Jeff Rowland

03-09-15: Ricred1
Speakers are as follows:
the rear of the speakers are 4' 2" from the front wall
8' apart, 4' 8" from sidewalls, I sit 10'away, my head is 6'away from the rear wall
I have 2 GIK Soffit Bass traps in each front corner from floor to ceiling, 6 GIK 242 panels-2 each on the left and right at the first reflection points and 2 on the ceiling

OK, so rear wall reflections will result in a suckout centered at a frequency of 282/6 = 47 Hz. It's hard to say how far above and below that frequency the suckout would extend to an objectionable degree, but I wouldn't be surprised if the affected frequency range is wide enough to be a significant contributor to the issue.

For experimental purposes, just to gauge the significance of that effect, if practical you might temporily relocate the two bass traps that are in the front corners to a position such that both of them are in a line extending directly back from the listening position. Perhaps one immediately behind the listening position, and one up against the wall. And it would probably be most useful to compare sonics between having the traps in that position and having them out of the room altogether, so that the comparison wouldn't involve changing two things at once (i.e., moving the traps away from the front corners, and placing them behind the listening position).

Also, again for experimental purposes, you might try to determine how severe that effect seems to be at differing listening distances. In doing so, it might be helpful to purchase a test CD, such as this one, further described here. Track 17 would facilitate assessment of frequency response flatness in the bass region.

Bombaywalla, I agree with your comment. It would be unusual for an amp to be able to fully quadruple its max power rating into 8 ohms when bridged, much less into 4 ohms, due to the current and thermal limitations you referred to. Although for an 8 ohm load the OP's 525 comes surprisingly close to doing that, the 8 ohm ratings being 250 watts and 950 watts for stereo and bridged modes respectively.

Best regards,
-- Al

Almarg,
Thanks for taking the time to provide assistance. You are a smarter man than me!!!I moved the bass traps from out of the corner and put them behind my listening position. I promise I'm not exaggerating...my wife was downstairs and game upstairs. She said,"I knew you did something, because it sounds so powerful downstairs." I haven't move the bass traps out of the room, but I will do it tomorrow. It addition, to more powerful bass, I hear more detail. The question is why? I thought bass traps were good?

Almarg,
My other question is about the volume control on my PS Audio DSD DAC. I guess it operates as a passive preamp; consequently I need to turn the volume up to 70-80 for it to be adequate(70 normal listening, 75-80 loud). How does that affect the amplifier? Would it sound better with an analog preamp?

The output of the DirectStream DAC is transformer coupled, and in that sense can loosely be considered to be passive, but unlike resistive-based passive preamps it has an output impedance that is low enough to be comparable to that of most active preamps, both tube and solid state. That is confirmed in John Atkinson's measurements.

Given that, as well as the 40K balanced input impedance of your amp, as well as PS Audio's claim that its volume control mechanism does not lose resolution at any setting (which if it occurred at all would occur at low settings of the control, not high settings), I see no technical reason that would call for the insertion of a preamp. Which is not to rule out the possibility that you might find adding a preamp to be subjectively preferable. But FWIW my own bias is to put the burden of proof on adding anything to the signal path that is not clearly necessary, and in this case I don't see it as being clearly or technically necessary.

The reason for the relatively high settings of the volume control you are using are most likely the combination of the "full scale" (maximum) output voltage of the DAC being a bit lower than usual, and the sensitivity of your speakers being somewhat low (Stereophile measured the speakers as 86.6 db/2.83 volts/1 meter, which for their 4 ohm nominal impedance is 83.6 db/1 watt/1 meter).

So as long as you never find yourself wanting to turn the volume control up beyond the top of its range, I wouldn't attach any significance to the fact that you are using it in the upper part of its range.

A couple of things to check, though:

1)Apparently the DAC's output can be set to two different levels via the menus. Check to see that it is set for the high level, i.e., that the output attenuator that is provided is deselected.

2)Check that the unit has the latest firmware (version 1.2.1) installed. User comments as well as PS Audio indicate that that update tightens up and improves the bass. I would expect that you can determine the firmware version somewhere in the menus, or perhaps it is displayed briefly at startup. If it is an earlier version, you can easily download and install that version per the instructions at PS Audio's site.

Regarding the bass traps, it's of course sometimes possible to have too much absorption in a room as well as too little absorption, especially from a subjective standpoint, and depending on the speakers, their placement, etc. I suspect that the main reason for the more powerful bass reported in your latest posts was removal of the traps from the front corners, rather than their placement behind the listening position, in part because the change was perceivable at other than the listening position. Hopefully after doing the remaining experiment (removing the traps from the room altogether), and some further listening, you'll be able to determine which of the four possibilities is preferable (traps or no traps in front; traps or no traps in the rear).

Continued good luck. Regards,
-- Al

Bombaywalla, You are right - not many amps quadruples or
even doubles power exactly. I don't even care for the one
that does, since in order for this to happen amp has to have
hefty power supply but also lots of negative feedback.

On the other hand listed power specification is useful only
if you listen to sinewaves. Music demands very little power
on average, since half of the loudness is 10% of the power
and music has gaps. Heavy orchestral pieces might demand
more power but Jazz trio needs very little. Maximum current
is perhaps more important. Power specifications are very
vague. It can be FTC, EIA, CEA or no standard at all. FTC
defines amplifier's power when both channels are driven over
full audio band 20Hz-20kHz for 5 minutes after one hour
preheat at 1/3 of power and meeting listed distortions. EIA
requires test at 1kHz and 1% THD without preheat for one
channel only (not sure how long). CEA test requires 5
minutes at full power at 1kHz without preheat, while other
channel is driven at 1/8 of max power (why 1/8 ???). Most
of class D amps would not even pass FTC test, having very
limited power at high frequencies. The only class D modules
manufacturer I know that specifies full power bandwidth is
PASCAL but it is useless anyway since music demands very
little power at high frequencies, not to mention size of the
tweeters. Most of manufacturers don't even specify what
standard, if any, they use for testing. For instance
Icepower module in my 200W Rowland model 102 is specified at
only 55W FTC power limited to 0-8kHz with explanation
"The power bandwidth is limited due to the output Zobel
network". Continuous module power is listed in
datasheet as only 40W @ 25degC and 25W @ 50degC. Bel Canto
specified S300 and M300 amplifiers as 300W with the same
Icepower module (200ASC). These modules can produce
momentary power of 290W at 10% distortion and only at 230V
supply. Useless specification but 300W looks better than
200W on the paper.