Considering Multichannel Audio System Options

[mcarr6]

Just noticed on the exasound website that they have: Limited Edition Balanced e38 DAC with Mini-XLR Line Outputs.

[electro]

On 8/23/2018 at 2:06 PM, Kal Rubinson said:

Yes.  87dB is reasonably low.

 

I had mine done at the factory, too, and it made a difference.  However, here's what they had to say:

With an ordinary amp (meaning gain around 29dB), there is audible hiss if my ear is about 8" from the tweeter.  I find that disturbing when working in the region of the speakers even though it is inaudible at the listening position.  With lowered gain, I need to have my ear less than 2" away to hear anything and that takes special effort.  It is not a biggie but a head's up.

 

Kal, we have conversed several times over the past 10 years.  I’m using the AR MP1 (following your advice)  I also have a Parasound P7 (now used elsewhere)  which I previously used. The MP1 is connected to a pair of JC1’s and an A31.

 

I am having problems though. Loud crack through speakers when switching inputs, muting or using the adjustments to change  channel gain. Hiss audible from 12 feet away. Through ML CLX Arts and especially through the surround channels.  All amps connected with balanced cables. 

 

the MP1 is currently with Absolute Sounds (UK importer) who tell me it measures to spec!

 

Frankly I haven’t heard such a poor S/N from an amp in 35 years!

 

Can you tell me what the AR guys did to lower the noise floor? Was it to lower the gain? Does it effect the sound quality? I would like to get the modification made in the UK if possible.

I have tried emailing AR but have been ignored.

 

My Multichannel sources are. Oppo 205. Exasound e28. Sony SCD9000ES.

[Kal Rubinson]

10 hours ago, electro said:

I am having problems though. Loud crack through speakers when switching inputs, muting or using the adjustments to change  channel gain. Hiss audible from 12 feet away. Through ML CLX Arts and especially through the surround channels.  All amps connected with balanced cables. ....................................The MP1 is currently with Absolute Sounds (UK importer) who tell me it measures to spec!

I have been through all that.  AR has said the same to me (after an expensive tune-up).

10 hours ago, electro said:

My Multichannel sources are. Oppo 205. Exasound e28. Sony SCD9000ES.

I have used the same sources. 

10 hours ago, electro said:

Can you tell me what the AR guys did to lower the noise floor? Was it to lower the gain? Does it effect the sound quality? I would like to get the modification made in the UK if possible.

Part 1:  The noise floor solution lies not with changing the MP1 but with lowering the noise level through the system by lowering the gain of the power amps.

 

First, can you confirm that the noise is constant and not changed with the volume control as is the case with mine?  This will permit you to take advantage of the very output levels (~18V) that the MP1 is capable of.

If so, for every dB that you can lower the input gain of the power amp(s), you can lower the S/N of the output to the speakers.  John Atkinson tells me:  "Almost all amplifiers I have measured have voltage gains into 8 ohms of 25-29dB. The old THX standard was IIRC 27dB." 

 

The Parasound A31 (I have one, too.) is 29dB, as is the JC1, but the A31 also has a +/-6dB trim adjustment.  So, with the A31, you can turn the gain down to 23dB and turn up the output of the MP1 to enjoy a 6dB reduction in noise.  That said, the 6dB improvement is effective but marginal dependent on the speakers, some of which emphasize the HF noise.  For example, switching from the B&W 802D3 to the Revel Performa f228BE resulted in a drastic reduction of audible HF noise all by itself and the -6db lower gain was sufficient.

 

Your problem is that the JC1 has no such adjustment and the recommended solutions are to  (1) insert balanced line attenuators (-10 to -15dB) into the input jacks of all your amp channels or (2) get amps with lower (or adjustably lower) input sensitivity.   You may have an innate objection to using the attenuators but they are a simple way to demonstrate the validity of this approach. 

 

My solution came with my acquisition of a set of Benchmark AHB2 power amps which, like other amps from the professional world, have adjustable input gain options and, with them, I can get a ~20dB improvement in S/N which, effectively, makes the MP1 (and the system) dead silent.   Full story here:  https://www.stereophile.com/content/music-round-94-benchmark-marantz

  

[Kal Rubinson]

Just now, Kal Rubinson said:

I am having problems though. Loud crack through speakers when switching inputs, muting or using the adjustments to change  channel gain.

Part 2:  I used to have that problem and it is due to AR's decision to make each channel's circuit on a plug-in card which makes a multiplicity of sliding unsealed contacts with the main system board.  These contacts oxidize.   

 

I schedule an annual cleaning in which I (1) completely disconnect the MP1 from everything, (2) remove each of the six boards, (3) clean all the contacts on both sides of each board and the contact sockets on the main system board with DeOxit Gold and (4) reassemble and reconnect.  It takes me about 45 minutes and it keeps the switching silent.   You may need to do it more or less often.