kzeprf22 said:
You can cool them down that way, but you will be dramatically altering the
open loop gain of the amp by increasing the impedances of the feedback loop
from 10 ohms to 2.5K ohms.
You can tolerate going from 10 ohms to maybe 20 or 30 ohms, but even
then you will see an increase in distortion for lack of feedback.
Ok if we are talking for the F5 distortion figures, yes we will increase distortion, by altering the feedback impedances. I wrote that because this is the way is done in most commercial amps (class ab-a). The feedback resistors are in kohms and provide high gain ratio (in most of the cases). Of coarse for commercial amps the distortion difference due to this does not contribute much in the total distortion figures. In F5 as you said it will make difference.
Good point, Thanks
Good point, Thanks
The thing that tends to get lost in the shuffle is that the feedback on the F5 isn't 'normal' feedback. Well...it is, in the sense that it acts like (and is) negative feedback, but the fact that the feedback signal feeds into the Sources instead of the Gates is crucial. Tube folks do this sort of thing all the time, but for some reason it's uncommon in solid state.
Try thinking of it this way--pretend that there's one and only one JFET, not a complementary pair. (Remind me to tell you a story about how my love of puns got me in trouble with Nelson over the word 'complementary.' Very embarrassing. I embarrass myself regularly--keeps me humble. [No comments from the peanut gallery!]) The signal comes in at the Gate and exits via the Source. This is Common Source. No conceptual problems, right? Now look at the Source as an input--the node you will be routing the feedback into, in fact. Remember that the Source can run as either input or output. When used as an output, the configuration is known as a Source Follower. And what do you know about a Source Follower? That the Source is a low impedance node. Bear in mind that that does not change based on whether the node is used as an input or an output or not used at all...the Source is always a low impedance node! The idea that there are two JFETs back-to-back doesn't change that in the least.
And if you're trying to push a low impedance node, you're (generally) going to find that it's best to push it with another low impedance node. In this case that means the resistor network between the output and the input pair will need to be relatively low in impedance; lots less than a "normal" pair of feedback resistors, where the resistors would be many thousands of Ohms.
Grey
Try thinking of it this way--pretend that there's one and only one JFET, not a complementary pair. (Remind me to tell you a story about how my love of puns got me in trouble with Nelson over the word 'complementary.' Very embarrassing. I embarrass myself regularly--keeps me humble. [No comments from the peanut gallery!]) The signal comes in at the Gate and exits via the Source. This is Common Source. No conceptual problems, right? Now look at the Source as an input--the node you will be routing the feedback into, in fact. Remember that the Source can run as either input or output. When used as an output, the configuration is known as a Source Follower. And what do you know about a Source Follower? That the Source is a low impedance node. Bear in mind that that does not change based on whether the node is used as an input or an output or not used at all...the Source is always a low impedance node! The idea that there are two JFETs back-to-back doesn't change that in the least.
And if you're trying to push a low impedance node, you're (generally) going to find that it's best to push it with another low impedance node. In this case that means the resistor network between the output and the input pair will need to be relatively low in impedance; lots less than a "normal" pair of feedback resistors, where the resistors would be many thousands of Ohms.
Grey
from peanut gallery
are you sure that you don't have some serbian roots ........
edit :
more important than fun with peanut/humbliness is -
I always have impression that that sort of feedback arrangement , which Papa use in F5 , have greater amount of .......... speed ..... naah - not speed , but immediacy ;
that's probably just result of lack of my regular education in electronics
but some things I just feel , or visualize like that ......
taking in account capacitances or not ......
yup ; immediacy is a word
GRollins said:
are you sure that you don't have some serbian roots ........
edit :
more important than fun with peanut/humbliness is -
I always have impression that that sort of feedback arrangement , which Papa use in F5 , have greater amount of .......... speed ..... naah - not speed , but immediacy ;
that's probably just result of lack of my regular education in electronics
but some things I just feel , or visualize like that ......
taking in account capacitances or not ......
yup ; immediacy is a word
Ah...another one who thinks that the mere manufacture of a piece qualifies it as a star in the audio heavens. This view usually comes up in the context of what constitutes a classic, but I suppose it's all the same thing in the end.
