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Using a BRIDGE RECTIFIER in an audio circuit

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  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

#454213 — Using a BRIDGE RECTIFIER in an audio circuit

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.
Resistors will help with the separation, but will cause a drop in output
from the preamp. I know that using a single diode from each channel (t
othe new center channel) will cause clipping, similar to the fuzz tone
sound used with guitars. 

Then it occurred to me. A bridge rectifier will allow both the positive
and negative halves of a wave to both pass thru, but not allow the
signal to go backward. 

Will this work?

In other words, I put a bridge rectifier on left channel to the new 3rd
channel, then do the same thing on the right channel. Thus, two bridge
rectifiers are used. One to the left, one to the right channels, and the
two rectifiers are joined in the middle, which then becomes the new mono
3rd channel.
The left and right channels coming from the preamp are then fed to a
stereo power amp in the usual manner. The combined 3rd channel is then
fed to a separate mono power amp. 

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#454215

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).

Choosing component values to give eg. -6dB at 60Hz and ~50k loading.

> Resistors will help with the separation, but will cause a drop in output
> from the preamp. I know that using a single diode from each channel (t
> othe new center channel) will cause clipping, similar to the fuzz tone
> sound used with guitars.
>
> Then it occurred to me. A bridge rectifier will allow both the positive
> and negative halves of a wave to both pass thru, but not allow the
> signal to go backward.
>
> Will this work?

It will sound like a terrible frequency doubler on a pure sine wave and 
much worse on more complex signals.

-- 
Regards,
Martin Brown

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#454277

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....


>Choosing component values to give eg. -6dB at 60Hz and ~50k loading.
>
>> Resistors will help with the separation, but will cause a drop in output
>> from the preamp. I know that using a single diode from each channel (t
>> othe new center channel) will cause clipping, similar to the fuzz tone
>> sound used with guitars.
>>
>> Then it occurred to me. A bridge rectifier will allow both the positive
>> and negative halves of a wave to both pass thru, but not allow the
>> signal to go backward.
>>
>> Will this work?
>
>It will sound like a terrible frequency doubler on a pure sine wave and 
>much worse on more complex signals.

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#454292

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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#454298

In article <obk122$s06$1@dont-email.me>, gnuarm@gmail.com says...
> 
> 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)
>                    |  |/
>                  -----

one could get real fancy and invert one of the channels before mixing 
it. It would then allow for you to hear the back of the row sounds more
so than the sum.
 
 Oh Well, just an idea I guess.

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#454332

On 3/30/2017 8:54 PM, M Philbrook wrote:
> In article <obk122$s06$1@dont-email.me>, gnuarm@gmail.com says...
>>
>> 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)
>>                    |  |/
>>                  -----
>
> one could get real fancy and invert one of the channels before mixing
> it. It would then allow for you to hear the back of the row sounds more
> so than the sum.
>
>  Oh Well, just an idea I guess.

It would be easy enough to do.

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

This removes the virtual ground, but with resistor values high enough 
and driven from typical audio outputs the crosstalk at the inputs will 
be very small.

-- 

Rick C

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#455077

On Thursday, March 30, 2017 at 7:49:30 PM UTC-4, M Philbrook wrote:
> In article <obk122$s06$1@dont-email.me>, gnuarm@gmail.com says...
> > 
> > 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)
> >                    |  |/
> >                  -----
> 
> one could get real fancy and invert one of the channels before mixing 
> it. It would then allow for you to hear the back of the row sounds more
> so than the sum.
>  
>  Oh Well, just an idea I guess.

a bad idea

most recordings are mixed such that the bass is essentially mono
and the purpose of this mixer is to capture a mono bass signal for the subwoofer. If you invert one channel, you will lose most of the bass. 

