Oh, BTW, if you haven't used the loop gain probes before, you'll need to go into the LTSpice control panel and enable the following three items on the "Save Defaults" tab
Save Device Currents
Save Subcircuit Node Voltages
Save Subcircuit Device Currents
This results in large ".raw" files being left behind. To fix this problem, you can go into the "Operation" tab of the LTSpice control panel and set "Automatically delete .raw files" to "yes".
Save Device Currents
Save Subcircuit Node Voltages
Save Subcircuit Device Currents
This results in large ".raw" files being left behind. To fix this problem, you can go into the "Operation" tab of the LTSpice control panel and set "Automatically delete .raw files" to "yes".
Hi Andy,
Those would be great tips for the spice threads. Would you mind terribly if I asked you to add your tips to that thread?
Thanks,
-Chris
Those would be great tips for the spice threads. Would you mind terribly if I asked you to add your tips to that thread?
Thanks,
-Chris
Okay. I'll try to post something on that today. There's a slightly easier way to do the loop gain thing, so I'll get the info together to describe that over in the SPICE thread.
Re: Capacitive load effect on HEC
Hi Bob,
Yes, I did a SPICE simulation, a couple of years ago. Without coil your amp is getting unstable with a load of 15nF or higher (according to Micro-Cap). But things getting worse if twisted leads of 5cm to the MOSFETs are inserted (L=50nH, K=0.7). Then the critical load is 1.5nF.
Nevertheless, it's a beautiful design, still hard to beat after all these years!
Cheers,
Bob Cordell said:
Hi Bob,
Yes, I did a SPICE simulation, a couple of years ago. Without coil your amp is getting unstable with a load of 15nF or higher (according to Micro-Cap). But things getting worse if twisted leads of 5cm to the MOSFETs are inserted (L=50nH, K=0.7). Then the critical load is 1.5nF.
Nevertheless, it's a beautiful design, still hard to beat after all these years!
Cheers,
Re: Re: Capacitive load effect on HEC
Try LTSPICE; it's free, and one of the best and fastest SPICE simulators out there. I think you'll love it. Just go to the Linear Technology site for a free download.
Bob
analog_guy said:
Try LTSPICE; it's free, and one of the best and fastest SPICE simulators out there. I think you'll love it. Just go to the Linear Technology site for a free download.
Bob
Re: Re: Capacitive load effect on HEC
Hi Edmund,
Thanks. I can't say I'm surprized that it gets destabilized with 15 nf, but I'll take a look and see if there are any tricks that can allow it to operate to a higher direct capacitive load without an isolating coil. Not that I really worry much about using a 0.5 uH coil and 0.5 ohms 🙂. A transitional output pickoff point for the EC circuit may do the trick.
Thanks,
Bob
estuart said:
Hi Edmund,
Thanks. I can't say I'm surprized that it gets destabilized with 15 nf, but I'll take a look and see if there are any tricks that can allow it to operate to a higher direct capacitive load without an isolating coil. Not that I really worry much about using a 0.5 uH coil and 0.5 ohms 🙂. A transitional output pickoff point for the EC circuit may do the trick.
Thanks,
Bob
Re: Re: Re: Capacitive load effect on HEC
Use BJT's like Hawksford did!
MOSFET's give a higher output impedance due to their lousy transconductance. And your large signal linearity will be much better too.
MOSFET's -
- Bahh!
Cheers,
Glen
Bob Cordell said:
Use BJT's like Hawksford did!
MOSFET's give a higher output impedance due to their lousy transconductance. And your large signal linearity will be much better too.
MOSFET's -
- Bahh!Cheers,
Glen
Re: Re: Re: Capacitive load effect on HEC
Hi Bob,
I think that's impossible without degrading the distortion figures. I have spiced numerous existing and new amplifiers and they all show a trade-off between stability and low distortion.
Besides, what's wrong with an output coil? The only thing I have learned from the discussion on this topic is that the (lack of) reasoning to remove the coil has convinced me that I will never build or buy an amplifier without output coil.
Cheers,
Bob Cordell said:
Hi Bob,
I think that's impossible without degrading the distortion figures. I have spiced numerous existing and new amplifiers and they all show a trade-off between stability and low distortion.
