Jeff Rowland

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.

Thanks Almarg for the feedback.
Thanks Kijanki for the feedback & some dope on how power supplies are spec'd. Lots of diff ways to specify a power supply & that adds to the confusion already prevalent in the audio community re. power amp output power, distortion & dynamic headroom.

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.

Almarg, I might be reading this incorrectly but in reading the Pascal Audio S-PRO2 data sheet (link provided by Kijanki in an earlier post by him) I noted that the bridged mode (Pascal Audio calls this BTL mode) power output is 700W/ch in 4 & 8 Ohms using a 120VAC power supply. It's higher for a 230VAC power supply (that they use in Europe) - maybe the OP is using a 230VAC power supply?
Again, if I'm thinking of this correctly, in bridged mode this Pascal Audio amp module has quite a large output wattage that it can sustain given its 30A max limit. Some serious watts with current delivery to backup these watts....

I also noted that the max current from the integrated SMPS is 30A & if you read the amp specs, you will see that the max power is rated for a 2.7 Ohms load!! wow, this is the 1st time I'm seeing an amp manuf spec his amp for such a weird load. I did the math & voila what did I find?? At 2.7 Ohms load, the output current is 14.9A - exactly half of the 30A max. This made sense to me - 30A max, stereo amp module, therefore each channel gets 15A max. Hence the lowest load impedance it can drive is 2.7Ohms before the integrated SMPS runs out of current delivery capacity.

Thanks, Bombaywalla. I see what you're saying. The module datasheet shows that when it is operated with 120 VAC it is rated to deliver 600 watts into 2.7 ohms in stereo mode, although with just one channel driven. That corresponding to an output current of 14.9 amps.

While the max rating in bridged mode that you cited of 700W into 4 and 8 ohms corresponds, for 4 ohms, to 13.2 amps from each channel, simultaneously but with the channels being operated out of phase.

A couple of inconsistencies in the numbers, though, which I don't know how to reconcile:

1)The 950 watt figure I cited for bridged mode, for an 8 ohm load, comes from the Rowland site (click "specifications"). That number being even higher than the 900W number that is indicated in the module datasheet for 230 VAC operation, for an 8 ohm load in bridged mode.

2)I would think that the indication in the module data sheet of 30 amps peak output current is likely to refer to the peak of a sinusoidal waveform. (For example, I've seen credible indications that Pass Labs specifies peak output currents on that basis). While the currents that can be extrapolated from the power ratings based on Isquared x R would be rms values. For a sine wave, 30 amps peak of course corresponds to 30 x 0.707 = 21.2 amps.

As I say, I'm not sure how to reconcile all of that. Assuming that the module for which Kijanki provided the datasheet is truly the one used in the 525, I suppose it all adds up to further confirmation of how, as he indicated in his last post, power specs are often not defined on a consistent basis.

Best regards,
-- Al