Yeah, but how much is the capacitance?
More importantly, what is the impedance of the *line*?
Mind that since both are dramatically low at the wavelength and distance concerned, neither will affect it.
So let's see, what are the pros and cons.
Pro - thinner wire.
Con - thicker insulation.
Speaker wire is cheap enough for 8 ohms under 200W...just go with 8 ohms.
However, if you were doing a large distribution system such as a stadium, you might have one large amplifier powering the whole thing. I^2R losses would be horrendous at 8 ohms, so you'd keep it at say 600 ohms (70V line, or at this power level, maybe more) and run that around to the speakers, each [set] of which has a transformer to sap its power allotment from the supply.
Same distribution theory that applies anywhere else, especially mains power distribution.
Note this has absolutely nothing to do with frequency, distortion or "sound quality", assuming you aren't letting psychoacoustics sway you. Sure, bad OPTs will sound bad, but WOW, they'll sound bad ANYWAY...
Tim
More importantly, what is the impedance of the *line*?
Mind that since both are dramatically low at the wavelength and distance concerned, neither will affect it.
So let's see, what are the pros and cons.
Pro - thinner wire.
Con - thicker insulation.
Speaker wire is cheap enough for 8 ohms under 200W...just go with 8 ohms.
However, if you were doing a large distribution system such as a stadium, you might have one large amplifier powering the whole thing. I^2R losses would be horrendous at 8 ohms, so you'd keep it at say 600 ohms (70V line, or at this power level, maybe more) and run that around to the speakers, each [set] of which has a transformer to sap its power allotment from the supply.
Same distribution theory that applies anywhere else, especially mains power distribution.
Note this has absolutely nothing to do with frequency, distortion or "sound quality", assuming you aren't letting psychoacoustics sway you. Sure, bad OPTs will sound bad, but WOW, they'll sound bad ANYWAY...
Tim
Looking on the lighter side..
.
Well it's feasible to make a 600R interconnect, but try making a 10K one, so 6C33 is in, and 211's are out. On an unmatched line at 10K, just a nF would be disasterous to performance.
A push pull output stage would be a real balanced source.
It would be just feasible to run the output of a low power, 600R PP amp down a screened balanced audio cable (such as used in professional audio) to a remote OPT. Best run the HT down a separate cable and keep the shield at ground.
.
Well it's feasible to make a 600R interconnect, but try making a 10K one, so 6C33 is in, and 211's are out. On an unmatched line at 10K, just a nF would be disasterous to performance.
A push pull output stage would be a real balanced source.
It would be just feasible to run the output of a low power, 600R PP amp down a screened balanced audio cable (such as used in professional audio) to a remote OPT. Best run the HT down a separate cable and keep the shield at ground.
For my instinct: Bad idea, Jaap. I can only echo the ideas by John and Tim. Furthermore, possibility of noise pick-up by the KT66 leads, plus possible h.f. instability with feedback with whatever L is added by these lengths. And he now needs 5 wires instead of 2 with feedback (7 with UL).
I seem to recall some 20 milli-ohm/meter/lead for moderately thick speaker cable; that gives 0.48 ohm for 12m or 6% power loss (less than 1 dB) - is he worried about that? It is surely inaudible!
The above plus high voltage risk, etc. would make me say: Nay! (otherwise back to distribution practices as Tim suggested).
I seem to recall some 20 milli-ohm/meter/lead for moderately thick speaker cable; that gives 0.48 ohm for 12m or 6% power loss (less than 1 dB) - is he worried about that? It is surely inaudible!
The above plus high voltage risk, etc. would make me say: Nay! (otherwise back to distribution practices as Tim suggested).
How about a teflon twinax? Under 15 pF per foot, insignificant series L and R relative to the OPT. The capacitance to shield is double, which could be left floating or resistor coupled to B+. I still much prefer short path point to point construction but would a remote OPT work under these conditions?
SY has it right - given the choice of a medium/high impedance (primary wiring) and a low impedance (secondary wiring) run of ANY distance it a "No Brainer". Always use the lowest impedance possible for wiring/cabling runs of any distance. Less noise, less losses, less phase shift into reactive loads.
