is it possible to split the common ground of pc headphone OUT into separate grounds with resistors?

[realflow100]

I was thinking i could possibly use two or 3 resistors between each positive and the negative to create ways to give a negative output one way and positive output the other.. (i know it'll reduce gain a bit but its the best idea i can think of thats super simple and the components i have for.
Could I possibly use 2 NPN and PNP transistors to re-gain the power to drive back into the input of the device?

My idea goes like this
I have a headphone level output from a computer going into a stereo.
The stereo I want to invert the phase of one channel on it without doing so with computer software.
to hook up 3 speakers at once rather than only two. creating an easy way to have a 2.1 speaker setup.
the stereo can go very loud and has its own volume buttons.

I was thinking i could simply use 4 resistors. two for each channel. then invert the output of only one. and leave the other in correct polarity. to create a virtual phase-split for stereo-output.. i know the output would be low. but its going into a stereo so the stereo should be able to be turned up plenty loud to compensate if neccessary..

If it could work. what would be the recommended values of resistors to use? with computer at full volume and stereo at an average (room-listening) volume.

 

[audioguru]

A 2.1 speaker setup has two stereo speakers that are in phase producing left and right lows, midrange and high audio frequencies. These left and right channels have highpass filters feeding their amplifiers.
The subwoofer channel mixes the original in phase channels into mono and produces only very low frequencies with its lowpass filter and separate amplifier.

I do not know why you want to have one stereo channel out-of-phase (which will sound WRONG) and somehow get subwoofer frequencies without a filter and without a subwoofer amplifier.
But you cannot invert the phase of one channel of a 3-wires headphones output anyway without an opamp or transistor to do it.

 

[realflow100]

I want to hook the subwoofer between the two positive speaker outputs. then invert the bottom right channel. then reverse the speaker leads going to the right speaker. therefore making all the speakers in-phase as well as the subwoofer become powered-yet connected to left and right channels at the same time without the seperate channels being merged to mono. (also not considering changing high or low frequencies to the subwoofer just simply leaving the frequencies as-is)
I dont think what i said before is very accurate..
but I was thinking I could do it with a few resistors and capacitors? Maybe a small inductor or so? The stereo only has stereo input but is completely capable of running bridged at the output if one of the stereo channels is inverted (headphone output has a joined ground wire so its a bit difficult to do without inverting one audio channel with some kind of computer audio-editing software

 

[audioguru]

The stereo amplifier has balanced outputs (one wire goes positive when the other wire goes negative).
1) The subwoofer is connected to both positive speaker outputs causing all mono and low frequencies to be cancelled.
2) The right amplifier channel is inverted which causes the subwoofer to produce positive from left channel and negative from right channel which produces 3.5 times the normal power and it might overload the amplifiers.
3) The right speaker is connected backwards so it is in-phase with the other speakers.

The subwoofer might SHRIEK because it is designed to have a filter to cut its higher frequencies where most woofers have a peak.
The stereo speakers might be destroyed by the lower frequencies.

If you connect a high power resistor in series with the subwoofer speaker so that it does not overload the stereo amplifier then its loudness will be too low. Then resistors might be added in series with the stereo speakers to also reduce their loudness. Then all speakers will sound boomy because they are designed to have their resonances damped by the extremely low output impedance of a modern amplifier.

 

[gophert]

I want to hook the subwoofer between the two positive speaker outputs. then invert the bottom right channel. then reverse the speaker leads going to the right speaker. therefore making all the speakers in-phase as well as the subwoofer become powered-yet connected to left and right channels at the same time without the seperate channels being merged to mono. (also not considering changing high or low frequencies to the subwoofer just simply leaving the frequencies as-is)
I dont think what i said before is very accurate..
but I was thinking I could do it with a few resistors and capacitors? Maybe a small inductor or so? The stereo only has stereo input but is completely capable of running bridged at the output if one of the stereo channels is inverted (headphone output has a joined ground wire so its a bit difficult to do without inverting one audio channel with some kind of computer audio-editing software

I think you should try it. I would start with 1000 ohm resistors.

Let us know how it sounds. I am interested in the "center" channel.

Good luck.

