[Dyoel182]

So with all the bitching and moaning about the inline volume control on the Radio Shack special 75s I decided to break out the voltmeter and take some readings.

First I measured my regular 75s with both channels coming out at 57 ohm. My sportapros came in at 54/55 ohm and I only tested them because I could reach them from where I was sitting. 55-57 is close enough to 60 in my book so I forged ahead.

With the 75s with the volume control I found things way more interesting. With the slider on full volume both channels read 57 ohm and with the slider all the way off they each read 3 ohm. This would explain why you can still hear a little music when its all the way down. However what interested me most was as at half volume the resistance was 190 on each channel, way over the spec 60 + a 75 or 100 ohm resistor added inline.

This probably wont suprise many of you who already knew the volume slider varied the resistance, but maybe it will make some realize instead of hacking up the cord and wiring stuff in that they can just turn them to half volume and turn up the volume on the source. I will say that it smoothes the sound out a noticeable amount.

 

[mapleleafs]

Hmm interesting findings. Can anyone else with the inline volume version comment on this?

 

[Meyvn]

I just bought a pair the other day, but they're back at home; now I'm tempted to purchase another for testing purposes. Head-Fi chipping away at my low funds again..

 

[Dyoel182]

When I get back home I'll try and take some readings throughout the dial range just to really see what the numbers do.

 

[Jahn]

I never even thought about that. Use the variable resistor in the inline control as an ohm adapter to add the requisite impedance to improve SQ when hooked into an amp...I'm going to groove to that on the way home and let you all know!

 

[Dyoel182]

Please do. I know I prefered listening to them at half but I didnt know why they sounded better until now.

 

[threepointone]

someone correct me if i'm wrong, but doesn't measuring resistance using a meter apply a DC voltage? and doesn't applying DC to headphones usually damage them? I don't think you're not really supposed to directly measure the headphone impedance.

 

[Dyoel182]

Never heard of damage, just distortion.

 

[chesebert]

KSC 75 with pot at 200ohm vs KSC75 with no pot

Here is the quick run down:

KSC 75 with pot at 200ohm made the phone alot darker sounding without providing any resolution increase, which is what the poster heard as "smooth". The inline resistor seemed to act as a band pass filter cutting the top and bottom end off. So that's why the soundstage suffers, as well as any resolution cues. The human voice just sound so dull and instrument timber is all messed up too, which made HD600 fun sounding ...LOL.. And I did try the pot at 150ohm and 125 ohm respectively. This is from Pimeta with AD8610 and STEPS, via 0404.

So that's my 2c on inline pot.

 

[chesebert]

Quote:

Originally Posted by threepointone someone correct me if i'm wrong, but doesn't measuring resistance using a meter apply a DC voltage? and doesn't applying DC to headphones usually damage them? I don't think you're not really supposed to directly measure the headphone impedance.

...sure it can if you put like 3V through your cans for an hour

 

[Dyoel182]

I havent noticed that it cuts off the top and bottom or that anything sounds duller than usual but I'll give it some more time and see what I think.

 

[VR6ofpain]

Interesting stuff. I always thought it was strange that everyone want pure sound, by getting rid of foam, and or cutting holes in the grille, but they also put a resistor in line with the signal.

I might try the resistor mod on my KSC's, since using my portable radio I have accidentally blasted them just brushing the volume wheel up just a hair. The impedence is a little low I think.

 

[Dyoel182]

I wouldnt say that 60 ohm is low for a low end headphone.

Jahn, any findings from yesterday?