using an impedance adapter to make an external DAC drive 32Ω headphones? - Page 2 - diyAudio
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Old 23rd April 2010, 10:13 PM   #11
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I actually tried it, but there's a huge FR mismatch...the sound is unbearably bright and harsh..

just like they show on that link if you click on "TechNotes": Auzentech

Click the image to open in full size.
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Old 23rd April 2010, 10:21 PM   #12
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another solution could be one of those: SM PRO AUDIO NANO PATCH PLUS SILBER - U.K. International Cyberstore
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Old 23rd April 2010, 11:11 PM   #13
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ok I'll send an email to that german manufacturer

apparently the Shure attenuator is called a "L-Pad": l-pad attenuator - Google Search
Quote:
An L-Pad is a very simple, purely resistive, voltage divider attenuator. It consists of 2 resistors, one in series with the speaker, and one in parallel with it. The ratio between the 2 forms a voltage divider.
I'd like one w/ perfect stereo tracking and matched stereo output impedance

Last edited by leeperry; 23rd April 2010 at 11:18 PM.
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Old 24th April 2010, 01:26 AM   #14
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ok, found some links!

http://www.diyaudio.com/forums/headp...ttenuator.html

Constant impedance relay-resistor logarithmic attenuator

T-link attenuator with constant impedance

A PI and T attenuator

too bad they don't mean much to me

http://www.ehow.co.uk/about_6331454_...chematics.html
Quote:
"L-Pad" is an audio electronics term that refers to a resistive attenuator network that reduces the signal to a speaker while matching the impedance to that of an amplifier. The network consists of two resistors, either fixed or variable, that are connected so that one is in series and the other is in parallel with the speaker load.
could I easily build one w/ a fixed value somehow? I've got a soldering iron and I'm not afraid to use it

Last edited by leeperry; 24th April 2010 at 01:31 AM.
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Old 26th April 2010, 08:16 AM   #15
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impedance mismatch on DAC side will result in different voltage levels because of the 100ohms output impedance of the DAC. But I suspect this would be a real problem..

Of course it is a good idea to find a good position of the Shure attentuator and to keep this position. If you want to really fix it, measure the impedance and replace the pot by four fixed value resistors.

bocka,
this sounds interesting. I'm just not shure whether leeperry is willing to solder inside his DAC.. and this solution would give a much bigger 'impedance mismatch'.. probably a parallel resistor + capacitor would help and offer a great solution.
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Old 26th April 2010, 11:11 AM   #16
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yes, I'd really like to make a fixed L-Pad...if only I knew what resistors values to use?
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Old 26th April 2010, 11:15 AM   #17
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ehm.. I did mention some values above (to start with).
It would be even better to find a good sounding position of the Shure attentuator, measure resistance between a) input and output (this will be R1) and b) between output and ground (this will be R2).
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Old 26th April 2010, 11:39 AM   #18
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well, you didn't mention "L-Pad" as this is what I want to do...and apart from cheapo attenuators, noone makes serious ones

but I'd rather get a passive attenuation than adding opamps/caps/psu in the audio path

ok I will measure everything you told me and will come back w/ figures..thanks for your help!
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Old 26th April 2010, 05:10 PM   #19
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ok, the manufacturer of this thing: SM PRO AUDIO NANO PATCH PLUS SILBER - U.K. International Cyberstore

tells me that it's not a "L-Pad" but that it will work fine w/ headphones...I've asked for more details to triple-check with you, but so far he told me:
Quote:
The nanopatch+ has an inline-potentiometer so you can simply attenuate the volume of your DAC. You, of course, can use the nanopatch+ as an attenuator for your headphones..but not as a L-Pad. The resistors are in series with the speakers/Headphones, that's why it's not a L-Pad.
I guess the pot would work as a voltage divider? and not change the impedance on the DAC side? and it looks so neato in silver, tell me it can work...puh-lease

Last edited by leeperry; 26th April 2010 at 05:22 PM.
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Old 27th April 2010, 01:45 AM   #20
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hehe, I'm not that retarded after all...that's what an amp manufacturer just told me:
Quote:
I've been thinking about your idea. It was/is a very good idea.

Essentially 100% passive headphone amp - for those people who have a low enough output impedance signal source (with a large enough output signal) to drive their phones.

I do not know if you know how good of an idea that is. I think it is really good.

So what I brought to the table was the info about the possible L-pad configuration.

I would like to try this out. I still want to open up one of the Shure headphone volume controls you showed me - to see exactly what they did inside, at least impedance wise. Then perhaps it could be emulated/replaced/improved with a stepped attenuator circuit of some kind.

The best thing that could happen would be the new product name: "leeperry 100% Passive Headphone Controller".
but he's also selling grossly overpriced passive stepped attenuators...when I can get a nicer looking/more convenient NanoPatch+ for 50 bucks

Last edited by leeperry; 27th April 2010 at 01:47 AM.
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