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 |
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My guess is that the Crown amp is going to be really weak in regards to controlling the speaker (even though it’s rated at a higher power) -- Class D circuits can have a problem with weak bass when driving woofers. The Modwright amp is probably going to have a much better overall power supply and current delivery. One quick experiment you can try is to switch around the amps so that the Modwright is powering the woofer and the Crown is powering the mids/highs. If you get strong bass with the Modwright, you’ll know that the Crown is severely lacking. I’m going to guess that the Crown is going to sound weak when driving the mids/highs as well. If the Modwright does sound better than the Crown when driving the woofer and you still want to bi-amp, you will want to look for a really strong high-current amp. Some thoughts would be to look for a pair of Emotiva XPA-1 monoblocks. For slightly less, you could try a pair of XPA-1L monoblocks (smaller) and then run them in Class A mode. They will still give a smooth/full midbass but they won’t have quite as much weight in the bass (though this difference is very very small). If you want to spend more, I have heard that Parasound A21 has very strong bass. It may be sweeter/nicer sounding than the Emotiva’s. Anything less is likely not going to be able to match the Modwright. |
Something doesn't seem right here; the 225 wpc should drive the bass driver well. Is this an open baffle design, which might account for the disappointment in low end. More info needed. While the Crown may be poor quality there should be plenty of bass happening. I suspect something else wrong. I concur with Al that it may be in the setup. Even a poorer amp will not sound "horrible" or unlistenable when set up correctly. A profound lack of bass and horrible sound is evidence something is way off track. I suspect mis-wiring in the system. |
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 |
So can we assume you have bypassed the internal crossovers and replicated them in miniDSP? That's usually the easiest way to go. Test 1 driver with the passive crossover. Adjust miniDSP until your active filter looks the same. Repeat with next. Make sure your sensitivity matches before and after. Best, Erik |
@almarg - You are totally correct. I didn't even think about the miniDSP. In addition to the input impedance issue, all the miniDSP devices will convert the analog input to digital before doing the crossover processing - then converting back to analog. These conversion steps as well as the very poor power supply section of the miniDSP will just kill any sound quality benefit you would be getting from the Modwright preamp or audio source. You would do better to look for an analog-only crossover. There are a couple of Bryston 10B crossovers for sale on Audiogon. They have input impedance of 15k ohms, much better than miniDSP. Also, completely analog and much superior power supply. That being said, I did think of one more thing. You should consider any built-in passive crossover inside your speaker. Are you using a manufactured speaker? Or something you built yourself (DIY). The internal crossovers of the speaker will conflict with any active crossover. While you could potentially set the active crossover above/below the internal crossover points, you are just wasting a step. If you do have internal crossovers in your speakers, you are just better off using a Y-splitter cable to go to two separate amps and take the active crossover out of the system completely. On a 2-way speaker, you could potentially just bypass any crossover wiring internally and wire directly to the speakers. If it is a 3-way (or higher), this becomes more complicated because you'll need to have some sort of internal speaker crossover to separate between mid/tweeter. The internal crossover will have this, but it will also have a high-pass section to rolloff the woofer frequencies. If you can't control this and it's a manufactured speaker, an idea would be to connect the Modwright amp to the mid/high binding posts and not use an active crossover for this at all. For the woofer, you could use an active crossover to the Crown amp, but then wire the crown amp directly to the woofer (do not use the internal woofer crossover). All this will require some DIY work on the speaker to accomplish. Let me know if I haven't explained these ideas correctly. |
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 |
