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2252 Preamp Out

Discussion in 'Marantz Audio' started by reddog48, Jul 11, 2018.

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  1. reddog48

    reddog48 Active Member

    Messages:
    262
    Location:
    Dallas, TX
    I have been trying to get output from my 2252 Marantz receiver. This unit came from the factory without any jumper between the "pre out" and the "Main In". Just four RCA jacks. When I hook up to the "Pre Out" jack I don't get any signal.

    My research shows a "internal" jumper - that seems to be some type of mechanical switch that is engaged when an RCA plug is inserted into the Pre Out. My question is do BOTH the "pre out" and the "main in" jacks require an RCA plug inserted BEFORE there is any output on the "Pre Out"?

    Is there a common failure modality associated with using the "Pre Out" on this unit? I doubt if the "Pre Out" has ever been used on this receiver. Could the mechanical switch - assuming that such is inside the component - have failed over the 43 years since its manufacture? Could this switch have "grown" together over time due to the constant passage of current?

    Help is greatly appreciated.
     

     

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  2. jd3rdcoast

    jd3rdcoast AK Subscriber Subscriber

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    Are the RCA jacks single jacks with no cable and not connected like a short patch cord? I have heard this internal switch mechanism can be problematic.

    With nothing plugged into either PreOut or Main In your unit should function. Get a set of patch cords and jump Pre Out to Main In to bypass the internal switch and if works leave as is and you will know the switch is not functioning. Possibly just needs contacts cleaned.

    Plugging the RCA’s into the Pre Out will open the switch and you will not get anything out of your amp. You can run that to another amp and check your Pre amp or vice versatility run another units Pre Out to the 2252 Main In to test your Amp section.
     
  3. willyrover

    willyrover Super Member

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    3,124
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    Hamilton
    Just to be clear, I assume you are trying to get a PREOUT signal to send off to another amp?

    The switch mechanism is normally closed so that when the jacks are empty, the signal is passed through to the amplifier.

    Inserting RCAs into the PREOUT jacks should give you signal even if the switch mechanism is faulty.

    Failure on these is usually a bad connection between preamp and amplifier sections. I wonder if this happened at some point and someone internally bypassed the preout/main in jacks?
     
  4. reddog48

    reddog48 Active Member

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    262
    Location:
    Dallas, TX
    Thank you, Jd3rdcoast and willyrover - I do appreciate your help.

    Yes - I am trying to get a pre out signal to drive some Dynaco ST-70 tube amps (rigged as monoblocs). Right now I am getting nada, zip, nothing. I guess I am going to have to go "into" the unit and see if I can determine what is happening. I have the schematic for the 2252 and it does NOT show a relay or electrically controlled switch - the schematic seems to indicate a mechanical switch that with an RCA plug installed breaks the connection between the pre out and main in.

    The receiver works "good enough" - I can get about 50% volume to drive speakers - evenly on both channels. I "think" the power supply caps are starting to die - at shut down I get a loud pop from the unit and cannot get much more than 50% on the volume knob (course I am running 4 ohm speakers).

    Maybe I should see if the receiver works as a unit with an RCA into the "pre out" jacks.

    Next I will try to install RCAs into BOTH the pre out and the main in - perhaps BOTH need to have a prong pushing in to break the connection between the two halves of the circuit - thus sending signal out on the "pre out" jack?

    Worst case I will hard wire the pre amp out to the RCA connection.

    I have attempted to include a cut from the 2252 schematic that shows the connection between the pre and main sections of the amplifier. Don't know if it loaded or not.

    [​IMG]
     
  5. reddog48

    reddog48 Active Member

    Messages:
    262
    Location:
    Dallas, TX
  6. wlhd1610

    wlhd1610 Penny and her new friend Sponsor Subscriber

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    No something is not right,
    In a properly working unit connecting cables from the Marantz preamp out jacks to your out board amp should work.
    You shouldn't have to insert anything into the Marantz amp in jacks.

    First I would determine if you even have a "healthy" Marantz by connecting a pair of RCA cables to the preamp out and amp in jacks to see if the unit even works right.

    Bob
     

     

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  7. jd3rdcoast

    jd3rdcoast AK Subscriber Subscriber

    Messages:
    170
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    2nd Bob’s advice.
     
