What's the correct math for ohms/watts

Nightfall

I find different things online so I ask the gurus here. How do you do the math to figure out how many watts an amp/receiver will put out at a certain impedance. I realize this only gives you a rough figure but good enough for me and I want to know how to calculate it correctly.

Let's say you know piece of equipment X will put out 90x2@8 ohms and 120x2@4 ohms. What will this same piece of equipment put out at 30 ohms?

heiney9

You really can't as it's not a linear measurement. As frequency changes so does impedance, so it's constantly changing as the musical signal changes. There is no linear formula, it's an algorithm. Certainly you can use bursts of single frequency test tones, but then you are far from the real world and those measurements really don't mean much when relating to listening to real music or reflect the environment you are listening to music in.

H9

heiney9

Think of it this way; it's like calculating horsepower for an automobiles engine, you can get a raw number based on the design parameters and parts used in the motor. But it's relatively meaningless because of all the variables involved to get that power to the pavement and get the car moving.

I've heard 20wpc systems all the way up to 350wpc systems. The number doesn't mean much when it's an average figure in a very specific set circumstances of which said circumstances don't happen in real life; ie.....listening to musical content.

H9

Nightfall

Does there exist such a device that you can wire into the speaker taps that creates a sort of "dummy" load and measures output in watts?

megasat16

Yes, it is called a dummy load resistors and parts express sells them. It come in 4 ohm or 8 ohm version with 100W, 200w power ratings.

In order to calculate power, you need to know the input voltage to the amp, gain of the amp, AC ammeter (current meter) between the load and the amp speaker terminal, and the voltage at the dummy.

May I ask why you want to check that? It's a little more complicated than just having some fun with the amp.

heiney9

Nightfall wrote: »

Does there exist such a device that you can wire into the speaker taps that creates a sort of "dummy" load and measures output in watts?

Do you listen to dummy loads? It doesn't really relate to how something performs in the real world when listening to a musical signal. I don't understand what you hope to accomplish or discover?

Nightfall

For running headphones off of an amps speaker taps. This is more common than you might think and some headphones have an impedance as high as 600 ohms so I'd like to know what I'd be feeding them with different equipment I have and if I'm being safe or if it would be a good investment to get a smaller less powerful amp for this purpose.

megasat16

You will find it's extremely unpleasant to run headphones off a speaker terminal. Some preamps and most processor have headphone jack and it's what you want to use.

Nightfall

megasat16 wrote: »

You will find it's extremely unpleasant to run headphones off a speaker terminal. Some preamps and most processor have headphone jack and it's what you want to use.

123 pages of people running various headphones off a 50x2@8 ohm amp

http://www.head-fi.org/t/629352/he-500-lcd2-d5000-dt770-sr80-on-a-speaker-amp-emotiva-mini-x-a-100-project

megasat16

There is an easy way but you want the hard way to do it, Get your read on.

Are you handy with electronics and tools and make sure not to blow up while doing it?

cnh

Not sure what you're trying to do. But I assume it involves the phones in your sig. So let's take a look at the specs:

10-40Khz Freq response
100db @ 1mW "sensitivity". This is VERY sensitive meaning a mere .001 watts will yield 100db which is very loud.
500mW Maximum input
30 ohms (so this means you have easy to drive phones)

Think of it this way. One or two watts of output from a H-phone amp is a lot, will drive most phones quite well--and you'll probably never use that much unless you want to go deaf.

The question still remains, if I'm understanding you, "what is the headphone section of my amp putting out?" Not sure there? But lots of amps do specify what the headphone "output" is in their literature or used to.

cnh

Nightfall

cnh wrote: »

Not sure what you're trying to do. But I assume it involves the phones in your sig. So let's take a look at the specs:

10-40Khz Freq response
100db @ 1mW "sensitivity". This is VERY sensitive meaning a mere .001 watts will yield 100db which is very loud.
500mW Maximum input
30 ohms (so this means you have easy to drive phones)

Think of it this way. One or two watts of output from a H-phone amp is a lot, will drive most phones quite well.

The question still remains, if I'm understanding you, "what is the headphone section of my amp putting out?" Not sure there? But lots of amps do specify what the headphone "output" is in their literature or used to.

cnh

I forsee myself trying and experimenting out more expensive/harder to drive headphones in the future, trying to find what I'm looking for, before doing too much more to my stereo setup (I had planned on a Pioneer SC unit) being in an apartment and all. Perhaps a pair of the planar HiFimans. Just trying to plan ahead for that.

cnh

Got you. Planars are TOUGH to drive, no doubt. Even my Bravo amp which can handle almost everything in my sig fine, would probably be taxed by a high grade planar.

But there are a lot of amps out there for, let's say, TOTL HiFiMans?