Besides, what's wrong with an output coil? The only thing I have learned from the discussion on this topic is that the (lack of) reasoning to remove the coil has convinced me that I will never build or buy an amplifier without output coil.
Cheers,
Re: Re: Re: Re: Capacitive load effect on HEC
Hi Glen,
You don't like these stinking MOSFET's, do you?
As a matter of fact, I have designed (not yet built) an amp with MOSFET's in the O/P stage, showing a THD20 of 10 ppb.
So, MOSFET's aren't that bad. 😀
Cheers,
G.Kleinschmidt said:Use BJT's like Hawksford did!
MOSFET's give a higher output impedance due to their lousy transconductance. And your large signal linearity will be much better too.
MOSFET's -
Cheers,
Glen
Hi Glen,
You don't like these stinking MOSFET's, do you?
As a matter of fact, I have designed (not yet built) an amp with MOSFET's in the O/P stage, showing a THD20 of 10 ppb.
So, MOSFET's aren't that bad. 😀
Cheers,
Re: Re: Re: Re: Re: Capacitive load effect on HEC
Well I dunno, I just can’t fathom why anyone would desire to use such unappealing devices. It just doesn’t make any sense to me, especially so, when there are so many lovely BJT’s available, with all their uniquely desirable characteristics.
If, from tomorrow onwards, I am to be imprisoned in a place in which high power BJT’s are banished, and I am not even permitted to read about them in magazines, then maybe I would break down 15 or 20 years hence and resume building audio power amplifiers with the MOSFET devices.
Or then again, maybe not. I dunno. Fortunately, I’m a rather tolerant kind of chap, so I’m not particularly bother by the MOSFET devotees. What ever floats your boat, I say – so long as you don’t try to coerce me onto your love boat.
EDIT:
Gosh, I'm particularly full of crap this evening.
Must be this stuff in my glass to blame.....
estuart said:
Hi Glen,
You don't like these stinking MOSFET's, do you?
As a matter of fact, I have designed (not yet built) an amp with MOSFET's in the O/P stage, showing a THD20 of 10 ppb.
So, MOSFET's aren't that bad. 😀
Cheers,
Well I dunno, I just can’t fathom why anyone would desire to use such unappealing devices. It just doesn’t make any sense to me, especially so, when there are so many lovely BJT’s available, with all their uniquely desirable characteristics.
If, from tomorrow onwards, I am to be imprisoned in a place in which high power BJT’s are banished, and I am not even permitted to read about them in magazines, then maybe I would break down 15 or 20 years hence and resume building audio power amplifiers with the MOSFET devices.
Or then again, maybe not. I dunno. Fortunately, I’m a rather tolerant kind of chap, so I’m not particularly bother by the MOSFET devotees. What ever floats your boat, I say – so long as you don’t try to coerce me onto your love boat.
EDIT:
Gosh, I'm particularly full of crap this evening.
Must be this stuff in my glass to blame.....
Re: Re: Re: Re: Capacitive load effect on HEC
Hi Edmund. I agree. I've seen reviews when amplifiers may have gone unstable under some conditions, and it may have been the lack of an output coil.
My guess is that on those occasions when a degradation in sound was perceived due to the use of an output coil, it may not have been a good implementation in some way or another. But its only a guess. I wish we had more specific information on what it might have been about the presence of the output coil that may have caused a degradation. I do think it is fair to say that if an output coil is going to be used, it should be a fairly small value that is implemented carefully so that there are no coil nonlinearities and there are minimal opportunities for the magnetic field of the coil to radiate. It is still a very interesting and important discussion, however.
Bob
estuart said:
Hi Edmund. I agree. I've seen reviews when amplifiers may have gone unstable under some conditions, and it may have been the lack of an output coil.
My guess is that on those occasions when a degradation in sound was perceived due to the use of an output coil, it may not have been a good implementation in some way or another. But its only a guess. I wish we had more specific information on what it might have been about the presence of the output coil that may have caused a degradation. I do think it is fair to say that if an output coil is going to be used, it should be a fairly small value that is implemented carefully so that there are no coil nonlinearities and there are minimal opportunities for the magnetic field of the coil to radiate. It is still a very interesting and important discussion, however.
