IIRC the outputs on the CR-1040 are pretty much unobtanium. I would go easy on such things. Blow one and your CR-1040 is either a mono unit or a door-stop.
Why 4 Ohm Loads Stress Your Amplifier
- Thread starter 240 Volts
- Start date
subdermis2000
Soviet Canuckistanian
The reason I asked is that I've always erred on the conservative side of things- nothing less than a nominal 8 ohm load on each channel - on any recevier or amp I've ever used. While this may restrict my options when it comes to speaker selection, I'd rather listen to my gear than wait for it to come back from the shop.
Magnat10
Active Member
looks like you are close here
I asked my Romanian Engineer friend who is in Germany on
vacation if he would look at and comment on your findings, for the 5 years I have known him he is just below the genius level. He drinks beer and has a great personality so I guess just really smart is good for him, here is his answer
Steve,
this guy is close to the truth ... impedance is what I remember killing
the amplifiers when the wrong Ohms are used - short usage of lower or
higher ohms at low volume allows you to test functionality but not long
performance ... to cover wider range of Ohms the tool missing is a
'reostat' (not sure of the English spelling) ... what this one does is
correlates / controls the current exactly like a manual gear box on a
car ... the old trams were designed like that so they were able to
accelerate and decelerate using the current rather then brakes ...
imagine a quarter of a circle made of metal (coper) and a level like a
needle in the circle center and as you move left right the level
covering more of the quarter the higher the current therefore the
faster the tram ... Ideally amplifiers should have outputs specific for
different Ohms levels otherwise you risk a lot ...
old gear is more solid newer stuff is more sensitive since they assume
new loudspeakers ... russian amplifiers were well known for their
resilience because they used rock solid components rather then pnp npn
semiconductors in transistors ... those semiconductor materials are
cheap, reduced sizes and somewhat reliable but you don't have lots of
flexibility like a using a decent old wire ...
If I have time (taking vacation for 10 days this Thursday) I'll go over
his calculations ... hope my comments help
Take care Steve
Alin
240 Volts said:There have been quite a few questions lately regarding the safety (or otherwise) of driving 4 ohm speakers from amplifiers only rated to drive 8 ohm loads.
Rather than just add to the mass of unsubstantiated conflicting opinions (e.g. "amplifier XXX is built like a tank, so it must be able to drive 4 ohm loads"), I thought I'd attempt to apply a bit of science to the subject. Hopefully this will make people aware of some of the issues involved in driving low impedances.
In relation to ensuring reliable long-term operation, three of the most important parameters for a transistor are it's voltage, current, and power ratings. Exceed any of these three at your peril.
Voltage : In any half decent amplifier design the output transistors will have a sufficient voltage rating to withstand all "normal" operating conditions. Only abnormal events such as lightening strikes are likely to cause failures.
Current : The transistors need to be able to handle the maximum currents taken by the load. Speaker impedance can (and does) vary considerably with frequency, and often dips well below the nominal 4 or 8 ohm value. Amplifier designers are well aware of this fact and counter it either by using higher rated transistors with large peak current capability (good) and/or by incorporating current limiting circuitry (not quite so good, but better than blown outputs!). In practice a good amplifier design will withstand the ultimate over-current event - the accidental short circuit of it's outputs (but don't blame me if yours doesn't!).
Power : Every transistor has a maximum power dissipation rating. This is not a fixed figure but varies with the temperature of the transistor. For example, a transistor might be rated to dissipate 100 watts at 25 degrees centigrade but only 20 watts at 100 degrees centigrade. The amplifier designer should provide cooling, in the form of heatsinks, to ensure that the maximum temperatures are not exceeded.
It has been suggested by some here on AK that if you want to drive 4 ohm speakers with an amplifier only rated for 8 ohm loads, then everything will be OK if you limit the volume so that the output current is kept below that which would have been taken by the 8 ohm speakers. The following calculations will show just how wrong this is. :nono:
I have used "Excel" to calculate the output transistor power dissipation for a typical 200 watt class AB amplifier when driving an 8 ohm load at full output and 4 ohm load at half output (so that the output currents are the same for both 8 and 4 ohm loads).
