Ipod to stereo amplifer: getting volume

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Yeah, I know.  I was just having fun rattling Graham\'s cage,
spoilsport. ;)

It is also a waste of bandwidth. You are posting this for people who already know RIAA equalization.

Lurk more, say less.

the

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Really? 

How much is "significant" and where do you think it'll lie,
spectrally?

No you're not.

You're just being a deliberately ignorant prick as usual.

Graham

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Deliberately ignorant???

Isn\'t that an oxy, moron?

I think as the original poster of this thread, I should first update my question: rather than "resistivity", I should probably have used the term "impedance". I was wondering if anyone has any knowledge about the impedence and power at the Ipod headphone jack?

I was wondering if an impedence mismatch might explain the lack of volume?

Regarding the stereo amplifier, it is a high end unit, about 250 Watts, accepting essentially any signal one could imagine for a stereo amplifier (CD/DVD, phono, tuner, AUX, etc) through RCA jacks. The cable used is common stereo cable without specifications more than the connectors.

From what I am reading so far, it might be worthwhile to add some low value resistors on the input cable, yes?

Dominic

Which iPod do you have?

Have you set the output limiting option to give you the output level you need?????????????????????????????

My 'kluge' worked, though- any ideas why? I wonder if the DC biasing is routed through the phones, perhaps as a sensing function.

check your head phone's impedance. I think you'll find them in the low area like 4, 8, 16,32 ohms etc// If this is the case, you could use a simple approach which might cause a little audio quality drop and that would be to use a matching audio transformer which will bring the output up to line level voltages and place a load on the IPod. You would need 2 since there is a stereo signal involved here.

if you don't do the transformer method, you could employ a dual audio op-amp with a loading resistor on the Ipod output. the audio amp would then bring the signal up to line level voltages.

This is just a basic run down..

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"I\'d rather have a bottle in front of me than a frontal lobotomy"
http://webpages.charter.net/jamie_5

--- The impedance of the headphones ("earbuds") is 32 ohms, but I haven't been able to find the power level into them.

Backing into it, though, the threshold of human hearing sensitivity is:

P0 = 1 * 10E-12W

and conversational-level voice is about 70dB above that, so assuming that the Ipod can put out stuff 10 times louder than that (80dB) means that what the Ipod's earbuds put out, to each ear, will be about 100 microwatts.

Now, assuming that the Ipod's earbuds are 10% efficient (I have no clue whether they are or not, I'm just interested in how the numbers go) means that in order to get that SPL into each ear the input to each earbud must be must be 90 dB above P0, which is 1 milliwatt per transducer.

Knowing the power into the transducer and its impedance will allow us to calculate the voltage across the transducer:

E = sqrt(PR) = sqrt (1.0E-3W * 32R) = 0.179 volts RMS.

If the guys at Apple are doing a power match into the transducers, that means that when you hook your relatively high impedance stereo inputs to the Ipod outputs you could expect roughly 350 millivolts into the stereo.

Worse yet, if they were driving the transducers with voltage sources your stereo inputs would see about 179mV per channel, max.

If your high-level inputs are expecting to see something like a volt, the Ipod's output could very well be the problem.

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--- Since the input impedance of your system is so much higher than the impedance of the earbuds, I wouldn't think so.

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--- Dunno...

Try it.

-- JF

Thanks John for bringing me into some logical reasoning. I'll check my stereo specs and think on the math you have offered.

Dominic

Errr uhhh, I'll check the specs, but I stereo was lower:

Ipod earbud: 32 Ohm Stereo amp: 8 Ohm (I'll check again)

Dominic

No.

The "8 ohms" is certainly the output of the stereo amplifier, and has no relevance to the topic.

It's the input impedance that matters. But it won't matter since it will be very high, tens of thousands of ohms.

Since that will not place a load on the iPod, there will be no problem.

The only caveat is if, as someone suggested, the output of the iPod really does depend on a low impedance load to operate. And as I said, while that would explain the problem, I've not seen any units that actually do require a load in order to operate properly.

Michael

The input impedance of you amp is absolutely NOT 8 ohms. More likely to be in the region of 47-100 kohms.

8 ohms is imply the recommended load impedance of the speaker outputs (which will have an output impedance of ~ 100 milliohms or so ) .

Graham

It's a red herring. The ipod's headphone output is just fine for driving an amplifier input.

Graham

I no longer have the specific device handy. A collegue brought it with him to a PhD defense party.

Asking around, no one here is aware of this "output limiting option". Could you please explain?

Dominic

Thanks all, and I certainly stand corrected on the input impedence of my stereo.

As for this being a red herring, I point out that the reason for my original post was that I do not get much volume at my stereo speakers through my stereo amplifier when I connect an Ipod via the headphone jack. I asked if this could be an impedence mismatch or too low power (or something else). John Fields suggests that the output voltage may be too low, and I have now seen there are amplifiers for Ipods that are apparently intended to boost the signal for connecting to stereos. Seeing as the Ipod is a very small portable device, I could guess that maybe the output to the headphones drops off sharply as the battery runs down.

Dominic

No. That doesn't happen either.

Graham

Thanks Graham! Asking a couple of collegues, your remark holds true for at least the one specific Ipod on this side where I could ask the Ipod owner and the owner knew the answer with certainty. Apparently the volume remains pretty stable until a warning message finally pops up, and then the device basically just shuts down altogether.

These appear to be our axioms:

1. Volume through stereo AUX is low (compared to other inputs)
2. Volume is low when Ipod volume dial is turned all the way up
3. Impedence (Ipod 32 Ohm, stereo input thousands Ohms) is not problem
4. Battery rundown does not cause volume drop on Ipod
5. Adding a 30 Ohm resistor has improved volume for some people
6. Output voltage from headphone jack might be lower than ideal

I can easily test point 5, and I will put my trusty meter on an Ipod headphone to investigate point 6 by comparing to me receiver input specs.

Dominic