: Stereo / Speaker Question



behind-bars
04-13-10, 10:28 PM
I scored a free Sony STR-D515 receiver today, in great shape once I cleaned it up.

Problem is that it wants 8-16 ohm speakers. I put the ohm meter to my pair of speakers and they are only 4. I plugged them in to the "front" channel jacks and they worked for a few seconds then stopped, I moved them to the rear surround sound jacks and they work consistently, but it sounds weird with movies because you are effectively missing the front channel and the receiver will not compensate for lack of front speakers like it will for lack or rear. Does this sound right? I am not sure why the last people threw it out, so I don't know if they had problems with the jacks as well.

I took the cover off and the 2 jacks have different plug types so i cant reverse them inside to isolate the problem.

Any gurus have a way to pin down my problem, don't really want to buy new speakers, especially not knowing if the receiver works correctly

EChas3
04-13-10, 11:34 PM
Buy some 8 Ohm resisters & put them in series with the speakers.

behind-bars
04-14-10, 12:20 AM
Buy some 8 Ohm resisters & put them in series with the speakers.

I wish I remembered my physics classes :bigroll:

I tried putting the two 4 ohm speakers in series and it came out with 2 ohms. Will an 8 ohm resistor in line give me 8 ohms, or 5 something?

Also I am guessing I will need 4 resistors total for 2 speakers correct? Do I have to put one on each of the 4 individual wires?

I read some online, but I dont know all the technicals about audio. Some people said resistors overheated / distorted things, but I am not sure if they were in my position

codewize
04-14-10, 12:33 AM
You must be confusing series with parallel.

In series you add the total resistance. In parallel you use a formula shown here (http://www.1728.com/resistrs.htm)

If you put a 4ohm resister in series with a 4 ohm speaker you'll end up with 8 ohms.

If you put 2 4 ohm speakers in parallel you'll end up with 2 ohm

Usually putting resistors inline with speakers doesn't yield very good results. It will correct the resistance problem but a crossover is a better solution. If you do it with resistors you'll only use one per speaker on the + side.

Another very good reference http://www.kpsec.freeuk.com/resistan.htm

behind-bars
04-14-10, 01:11 AM
Thanks, that makes sense now, guess I will swing by radio shack tomorrow and see if they have some, If it sounds bad then I will just look for some other speakers, but at least I will know the receiver works, maybe who ever tossed it to the curb will toss the speakers tomorrow lol.

I just want it to sound good, I am not a huge audiophile who wants thumping bass etc, I only have a 500 sq/ft apartment so I dont need tons of power

eldorado99
04-14-10, 01:51 AM
Doesn't putting an ohm meter on speakers run a pretty high risk of burning them out?

behind-bars
04-14-10, 01:41 PM
I wouldn't think an ohm meter would hurt them , they were unplugged when i tested them, the ohm meter should not run much power to them, just test resistance.

I hooked them up in proper series and got 8 ohms, plugged them in and it worked for about 5 mins, then the receiver clicks and the sound stops. I am still not sure if the receiver is broken, or just not compatible with the speakers. I may try resistors,but technically it should be the same ohms as hooking them up in series.

codewize
04-14-10, 07:05 PM
Ummm no, not at all. How else would you measure it?


Doesn't putting an ohm meter on speakers run a pretty high risk of burning them out?

behind-bars
04-14-10, 10:02 PM
Well an 8ohm resistor did not work, still cuts off after 5 mins, the receiver stays on but the sound stops. Guess I will have to get another pair of speakers to try.

Submariner409
04-14-10, 10:51 PM
Resistance is one fixed electrical value while speaker impedance is an entirely different can of dynamic worms: depending on drive voltage and enclosure effects impedance varies all over the place, from near 0 Ohms to well over 100 Ohms.

Unless you're the electrical engineer who designed the circuits and speaker loading as well as the crossover characteristics you're clutching at needles in a haystack: exactly why my 12" woofer in a 3 cu/ft cabinet will not sound like your 12" woofer in your 3 cu/ft cabinet.

EChas3
04-14-10, 11:10 PM
Your receiver is junk. Put it back on the curb and hope they don't charge you to take it away.

behind-bars
04-14-10, 11:36 PM
Haha, yeah its old, but I only have time invested in it. I finally figured out the problem though. It looks like the relay for the front channel is goofed up and dying. The receiver clicks every few minutes and that corresponds to when the sound cuts out. I can hook the speakers up any way, 4 ohm, series, resistor whatever to the rear channel and it works fine and never cuts out, just sounds weird. Was fun to tinker with though lol.

I can mess with it without fear and may hack it up to where its usable, if not then oh well.

EChas3
04-14-10, 11:52 PM
If it's like a Sony I used up, the 'relay' is actually a circuit protector on the outputs from the IC Amp. The proprietary amp chips are bad. If you can get replacements you might be able to repair it.

The reason your back channels work is that they are driven from a different chip(s).

I do wish you luck but I think you'll find it cheaper to replace with new than to repair.

codewize
04-15-10, 01:00 AM
By 'chips' are you refering to power transistors or is the whole deal in an IC?

EChas3
04-15-10, 11:01 PM
Modern Amps don't use power transisters like they used to. It's an Integrated Circuit, now.

behind-bars
04-16-10, 12:14 AM
Yeah, I am not going to spend any money trying to fix it, I just wired my speakers into the rear surround sound where they work fine, then plugged rca cables into one of the other outputs and was able to put the front channel back into my TV and use those speakers.

It is not true surround sound by any means, and I know the receiver is old and not worth repairing, but it is better then just the 2 small speakers in the TV like I had for the time being. One day I'll run across another receiver that works better or get a new one lol

codewize
04-16-10, 01:38 AM
I have a very nice Pioneer SX-626 I'll sell you

Submariner409
04-16-10, 08:06 PM
IC's (integrated circuits) and sometimes an intermediate stage drive the (power) output transistors in all but the tiniest pocket screechbox.

Check out the output transistors of several large home and car audio amps: those outputs are as large as a book of matches in some cases, there may be as many as 8 per channel, and they're configured in push-pull to produce some incredible output power voltage swings - no IC will do that.