2 100k resistors will make a simple passive mixer that will work well for this application

m

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#455506

On Tuesday, April 4, 2017 at 8:30:46 AM UTC-7, mako...@yahoo.com wrote:
> On Thursday, March 30, 2017 at 7:49:30 PM UTC-4, M Philbrook wrote:

> > > >>> My object is to combine the right and left channel coming from the
> > > >>> preamp into one combined mono channel.


> a bad idea
> 
> most recordings are mixed such that the bass is essentially mono
> and the purpose of this mixer is to capture a mono bass signal for the subwoofer. If you invert one channel, you will lose most of the bass. 
> 
> 2 100k resistors will make a simple passive mixer that will work well for this application

But, if 'most' are mixed that way, some might have an inversion.   One 100k resistor,
and one 75k resistor, will also work, and won't lose all the bass if the phono cartridge
was wired in the wrong phase.

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#454224

On Thursday, March 30, 2017 at 3:55:51 AM UTC-4, olds...@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.
> Resistors will help with the separation, but will cause a drop in output
> from the preamp. I know that using a single diode from each channel (t
> othe new center channel) will cause clipping, similar to the fuzz tone
> sound used with guitars. 
> 
> Then it occurred to me. A bridge rectifier will allow both the positive
> and negative halves of a wave to both pass thru, but not allow the
> signal to go backward. 
> 
> Will this work?
> 
> In other words, I put a bridge rectifier on left channel to the new 3rd
> channel, then do the same thing on the right channel. Thus, two bridge
> rectifiers are used. One to the left, one to the right channels, and the
> two rectifiers are joined in the middle, which then becomes the new mono
> 3rd channel.
> The left and right channels coming from the preamp are then fed to a
> stereo power amp in the usual manner. The combined 3rd channel is then
> fed to a separate mono power amp.

How about an opamp summing circuit?  That's easy.  

George H. 

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#454233

On Thu, 30 Mar 2017 02:55:04 -0500, 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.
>Resistors will help with the separation, but will cause a drop in output
>from the preamp. I know that using a single diode from each channel (t
>othe new center channel) will cause clipping, similar to the fuzz tone
>sound used with guitars. 
>
>Then it occurred to me. A bridge rectifier will allow both the positive
>and negative halves of a wave to both pass thru, but not allow the
>signal to go backward. 
>
>Will this work?

It would sound awful.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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#454234

On 03/30/2017 11:33 AM, John Larkin wrote:
> On Thu, 30 Mar 2017 02:55:04 -0500, 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.
>> Resistors will help with the separation, but will cause a drop in output
>>from the preamp. I know that using a single diode from each channel (t
>> othe new center channel) will cause clipping, similar to the fuzz tone
>> sound used with guitars.
>>
>> Then it occurred to me. A bridge rectifier will allow both the positive
>> and negative halves of a wave to both pass thru, but not allow the
>> signal to go backward.
>>
>> Will this work?
>
> It would sound awful.
>
>

In the year 2k17 some things just make more sense to buy "off the shelf":

<http://www.ebay.com/itm/DC-12V-24V-Low-pass-Filter-NE5532-Subwoofer-Process-Pre-Amplifier-Preamp-Board-/332006640502?hash=item4d4d234b76:g:24kAAOSwCU1Y24AN>

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#454276

On Thu, 30 Mar 2017 11:36:38 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>On 03/30/2017 11:33 AM, John Larkin wrote:
>> On Thu, 30 Mar 2017 02:55:04 -0500, 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.
>>> Resistors will help with the separation, but will cause a drop in output
>>>from the preamp. I know that using a single diode from each channel (t
>>> othe new center channel) will cause clipping, similar to the fuzz tone
>>> sound used with guitars.
>>>
>>> Then it occurred to me. A bridge rectifier will allow both the positive
>>> and negative halves of a wave to both pass thru, but not allow the
>>> signal to go backward.
>>>
>>> Will this work?
>>
>> It would sound awful.
>>
>>
>
>In the year 2k17 some things just make more sense to buy "off the shelf":
>
><http://www.ebay.com/itm/DC-12V-24V-Low-pass-Filter-NE5532-Subwoofer-Proc
>ess-Pre-Amplifier-Preamp-Board-/332006640502?hash=item4d4d234b76:g:24kAAOSwCU1Y24AN>

I wish they'd give more information, but this looks like a simple
solution. Lacking that info, I can only guess that the L+R inputs go to
that blue terminal with 3 screws, and the one with 2 screws goes to the
mono power amp. (The other 2 screw blue thing is for DC volts).