Bob
Re: Re: Re: Re: Capacitive load effect on HEC
You really like to stir the pot, don't you? That's a good thing. Stimulates good dicussion.
How much experience do you have building vertical MOSFET amplifiers? And in what way was that experience bad?
For someone who seems to promote the use of BJTs with an ft of only 4 MHz, as opposed to those really nice ones that John uses with an ft of 60 MHz, you don't seem to be taking maximum advantage of the best of BJTs. Have you ever built a BJT amplifier with the ring emitter transistors. I think if you had, you would never look back.
Cheers from the loyal opposition. As you said, whatever floats your boat.
Bob
G.Kleinschmidt said:
Use BJT's like Hawksford did!
MOSFET's give a higher output impedance due to their lousy transconductance. And your large signal linearity will be much better too.
MOSFET's -
Cheers,
Glen
You really like to stir the pot, don't you? That's a good thing. Stimulates good dicussion.
How much experience do you have building vertical MOSFET amplifiers? And in what way was that experience bad?
For someone who seems to promote the use of BJTs with an ft of only 4 MHz, as opposed to those really nice ones that John uses with an ft of 60 MHz, you don't seem to be taking maximum advantage of the best of BJTs. Have you ever built a BJT amplifier with the ring emitter transistors. I think if you had, you would never look back.
Cheers from the loyal opposition. As you said, whatever floats your boat.
Bob
Re: Re: Re: Re: Re: Capacitive load effect on HEC
G'day Bob.
I have stopped spiking my carbonated mineral water with cheap raspberry cordial now, so I should be a little more level-headed from now on (although I make no promises).
I have no experience with Vertical MOSFET's and you are right about the BJT's, but I am using the best ones Sanken have to offer in the Class AB and the Class A, error-corrected output stages of my fully differential super duper 512W rms tracking-rail amp.
When my 4MHz BJT stock runs out, I might make the shift to 30MHz On-Semi devices exclusively.
Cheers,
Glen
Bob Cordell said:
G'day Bob.
I have stopped spiking my carbonated mineral water with cheap raspberry cordial now, so I should be a little more level-headed from now on (although I make no promises).
I have no experience with Vertical MOSFET's and you are right about the BJT's, but I am using the best ones Sanken have to offer in the Class AB and the Class A, error-corrected output stages of my fully differential super duper 512W rms tracking-rail amp.
When my 4MHz BJT stock runs out, I might make the shift to 30MHz On-Semi devices exclusively.
Cheers,
Glen
Hi Estuart,
---What's wrong with an output coil? The only thing I have learned from the discussion on this topic is that the (lack of) reasoning to remove the coil has convinced me that I will never build or buy an amplifier without output coil.---
Never say never, but true, the discussion was not convincing at all when advocating to design amplifers with the idea of avoiding an output coil in mind.
---What's wrong with an output coil? The only thing I have learned from the discussion on this topic is that the (lack of) reasoning to remove the coil has convinced me that I will never build or buy an amplifier without output coil.---
Never say never, but true, the discussion was not convincing at all when advocating to design amplifers with the idea of avoiding an output coil in mind.
forr said:
Hi Forr,
Read between the lines to understand what I really mean.
I would like to be more explicit, but I don't like being banned from this forum.
Cheers,
estuart said:
I have not seen any convincing technical argument that coils are audible. While I certainly believe in "never say never" and in the X-factor in audio, there seems no linear (frequency response/transient response) argument that holds water (at least if the L-R combination is less than 2 uH and 2 ohms).
If the coil degrades sound for a nonlinear reason, such as core saturation, proximity to steel, nonlinear coupling of radiated magnetic fields back into other parts of the amplifier, then one would expect that that would show up on a high-frequency distortion analysis.
Also, those that claim them to be audible have not described in detail the conditions under which they were audible. Maybe it was a very poor implementation of an output coil, for example.
Cheers,
Bob
Bob Cordell said:
Hi Bob.
I think you’re wasting your time. Convincing technical arguments are scarce in the kingdom of marketing, as they are amongst the Golden Ear fraternity – a group whose collective reasoning is immune to a reality in which supernatural hearing abilities are only evidence of self-delusion.
Cheers,
Glen