Hey, that should work.
So, have we decided on the output impedance issue? My vote goes to some form of variable output impedance, since not all headphones conform to the 120 ohm standard. My preference would be a wirewound pot, but we could simply add a trimmer at the output so that one could adjust to their personal headphones and be done with it.
Also, we could use a relay for the muter instead of a switch, I'm thinking this would prevent old switches from causing snaps and pops...
- keantoken
So, have we decided on the output impedance issue? My vote goes to some form of variable output impedance, since not all headphones conform to the 120 ohm standard. My preference would be a wirewound pot, but we could simply add a trimmer at the output so that one could adjust to their personal headphones and be done with it.
Also, we could use a relay for the muter instead of a switch, I'm thinking this would prevent old switches from causing snaps and pops...
- keantoken
Okay, simple means the user has to get fancy if he wants to hook it up some special way. Fine with me, It's not something we're not all familiar with. But are we sure we don't want to have some flexibility in the output impedance? Most people will probably only use one set of cans, but some people switch between two. With multiple output jacks we could use two separate trimmers, and so only initial adjustment is necessary even for two sets.
Does anyone have anything to say about the sonic affects of the series resistance?
Not just an Ipod, but say a portable CD player. You might want to connect it through a double-male 3.5mm connector cable to the headphone amp. You can also connect it to the computer this way. But for this we need a 3.5mm "line in" jack. And what if someone wanted to use it as a preamp? We could add a "line out" jack for this (simple connected to the output).
- keantoken
Does anyone have anything to say about the sonic affects of the series resistance?
Not just an Ipod, but say a portable CD player. You might want to connect it through a double-male 3.5mm connector cable to the headphone amp. You can also connect it to the computer this way. But for this we need a 3.5mm "line in" jack. And what if someone wanted to use it as a preamp? We could add a "line out" jack for this (simple connected to the output).
- keantoken
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Hmmm, Ipod output, that's interesting, I guess it's something to consider if we want to keep the Ipod generation on board.... after all, both my daughters have nanopods, bought 'em myself with Paul Kaplan in NYC two years back.
Can these plugs be bought easily in the market, KT? Where?
Aspen Princeton, Nico? Hmmm, that's a bit grand isn't it? And what if I design one for commercial sale, an upmarket version, what would I call it then? Could we trump Princeton? (Don't answer that!
)
Cheers,
Hugh
Can these plugs be bought easily in the market, KT? Where?
Aspen Princeton, Nico? Hmmm, that's a bit grand isn't it? And what if I design one for commercial sale, an upmarket version, what would I call it then? Could we trump Princeton? (Don't answer that!
)Cheers,
Hugh
Mute circuit
Sheldon,
On the mute circuit above, the capacitor C1 will normally operate with 12 volts (assumming a 24 volt rail) across it. However at startup it will have zero volts across it.
If no headphones are attached, then R1 (1kohm or bigger) will provide current to allow C1 to settle to +12volts.
When the mute circuit is in operation, R2 does the following:
- Speeds up the bias across C1 (by providing a load similar to a headphone),
- Ensures that there are no clicks when the mute switch is operated.
The `no click' feature is the main one. Note also that typical switches have contact bounce, so it is not a simple make/break operation.
Paul Bysouth
Sheldon,
On the mute circuit above, the capacitor C1 will normally operate with 12 volts (assumming a 24 volt rail) across it. However at startup it will have zero volts across it.
If no headphones are attached, then R1 (1kohm or bigger) will provide current to allow C1 to settle to +12volts.
When the mute circuit is in operation, R2 does the following:
- Speeds up the bias across C1 (by providing a load similar to a headphone),
- Ensures that there are no clicks when the mute switch is operated.
The `no click' feature is the main one. Note also that typical switches have contact bounce, so it is not a simple make/break operation.
Paul Bysouth
A 3.5mm jack is the standard nowadays for headphones, CD players, etc. It's possible that the Ipod, or different versions of it, use stranger jack types.
Here's one product. Digikey gives billions of different types and I'm no expert... Just search for "3.5mm audio" or something like that.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-3504-ND
- keantoken
Here's one product. Digikey gives billions of different types and I'm no expert... Just search for "3.5mm audio" or something like that.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CP-3504-ND
- keantoken
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Wow, I said I'd wait a couple of pages - and things move a million miles an hour...
Be careful with the ipod. The line-out is hard to access without a special connector and before you know it we're adding an ipod docking station to the list. The ipod is currently crippled by the quality of the internal DAC. Apple protects access to the digital stream and have only recently licensed access - Wadia now have an ipod 'transport' for example. In the consumer market, things can suddenly change and leave your product out in the cold.
Be careful with the ipod. The line-out is hard to access without a special connector and before you know it we're adding an ipod docking station to the list. The ipod is currently crippled by the quality of the internal DAC. Apple protects access to the digital stream and have only recently licensed access - Wadia now have an ipod 'transport' for example. In the consumer market, things can suddenly change and leave your product out in the cold.
Quite right. The Sony MDR-7506 run about 24 ohms, while the Sennheiser HD-580 family and its successors are 300 ohms.
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The output resistor seems like a very valuable addition - I find it interesting how this subtle change came in late in the design process and yet it might prove to be a critical item - the committee approach is looking good
The cross-feed from Nico in post 375 seems to meet everyone's needs - output resistor, phase shift, cross-channel mix, adjustable, swticheable and simple. I don't think we'll find better than that.
