Is my amp the problem?

More info is needed. What model is the other amp; what preamp are you driving the two amps with; is there an electronic crossover "ahead" of the amps; if there is no electronic crossover how is the preamp connected to each amp (e.g., XLR or RCA); what speaker is it; does "10 woofer" mean 10 ohms or 10 inches? Does the bass weakness seem to occur at any volume level, or just at high volume levels?

Regards,
-- Al

Thanks for the additional info. I can’t say what the answer is at this point, but here are some thoughts and possibilities to consider:

1)You didn’t say which miniDSP model you are using as the crossover, but I see that the "2x4," which appears to be a likely possibility, has a maximum rated output of 0.9 volts. The sensitivity of the Crown amp is selectable as either 1.4 volts or 0.775 volts. If you have not set it to 0.775 volts that could certainly be a contributing factor. Also, my suspicion is that those two numbers apply to its balanced inputs, which could mean that the corresponding figures for the unbalanced inputs are twice those numbers. If so, it can be calculated that even if you are using the 0.775 volt setting an input of 0.9 volts would not drive the amp to more than about 72 watts into the 8 ohm nominal impedance of the woofer, which is about 1/3 of its rated power capability.

2)The miniDSP 2x4 has a very low input impedance of 6K. While your Modwright tube preamp has a specified output impedance of 300 ohms, I suspect that as with most tube preamps its output impedance rises to much higher values in the deep bass region, due to the coupling capacitor it most likely uses at its output. Many tube preamps having nominal output impedances of a few hundred ohms have output impedances in the area of 2K to 4K at 20 Hz. If that is the case with the LS100 (and you might check with Dan Wright on that), and if you are using the 2x4 or some other miniDSP model having a similar input impedance, it would certainly explain a weakness in the deep bass region.

3)Although you stated that "all the right adjustments" have been made, between the plethora of settings in the amp and in the miniDSP there is lots of opportunity to go wrong. So double and triple checking everything would seem to be in order. For starters, be sure of course that your settings result in the amps being properly gain matched. And be sure that the high pass, low pass, and bandpass filter functions the amp provides have been either turned off or set to values that would not contribute to the problem.

4)Regarding the comments by the others, the woofer you are using does not seem to be a particularly difficult load, and I would not expect it to require a particularly high current amp. See the impedance plot in this datasheet, which shows its impedance as being at or above 7 ohms at all frequencies, and not having particularly negative (capacitive) phase angles at most frequencies. Although it should be noted that the rise to as much as 30 ohms in the vicinity of 30 Hz means that at frequencies in that vicinity the amp’s power capability will be far less than the 215 watts it can supply into 8 ohms. Although a similar reduction in power capability into the high impedances at those frequencies would occur with nearly all solid state amps.

Hope that helps. Regards,
-- Al

Erik, I have no experience with miniDSP products. But for example if the OP is using the 2x4 model or the 2x4HD model I would be skeptical that a product incorporating two channels of A/D conversion, four channels of D/A conversion, sophisticated digital signal processing, as well as USB and Toslink digital audio interfaces in the case of the 2x4HD, while selling for list prices of $105 and $205 respectively, would not significantly compromise the sonics of Modwright electronics. So I don’t find Auxinput’s comments about it to be surprising.

But yes, measurements would most likely be necessary to properly match the mid/high and low frequency gains and sensitivities.

Best regards,
-- Al

Good comments by Auxinput.  I just noticed something further about the Modwright amp.  I had stated its input impedance as being 23K, because the impedance is indicated on its webpage as "Min. 15K 50Khz; 23K 1Khz," and I considered the 50 kHz impedance to be irrelevant.  Although I wondered a little why he would bother specifying a 50 kHz impedance.  However I now see that its manual (in contrast to the webpage) indicates an input impedance of "Min. 15K at 50Hz [not kHz]; 23K at 1Khz."

So that makes it all the more important to avoid requiring the LS100 to drive a low input impedance device in addition to the Modwright amp.  My suggestion at this point is that you communicate with Dan and ask him what minimum load impedance he would recommend be used with the LS100.  While you're at it, also ask him to clarify if the amp's specified input impedance applies to its balanced input or its unbalanced input or both.

Regards,
-- Al
   

OK. The 2x4HD has a rated maximum output of 2 volts, which should be fine relative to the 0.775 volt sensitivity the Crown is set for.

However the 2x4HD’s input impedance of 10K is still fairly low. And if I’m correct in understanding that you have been connecting the LS100 to both the miniDSP and the Modwright amp, the LS100’s output stage is most likely seeing the combined parallel impedances of the miniDSP (10K) and the Modwright amp (23K). That combined impedance would be (23K x 10K)/(23K + 10K) = 6.97K, which again could very well be too low for the LS100 to drive without significant rolloff in the deep bass region. And with adverse effects perhaps resulting at higher frequencies as well, that are handled by the Modwright amp and the mid/hi drivers.

That would most likely be the case regardless of whether you have been using the LS100’s XLR output or its second RCA output to drive the Modwright amp, because its XLR output is described as being driven with a single-ended signal. Which I would feel very confident means that the same output stage (and output coupling capacitor) is driving both of the RCA connectors AND the XLR connector.

So that’s one more reason why eliminating the mini may very well be helpful.

Regarding your question about a Zobel network, as Auxinput indicated I believe what that would make possible is just a reduction or elimination of the impedance rise of the woofer that occurs at midrange and treble frequencies, as a result of its inductance. I don’t think, though, that a Zobel would allow you to reduce the relatively narrow impedance peak I referred to that occurs in the vicinity of 30 Hz. But that peak may very well not be an issue anyway, its only significance perhaps being that the maximum power capability of the amp at frequencies in that vicinity would be a good deal less than its 8 ohm rating.

Good luck. Regards,
-- Al

Thanks for the update. Although the input impedance of the Crown XLS 1002 is not specified (as Auxinput had indicated earlier), its similarly rated predecessor model, the XLS 1000, was specified as having input impedances of 10K single-ended and 20K balanced. Given also that pro-oriented equipment very often seems to have relatively low input impedances I would think it to be a good bet that the input impedance of the XLS 1002 is the same or similar. 10K happens to be the same, of course, as the specified input impedance of the miniDSP 2x4 HD.

Also, the 20K balanced input impedance probably means 10K per leg (i.e., a 10K load being applied to each of the two signals in the balanced signal pair). And the output stage of the LS100 will see that 10K load in parallel with the 15K to 23K input impedance (at various frequencies) of the KWA 100SE regardless of whether the connection to either amp is via XLR or RCA, since as I indicated earlier the LS100’s XLR output is driven with a single-ended signal.

15K in parallel with 10K is 6K. 23K in parallel with 10K is 6.97K. Both values are of course far below what Dan recommends.

The input impedance of the Pioneer SF-700 Electronic Crossover is spec’d at 100K. Much better! Although it appears that the SF-700 dates back to the early 1970s, so the possibility that it may be in less than top condition is something to keep in mind.

Good luck. Regards,
-- Al

The input impedance of the ART (Applied Research and Technology) SLA-2 is 22K unbalanced and 44K balanced, the latter probably corresponding to 22K per leg. Too low to be optimal, or even close to being optimal, when driven in parallel with your Modwright amp by the LS100.

Also, the fact that its rated maximum power into 4 ohms is only 40% higher than its rating into 8 ohms says nothing positive about the robustness of its design.

I’ve used some other ART products for non-audiophile purposes, and in those non-critical applications I found them to be an excellent value. But I suspect that in a high quality audiophile-oriented system they would likely be disappointing, even if no impedance or other technical issues were present.

Regards,
-- Al