Why 4 Ohm Loads Stress Your Amplifier

Here's a scenario that confuses me: I've read several times in this thread that if you have only one speaker pair hooked up and you don't get sound when you switch to A+B, that means that your receiver runs two speaker pairs in series, not parallel. My receiver (Kenwood KR-7050) does this, but when I look at the service manual it certainly looks like the A+B is wired in parallel. Can anybody confirm that this is really true?

The reason I'm trying to figure this out is that I'm currently running a pair of 8 ohm speaker and a pair of 4 ohm speakers at the same time. Presumably, if they were in series that would mean the receiver is going into 12 ohms of impedance, which shouldn't be a problem (at least not in the "damaging the receiver" sense). Whereas if it's parallel, I believe that would come out to around 2.6 ohms. According to the manual, the receiver is rated for 8 or 4 ohms, but definitely not 2. I obviously want to avoid frying my receiver if possible.

Help?
 
Regardless of whether it's wired in series or parallel, IMO it's never a good idea to mix speakers that have different impedances. I can't make head's or tails for sure but the switch looks parallel. Gimme a rotary anytime.

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Since the negative of "B" speaker runs through the switch, I think that's a clue they're likely in series for A+B.

If you slide the switch to the far left I believe you'll be able to trace out the series circuit.

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Ok, I'll drink the Kool Aid. I just had my Realistic receiver repaired and my tech suggested that I check the speakers and make sure that they are ok. I tested them at 5 ohm each, so I'm calling them 4 ohm speakers. My receiver says to use 8 or 16 ohm speakers. It suggests reading the manual if I want to use 4 ohm speakers.

1) Does anyone have access to a Realistic STA-64B manual ?
2) Where do I start to get some 8 ohm speakers? I'd prefer to get a pair of vintage speakers as I can't stand all the cheap Chinese crap sold these days. Any suggestions?
 
my technics. su v9 has a servo regulated power supply and measures the impedance of the speakers connected to it and adjusts itself.

pretty cool for a 1979 amp
 
That is the same thing that McIntosh does with their Autoformers. I think the Mac amps sound tubby 9which is sad because I really like the way they look) because they don't increase with decrease ohm load - a 500 WPC amp is just that 500 WPC.

That is a pretty good idea McIntosh has.
 
Ok, I'll drink the Kool Aid. I just had my Realistic receiver repaired and my tech suggested that I check the speakers and make sure that they are ok. I tested them at 5 ohm each, so I'm calling them 4 ohm speakers. My receiver says to use 8 or 16 ohm speakers. It suggests reading the manual if I want to use 4 ohm speakers.

1) Does anyone have access to a Realistic STA-64B manual ?
2) Where do I start to get some 8 ohm speakers? I'd prefer to get a pair of vintage speakers as I can't stand all the cheap Chinese crap sold these days. Any suggestions?

What you measured is DC resistance. That is not the same as the speaker impedance. If you measured 5 ohms that's not unusual DC resistance for a speaker having nominal 8 ohms rated impedance.

You would call those "8 ohm" speakers.
 
hello,
kinda new to this so excuse me if i do something wrong !, i have a new soundcraftsmen pro power 10. great amps. am currently running 2 ma5002's bridged together with the bridging adapter. cleanest sound i've ever heard !.
my question is on the prop ower ten ohm loads. its a independent 4 channel amp with 2 bridging circuits. these amps are 2ohm stable. so if i bridge the amp(s) i essentially have a 2 channel amp capable of running 2 speakes. so if i have 4ohm speakers attached to the pro power 10 in bridged mode, am I running the amp at a 2ohm load ? or a 4ohm load ? since its bridged ? my concern is blowing the amp.. although the speakers are rated at 4ohms, the spec out at about 3.7 ohms..
 
The impedance of the speakers doesn't change so they would still be called 4 ohm speakers. But the 4 ohms is only nominal, that changes across the frequency spectrum so there could be dips to lower impedance at some frequencies. There is probably an impedance curve for your speakers somewhere. The real question is whether the bridged amp is stable into a nominal 4 ohm load. I have only seen the output rated when bridged into 8 ohm loads which doesn't really say either way.
That sounds like a very nice set up you have going.
 
so if i bridge the amp(s) i essentially have a 2 channel amp capable of running 2 speakes. so if i have 4ohm speakers attached to the pro power 10 in bridged mode, am I running the amp at a 2ohm load?