 

[realflow100]

I normally dont run the speakers loud enough to harm them. And I could put a 47uF or so capacitor to block low frequencies for both stereo speakers if need be. High frequencies to the subwoofer doesnt bother me too much since it muffles well on its own And the stereo has a low frequency filter to block frequencies lower than 25hz
The stereo is capable at 2ohms per channel and its only getting 8 ohms per channel and the 8ohm subwoofer. so the subwoofer feels like 4 ohms and the stereo gets maybe 2ohms at most in total

My idea was thinking of making a voltage divider for each channel with two 1K resistors between + and - of both channels. then inverting one channel. (I think i could do it a lot better if i had two seperate audio 1 to 1 transformers and then inverting the output of one of them.

That way I could make a center channel by just hooking the subwoofer between the two speaker +'s on the stereo output. and have stereo and mono at the same time. and since the right channels + is inverted. the subwoofer will get its power from there. without interfering with the speakers.

 

[audioguru]

A 2.1 sound system does not have a center channel. It has two stereo speakers without low sound frequencies and a mono sub-woofer without high sound frequencies. A 5.1 surround sound system has a center channel and a sub-woofer.

A simple calculation shows that a 47uF capacitor in series with an 8 ohm speaker cuts frequencies below 426Hz so it will sound like a tweeter without a woofer. One capacitor produces only a gradual frequency filter. The crossover filter to a subwoofer should be 2 or 3 times sharper and cutoff at 100Hz to 150Hz.
The crossover filters prevent the cutoff frequency from being amplified twice and boosting the level of the crossover frequencies.

Transformers were used for audio 60 years ago. They produce distortion and cut low and high frequencies. An audio opamp is used as an audio inverter today.

As I explained before, connecting an 8 ohm sub-woofer to the bridged stereo amplifier doubles the output current the same as if each channel is driving 4 ohms. But each channel also drives an 8 ohm speaker so the total load on each channel will be 2.7 ohms which increases distortion a lot and might destroy the amplifiers.

EDIT: One missing word "low" was added.

 

[Nigel Goodwin]

But each channel also drives an 8 ohm speaker so the total load on each channel will be 2.7 ohms which increases distortion a lot and might destroy the amplifiers.

Which could well be a good thing - as it's going to sound completely crap anyway as his entire premise is incorrect.

 

[gophert]

Which could well be a good thing - as it's going to sound completely crap anyway as his entire premise is incorrect.

Which is why I told him to try it - scientifically sound arguments haven't worked.

 

[realflow100]

I purchased two 1-1 audio transformers and tested and it sounds much better than I expected...!
I used 100uF capacitors instead and it sounds more balanced now.
and i left the subwoofer alone because it muffles the high frequencies on its own and produces smooth midrange to keep the balance its 6.5 inch in-phase with the rest and it actually works well. The stereo has an oversized heatsink with grills and a silent fan that only turns on at ear-shreddingly loud volumes

the stereo is rated stable at its peak power to 2 ohms per channel for an extended period of time without issue (which is ear shreddingly loud and not tolerable to hearing!) so I don't even approach that watching videos or listening to music at normal volumes

 

[audioguru]

Did you know that "peak power" or "maximum power" is actually double the instantaneous RMS power? Many audio amplifiers advertise "200W" which is a lie because it is actually 200 Whats. It is 100W RMS only for a moment. A long duration tone might produce only 50W RMS continuously. That is with horrible-sounding 10% distortion. With low distortion the power is 40W. Sometimes they say "music power" which is the distorted instantaneous peak power multiplied by the age of the salesman's grandmother. Then of course these numbers are the total of all the channels so the power is half for each channel of a stereo amplifier.
Car amplifiers have 4 amplifiers. The entire amplifier is advertised at 200W. But each channel actually produces only 14W.

One of my few jobs was working for a Japanese PRO audio manufacturer. Their best 800W amplifier was excellent and had full protection. It was guaranteed with no questions asked and none were ever returned for repair or replacement out of the thousands that were sold. It did not have a fan but instead it had a massive heatsink chimney. I was asked to test an American competitor's amplifier and it soon smoked and failed.

