Monday, June 15, 2015

Surprise Discoveries

Little can top the discovery recently that my Krell amplifier is working OK.  But the discoveries continue.

Last weekend I wired up a second set of speaker wires and terminated all speaker wires on the speaker end with banana plugs, so it only takes a minute to switch from Krell to Aragon or back.  In all the time that I have owned both amplifiers, I've never had the capability to compare either amplifier quickly since previously I only had speaker wires running to the center amplifier position, and they wouldn't reach the side, and moving the amplifiers around is a big job.  Attaching wires to the speakers is a very touchy and difficult job which seems to take longer than the 30 minutes or so it actually does.  I manage to insert the wire into the small hole in the binding posts and then tighten them down.

Since wiring the new cables, I've been just plugging either set of wires into the 5 way binding posts in back of the Acoustats.  My plan had been to have a short stub wire screwed on the the Acoustats with bananas on the other end to connect to the amplifier cable bananas--because I recall bananas slowly falling out of the Acoustat posts.  But the new bananas fit quite tightly into the Acoustat posts, and when disconnecting the old wires I discovered that some of the wires I had screwed onto the Acoustats a couple years ago were already loose anyway--the very thing I had been trying to avoid with a direct wire connection.  I wonder how that was affecting the sound.  You just can't make a permanent friction connection to loudspeakers!  Perhaps speakers should have hookup posts that you solder your cables to.

BTW I continue to use 16 gauge zip cord, though it does happen to be either Monster or PureSound wire.  It's actually hard to beat 16 gauge zip cord for "neutrality."  Thick wires have far more inductance, creating relative loss at higher frequencies.  That's far more important than a fraction of a dB in spectrum-wide SPL loss.  Few, very few, audiophiles understand this--that inductance is a key factor in speaker wire.  The solution is to weave multiple conductors as closely as possible, and many exotic wires do this.   But I also get away with 16 gauge wires because my wires are only about 5 feet, at least to the center amp position.  Somewhat unfairly to the side amp position, the Aragon wires run about 9 feet.  The Monster and PureSound zip cords I have use a polyethylene dielectric around the conductors, which protects the copper wire from coming in direct contact with the vinyl outer cord.  Polyethylene is one of the best cable dielectrics and vinyl is one of the worst, and you get most of the benefit from a thin layer.

My plan for speaker wire is ultimately to switch to a 4 cross wire such as Canare 4S11.  By having 4 conductors carrying signal in both directions, inductance is enormously reduced.  That also reduces the external magnetic field, and even Blue Jeans Cables says that is useful under some circumstances.  With all my jumble of wires, I fit one of those circumstances too.  Canare also uses polyethylene dielectric, as most serious or professional cables do.

Switching back and forth a few times between the amplifiers has only reinforced my previous opinion that the Krell is better sounding.  Not only does it seem to have more solidity, a more infinitely layered depth, it sounds more pleasant and relaxing, whereas the Aragon can have some edginess.  I attribute this to the no-feedback output stage of the Krell, and since the back energy from the speaker is handled by the class A output transistors and doesn't get looped through the whole amplifier as would happen with normal feedback.  This could be pure fantasy.

But another discovery was that neither amplifier was balanced to anything like 0.1dB.  I made a nice 880Hz -20dB test tone using sox, and then played it at -6dB.   On the Krell, the left channel was 0.33dB higher--not great.  On the Aragon, the left channel was 0.58dB higher--completely unacceptable.  Reversing the connections on the Aragon improved things considerably.  I'm now using the right side of the amplifier to amplify the left channel and so on.  That reduced the imbalance to 0.14dB on the Aragon, with the left channel still higher.  The fact that I was able to reduce the imbalance so well this way suggests that about half of the imbalance is in the DAC output and the other half is in the amplifier.  Given that the imbalance tilts left even when run through the opposite amplifier channel indicates that the DAC has more imbalance than the amplifier, so that even run through the opposite channel the amplifier can't cancel the difference--though it does come close.  I can't just reverse the inputs to the DAC--since it's an interleaved SPDIF signal.  Each amplifier uses a different DAC, the Aragon is running from the Onkyo RDV-1 and the Krell is run from the Audio GD DAC 19.