The following assumptions have been made :
(1) The load is purely resistive.
(2) The output waveform is symmetrical about zero, so the calculation only needs to be done for the positive half cycle (180 degrees).
(3) The amplifier output can swing to within 5 volts of the supply rails before clipping.
(4) Bias current is neglected as it's contribution to the maximum power dissipation is relatively low for a typical class AB design.
The basic amplifier topology for the analysis is shown below :
The voltage, current, and power dissipation waveforms for 8 ohm load at full output and 4 ohm load at half output are shown below (NOTE: The "Output Transistor Dissipation" figure is the total power dissipation per channel, so to get a "per transistor" figure simply divide by the number of output transistors (not pairs of transistors) per channel).
The dark blue trace is the DC supply voltage from the main filter capacitors.
The sum of the output voltage (pink) and the voltage across the output transistor (green) must always add up to this DC supply voltage.
The yellow trace is the current which flows through the output transistor and into the load.
Output power (light blue) is simply the output current (yellow) multiplied by the output voltage (pink).
Output transistor power dissipation (red) is likewise simply the transistor current (yellow) multiplied by the voltage across the transistor (green).
So, for the 8 ohm load we have : Peak Current = 7.5 Amps, Output Power = 225 Watts, Output Transistor Dissipation = 85 Watts.
And for the 4 ohm load we have : Peak Current = 7.5 Amps, Output Power = 112 Watts, Output Transistor Dissipation = 198 Watts.
Despite keeping the maximum currents the same by halving the power into the 4 ohm load, the power dissipation in the amplifier output transistors is massively increased compared to full output into 8 ohms.
The following graph shows how the power dissipation (i.e. internal heating) of this amplifier would vary with output power for 4 and 8 ohm loads. Note that the figures are "per channel" and so the heating is doubled for stereo operation.
I have noticed that Pioneer specify output powers for their SX-x3x, SX-xx50, and SX-xx80 receivers into both 4 and 8 ohms, except for the SX-1280 and SX-1980 for which output power is quoted into 8 ohms only. Similarly, the SPEC 4 is rated at 150 watts into 8 ohms and 180 watts into 4 ohms, whereas the output power for the larger SPEC 2 is only quoted into 8 ohms (250 watts).
My suspicion is that this is because the cooling on these higher power units is insufficient to allow them to develop the same (or greater) continuous power into 4 ohms as they can into 8 ohms (output power being measured by the old FTC regulations which required 1 hour pre-conditioning at 1/3 of rated output, i.e. near maximum heating of the output transistors).
Pioneer could of course have specified an output power into 4 ohms for these models, but how good would it look if the output into 4 ohms was considerably less than that into 8 ohms?? Better for them simply not to give a power rating into 4 ohms. Of course, this is only my opinion and I'm open to suggestions from more knowledgeable AK'ers. :scratch2:
To conclude then : For conventional class AB amplifiers the use of 4 ohm speakers greatly increases amplifier heating compared to when using 8 ohm loads - even if the maximum output currents are kept the same by exercising restraint with the volume control.
OK guys, I've set myself up to be shot down in flames - who's going to take the first shot??
- Richard B.
I asked my Romanian Engineer friend who is in Germany on
vacation if he would look at and comment on your findings, for the 5 years I have known him he is just below the genius level. He drinks beer and has a great personality so I guess just really smart is good for him, here is his answer
Steve,
this guy is close to the truth ... impedance is what I remember killing
the amplifiers when the wrong Ohms are used - short usage of lower or
higher ohms at low volume allows you to test functionality but not long
performance ... to cover wider range of Ohms the tool missing is a
'reostat' (not sure of the English spelling) ... what this one does is
correlates / controls the current exactly like a manual gear box on a
car ... the old trams were designed like that so they were able to
accelerate and decelerate using the current rather then brakes ...
imagine a quarter of a circle made of metal (coper) and a level like a
needle in the circle center and as you move left right the level
covering more of the quarter the higher the current therefore the
faster the tram ... Ideally amplifiers should have outputs specific for
different Ohms levels otherwise you risk a lot ...
old gear is more solid newer stuff is more sensitive since they assume
new loudspeakers ... russian amplifiers were well known for their
resilience because they used rock solid components rather then pnp npn
semiconductors in transistors ... those semiconductor materials are
cheap, reduced sizes and somewhat reliable but you don't have lots of
flexibility like a using a decent old wire ...
