Monday, December 30, 2013

Amplifier Raised on Brass Feet from Mapleshade

Raising my Aragon 8008 BB on a quad set of custom order brass Mapleshade Threaded Thick Carpet Heavyfeet has lowered the operating temperature of the amplifier considerably, and improved the sound slightly.  The feet allow the amplifier to sit directly above the carpet without a wood platform underneath.  The lack of a makeshift wood platform (a repurposed shelf from an audio rack) has also cleaned up the appearance considerably, created more foot room, and for their part the brass feet look very nice too.

I was very surprised from the large drop in heatsink temperature.  In fact, one of the many excuses for not putting these feet on the amplifier sooner (I actually bought them about two years ago) was that I feared that while the amplifier might sit slightly higher above the visible surface of the carpet than it previously sat on the wood shelf, the (plain pile) texture of the carpet would still impede airflow more than the wood, and the last thing I would want for the already too hot Aragon amplifier (which used to idle at about 133 degrees F at the top of the heatsinks) would be for it to run hotter.  Of course the actual feet that I purchased (which required a custom order because of the stud size of the amplifier) were the carpet-ready variety, with a 3/4 slender spike which pushes through the carpeting.  But I still worried that it wasn't enough.  The total foot size is 2 1/4 inch, leaving at least 1 1/2 inch above the carpeting.

As it turned out, not only were my fears unwarranted, I now regret that I did not put these feet on the amplifier at the very first moment I could to keep it cooler.  The heatsink temperature at idle has now lowered to about 117 degrees F, a 16 degree drop in temperature, which might mean a twofold or greater increase in longevity, or technically MTBF (mean time between failure).  For quite awhile, I even ran the amplifier night and day (mainly because it was more convenient, and I figured that it might sound better, but the truth is the idle bias on this amplifier is so high it probably makes little difference, it pops right up to full idle current within a minute of being turned on, and for longevity reasons it's desirable not to keep the amplifier hot so much).

As to the sound, it seems a bit clearer and cleaner, and sounds slightly more relaxed as well.  No minuses whatever.

Since my listening position is now just a couple of feet back from the speaker plane, the extra foot room is appreciated also, and this makes the new listening position much more guest-friendly for taller people than me, which most people are.

Given that I now have (and have had for about two years) a great infrared thermometer to verify before and after temperatures, putting the feet was about as easy as an audio modification can get.  Disconnect amplifier, turn on side, remove old feet, then add new feet.  The old "feet" were three layers of adhesive felt sliders.  The amplifier came with one set of adhesive feet like this, which were only about 1/4 inch thick.  Once I became aware of how hot the amplifier was running,  after a few more months of inaction, I added two more adhesive felt feet on top (or underneath, actually) the existing feet.  All this time I had the amplifier's feet resting on a solid wood board.  Strangely, i don't recall that adding the extra felt feet made any difference in the operating temperature, though I do remember seeing idle temperatures as high as 136 degrees previously, so I'll give the benefit of the doubt to a 3 degree improvement.  (Given changes in ambient temperature, HVAC operation, and so on, all these measured differences should be taken with a grain of salt anyway.  But I measured the 16 degrees of improvement with the Mapleshade feet on the same afternoon/evening, and I've been seeing the 133 degree idle temperatures for a fairly long time), so while I'm uncertain about how much if any change was made by trebling the felt feet, the big brass feet have made a large and clearly measurable different in amplifier temperature.

Although this was fast, I chose to do some extra stuff that other people might not have bothered with.  Rather than simply assuming all was OK after screwing on the feet, I took the small cover off the top of the Aragon to check the wiring on the right side.  Those feet are right underneath the active guts of one channel.  I could see into the area just a bit using a flashlight, but not well enough, so I removed the cover after I'd set the amplifier back down.  (One problem with this is that you can't screw the feet on and have the covers removed at the same time.)  Toward the back of the amplifier there was no interference with the new screw stud.  But in the front there was a bundle of wires running through.  Most of that bundle simply got pushed up by the stud, leaving just one insulated wire running a bit closer to the nearby power transistor than desirable.

I first put a nylon wire tie onto the screw stud itself.  That meant that no wire was directly contacting the screw.  But then it was clear that no matter how I wrapped the wires, the straggler still turned rather close to a power transistor.  So I then put a second wire tie around the entire bundle of wires, just above where the first screw tie wraps around the screw.  The effect of that is to keep the straggler wire in place with the rest of the bundle, AND to lock the whole bundle in place, just slightly above the screw and separated by nylon and air for thermal insulation.  After examining that for awhile, I put the cover back on.  I didn't remove the larger cover on the right side of the amp because there is no circuitry where those screw holes are, or any power transistors, though the screw studs could have pushed a wire out of the way, it would be otherwise harmless.