Might want to PM Mike, FACE, as he has experience with powering those, etc. Could probably recommend something in a number of price ranges?

cnh

Nightfall

Also, neither of my receivers (especially the AVR) get my headphones to a point of very loud. The CA-1010 does better but once it gets to the volume I want the bass falls flat on it's face as if it's just gone. I can only assume this is a power issue and aside from planning ahead on harder to drive headphones would also like to test this theory.

Something about the output impedance of the 1/4" jack not being suited to the headphones impedance? 1/4" jacks on receivers are setup for a higher impedance than 30 ohms as most headphones are 150 ohm+ ?

Nightfall

cnh wrote: »

Got you. Planars are TOUGH to drive, no doubt. Even my Bravo amp which can handle almost everything in my sig fine, would probably be taxed by a high grade planar.

But there are a lot of amps out there for, let's say, TOTL HiFiMans?

cnh

From reading the thread I linked everyone is saying to can get as much performance using this $200 mini Emotiva amp as much more expensive dedicated headphone amps. I'm sure there are differing SQ's, especially when you get into the tube headphone amps, but this seems like a cheaper option with plenty of power for anything you'd hook up to it?

cnh

So what they're doing is running cable from the speaker leads on the mini Emotiva to the headphones directly? It would seem to me if you did that with any amp you'd have gobs of power if it was a clean connection, so now I'm confused.

People have also, somehow used T-amps (Topping, etc.) in this way--also a cheap solution since you can get one of those 50 watt x 2 for less than $130.

cnh

Nightfall

cnh wrote: »

So what they're doing is running cable from the speaker leads on the mini Emotiva to the headphones directly? It would seem to me if you did that with any amp you'd have gobs of power if it was a clean connection, so now I'm confused.

People have also, somehow used T-amps (Topping, etc.) in this way--also a cheap solution since you can get one of those 50 watt x 2 for less than $130.

cnh

Correct. You get one of these cable companies, or yourself if you're inclined, to make a short cable with 4 banana plugs (or spades, what have you) on one end going to a 1/4" female on the other.

Most receivers and AVR's 1/4 jacks are run off the same amp the speaker taps are run off of, but with a highly restrictive resistor in place. Essentially all you're doing is the same thing without the resistor and by the time you figure you're running a 50 watt @ 8 ohm amp at 600 (or whatever) ohms it's only putting out a few watts. Obviously you wouldn't want to do this with a several hundred watt amp. This was the reasoning behind me starting this thread to begin with. Can I try this off my CA-1010's speaker taps which is 90w @ 8 ohms or should I just buy the smaller and weaker Emotiva?

Edit: The amp also has to be common ground as most headphones have 3 wires.

megasat16

Nightfall wrote: »

Correct. You get one of these cable companies, or yourself if you're inclined, to make a short cable with 4 banana plugs (or spades, what have you) on one end going to a 1/4" female on the other.

Most receivers and AVR's 1/4 jacks are run off the same amp the speaker taps are run off of, but with a highly restrictive resistor in place. Essentially all you're doing is the same thing without the resistor and by the time you figure you're running a 50 watt @ 8 ohm amp at 600 (or whatever) ohms it's only putting out a few watts. Obviously you wouldn't want to do this with a several hundred watt amp. This was the reasoning behind me starting this thread to begin with. Can I try this off my CA-1010's speaker taps which is 90w @ 8 ohms or should I just buy the smaller and weaker Emotiva?

Edit: The amp also has to be common ground as most headphones have 3 wires.

People are not very smart these days thinking they should because they can! But if you want, you can do it with any amp. But it's very unpleasant to listen to through that conversion if you think logically.

Most preamps that have a headphone output comes from the preamp stage (not through the amp) and it usually is very clean signal and enough impedance to drive a headphone. I think most integrated processor may just use a limiting resistor from the amp output which is just a cheap way of doing it.

But this is what you want to know. Google your amp spec and look for voltage gain in dB. You can then convert from dB to actual number like 20 or something.

http://www.sengpielaudio.com/calculatorVoltagePower.htm

You want to look at the calculation table for voltage gain (Gain Factor v=V2/V1). Put the dB number from your amp spec into the dB field and it will give you the voltage gain factor in numeric.

At the very end of that page - "Voltage gain (dB) = 20

megasat16

Nightfall wrote: »

From reading the thread I linked everyone is saying to can get as much performance using this $200 mini Emotiva amp as much more expensive dedicated headphone amps.

People says that? This is some crazy $hit to hear actually. Most preamps (headphone jack) and headphone amps run in Class A Watts because they are very small amps. Instead of that Class A amp, feed the signal through Class AB amps, and then divide the amp output with a resistor and calls it is better than using the actual class a head-amps? It may probably give you a little better dynamics due to higher gain but it's not the actual sound quality or the signal purity.

This is exactly my reason why I says "it will be unpleasant" in the very beginning.

Nightfall

megasat16 wrote: »

People says that? This is some crazy $hit to hear actually. Most preamps (headphone jack) and headphone amps run in Class A Watts because they are very small amps. Instead of that Class A amp, feed the signal through Class AB amps, and then divide the amp output with a resistor and calls it is better than using the actual class a head-amps? It may probably give you a little better dynamics due to higher gain but it's not the actual sound quality or the signal purity.

