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Crest CPX 1500 & other questions

Discussion in 'Amps and Cabs [BG]' started by atomic_turtle, Mar 14, 2004.


  1. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    Ok so I broke down and bought a power amp and yes it was not a QSC. I had my eye on a new QSC RMK1450 but the owner of the store would not budge on the $450.00US price tag. SO anyway I was at another store looking at their power amps and naturally the store owner says yeah we just had two QSC amps but one just sold the other day and the other one was put on lay-a-way. This is a mom and pop store by the way. Anyhow the 3 sales people begin giving me the run-down on all amps they had (stewarts, crown etc). All of which were out of my 400.00 price range. I tell them that I wanted to pick up a qsc 1450 which has 1400w on a 4ohm load bridged mono. This amp would power my SWR Goliath Senior 6x10cab (1000w rated). They then began the pitch on a Crest Cpx1500 which is 1500w @4ohm bridge mono. So after some haggling and their bashing of QSC and they all instantly became bass players who would swear by this crest amp, I bought the amp.

    Now my current set-up uses an Ampeg B2R head that I am using as a Preamp into the Crest CPX 1500 via an XLR Cable and then a speakon cable from the power amp to the cab.

    1. On my preamp (b2r) how do I set the gain when running into a power amp. When i was just running the b2r i would max the volume then adjust the gain to just before the clip induicators would come on. How would i set the gain on the power amp (crest cpx1500).

    2. I was a little dissapointed with my perceived loudness of the cab with the new amp running bridged mono. I definitely noticed a differnce in the lows (shaking the floor) but to me the midrange and overall loudness did not seem to improve. Could this just be me?

    3. Finally, the one thing that surprised me was how hot this amp got. The top of the amp was not to the touch. Not hot enough to burn your hand but the b2r i had never even got warm. Is this typical? Should I be concerned abouth this. The amp has a 5 year warranty.

    I know I probably should of got the QSC but my income tax money was burning a hole in my pocket! Any help on the set-up of this combo would be appreciated!
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Does the B2r's volume control setting affect the XLR output?

    Does the Crest have an internal fan? If so, is it running?

    Do you know how the Speakon plug is wired and how it needs to be wired for bridging?

    If you have a dedicated bridged output Speakon for the Crest, it might be wired 1+ and 1-. However, if you just have Channel 1/Channel 2 ouput jacks, then you would probaby have to have the plug on the speaker cable wired 1+ and 2+. If it's not wired correctly, you might not be getting full power from the amp.

    Check the manual!!!!
     
  3. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    OK, I looked at www.crestaudio.com and found the page for the CPX1500. I could find a link to a manual on-line but there were some pictures.

    You'll have to check the manual to learn how the bridged cable needs to be wired. Logically, since there's a dedicated Bridged output speakon jack, I would think it would be 1+ and 1-...but only Crest knows for sure.

    There is a two speed fan. Is it running faster when the amp gets hot than it does when the amp is first turned on? If not, there's a problem with the amp.

    Are you pushing in the little blue bridging button? Make sure that's pushed in.

    Have you tried taking a shielded instrument cable and running from the B2R's Preamp Output jack to the Channel 1 1/4 in. input jack on the Crest and leaving the Ampeg's XLR jack alone altogether?

    Make sure none of the other filter buttons on the Crest are pressed.

    Please keep us posted on your progress. I'm particularly interested in how well the B2R's preamp section works as a preamp. I owned a SVT-350H (same internals, different case) and loved the tone but needed more power.
     
  4. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    The volume control setting on the B2R does not appear to affect the XLR output only the gain knob it is also important to note that the b2r has a button on the back to select the post/pre eq for the xlr jack. i have mine pushed in for post eq.

    Crest does have the internal fan and does switch between the slow and high speeds.

    As for the speakons this could be were im having issues cause I know absolutely nothing about them. I managed to get the only speakon to speakon cable that the 3 stores near me had. It says nothing on the cable or the package as to how its wired. My crest manual says the following: For the bridge Speakon, Channel A appears on pins 1+ and 2+, and Channel B appears on pins 1- and 2-. Im not sure what this means or how to check speakon cable. I will try the 1/4" instead of the xlr today at 3pm and report back. Ongoing help is appreciated.
    Thanks
     
  5. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    It would seem that connecting to 1+ and 1- on the bridged jack would indeed give you the bridged output.

    You would have to unscrew the two lock nuts (for lack of a better name) on the speakon connector then slide the body away. The terminal numbers are molded into the plastic near the wiring terminals. Make sure the wires on yours are connected to 1+ and 1-. The cabinet end should be the same way.

    Please keep us posted.
     
  6. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    To my surprise the speakon cable that I have has two Neutrik NL2fC connectors on it so the cable comes as 1+/1- on both ends. There are no set screws or anything to change teh configuration. I think I would need the Neutrik NL4FC. Are you sure I would not want to make the amp end 1+/2+ and leave the speaker end as is with the 1+/1- configuration? If I do this i think I will need to get another connector or cable with the NL4FC ends (this means ordering online as none of my local stores have cables in stock with neutriks on both ends). Your continued help and understanding in this matter is appreciated.
    Thanks
     
  7. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    As an aside, I too am using an Ampeg B2R as a preamp and running it into a QSC 1850HD in turn to an Ampeg SVT-410HLN. The Ampeg does a good job as a preamp, however my BBE BMax arrives today and I cant wait to try it out.

