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Heat Dissipation Question?

 

colleycol
Unregistered guest
I recently talked to someone at Rotel about running 4 ohm speakers with the Rotel RSX1056 and he told me this:
"..but it is not recommended to connect 4 ohm speakers to the RSX-1056 since the unit is not designed to dissipate the amount of heat that would be generated from this type of load. I know that there are people who have connected them without problems but it is not recommended by us to do so."

Is their a product that allow one to add a fan or more ventalation to your component? I have seen them for a rack system but how about for a component?

Trying to decide between Rotel, Nad or used separates to drive 4 ohms? My budget is around $1000.

Thanks for any help.
Cory
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4168
Registered: May-04


Adding a fan to the Rotel might not let you run 4 Ohm speakers since most 4 Ohm speakers actually dip beneath that point in the load they show the amplifier. It becomes more than just a matter of dissipating heat. This is a case where I would suggest when you are told to not do something you don't go ahead and do it anyway.

Try looking at an amplifier that can handle the load you want to use.









 

Silver Member
Username: Artk

Albany, Oregon USA

Post Number: 844
Registered: Feb-05
NAD T763 will handle a 4 ohm load with smile. You can get one for about $1120 if you negotiate and can swing it.
 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 208
Registered: Feb-05
" All HK receivers will handle most 4 and 6 Ohm speakers on the market today". From their website
 

colleycol
Unregistered guest
Do you guys know what speakers H/K is talking about? I am considering Magnepan MMG, MMg-W and a MMGC for surrond sound.

"All Harman Kardon Audio/Video receivers can handle most 4 and 6 ohm speakers on the market today. However, there are some manufacturers' speakers that have a minimum impedance well below the 4 and 6 ohm nominal impedance. In this situation, the receiver will protect itself by going into standby mode. This will not damage the speakers or the electronics, but it is an indication that the speaker in question is not compatible with our receiver. Note: The continued use of the receiver with speakers that cause it to shut down can result in eventual failure of the receiver which is not covered by the warranty."
 

Silver Member
Username: Diablo

Fylde Coast, England

Post Number: 128
Registered: Dec-04
The Magnepans you are considering are probably safe to use with HK, though it would be as well to check with the dealer, or email HK about them, to check.

There are some 4 ohm speakers which actually go as low as 1 ohm at certain frequencies, I suppose those are what they are referring to. You would need something like a NAD to drive such things.
 

Silver Member
Username: Dmwiley

Post Number: 820
Registered: Feb-05
Colleycol, if you run an amp contrary to the specifications and you experience a problem, your warranty will likely be voided. If that doesn't matter to you, then by all means, get yourself a fan and blow away. Good luck.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4169
Registered: May-04



The MMG's and a HK stereo receiver have been reviewed together in Stereophile and given a very good report. Check the Stereophile archives.




 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4171
Registered: May-04


diablo - I haven't kept up with the entire NAD line, but I don't remember seeing any of their amplifiers that will deal with a 1 Ohm load. Not even momentarily. How about a model number for the amp that can do that job.




 

Silver Member
Username: Diablo

Fylde Coast, England

Post Number: 129
Registered: Dec-04
Jan,
NAD don't usually quote anything less than 2 Ohms in their handbooks or advertising, but why would they?
The current limiting circuitry will allow them to have 1 Ohm loads connected, but at higher output levels this will produce distortion. Real life speakers and sources should rarely produce a load as low as this except over a limited frequency band for a short period.

A Google search revealed many links like these -

The T760 was quoted into 1 Ohm - http://www.hifichoice.co.uk/review_read.asp?ID=1007

Stereophile tests of C370 into 8,4,2 and 1 Ohm -
http://www.stereophile.com/budgetcomponents/633/index5.html
 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 209
Registered: Feb-05
Most receivers will have trouble with a speaker that dips to a 1 Ohm impedence. Some speakers such as Snell's THX series will at certain frequencies drop to 1 Ohm or even slightly less! While the Snell's are fairly well regarded in their presentation such a characteristic in a speaker is at the least rather undesireable, and will spell trouble for even many large, powerful, multichannel amps. This could be construed as a good sounding speaker with a poor design.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4174
Registered: May-04


The Stereophile measurements of the C370 are impressive for a $699 power amplifier and even more so for an integrated at that price. I do now remember reading that review and thinking NAD had done quite a good job on this amp.

I did have to laugh a bit at: "The current limiting circuitry will allow them to have 1 Ohm loads connected ... " Yes, many amps will let you hook up a 1 Ohm load (should you be so foolish), but not many will let it stay connected while you take the amp into be repaired.

I would think the original poster might want to explore this sort of approach to amplification with a NAD if he needs serious grunt with a 4 Ohm load. Does anyone have any idea what the C370 is worth on the used market?


Eric - The Snell is one of many speakers that seem to be designed with little if any thought to what amplifiers might be needed to drive it successfully. The old Apogees and Infinity's were also in this game of 1 Ohm impedance and then up to 65 Ohms at some point for the Infinity. The Apogee was a purely reactive load with large amounts of capacitance that would eat amplifiers for breakfast. This always seemed the equivalent of what car could manage the 1/4 mile the quickest while towing a house - or two.




