Ipod to stereo amplifer: getting volume

[Bob Masta]

On Fri, 30 Nov 2007 08:42:18 -0800, Jitt <tser827@yahoo.com> wrote:

In article <475009b0.1246905@news.sysmatrix.net>,
NoSpam@daqarta.com says...
On Thu, 29 Nov 2007 08:55:27 -0800, Jitt <tser827@yahoo.com> wrote:


My kids had Creative mp3 players that would not produce
sufficient sound volume when connected to "aux" inputs
directly. I made an adapter cable that loaded each headphone
output with a 33 ohm resistor; this gave useable volume.
A later Samsung unit did not have the problem.

OK, I just have to ask: How does loading with a 33 ohm resistor
*increase* the volume? Normally we would expect a load to only
*decrease* volume, since it becomes the bottom leg of a voltage
divider with the output impedance of the source the top leg.

Or is there some sort of automagical sensing in the output circuit,
that increases the level when it sees a low load impedance?
Seems possible, and maybe even logical, so the same connector
can serve as headphone and line out. But I haven't encountered
it before... it this common?

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

I was thinking the current-oriented output was unable to
drive the relatively high impedance input; the 33 ohm load
allowed the output circuit to function, developing enough
signal voltage across the resistor to give useable volume.

I'm not sure what a "current-oriented output" would be.
Outputs are almost always voltage sources; they may have
low or high current capability, just like a battery, but they are
still voltage sources. (You wouldn't want to use a current source to
drive phones or speakers. They are specifically designed to be
driven by voltages sources, and their frequency response goes
south if driven by a current source.)

It's true that some outputs (like LM324) switch from class A to
class B when the current demand increases, but that doesn't
change the voltage gain.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[John Fields]

On Sat, 1 Dec 2007 11:55:13 -0000, "Fleetie"
<fleetie@fleetie.demon.co.uk> wrote:

"John Fields" <jfields@austininstruments.com> wrote
On Fri, 30 Nov 2007 02:38:20 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:
John Fields wrote:

If they still make stereos with phono inputs and yours has 'em, it
seems that should work.

Phono inputs have RIAA equalistaion on them you daft bugger. They would be
COMPLETELY unsuitable.

---
I see...

So if something is plugged into the phono inputs the tone controls
stop working?
JF

Well I'm not interested in getting involved in the ad hominem stuff
going on here, but on this occasion, Graham "Eeyore" is absolutely and
totally right.

There's no way that you could get acceptable sound by plugging a
nominally frequency-flat source (e.g. an iPod) into a phono input,
no matter how much the source was attenuated. The phono input has a
_severely_ tailored frequency response designed specifically and only
for turntable playback. Tone controls will only make the mess worse,
or at least, will go no way to sorting out the response.

The sound would be VERY bass-heavy, and there'd be almost no treble.
For a SMALL range of frequencies, somewhere in the middle of the frequency
band, the response would be flat. All of this assumes an ideal RIAA
response on the phono input.

You need to wiki "RIAA Equalisation".

The response used in phono inputs - being the opposite of that used
when driving the cutting head - has 2 main features:

1) It boosts bass, and lower frequencies are boosted more.
2) It attenuates treble, and higher frequencies are cut more.

The reasons are as follows:

1: To get decent bass playback without boosting bass on playback,
the groove excursions would be *enormous* and the stylus could and would
never, ever track. So you cut bass on recording and boost it back
on playback. That way, groove excursion is kept under control. Lower
frequencies need this treatment even more.

2: To mitigate surface noise, it is good to cut treble on playback,
so you boost it when cutting. That way, you maintain a good signal
from the original music, but severely attenuate high-frequency
surface noise. This is a good thing.

This is all "hi-fi 101".

---
Yeah, I know. I was just having fun rattling Graham's cage,
spoilsport.


--
JF

 

[Don Bowey]

On 12/1/07 3:55 AM, in article xsidnTxEosQ91szanZ2dnUVZ8vWdnZ2d@bt.com,
"Fleetie" <fleetie@fleetie.demon.co.uk> wrote:

"John Fields" <jfields@austininstruments.com> wrote
On Fri, 30 Nov 2007 02:38:20 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:
John Fields wrote:

If they still make stereos with phono inputs and yours has 'em, it
seems that should work.

Phono inputs have RIAA equalistaion on them you daft bugger. They would be
COMPLETELY unsuitable.

