Mono amps for RS1a

Discussion in 'Infinity Loudspeakers' started by mtho33, Feb 22, 2017.

  1. mtho33

    mtho33 New Member

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    Hi,
    I have the Infinity RS1a four tower speakers that I have bought for a long time. I never hook them up as I do not have the amplifiers. Now that I have the space to use these speakers I plan to buy used amplifiers to run the bass towers and mids towers.

    After reading the manual it seems that I can use mono amps for the mid tower with no problem. Based on my research with forums I found that I should not use mono amp for the bass tower because there are bridged amp. But at the same time there are people who have used mono amps for the bass tower. So I am confuse.
    I have the standard crossover box.

    Would I be able to use monos amp like Odyssey monos or Threshold SA-1 to drive the bass tower? I plan to use tube amp for the mids tower like one Mcintosh M275 amp. Thank you in advance for your assistance.
     
  2. swechsler

    swechsler Frog Whisperer

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    In this article the reviewer states that he successfully used the Threshold SA-1 with the Infinity RS-1B bass columns. They should therefore work with the RS-1As.
     
  3. mtho33

    mtho33 New Member

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    Thank you. I assumed he use the standard crossover. I read that people use custom crossover which enable them to use any amp.
     
  4. swechsler

    swechsler Frog Whisperer

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    A custom active crossover/servo controller seems unlikely to me - the circuitry for the servo control is pretty complex and is customized for this speaker. In fact, I'm pretty sure it's the servo control that prohibits using a bridged amp (although I'm unclear as to exactly why). If you were to run these with a custom crossover without any servo circuit, you could use any amp you wanted (however, I believe the benefits of the servo outweigh the benefit of being able to use any amp).
     
  5. mtho33

    mtho33 New Member

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    The manual specifically mentioned not to use bridged amp for the bass tower. Here's what I found from another forum. I have little knowledge with electronics and so I do not know what it meant.
    "you can not us bridged amps with the bass section of the RS1b's because they will go into positive oscillation. (very loud painful and costly)"

    Am I correct to say that not all monoblock amplfiers are bridged amp?
     
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  6. chef free

    chef free AK Subscriber Subscriber

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  7. swechsler

    swechsler Frog Whisperer

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    Yes, oscillation would be caused by the servo circuit.

    And I believe that many monoblocks are just straight amps with neither bridging nor strapping.
     
  8. kurtgo

    kurtgo AK Subscriber Subscriber

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    Mtho33 - I too am recently bringing my RS-1a's out to hook up. Bought them 3 years ago and had the crossovers - box and in the midrange panels - rebuilt. I am planning on using a Parasound 3500 amp for the bass and 2 - Carver M180 tube monoblocks for the wings. I am very familiar with the Parasound as I have used it to power my RS4.5's that I had. Used them in a vertical bi-amp mode instead of a horizontal setup as the instruction manual indicates. The Carvers have been used for the past few years powering the mid/tweets in speakers that have a built in amp/servowoofer so don't really know how they would perform on the lower end. At 180 watts/channel I'd suspect they would do, but, I can't get the way the Parasound grabs the bass regions out of my head. Keep us posted on what you do and photos!
     
  9. mtho33

    mtho33 New Member

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    At this moment I have a Threshold s/500 II and a Mcintosh tube MC275.I plan to use the Threshold amp for the bass.
    I am also getting a very old Odyssey Stratos monoblocks in the near future. For the mid towers I plan to use SS amp for fast music and tube amp for vocal & instrument.
    Right now I am in the middle of running wires in my basement for 7.1.4 atmos home theater with projector and so my RS1a speakers are stored in the unfinished part of the basement.
    I hook up the two used amps I got this year to test them with my home theater speakers Polk LSIM 705.

    For the Threshold/Mcintosh 275 combinations do you recommend that I hook them up in vertical biamp mode or just follow the manual horizontal mode?
    What about the Threshold/Odyssey monoblock?

