What is wrong with the miniDSP

[DrWho]

95 watts into 8ohms is just under 29dBV (28Vrms) max output.

We use 2.83Vrms to measure speaker sensitivity, which is 9dBV.

This
means your amplifier has enough power to raise the SPL 20dB beyond the
rated speaker sensitivity. Let's say you're pushing 114dB SPL with 9dBV
at 1m....Max output (if the speaker could handle it) would be 134dB SPL
at 1m. The S/N of your amplifier is 80dB, which means your noise floor
is 80dB lower than the max output. That puts your noise floor with this
amplifier at 55dB SPL measured at 1m....which is really loud.

Sometimes
people use "daft" numbers when measuring S/N....let's say it was
measured with a -10dBV "consumer level". That means the true dynamic
range of your amplifier is closer to 90dB, putting the noise floor at
45dB SPL at 1m, which is still going to be annoying. I personally would
target being below 30dB, which means you need another 15dB of
attenuation after the amplifier in this particular scenario. That amount
of attenuation would also bring your clipping point down to 119dB SPL,
which is still more than plenty.

At the end of the day, your
amplifier is way overpowered. I would recommend something closer to a
10W amplifier for the HF in this configuration.

That said, Bob
Crites does sell autoformers that you could use to attenuate the output
after the amplifier. I bought a pair a while ago, but haven't gotten
around to installing them yet so can't attest to their distortion /
frequency response signature. I think whatever they add to the signal
path though would far outweigh a dramatically loud noise floor.

[bracurrie]

That puts your noise floor with this amplifier at 55dB SPL measured at 1m

This is pretty close to what I measured with my RS meter before I modded the amp and installed attenuation. After talking to Manley Labs I followed their recommendation to replace the AT7 tubes with AU7s and installed a resistor to ever so slightly increase the negative feedback to reduce gain. I do not know how much reduction there was, but with the 12dB of attenuation with my Crites 3636 autoformer I have reduced the noise to the point where most of the source material I play has more. To my ear it sounds excellent. The sparkle of the vibes and cymbals is as good as I have ever heard. I may have even created a situation where I may want to improve my TT cart.

Many thanks for lending your technical expertise to reviewing the numbers and helping me understand them. Attached is a picture of my attenuator rig.