[jpelg]

OK, although I think my retinas are permanently scarred after reading PinkFloyd's Mullard post, I'll manage to type out my query for the day.

It seems that low imdepance cans match well with amps that provide a high current output. Now I have no idea, from a technical standpoint, what that means exactly or how it is done by the electronics. But assuming that low-impedance cans (ie. Grado/Sony/A-T) match well with high current output amps, would the same amp necessarily not match well with a high impedance can (ie, Sennheiser)? Are there other variables at play here? If so, what are they?

 

[mkmelt]

It's more about being able to handle relatively large voltage swings, peak to peak, when driving high impedance loads than at the normal speaker imedances of 4 and 8 ohms.

For a good explaination, read the following thread:

http://www4.head-fi.org/forums/showt...threadid=20954

 

[ServinginEcuador]

According to MarkL the Melos pre/head amp is really incredible at driving low impedance cans, but is bad at driving high impedance cans. Go figure!! Tubes are supposed to be better a outputing voltage thant current, which explains why the MG Head works so well with the Sennheiser's 300ohms of resistance. I think that the solid state output on the Melos explains why it works the way it does.

Basic Elcetronics lesson of the day:

Impedance is just the resistance to current flow. When you have low impedance cans, the demand on the amp to push more and more current can be taxing. Higher impedance cans make it easier since the demand for current is lessened. The voltage out of an RCA jack is independent of headphone resistance, the only variable is current, and that depends on resistance.

Here's the skinny. E=I*R or voltage is equal to current times resistance. Transpose the equation to solve for current and you get I=E/R Current is directly proportional to viltage and inversely proportional to resistance. Big words that mean as voltage increases current increases, and vice versa. As resistance increaces current decreases, adn vice versa.

 

[jpelg]

Thanks ServinginEcuador for that nice explanation. I am here with you (directs my pointer and pink fingers between my eyes and yours).

So what I am after really is, can one amp serve both types of headphones with equal aplomp? By definition, my guess the answer is no. Can anyone point to specific amplifier examples to the contrary?

 

[Hirsch]

Quote:

Originally posted by jpelg So what I am after really is, can one amp serve both types of headphones with equal aplomp? By definition, my guess the answer is no. Can anyone point to specific amplifier examples to the contrary?

Berning MicroZOTL
Musical Fidelity X-Can v2 w/ X-PSU
Grado RA-1
Grado HPA-1
antness' Gilmore amp
Headroom Max
Melos SHA-1 (worked fine with HD-600 last time I tried it)
Corda HA-1 (has high and low impedance outputs)
EAR HP4 (uses separate transformers for high and low impedance cans)
Fisher 400 (has separate impedance taps up to 16 ohm)

That's off the top of my head...

 

[jpelg]

So basically, if an amp has a high-current output to service low-impedance cans well, there is not necessarily a tradeoff or downside to using that same amp with high-impedance cans also?

 

[ServinginEcuador]

Quote:

Originally posted by jpelg So basically, if an amp has a high-current output to service low-impedance cans well, there is not necessarily a tradeoff or downside to using that same amp with high-impedance cans also?

Yes and No. Sometimes the mismatch is enough that some aspect of the music gets smeared, or degraded sounding. Take for example the EarMax headphone amp. They designed two models, the standard and Pro. The standard was designed for high impedance cans, like 200+ ohms, while the Pro was designed to handle like 32-1000 ohms. To pair them up with the wrong set of cans MIGHT change the sound enough to make it not so enjoyable.


Electronically the difference between a set of 40 ohm and 300 ohm cans isn't that great when you're talking about headamp outputs. The voltage of a headphone amp averages about 2-3v, with peaks of 5-8. Take the 40ohm cans and you come up with a mere .05A min to .2A max, while the 300 ohm cans would draw .0067A min and .0267A max. These numbers might seem large, but they are actually quite tiny. Remember that a wall circuit is capable of 15 amps.


PS - to clear up the misnomer, an amp doesn't vary the output current on its own. Current is the by-product of the amount of both electricity and resistance. You can't push more current thru the same amount of resistance, like headphones. All you can do is switch headphones to change output current. To say that an amp is high current means that it is capable of driving low impedance values and large amount of voltage/power.


Basic electronics lesson for today - a transistor cna be configured in one of three ways: common base, common emitter, and common collector. What that means is where the input comes in and output goes out. The one left out is called "common" since it is common to both input and output as the signal flow thru it also. Here's a chart to teach you about what each one is capable of, characteristics, and circuit gain

B E C describes the circuit design - common base/emitter/collector
V P I best circuit usage - voltage/power/current capability
A B G gain amount - alpha/beta/gamma
L M H input impedance - low/medium/high
H M L output impedance - high/medium/low
I O I phase comparison of input to output signals - in/out/in

Post any questions about this info and I'll do my best to elaborate!!