If I have time (taking vacation for 10 days this Thursday) I'll go over
his calculations ... hope my comments help
Take care Steve
Alin
ron-c
Addicted Member
You can design an amplifier to have maximum performance into many load points. It does not have to be 8 ohms at all. The McIntosh MC402 amplifier is most efficient at about 2.2 ohms. Great as long as you have a 2.2 ohm speaker. So we have 400 watts at 2.2 ohm and about 200 at 4 ohms and 100 at 8 ohms. This is the way all amplifiers work, they halve their power into doubling impedance. The problem is you pay for a 400 watt amp, buy 8 ohm speakers, get 100 watts and clip the amp constantly until the tweeters fail...
Or you use an output autoformer which has 2,4, and 8 ohm taps then you get in excess of 400 watts into 2,4, and 8 ohms. The amp thinks it always is connected to 2.2 ohms and you can use any speaker you would like.
In the drawing above once the sine wave exceeds the DC supply voltage it will clip. Peak power is not the issue only the size and voltage of the power transformer. You can connect all the capacitors you want in the circuit and the sine wave power will not increase one watt. That is the way transistors and Ohm's law works. Rail voltage defines the limit of power.
thanks,
Ron-C
Or you use an output autoformer which has 2,4, and 8 ohm taps then you get in excess of 400 watts into 2,4, and 8 ohms. The amp thinks it always is connected to 2.2 ohms and you can use any speaker you would like.
In the drawing above once the sine wave exceeds the DC supply voltage it will clip. Peak power is not the issue only the size and voltage of the power transformer. You can connect all the capacitors you want in the circuit and the sine wave power will not increase one watt. That is the way transistors and Ohm's law works. Rail voltage defines the limit of power.
thanks,
Ron-C
Been Missing, Got Three SAM-1200 Accumatch Transformers
Yippie! Got three top of the line Accumatch SAM-1200 transformers. The eBayer said that they were new and not hooked up. One came new and the others, well. After a lil cosmetic doctoring with steel wool and some wire cutters plus ... everything's okay.
Have yet to play with them other than cleaning them up and checking continuity.
Yes, amplifiers CAN be optimized for a load.
When properly optimized, distortion products, IM and THD, do not suffer.
Phoenix Gold, for home, PA, sound distribution, have a very good looking setup. Sold at MCM, part numbers 50-7000, 7005, 7010, & 7015, represent using multiple speakers for distibution without destroying frequency response. Try this URL: MCM PHOENIX GOLD POWER DISTRO
Hey, those resistors, although inductive (speakers are), are the type I use to test amplifiers-->0--10 Ohm 275W Ohmite.
They have some inductance but won't hurt any measurements despite what most surmise--speakers are inductive. Best test an amp with a very lil I'd guess than springing for those huge non-inductive Dale/Vishay.
Yippie! Got three top of the line Accumatch SAM-1200 transformers. The eBayer said that they were new and not hooked up. One came new and the others, well. After a lil cosmetic doctoring with steel wool and some wire cutters plus ... everything's okay.
Have yet to play with them other than cleaning them up and checking continuity.
Yes, amplifiers CAN be optimized for a load.
When properly optimized, distortion products, IM and THD, do not suffer.
Phoenix Gold, for home, PA, sound distribution, have a very good looking setup. Sold at MCM, part numbers 50-7000, 7005, 7010, & 7015, represent using multiple speakers for distibution without destroying frequency response. Try this URL: MCM PHOENIX GOLD POWER DISTRO
Hey, those resistors, although inductive (speakers are), are the type I use to test amplifiers-->0--10 Ohm 275W Ohmite.
They have some inductance but won't hurt any measurements despite what most surmise--speakers are inductive. Best test an amp with a very lil I'd guess than springing for those huge non-inductive Dale/Vishay.
Really oversimplified...
Amplifiers are not 100% efficient. That is, they do not transform all of the electrical energy from the outlet into music.