As it turned out, only one of the feet allowed the stud to screw nearly all the way in.  On the other feet, the screws would turn in leaving about 3/8" above the foot.  For most of the feet, I screwed the stud in first as far as it would go, then I screwed the foot and screw assembly onto the amplifier.  In every case this made it impossible to feel the screw starting position by turning the screw backwards (as I usually do) so I had to simply screw the screws on clockwise as most people do, and it wasn't easy to get the screws lined up.  For the other foot, I screwed the screw in not as far as it would go, but to the same distance as the others.

Had I really examined the amp first, I might have used the special foot (which allows the screw to go nearly all the way in) just at that location where I was forced to use wire ties, that way I could have avoided the wire ties.  But it was that sort of endless thinking that kept me from doing this otherwise fairly simple but very important upgrade.

Friday, December 27, 2013

New Crossover and EQ for the Living Room System

I spent much time over the 2-day pre-Christmas weekend, and the 2-day Christmas Eve and Christmas Day holiday I also enjoyed, adjusting the Behringer DCX 2496 that serves as a digital crossover, eq, and time alignment device for the living room system.

When I started, I was thinking the sound was a bit thin.  The adjustments I made added solidity to the sound without adding too much bass heaviness, punch without bloat, impact without boom.  It takes skill and patience to do this.

In the process of adjusting, I used several tools.  I used my Kurzweil keyboard, which I temporarily moved in front of the listening position.  I created an instrument (Kurzweil calls any configured sound a "program") that's just a pure sine wave, extending as low as 16 Hz.  I started with the Default Program 199 and just changed "piano" to "sine wave", then I lowered the notes by two octaves.  Being able to play sine wave bass tones makes it easier to hear which ones need to be lowered and which ones needed to be raised.

I also used my B&K oscillator, which has digital readout.  Actually, this little oscillator is not as easy to use as it could be.  I choose a 100Hz range which actually gives me 10Hz to 200 Hz, with 100Hz in the middle.  But adjusting to specific frequencies below 50Hz gets harder and harder, as only tiny changes of the knob can scroll past a bunch of frequencies.  It works well enough to do slow sweeps to pick out problems.  But it might even have been better if I had used the Kurzweil and assigned a slider to do frequency adjustment.

I did not use any level measuring instruments.  I used my own ears, either at the listening position, or in other locations.

Let me run down the changes I made (and not elaborate all the history of what I tried to do, which would take too much time to describe).  I'll just give a few historical observations and/or rationalizations.

1.  I changed the crossover between the subwoofer and the Acoustat panels to 24 dB/octave Linkwitz-Riley at 80 Hz on both sides.  I am using this crossover with no polarity inversion on either side, and it is a nice property of the 24dB/octave linkwitz-riley that it does not require any polarity inversion.

Previously I had been using the crossover in a more ad hoc fashion.  I had been crossing over the bass side with 48dB/octave linkwitz riley, but left the highs with a gentler 24dB/octave slope.  My reasoning was that the subwoofer had best not be producing any mid bass since the panels do it so much better.  Well doing things this way there seemed to be a peak in the 82Hz region.  So I then also separated the crossover frequencies so that the panels were being crossed over at 88 Hz, and the bass around 80 Hz or maybe even lower.  This sort of worked.  But when I changed both sides to LR24, the peak at 82 Hz went away, and generally sound was smoother on both sides it seemed.  My ad hociness was requiring more ad hociness to fix.  Previously I didn't take the crossover settings very seriously, on the grounds that the speaker drivers are introducing so much additional frequency-related variation any crossover setting is really only an approximation.  It seems now that I should have been taking the actual crossover settings more seriously, especially when I was not seriously analyzing what the additional variation was that needed to be corrected anyway.  Given that you don't really know what else needs to be done, the nominal crossover is a good place to start.

2.  I eliminated the frequency contouring I was using for the super tweeters.  I removed the lowpass above 20kHz, which was rolling them back down again on the high side.  Now the super tweeters are crossed over at 15.5kHz, and that is it, they then continue on as high as their response (or more likely, the signal source) allows.   The effect of removing the lowpass was that the output level increased slightly, but I could not hear it as such, I just occasionally see a level indicator bar on the Behringer when previously I would see none.  I tried reducing the levels of the super tweeters, but ended up back where I had set them before, with the left channel only reduced 2db because it seemed to have about 2dB more output.  I confess the level settings make little sense to me and no measurements I've done have clarified the matter at all.  I would think the level settings should be much lower, but making it lower and the super tweeters lose the magic.  BTW, the magic is not at all brightness.  It's actually a kind of smoothness, where grain and grit go away.  As you increase the the level of the super tweeters (which actually have very little output that I can hear directly, as one would expect with crossover at 15.5kHz) the sound just gets smoother and more palpably real.  I just quit increasing the level because turning it up even more seems--to my mind--obscene.  I wish I was better able to do high frequency measurements to determine where the super tweeter level should be set.  But ultimately it comes down to what feels right anyway.