 

[realflow100]

ok ive disabled front jack detection and used a separate push pull amplifier to power the subwoofer individually. (Plenty loud enough with -11v and +11v) didn't even need a single capacitor. very low noise and plenty of gain
Its built with two 40-50W transistors. a PNP and NPN Two diodes and two 1K resistors and thats all it seems to need to work well to drive the subwoofer strongly
Do you know of anything I could do to improve the power level? The transistors have their own separate heatsinks that are enormous. I want them to go closer to full rail voltage.. They only seem to go about half.
Do I need some gain transistors to increase how much the transistors actually turn on?

 

[audioguru]

Are your two transistors emitter-followers which have no voltage gain? They are the output stage of a power amplifier, they are not an amplifier. If you want an output into the subwoofer of 8V peak and it is 8 ohms then the peak output current is 1A. If the transistors have a current gain of 80 then their peak base current must be 1A/80=12.5mA then the 1k resistors cannot supply the required 12.5mA peak.

Your amplifier needs a driver transistor and at least one input transistor. It will also need a few resistors and a few capacitors.

 

[realflow100]

my subwoofer is 4ohms.
how would I make the transistors have the required current?

could I use an 2N3904 or something? I have a supply of 10 1K's and 100 10K resistors. each 1/2 watt

20 NPN 2N3904 and 20 PNP 2N3906

The smallest and largest capacitors i have is 250v 120uF and largest is 3,300uF 50V

the power supplies I have is -12v to +12v with 15A capacity

 

[audioguru]

With a plus and minus 12V supply you could use a TDA2030A IC power amplifier to produce 10W into 4 ohms with low but maybe audible distortion. 10W into 4 ohms is 9V peak and the current is 2.25A peak.

You could make your own amplifier by using TIP31 and TIP32 output transistors and another TIP31 as the driver. For 2.25A the minimum current gain is about 18 then the maximum base current is 2.25A/18= 125mA. The maximum base-emitter voltage is 1.5V and the max voltage across 0.22 ohm emitter resistors is 0.5V then the pullup resistor must have 12V - 9V - 2V= 1V across it when it has 125mA so its value is 8 ohms which is ridiculous. Therefore the pullup resistor should be bootstrapped with about 10V across it then its value is 80 ohms but 82 ohms is available. When the driver conducts enough to produce -9V at the output then the base of the TIP32 will be pulled down to about -11V then the pullup 82 ohms resistor will have 12V + 11v= 23V across it then the collector current of the driver transistor will be (23V/82 ohms) + 125mA= 405mA. The pullup resistor must be two resistors of 39 ohms in series then a bootstrap capacitor from the output to between the resistors is used. Calculate the power rating for the resistors. The first transistor needs to drive the base of the driver transistor and negative feedback needs to be added. The negative feedback sets the gain, reduces distortion and causes the need for a frequency compensation capacitor.
Simple stuff.

 

[realflow100]

Im sorry it just goes through one ear and out the other. What I currently have is one transistor doing the top 12V and the bottom doing the bottom -12V
Its plenty loud enough for listening and such but it doesn't drive the speaker all that much at frequencies above 25hz or so. it begins to stop producing much power.
I have these two transistors
**broken link removed**
and
**broken link removed**

and also i have
20 NPN 2N3904 and 20 PNP 2N3906
but the lowest resistor value I have is 57 or so ohms and I dont know where I lost it to. I might need to purchase a multimeter and some more resistor values. and possibly some capacitors.

at the moment i dont have any emitter resistors. only two 1k's and two diodes for the input signal. direct coupled between 0v and emitters of the transistors.. (virtual ground) so when plugging in the speaker theres no audible pop noise or movement of the speaker (where if it was capacitor coupled between -v and emitters. it'd make a pop noise)

 

[audioguru]

You need an amplifier circuit. Instead you have only part of an amplifier.

 

[realflow100]

how would I make a simple amplifier circuit? I have a breadboard and jumpers for the 2N's

 

[audioguru]

The capacitance between the many rows of contacts and the jumper wires all over the place on a solderless breadboard cause many opamp and amplifier circuits to oscillate. The contacts are frequently intermittent. Therefrore a pcb or properly setup stripboard should have everything laid out in a compact fashion and soldered.

I described a simple 4-transistors amplifier but you said, "it just goes through one ear and out the other" so you do not understand a simple amplifier circuit, then you should buy a kit or an amplifier already made.

 

[realflow100]

I have some questions about reverse breakdown voltage of a transistor. should I make a new thread? so not to clutter this one?