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AKG K1000 Impedance and amplifier load

post #1 of 21
Thread Starter 
How does an amplifiers power rating react when connecting the AKG K1000 rated at 120 ohms to the speaker outputs as recommended?

Amplifier power and current demand rises when impedance drops, Correct? Will the 120 ohm load present a problem?

Are most amplifiers rated at 8 and 4 ohms comfortable with this high impedance load?

John
post #2 of 21

Output Power

Normally an amplifier's output power is directly proportional to the impedance of the load being driven.

E.g.- An amplifier rated at 50 watt/channel into 8 ohms will deliver 100 watts/channel into 4 ohms, unless the amplifier circuits are intentionally designed to be current limited. Some amplifier designs can drive loads down to 2 ohms or even less. With very low impedance loads, the maximum amperage rating of the output fuses of the amplifier become the limiting factor. The fuses would blow long before the maximum theoretical power level is reached.

Conversely, the same 50 watt amp would capable of delivering 25 watts into a 16 ohm load, 12 watts into 32 ohms, 6 watts into 64 ohms. and 3 watts into 128 ohms.

Some amplifiers, most McIntosh amps come to mind, use output transformers that match the output impedance of amp to the load being driven. With this design, the output power level is always the same, within the range of the different taps available at the output transformer, i.e. 4,8, or 16 ohms. The ouput of a 50 watt McIntosh amp equipped with autoformers (McIntosh's trademark name for output transformers) would be 50 watts at any of the above speaker impedances.

A 10 watt/channel amp (rated at 8 a nominal ohms), which is the minimum recommended power output for driving the K1000 Earspeakers, would be able to deliver approximately 0.625 Watts continuously at the rated impedance of 120 ohms for these headphones. This does not seem like much power, but remember that most headphones need far less than 1 Watt to achieve a 90db level of sound. 90db is plenty loud, loud enough to cause hearing damage over an extended listening period.

Also many amps can deliver, for brief fractions of a second (a few hundred milliseconds), power output levels that are 50% higher, even 100% higher (double their rated power) or more without clipping. This is a good match to the power demands of most music, where the average power levels are 10db or more below the peak level. 10db represents a 10X increase or decrease in power demand.

A seemingly modestly powered 10 watt/channel amplifier can handle the peak power demands placed on it because the average power output is rarely even 1 Watt of power, so a 10db musical peak would require no more than 10 Watts of output power from the amp to avoid clipping the signal. Factor in some amplifier output headroom of 50-100% for momentary peaks and the 10 watt amp should be adequate for producing sound levels as loud as most people would ever require, assuming either an average sized room and loudspeakers of average or better efficiency, or headphones capable of producing at least 90db sound levels with less than 1 Watt or less of input power. Also remember that amplifier clipping, while undesirable, is not usually audible during brief musical peaks.

Increasing the size of the room significantly, or selecting low efficiency speakers or headphones, while turning up the volume just a bit, and the power requirements could easily double. Remember that a 3db increase in sound level, which is audible but not a dramatic increase in volume, will double the power requirement.
post #3 of 21
Thread Starter 
Thanks for the reply mkmelt.

Quote:
A 10 watt/channel amp (rated at 8 a nominal ohms), which is the minimum recommended power output for driving the K1000 Earspeakers
I was planning on driving them with a SS amp rated at 30W per channel @ 8 ohms. It sounds like this might be ideal. Or should I consider stepping up to 85-100 watts per channel @ 8 ohms with the 120 ohm load for some head room?

I know some amplifiers become unstable driving low impedance loads unless designed to do so,
Can an amplifier be affected when presented with a high impedance load such as 120 ohm?

John
post #4 of 21
Well, I'm using an ASL tube amp rated at 8wpc for the K1000. And they sound fantastic with plenty of "headroom". The K1000 are hooked up to the 8ohms terminals. I've tried the 16ohms terminal but they didn't sound as good, can't recall why though.
post #5 of 21
What type of amp? If you have the manual look for "Dynamic Headroom" I believe this is the peak power (not continuous power) before clipping. Mine says 3 db, which would be double what its power rating is. 60 watts continuous and 120 watts peak power.

Since they recommend 8-10 and yours is 30 watts, you should be set.
post #6 of 21

problems with high impedance loads

I suppose it is possible that a particular amplifier may have problems driving a high impedance load, but I can't think of any headphones that would have a higher impedance than 300 or 600 ohms, and even then only at one or a few resonant frequencies for the earphone driver.

Also, an amplifier could become unstable if the backwards EMF generated by the voice coil of a loudspeaker (kind of like a reflection of the original output signal) was able to come back through speaker terminals and reach the driver circuit. A sufficiently high impedance at the at output terminals would minimize the possibility of this happening.
post #7 of 21
Thread Starter 
Quote:
What type of amp? If you have the manual look for "Dynamic Headroom" I believe this is the peak power (not continuous power) before clipping.
I am going to use a Parasound ZAMP

I will feed it from the preouts of a Headroom MOH, Wheatfield HA-1 and Mapletree Ear+ via a line level switcher for a variety of pre amp selections.