For that price, it's worth a try. 

The only simple thing I found, was someone suggesting putting a 10K
resistor from each channel preamp out to create a common 3rd channel,
but I would think there would be crosstalk and a loss of stereo
separation. (and possibly result in a weak signal for that 3rd channel).

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#454282

On 3/30/2017 5:40 PM, oldschool@tubes.com wrote:
> On Thu, 30 Mar 2017 11:36:38 -0400, bitrex
> <bitrex@de.lete.earthlink.net> wrote:
>
>> On 03/30/2017 11:33 AM, John Larkin wrote:
>>> On Thu, 30 Mar 2017 02:55:04 -0500, 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.
>>>> Resistors will help with the separation, but will cause a drop in output
>>> >from the preamp. I know that using a single diode from each channel (t
>>>> othe new center channel) will cause clipping, similar to the fuzz tone
>>>> sound used with guitars.
>>>>
>>>> Then it occurred to me. A bridge rectifier will allow both the positive
>>>> and negative halves of a wave to both pass thru, but not allow the
>>>> signal to go backward.
>>>>
>>>> Will this work?
>>>
>>> It would sound awful.
>>>
>>>
>>
>> In the year 2k17 some things just make more sense to buy "off the shelf":
>>
>> <http://www.ebay.com/itm/DC-12V-24V-Low-pass-Filter-NE5532-Subwoofer-Proc
>> ess-Pre-Amplifier-Preamp-Board-/332006640502?hash=item4d4d234b76:g:24kAAOSwCU1Y24AN>
>
> I wish they'd give more information, but this looks like a simple
> solution. Lacking that info, I can only guess that the L+R inputs go to
> that blue terminal with 3 screws, and the one with 2 screws goes to the
> mono power amp. (The other 2 screw blue thing is for DC volts).
>
> For that price, it's worth a try.
>
> The only simple thing I found, was someone suggesting putting a 10K
> resistor from each channel preamp out to create a common 3rd channel,
> but I would think there would be crosstalk and a loss of stereo
> separation. (and possibly result in a weak signal for that 3rd channel).

If you really want to know the circuit, the photos have enough detail to 
trace out the circuit.  It's not like this is a complex device.  I bet I 
can figure out the front end without even looking at the wiring.  I'm 
not sure how the pots are connected, but I'd guess they are independent 
left and right channel volume.

I recall a recent thread on something much like this, but from speaker 
outputs.  Someone suggested a purely passive circuit that would 
significantly attenuate any crosstalk (or backtalk depending on how you 
view it).

Obviously you aren't trying to simply drive a single speaker rather than 
a subwoofer as you care about crosstalk.  I assume you don't want to 
just buy an amp that supports a subwoofer because you have amps you like?

-- 

Rick C

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#454736

rickman wrote:
>
> If you really want to know the circuit, the photos have enough detail > totrace out the circuit.  It's not like this is a complex device.  I
> bet I can figure out the front end without even looking at the
> wiring. I'm  not sure how the pots are connected, but I'd guess they
> are independent left and right channel volume.


    The board is clearly marked 'Volume' and 'Frequency' by the pots.


-- 
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

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#454261

On Thu, 30 Mar 2017 02:55:04 -0500, oldschool 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.
> Resistors will help with the separation, but will cause a drop in output
> from the preamp. I know that using a single diode from each channel (t
> othe new center channel) will cause clipping, similar to the fuzz tone
> sound used with guitars.
> 
> Then it occurred to me. A bridge rectifier will allow both the positive
> and negative halves of a wave to both pass thru, but not allow the
> signal to go backward.
> 
> Will this work?
> 
> In other words, I put a bridge rectifier on left channel to the new 3rd
> channel, then do the same thing on the right channel. Thus, two bridge
> rectifiers are used. One to the left, one to the right channels, and the
> two rectifiers are joined in the middle, which then becomes the new mono
> 3rd channel.
> The left and right channels coming from the preamp are then fed to a
> stereo power amp in the usual manner. The combined 3rd channel is then
> fed to a separate mono power amp.

What everyone else said.

You need to figure out what these components do in more detail.  You're 
confusing the flow of current to the "flow" of a signal -- diodes only 
allow current to flow in one direction, but what they do to signals is 
way more complicated.

As far as your actual problem, I would buffer the two channels with 
voltage followers, then add the results to get your monaural channel for 
the sub-woofer.

Or, just go buy something.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

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#454271

On Thursday, 30 March 2017 08:55:51 UTC+1, olds...@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.

the usual is to use resistors

> I know that using capacitors will allow leakage from the left and right
> channels into each other, and cause a loss of stereo separation.
> Resistors will help with the separation, but will cause a drop in output
> from the preamp.

that's life

> I know that using a single diode from each channel (t
> othe new center channel) will cause clipping, similar to the fuzz tone
> sound used with guitars. 

it won't cause clipping, it won't pass anything... assuming it is a standard hifi input.

> Then it occurred to me. A bridge rectifier will allow both the positive
> and negative halves of a wave to both pass thru, but not allow the
> signal to go backward. 
> 
> Will this work?

Oh gawd. That is a real car crash of concepts. NO it won't.


> In other words, I put a bridge rectifier on left channel to the new 3rd
> channel, then do the same thing on the right channel. Thus, two bridge
> rectifiers are used. One to the left, one to the right channels, and the
> two rectifiers are joined in the middle, which then becomes the new mono
> 3rd channel.
> The left and right channels coming from the preamp are then fed to a
> stereo power amp in the usual manner. The combined 3rd channel is then
> fed to a separate mono power amp.

that channel will stay more or less silent due to the 0.65v required before the diode begins conducting to a significant extent. All you'd get is a tiny bit of high frequency passing through the diode's capacitance.


NT

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#454280

What you're after is a mixer, aka, combiner.  These circuits have been
done ad nauseam.  You can get a gaggle of these circuits on Google by
searching for 
stereo to mono mixer circuit OR schematic

The opt put impedance of the preamp is going to be pretty low, and the
high resistances involved in the summing circuit makes the effect on the
preamp signal negligible.  If you're worried about signal loss, just add
a simple opamp or FET amplifier stage to get it back.  Again, Google is
your friend.

Diodes in the signal path will distort it at best, or make it downright
unintelligible at worst.

Cheers,
Dave M


On Thu, 30 Mar 2017 02:55:04 -0500, 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.
>Resistors will help with the separation, but will cause a drop in output
>from the preamp. I know that using a single diode from each channel (t
>othe new center channel) will cause clipping, similar to the fuzz tone
>sound used with guitars. 
>
>Then it occurred to me. A bridge rectifier will allow both the positive
>and negative halves of a wave to both pass thru, but not allow the
>signal to go backward. 
>
>Will this work?
>
>In other words, I put a bridge rectifier on left channel to the new 3rd
>channel, then do the same thing on the right channel. Thus, two bridge
>rectifiers are used. One to the left, one to the right channels, and the
>two rectifiers are joined in the middle, which then becomes the new mono
>3rd channel.
>The left and right channels coming from the preamp are then fed to a
>stereo power amp in the usual manner. The combined 3rd channel is then
>fed to a separate mono power amp. 