Amplifiers efficiency is not the same at differing power levels.
When idling, the Class A requires a large amount of current to just keep the devices "ready".
Class AB are better and require less of that current.
When at full tilt, amplifiers are at their best efficiency, turning a great deal of the wall voltage current into musical current/voltage.
That way, the heating effect is lower. Anywhere below that maximum effieciency point, a predictable portion of the energy is wasted as heat.
My M-2's idle warmer than when playing! They are probably going to get hotter idling than when playing a two Ohm Sub and satellites!
Oh yes, I haven't hit the current limit wall yet at the power levels I frequently listen.
Amplifiers are not 100% efficient. That is, they do not transform all of the electrical energy from the outlet into music.
Amplifiers efficiency is not the same at differing power levels.
When idling, the Class A requires a large amount of current to just keep the devices "ready".
Class AB are better and require less of that current.
When at full tilt, amplifiers are at their best efficiency, turning a great deal of the wall voltage current into musical current/voltage.
That way, the heating effect is lower. Anywhere below that maximum effieciency point, a predictable portion of the energy is wasted as heat.
My M-2's idle warmer than when playing! They are probably going to get hotter idling than when playing a two Ohm Sub and satellites!
Oh yes, I haven't hit the current limit wall yet at the power levels I frequently listen.
OK, I've waded through this thread and have yet another question. Are all 4 Ohm loads created equal, so to speak? Is running a single pair of 4 Ohm rated speakers with 12" woofers any different than running 2 pairs of 8 Ohm rated speakers with 15" woofers? Would the larger woofers, and the fact that there's 4 of them, cause the impedance to dip lower than the single pair? Is it more of a stress than a single pair? I have my Pioneer SX-1010 running CS-99a's and Goodmans Magisters on the A and B terminals and like to play them together. So far, I havn't seen any adverse effects, but I don't want to fry the receiver. It doesn't seem to get any hotter than when playing a single pair. Also the power ratings at 8 and 4 Ohms aren't that different on the SX-1010. Any thoughts on this?
doctorbongo
Super Member
That's IMMENSE, Mister 240.
I'm literally going to need to study some tomes I have here to grasp all of it, because I'm functionally illiterate here. Hey, and cheers to the UK. I was over there about 17 years ago now, got to do a tour of countryside pubs with a bitters aficionado named Derek who worked as an audio engineer for the BBC. He knew all of the specific gravities and such. Bravo.
I'm literally going to need to study some tomes I have here to grasp all of it, because I'm functionally illiterate here. Hey, and cheers to the UK. I was over there about 17 years ago now, got to do a tour of countryside pubs with a bitters aficionado named Derek who worked as an audio engineer for the BBC. He knew all of the specific gravities and such. Bravo.
If I look at the Marantz2270, it`s power transistors are able to handle 20-30A at 100-150V each. Some testers measured 110-140W at 4Ohms with 1% distorsion, others found regarding to high IM-distorsion about 50W.
I don`t understand, why the transistors should not accept the current at 4Ohms, there are less than 2A at 46V each transistor necessary?
Herbert
I don`t understand, why the transistors should not accept the current at 4Ohms, there are less than 2A at 46V each transistor necessary?
Herbert
Most everyone here knows that if you put an ohm meter across an 8 ohm speaker you don't get 8 ohms. In fact, a single speaker may be near 8 ohms but a combo with a x-over may be somewhere between 4 and 8 ohms. That's just the resistive stuff. When you factor in the reactance of a speaker you may find that the speaker is stressed as the frequency changes. So, depending on if you are listening to classical, rock, jazz, country, or rap, you may have to consider your speaker choices not only in the standard load categories but in the loaded frequency ranges.
When it comes to 4 ohm speakers it would seem that you are doubling the load on your amp by not using 8 ohms. I know that it doesn't work out to that neat a number but it would seem that your amp is givin' its all to get the power to the 4 ohmers.
Or is everyone here just trying to play loud?
:guitar:
:guitar: :guitar: :guitar:
When it comes to 4 ohm speakers it would seem that you are doubling the load on your amp by not using 8 ohms. I know that it doesn't work out to that neat a number but it would seem that your amp is givin' its all to get the power to the 4 ohmers.
