I never said capacitors don't block DC.
A DC signal as high as a thousand volts can be blocked with nothing more than a $1 capacitor, for decades, while allowing the AC components through
Anyone who's ever build or modded an amplifier will disagree with you. Including myself.
I never said capacitors don't block DC.
No, it isn't.I was implying that a 1$ capacitor is going to sound horrible...
Yeah, well, Let's check my assumptions. It's my understanding that the USB signal is a complex bit stream. The complexity means that it needs to be constantly analyzed to determine what the original analog signal was. That analysis is done in a CPU, which ultimately keeps a 32 bit number internally representing the next analog value to output. Is that number externally accessible on some output pins anywhere inside the DAC? I assumed not, so let's check that. Do you have a schematic for the DAC?Also I am wondering, you mentioned that I cannot use my dac as an on/off indicator because of the way it works.
Why not make an alternative usb dac specifically for this purpose? Both signals will be the same coming out of the PC.
I'm not going to have this conversation, it's been done a million times before elsewhere. The difference in sound between a crappy capacitor and a high end capacitor in the interstage position is nearly 100%, nothing subtle about it. It's like having two very different amplifiers. No I am not quoting someone else, I only believe my own experience. Also in my experience the only people that claim that things don't make a difference are people that have never personally tried it themselves, also people that think THD (emphasis on T)is the only thing that matters in the signal. But anyway please, don't bring this up again, it's turning the thread off topic.No, it isn't
No no no, for example, in normal operation the cathode is heated and electrons are "boiled" off of it which then fly toward the plate at high speed because the plate is positively charged, if this happens unhindered the plate will melt and the tube will be destroyed.From your first post I got the impression you wanted to switch the grid bias in order to protect the output amplifier tube. That's why I asked about the reference information, because I can't find anything that says the tube needs that kind of protection. Even so, I can see how it could help by preventing electrons from hitting the plate when they're not needed. Now I think you may be thinking that cutting off the electron flow will eliminate some random noise. Is that true?
Anything I have on the dac is here http://www.audio-gd.com/Pro/dac/NFB12015/NFB12015EN.htmDo you have a schematic for the DAC?
Yes. You can "tap" the serial bitstream that is entering the DAC, pick off the frame numbers, and know the exact start and end points of any track. That's what a CD player does and how the track select operation works.But I'm wondering, if the dac is able to "find" this signal, why can't we? I'm assuming it would take a software solution.
Its operating point is whatever bias you set it to i.e. the difference in voltage you set between the cathode and grid.So I don't see why a tube would overheat while sitting at its operating point.
25 and USA.To prevent some language problems, two questions. How old are you and where are you?
OK, thanks, that's consistent with what you said in your first post, so you're keeping me on track. In my experience there are two ways to control electron flow to the plate, not counting the grid. If you reduce the cathode heating, you reduce the electron flow. And if you reduce the potential of the plate with respect to the cathode, you reduce electron flow. In fact, if you leave the plate unconnected, virtually no electrons leave the cathode and hit the plate, they just cluster in a cloud around the cathode.I'm not going to have this conversation, it's been done a million times before elsewhere. The difference in sound between a crappy capacitor and a high end capacitor in the interstage position is nearly 100%, nothing subtle about it. It's like having two very different amplifiers. No I am not quoting someone else, I only believe my own experience. Also in my experience the only people that claim that things don't make a difference are people that have never personally tried it themselves, also people that think THD (emphasis on T)is the only thing that matters in the signal. But anyway please, don't bring this up again, it's turning the thread off topic.
No no no, for example, in normal operation the cathode is heated and electrons are "boiled" off of it which then fly toward the plate at high speed because the plate is positively charged, if this happens unhindered the plate will melt and the tube will be destroyed.
This is why we have a grid, the grid applies voltage fluctuations (AC signal) between the plate and the cathode, when the grid becomes negative the electrons are repelled, when the grid goes positive, the electrons are sling shotted toward the plate.
What happens if there is no ac signal? This is why you have to bias the tube so the grid is always x amount of voltage below the cathode so if the signal is not applied then the electrons do not flow to the plate and cause catastrophic failure.
So basically instead of having a permanent bias, I want to switch the bias in and out when needed.
Anything I have on the dac is here http://www.audio-gd.com/Pro/dac/NFB12015/NFB12015EN.htm
But I'm wondering, if the dac is able to "find" this signal, why can't we? I'm assuming it would take a software solution.
It depends entirely on the tube, most aren't designed to withstand no bias.I think the tube is designed to operate at some normal electron flow in a steady state condition for as long as the cathode can function, the heater doesn't open circuit, and the grid isn't contaminated, I.e., years to decades.
Not at all, I've never seen a tube like this, Tubes are designed from the beginning to run on crazy voltages, except maybe some low voltage radio tubes or something. It is not like overclocking a CPU, overclocking a tube would be doing pushing voltages above the rated specs, this can be done and tubes are usually pretty robust and can handle it, but it reduces the lifespan of the tube by a lot.Now, if I choose to run the tube at such a high plate-cathode voltage that enough electrons flow to burn up the plate, then I'm likely operating outside the design range of the tube
No but I just ordered one.Do you have an oscilloscope?
Isn't that basically the same as my binary interception idea? It's all binary before it hits the dac.But here's a thought. Why not switch the bias when the USB signal starts and stops? Even if the USB audio signal is basically quiet, it's still the incoming signal, so it should be amplified
Yes, it's a binary bit stream coming in over the USB port. But I understood that you wanted to switch bias voltages whenever the audio went below some threshold value. Now I understand that's not accurate. You want to switch off the bias when there is no input stream. Very different requirement.Isn't that basically the same as my binary interception idea? It's all binary before it hits the dac.
I want to switch on the the bias when there is not input. So like if a track ends and no signal is going to grid, the tube wont die on me.. You want to switch off the bias when there is no input stream.
It really just depends on the tube, for example the 6080 tubes in my current amplifier are only dissipating about 7.5 watts of their 11 watt maximum even with no bias, but some tubes will glow red as soon as there is no bias applied which is known as the "death glow".In my experience, a tube that is biased per its operating specs will not self destruct.
I have found that tube innovation has remained stagnant since the 60s.I've never come across a circuit to switch grid voltages like you propose.
Ummm sure, I have no idea what a multiplexer is, my experience is limited to analog electronics at the moment which my brain is already overloaded trying to figure outAt this point, I propose the following for a solution, no matter if it's a good idea or not, it's your idea to pursue.
You need two things. First, a detector to know if there is incoming audio to the DAC. Easy. Second, a multiplexer that can deal with higher voltages. A little trickier, but doable. Agree?
by Duane Benson
by Aaron Carman
by Aaron Carman