3.  I changed the bass EQ's.  I retained the huge notch at 45 Hz with -11dB.  I tried changing that big notch also, but whenever I flatten that notch, even to a very similar -9dB, the sound goes to boomy fast, without any improvement in bass tunefulness.  But many other bass eq's are changed, and many are new.  One thing that's also new is that I eq'd each channel differently, depending on several factors, both the pre-existing response, and the additional level that could be handled without causing distortion.

Notably, compared to before, I added various degrees of boost at or below 32 Hz.  That's because just just below 34 Hz or so the bass was tending to sound very weak overall, especially compared with the boom in the range 36-48Hz.  I specifically added a boost at 32Hz in both channels, since 32Hz is often found in music, and it needed boosting a lot (probably more than I actually boosted it).  Then I boosted tiny amounts at 27hz, 25Hz, and 20Hz.  The right channel starts to buzz when I boosted it for the lowest two frequencies, so i did that boosting on the left channel only.  Then, corresponding, I left out the 27Hz from the left channel, since it was already boosting 25 hz.  These are little 2db boosts, but they help.  The 20Hz and 32 Hz boosts are fairly narrow around 1/3 octave, but the 25Hz boost is a wider 1/2 octave or so.

I left the 45Hz notch alone in the end, but that was not without trying many other variations, such as moving it to 44Hz and then moving another notch at 57 Hz down to 48 Hz.  No matter what else I did, the 45Hz notch seems to be needed, so I ended up keeping it.  But the 57 Hz cut has been changed depending on the needs of that channel.  On the right side, there is more boominess above the 45 Hz notch, so it now gets notched out at 48 Hz.  On the left side, there is more boominess in the upper 30's, so it gets a notch at 39 Hz.  With the full LR24 crossover on both sides, there was no special boom that needed cutting in the upper 50's, so the 57 Hz cut is gone gone gone.

[I will be adding in here the last adjustments made in this time frame.]

Saturday, December 21, 2013

Don't forget the center

Did some serious listening this week.  Listened to Infrared Roses by Grateful Dead.  This is one of my favorite albums.  All instrumental, mainly percussion.  Did Grateful Dead produce anything else like this?  I confess I'm not so attracted to the usual Grateful Dead hit albums.  My taste runs to instrumental recordings (I have Shadowfax in the background right now), and hummable melody is optional.

On living room stereo this was fantastic and real at the same time.  Very 3 dimensional.  Much of it sounds like real stereo miking, but other parts seem dubbed in, particularly the parts where one thread goes swinging back and forth between the speakers.  But at one part I wondered, is this a drum with pan-pot, or more than one different drum across the stage?  Anyway, it was very enjoyable.  There was a feeling like I was listening through giant electrostatic headphones, an incredible sense of transparency.  I can't remember if I'd listened to this seriously on living room stereo before.  I certainly never experienced it like this, the incredible spaciousness.  There was in a few parts a slightly, very slightly, grating quality to the highs.  Is this because my Acoustat panels are old and need to be replaced/refurbed?  I sometimes worry about that.  Or is it because electrostats including my Acoustats are very "revealing"?  It might be useful to fire up the electrostatic headphones one day and investigate further.  Last time this really bothered me and I had time, I replaced the old electrolytic caps in one of the Acoustats with a Solen, and that seemed to make it better.  That was in 2011 I believe.  I do need to do the other side soon.  How about 2014?

It was sounding a bit ping-pong on bedroom stereo.  I wasn't paying close attention at first, but then I noticed how the new adjustable bed was not centered vs the triple width record cabinet in the front center.  Hadn't I done that for the new bed yet, or had it moved by itself?  Anyway, I moved the bed, then the sound became wonderful again.  The center image was restored.  So many times I've heard other people's system with no center image, and my own systems have often fallen that way out of neglect and lack of serious listening.  A good center image is not just critical, it's crucial.

Compared to the living room system, bedroom system sounds smoother in some ways, but lacking in depth.  It was not the mind blowing experience it was in the living room.  But with center image fixed, it was still very satisfying.