---
I see...

So if something is plugged into the phono inputs the tone controls
stop working?
JF

Well I'm not interested in getting involved in the ad hominem stuff
going on here, but on this occasion, Graham "Eeyore" is absolutely and
totally right.

There's no way that you could get acceptable sound by plugging a
nominally frequency-flat source (e.g. an iPod) into a phono input,
no matter how much the source was attenuated. The phono input has a
_severely_ tailored frequency response designed specifically and only
for turntable playback. Tone controls will only make the mess worse,
or at least, will go no way to sorting out the response.

The sound would be VERY bass-heavy, and there'd be almost no treble.
For a SMALL range of frequencies, somewhere in the middle of the frequency
band, the response would be flat. All of this assumes an ideal RIAA
response on the phono input.

You need to wiki "RIAA Equalisation".

The response used in phono inputs - being the opposite of that used
when driving the cutting head - has 2 main features:

1) It boosts bass, and lower frequencies are boosted more.
2) It attenuates treble, and higher frequencies are cut more.

The reasons are as follows:

1: To get decent bass playback without boosting bass on playback,
the groove excursions would be *enormous* and the stylus could and would
never, ever track. So you cut bass on recording and boost it back
on playback. That way, groove excursion is kept under control. Lower
frequencies need this treatment even more.

2: To mitigate surface noise, it is good to cut treble on playback,
so you boost it when cutting. That way, you maintain a good signal
from the original music, but severely attenuate high-frequency
surface noise. This is a good thing.

This is all "hi-fi 101".

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

Lurk more, say less.

Martin

 

[John Fields]

On Sat, 01 Dec 2007 09:40:07 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

John Fields wrote:

On Fri, 30 Nov 2007 17:14:02 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:



John Fields wrote:

Eeyore wrote:
John Fields wrote:

If they still make stereos with phono inputs and yours has 'em, it
seems that should work.

Phono inputs have RIAA equalistaion on them you daft bugger. They would be
COMPLETELY unsuitable.

---
I see...

So if something is plugged into the phono inputs the tone controls
stop working?

Is that the best stupid response you can offer ?

The tone controls will not even remotely provide a decent inverse match to the
RIAA characteristic.

Furthermore the input will likely be grossly overloaded (especially at low
frequencies) when driven from a headphone output of the type mentioned.

---
Geez, isn't there a volume control on an Ipod?

You even more ignorant piece of shit.

If you tuern down the volume control you'll still get significant output noise.
---

Really?

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

The
volume control is not some passive attenuator acting directly at the output.

So the output noise will be amplified by the high gain phono input and the
signal-to-noise ratio will be atrocious.

---
Really?

What will the signal to noise ratio be across the band?
---

You really shouldn't try to give advice about areas of technology you're completely
ignorant of. But of course you simply can't resist butting in and trying to look
'smart' can you, you utter fuckwit.

---
Geez, Graham, you don't have to be so mean, do you? I'm just trying
to help, and if I make mistakes I would expect that someone as
sagacious as you in all matters audio would be gracious in
correcting me.

BTW, in an effort to (try to) complement the Recording Industry
Association of _America_'s recording curve, couldn't you just turn
louduness ON, the bass all the way up, and the treble all the way
down?


--
JF

 

[Eeyore]

John Fields wrote:

I'm just trying to help

No you're not.

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

Graham

 

[John Fields]

On Sat, 01 Dec 2007 15:37:49 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

John Fields wrote:

I'm just trying to help

No you're not.

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

---
Deliberately ignorant???

Isn't that an oxy, moron?


--
JF

 

[Dominic-Luc Webb]

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

 

[Don Bowey]

On 12/1/07 12:47 PM, in article
Pine.LNX.4.44.0712012137390.21942-100000@uno.canit.se, "Dominic-Luc Webb"
<dlwebb@canit.se> wrote:

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?????????????????????????????

 

[Jitt]

In article <4751638e.721944@news.sysmatrix.net>,
NoSpam@daqarta.com says...

On Fri, 30 Nov 2007 08:42:18 -0800, Jitt <tser827@yahoo.com> wrote:

In article <475009b0.1246905@news.sysmatrix.net>,
NoSpam@daqarta.com says...
On Thu, 29 Nov 2007 08:55:27 -0800, Jitt <tser827@yahoo.com> wrote:


My kids had Creative mp3 players that would not produce
sufficient sound volume when connected to "aux" inputs
directly. I made an adapter cable that loaded each headphone
output with a 33 ohm resistor; this gave useable volume.
A later Samsung unit did not have the problem.