Or is everyone here just trying to play loud?
:guitar:
:guitar: :guitar: :guitar:
restorer-john
Addicted Member
Great thread!
Bottom line- the old gear was conservatively designed, it had to be. The Japanese were trying to impress the world, the FTC and each other. They were also working within the limitations of current technology and cost and produced world class products that we love today.
They used way too much current limiting to keep their gear safe and many a great amp has been hamstrung by three or four levels of overload 'protection'.
I haven't blown an output stage even when torture testing big old gear into 2 or 1 ohm impedances. Why? because the gear we love had to be able to handle drunken revellers shorting speaker cables at full power on a Saturday night 1970's party and still front up for the Sunday afternoon Fleetwood Mac blasting session.
Get your latest top of the range HT receiver and short the speaker terminals at full power and see what happens. BER (Beyond Economical Repair is what we describe them as). New gear is generally expensive rubbish all tarted up to impress the punters and garner a few 'rave' reviews in the latest hifi rag and guess what, the company will be out of business in a few years and you'll have something so ugly and out of date you can't give it away.
It's funny, I used to sell HT because people wanted it, but everyone had to endure my two channel demos afterwards. Guess what? It was only the men who wanted the HT, their wives liked 2 channel (extra speakers sure didn't help either).
More caps, more transistors and a bigger transformer is all we need and the vintage gear has it all in spades.
Bottom line- the old gear was conservatively designed, it had to be. The Japanese were trying to impress the world, the FTC and each other. They were also working within the limitations of current technology and cost and produced world class products that we love today.
They used way too much current limiting to keep their gear safe and many a great amp has been hamstrung by three or four levels of overload 'protection'.
I haven't blown an output stage even when torture testing big old gear into 2 or 1 ohm impedances. Why? because the gear we love had to be able to handle drunken revellers shorting speaker cables at full power on a Saturday night 1970's party and still front up for the Sunday afternoon Fleetwood Mac blasting session.
Get your latest top of the range HT receiver and short the speaker terminals at full power and see what happens. BER (Beyond Economical Repair is what we describe them as). New gear is generally expensive rubbish all tarted up to impress the punters and garner a few 'rave' reviews in the latest hifi rag and guess what, the company will be out of business in a few years and you'll have something so ugly and out of date you can't give it away.
It's funny, I used to sell HT because people wanted it, but everyone had to endure my two channel demos afterwards. Guess what? It was only the men who wanted the HT, their wives liked 2 channel (extra speakers sure didn't help either).
More caps, more transistors and a bigger transformer is all we need and the vintage gear has it all in spades.
If it ain"t and I repeat aint""""t heavy---- like 40 pounds, solid state--
forget 4 ohms at high power.
Heat then SMOKE then ---fuses are no good for anything but primary circuits.[no speakers, just kills damping factor] They blow like the wind I hear from these trees. You guys are cutting and pasting
specs from places that do not answer the QUESTION: and I think the question is about driving a load. What load? Is it theoretical or real or a test load ' theoretical load, iductive, capacitive, ahh
we finally get to a speaker. I do not hear a properly stated question. Why does my Chevy stop on rainy days at the corner of 5th and 1st with a quarter tank of gas and my dog is in the back seat? At 2pm Sunday?
C'mon guys, ask a question I can answer. What you drivin and what with?
forget 4 ohms at high power.
Heat then SMOKE then ---fuses are no good for anything but primary circuits.[no speakers, just kills damping factor] They blow like the wind I hear from these trees. You guys are cutting and pasting
specs from places that do not answer the QUESTION: and I think the question is about driving a load. What load? Is it theoretical or real or a test load ' theoretical load, iductive, capacitive, ahh
we finally get to a speaker. I do not hear a properly stated question. Why does my Chevy stop on rainy days at the corner of 5th and 1st with a quarter tank of gas and my dog is in the back seat? At 2pm Sunday?
C'mon guys, ask a question I can answer. What you drivin and what with?
They run cooler because the cosmic winds through the heat sinks were denied until you opened them up and poured in the output current desired by the class "b" stage that was waiting for the class "a" stage that drives them to drive them and unleash their waiting power .