Results 1 to 11 of 11

Thread: Help with connection of balanced audio output into unbal power amp

  1. #1
    Premium Member
    Join Date
    Aug 2011
    Location
    Planet Earth
    Posts
    346
    Thanks
    333
    Thanked 113 Times in 67 Posts
    Rep Power
    205
    Reputation
    2000

    Default Help with connection of balanced audio output into unbal power amp

    First post here and I stick up my hand, I can build circuits from schematics but I have little to no clue on design principles. I would like some help if possible please .

    I have a 2 way speaker (passive) that I want to make into a basic active monitor.

    I purchased a 150w module off the net, it’s a 12vdc power so I purchased a 5 amp power supply and we are away, the amp works ok I think it’s designed to be an in car stereo power amp.

    I want to take a balanced audio out from my sound desk to the unbalanced input on the amp. I am taking pin 2 hot and ground leaving pin 3 inverted out of the equipment thus far

    Level was too distorted so I put a 10k pot in line and can adjust it by only a minor crack and have a useable sound, but move the pot another couple of cracks and back to high distortion

    So the questions are

    Should I be using a basic preamp with smooth gain control ?

    If that answer is no, how should I be better able to smoothly attenuate my input to the amp?

    Thank you in advance from a novice



Look Here ->
  • #2
    Senior Member
    Reschs's Avatar
    Join Date
    Aug 2010
    Location
    Outside a few schooners
    Posts
    3,080
    Thanks
    907
    Thanked 2,147 Times in 1,058 Posts
    Rep Power
    933
    Reputation
    33238

    Default

    Firstly is the 10K pot Log and not Linear.
    Put a 100K Resister in series with pot.
    So, pin 2 100K to one end of pot and the other side of the pot to ground. The wiper, middle pin, to the Input of the Amp.
    See if that helps.
    Then we will worry about the proper way to do it.

  • The Following User Says Thank You to Reschs For This Useful Post:

    mrtor (13-04-21)

  • #3
    Premium Member
    Join Date
    Aug 2011
    Location
    Planet Earth
    Posts
    346
    Thanks
    333
    Thanked 113 Times in 67 Posts
    Rep Power
    205
    Reputation
    2000

    Default

    Quote Originally Posted by Reschs View Post
    Firstly is the 10K pot Log and not Linear.
    Put a 100K Resister in series with pot.
    So, pin 2 100K to one end of pot and the other side of the pot to ground. The wiper, middle pin, to the Input of the Amp.
    See if that helps.
    Then we will worry about the proper way to do it.
    Definitely a 10k log pot
    Will try that tomorrow and report back
    Thank you for your input

  • #4
    Banned

    Join Date
    Jan 2017
    Location
    still above ground level
    Posts
    1,779
    Thanks
    5,562
    Thanked 1,964 Times in 714 Posts
    Rep Power
    0
    Reputation
    35657

    Default

    the problem you are experiencing is one of mismatched impedance playing with resisters can "make it work" but the correct way is to use a transformer . Theres one glaring mistake you have made ?
    12 volts at 5 amps dont equal 150 watts only 60 watts 12x5 = 60 so you are asking for trouble before you start if the power supply sags all sorts of problems will come out of your amp , also from memory the desk output should be around 2.5-5k impedance therefore a 5k linear pot is more appropriate good luck

  • The Following 2 Users Say Thank You to hinekadon For This Useful Post:

    RFI-EMI-GUY (12-04-21),tristen (12-04-21)

  • #5
    Premium Member
    Join Date
    Aug 2011
    Location
    Planet Earth
    Posts
    346
    Thanks
    333
    Thanked 113 Times in 67 Posts
    Rep Power
    205
    Reputation
    2000

    Default

    Quote Originally Posted by hinekadon View Post
    the problem you are experiencing is one of mismatched impedance playing with resisters can "make it work" but the correct way is to use a transformer . Theres one glaring mistake you have made ?
    12 volts at 5 amps dont equal 150 watts only 60 watts 12x5 = 60 so you are asking for trouble before you start if the power supply sags all sorts of problems will come out of your amp , also from memory the desk output should be around 2.5-5k impedance therefore a 5k linear pot is more appropriate good luck
    Such an obvious point that I failed to even think about, i think they have lied big time about the power
    When I had it on the bench supply it was drawing about 3 amps under load at 12 vdc