 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 211
Registered: Feb-05
Yes, How ironic Jan that a quite decent sounding speaker could be so miserable from an electrical standpoint. As far as receivers go folks here can forget about 1 Ohm loads. I'm very doubtful any receiver made can handle such a demand. This is rather stressful even for high current,high wattage, amplifiers. Such a demanding design probably should be avoided since there are many speakers out there that sound far better that are much more reasonable with respect to their electrical characteristics: Impedence swing, amount of inductive and capacitive reactance,etc.
 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 212
Registered: Feb-05
I forgot to mention also that i'm not really familiar with the NAD C370 or it's used value, I know much more about their AV receivers. One thing is for sure though, if your going to use the Maggies or Snell's you had better get a STOUT amp. No reciever will fare well with these speakers. Sound and Vision mag tested the Sherbourne 7000 with the Snell's and it was able to cope very well with them,producing high volume with good clarity. Sorry not sure which issue. I mentioned this amp to you before in a previous thread Jan. This amp is a KILLER! Two true power supplies with two power cords and 400W per channel/7 channels @4 Ohms and 115 lbs in weight!
 

Gvenk
Unregistered guest
For the original question, forget about any external heat dissipation systems. It just won't work if there is a heating problem within the chassis (most consumer chassis designs are not designed for external cooling to help).

For the question on Magnepans...
The smaller Magnepans (SMGs, MMGs, MMG-W, MMG-Cs) are reasonably easy to drive from any receiver that has sufficient high current (dynamic headroom) availability to quote 4-ohm power or known to be OK with 4-ohm speakers such as the receivers from NAD and H/K. The MMG-Ws and MMG-Cs are actualy 5-ohm nominal and don't dip too much down.

Even the lowly NAD L53 drives a pair of MMG-Ws just fine.

One thing to worry about if you are using 4-ohm speakers in a multi-channel set up, you have to use matching speakers all the way around (preferably of the same make AND impedence). Mixing 4-ohm and 8-ohm speakers in a multi-channel environment makes it difficult to get a good balance and some receivers, even if they have the current capability, may run out of room to adjust the gains individually sufficiently to match and balance the sound properly. There is no way to predict whether this problem will occur until you actually try it out.
 

Silver Member
Username: Eramsey

South carolina United States

Post Number: 213
Registered: Feb-05
Perhaps your right about the Maggies Gvenk. What I'm referring to are the 6' tall electrostatic panel speakers,which are difficult for an amp and extremely difficult for a multichannel receiver to handle. I myself have 4 Ohm right and left fronts, 6 Ohm center and 6 Ohm right and left surrounds. Again though, these specs are rather meaningless as these impedences only occur at certain frequencies. My HK has no trouble at all with these, in fact it runs for hours before it even gets warm. I think the original poster should try the speakers with the Rotel if it is able to play for several hours without getting hot or going into protection then the speakers in question are probably safe. A cooling fan seldom hurts but he should make sure that the fan pulls the warm air away from the receiver vents, not blowing air into the receiver.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4177
Registered: May-04


Gvenk - I'd like you to clarify a statement or two:

"The smaller Magnepans (SMGs, MMGs, MMG-W, MMG-Cs) are reasonably easy to drive from any receiver that has sufficient high current (dynamic headroom) availability to quote 4-ohm power ... "

The ability to deliver 1) high current; 2) dynamic headroom and 3) [quoted] 4 Ohm power are not one and the same thing. It is quite possible for an amplifier to deliver on one of those properties without managing the other two. Could you please explain what you mean by that remark.

Also I have found no reason to believe mixing impedance loads in a multichannel amplifier system should cause any particular problems unless the power supply of the amplifier is very poorly designed. Each amplifier is a separate unit and balancing levels should not be a substantial difficulty. At the most extreme situation the difference in the amount of power delivered to an 8 Ohm load vs. a 4 Ohm load is 1/2 the power or the equivalent of 3dB. Most real world situations should prove to be even less dramatic in actual volume differences. Please, once again explain why you believe this is a situation to be avoided. Can't most receivers manage to adjust for 3dB difference in level?




 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 4178
Registered: May-04


Regarding the intent of the original post; it is unfortunate if the technical assistant at Rotel led colleycol to believe the only problem that would arise from running an impedance load beneath the capacity of the amplifier is a matter of heat dissipation. The essential problem is one of the power supply not having the capacity to deliver voltage and current in large enough quantities and at a fast enough rate to acommodate the circumstances. At this point it is the output section of the amplifier drawing current literally from the AC receptacle which causes the heat. In this condition the power supply rail fuses will almost always blow long before the amplifier actually overheats. So you can see there is much more to this than an issue of heat disipation.




 

colleycol
Unregistered guest
I guess I will have to go with a NAD or H/K for my setup. I think I can find a NAD T763 for $999 refurbished and I saw a H/K 7003(?) for $900 refurbishes on ebay by Harmon Audio.

Thanks guys for the input, I learned alot.
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