OK, I just have to ask: How does loading with a 33 ohm resistor
*increase* the volume? Normally we would expect a load to only
*decrease* volume, since it becomes the bottom leg of a voltage
divider with the output impedance of the source the top leg.

Or is there some sort of automagical sensing in the output circuit,
that increases the level when it sees a low load impedance?
Seems possible, and maybe even logical, so the same connector
can serve as headphone and line out. But I haven't encountered
it before... it this common?

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

I was thinking the current-oriented output was unable to
drive the relatively high impedance input; the 33 ohm load
allowed the output circuit to function, developing enough
signal voltage across the resistor to give useable volume.

I'm not sure what a "current-oriented output" would be.
Outputs are almost always voltage sources; they may have
low or high current capability, just like a battery, but they are
still voltage sources. (You wouldn't want to use a current source to
drive phones or speakers. They are specifically designed to be
driven by voltages sources, and their frequency response goes
south if driven by a current source.)

It's true that some outputs (like LM324) switch from class A to
class B when the current demand increases, but that doesn't
change the voltage gain.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

My 'kluge' worked, though- any ideas why? I wonder if

the DC biasing is routed through the phones, perhaps as a
sensing function.

 

[Jamie]

Dominic-Luc Webb wrote:

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

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..



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

 

[John Fields]

On Sat, 1 Dec 2007 21:47:19 +0100, Dominic-Luc Webb
<dlwebb@canit.se> wrote:

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?

---
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.
---

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

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

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?

---
Dunno...

Try it.


--
JF

 

[Eeyore]

Dominic-Luc Webb wrote:

On Sun, 2 Dec 2007, John Fields wrote:

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

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

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

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

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

 

[Eeyore]

Michael Black wrote:

Dominic-Luc Webb (dlwebb@canit.se) writes:
On Sun, 2 Dec 2007, John Fields wrote:

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

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

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

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

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.

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

Graham

 

[Dominic-Luc Webb]

On Sat, 1 Dec 2007, Don Bowey wrote:

Which iPod do you have?

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

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

 

[Dominic-Luc Webb]

On Wed, 5 Dec 2007, Eeyore wrote:

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

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

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

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.

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

Graham

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

 

[Eeyore]

Dominic-Luc Webb wrote:

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.

No. That doesn't happen either.

Graham

 

[Dominic-Luc Webb]

On Wed, 5 Dec 2007, Eeyore wrote:

Dominic-Luc Webb wrote:

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.

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

 

[Bob Masta]

On Wed, 5 Dec 2007 13:29:50 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:

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.

The meter test will be a problem, unless you have a very good meter...
and even then it won't be simple. Your meter will at least have to
have a sensitive AC Volts range, and preferably true RMS. The
problem is that ratings on inputs and outputs are based on maximum
sine wave levels before distortion, which are way higher than the
average RMS levels of normal program material. So, for example,
if your stereo Line In specs say 1 VRMS sensitivity, that means that
a 1 VRMS sine wave will produce a full-power output when the volume
control is all the way up. But you probably don't have any pure sine
"music" handy to play through the Ipod. (Though I'm sure there are
test tones available for download.)

If you do get 1 VRMS from a test tone on the Ipod, note that this will
correspond to the peaks of the music, easily 12 dB or more above the
average level of normal music. I'm not talking about sustained
crescendos, but instantaneous waveform peaks that your ear doesn't
notice as being especially loud because they are brief. The system
must be able to reproduce these at their corresponding level, because
if it can't it will clip them off and you will easily hear that as
distortion.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[Eeyore]

Bob Masta wrote:

If you do get 1 VRMS from a test tone on the Ipod .......

..... he wouldn't have any trouble with the volume being low.

Graham

 

[Don Bowey]

On 12/5/07 12:38 AM, in article
Pine.LNX.4.44.0712050936330.23729-100000@uno.canit.se, "Dominic-Luc Webb"
<dlwebb@canit.se> wrote:

On Sat, 1 Dec 2007, Don Bowey wrote:

Which iPod do you have?

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

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

Using the iPod Nano as an example, in the Settings Menu there is an Audio
Menu wherein you can set the desired maximum audio output level.

My Nano can overdrive my home audio system if I do not reduce it's output
volume.