Regarding A/D, DSP and D/A. I have done comparisons on a high-end device. The Bryston SP3 has very high end power supply, audio stages, and A/D, DSP and D/A. Even on this device, when comparing audio using Bryston complete pass-through (just going through it's discrete Class A audio stages) and the Bryston DSP (using A/D, DSP, and then D/A). When using the A/D - DSP - D/A, the sound became much brighter and I did lose some midbass/midrange body - probably lost detail in areas as well. I suspect it will be far worse with a product like miniDSP. |
Wow lots of great suggestions THANK YOU ALL!! very, very, kind. I am using the 0.775 input setting on the crown. The minidsp is a 2x4 HD. Speakers are DIY. Woofer is sealed and midrange is OB. I removed the passive XO from the woofer cabinet. Aux, I can reinsert the passive XO external to the cabinet and not use the mini: Good suggestion. Note: I was able to get some improvement volume wise by adjusting the gain to +6db on the mini. That helped. regarding the 30 ohms impedance on the woofer, I could put in a zobel to tame that right? Now it seems to be a qualitative issue, bass is blah. Lots of great suggestions.I can't thank everyone enough. Question: exchanging the crown for another similar amp (QSC) would not yield an improvement correct? also, more power wouldn't help right? I think the Emotiva or used A/B amp with a good supply would yield better results. |
Agreed, if you are using active crossover, especially with two different types of amps, you really need to get actual speaker response measurements. This does become more difficult in your own home, unless you build some sort of sound absorbing tunnel (or do something outside aiming the speaker up with an infinite baffle type of area. You’ll need some sort of gain adjustment if you use different amps, or you will have to put in some sort of level adjustment in the passive crossover. Generally, people who bi-amp will use the exact same amp for highs/lows, but it may be a waste of expense to buy a second Modwright amp. I guess the pro audio amps are good because they do come with a gain adjustment. You could change to a QSC amp if you wanted to if you look for a Class A/AB. Pro audio amplifiers are designed to work in extreme environments, push a lot of -general- power to speakers that are extremely efficient (i.e. 98db/watt) and be as efficient with the A/C power as possible. Hence, more Class D/H/I style amps with switching power supplies and fans. What you want is more of a linear power supply with huge amounts of power supply capacitance and lots of output transistor devices. Usually, this does mean looking for an amp that has a lot more watts (since you need that bigger power supply to be able to push the watts), but it does not mean you have to use all the power. It just means that you have enough brute force from the power supply to drive speakers with low or radical impedance curves. I have used a Crown CTS600 and a Crown CTS2000. The CTS 600 was a Class AB amp. The sound quality was okay, but somewhat dry. The CTS2000 was definitely stronger and better for woofers, but it was a Class I (Class D variation) and it definitely had some tube-like overtones/colorations in the sound. The Emotiva XPA-1 monoblock was significantly better than either of these Crown amps. Emotiva was totally stronger than either and just sounded better overall. Much more current on tap. As far as I remember, a Zobel will not change the basic impedance of the speaker. It will still be 4 ohms. A Zobel is to control the rising impedence as the woofer tracks towards the higher frequencies. It’s good to put in a Zobel for the woofer anyways. See this: https://trueaudio.com/st_zobel.htm The Modwright is an excellent amp. My suggestions of the Emotiva XPA-1/1L and the Parasound A21 was to try to get a good enough amp to match the resolution/fidelity of the Modwright for the lower woofer registers. You don’t have to spend as much if you don’t want to. You could even go with a single Emotiva XPA-2 (2 channel), or other alternative. In the end, you get what you pay for. Actually, the Parasound A21 has a gain adjustment on the back, so it may work well unless the internal gain of the Modwright is so much higher. |
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 |
Taking almarg’s comments... Emotiva XPA-1 unbalanced input impedance: 23.5k ohms -- means (23k x 23.5k) / (23k + 23.5k) = 11.6k ohms combined. Parasound A21 unbalanced input impedance: 33k ohms -- means (23k x 33k) / (23k + 33k) = 13.5k ohms combined. So, comparitively speaking, the increase of impedance when using these amps directly instead of using the miniDSP for low-end will significantely improve the impedance load on the Modwright preamp. That and the fact that these amps are just stronger in controlling the woofer in general would lead me to think that it’s better just to drop the miniDSP out of the mix. I would just use the passive crossovers in the speakers unless you wanted to use something like the Bryston 10B to do BOTH the high and low amplifiers. |