I have no potentiometers in the system at all.  The level was reduced to -6dB digitally, and the 880Hz tone was synthesized at exactly -20dB.  The midrange signal may be reduced very slightly by the 80Hz crossover (also digital).  The outputs of the DAC's feed the amplifiers directly.  The differences must come only from the DAC's and the Amplifiers themselves, and previously I would have imagined them as being well within 0.1dB.

The voltages after adjustment were: Krell 1.132 left and 1.092 right, Aragon 0.940 left and 0.925 right.  Before swapping channels, the Aragon outputs measured 0.970 and 0.906.  I suppose some of the left-right difference could also be in the loads that the speakers present to the amplifier.

It was also surprising that the Krell with it's DAC has more 1.6dB right/1.4dB left gain than the Aragon with it's DAC.  (Much of the difference could be between the two DAC's).  I had believed it to be the reverse…forgetting the DAC change I had even dialed in a 1.7dB reduction when switching to the Aragon (remembering that as the difference--perhaps wrongly).  The Krell did sound more solid…but I figured it was the character  not the loudness.  Well you can see here that not only are all my judgements so far wrong--they should probably never be believed!

Fixing the imbalance on the Aragon made it sound a little more like the Krell.  The image was better focussed and the depth seemed to have more layers.  The Aragon still was a bit edgy compared with the Krell.

This was not something I observed when doing the last room eq measurements because basically I don't pay attention to differences less than 1dB, and I don't trust my ability to measure balance that well acoustically.

I decided to take a chance running both amplifiers through Insteon on/off modules, which are rated at 15A and 1800W.  That should be OK though Krell advises only a direct wall connection.  Both amplifiers also go through a single wattmeter so I can keep track of how much power they are using.  The Krell typically uses 550-1200W, typically 750, and the Aragon uses 150-200W.

Two of my Insteon wall keypads, in the kitchen and in the lab, have two buttons for the amplifiers.  The buttons light up when the amplifier power is toggled on.  When I turn on the power for the Krell, it goes into standby, but I can fully turn the Aragon on or off from the keypads since I'm leaving the amplifier switch turned on.  This makes it much easier to keep the amplifiers from using too much power, since I can turn them off walking away from the living room in either direction.

Despite it's monstrous power and looks, the Krell is very soft on the power.  When turned on it only slowly charges the capacitors, using a slow-start circuit that is really slow and deliberate.

I've determined I need about 2 degrees setback for the thermostat in the living room when I am running the Krell.  This prevents the AC from super chilling the rest of the house to keep the living room cool.

After a surprisingly good recording session turned up by surprise the previous weekend, I had all the bedroom side equipment disconnected so I could remove the Masterlink for the recording session.  As I started moving equipment back last Sunday, I started thinking about hooking up the "new" Sonos zone player I rotated out of the living room after I bought a new zone player the previous month.  The new one was placed in the most critical spot (living room) with the old one renamed for being the second master bedroom unit.  It started to occur to me I had only one more Cat6a connection in my bedroom wall panel, and I already had many other ideas as to how I would use it.  I'd have to wire the new Sonos in daisy chain to the first master bedroom zone player.  But while I had the second bedroom connected with a UTP wire (all the ceiling wires are STP) to avoid hum, I used the shielded wire in the bedroom.  Wait!  Maybe that was causing the hum I had noticed in the previous few months, and had me worried that my Parasound HCA-1500A was going bad.

I managed to find one remaining 1ft Cat6a UTP wire and a Cat6a shielded coupler, and connected it just before the already-in-use zone player.  The hum completely disappeared!  Now I know I should not be running shielded ethernet wires to stereo systems.  I'm thinking I'll also use an unshielded Cat6a for the connecting the two zone players in the master bedroom, since that would also avoid a ground loop.

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