Cheers,
Ian
Cheers,
Ian
> output transformer next to the loudspeakerboxes and uses 12 meter cable to connect the OPT to his KT66
> long cable has less influence with the high impedance than with 8 ohm.
40 feet... his room is too big. Anybody has a room that big can do what he wants.
40 feet #14 cable is ~1,200pFd and 0.2Ω.
At 8Ω load from a zero-Z source, the 0.2Ω causes a 0.2dB broadband loss. A typical "8Ω" load may rise to 50Ω at some frequencies; loss will vary from 0.2dB to 0.03dB, or a +/-0.09dB variation. No speaker alive is that precise, nor is the 0.2dB broadband loss at all significant.
So low-Z lines can work OK.
At 5KΩ assumed plate load impedance: the broadband loss is 0.0004dB, so is "better" than 0.2dB, but who can hear it? The 1,200pFd will tend to be down 3dB at 26KHz, -1dB at 13KHz, 0.5dB at 6KHz.
So the high-Z line is better (less loss) below ~3KHz, higher-loss above 3KHz, and an audible loss in the top octave.
If the amp is run without feedback, with typical speakers, you usually want some added capacitance in the plate circuit, to tame the inductive rise of many loudspeakers. 5,000pFd was commonly thrown on cheap AM radio output primaries.
With feedback, the ~1,200pFd will add to the 500-2,000pFd inherent in a large winding, mildly upsetting the NFB compensation. (Note that this same 1,200pFd sitting on the 8Ω side reflects only 2pFd to the primary.)
> teflon twinax?.... would a remote OPT work under these conditions?
Within broad limits, in audio there isn't much that WON'T "work". Your low-C cable shifts the treble droop an octave up from my calculations... still down most of one dB at the top of the audio band, unless you use NFB to fight the droop.
So from audio perspective: it may be negligible, or a slight treble droop may be "good" for that specific system. And any "exotic technique" that does not suck is sure to "sound better".
From a safety standpoint: this is really risky. The power wires inside your walls are never more than 240V, because any more is dangerous. And even 240V is considered dangerous unless you have good insulation and good plugs: in the US we electrified without good rubber and with stupid plugs, and we never have more than 125V to ground on residential electric systems. 400-some volts running around the room, on insulation that may have never been tested for high voltage (over time, high voltage degrades plastic), sounds like a Bad Idea to me.
Background: Once upon a time I was messing inside a power amp. I took B+ through my little finger. That first day, I thought my finger was going to die and fall off. It didn't, and it healed some, but 30 years later I still don't have good sensation or control in that finger.
While messing with power amps, I have seen "600V B+" throw BIG arcs that had to be KiloVolts. An unloaded transformer acts just like the spark-coil in a car ignition. The spark coil kicks 12V up to 400V (the secondary transforms the 400V kick to 10,000+V). An OPT is not a perfect kicker, but a good one isn't bad, and it can kick FAR above the B+ and throw BIG arcs.
> long cable has less influence with the high impedance than with 8 ohm.
40 feet... his room is too big. Anybody has a room that big can do what he wants.
40 feet #14 cable is ~1,200pFd and 0.2Ω.
At 8Ω load from a zero-Z source, the 0.2Ω causes a 0.2dB broadband loss. A typical "8Ω" load may rise to 50Ω at some frequencies; loss will vary from 0.2dB to 0.03dB, or a +/-0.09dB variation. No speaker alive is that precise, nor is the 0.2dB broadband loss at all significant.
So low-Z lines can work OK.
At 5KΩ assumed plate load impedance: the broadband loss is 0.0004dB, so is "better" than 0.2dB, but who can hear it? The 1,200pFd will tend to be down 3dB at 26KHz, -1dB at 13KHz, 0.5dB at 6KHz.
So the high-Z line is better (less loss) below ~3KHz, higher-loss above 3KHz, and an audible loss in the top octave.
