Be careful guys about balanced phono. It was patented:
Balanced Input Phonograph Preamplifier Circuit. US patent 4,293,823
😉
Balanced Input Phonograph Preamplifier Circuit. US patent 4,293,823
😉
Be careful guys about balanced phono. It was patented:
In 1981.
The patent has since expired.
se
PMA, please look, before you jump! ;-)
The case is that your posts do not follow time causality principle. They just appear in between the posts that have already been posted several minutes before 😀 Please ask SY to correct this invariance.
Far as I'm aware, what the twisting does is assure that the interference is picked up equally on both lines so that more of the interference can be rejected.
se
Geometry of twisted pair results in partial interference cancelation. Polarity of the induced interferention is oposit in consecutive half-turns.
Geometry of twisted pair results in partial interference cancelation. Polarity of the induced interferention is oposit in consecutive half-turns.
Aye, true.
se
Be careful guys about balanced phono. It was patented:
Balanced Input Phonograph Preamplifier Circuit. US patent 4,293,823
😉
As usual they missed the fact that IA's were used in geophones since the 60's.
Yes, thank you SY, now mention it to Scott, if you please. He was off by even more than me.
Well, maybe that's a feature.

The decoupling was due to shielding the electrical field, not the magnetic field. You got it wrong. Now go back and measure magnetic field with a gauss meter and you'll not only get the right answer, you'll learn something. What you changed was capacitive coupling, not mutual transconductance due to magnetic coupling.
Sorry been away. Good news the test set up was still sitting untouched on my bench. Results are:
.001" aluminum foil alloy 2024 No decrease in measured level!
.062 aluminum 5052 same result
.125" aluminum 5052 more loss
2 pieces .125 aluminum 5052 (touching) even more loss
Using a hall effect sensor shows the same results! But It is not calibrated so I cannot give exact values. However all the ratio's from induced voltage in the coil vs Hall effect sensor out are the same.
The capacitance between the coils is on the order of e-12 farads. The resistance of the pickup coil is less than .05 ohms. So the "Electrostatic" coupling should be extremely low.
No it is pretty clear the losses are eddy current. You are certainly welcome to try your own measurements.
Physically a twisted pair has a greater loop area than a parallel pair. Far as I'm aware, what the twisting does is assure that the interference is picked up equally on both lines so that more of the interference can be rejected.
se
Whether or not it has a greater loop AREA depends on spacing.
A 10 cm length of wire spaced 1 cm apart is 10 cm sq in loop AREA.
Assuming twisting adds 1.5 times the wire needed for a given running length:
A 15 cm length of wire spaced .1 cm apart has 1.5 cm sq of loop AREA.
These numbers are obviously exaggerated to show how AREA can greatly increase with spacing. It is the AREA that matters, not the total running length of wire.
Therefore, a twist can minimize loop AREA for hum pickup in the first place, and make the loop sizes consistant. True, the reversals cancel what pickup is made, but AREA determines the amount of pickup in a loop.
Last edited:
I remember your layouts.
It always interested me the way you
used all right-angle turns on the traces.
( I always strived for as gradual of curve
as possible )
( In order not to jerk the electron flow 🙂 )
Right angles on PC traces become a problem with thin traces. Most of the copper is removed as the etchant reacts with the unprotected surfaces, but there is always some side or undercutting action. The corners catch more etchant in some processes. This can result in thin spots or even opens.
Came across this platinum paint that claims "orders of magnitude" better conductivity than silver paint. The $2500/oz or so cost should not be an issue with Blowtorch customers.
Platinum Paint Conductive Suspension - SPI Supplies
If colloidal silver can cure anything, think what colloidal platinum can do!
John
Over here, an engineer is just a guy who drives a train.
Actually the first guys to run the trains were the ones who built them! Those were real engineers, so the name got applied to all the folks after that who got to run them!
Balanced operation has been around more than 100 years, mostly for telephone service.
Samuel Christie made what is now called the Wheatstone Bridge, the first balanced circuit around 1833!
Whether or not it has a greater loop AREA depends on spacing.
A 10 cm length of wire spaced 1 cm apart is 10 cm sq in loop AREA.
Assuming twisting adds 1.5 times the wire needed for a given running length:
A 15 cm length of wire spaced .1 cm apart has 1.5 cm sq of loop AREA.
These numbers are obviously exaggerated to show how AREA can greatly increase with spacing. It is the AREA that matters, not the total running length of wire.
Therefore, a twist can minimize loop AREA for hum pickup in the first place, and make the loop sizes consistant. True, the reversals cancel what pickup is made, but AREA determines the amount of pickup in a loop.
Great.
Now let's compare apples to apples instead of apples to oranges.
Take a pair of insulated wires with a given outside diameter.
Run them parallel right next to each other for a length of say 1 meter.
Now take another pair of the same insulated wires and twist them together again for a length of 1 meter.
The twisted pair will have the greater loop area.
se
There are better ways then a twisted pair but is there still interest that we work on a better phonostage ? We can pack and wire it later.
Right angles on PC traces become a problem with thin traces. Most of the copper is removed as the etchant reacts with the unprotected surfaces, but there is always some side or undercutting action. The corners catch more etchant in some processes. This can result in thin spots or even opens.
I have a friend (whos ears I trust very much)
(way more than mine)
He says right angle traces sound bad because
of the "lack of smoothness" brought on by the
electrons changing direction so abruptly.
Great.
Now let's compare apples to apples instead of apples to oranges.
Take a pair of insulated wires with a given outside diameter.
Run them parallel right next to each other for a length of say 1 meter.
Now take another pair of the same insulated wires and twist them together again for a length of 1 meter.
The twisted pair will have the greater loop area.
se
That's assuming you use the same SPACING for each, which is not likely for a PRACTICAL twisted pair vs. a coax, for example. But since, as usual, you HAVE to have the last word, you can make up another scenario and argue with yourself. Since it is clear that reverse loops affect the cancelling, I am done with this topic.
- Status
- Not open for further replies.
- Home
- Member Areas
- The Lounge
- John Curl's Blowtorch preamplifier part II