  8. reddog48

    reddog48 Active Member

    Messages:
    262
    Location:
    Dallas, TX
    The solution was arrived at. I opened the 2252 up - removing top and bottom panels. Plugged the unit in to AC and set the selector to AM so I had a signal to trace across the various boards. Bottom line? The 2252 WAS DELIVERING OUTPUT FROM THE PRE OUT JACKS. I spent some time looking at the output jacks for "Pre Out" and "Main In" and as far as I can determine there is no switch or other connector at that point - the signal is delivered to the rear of the RCA connector and then goes off to the amp board. Same with the Main In - nothing there but a feed to the Amp Board. I was really impressed by how clean and logical the Marantz 22xx series layout was done - superb.

    It appears that even with the Pre Out being used there is still signal being delivered to the amp board - but since there is no load on the speaker terminals the amp board is just idling. No heat at all.

    The problem? Well it is kindly referred to as a "Short in the Head Set", i.e. operator error. First error was the signal from my DVD player had been hooked - on one jack - to the video out of the player. Hence one tube amp was being exposed to leaky 60 Hz - and that was the cause of the motor boating. When the jack was moved to the correct output the pre and tube amp worked wonderfully. The other tube amp - both had their 7199 driver tubes replaced with 6JU8s which require a short standoff device to reroute the socket wiring appropriately. I installed the standoff device BUT then put the 7199s back into the sockets - thus ensuring that the driver tubes were not working correctly. Once I discovered this bonehead move and installed the correct tubes the Dyna worked wonderfully.

    Now I have a 2252 serving as a preamp - golden toned beauty that it is - and two Dynaco ST-70s rigged as monoblocs for my amplification. Talk about sweet sounding. Lot more power than the 2252 since the Dynacos are producing about 60+ watts per side while the 2252 was down to about 30 watts per channel - dying amplifier section.

    All of this driving a set of pristine AR-91s - which I feel is the very best of the AR 3 way speakers - featuring the 12" woofer and the modern - AR-9 - tweeter and midrange. A very sweet 1970s style sound.
     
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  9. willyrover

    willyrover Super Member

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    3,124
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    This arrangement makes those pre-outs useful for a powered subwoofer without using Y-adapters.
     
  10. wlhd1610

    wlhd1610 Penny and her new friend Sponsor Subscriber

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    Nothing else quite like a happy ending!

    Bob
     
  11. _tk

    _tk New Member

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    I did a brief test on my 2265B and it seemed like the preouts didn't shut off the main amp when I plugged an RCA into them. Can anyone confirm how they are supposed to work? Because I agree...at that point it can be a sub-out for many of us.
     

     

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  12. willyrover

    willyrover Super Member

    Messages:
    3,124
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    Connecting RCA cables to the PRE OUT jacks does NOT break the connection between preamp and amplifier. (There is an internal switch but it's not connected to anything.)

    Connecting RCA cables to the MAIN IN jacks DOES break the connection between preamp and amplifier.

    As shown on schematic:

    Screen Shot 2018-07-18 at 10.31.02 PM.png
     
  13. _tk

    _tk New Member

    Messages:
    48
    So....why does everyone talk about using the RCA "Y" adapter method for adding a sub? I just assumed this was the only way.

    I assume it was changed later on in the 22xx run?
     
  14. willyrover

    willyrover Super Member

    Messages:
    3,124
    Location:
    Hamilton
    Some designs require external jumpers to connect preamp and amplifier sections. Removing the jumpers breaks the connection between preamp and amp.

    On these units you need Y-adapters to split the PRE-OUT signal - sending it to your subwoofer, AND back into the MAIN-IN jacks

    Here is the pre-out/main-in arrangement on a Marantz 1060 - notice the external jumpers and NO internal switching.

    Screen Shot 2018-07-19 at 7.08.25 PM.png
     
    Last edited: Jul 19, 2018
  15. willyrover

    willyrover Super Member

    Messages:
    3,124
    Location:
    Hamilton
    Here is a comparison of the two designs.

    Screen Shot 2018-07-18 at 10.31.02 PM.png Screen Shot 2018-07-19 at 7.10.43 PM.png
     
  16. _tk

    _tk New Member

    Messages:
    48
    Is it a lack of people trying this out/looking at schematics or people just repeating what they've heard?

    Is there anyone in here that's actually using the pre-out for a sub? If it's a non-issue then not sure why it's not discussed more. It's a great option to have on these older receivers.
     

     

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  17. willyrover

    willyrover Super Member

    Messages:
    3,124
    Location:
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    No idea.

    When running my Marantz 2275 or 2270, I hook up my subwoofers to the PREOUT jacks - no Y-adapters necessary.

    My 1060 has external jumpers so I have to use Y-adapters.

    My Yamaha CA-1010 has a COUPLE/DECOUPLE switch between the PREOUT and MAIN IN jacks. Again, no Y-adapters required.
     

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