If the amp is run without feedback, with typical speakers, you usually want some added capacitance in the plate circuit, to tame the inductive rise of many loudspeakers. 5,000pFd was commonly thrown on cheap AM radio output primaries.
With feedback, the ~1,200pFd will add to the 500-2,000pFd inherent in a large winding, mildly upsetting the NFB compensation. (Note that this same 1,200pFd sitting on the 8Ω side reflects only 2pFd to the primary.)
> teflon twinax?.... would a remote OPT work under these conditions?
Within broad limits, in audio there isn't much that WON'T "work". Your low-C cable shifts the treble droop an octave up from my calculations... still down most of one dB at the top of the audio band, unless you use NFB to fight the droop.
So from audio perspective: it may be negligible, or a slight treble droop may be "good" for that specific system. And any "exotic technique" that does not suck is sure to "sound better".
From a safety standpoint: this is really risky. The power wires inside your walls are never more than 240V, because any more is dangerous. And even 240V is considered dangerous unless you have good insulation and good plugs: in the US we electrified without good rubber and with stupid plugs, and we never have more than 125V to ground on residential electric systems. 400-some volts running around the room, on insulation that may have never been tested for high voltage (over time, high voltage degrades plastic), sounds like a Bad Idea to me.
Background: Once upon a time I was messing inside a power amp. I took B+ through my little finger. That first day, I thought my finger was going to die and fall off. It didn't, and it healed some, but 30 years later I still don't have good sensation or control in that finger.
While messing with power amps, I have seen "600V B+" throw BIG arcs that had to be KiloVolts. An unloaded transformer acts just like the spark-coil in a car ignition. The spark coil kicks 12V up to 400V (the secondary transforms the 400V kick to 10,000+V). An OPT is not a perfect kicker, but a good one isn't bad, and it can kick FAR above the B+ and throw BIG arcs.
Electrodynamic
I think that's what you are thinking of. The power supply choke and the transformer where mounted on the speaker basket. This is because they used the field from the choke to create the magnetic field for the speaker. The output transformer shared some connections, so they stuck it there with everything else. You may find a hum bucking coil on the better units.
Extension speakers were normally 16 ohms to the best of my knowledge.
Later, as this was common practice, the transformer may have stayed on the early PM speakers. It did save chassis space and it ran cooler. The main chassis was close by, from 8" to 16" away in most cases.
Later tube radios from the late 40's through the last ones retained that position as they were built on phenolic PCB's. Not good for supporting a transformer. Plus it was less expensive in terms of space to mount the transformer on the speaker. It was all about cost, don't kid yourself. That and there's nothing wrong with putting the transformer on the speaker basket. We still do that with speakers intended for 70 V line distribution (building PA) as they are easier and less expensive to install that way.
-Chris
I think that's what you are thinking of. The power supply choke and the transformer where mounted on the speaker basket. This is because they used the field from the choke to create the magnetic field for the speaker. The output transformer shared some connections, so they stuck it there with everything else. You may find a hum bucking coil on the better units.
Extension speakers were normally 16 ohms to the best of my knowledge.
Later, as this was common practice, the transformer may have stayed on the early PM speakers. It did save chassis space and it ran cooler. The main chassis was close by, from 8" to 16" away in most cases.
Later tube radios from the late 40's through the last ones retained that position as they were built on phenolic PCB's. Not good for supporting a transformer. Plus it was less expensive in terms of space to mount the transformer on the speaker. It was all about cost, don't kid yourself. That and there's nothing wrong with putting the transformer on the speaker basket. We still do that with speakers intended for 70 V line distribution (building PA) as they are easier and less expensive to install that way.
-Chris
Yes Chris, I know what you mean. Radios of that ilk used a system we called "mains energized" speakers. The speaker had an electromagnet that doubled as the HT choke. The resultant hum was cancelled by a small winding that was wired in series with the voice coil.
But even after the introduction of permanent magnets, some manufacturers continued to mount the OPT on the speaker frame.
But even after the introduction of permanent magnets, some manufacturers continued to mount the OPT on the speaker frame.
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