Actually, looking at the Crown XLS 1002, it has a built-in low pass crossover as part of its DSP. You can setup a Linkwitz-Riley 24dB/octave low-pass crossover point anywhere from 30 Hz and 3,000 Hz. See page 8-9 of the manual. It does not publish the input impedance, but it -might- be better than using the miniDSP. |
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 |
One thing one thing to mention ,the amplifier is nothing special to begin within for sure invest in a known product such as Wyred 4 sound ,Pass labs 1st watt evrn Nad ,or tons of other proven companies. iwith your speakers who built them and how to know if they knew about proper speaker building Xovers very important and not easy to get right .usjng a online computer program Essential . I have bought from little companies before I won't name ,that had no clue ,no matter what cable or amp,preamp upgrade it was not seamless I tried my own Xover upgrading since I have modded caps, resistors,inductors for years f the design is flawed yiu can hear it . with the price of new Elac products ,and evrn lower priced excellent JL audio subs for under $1k you can build a great starter system for under $2-3 k for Everything including digital and cables. Just advise I have had single drivers and passive is not always so a inductor or resistors change the driver in some fashion.seek local Audiophiles many would love to help including myself . where are you located? Myself New England.If you don't know Ask I have been doing this for 40 years and still learning . No one knows everything !! |
Uh- all good suggestions, but before you do anything else, check to see that the woofers are in phase. That is to say, if the red connection on the back of the amp is connected to the plus terminal of the speaker, that such is also the case with the other channel. This way both speakers are pushing and pulling in unison. Otherwise they are fighting each other, and you would have some pretty 'blah' bass! |
Aux i got a HCA 1000. They are supposed to have high current capability. If I need to move up the ladder eventually Ill do so. The XO is a Pioneer SF 700. I will use it only as a low pass at approx 200hz. This is to compare with the mindsp re input impedance and output voltage. I am using a cap on the input of the Modwright as a hi pass. |
Yes, I would agree that the HCA 1000 would have better current capability than the Crown. Looks like it has 48,000 uf total capacitance (24,000uf per channel). Not a huge amount, but the amp is only 100w/8ohm. Crown XLS: http://s290.photobucket.com/user/iso_da_baric/media/IMG_3047.jpg.html Keep us posted how things work out! |
The XO is a Pioneer SF 700. I will use it only as a low pass at approx 200hz. This is to compare with the mindsp re input impedance and output voltage. I am using a cap on the input of the Modwright as a hi pass.Just as an experiment, what happens if you bypass the crossover and drive the preamp straight into the power amp driving the subs? The question is, how is the bass then? |
almarg, Dan agreed with you. he said 20K is good input impedance 30K is ideal. He is very helpful, one of the nicest guys to deal with. Love his product and his attitude, good karma for sure. I purchased (on his suggestion) 2 output coupling caps to help solve the problem. Your suggestions and help are greatly appreciated. Thanks all was I work through this. I am confident it will be solved in time and with money Lol |
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 |
Al, the pioneer is just for testing purposes. If I decide to go for an active XO I will shop for a better one. BTW, I just checked, the input impedance of the parasound is 33k!!!!! Thats great! and the sensitivity is 1.1 for full rated output. This is going to get interesting. I believe I am headed in a better direction. BTW, if you have any suggestions on XO's please suggest. Thanks again. |
The Bryston 10B (that I mentioned above) is likely your best choice for active analog crossover to keep the resolution of your preamp. It has fully discrete analog circuits (probably running in Class A mode) and an excellent power supply. Input impedance is 15k. There’s one on audiogon for $995. They typically sell for well over a thousand. There’s a Krell KBX for $1360 on ebay. It will probably sound more relaxed than the Bryston, but would probably need to be recapped. Also, the front dials do not show crossover frequency steps, so it will be impossible to determine actual crossover frequency without some sort of mic or line measurement device. If you want to go cheaper, you could look at a new Ashly XR-1001, but you’d have to use some special cables (either XLR or 1/4" TRS). It is a pro audio crossover, but it is still