    I am using an instrument cable from my B2R to my power amp then a Speakon from the power amp to the cab.
     
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    The way I read this is that a typical 1+/1- cable would pickup the positive terminals from each channel, which is exactly what you need for bridging.

    It seems like a phone call or email to Crest is in order to confirm that a 1+/1- cable inserted into the Speakon marked "Bridged" with the bridged button depressed will give you what you want.
     
  9. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    Fired off an email 2minutes ago from work so I will keep you updated when i get a response back from Crest Audio. Ive tried teh 1+/1- cable I had in bridged mono mode and I am disappointed that I seem to be making teh power amp clip very easily. I need to mess around with the gains on both amps to find out what teh best combination is to maximize sound levels while minimizing teh clipping. As far as using the B2R as a preamp it seems to be working out fine however when you put teh B2R and this 45lb CPX1500 in the same rack that sucker is heavy!!! I may need to think about unloading the B2R and picking up a real and hopefully lighter preamp.
    Thanks again for teh help.
     
  10. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    Response from crestaudio (Mike Mandala).

    "When connecting to the Bridged output Speakon use 1+ and 2+ for ChA and 1- and 2- for channel B. The connector that you have will work with the CPX Bridged output. "

    I guess this means that I have the right cable with a 1+/1- configuration. This being teh case I guess I am a little disapointed with the power amps output in bridged mono mode.
    :crying:
     
  11. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I guess the only unknown is whether the B2R's preamp puts out enough signal to drive the Crest to full output.

    Even if it did, with a particular cabinet, 1500 watts won't sound that much louder than 350. It could be a case of the Goliath Sr.'s efficiency too...
     
  12. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    yeah isnt the rule of thumb, if you want twice the volume you need 10 times the wattage?
     
  13. rok51

    rok51

    Sep 2, 2002
    Crawfordville, FL
    Don't feel bad that you got the CPX instead of the RMX. The CPX is every bit the hoss that the RMX is. The QSC has their nifty switch panel in the back. The CPX has a built in crossover. Both are very rugged amps. The CPX is virtually identical to the Peavey PV series amps (crossover points are different, according to cut sheets). Peavey/Crest have now dropped their MAP on the amps and they now undercut (for the first time) the QSC RMX series. As mentioned above, overall volume will be more, but not as much as you might expect. What you will notice (as you already seem to have) is that your bottom end is a lot more "effortless"...due to the increased headroom of the Crest. Evidently you are coming out of your DI on your B2R...it may not be hot enough to drive the Crest efficiently. If you do not have a level control on it, be sure that you use the "post" setting, so your eq changes carry over to the Crest...otherwise, all it will be seeing is your bass at the input stage and no eq changes you make on your B2R will carry over.
     
  14. Pete

    Pete

    Jan 3, 2004
    Seattle, WA
    Use the Speakon output in the middle labeled Bridged. The cable should be wired +1 & -1. Generally hot will be +, but as long as you are consistant go with it. Next make shure the bridge switch is on as well. Use the low cut switched next to the inputs as well since bass below 30hz is a waste of good power (it is!).

    On the ampeg, use a 1/4" line level output. There may not be enough level from the head to drive the crown to full power. Check the nominal level of the B2r (prolly -10dB or 0dB) and the nominal input of the crest (prolly +4dB). This is the most confusing part about getting the full amount out of the amp.

    pete
     
  15. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx

    I think this is the big problem. As you read above I was using a B2R as a preamp to my QSC 1850HD. Tonight I put my new BBE BMax preamp to the test with the QSC 1850HD. I achieved the same volume I had before with a lot lower setting on the BBE as compared to the B2R.

    Before on the B2R I had the gain at 5 (12 o'clock)and the Master at about 7 (2 o'clock)with the gain setting on the power amp around 8 (3 o'clock). By the way the power amp is being ran in stereo.

    With the BBE my current setting is Gain at 4 (11 o'clock), Master at 4 (11 o'clock), and get this the Gain on the power amp around 4 (11 o'clock).

    Now there is way more headroom than before. Oh and the sound the BMax puts out is awesome as well. I thought about trading in my SVT-410HLN on an Aguilar 212 but now I probably wont because I am acheiving great volume with incredible lows and low mids (credited to the Model J pups and BBE preamp probably). This preamp puts out tons of booty.
     
  16. atomic_turtle

    atomic_turtle

    Jun 22, 2003
    Dracut, MA
    That is very interesting, so it may be the fact that I'm trying to use the B2R as the preamp when it is originally made to be a separate power amp. Guess i will need to save up for one of those Sansamp preamps. Everything is hooked up correctly I will try the 1/4 output (i know i said i would do this earlier but i didnt), but it sounds like it may be the fact that Im not using a real preamp. Thanks you guys have been a real help.
     
  17. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    An interim fix would be to buy a small Behringer mixer...I think that they're like $40 or so and place it between the B2R preamp output and the power amp input.

    At home, I use a larger Behringer mixer between my preamps and power amp and it also allows me to run my drum machine and guitar amp modeler through my bass rig...