Found my old Polk Cobra cables and wonder if the horror stories of the high capacitance could be a problem with amplifiers using the THF51?
Mine are in ra7's TDV configuration - a buffer - if that makes any difference.
Are these devices sensitive to the high capacitance? I am planning on using them in triplicate which would only make the capacitance even higher.
Any opinion or counsel?
Mine are in ra7's TDV configuration - a buffer - if that makes any difference.
Are these devices sensitive to the high capacitance? I am planning on using them in triplicate which would only make the capacitance even higher.
Any opinion or counsel?
Capacitive loads are always difficult for amplifiers. But how bad this is depends on your particular amplifier.
Even worse are the stories about defective Cobra Cables shorting out the amplifier.
Even worse are the stories about defective Cobra Cables shorting out the amplifier.
I will have to make them into shorter lengths so I will know they have no shorts. As it is the original 32 foot lengths are not shorted.
I intend to use them in multiple four foot lengths. Three for the compression driver and five for the woofers which will increase the capacitance.
Just wondered if the TOKIN devices were like single ended triodes and immune to the problems some amplifiers had with the cables.
I intend to use them in multiple four foot lengths. Three for the compression driver and five for the woofers which will increase the capacitance.
Just wondered if the TOKIN devices were like single ended triodes and immune to the problems some amplifiers had with the cables.
Any amplifier using feedback can have stability problems with capacitive loads, depending on the circuit.
Usually there is a certain range of capacitance that will cause instability, and less (or more) capacitance will be ok.
This might be a good candidate for simulation before the actual building.
Usually there is a certain range of capacitance that will cause instability, and less (or more) capacitance will be ok.
This might be a good candidate for simulation before the actual building.
Well, the amp in question has no feedback at all. I will try with a single four foot length and see/hear what happens before trying with multiple lengths in parallel.
I would not know where to begin with simulation. I have used LTSPICE but not enough to be able to do this.
Thanks for your advice.
I would not know where to begin with simulation. I have used LTSPICE but not enough to be able to do this.
Thanks for your advice.
A follower (source, emitter, cathode, etc.) has 100% feedback.
That's why it has no voltage gain.
That's why it has no voltage gain.
There's no way to know what will happen for sure, until you breadboard or simulate the buffer, with a realistic R//C loading.
Maybe ra7 has some experience with this.
Maybe ra7 has some experience with this.
True but I find that statement misleading.
In my book a regular gain stage, from a single transistor to a complex Preamp or Power Amp can have have 100% feedback, no doubt, yet those behave in an absolutely different way to an emitter/cathode/source follower.
Gain with built - in high gain which has been nuked by NFB into unity can easily oscillate; try that with a follower.
A follower or buffer can have an input stage. But even a basic emitter follower will have problems with capacitive loading.
Try running this (choose time domain simulation) and see.
https://www.circuitlab.com/editor/#?id=m8v4jb
Try running this (choose time domain simulation) and see.
https://www.circuitlab.com/editor/#?id=m8v4jb
I realize this is not something too many are interested in ...
Last night I measured the capacitance of a four foot length and it is approx 1700 pf - stayed about the same from 20 hz to 100kHz. I measured a three foot length of 20 gauge DUELUND tinned copper and it is about 1/100th less.
The 32 feet length would have been a good sized capacitor!
What baffles me (haha) is how is this different than having a capacitor in parallel with a driver? Of course, a capacitor in that position would usually be much larger in value than the speaker cable would present.
Tonight I will hold my breath and see how one four foot length works into a Celestion Axi-periodic driver. (The stuff is a pain to separate plus and minus wires)
Last night I measured the capacitance of a four foot length and it is approx 1700 pf - stayed about the same from 20 hz to 100kHz. I measured a three foot length of 20 gauge DUELUND tinned copper and it is about 1/100th less.
The 32 feet length would have been a good sized capacitor!
What baffles me (haha) is how is this different than having a capacitor in parallel with a driver? Of course, a capacitor in that position would usually be much larger in value than the speaker cable would present.
Tonight I will hold my breath and see how one four foot length works into a Celestion Axi-periodic driver. (The stuff is a pain to separate plus and minus wires)
Never had that problem but it is easy to see happen.
Cobra Cable blew up a lot of PS Audio amplifiers (the first 40w one)
dave
If there is anyone out there interested:
Finally got around to installing a 4 feet Cobra cable between a THF51 amp using ra7's TDV circuit and a Celestion Axi-Periodic compression driver and there is no protest from the amplifier.
The sound is superior to the 20 gauge Duelund which I suspect was too skimpy. The overtones of cymbals has greatly increased definition and tone. All of the usual attributes associated with the cable are plainly there. Spaciousness is improved throughout the 450 to 22KHz range - they really are something.
I want to try adding a parallel length just to hear if that makes it better or worse.
They will remain in place one way or the other. Mr. Salvatore is right about these things. Maybe there are one thousand dollars cables that sound as good or better but I will never know!
Now to hear if they make a difference below 450 Hz feeding the woofers ...
Finally got around to installing a 4 feet Cobra cable between a THF51 amp using ra7's TDV circuit and a Celestion Axi-Periodic compression driver and there is no protest from the amplifier.
The sound is superior to the 20 gauge Duelund which I suspect was too skimpy. The overtones of cymbals has greatly increased definition and tone. All of the usual attributes associated with the cable are plainly there. Spaciousness is improved throughout the 450 to 22KHz range - they really are something.
I want to try adding a parallel length just to hear if that makes it better or worse.
They will remain in place one way or the other. Mr. Salvatore is right about these things. Maybe there are one thousand dollars cables that sound as good or better but I will never know!
Now to hear if they make a difference below 450 Hz feeding the woofers ...