That usually happens after a page or three.
It often feels like old grannies coffee or tea corner.
Just ignore any real information and just keep chit chatting for the hell of it. 😆 🤣
(and then people wonder how to learn more .........)
But the opamp controls the global feedback taken from output over R14/R8. I see only voltage amp.
If you read my paper, you will see that this is not just a voltage amp. In the example given, the output impedance is approx. R14/1000, so that if R14 were increased to 4 K Ohms, the output impedance would be 4 Ohms (I have measured this, and it is so). In the limit, when R14 approaches infinity, the amplifier becomes a trans-conductance device, giving a true current output.
John.
John.
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No, I'm afraid not. I'm in my eighties now, and I don't want the hassle.
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Now i see. So if no R14 is there, the stage after opamp should be pretty linear as opamp don’t provide any correction.
That's right. The op-amp just defines the current through R8. The following stage is, in fact, very linear, provided attention is paid to matching the two halves.
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Yes, I have. I have built 12 of these amplifiers (not simulations, but real hardware) and the performance figures are shown in my original paper, and also in my post: "Amplifier with Predictable Output Impedance". The output Z is easily measured by changing the load resistance from (say) 8 Ohms to 4 ohms, and measuring the drop in output voltage.
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What is the highest Zo you have built & measured with your circuit?
Your very impressive paper shows a configuration with Zo not too different from a valve amp.
Your very impressive paper shows a configuration with Zo not too different from a valve amp.
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I have used Zo=8 Ohms in the past. Probably up to 1 K is possible with a little care. The example in the paper represents the lowest practical value (about 0.5 Ohms), due to power dissipation limits in the feedback resistor.
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I looked at the very first post and jumped to here, and will go back and follow the chain of thought. I just want to say I have been making contact with current source vacuum tube amplifier topology for 15 years, and at this point. I have been selling them for 10 years, starting with custom amplifiers and then moving to a production amplifier about five years ago. Then about three years ago I started making open baffle loudspeakers for sale as DIY parts and driver kits that work well and take into consideration current drive, but I am moving more and more in that direction.
Simply put this is so much better a relatively inexpensive system using current drive of the loudspeaker can be such that it can rival something costing many many times more without as much cost. Mix this with higher sensitivity speakers, add in tubes as well, and you then get things that sonically become so unique nothing sounds like them in many ways. I disagree with how most of this compensation of current drive amplifier/speakers is dealt with, I prefer more practical and less harmful ways of dealing with the resonance hump and the increase in driver impedance. If you rethink the base, then the practical application becomes intuitive. You have to throw out much of what you think from past ways of doing things and focus on the practical application of all this. It is the final result that is the focus not how can we make it work for current products, everything needs to be reconsidered.
Simply put this is so much better a relatively inexpensive system using current drive of the loudspeaker can be such that it can rival something costing many many times more without as much cost. Mix this with higher sensitivity speakers, add in tubes as well, and you then get things that sonically become so unique nothing sounds like them in many ways. I disagree with how most of this compensation of current drive amplifier/speakers is dealt with, I prefer more practical and less harmful ways of dealing with the resonance hump and the increase in driver impedance. If you rethink the base, then the practical application becomes intuitive. You have to throw out much of what you think from past ways of doing things and focus on the practical application of all this. It is the final result that is the focus not how can we make it work for current products, everything needs to be reconsidered.
That's something to be proud of. I've never sold a thing in audio that was of my own conception / build. Nevermind put anything into production. Which I assume means enough people want it, you can invest in a "run".
Others here have done these things.
Personally I am not trying to "make it big" or even make a lot of money, but share a sound. So you have to have a passion for that, not a strong desire to make money. I sell enough amplifiers to keep doing it, and mostly this funds my further research into all this. Everyone thinks their system is the best, I never thought that. There is always somethings you're leaving on the table.
Yea current drive on open baffle speakers really good and cheap combo. Done that many years ago. That bump from current drive at resonance fits very well in open baffles. Usually it is wise to use disadvantage as advantage in anything you do.
Just few minutes ago I did fun experiment with closed box bass. If I just drum the cone with my bare hands there is distinct boom to the sound, like a drum, which also blooms audibly if I drum the baffle. This was driver unhooked, and there is no passive impedance network. Now, shorting the terminals, or connect it to an low impedance voltage amplifier, the boomines goes away. Use the other hand to drum and short the driver with another and it's very easy to notice. This is electrical damping, so for a boxed speaker it seems to be better to maintain electrical damping at resonance.
Back in the day, like when/before I was born, some tube amps had a "damping factor" control. I'd look at such a knob as a kid and wonder what the numbers and scales meant - didnt seem to do anything AFAICT back then.
But what it was is an output impedance control. It had scales for 4, 8 and 16 Ohm speakers. I'll assume "1" meant the amp output Z was the same as the speaker Z; 2 was half the speaker Z and so on.
Imagine that. An amplifier with a scaled output impedance control. Go from "Voltage source" to "Current source" and anywhere in between.
Somewhere along the line, someone decided that all anyone would ever need is an amplifier with a damping factor of 1000 and that control lost favor. I'll guess around the time acoustic suspension was invented.
Full rangers work great with it.
Single ended tube amps opproximate current amps if no feedback is used.
A normal amp with a 15 ohm resistor in series with it gives a similar effect at the expense of power.
Single ended tube amps opproximate current amps if no feedback is used.
A normal amp with a 15 ohm resistor in series with it gives a similar effect at the expense of power.
@already smaller amounts of resistance change the sound considerably.
If I not were so much into fullranges building more multiways I would buy only cheaper small wire diameter air core coils (inductivities) to make crossovers.
Don Highend loudspeaker builder usually does that in his designs.
Like in the box "Lets dance" with Visaton BG17. Using over five ohms in line to bring sensitivity to level.
If I not were so much into fullranges building more multiways I would buy only cheaper small wire diameter air core coils (inductivities) to make crossovers.
Don Highend loudspeaker builder usually does that in his designs.
Like in the box "Lets dance" with Visaton BG17. Using over five ohms in line to bring sensitivity to level.