Yes, a bridged amp feels 4 ohm speakers as 2 ohm load. If the amp doesn't list 2 ohms unbridged operation in the specs it may be wise to reconsider bridged + 4 ohms.
 
I found this in another forum. It lists the Pro Power Ten as 900 watts into 4 ohms. That implies it is stable when bridged into 4 ohms. That and since it is listed as stable into 2 ohms unbridged you should be OK.


PRO POWER 10 - (FULL CHASSIS 4 CH, 2 PM860S IN ONE PACKAGE, 6 HITACHI TO3-METAL MOSFETS/CH, DUAL LED DISPLAY, DUAL PCR PS, DUAL FANS, A BEAST, 205W/CH@8R, 315W/CH@4R, 450W/CH@2R or 600WX2@8R and 900WX2@4R, HIGH CURRENT, INTEGRATED BRIDGING).
(from)
http://www.audioheritage.org/vbulle...elp/page11&s=b07de8602b2af60fd59586bd8319d5f4
 
Yes, a bridged amp feels 4 ohm speakers as 2 ohm load. If the amp doesn't list 2 ohms unbridged operation in the specs it may be wise to reconsider bridged + 4 ohms.
Thanks for the clarification !, the soundcraftsmen pro power 10 is positively rated at 2ohm stable, however if the 4 ohm speakers are rated at 2ohm, but spec at 3.7, is that 3.7/2=1.35 ohms (bridged) ? which is under 2ohms, do you see my concern ? thanks agian steve
 
I would just go by the nominal rating of the speakers. If you measured them with an multimeter you measured DC resistance, which is different than the impedance.
 
I found this in another forum. It lists the Pro Power Ten as 900 watts into 4 ohms. That implies it is stable when bridged into 4 ohms. That and since it is listed as stable into 2 ohms unbridged you should be OK.


PRO POWER 10 - (FULL CHASSIS 4 CH, 2 PM860S IN ONE PACKAGE, 6 HITACHI TO3-METAL MOSFETS/CH, DUAL LED DISPLAY, DUAL PCR PS, DUAL FANS, A BEAST, 205W/CH@8R, 315W/CH@4R, 450W/CH@2R or 600WX2@8R and 900WX2@4R, HIGH CURRENT, INTEGRATED BRIDGING).
(from)
http://www.audioheritage.org/vbulle...elp/page11&s=b07de8602b2af60fd59586bd8319d5f4
That sounds hopeful !!, thank you very much for the answer. this place is great, helped me rebuild a soundcraftsmen ma5502 years ago. i'm tempted to get a pair of the eminence lab 15 sub woofers which are rated at 6ohms so, 3 ohms bridged. but at that rate my ears will fail before the amp does.!
Thanks Again
Steve
 
I would just go by the nominal rating of the speakers. If you measured them with an multimeter you measured DC resistance, which is different than the impedance.
thank you, from all the information i'm getting it looks pretty good to run it bridged into 4ohms, risky, but it should hold...guess igotta make the decision !
Thank Again
steve
 
The impedance of the speakers doesn't change so they would still be called 4 ohm speakers. But the 4 ohms is only nominal, that changes across the frequency spectrum so there could be dips to lower impedance at some frequencies. There is probably an impedance curve for your speakers somewhere. The real question is whether the bridged amp is stable into a nominal 4 ohm load. I have only seen the output rated when bridged into 8 ohm loads which doesn't really say either way.
That sounds like a very nice set up you have going.
Thank You, Yes it's extremely clean at loud volumes !, it's been a life long passion to build the perfect system. kinda like the vintage amps rather than the new dj stuff. speakes are home built eminence 15" woofers, 8" mids and horn tweeter, with a seperate 15' sub woofer (passive) built into each cabinet. built a "antique" style cabinet to house everything in. once i got all the amps in, i couldn't lift it !!
Thanks Again
Steve
 
Thanks for the clarification !, the soundcraftsmen pro power 10 is positively rated at 2ohm stable, however if the 4 ohm speakers are rated at 2ohm, but spec at 3.7, is that 3.7/2=1.35 ohms (bridged) ? which is under 2ohms, do you see my concern ? thanks agian steve

Actually 3.7/2 = 1.85 so it is a little closer, but concern is definitely appropriate.
 
For what its worth, it seems to me that the DC resistance is frequently lower than the nominal impedance of a speaker system. This is just an observation so nothing to bank on.
The impedance is like the DC resistance plus reactance of any inductance in the circuit so maybe it makes sense that the impedance would usually be higher but don't take my word for it.
 
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