DIY Sennheiser HD800 balanced cable - Page 2

Quote:

Originally Posted by Lil' Knight 

How did you measure the resistance of the cable?

Some DMMs might not be accurate enough to measure <1ohm.

LOL, you really think I'd make a public post if my DMM couldn't? 

ermm sorry but lil'kight has a point; even if your DMM says it measures that low, chances are its VERY innaccurate down that low. to measure resistance that low, usually a known voltage is passed over the resistor and the resulting current is amplified and measured. but to do it accurately usually something such as a wheatstone bridge is needed. at levels <1R0 even blowing on the resistor will cause it to change value and the resistance of the DMM leads comes into effect, how do you measure the resistance of your DMM leads? now you see a problem?

the below is taken from wikipedia

A Wheatstone bridge is an electrical circuit invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstonein 1843. ^[1] It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer.

Operation

In the figure, R_x is the unknown resistance to be measured; R₁, R₂ and R₃ are resistors of known resistance and the resistance of R₂ is adjustable. If the ratio of the two resistances in the known leg(R₂ / R₁) is equal to the ratio of the two in the unknown leg (R_x / R₃), then the voltage between the two midpoints (B and D) will be zero and no current will flow through the galvanometer V_g. If the bridge is unbalanced, the direction of the current indicates whether R₂ is too high or too low. R₂ is varied until there is no current through the galvanometer, which then reads zero.

Detecting zero current with a galvanometer can be done to extremely high accuracy. Therefore, if R₁, R₂ and R₃ are known to high precision, then R_x can be measured to high precision. Very small changes in R_x disrupt the balance and are readily detected.

I've got cables here that consistently measure in the 0.02 ~ 0.04 ohm region at this length on the same DMM repeatedly (single core silver plated microwave coax). The HD580 cable comes out around 0.9 ohms.

Accurate in terms of real world resistance or not the HD 800 cable is consistently higher which indicates a change.

http://www.uni-trend.com/manual2/UT70DEng%20ManualLVD.pdf

That's the meter I'm using. Like I said above the above values I get hold with all cables every time (I set the meter to subtract the approx probe value). What the real levels are maybe a percentage within the shown reading but the change is consistent on the Senn cable.

Quote:

Originally Posted by raja 

Quote:

Originally Posted by Lil' Knight 

How did you measure the resistance of the cable?

Some DMMs might not be accurate enough to measure <1ohm.

LOL, you really think I'd make a public post if my DMM couldn't? 

 

Nothing worth LOL-ing here. I asked you a question and got a LOL, nice reading comprehension.
 

Quote:

Originally Posted by Lil' Knight 

Quote:

Originally Posted by raja 

Quote:

Originally Posted by Lil' Knight 

How did you measure the resistance of the cable?

Some DMMs might not be accurate enough to measure <1ohm.

LOL, you really think I'd make a public post if my DMM couldn't? 

 

 nice reading comprehension.
 

Gee thanks!!
 

Repeatable consistent DMM readings have nothing to do with low resistance accuracy.

Best idea is to short both leads and note the reading e.g. 0.25 Ohms.

Then measure the lead and note the reading e.g. 1.24 Ohms.

Subtract the second reading from the first e.g 1.24 - 0.25 = 0.99.

Resistance is 0.99 Ohms give/take experimental error, connection cleanliness and meter inaccuracy.

Good enough for the bush.

You could use an Agilent 3458A or 34401A and do it in a 4 wire measurement down to micro Ohms, but that's not necessary here.

Anything within 0.1 Ohms is sufficient, and the above will do it.

Quote:

Originally Posted by wink 

Best idea is to short both leads and note the reading e.g. 0.25 Ohms.

Then measure the lead and note the reading e.g. 1.24 Ohms.

Subtract the second reading from the first e.g 1.24 - 0.25 = 0.99.

Resistance is 0.99 Ohms give/take experimental error, connection cleanliness and meter inaccuracy.

 

Good enough for the bush.

 

You could use an Agilent 3458A or 34401A and do it in a 4 wire measurement down to micro Ohms, but that's not necessary here.

Anything within 0.1 Ohms is sufficient, and the above will do it.

Hi wink,

My meter has an offset built in for subtracting out the series resistance of the probes from the measurement (which I already did for the measurements stated above). In hindsight I should have stated my methods in my opening post as it would have saved all the tit for tat that followed. My post was too curt, I'm quite thorough before I post stuff, but that's forums for you - a low post count or curt post may give rise to people thinking you've not done things right, I should know better. I've been building amps, and line level stuff for over 10 years now, so am not a complete "noob" despite having a low post count on this forum. I've been a member here for a few years now and I don't post much until I'm gonna buy something new or have something I want to share.

Just for clarification purposes here's a couple of pics of the meter measuring a couple of 1.5r 5% tolerance resistors in parallel (it's all I have in house at present in this range). 

1.5r

http://img69.imageshack.us/i/img20110212001.jpg/

2x 1.5r - (limited by ADC bit depth, but close enough). As was suggested by the cable guy above,blowing on the probes or resistors does not change the reported value unless you've got extreme hot halitosis or are Ice Man - (sufficient change in Celsius to cause drift due to the temp co-efficient) LOL. That was a bit of humour by the way! :)

http://img602.imageshack.us/i/img20110212002.jpg/

The pictures aren't that great as i took them with my phone. If you look carefully at the LCD you'll notice a triangle sign towards the top left corner of the screen; that's the relative function, you just short out the leads prior to measurement and it zeros the scale. Hope this clears things up. 

-Raja

Quote:

Originally Posted by sperandeo 

Can someone please show how you wire 2 mini XLR cables to a stereo 1/4"

Thanks

The question is a little ambiguous. Do you want to make a balanced cable or return a balanced cable to single ended? 

If returning a balanced cable to single ended, you'll need to connect both of the "inverted" signal -ve wires to the TRS ground and run the +ve for each driver to the respective left and right solder tags on the TRS conector.

Refer to this picture to see which part of the connector relates to +ve left and right. You can always run a continuity test on your multimeter to trace the +ve solder tags for each side and also the positive driver terminals.

-Raja

Quote:

Originally Posted by Steve Eddy 

Quote:

Originally Posted by nattonrice I'd love it if having 3-pin and 4-pin headphone outs like on the woo22 became a dual standard.

NOOOOOOOOOOOOOO!!!!!!!!

Stupid should never be "standard."

This is what must happen to dual 3 pin.



se

agree which retard created double  dual 3 pin ??

Its so ugly and wasted of material ,,,

4pin balanced is the future !!!