John
post #8 of 21
Quote:
Originally posted by jvh
I was planning on driving them with a SS amp rated at 30W per channel @ 8 ohms. It sounds like this might be ideal. Or should I consider stepping up to 85-100 watts per channel @ 8 ohms with the 120 ohm load for some head room?
30Wpc SS will work just fine (and yes, I'm speaking from experience on this one ) 80W would be complete overkill.
post #9 of 21
My AKG K1000 is connected to the 16ohm terminals of my ASL AQ-1005DT amplifier and the sound is fabulous. I didn't try connecting to the 8 ohm terminals.
post #10 of 21
Resurrecting a VERY old thread, but it's the closest I can find to the topic.

Most basically, I don't understand amplifier math --- ohms, watts, and so on.

So there are two amps that I am considering to drive the K1000s. I'll just give the available specs without giving the names (though some of you might be able to guess).

Amplifier A:
Power Bandwidth:

Power Output driving Senn HD600s: L/H 650 mW

Power Output driving Grado RS1: L: 500mW/ H 150mW

Source Resistance: L=3ohms/ H=12ohms

Gain: L=8dB/ H=18dB

Wide band noise less than 250uV

Amplifier B:

16 Watts

Frequency Response: 6Hz ~ 300kHz, -1dB at 8 ohms

Output: Max. output 8 Vrms (8W at 8 ohms per channel, 12W at 4ohms)

Output Resistance: Zo<0.01 ohms

Power Input: 30VDC 2A max

Is that enough information to determine which might better drive the K1000s? A post above says that 10 watts/channel would be sufficient, and if so, that means Amp B will work. But what of Amp A?
post #11 of 21
Power = Voltage squared divided by impedance.

For Amp A when driving the Sennheiser: Sqrt (.65 * 300) = V = 13.96Vrms

The max power for the 120 ohm K1000 is 1000mW or 1W. Sqrt (1 * 120) = 10.95Vrms.

Amp A can generate more maximum voltage than the K1000 can accept. So this means Amp A can drive the K1000 to maximum power and still have some headroom.
post #12 of 21
Thanks very much for simplifying! Any thoughts about amp B?
post #13 of 21
Quote:
Originally Posted by West726 View Post

Amplifier A:
Power Bandwidth:

Power Output driving Senn HD600s: L/H 650 mW

Power Output driving Grado RS1: L: 500mW/ H 150mW

Source Resistance: L=3ohms/ H=12ohms

Gain: L=8dB/ H=18dB

Wide band noise less than 250uV
I'm not terribly fond of my K-1000 out of my Zana Deux. Even Craig told me that it's not the best combination. It does work, but it won't bring out the best in the K-1000. I much prefer the K-1000 from the Moth (SE 2A3, 3W) or a Conrad-Johnson MV52 (push-pull EL34, 45W).
post #14 of 21
Quote:
Originally Posted by Donald North View Post
Power = Voltage squared divided by impedance.

For Amp A when driving the Sennheiser: Sqrt (.65 * 300) = V = 13.96Vrms

The max power for the 120 ohm K1000 is 1000mW or 1W. Sqrt (1 * 120) = 10.95Vrms.

Amp A can generate more maximum voltage than the K1000 can accept. So this means Amp A can drive the K1000 to maximum power and still have some headroom.
If you do the same math on the rs1 it only comes out to 2.19 Vrms(using the high output 150mw). The output isn't 0 ohms and is going to change a lot on different loads. I don't think it will work well with a K1K at all. The amp will most likely have to be nearly maxed out just to get 95-100 db. This is all assuming the amp will be able to swing the current fast enough to make the K1K sound good too.

Also I used 2 shanling ph100's bridged to run mine before I got the F1. A single ph100 is rated at about 300mw for 128 ohms so 1.2w when bridged. On some recordings that were just not as loud as most, like old Iron Maiden, I had to turn the shanlings up to 9 out of 12 on the dial. Just another reason why I don't think that amp will work.

Edit: The current output for the max power on the on 300ohms would be 46.6ma. On the rs1(using high output impedance again) it would be 68.5ma. For 1 watt into the k1000 you will need 91.3ma = beyond what the amp can do.
post #15 of 21
Quote:
Originally Posted by Uncle Erik View Post
I'm not terribly fond of my K-1000 out of my Zana Deux. Even Craig told me that it's not the best combination. It does work, but it won't bring out the best in the K-1000. I much prefer the K-1000 from the Moth (SE 2A3, 3W) or a Conrad-Johnson MV52 (push-pull EL34, 45W).
Busted. No fair figuring out which amp it is from the specs. I'm trying to decide whether I'd get a better sound out of the ZD or something cheap like the Winsome Mouse or the Big Joe. I love the ZD with everything else; I'd just like to have a feel for things before I drop the $ on a K1000. So now that I've spelled it out, further thoughts?
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