[rabident]

Well not exactly since there's no clock, but in the same way you can drop the temperature of your CPU transistors and then push the Mhz up - could I drop the temperature of my amp's transistors/heatsinks and push the wattage potential up?


With the right cooling could you, say, run an amp into a 2 ohm load without frying it?

 

[eaadams]

u need 2 ohm speakers ... who makes 2 ohm speakers

 

[JonFo]

Quote:

Originally posted by eaadams: u need 2 ohm speakers ... who makes 2 ohm speakers

Um, Martin Logan has some that will dip below 2 ohms.


Both the CLS and the Monolith III hit 1.5 ohms. It takes a well-designed amp, capable of high current flow to deal with these speakers.


Why bother with cooling and other tweaks. Just get an amp that does not generate any heat worth mentioning in the first place, can drive any load, and has tons of power. They do exist, their called Sunfires.


I use Sunfire Cinema Grand and Sunfire Stereo 300wpc to drive my Martin Logans, and even after hours of very high volume sessions, the amps are still cool to the touch. Any other amp would have been in flames, or its thermal circuits shut it down. I know, I've seen several well-respected brands of amps do this when driving M-L speakers.


And a Sunfires ability to double it's output for every halving of the impedance is a rare thing to find (the 300wpc puts out 1,200wpc into 2 ohms). This is something that does impact the sound of the amp/speaker combo. If the amp can't deliver the current required at the frequencies where low impedance exists, then it will alter the sound the speaker generates.

That's why I'll only ever purchase and amp that can deliver linear power across the impedance range. That restricts the field to a very small number of amps, most of them big, expensive and inefficient.

Makes a Sunfire look like an efficient bargain ;-)



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Jonathan

 

[rabident]

That's why I asked about the 2 ohm load. Maggie's are 4 ohm speakers. My amp is bridged making, so they'll look like a 2 ohm load to it. I can proabably overcome the heat problem with a cooling tweak, but is that the only issue?


As far as getting a better amp, I don't think that's the best option for me. I bought as much amp as I could afford. Now I have a some extra cash, but I don't really want to sell my 2 month old amp at a loss and get another one if I don't have to. I have to build/buy a cabinet for my gear anyway. I was hoping that I could include a relativly low cost, but effective cooling solution and get more out of my existing amp.


Will keeping it cool enough prevent it from death? Will it have a negative effect on the sound quality? I don't listen to very loud volumes, so is 2 ohms ever a problem at low volumes? I checked my owners manual and it didn't say anything about 4 or 2 ohms. Only 75w per channel into 8 ohms and I've got the channels bridged for 150w per channel.

 

[JonFo]

Quote:

Originally posted by flegal: ESL speakers don't need high current, even if their impedance drops to very low levels. How many amps on the stators? Close to 200 mA or so for most ESLs. How many volts? Lots, in the kV range.

Apples and oranges there. ESL systems have two sources of power, one is the panel energizer, and yes that is high voltage, low amperage. This provides the power gradient needed to make the stators easier to drive. But it's driven by the internal power supply of the speaker itself (that why ESL have an AC plug).


The audio power amplifier 'sees' and drives the two stators (perforated metal front and rear sections of the ESL). It this circuit that has extremely low impedance and requires massive amounts of current to adequately drive. Read a review of an ESL that includes impedance charts in it. Makes a roller coaster look tame ;-)


For more on ESL theory and operation, read the excellent white papers at the Martin Logan web site: http://www.martinlogan.com





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Jonathan

 

[JonFo]

Quote:

Originally posted by rabident: That's why I asked about the 2 ohm load. Maggie's are 4 ohm speakers. My amp is bridged making, so they'll look like a 2 ohm load to it. I can proabably overcome the heat problem with a cooling tweak, but is that the only issue?

Warning! Danger Will Robinson, danger...


Problems guaranteed. You are correct, the critical piece here is 'Bridged amp'. Most solid-state amps have a problem with low impedance loads when bridged. A typical amp that handles 4 to 8 ohm loads just fine, will stipulate a 6-ohm lower limit when running in bridged mode. The intricacies of the why's can best be described by others.


With your 4ohm Maggies, the bridged amp will 'see' them as closer to a 2ohm load. Therefore, unless it's a Krell or a Sunfire, I'd be very careful here. Not only are you vulnerable to thermal shutdown, but also one has to wonder how the amp behaves in ultra low impedance ranges. It might clip, distort or also shut down. Some amps have 'short circuit' protection (besides a fuse) that will cut the amp out if it sees less than one-ohm impedance on the outputs.


Now, if you still want to cool your amp, I would recommend using low speed but high volume (large diameter) fans placed strategically around the amp. These are less noisy than smaller fans.


But even so, the thermal wear on the unit is going to affect it in the long haul.


You might just want to live with the 75Wpc normal mode on your amps.