    That sure isn’t anywhere near 150 watts... I feel very silly 😂 now

    Thank you for your input

  • #6
    Senior Member
    Reschs's Avatar
    Join Date
    Aug 2010
    Location
    Outside a few schooners
    Posts
    3,080
    Thanks
    907
    Thanked 2,147 Times in 1,058 Posts
    Rep Power
    933
    Reputation
    33238

    Default

    Quote Originally Posted by hinekadon View Post
    the problem you are experiencing is one of mismatched impedance playing with resisters can "make it work" but the correct way is to use a transformer . Theres one glaring mistake you have made ?
    12 volts at 5 amps dont equal 150 watts only 60 watts 12x5 = 60 so you are asking for trouble before you start if the power supply sags all sorts of problems will come out of your amp , also from memory the desk output should be around 2.5-5k impedance therefore a 5k linear pot is more appropriate good luck
    The Desk output would be low source impedance designed to work into any load over 600 ohms. I will not go into the full theory of balanced lines and bridging and termination.

    Modern Desks are Electronically Balanced and hence the pin 2 and Earth works. Will not work on transformer out.
    The desk will output around 1 Volt whilst the car power amp is only looking for about 100 mv.

    He should try my solution as a stop gap and then we can get the actual specs of the power amp and give him the definitive answer.

  • The Following User Says Thank You to Reschs For This Useful Post:

    mrtor (13-04-21)

  • #7
    Banned

    Join Date
    Jan 2017
    Location
    still above ground level
    Posts
    1,779
    Thanks
    5,562
    Thanked 1,964 Times in 714 Posts
    Rep Power
    0
    Reputation
    35657

    Default

    Just trying to help , you have to remember they want a sale regardless of the truth or they are fresh outa kindy and just dont know but thats the reason for austech cos some got old grey hair hahaha lol cheers don

  • #8
    Senior Member
    Reschs's Avatar
    Join Date
    Aug 2010
    Location
    Outside a few schooners
    Posts
    3,080
    Thanks
    907
    Thanked 2,147 Times in 1,058 Posts
    Rep Power
    933
    Reputation
    33238

    Default

    Quote Originally Posted by hinekadon View Post
    Just trying to help , you have to remember they want a sale regardless of the truth or they are fresh outa kindy and just dont know but thats the reason for austech cos some got old grey hair hahaha lol cheers don
    Your point about the power amp was never in question.

    I just wanted to give him a simple solution and then ask for the specs of the amp.

  • #9
    Senior Member
    Reschs's Avatar
    Join Date
    Aug 2010
    Location
    Outside a few schooners
    Posts
    3,080
    Thanks
    907
    Thanked 2,147 Times in 1,058 Posts
    Rep Power
    933
    Reputation
    33238

    Default

    Light Bulb moment.
    Did you wire the Log Pot the correct way round.
    Try reversing the wires on the outer terminals.
    This would cause exactly you problem.

  • The Following User Says Thank You to Reschs For This Useful Post:

    mrtor (13-04-21)

  • #10
    Premium Member
    Join Date
    Aug 2011
    Location
    Planet Earth
    Posts
    346
    Thanks
    333
    Thanked 113 Times in 67 Posts
    Rep Power
    205
    Reputation
    2000

    Default

    Quote Originally Posted by Reschs View Post
    Light Bulb moment.
    Did you wire the Log Pot the correct way round.
    Try reversing the wires on the outer terminals.
    This would cause exactly you problem.
    This was part of my issue so well thought from you and a learning opportunity for me

    I also put the 100k resistor in and much lower signal
    So after some experiments I have ended up with a 27k resistor in series and I am pleased to say good control (smooth) from my input pot

    Thank you for your input

    I am very happy

    Cheers
    Mike

  • #11
    Senior Member
    Reschs's Avatar
    Join Date
    Aug 2010
    Location
    Outside a few schooners
    Posts
    3,080
    Thanks
    907
    Thanked 2,147 Times in 1,058 Posts
    Rep Power
    933
    Reputation
    33238

    Default

    Glad to be of assistance.

  • Bookmarks

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •