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Equal length wiring
Equal length wiring
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Old 21st July 2021, 09:33 PM   #1
elwood625 is offline elwood625  United States
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Default Equal length wiring

When I was in highschool back in the 70's, my electronics shop class built el84 pp integrated amplifiers for our project. My shop teacher, Mr. Ballard stressed to each of us the importance of keeping the hookup wiring the same length for each channel so that there was no time smear distortion.
I continue to follow his rule, however I have always wondered how accurate his advise was. Any thoughts?
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Old 21st July 2021, 09:36 PM   #2
dotneck335 is offline dotneck335  United States
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That's total B.S.
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Old 21st July 2021, 09:51 PM   #3
Richard Ellis is offline Richard Ellis  Argentina
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Well, considering the speed of electricity propagating thru a wire is some 90 % of the speed of light at 0.00000000000833 inches per second,????
I'd bet your instructor was mixing up audio frequencies propagating thru a wire OR was more concerned with changes in current capacities with longer wires...either of which is truly inconsequential.






------------------------------------------------------------------------------Rick...
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Old 21st July 2021, 11:58 PM   #4
Enzo is offline Enzo  United States
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Admiral Grace Hopper used to hand out pieces or wire almost a foot long. She called them her nanoseconds. They represent the distance a signal travels in a nanosecond. A billionth of a second. If one signal was delayed a nanosecond or two, it would not be audible.
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Old 22nd July 2021, 12:08 AM   #5
wiseoldtech is offline wiseoldtech  United States
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Originally Posted by dotneck335 View Post
That's total B.S.

Indeed, I agree.
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Old 22nd July 2021, 01:12 AM   #6
dotneck335 is offline dotneck335  United States
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"My shop teacher, Mr. Ballard stressed to each of us the importance of keeping the hookup wiring the same length for each channel so that there was no time smear distortion."
That's why he was a high school shop teacher and not an audio engineer.

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Old 22nd July 2021, 05:05 AM   #7
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by dotneck335 View Post
"My shop teacher, Mr. Ballard stressed to each of us the importance of keeping the hookup wiring the same length for each channel so that there was no time smear distortion."
That's why he was a high school shop teacher and not an audio engineer.


I have to admit, my HS electronics shop teacher, Mr Connelly, was a great teacher.
Strict, yet somewhat forgiving, and open to reason.


One class project, a simple power supply provided by Graymark Kits, bored the hell out of me.
The thing was in a cheap plastic box and had a switch to select 6 or 9 volts, a center tapped transformer, bridge diodes (4) and a capacitor.
Dumb, I thought.


So I stopped by my local Allied Electroncs store and bought an aluminum chassis box, a 12 volt meter, 10V ac transformer, a 1P 8P rotary switch, diodes, filter caps, several WW resistors of same value, a neon panel indicator, toggle switch, binding posts, even a heyco strain relief and power cord.


At home, I pre-cut the meter opening, and other holes, and took it to class.
Connelly gave me looks, and insisted that I had to give a full explanation to the class of how my contraption worked.
I remember him saying that "I was getting way ahead of the rest of the class".


Well, this power supply outputted 1.5 to 12 volts depending on the selector switch, and the meter monitored the output.
Basically a voltage divider type supply.

Yeah, I had to explain the how and why of it in front of the class, but I got an A+ for that project, and dirty looks from some classmates.
Screw 'em.
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Old 22nd July 2021, 06:07 AM   #8
BKnut is offline BKnut  Australia
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Wiseoldtech, do you still have the power supply?


I made my first power supply o/p 1.2 to 30V at 1 amp.

Built from from scratch, sheet metal case to PCB layout & front panel photo sketching. Had to replace the Dick Smith capacitors as they dried out after 40 years. I expected it to be bulletproof after all these years.



In the same class, the fella in front of me, he wired the 20A toggle switch to one side of the green mains lead and the next thing I saw, a mighty bang to green continuing flashing explosions and the shadow of his head on the high ceiling and the fluro lights started dimming. The teacher ran over to cut out the safety mains by the wall. The poor fella could only see green for the rest of the class and all the students looked over in awe of the what's left of the heavy duty switch on his power supply.
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Old 22nd July 2021, 02:43 PM   #9
wiseoldtech is offline wiseoldtech  United States
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Originally Posted by BKnut View Post
Wiseoldtech, do you still have the power supply?

That High School class was in 1970, 51 years ago, so no, it's long gone, only a memory.
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Old 23rd July 2021, 02:29 PM   #10
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by elwood625 View Post
When I was in highschool back in the 70's, my electronics shop class built el84 pp integrated amplifiers for our project. My shop teacher, Mr. Ballard stressed to each of us the importance of keeping the hookup wiring the same length for each channel so that there was no time smear distortion.
I continue to follow his rule, however I have always wondered how accurate his advise was. Any thoughts?
Well in a valve amp stray capacitance can be significant at audio frequencies due to the high signal impedances (100's of kilohms). 1pF stray capacitance is 8M ohms, 4pF stray is 2M, all at 20kHz frequency.

So varying wire lengths could lead to small subtle differences in high frequency response (unlikely to be audible though).

But apart from this its a false precaution.

What can be important is to follow the same layout as documented for stability reasons - and if you build two channels with the same layout, the wire lengths will be the same of course. Picking your own layout without regard to unintended capacitive feedback is a possible pitfall.
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