Using a BRIDGE RECTIFIER in an audio circuit

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.

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

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Regards, 
Martin Brown

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

George H.

It would sound awful.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

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

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!

the usual is to use resistors

that's life

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

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

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

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).

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....

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

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?

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Rick C

"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.

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Rick C

** 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

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.

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Rick C

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! ;-)

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

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.