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IEM resistor cable assistance/advice please?

post #1 of 43
4/25/10 at 2:31am
Thread Starter 
I've been using a pair of Unique Melody custom Shure SE530 with a Benchmark DAC1. Sounds great, but the Shures are far too sensitive for the HPA2 attenuation steps.

I presume the cheapest way around this is to make a cable between the Benchmark and my Shures with a resistor in it? Is this likely to impact on sound quality in any way? I find the HPA2 as it is about 3 or 4 times louder than I would like it to be. What resistor(s) should I be using to make such a cable?

Is there a better way to achieve what I'm trying to do? And if I'm on the right track can someone please explain exactly how I should wire up aforementioned 'resistor cable'. Speak slowly please!

Thanks
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post #2 of 43
4/25/10 at 6:25am
Cheapest way? You're probably right with the resistor cable. I have never heard a pair of 530's though so can't comment on the effects of using one with them but there will be one (I assume, as every other IEM I've tried one with does...)

To make one all you need to do is put a resistor in the left and right signal wires, for a test to see how it sounds just use the resistor as the wire between the plug and jack. You'll want as closely matched resistors (0.5% if you can find/afford or buy lots of less expensive/accurate ones and measure them yourself) as you can or one side could be noticably quieter than the other.

The Etymotic P->S (S->P?) adaptor is 75 ohms as is the airline adaptor that came with my UE's so this is probably a good value to start with? I've seen people using anything between 50 and 150, there may be more extreme values out there.
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post #3 of 43
4/25/10 at 1:58pm
I agree, anything between 50 and 75 ohms is a good place to start. I actually made a little interconnect with the resistors soldering into the wires for this purpose, and yes it achieves what you are trying to do without negatively impacting the sound.
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post #4 of 43
4/25/10 at 2:10pm
http://www.head-fi.org/forums/6059302-post4653.html

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post #5 of 43
4/25/10 at 10:34pm
Thread Starter 
Thanks suicidal_orange, great explanation. I'm trying to get the Shures to be at a comfortable listening level when the HPA2 dial is between 11 and 3 o'clock (supposedly best case for the Benchmark) so will probably start with a 100 ohm and go from there. Any advice as to the type of resistor I should use (film?) for this application?

Wow, awesome looking work cyberspyder! I'm not sure I'll end up with something so nice as that, but it's exactly what I'd like to achieve.
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post #6 of 43
4/25/10 at 10:38pm
I would use metal film resistors.
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post #7 of 43
4/25/10 at 11:07pm
Thread Starter 
Thanks Punisher. And just to be sure, if I'm trying to make an adaptor like cyberspyder's (which will just have two resistors soldered internally from female plug to male jack), I presume I ignore ground?
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post #8 of 43
4/25/10 at 11:50pm
Yes, ignore ground and just connect it to the other ground as usual.
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post #9 of 43
4/26/10 at 12:06am
Thread Starter 
Thanks Punisher, but in this case it isn't a normal cable job in the sense that I'm not using a cable, just two resistors inside the adaptor itself, so there won't be a ground wire present. My question is, do I need to add a little wire between the plug and jack to act as ground (as if it were the ground wire within a cable), or just leave them disconnected? Given the tight space I will have to work within for this adaptor, it will be much easier if I can actually cut off the ground connectors on both the plug and jack altogether, but I'm not sure if that's OK to do...
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post #10 of 43
4/26/10 at 10:42am
You need to use a stereo connector with three leads (for tip, ring, sleeve) and you need to connect the grounds. Just use a spare piece of wire or a clipped resistor lead. And be sure to insulate the ground wire and the left and right "wires" (I realize in your case they'll just be the resistors) with shrink tubing or electrical tape.
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post #11 of 43
4/26/10 at 11:10am
As a comment, experimentation will yield the best result.

From my experience with the Shure E5c if the resistors are too large the effect on sound quality is awesomely bad.

I would get a bunch of resistors between 10 and 100 ohms, perhaps in the radio-shack sampler pack. Get creative with putting them in series and parallel to get various values on one of those cheap solderless breadboards. Once you have settled on a value you like get the closest thing you can in a nice single resistor and make the permanent cable.

Im undecided whether a metal film resistor is clearly better for this kind of thing. yes, they sound clearer, but the point of this cable is to make the sound less clear and thereby reduce the random noise. A carbon resistor may be just what the doctor ordered here.
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post #12 of 43
4/26/10 at 11:43am
Hey there, poo...

I highly recommend NOT putting resistors between a set of headphones and any headphone amp. The reason is that it will increase the source impedance, which will diminish the damping ratio - a major factor in the quality of a headphone system.

The HPA2 has less then 0.1 ohm output impedance. This optimizes the damping ratio. The proper place in the circuit to attenuate is before the amplifier. Because of user feedback such as yours, we included a 10 dB attenuation option in the DAC1 USB and both a 10 dB and 20 dB attenuation option in the DAC1 PRE and HDR.

What is your source? If you have the option to use digital attenuation, it may be far less degrading then adding source resistance. From your signature, I assume you are using the Airport Express...yes?

Best,
Elias
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post #13 of 43
4/26/10 at 12:02pm
Quote:
Originally Posted by EliasGwinn View Post
This optimizes the damping ratio.
Not knowing what damping ratio the speakers/headphones were designed for you cant say optomised, only maximized. They are not necessarily the same.

I do agree though, the multi-driver IEM's do tend to sound better with lower source impedance. OTOH everything tends to sound better when it dosnt hiss. So it looks like the IEM MFR's have designed the users into a compromised situation. Perhaps designing an IEM with lower sensitivity that was less of a hiss-o-matic would be better.
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post #14 of 43
4/26/10 at 1:37pm
Quote:
Originally Posted by nikongod View Post
Not knowing what damping ratio the speakers/headphones were designed for you cant say optomised, only maximized. They are not necessarily the same.
Subjectively speaking, you may be right. That is, a lower damping ratio may give the headphones a certain coloration that one may enjoy.

But objectively speaking, the lower the damping ratio, the less accurate the headphones are. Mechanical drivers (physical speakers) have mechanical resonances. These resonances are dependent on the shape, size, material, etc, and will cause certain frequencies to be accentuated. Likewise, the physical impedances of the headphones may attenuate other frequencies.

The damping ratio determines how much the speakers will react to the electronic signal from the amp or how much they will submit to their own physical non-linearities. The higher the damping ratio, the more the speaker reacts to the electronic signal. The lower the damping ratio, the more the speaker submits to its physical non-linearities.

Again, someone may subjectively enjoy the coloration of certain non-linearities, but it is less accurate.

All the best,
Elias
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post #15 of 43
4/26/10 at 1:55pm
In my experience, drivers' frequency response is easily changed by adding a resistor adapter. This is especially true with multiple driver iems with crossovers. The amount of change is directly proportional to the resistor value. This change is not a good one, because the earphone loses all of its original characteristics.

With dynamic drivers, the change isn't as severe, but still noticeable.

I built a board with swappable resistor sockets. I tried resistors from 10 ohms to 150 ohms I believe.

In the end, getting an amp with clean sounding output and low gain was my best bet.
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