Hello
Using 1:1 15kOhm line transformers salvaged from standard audio ground loop isolator filters and a bunch of 10kOhm resistors one can put together a crude yet functional and experience boosting surround "decoder" generating both rear and centre mono channel line outputs from standard 2ch stereo speaker level inputs.
This is far from a new approach, and I'm sure you guys here could draw a correct schematic in dark if so inclined, in its basic form these circuits are very simple.
But now I'm wondering if there is a way to get rear right and left channel separation as this signal is in its basic form simply the difference between the left and right channels, a mono signal, one channel, but I'm not sure how to accomplish this, perhaps mixing in a bit of the original left channel in the rear left channel and vice versa, could this work?
This circuit is completely passive, only transformers and resistors are used.
I will post some schematics later to aid understanding.
Using 1:1 15kOhm line transformers salvaged from standard audio ground loop isolator filters and a bunch of 10kOhm resistors one can put together a crude yet functional and experience boosting surround "decoder" generating both rear and centre mono channel line outputs from standard 2ch stereo speaker level inputs.
This is far from a new approach, and I'm sure you guys here could draw a correct schematic in dark if so inclined, in its basic form these circuits are very simple.
But now I'm wondering if there is a way to get rear right and left channel separation as this signal is in its basic form simply the difference between the left and right channels, a mono signal, one channel, but I'm not sure how to accomplish this, perhaps mixing in a bit of the original left channel in the rear left channel and vice versa, could this work?
This circuit is completely passive, only transformers and resistors are used.
I will post some schematics later to aid understanding.
Until I get a chance to post some pictures I can try to explain in writing what the circuit looks like.
Rear surround channel:
The inputs are taken from the normal stereo amplifiers left and right positive speaker terminals, no negative/ground is used, these two signals each needs to be attenuated down to line level before we do anything else, we accomplish this by putting one 10kOhm resistor on each right and left speaker level leads, now that we have line level we need to extract the difference between the left and right positive line signals.
Enter the 1:1 15kOhm line transformer salvaged from the ground loop isolator filter, we connect the right and left positive signals to the pins for one of the windings on the transformer, let's call it the primary side, this means that only the stereo content will pass through and mono content will be cancelled out.
The amplifier left and right positive outputs will see a connection of ~20,2kOhms, which should be safe, the additional 200 Ohms stems from the winding resistance of the transformer, the 20kOhm stems from the two 10kOhm resistors in series before and after the transformer.
On the secondary side of the transformer we simply pick one pin as signal and the other as ground and connect this channel to an amplifier for the rear speakers.
This means that the difference between the two front channels now are presented behind you, hence the term surround, and it works with all stereo content, and it does give a rather rewarding experience.
Rear surround channel:
The inputs are taken from the normal stereo amplifiers left and right positive speaker terminals, no negative/ground is used, these two signals each needs to be attenuated down to line level before we do anything else, we accomplish this by putting one 10kOhm resistor on each right and left speaker level leads, now that we have line level we need to extract the difference between the left and right positive line signals.
Enter the 1:1 15kOhm line transformer salvaged from the ground loop isolator filter, we connect the right and left positive signals to the pins for one of the windings on the transformer, let's call it the primary side, this means that only the stereo content will pass through and mono content will be cancelled out.
The amplifier left and right positive outputs will see a connection of ~20,2kOhms, which should be safe, the additional 200 Ohms stems from the winding resistance of the transformer, the 20kOhm stems from the two 10kOhm resistors in series before and after the transformer.
On the secondary side of the transformer we simply pick one pin as signal and the other as ground and connect this channel to an amplifier for the rear speakers.
This means that the difference between the two front channels now are presented behind you, hence the term surround, and it works with all stereo content, and it does give a rather rewarding experience.
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Centre channel:
This is rather similar to the circuit described in the previous post, infact it uses pretty much the same components in the same quantity, but this one makes use of the the front amplifiers ground and requires the ground to be common for the two channels.
It is basically just a line level stereo sum put through the primary side of the transformer, and on the secondary side we take out the same signal but galvanically isolated, nothing complicated in other words.
Detailed description will follow soon.
This is rather similar to the circuit described in the previous post, infact it uses pretty much the same components in the same quantity, but this one makes use of the the front amplifiers ground and requires the ground to be common for the two channels.
It is basically just a line level stereo sum put through the primary side of the transformer, and on the secondary side we take out the same signal but galvanically isolated, nothing complicated in other words.
Detailed description will follow soon.
Centre channel (continued):
The inputs are taken from a normal 2ch stereo amplifier positive left and right terminals, a 10kOhm resistor is connected in series on each of these signals after which they are connected together and connected to one of the pins on the primary winding of a 1:1 15kOhm line transformer, the other pin is then connected to the amplifier negative/ground terminals.
On the other, secondary winding we choose one of the pins as signal and the other ground, we now have a galvanic isolated mono channel consisting of both the front stereo channels that forms a crude center channel.
Pictures to be added shortly.
The main question was of the is a way to get channel separation in the rear surround channel, a way to subtract the mono content from each right and left stereo channel if you will, and do so using similar passive components.
The inputs are taken from a normal 2ch stereo amplifier positive left and right terminals, a 10kOhm resistor is connected in series on each of these signals after which they are connected together and connected to one of the pins on the primary winding of a 1:1 15kOhm line transformer, the other pin is then connected to the amplifier negative/ground terminals.
On the other, secondary winding we choose one of the pins as signal and the other ground, we now have a galvanic isolated mono channel consisting of both the front stereo channels that forms a crude center channel.
Pictures to be added shortly.
The main question was of the is a way to get channel separation in the rear surround channel, a way to subtract the mono content from each right and left stereo channel if you will, and do so using similar passive components.
Here are the pictures as promised:
First the rear surround channel:
Then the center channel:
And lastly the untested, unconfirmed and "not recommended to try" alternative, do not use, I put it here just to show where I'm at.
Now for the questions, can anyone see why the combined proposal should not work, what have I missed here, if anything, and what would the consequences be?
Secondly, has anyone any idea if it is at all possible to get two separated, or partly separated rear surround channels using more of the same, or similar components, still staying all passive, in the case of the rear surround circuit shown first in this post?
First the rear surround channel:
Then the center channel:
And lastly the untested, unconfirmed and "not recommended to try" alternative, do not use, I put it here just to show where I'm at.
Now for the questions, can anyone see why the combined proposal should not work, what have I missed here, if anything, and what would the consequences be?
Secondly, has anyone any idea if it is at all possible to get two separated, or partly separated rear surround channels using more of the same, or similar components, still staying all passive, in the case of the rear surround circuit shown first in this post?
Hi, I’m a bit late to the party, having only just signed up, but this is an interest of mine, though unfortunately my technical knowledge is probably behind yours.
You might get some help from Michael Gerzon’s paper “A year of surround sound” (you’ll find it easily if you search the title and his name together). But you’re possibly aware of this already. It took me off in another direction, using multiple delays, but only because I had them handy.
I have to say commercial surround sound has its moments but so does Hafler. Just different ones. It’s useful to me as I have three stereo systems in my listening room but my surround (5.1) setup is in the main house.
You might get some help from Michael Gerzon’s paper “A year of surround sound” (you’ll find it easily if you search the title and his name together). But you’re possibly aware of this already. It took me off in another direction, using multiple delays, but only because I had them handy.
I have to say commercial surround sound has its moments but so does Hafler. Just different ones. It’s useful to me as I have three stereo systems in my listening room but my surround (5.1) setup is in the main house.