The wall-wart looks very compelling. I have used the interchangeable version John posted, in USB format for my mobile communication device. It's very light-weight, inexpensive and I'm sure each country does in fact have some options available. I wonder if there's a 'common voltage' that is most widely available - it could be that the 24V we want is rare. A dc input to the chasis for use of a wallwart would also allow experimenters to use out-board fancy smancy power supply designs of their own.
The cross-feed from Nico in post 375 seems to meet everyone's needs - output resistor, phase shift, cross-channel mix, adjustable, swticheable and simple. I don't think we'll find better than that.
The wall-wart looks very compelling. I have used the interchangeable version John posted, in USB format for my mobile communication device. It's very light-weight, inexpensive and I'm sure each country does in fact have some options available. I wonder if there's a 'common voltage' that is most widely available - it could be that the 24V we want is rare. A dc input to the chasis for use of a wallwart would also allow experimenters to use out-board fancy smancy power supply designs of their own.
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Those are, of course, the impedances of the headphone drivers themselves, and have almost nothing to do with those headphone's preferred output impedance, which, in my (limited) experience, is almost always "as close to zero as you can get it" regardless of the 120 ohm "standard".
Agree - higher damping factor, for what that's worth.
I think the output impedance issue is a non-issue.
Many people own more than one pair of headphones, and listen to them with different kinds of music. The ATH W1000 for example, is a highly revealing pair of headphones. In fact , too revealing if not driven correctly. Some people use a second pair of headphones, which has less detail and accuracy, when they want augmented low end response.
Perhaps a sensible alternative would be to use 2 separate headphone jacks. Assuming the amplifier has a low output impedance, one socket could have , for example, a 10 ohm (or thereabouts) series resistor at the output, which would not only give an added degree of protection to the amplifier, but to both the listener and the headphones. The second jack could meet the requirements of the I.E.C. standard and incorporate a 120 ohms series resistor.
I also refer to the comment from the English designer Graham Slee who designs and manufactures Phono Preamps and Headphone amplifiers, and has received a few awards from Stereophile magazine .
" Re: IEC61938 on driving headphones
« Reply #4 on Jun 12, 2007, 2:54am »
--------------------------------------------------------------------------------
Quote:Some frequency/impedance curves look likes as the skyline of the alps
Think about it...
Sennheiser have 400 outlets in the UK (or so the rep said). They are not exclusively selling to the head-fi or rock-grotto fanatic like us. They are selling to people with amplifier headphone jacks, CD headphone jacks, booth headphone jacks. What do Sennheiser base the foundations of their designs on?
Do they buy every piece of equipment in existence just to make sure they're OK? I doubt it.
Now let's broaden it to ALL headphone manufacturers.
I'd guess a good number will have seen IEC61938?
I'd also guess the impedance frequency curves are meant to be like that
Why? If they weren't I don't think they'd sound all that good.
I reckon the sound would be mostly inside your head.
If you take a look at a constant power 90 degree phase filter, you'll see it does a similar thing to the phase - in and out instead of up and down.
This type of filter is used to create spatial effects, and was also used by some mono BBC radio stations to make stereo records sound more natural (and not by many commercial AM stations on grounds of cost or simply not knowing about them).
So if you drive these headphones from a zero impedance you can bet they'll sound different, but that may not be what the designer intended.
I'll let you into a little secret - the Solo output impedance is 120 Ohms.
Perhaps a sensible alternative would be to use 2 separate headphone jacks. Assuming the amplifier has a low output impedance, one socket could have , for example, a 10 ohm (or thereabouts) series resistor at the output, which would not only give an added degree of protection to the amplifier, but to both the listener and the headphones. The second jack could meet the requirements of the I.E.C. standard and incorporate a 120 ohms series resistor.
I also refer to the comment from the English designer Graham Slee who designs and manufactures Phono Preamps and Headphone amplifiers, and has received a few awards from Stereophile magazine .
" Re: IEC61938 on driving headphones
« Reply #4 on Jun 12, 2007, 2:54am »
--------------------------------------------------------------------------------
Quote:Some frequency/impedance curves look likes as the skyline of the alps
Think about it...
Sennheiser have 400 outlets in the UK (or so the rep said). They are not exclusively selling to the head-fi or rock-grotto fanatic like us. They are selling to people with amplifier headphone jacks, CD headphone jacks, booth headphone jacks. What do Sennheiser base the foundations of their designs on?
Do they buy every piece of equipment in existence just to make sure they're OK? I doubt it.
Now let's broaden it to ALL headphone manufacturers.
I'd guess a good number will have seen IEC61938?
I'd also guess the impedance frequency curves are meant to be like that
Why? If they weren't I don't think they'd sound all that good.
I reckon the sound would be mostly inside your head.
If you take a look at a constant power 90 degree phase filter, you'll see it does a similar thing to the phase - in and out instead of up and down.
This type of filter is used to create spatial effects, and was also used by some mono BBC radio stations to make stereo records sound more natural (and not by many commercial AM stations on grounds of cost or simply not knowing about them).
So if you drive these headphones from a zero impedance you can bet they'll sound different, but that may not be what the designer intended.
I'll let you into a little secret - the Solo output impedance is 120 Ohms.