fully analog (as opposed to digital/dsp like most of the pro audio crossovers nowadays). Input impedance is 20k ohms balanced (this is probably 10k ohms single ended as I can see a 10k ohm resistor on the input of each XLR leg). You can pick it up for $250 at many musician websites (sweetwater, parts express, etc.). http://s298.photobucket.com/user/maryna1109/media/music/DSCN8468.jpg.html?t=1254515907 The Ashly is not going to be anywhere near the resolution/quality of the Bryston. If I did the Ashly, I would be making significant mods to it. First, Ashly likes to supply power at +/-18V, which is on the high side for normal op amp circuits, but they use normal 7818/7918 regulators. I would be doing the following: - replace the 7818/7918 monolithic regulators with Sparkos Labs discrete regulators and drop the voltage down to +/-15V. - Put in the largest power supply capacitors I could fit in the board/chassis (currently they are only 2 x 1000uf). - Swap out all the op amps with AD797 on dual-channel DIP8 adapters. - Solder 47uf Muse + 0.01uf metallized poly directly to the power pins on each op amp. - Replace all the op amp negative feedback caps with film/foil or silver mica. This is probably $450 worth of components (not including labor). I’ve seen dbx, Ashly and other analog pro audio crossovers. |
Yep, saw that one. There's a B4 on audiogon/reno-hi-fi for $995. I didn't mention it because it actually has a lower input impedance of 10k ohms. Also, I'm highly suspect about the power supply -- it looks like a basic laptop power supply, so you may have to buy/build a high-quality high-current linear DC power supply to get any sort of performance out of it. I also read that is uses bare JFET transistors with zero feedback instead of full op-amp circuits. The JFETS are biased into Class A, so this crossover will definitely draw some power supply current. I can't comment on the performance of this specific device, but I have seen instances where a bare JFET will sound nice but not have enough brute force to provide enough gain for bass/midbass punch, especially without negative feedback. JFETs in preamp circuits can sound nice - they tend to have a nice rich/lush type of sonic signature, but they are not as crisp/clear as bipolar devices (this is largely a personal preference on sound signature here). The Bryston power supply provides +/-24V (for a total of 48 volts), so the analog circuits definitely have a lot of current to play with for good bass/midbass power. And I confirmed that the circuits are all Class A discrete and use bipolar devices instead of FET based. There's always the Pass XVR-1, which is probably the best of the best, but at $5k+, I suspect it is out of range here. |
Okay, further research on the Krell KBX. It looks like this thing has the crossover frequency/slope hard-coded into the unit by Krell factory and cannot be modified. Krell no longer services these things (possibly), so it may be difficult to impossible to change this KBX to work with you system. And there is no way to "experiment" with different frequencies/slopes, so I'm going to give this KBX a big NO on the recommendation. |
Oh, if you do decide to look at the Bryston, be aware they come in several variations. Some have RCA inputs/outputs. Some have XLR. Also, some models have a hard-wired power cord and others have IEC inlet so that you can upgrade the power cord. The $900 agon is hard-wired power with RCA. There is another that's on auction with RCA and IEC power cord. |
Well the parasound amp arrived. And I have to say if I didnt have bad luck I would have no luck at all. I turned it on and it does have more balls than the crown but then I noticed the current limit LED's lighting/ I called Parasound and they said it is probably defective. Sure enough, I opened the unit and the electrolytics are leaking. Thats what I get for buying an old piece of equipment. I'll look for a newer and more powerful amp. Whose got the stamina to hang in there with me ha ha :-P |
Wow, yeah the HCA1000 could be as old as 1999. Time for a re-cap job! I’ll hang on til the end, lol! There’s a Emotiva XPA-200 on audiogon for $399. That’s $100 off retail, but amp is probably going to be 3-4 years old max. It has more power supply capacitor bank than the HCA 1000, but transformer is smaller. It’s not going to have the brute force of the larger monoblocks, but it’s definitely cheaper, and I’m sure it will be competitive with the HCA 1000. |
Looking at the specs, the gain on these Emotiva amps is 29db, where the gain on your modwright is 26db. If you don’t use an active crossover, you’ll probably want to use a speaker LPAD attenuator (parts express) on the woofers to bring down the level. Or spend more and use a passive preamp before the woofer amplifier. |
