[Russtafarian]

Last Saturday I had the opportunity to hear the Ref 9SE amps for the first time at a friend’s house.  It was a fun afternoon with a half a dozen audio buddies getting together for some listening and chatting.  For the first few hours we listened to our host’s tube amp.  Then the 9SE’s, brought over by one of the attendees, were inserted into the system.  The difference in sound was fascinating, but what has me scratching my noggin was a technical glitch that none of us could figure out.

When we hit play for the first time with the 9SE’s, we heard lots of high frequency spitting and crackling behind the music.  Stopping the disc stopped the noise.  We spent the next twenty minutes playing with power cords, interconnects, etc. and could not get rid of the noise.  Making a WAG, I suggested switching from the SACD layer to the CD layer of the disc we were playing.  The noise went away. 

So we started throwing different discs into the Denon 3910 to get to the bottom of this.  CDs sounded fine, the CD layer of SACDs sounded fine, DADs and DVD-As sounded fine.  But all the SACDs we tried gave us that rice krispie experience.  We played with SACD filter setting on the Denon.  Changing the filter from 50khz to 100khz made the noise worse.  This was a real puzzler for the owner of the 9ES’s because he’s never had this problem playing SACDs through the 9SE’s with his Modwright Sony SACD player. 

My guess is that we were hearing some sort of interference between the SACD filtering process in the Denon and the RF modulation/filtering process in the Nuforce amps.  So here are my questions:

Were the amps radiating so much RF into the air that it was messing with the Denon’s circuitry?  We had the amps 5 to 6 feet away from the Denon and moving the amps around didn’t reduce the noise. 

Was RF from the amp radiating into the interconnects?  We were running shielded, single end interconnects from the Denon through a Krell preamp into the amps. 

Was the amp picking up remnants of DSD noise from the Denon and modulating it down into the audio signal?  That would be my guess.  This may be a case of two devices interfering with each other by trying to use the same part of the frequency spectrum.  Kind of like a microwave oven wiping out the reception of a 2.4ghz cordless phone.

So why does this happen with a stock Denon SACD player but not with a Modwright Sony SACD player?   Again, my guess is that the Modwright Sony either uses a different DSD filtering scheme or the tube output stage bandwidth-limits the SACD signal, helping to filter some of the high frequency DSD noise.

Last question:  Is this a potential product design flaw or a problem with that particular set of amps?  Both amps made the noise though one was louder than the other.

Thoughs?  Comments?  Inquiring minds need to know.

Russ

[ted_b]

It's not the amp.  Denon 3910's have a function called Source Direct (toggle on/off in the setup menu), which allows SACD's to play in full DSD splendor.  However, when this occurs the spurious noise from early DSD decoders can filter through quite substantially; it's reported on many forums.  I have a modded Modwright 3910 that does it with spades, cuz the bandwidth, after Dan's mod work, is so high.  My previous deck, the Modwright Sony 999ES was fine, but not nearly the bandwidth either.  He now puts ultrahi frequency filters in the path for this reason, and mine was bought as a demo from previous owner, and built before this was found (Dan's customer service is excellent, he shipped me the filters cuz i first thought a buddy of mine could help, but on further thought I will take him up on sending the unit to him for update).   Since the Ref 9SE's are likely quite revealing, the noise problem is exarcerbated.  My amp is an 18 yr old Krell KSA-100 and it exhibits the noise quite loudly.

Short term fix is turning Source Direct off (listening in PCM mode).  Also notice that later DSD recordings don't exhibit the noise.  My Peter Gabriel IV (Security) is almost unlistenable, but Beck's Sea Change is fabulous in pure DSD.

[modwright]

I just wanted to chime in and confirm that it does have to do with the ulti-high bandwidth present in some DSD recordings.  Ironicly enough, it is probably the TRUE DSD recordings that do this only, because those that have been PCM mastered are likely to have reduced bandwidth overall.

Switching from 50Khz to 100Khz BW setting on the Denon will make the situation worse because of course you are allowing more of this noise content through.  You might wonder how noise artifacts that are in fact beyond the audible (human) threshold can effect the audible BW.  I am not 100% sure of the answer to this, except to say that it is my understanding that this high-BW noise has artifacts that fold down into the audible range.  The human ear is also a pretty amazing thing and while we may not be able to readily 'hear' anything beyond 20Khz, we do 'perceive' it and our mind does accept and interpret this information in the form of phase-cues, etc.  I am not an expert in this regard by any means, but I do know that because of how the human ear is 'made', there is more going on than meets the...ear.

We have implemented ultra-high frequency filters in our tube circuit for the Denon 3910 mod that address this.  Our mods for the Sony 999ES used a tube circuit that didn't have quite as broad of a BW as the Denon mods.  Also, the Sony 999ES DAC chip had on-board filtering that probably dealt with it before the analog signal left the chip.

I hope this helps.

Thanks,

Dan W.

[Wombat_VC]

Phew.  I play SACD extensively and prefer to throw the BW wide open. Fortunately I had decided on another amp instead.