 

[jpelg]

Quote:

To say that an amp is high current means that it is capable of driving low impedance values and large amount of voltage/power.

How? What is(are) the variable(s) in the amp that allows it to do that as opposed to an amp that does not?

 

[ServinginEcuador]

Power supply.
Wiring of output transistor/tube.
Circuit design of output gain circuit.
And possibly more, but my electronics knowledge doesn't extend into amp designs like this.

 

[morsel]

A rough rule of thumb: Low impedance phones need higher current, high impedance phones need higher voltage. If your amp can provide high current at high voltage, you are set.

 

[useridchallenged]

So... if I bolt the speaker outputs of some monster amp - like a Krell or Levinson - directly to a Sennheiser HD 600, then I don't need an impedance matcher between the amp and the headphone because the amp has high voltage and high current capacity?

Seems too easy, but then again, most headphone amps are relatively low power, so impedance matching may be a much bigger deal.

Does anyone have any experience with connecting the speaker outputs of some high-end high power amp to their headphones? If so, how did your experience compare with a headphone amp?

 

[mkmelt]

Modern power amplifiers intended to drive loudspeakers are usually designed to deliver full bandwidth audio into either 4 or 8 ohm loads. A few are rated down as low as 2 ohms. Rarely are power amplifiers designed for high impedance, i.e. 120, 300 or higher loads. With high impedance loads, some amplifiers may suffer from roll off of frequency response at both ends of the spectrum. So trying to use one of these to drive headphones, especially high impedance headphones may yield less than great sound, but it is worth trying.

That said, the power supplies in big amps such as Krell, Levinson, and Rotel will have no problem providing the peak to peak voltages needed to provide peak power, say 1 watt or so, into such a high impedance load. Most of the headphones in this category don't need even a fraction of a watt to reach levels louder than most people would want to listen to music. One model of headphone, the AKG K1000 earspeaker, is noted for being of low efficiency and high impedance (120 ohm).

Many solid state amplifiers can't provide the needed voltage swing to drive this particular headphone to a satisfactory level. On the other hand, many tube amplifiers can drive the AKG K1000 headphones to very satisfactory sound levels, not because they have exceptionally high power output, but because the design of these tube circuits have the advantage of being better able to provide the high peak to peak voltage swing needed to drive a high impedance load and produce power level of 1 or more watts peak power.

An impedance matcher is a type of transformer. As with using any transformer you are stepping up or stepping down a given input voltage to get to a desired output voltage. But transformers can also effect the signal being passed through them and thus act as filters. The better the quality of the construction and assembly of the transformer, the higher the quality of the resulting audio signal passing through the windings of the transformer. So if you are going to put a transformer in the output signal path, it needs to be of very high quality if you are going to achieve good quality audio at your speakers or headphones. Also, since the impedance matcher is used with a variety of amplifiers, the results will vary.

Many tube amplifiers need to use output transformers because the natural output impedance of the tube circuit is otherwise too high to be able to be an efficient match to the impedance of the desired speaker or headphone. There are a few tube amplifiers that can directly drive high impedance headphones, and even some that can drive low impedance designs but these are the exception.

Try using your amplifier without a matching transformer first, to see if you you really need one.

 

[Joe Lau]

Quote:

Originally posted by useridchallenged So... if I bolt the speaker outputs of some monster amp - like a Krell or Levinson - directly to a Sennheiser HD 600, then I don't need an impedance matcher between the amp and the headphone because the amp has high voltage and high current capacity? Seems too easy, but then again, most headphone amps are relatively low power, so impedance matching may be a much bigger deal. Does anyone have any experience with connecting the speaker outputs of some high-end high power amp to their headphones? If so, how did your experience compare with a headphone amp?

Yes ! You are correct. If you use a high power amplifiers to drive Headphone amps will kill your ears & Can !

You should limit the Volatage swing to reasonable level.
Lower output impedance is better ? May be true but actually not ! (My own opion). It will damp your Headphone driver units too much. Sound will not life ! Why MG-Head OTL sound good ? It output impedance not too low.

 

[JaZZ]

Quote:

Originally posted by ServinginEcuador ...Take for example the EarMax headphone amp. They designed two models, the standard and Pro. The standard was designed for high impedance cans, like 200+ ohms, while the Pro was designed to handle like 32-1000 ohms. To pair them up with the wrong set of cans MIGHT change the sound enough to make it not so enjoyable.

The reason some low-impedance headphones might not sound at its best with the EMP is its high output impedance (I guess it's around 120 ohm or so). Neverteless it sounds great with Grados (if you like the Grado signature) and even the 12-ohm Sony F1 – just because their impedance curves are very flat, so there's little coloration despite the high serial resistance.