    I attached picture of the connections from the manual and another picture for vertical bi-amp. Is the picture for vertical bi-amp correctly illustrate the vertical connections you have in your system?
    I will keep you posted when I got a chance to hook up the rs1a but it can take a while as I need to finish my home theater project first.
     

    Attached Files:

  10. mtho33

    mtho33 New Member

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    Thank you for the information.
     
  11. mtho33

    mtho33 New Member

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  12. chef free

    chef free AK Subscriber Subscriber

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    That's right, I assumed you meant making a mono block out of a stereo amp since you mentioned bridging. A mono block amp is just a one channel amp.
     
  13. kurtgo

    kurtgo AK Subscriber Subscriber

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    I would hook them up first horizontally. That way you can follow the diagram and have your inverting/non-inverting issue worked out as well.
     
  14. mtho33

    mtho33 New Member

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    OK, thank you again.
     
  15. kurtgo

    kurtgo AK Subscriber Subscriber

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    Mtho33 - Finally got mine hooked back up and tuned in a bit. I tried these originally when I bought them several years back and was severely disappointed in them. As mentioned, I sent the crossovers - passive and active crossover box - to CDFAC and he did a superb job of rebuilding them to RS-1b specs. They then sat for the next 2 yrs without being hooked up. So after finally settling in at the new house decided to give them a go. I am using the Parasound 3500 amp to run the bass towers. The Carver M180's (tube monoblocks) do the mid/tweeter towers. All hooked up as specified in the manual. What a difference the rebuilding of the crossovers make DSCN0698.JPG DSCN0711.JPG ! Now they perform like I imagined they would. I have heard others mention perhaps there wasn't enough bass output from the towers. I'm not having that problem at all. I'm going to hook up my SVS sub just to see if I want a little more. Photos attached.

    How's your setup coming along?
     
  16. mtho33

    mtho33 New Member

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    Since my last post I received purchased more amplifiers. I have not decided on the preamp yet.
    I received the speakers wires and banana binding post wall plate from Monoprice a few days and have not install them yet. Beside running wires for the projector I need to run another two dedicated lines for the home theater.

    I moved into the house more than two years ago and last August the basement got flooded when the water heater leak. Since then I have added new flooring and have someone ran four dedicated power lines for hi-fi purpose.

    I decided to add projector for home theater (Atmos 7.1.4 layout) just recently and so I repainted the wall you see in the picture to dark blue for projector screen. All the speakers (except ceiling speakers) and hi-fi equipments will be at the blue wall. The blue wall is only 16ft wide and so it will be crowded when I have the speakers, projector screen and hi-fi equipments there.

    Home theater equipment will be in the unfinished part of the basement. My Rs1a speakers are in the unfinished part of the basement as shown in the picture. There were moved there when the basement was partially flooded.

    Currently I am testing the amps with home theater speakers Polk LSIM 705. The Polk LSIM speakers are actually quite musical. The equipments in the picture are:

    - Odyssey mono amp Extreme upgraded to Kismet for RS1a Mid tower
    - Odyssey mono amp regular
    - Mcintosh MC275 VI tube amp for RS1a Mid tower (interchange with Kismet amp depending on music)
    - Wadia 6
    - Threshold S/500 II amp for RS1a woofer tower

    I will let you know when I got a chance to listen to the RS1a speakers.

    Where is CDFAC? In the future I am interested to change the old electronics in the crossover as well?

    Wall.gif RS1a.gif Equipment.gif
     
  17. mtho33

    mtho33 New Member

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    The color of your rs1b looks like mine. But the wood condition of your speakers look better than mine.

    Is the Carver M180 monoblock at 180 watt powerful enough for the Mid tower? I am not sure the Mcintosh MC275 at 75 watt is enough. (maybe I need to get another one for mono)
     
  18. kurtgo

    kurtgo AK Subscriber Subscriber

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    AK member CDFAC. Lives in IA. Great guy and big help!

    The M180's are more than enough for the mid towers. Your MC275 should do ok.
     
  19. mtho33

    mtho33 New Member

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    Ok, thanks.
     

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