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I am using an Onkyo receiver to power my 5.0 system. I am not using the .1 channel because I have 4 powered subs... one on each front and one on each surround. I also have a TST in my couch which I am running full range off the front left and right preouts of the Onkyo. My problem: when I hook up the Y adapter to combine the left and right preout signal to a single RCA to run to the amp that powers my TST, the channels bleed into one another back through the receiver to the front speakers. I hear my right channel in my left front speaker and my left vice versa which gives me no balance control and essentially no stereo separation. When I remove the Y connector the problem goes away. Can anyone tell me why I would be getting feedback on the preouts? Also, does anyone have any suggestions as to how I should set up the TST if this problem can't be avoided. I really don't want to hook the TST to the sub preout b/c the max I can set the internal crossover is 120 hz and the TST is tactile up to 800 hz. Any help would be much appreciated!
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AJPoe - - Growing old is inevitable, growing up is optional! -
ajpoe,when I hook up the Y adapter to combine the left and right preout signal to a single RCA to run to the amp that powers my TST, the channels bleed into one another back through the receiver to the front speakers.
The method you're using isn't combining, it's 'shorting' two outputs together - a real no-no in the electronics world.
It's possible to combine line level outputs of a receiver or preamp if you use a proper 'mixer', either purchased or home made, but don't ever combine outputs with a 'Y' splitter used backwards.
You have a couple of options here.
You can make a little combiner yourself out of a few resistors, but it will have some insertion loss and perhaps the TST amp will not be able to make up for the loss. I suspect it would be fine though.
The other option is a small line amp that also has a mono out feature. This is essentially a combiner/line amp - quite cheap to purchase. No doubt radio shack would have one.
I don't know if you're interested, but I'll tell you how to put together a simple two resistor combiner that would do the job. I won't tell you how to mount this arrangement, but take the left and right line level RCA cables (the ones you were shorting together) and short only their shield (grounds) together and then connect each hot (positive) pin to a 10kohm resistor (Radio Shack). The free ends of the two 10kohm resistors are now connected together. Then connect the shorted end of the resistors (mixed mono signal) and the shield to a single RCA connector and send this to your TST. As I said, you can decide the mechanics of it - probably best to cut the existing RCA's off the two cables and go from there.
This mixer will have an input impedance of 10Kohms and an output impedance of about 5kohms. It will have an acceptable insertion loss of about 6db. Any loss of high frequencies because of line length and high output impedance of 5K is insignificant here because you're driving a low frequency device. This arrangement is basically what's inside a passive mixer you would purchase if you didn't want to make one.
brucek -
thank you VERY much for the info. i will put one of those together tonight. i guess i was naive to think using the Y adapter was ok, it was too easy!
is it ok to assume that if i had done any damage to my receiver, that i would know it already? everything sounds so much better since i removed the Y cable.
thanks again,
anthonyAJPoe - - Growing old is inevitable, growing up is optional!Comment
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anthony,
Well, the output of a pre-amp isn't designed to supply much current, they're essentially a low output impedance (~100 ohms) voltage source with an intent to drive a high input impedance (~10-50 kohm) load (power amplifier).
The connection is basically a voltage bridge - this feature allows you to split the output of a preamp many times before you affect the signal. But it wouldn't take kindly to being shorted to another low output impedance device. No doubt the sound was somewhat distorted...... :roll:
Anyway, if it seems OK now that you've removed the offence, you're probably all-right.....
Note those resistors are 10kohms = 10000 ohms...........1/4watt will be fine (no power present here)
brucekComment
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ok, i have constructed my new Y adapter with resistors and hooked it up. i live about 5 minutes from parts express retail store so i just went there to get the supplies. i got 10k ohm resistors but they only had .5 watt, not .25. i assume that doesn't matter since you stated there is no power present. after hookup, i still have the balance control and stereo separation that i had without the cable hooked up. i did pick up an ever-so-slight sound in the left channel when i balanced 100% to the right and vice versa with the right channel while the new combiner Y adapter was connected. i don't think i hear it when it's not plugged in, but we're talking about such a small amount of sound that i had to press my ear against the tweeter with the grills off to detect it. i assume everything is working correctly even though i have this slight sound?
thanks again for all your help and input!AJPoe - - Growing old is inevitable, growing up is optional!Comment
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Anthony,
It's good that it worked, but since this is a passive solution without any active buffering or isolation, there will be a small amount of interaction and reduced separation, and as such must be considered a compromise.
A couple of resistors will work (as you've seen), but personally I would work toward an active solution in the form of a small stereo line amp with a combined mono output - or with the passive combiner attached to the output of a line amp that only possessed a stereo output. This would isolate the combining of your left and right channel.
A line amp would also give you some control over the level you feed the TST.
There are also transformer based passive solutions that will work....
Here's a cheap active amp that would probably do the job.
Here's a transformer passive solution - better isolation than the resistors provide.
Then there's always the possibility of finding a crappy old receiver that someone is throwing out that you could use the preamp from to do the job.. 8O
brucekComment
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awesome! thanks for the links and info!
ajpoeAJPoe - - Growing old is inevitable, growing up is optional!Comment
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