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Need help with a Carver PT1250

Discussion in 'Amps and Cabs [BG]' started by Chef, Dec 15, 2004.


  1. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    I have a 1990 Carver PT1250 that I've run in stereo for years biamping 1820 ccab, sending highs to the 10's, lows to the 18's. I recently ordered a Schroeder 410 to replace my 1820's:)

    I now want to run this amp in mono. The owner's manual says:

    "internal jumpers must be moved before mono operating mode is allowed. These changes must be made at the factory, or by a qualified service technician."

    Carver does not answer their customer service phone:360.862.1742. I've left voice mail...

    Can any of you hotshots walk me thru this, or guide me to some one who can? Please?
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I presume by "Mono Mode" you mean bridged? I assume that the Schroeder is a 4 ohm cabinet, can your power amp be bridged into 4 ohms? Running bridged into 4 is like running stereo into 2 ohms/channel.

    If you can post some photos of the inside of your amp, perhaps I/we can help.
     
  3. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Photos: I can try to do that tomorrow.
    Yeah, by mono I mean bridged.
    The Schroeder is 4 ohms, the carver should be 1200 watts in bridged/mono which ought to be fine with a 1400 watt 410 cab...
    Wish I had a schematic... and a bigger brain:)
     
  4. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    It's not the power rating that I'm concerned about... Does the manual for your Carver state that you can bridge into a 4 ohm load?

    In another thread, a smaller Carver was limited to 8 ohms in the bridged mode.
     
  5. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    The owners manual sez it's o-tay...
     
  6. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    I just checked this in the on-line manual:

    ftp://208.187.38.55/Carver/Manuals/pt/pt-manual.pdf

    I gathered that the internal jumpers must be set for 'parallel mono' mode (that's when you want to send one signal in and have it go to both output channels). The PT1800 and PT2400 have a switch on the back for this (see manual that I linked to that has all three models). I have a Carver PM 1400, and I have to slip a small board out and flip a switch on mine to engage parallel mode mode.

    I think for bridged mode on yours, you only have to engage the 'series mono (bridge) switch' and then hook up the speakers to the correct posts with the correct polarity. See the diagrams on the manual that I linked to. The diagrams are down in the PT1800/2400 section, but I'm almost certain that the one showing bridged mode is for the PT1250 too.

    I don't think the PT1250 goes down to 2 ohms per channel (which is the same as bridged into 4 ohms). They show it in the specs for the PT1800 and the PT2400, but not for the PT1250.
    Be careful..
     
  7. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I'm with Zombywolf5050...doesn't look like the 1250 can be bridged at all. Also, in the stereo or dual mono mode, you're limited to 4 ohms per channel minimum.

    I imagine that the Schroeder would make enough racket with the 625 watts that one channel will produce anyway...

    Maybe if you're only driving one channel, you'd be able to get more than 625 watts out of the amp.
     
  8. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    I finally got Carver customer service. It can run "parallel mono", 1200 watts into 4 ohms, two speaker outputs. It's a matter of moving three internal jumpers, and tying the red binging posts together. $50 mod at the factory.
     
  9. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    'Parallel Mono' is the same as 'Dual Mono', and those are different than 'Bridged' (which Carver refers to as 'Series Mono').

    Parallel/Dual Mono is where you plug into only one of the power amp's inputs (channel 2 on the Carvers), and that one input signal is sent to both output channels of the amp (you would separate speaker cabs connected to both channels of the power amp).

    Bridged (same as Series Mono) is where both output channels of the power amp go into only one cabinet (there is a special hookup involved where you don't use all the posts for both channels).

    If you want to run bridged then you don't want 'parallel mono', because they are different.

    You should have asked the support guy about running the amp in bridged mode.
     
  10. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    If they say so... tying the outputs of two solid state amps together sounds like a recipe for disaster to me...

    If it actually would work (and I've never, ever heard of anyone doing this), paralleling the outputs with a 4 ohm load would essentially load each channel to 8 ohms and I'd think that you'd get 930 watts into your 4 ohm load (2 x 465 W (the 8 ohm power output specification)).
     
  11. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    From the owners manual:

    Power Output:
    4 ohms, both channels driven 625 watts
    4 ohms parallel mono 1000W
    (other ohm options omitted here by me)

    Output Connector wiring:
    Unlike most solid state amps, the pt1250 can be operated with it's output connections paralleled. *Internal jumpers must be moved before this connection or operating mode is allowed. These changes must be made at the Carver factory or by a qualified technician. Only the left input connectors and level control are used in parallel mono mode. The minimu load impedance is 2 ohms or greater. For driving a single load (which may be compromised of one or more speakers in series, parallel, or series parallel) the red binding posts must be wired in parallel(together) and the load connected to either red and black binding post. In either case ensure that total load impedance is not lower than that listed in specs. for the mode of operation that you have selected.
     
  12. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    How about that...you learn something new every day...
     
  13. DJ Tim

    DJ Tim

    Dec 13, 2005
    I changed mine to mono at one time tears ago. I will look for instructions I recieved from carver. Will let you know if I find them. It involved some some simple desoldering and resoldering jumpers inside the amp. 15 minutes total job. Tim
     
  14. jgsbass

    jgsbass

    May 28, 2003
    Floral Park, NY
    The Carver literature I have read says that one channel can "borrow " power from the other channel. At least thats what my M 1.5 is purported to do. Run one channel and see if its enough. It should be
     
  15. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Holy retro thead! Sold that in Dec 04!
    But, I so0ld it to a fellow TB'er, so, carry on;)
     
  16. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Do you want bridged mono or parallel mono? In one post you say bridged, and in another you say parallel.
     
  17. fourstring44

    fourstring44

    Jul 22, 2003
    St. Louis
    I am interested in this as well, as I have a Carver PT1250. It has been my understanding that you can not bridge these amps and they will not run at less than 4ohms per side. But quite frankly it smokes my QSC plx 1602 in stereo.



    _Curt
     
  18. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    What do you want to do?
    You can bridge it, but only into a minimum load of 8 ohms.
    If you want to run it in 'parallel mono' mode (which Carver calls 'dual mono' mode), then you'll have to install some jumpers inside the amp because this model doesn't have a switch for that.
     
  19. fourstring44

    fourstring44

    Jul 22, 2003
    St. Louis
    Thanks Zombywoof5050, How would bridge it for use at 8 ohms? Is it easy to do or would I have to open the amp? There are times, when it would be nice to be able to bridge the amp.


    _ Curt
     
  20. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    Upon closer inspection of the manual, I would assume that the PT1250 is not really set up for bridging (which Carver refers to as 'series mono operation'), because it's not mentioned in the power output specs and there is no switch for it (like on the PT1800/2400).

    They do state that (for the PT1250) if you put in the internal jumpers (for 'dual mono' mode), that you can then 'drive a single load' by wiring the red output posts together and then connect the load to either of the red and black posts (it doesn't matter which because both red posts are now tied together and both black posts are already linked internally, just make sure you use a red AND a black post to connect your speakers to and observe polarity to the speakers).

    In this section (where they explain all of this) they state "The minimum load impedence is two ohms or greater" (and they mean per channel, of course). I'd be careful, because I really think they may just be referring to the PT1800/2400 here, as they do not list a 2 ohm load in the specs for the PT1250. I'm thinking that the minimum load per channel for the PT1250 is 4 ohms, since that's all they show in the specs for the PT1250. If you really want to know for sure, I'd call Carver and talk to the guy there. I've talked to him before and he's a nice guy and willing to help out.

    They really should have made a separate manual for the PT1250 instead of grouping it with the PT1800/2400.