Input signal boost to Crown XLS1002

Discussion in 'General Audio Discussion' started by GearHead454, Apr 18, 2017.

  1. GearHead454

    GearHead454 Still Lost Subscriber

    I just got a Crown XLS1002 to drive the woofers in my bi-amp setup speakers. Mister Pig's Hawthornes. I am finding that even with the Crown set at high sensitivity that I am not getting adequate signal from the source (I have tried 2 different sources). I have not been able to get the input signal meter on the Crown off the min level (unless I crank the preamp to unreasonable levels). Unreasonable because the non woofers are way too loud at that point.

    I would also note that I must completely peg the Crown to get any bass out of the woofers.

    I have tried connecting the Crown via the pre in / power amp out circuit on a restored Sansui AU-717 and I have tried it connected to a Modwright LS 100. The LS 100 was driving an MC 275 for the non woofers.

    I suspects that I need to boost the signal before it gets to the Crown.

    Anyone have any ideas if I am doing something wrong or if I need another piece of gear to boost the signal.

    Thanks
     
    Last edited: Apr 19, 2017
  2. loudnoises

    loudnoises Escalates Quickly Subscriber

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    Crown is only rated 1.4vrms in, your sansui is rated at 1v out, so thats not the issue i don't think.

    You need more power for the lows to match the sensitivity of the highs. Turn down the amp gain to the non-woofers until they match the woofers in level.

    You're now going to start reading threads about setting gains. :thumbsup: I usually start with the least efficient driver, almost always the low end. Bring the others up to match. Right now you're doing it the other direction, it's like running after a speeding bus, setting the gains on the most sensitive first is like giving the bus a mile headstart. two massively different amps running two massively different drivers will virtually never have identical gain settings unless the imbalances are corrected with an eq or active crossover beforehand.
     
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  3. loudnoises

    loudnoises Escalates Quickly Subscriber

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    Slightly more awake... what is your other amp running the highs?

    If nothing you do, even pegging the levels at pre and amp, makes that crown sing, then something else is wrong. Swap wires i assume?
    Since it's brand new (i dont know it's menus/options) maybe it has a -20db pad on the inputs, and maybe they set it to "on" from factory as a precaution. 500wx2@8ohms will fry most speakers used incorrectly, and i'm sure crown has had more than one customer complaining about how their amp blew "dad's old speakers".

    Still all about the gains, but i wouldn't be looking to boost signal to the crown, i'd be padding the signal to the highs. SQ wise cutting is generally preferred to boosting.
     
  4. whoaru99

    whoaru99 Epic Member

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    I think this is the general gist of it. Although, without the specific information on how everything is connected and set up it's a bit of a guessing game.

    The Crown can be set for 1.4Vrms or 0.775Vrms input sensitivity. In terms of net gain that means ~29.5dB or ~34.5dB, respectively, for 8 ohms load.

    The other amp mentioned is the MC275, which is rated 1.7V input sensitivity (unbalanced) and 75W at 8 ohms, which mean ~23dB net gain.

    So, if both amps were playing a full range signal then the Crown should play louder at any given input signal level because of higher gain.

    I don't know if the MC275 has "gain controls" but the Crown does. And, the input sensitivity spec, thus net gain, is with the controls fully clockwise. If they are turned down then the net gain of the amp is less than indicated above.

    As well, if the LPF is at 80Hz, the average content for 80Hz and down is less than the average content 80Hz and up. So, it isn't particularly unusual the meters don't show a lot unless you're really blasting the system.

    Then, as you mention, the sensitivity of the mid/high relative to the lows come into play. That has to be compensated by the relative gains/outputs of the amps.

    Based on the OP's comment that the Crown must be "completely pegged", it sounds like the gain controls are turned down. Turning the to the max setting is fine, they're not power controls, they simply control the ratio of output to input. The amp doesn't work harder simply based on their position, the amp works harder based on how much actually comes out for power.
     
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  5. GearHead454

    GearHead454 Still Lost Subscriber

    Thank you both for the detailed information.

    I will try to answer some of the above questions and provide more clarity.

    I do not see a -20db pad on the Crown. No physical switch for that front or back panel. The lcd screen menus don't reveal anything along those lines either.