------------------

Jonathan

 

[Gary McCoy]

The equivalent to overclocking an amp is to bias the amp to a different operating point. The common practice of biasing the output stage of an amp into Class AB or even the Class B region, then taming the resulting distortion with gobs of feedback, does not result in the best sound. (It does produce more rated power with a smaller/cheaper power supply.) Audiophile-quality monoblock amps are available which are biased Class A and utilize little or no feedback. They sound wonderfull but they are expensive and Class A operation dissipates lots of heat for the rated power.


Another option to increase power in a fairly linear fashion is to increase the power supply voltage. At some point, you exceed the voltage rating of the output devices and they die. The reason this works is the manufacturers reduce the PS voltages to increase reliability, building margins into the design which effectively trade off performance for reduced warranty support expenses.


In your case, I don't reccomend either practice, because you asked. Both of these options are best pursued by someone with a fairly good knowledge of electronics, who has and can read the circuit schematics for his equipment, and who has test equipment and soldering skills. The physics of the practices work against the desired result in any case - the modest power increases possible are not very audibly different from the original. I'm an EE by trade who works in the computer field but I've been tweaking and building my own audio gear for a couple of decades.


What is it exactly that leads you to believe you have not enough amplifier power? Did you pair your present medium power amp with terribly inefficient speakers? Are you using electrostatic panels or ribbons or other very low output speakers? There are lots of good alternatives to such today. You may even be able to pick up some very appreciable changes in volume by making use of "room gain", simply by re-positioning your speakers or changing their distance from a wall or corner. Perceived volume is largely in the mid-bass frequencies which are definately affected by room gain, especially in smaller rooms. But I'm puzzled by your mention that you do not listen at high volumes - is your amp at or near the maximum volume setting now, because of your speakers?

 

[rabident]

Gary -


I wanted to use my briged amp to drive 4 ohm electrostatic (Magnepan) speakers. That would be running the amp at 2 ohms and I know the amp would run very hot. My question was could I run an amp into a very low impedance if I kept the heat sinks cool enough using active cooling. I know that heat is a limiting factor in transitor based electronics.


So if I take care of the heat problem, am I safe running my amp at 2 ohms? Even if it's not rated for to drive 2 ohm loads? If the answer is no, then could someone tell me what the factors are that limit how low of an impedance can be driven by a given amp?

 

[Gary McCoy]

OK, I believe I understand your intent. (By the way, I LOVE electrostatics but I haven't owned any for over 20 years, since selling my Infinity Servo Static 1's. I still have some old but sweet electrostatic headphones.)


A basic bit of theory applies to what you are attempting: the maximum power transfer to the load occurs when the source impedance (the amp) and the load impedance (the speaker) are exactly equal. If your amp was designed to tolerate both 4 ohm and 8 ohm speakers, the designer probably set the internal amplifier impedance at a compromise between those two values. In bridged mode, the two amps togather would (ideally) deliver twice the power to the same load as a single amp in a standalone configuration.


The rub comes in because we are talking about impedance, not DC resistance. Directly-driven ESLs (which I think include Magnepans) are a huge capacitive load, which varies all over the place as a function of frequency. Transformer-coupled ESLs have the opposite problem, they are highly inductive. The amp impedance expressed in ohms is a function of the frequency, and in bridged mode not only does the power double, so does the variation in source impedance (the bridged amps). Directly-driven ESLs have a higher impedance with lower frequencies, while impedance decreases at higher frequencies, and there is interaction with the amp internal impedance. Such a load is highly likely to cause a destructive amplifier oscillation at a high frequency (I have heard that high pitched, barely audible screech which often means either your amp or your ESLs or both need repair).


Making matters worse, the amp's power supply may not be adequate to deliver 2X normal current in steady operation. The minimum load impedance could have been specified with this power supply limitation in mind, even if the output devices can tolerate the extra power - hard to say without examining the design. Another reality factor is that unless the output devices of both bridged amps are exactly matched - not just within the individual amps but from one amp to the other - the amps will load each other with more instability the result. Very high quality amps intended for bridged operation have had output devices perfectly matched to minimize such problems.


Forgive me, but if you are unhappy so soon after your amplifier purchase, it seems likely you neglected the basic hifi test principal: audition the exact equipment combination you think you want, either in your home or at least in a very similar sized room. Make sure that all factors including maximum volume and amplifier headroom are satisfactory by playing demanding source material. Most high-end dealers will work with you and offer favorable terms and let you exchange equipment for little or no cost for a reasonable period (as long as they make the sale).


As for "overclocking" your amp - with the same combination of speakers and amps, I would not try it myself. The risk of damage is too great. On at least one occasion, I repaired my ESLs and amp togather, it hurt financially. In your situation, I would experiment with speaker placement within the room and in relation to my listening position, to find a more ideal solution. You may trade off other factors for more volume with room gain - such as a very small "sweet spot" when listening. In any case, enjoy the music!