This is exactly my reason why I says "it will be unpleasant" in the very beginning.

My Yamaha is pure Class A until it hits 20 watts.

I appreciate your guys input! Thanks a lot for taking the time to write out those equations megasat!

megasat16

CA-1010? it is pure Class A till 20Watts? Do you know the bias current to the output transistors in the 100W receiver to claim it is Pure Class A to 20W?

It's a good receiver but......

cnh

I find it hard to believe that that Yamaha can't drive your cans to ear bleeding levels? As a quick test I just put my AKG Q701s on my Marantz 2265 and I could not keep them on long at past 12 o'clock on the volume knob. Plenty of power for a fairly difficult headphone to drive well.

cnh

Nightfall

megasat16 wrote: »

CA-1010? it is pure Class A till 20Watts? Do you know the bias current to the output transistors in the 100W receiver to claim it is Pure Class A to 20W?

It's a good receiver but......

Yes, only the CA-1010 and CA-2010 did this. Not the CR series. I think Marantz had a few that did this as well. Took a quick picture for you. It gets extremely hot in Class A.

Nightfall

cnh wrote: »

I find it hard to believe that that Yamaha can't drive your cans to ear bleeding levels? As a quick test I just put my AKG Q701s on my Marantz 2265 and I could not keep them on long at past 12 o'clock on the volume knob. Plenty of power for a fairly difficult headphone to drive well.

cnh

Ear bleeding levels, hardly. I'm not sure why? Could using the RX-V667 as a preamp have anything to do with this? I have not tried reconnecting the internal preamp on the CA-1010 and using the receiver by itself in this manor.

cnh

You haven't connected your phones to directly to the CA 1010 Yamaha? What are you waiting for? Those vintage receivers/amps have lots of power for high impedance cans. In fact they love the higher impedance, often do a better job with them than the lower level, easy to drive H-phones.

No way the H-phone section in that 667 is going to match what the older Yamaha can put out! And you can take that to the "bank". lol

cnh

Nightfall

cnh wrote: »

You haven't connected your phones to directly to the CA 1010 Yamaha? What are you waiting for? Those vintage receivers/amps have lots of power for high impedance cans. In fact they love the higher impedance, do a better job with them than the lower level, easy to drive H-phones.

No way the H-phone section in that 667 is going to match what the older Yamaha can put out!

cnh

No, no. I use the 1010's jack but only with the 667 as a preamp. I have not tried using the 1010 by itself as in disconnect it from the 667 and flip the switch on the back of the 1010 reconnecting it's own preamp.

The only reason I even think this may make a difference is because it makes a huge difference with the sound I get out of my RTA's whether or not I use the 1010 by itself vs only using the amp of the 1010 with the 667 as a preamp.

Hopefully this makes sense.

megasat16

Nightfall wrote: »

Yes, only the CA-1010 and CA-2010 did this. Not the CR series. I think Marantz had a few that did this as well. Took a quick picture for you. It gets extremely hot in Class A.

Nice close up shot. Very few some old marantz, yamaha, and luxman amps and receivers have that operating mode switch. Very few.

It can runs in class ab at 100W but no mentioning of where the Class A watts end.

In class a mode, it runs up to 20W. This is quite a gem and if it comes with a headphone jack, I would just use it and forget all other crazy things.

tonyb

I'm certainly no headphone guru, back in my day, 30 + years ago, any set of cans could be driven off a good analog receiver to ear bleeding levels. My problem with the OP's thinking is, he wants to move up to better cans, harder to drive cans yet, but then is looking for cheap power. Kinda fighting himself if the end goal is SQ.

That said, try running the cans off the vintage Yamaha alone. I would imagine by running both receivers together is creating some sort of impendence mismatch affecting the signal. Which also may affect your other sources as well. Keeping the signal as pure as possible from point A to point B is what should be sought after. Just a thought....

mhardy6647

So... just like loudspeakers, the nominal impedance of different headphones (and their frequency-dependent impedace curves) vary tremendously. There are some notoriously hard-to-drive headphones (the AKG K701 springs to mind)...

tonyb

mhardy6647 wrote: »

So... just like loudspeakers, the nominal impedance of different headphones (and their frequency-dependent impedace curves) vary tremendously. There are some notoriously hard-to-drive headphones (the AKG K701 springs to mind)...

Of course, but just like loudspeakers......the right tool for the right job is needed when talking power. If I was the OP, I would be more concerned about moving away from using 2 receivers, that seems to be the more limiting factor than the cans.

Nightfall

tonyb wrote: »

Of course, but just like loudspeakers......the right tool for the right job is needed when talking power. If I was the OP, I would be more concerned about moving away from using 2 receivers, that seems to be the more limiting factor than the cans.

I will certainly give this a try in the next few days and report back.