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#454295

olds...@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.
> Resistors will help with the separation, but will cause a drop in output
> from the preamp.
>

** Use the signals from the power amp, combining them with two resistors and attenuate as needed with a trim pot to ground. 

 Forget the barking mad diode idea. 


....  Phil 

....  Phil 

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#455298

I should have answered long ago but I am not always up to it. 

You want the volume to track the volume control. So just get like ten K resistors and run it off them, in fact you might want a two K resistor to speaker common, assuming that you have a normal amp that does not run out of phase or any of that shit. 

Most powered subs have speaker inputs, and outputs that may or may not be high pass filtered. But the input to the sub amp is mixed to mono and low pass filtered. 

If you want to have a little fun, get you a dual pot. Use it to feed a cap that acts as your low pass filter. Also work with the level control, which is not hard to provide. If you run two pots from the source into a cap, as you change the setting of the pot you change the crossover frequency. If you have a separate level control it gives you a hell of alot of flexibility. I find it most preferable to boost the really low end. Like 40 Hz and below. Problem is you have to have the speakers that can handle it. 

I got an unpowered sub that used to be powered, but I also got 260 watts per channel so I don't really care too much. The other side had a nice subwoofer ion a Boston Acoustics A-150 cabinet but the Phase Linear ripped the rubber right off of it. Actually I am selling it, I want to get something more reasonable. This thing has blown many of my speakers and I am getting sick of it. It sounded so good, you turn it up and then something pops. 

But for a powered sub, that is no problem. Now if you want to combine signals to an unpowered sub that poses a few other problems. I can do it. 

You need a normal amp that runs in phase and has a common ground for the speakers. You interrupt that ground and put the sub there, with a GOOD AC capacitor across it. What's nice about that setup is that it will not overload your amp. 

In fact I can set up a total surround system with a stereo amp with no active components. I shit you not. If Dropbox hadn't gone into asshole mode I could show you right now. You can have the main speakers, a center channel, a sub, and surround speakers all out of a regular stereo amp. 

If someone wants to dispute that, I will come to their house and do it. But actually all you need is the diagram to hook it up, throw up your email and I can send it to you. You can probably even make 7.1 out of this, but the way it is, it is 5.1. Out of a stereo amp like in the 1970s. You need one capacitor for sure. And I mean a ggood one. The ones that can handle the current and the AC and all that are not those elcheapo electrolytics they use in everything.

With a few resistors ad a cap, maybe a few other thigs but not major, I can get you 5.1 surround sound out of a Pioneer SX-850. You do have to have some real power to do this, but not ridiculous. 

I'll find some hosting service soon and then can show you how it gets hooked up. 

What's more, I believe you were the one who brought up where some yuppies said ground is eight volts off ? Well this will probably really fuck with your head. Grounds ? We don't need no stinking grounds ! Really. 

But going back to your OP here, you do not put audio through nonlinear devices. Rectifiers are among the most non-linear devices there are. Get a scope and try it. You want resistors that are linear. If you want the internal amp in the sub to do the powering, just two resistors will do it, ad the value is not that critical. use 22K or something. It will not screw up the rest of the sound. If the level is too high then use a shunt to speaker ground, the black terminals. 

What is the model of the amp ? If it runs the channels out of phase it all changes. Most amps don't, but if you got one that does, do not try the connection of mine on it. Something could get fried. If it runs reverse polarity from left to right, forget all of this. Some Carver amps do this, like the M1.5T for example. There are others. They do it so that both channels are not draining on one rail at the same time. It gives them a cunthair more power. Not much but they are taking all they can get. 

When they use inverse polarity in one channel like that they basically almost destroy your using my hookup for cheapo surround. What you can get in that case is like a 3.1 system. You got left and right, and you got center channel and maybe a sub. Rear speakers would require another amp. 

Also, you have to be aware if your amp is BTL. You can't do much with BTL amps. Well I could find some ways but the amps might not like it. 

If you are into tubes and these are tube amps, this is alot less of an issue.

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