amirm at ASR to be 96dB SINAD, 101dB SN at 5W, 119dB SN at full power (120W @8R) -- excellent even though not the very quietest.)

One solution tried when I had the horn running was to add a resistor L-pad at the horn driver terminals. That brought the residual noise -- mainly from the DSP crossover -- down without any audible effect on sound quality. Adjusting tweeter gain in the crossover to compensate did not seem to bring the residual hiss up much.