    I dont have the specs on the Hawthorne woofers. I do know that each woofer is 4 ohms and each speaker has a pair of these woofers wired in series. So the woofers are presenting an 8 ohm load to each channel of the Crown. The Crown xls1002 is rate at 215 wpc at 8 ohms. I don't see anything on the Crown to select the speaker loading. I had thought there might be a switch or menu for 4 ohm and 8 ohm at least.

    I tried this Crown and woofer setup on two systems last night but I will focus on the Modwright LS 100 and MC 275 combination for now.

    I have two sources going to the Modwright preamp, a tuner and a turntable. Both play roughly equal loudness through the MC 275.

    The LS 100 has two pair of unbalanced (RCA) outputs that run concurrently. The first output I ran directly to the MC 275. Just like normal. The second output I ran to the Crown.

    I set up the Crown through the menus as follows:
    Stereo, Low pass 80 hz, input sensitivity 0.775.

    To hear the woofers at all I turned the gain dials on the Crown full clockwise to maximum gain ( I called that "pegged" previously).

    The meter on the Crown is for input signal not output signal. This meter is a series of led's that light up as the input signal increases. I can never get it above the first bar unless I drive the preamp to 3/4 of maximum and at that point the mc275 is pushing the coaxial drivers to unreasonably high volumes.

    Because the Crown input meter is so low my sense is that it is not getting a strong enough signal from the preamp. That's why I was thinking of boosting the signal to the Crown.

    I have not pushed the factory reset button on the Crown yet and will probably try that.

    I also have an emotive xps-1 phono pre that I could try inserting between the Modwright and the Crown. Would that be a stupid idea?

    Sorry for the long ramble. I really appreciate the suport. Due to my day job I won't be able to experiment anymore until Friday.

    Thanks all
     
    Last edited: Apr 19, 2017
  6. loudnoises

    loudnoises Escalates Quickly Subscriber

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    You're getting into new territory, mixing older gear and new.

    Ok so until now, your system has been linear, so you're unmasking issues that weren't before.

    A second pre is not recommended.

    The issues are, as I see them, your mc275 has no gain controls, and your sources aren't incredibly hot. These are totally separate tho.

    The lack of gain control on the high end means you need to pad that signal, ideally more than it's relative overage in relation to the crown (see math above). Then you'll be turning down the crown from max gain to balance. This is much preferable to boosting the signal to the crown.

    The volume knob at 3/4 is only a issue if aesthetically bothers you. The level of the knob is dependant on the signal source, so turning it up means you're using more of the signal. Is good. Try a higher output source and your knob will be lower, at the same spl.

    Nelson pass has much to say about gain, throwing away signal, etc. Good reads. Imho all you need is an in line attenuator between the pre and mc275.

    And where's mr pig on this? I'm curious to hear his assessment.
     
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  7. twiiii

    twiiii Super Member

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    Just for grinns, what happens if you swap the 275 and the Crown? You don't have to turn the volume up. Just enough to know if you have an amp problem or sick woofers. I mean, if there is no bass with the 275 either you know its the woofers. If the problem becomes now have bass but no mid and highs you know the problem is with the Crown.
     
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  8. nedseg

    nedseg AK Subscriber Subscriber

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    It's been a while, but I had zero problems setting up my 1502XLS for subwoofer duty (4645C), and FWIW, I rarely get beyond the second LED/VU lighting up...and that's pulenty loud. I'm driving it (bridged) from the SW output of an Emo UMC-200....
    Have you tried emailing Crown directly? I was totally amazed at how quickly and competently they responded to questions I had about that amp vs others - the tech really knew this stuff, and recommended this amp over the other (pricier Crowns) for a variety of reasons (including variable inputs and much quieter fan). Suprising helpful & responsive.
    I haven't really bothered to look into it, since It Works, but the way I have it set, the volume knobs don't seem to do anything...it Just Works:)
    Good luck!
     
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  9. GearHead454

    GearHead454 Still Lost Subscriber

    This sounds like a nice simple solution Are there preferred options for an attenuator for unbalanced inputs?

    I don't know but that sounds like a good experiment for Friday.

    That's good to know. I am only getting the lowest led to light unless I dial up the preamp to 3/4 point. I have not contacted Crown but that seems like a really good idea as well.

