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Re: Using a BRIDGE RECTIFIER in an audio circuit

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On 3/30/2017 5:45 PM, oldschool@tubes.com wrote:
> On Thu, 30 Mar 2017 09:28:13 +0100, Martin Brown
> <'''newspam'''@nezumi.demon.co.uk> wrote:
>
>> On 30/03/2017 08:55, oldschool@tubes.com wrote:
>>> My object is to combine the right and left channel coming from the
>>> preamp into one combined mono channel. I want to do this so the preamp
>>> left and right channels remain separated as they are fed into a stereo
>>> power amp. -BUT- I want a combined mono channel to feed into another
>>> mono power amp to power a 3rd channel to be used as a subwoofer.
>>>
>>> I know that using capacitors will allow leakage from the left and right
>>> channels into each other, and cause a loss of stereo separation.
>>
>> Either use an active mixer so that the signals see a virtual earth or if
>> you want a passive only bodge then connect them together by an L+R+C
>> divider with the capacitor across the input to the bass amp. You want a
>> fairly steep low pass filter for the bass channel (there isn't usually a
>> lot of directional information in the bass content to lose anyway).
>>
>
> Is an active mixer the device suggested from ebay later in this thread,
> or am I missing your point?
>
> Is there any way you can show a drawing of this divider capacitor method
> you're suggesting? I am not sure what you mean....

"Active mixer" refers to resistors that are coupled to amplification so 
they still provide a gain of one (or any value you want).  The mixing is 
still done with resistors.  Mixing is a music term in this context.  I 
would use the term "summing" to distinguish from mixing in the radio 
world where signals are summed in a non-linear medium to create 
modulation.

There can be an opamp in front of the summing point to prevent crosstalk 
in your inputs or an amplifier only after the mixing point to set the 
gain value.  If the amplifier is used in an inverting configuration the 
opamp will act to maintain the summing point at a fixed voltage which 
will also act to minimize crosstalk without amps on the front end.
                   ,--< Virtual Ground
                   V

L -->>---/\/\/----+----/\/\/----+
                   |  |\         |
R -->>---/\/\/----+--|-\        |
                      |  >-------+----o  Output
                   +--|+/                -(L+R)
                   |  |/
                 -----
                  \ /
                   V

The action of the amplifier is such that if the inverting input (-) 
rises with respect to the non-inverting input (+) the output goes down. 
If the inverting input drops the output of the amp goes up.  In each 
case the voltage at the inverting input is maintained.  Since the common 
point (labeled virtual ground) will not see a change in voltage as the 
signals A and B vary, so there is no cross talk between them.

To add a gain adjustment for each input independently, the resistors 
connected to the L and R inputs can be replaced with pots.  To adjust 
the gain of both channels together the resistor from the output back to 
the virtual ground can be adjusted with a pot.  That seems to be what 
this circuit is doing.  The other control is labeled frequency on other 
listings.  So it must be adjusting the cutoff frequency.

-- 

Rick C

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Thread

Using a BRIDGE RECTIFIER in an audio circuit oldschool@tubes.com - 2017-03-30 02:55 -0500
  Re: Using a BRIDGE RECTIFIER in an audio circuit Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-30 09:28 +0100
    Re: Using a BRIDGE RECTIFIER in an audio circuit oldschool@tubes.com - 2017-03-30 16:45 -0500
      Re: Using a BRIDGE RECTIFIER in an audio circuit rickman <gnuarm@gmail.com> - 2017-03-30 18:35 -0400
        Re: Using a BRIDGE RECTIFIER in an audio circuit M Philbrook <jamie_ka1lpa@charter.net> - 2017-03-30 19:54 -0500
          Re: Using a BRIDGE RECTIFIER in an audio circuit rickman <gnuarm@gmail.com> - 2017-03-30 23:58 -0400
          Re: Using a BRIDGE RECTIFIER in an audio circuit makolber@yahoo.com - 2017-04-04 08:30 -0700
            Re: Using a BRIDGE RECTIFIER in an audio circuit whit3rd <whit3rd@gmail.com> - 2017-04-08 15:05 -0700
  Re: Using a BRIDGE RECTIFIER in an audio circuit George Herold <gherold@teachspin.com> - 2017-03-30 06:04 -0700
  Re: Using a BRIDGE RECTIFIER in an audio circuit John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-30 08:33 -0700
    Re: Using a BRIDGE RECTIFIER in an audio circuit bitrex <bitrex@de.lete.earthlink.net> - 2017-03-30 11:36 -0400
      Re: Using a BRIDGE RECTIFIER in an audio circuit oldschool@tubes.com - 2017-03-30 16:40 -0500
        Re: Using a BRIDGE RECTIFIER in an audio circuit rickman <gnuarm@gmail.com> - 2017-03-30 17:56 -0400
          Re: Using a BRIDGE RECTIFIER in an audio circuit "Michael A. Terrell" <mike.terrell@earthlink.net> - 2017-04-02 01:45 -0400
  Re: Using a BRIDGE RECTIFIER in an audio circuit Tim Wescott <seemywebsite@myfooter.really> - 2017-03-30 14:38 -0500
  Re: Using a BRIDGE RECTIFIER in an audio circuit tabbypurr@gmail.com - 2017-03-30 14:01 -0700
  Re: Using a BRIDGE RECTIFIER in an audio circuit Dave M <dgminala at mediacombb dot net> - 2017-03-30 16:51 -0500
  Re: Using a BRIDGE RECTIFIER in an audio circuit Phil Allison <pallison49@gmail.com> - 2017-03-30 16:16 -0700
  Re: Using a BRIDGE RECTIFIER in an audio circuit jurb6006@gmail.com - 2017-04-06 23:00 -0700

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