    Thanks
     
  10. loudnoises

    loudnoises Escalates Quickly Subscriber

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    Harrison labs makes some, they've got a good rep, but I've not used them. There's a thread on this exact subject currently in diy right now, making your own is very easy, and can be done precisely.
     
  11. GearHead454

    GearHead454 Still Lost Subscriber

    crown xls1002.JPG

    This is NOT my unit. This one has the LEDs lit up indicating proper output.

    Ok, so today I spoke with Dan at Modwright and with a tech at Crown. They were both very helpful.

    It may be a defective Crown amp but I have a test to run to see.

    How the Crown operates:
    With the Crown input sensitivity set at 1.4 v anything coming from the preamp that is in excess of 1.4 V (input sensitivity can also be set to 0.775 v) will run the Crown at maximum level. The Modwright specs show that it will put out 37 Vrms max. Therefore we have way enough output per spec to run the Crown at full bore. Supporting this theory is that the Modwright has been driving other amps and speakers fine so I am not suspecting it at this point.

    I did not previously understand the led meters on the crown. This is how they work: the bottom LED indicates that there is an incoming signal but it doesn't tell the strength of that signal. The LEDs above the bottom indicate the output signal strength. They climb up to indicate increasing output power all the way to clipping. In my tests the input signal is present but the output signal meter won't light at all until the preamp is dialed up to 3/4 full and then the first output lamp just barely lights up. This seems odd to the Crown tech and to me.

    The pots on the front of the Crown are attenuators. At full clockwise the crown is passing all the incoming signal through. Therefore any signal above 1.4 v should have the Crown blasting.

    The Crown tech felt that the lack of output signal meters lighting up was odd given what we discussed.

    He suggested a test of the Modwright output signal using a phone for a tone generator plugged into the Modwright then testing the RCA outputs on the Modwright. The goal is to confirm what signal voltage the Modwright is actually producing. If it is producing anything above 1.4v then the crown should be working at all volume levels and should be able to be driven to clipping using the attenuator pots on the front of the Crown.

    Like I said earlier my day job is in the way of important electronics experiments until Friday.
     
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  12. nedseg

    nedseg AK Subscriber Subscriber

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    Excellent! I've wondered about those pots...more sophisticated than I expected. Will have to play with mine some more.
    Yah, day jobs sure do interfere with fun stuff - don't miss it At All.
    Very interested to hear what you find out, & thanks!
     
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  13. loudnoises

    loudnoises Escalates Quickly Subscriber

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    I kinda hope you're lucky enough to have a bad amp (not really tho), you can't teach troubleshooting. Experience is golden.

    :lurk:
     
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  14. loudnoises

    loudnoises Escalates Quickly Subscriber

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  15. whoaru99

    whoaru99 Epic Member

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    They are not sophisticated at all. They're functioning same as any other input attenuator/gain control.
     
  16. whoaru99

    whoaru99 Epic Member

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    There are a few things that need to be cleared up to preclude wild goose chase/false assumption.

    That's yes and not necessarily.

    Yes, if the amp is running full range

    Not necessarily if you are using low pass filter, which you are. I will explain this in a bit with pictures even.


    Again, this is yes and not necessarily.

    Yes, I believe it can put out 37V if Modwright says it can. HOWEVER, output voltage is contingent on input voltage and gain of the unit. Modwright says the line level gain is 11dB. That means to get 37V out you'd need a minimum of 10V from your sources. 10V from sources is uncommon so the prospect of actually getting 37V out is unlikely in practical use.

    For the Modwright to put out the 1.4V requires at least 0.4V from the source. But, 1.4V is not all as it seems, as I will get to.



    What the Crown guy told you is basically true, IF the amp is being run full range. But, you are NOT running the amp full range, you're running with ~80Hz low pass filter. What this means is the output level LEDs reflect only the output content below the low pass filter. And, at 80Hz and down, the average content of the signal is typically just a small part of the total so the meters won't be expected to show much, relative to full range signal.

    To put this in rough context, for sake of discussion, let's say you have the preamp turned to the point where it is putting out 1.4V signal. The presumption is this should drive the Crown to full output...and it would (or at least close) if the Crown was amplifying 100% of the signal.

    But, the Crown is not amplifying 100% of the signal. It is only amplifying the portion of the signal that is around and below the low pass filter setting of ~80Hz. So, if ~80Hz and below signal only constitutes 15% of the total, then the amp is only amplifying that 15%. That is why the meters don't show what the Crown guy thought they should show or told you they should show. The following pictures illustrate this using my XLS 1000.

    This first picture is baseline. The amp is set in bypass so it's running full range. I have a 1kHz signal going into channel 2 and turned up the signal generator to make sure the clipping indicator is lit up. It's about 1.6V going in.
    FilterBypass_1kHz signal.jpg

    This next picture is same signal going into the amp (1.6V @ 1kHz) but I have now engaged the Low Pass Filter, set to 79Hz. As you can see, the meter shows only signal present, but not enough to light up any of the output indicators. Which is exactly what you're seeing.
    LowPass79Hz_1kHz signal.jpg

    This next picture is same low pass setting of 79Hz, but now I changed the signal to 1.6V @ 250Hz. As you see, even at 250Hz, the amp shows only signal but no appreciable output, because the low pass filter is still blocking it.
    LowPass79Hz_250Hz signal.jpg

    This next picture is same low pass setting of 79Hz, but now I changed the signal to 1.6V @ 125Hz. At 125Hz, the amp is just beginning to let some of the signal though as we approach the low pass setting. -20dB output represents 1/100 of the amp's power, or about 2 watts.
    LowPass79Hz_125Hz signal.jpg

    Things start to get interesting now. LPF is still set at 79Hz, signal voltage is still 1.6V but now @ 100Hz. Just a little change in the frequency from 125 to 100Hz has the amp now 10x more output because the filter is letting more of the signal through. -10dB is 1/10 power or about 20 watts.
    LowPass79Hz_100Hz signal.jpg

    In this final picture, LPF is the same 79Hz, signal voltage is the same 1.6V, but now the signal frequency is 60Hz. As you can see, the amp is back to clipping level. The input signal is now below the low pass frequency so it all, or at least most of it/enough of it, gets into the amp and thus is reflected in the power output.
    LowPass79Hz_60Hz signal .jpg


    So, hopefully you will now conclude it is unlikely the Modwright is broken and it's unlikely the Crown is broken. The amp and meters are simply exhibiting the effect of amplifying a limited portion of the total signal because of the low pass filter.

    If you want the bass to match up more with the mid/highs, I believe you are going to have to attenuate the signal to the mid/high amp or boost the signal to the Crown.

    You don't really need to do all that to test the theory. Just disconnect the speakers from the Crown so you don't blast out the jams (it will be perfectly fine without a load). Set the gain controls/attenuators to max (full clockwise) then switch the amp from Low Pass to Bypass so it's running full range. Put on some tunes and turn up the Modwright. I reckon you won't have much trouble making the meters dance, especially if you put it on the 0.775 sensitivity.
     
    Last edited: Apr 19, 2017
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  17. GearHead454

    GearHead454 Still Lost Subscriber

    Wow, Thank you. That is exactly the kind of step by step tutorial that I need. I really appreciate the effort and the pictures to help explain what is going on.

    I will do the simple test you noted at the bottom of your post.

    I will also do a test by running the Crown full range to the coaxials and see what the output meter looks like.

    What equipment did you use to run the various examples in the post. You mention a signal generator and I see you have the ability to know what voltage you were driving the signal at.
     
  18. whoaru99

    whoaru99 Epic Member

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    I used an old B&K 3010 to produce the signal.

    Monitored the signal frequency and voltage using a Fluke 97 Scopemeter.
     
  19. GearHead454

    GearHead454 Still Lost Subscriber

    Thanks. I Just did this test. You are correct without speakers connected and amp running at full range the meters lit up all the way yo clipping levels.

    Do you have any products that you can recommend for either (or both) of thees tasks?

    Thanks
     
  20. whoaru99

    whoaru99 Epic Member

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    I would probably start cheap since I have some pots on hand.

    Use a couple of pots to make attenuators/voltage dividers for between the preamp and the mid/high amp. See if you can dial that back enough to get the level of mid/high to match the bass as you see fit, yet still achieve all the overall volume you want/need.

    If you can still get the overall volume then I'd probably just go with attenuation on the mid high. If not, then might have to consider something to boost the low end.
     

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