For the sake of brevity, I'll simply note that nothing made by Counterpoint qualified as a 'runaway success,' regardless of feedback topology, if for no other reason than the fact that the stuff blew up all the time and was only so-so in sound quality. Note that Counterpoint went out of business years ago due to their reliability problems. It looked pretty; I'll say that for it. Wouldn't mind owning one of those old SA-3 preamps, just so I could look at it (separate and distinct from listening to it), but then again it was just a direct ripoff of the cosmetics of the Mark Levinson JC-3 preamp. Incidentally, I used to sell Counterpoint, so I'm a little more familiar with their equipment than the average guy on the street.
I don't have sales figures for the Moscode amps, but judging from the fact that I've never even met anyone who actually owns one I don't know that they have taken the world by storm. Are they out there? Of course they are. But do they qualify as runaway successes? Ummmmm...go get the sales figures before you try to convince me that it sold anything like the number of units that Nelson sells, for instance.
To the extent that persistence is an admirable quality, I'm sure that it's to your credit that you continue to misconstrue the point of my post. I apologize if I have confused you, especially since it seems to have caused you such distress. Perhaps you should consider hitting the "Ignore" button for my posts rather than risk getting further befuddled in the future.
Grey
P.S.: Something about this guy's tone reminds me of Fred. Hadn't thought about him in a while.
For the sake of brevity, I'll simply note that nothing made by Counterpoint qualified as a 'runaway success,' regardless of feedback topology, if for no other reason than the fact that the stuff blew up all the time and was only so-so in sound quality. Note that Counterpoint went out of business years ago due to their reliability problems. It looked pretty; I'll say that for it. Wouldn't mind owning one of those old SA-3 preamps, just so I could look at it (separate and distinct from listening to it), but then again it was just a direct ripoff of the cosmetics of the Mark Levinson JC-3 preamp. Incidentally, I used to sell Counterpoint, so I'm a little more familiar with their equipment than the average guy on the street.
I don't have sales figures for the Moscode amps, but judging from the fact that I've never even met anyone who actually owns one I don't know that they have taken the world by storm. Are they out there? Of course they are. But do they qualify as runaway successes? Ummmmm...go get the sales figures before you try to convince me that it sold anything like the number of units that Nelson sells, for instance.
To the extent that persistence is an admirable quality, I'm sure that it's to your credit that you continue to misconstrue the point of my post. I apologize if I have confused you, especially since it seems to have caused you such distress. Perhaps you should consider hitting the "Ignore" button for my posts rather than risk getting further befuddled in the future.
Grey
P.S.: Something about this guy's tone reminds me of Fred. Hadn't thought about him in a while.
Re: But do they qualify as runaway successes?
Once upon a time, before I became an author, I used to read the letters to the editor column in Analog and marvel at the things the people said in response to the stories. Mind boggling stuff. Enough so that I often wondered if people had even read the stories at all, or whether they simply made everything up in some drug-induced, stream of consciousness fog of poorly conceived verbiage. Then I became an author and started receiving letters of that sort myself. All I can say is that I still don't understand it.
In post #1990, I said, "Tube folks do this sort of thing all the time, but for some reason it's uncommon in solid state." Somehow, that one sentence appears to have caused such a delicious buzz in your mind that you lost track of all objective reality and decided that the entire post was about tubes vs. solid state.
Hmmmm...
I trust that even a casual read of #1990 will dispel that notion from everyone's mind but yours.
Can I have some of whatever you're smoking?
Now, if I cast a somewhat wider net, I find that perhaps you've conflated a dozen points that I made in a number of disparate threads into some sort of muddled, conflicted, confusing mess. In fact, I have to cast the net wide enough to include another website entirely separate from this one: EnjoyTheMusic.com, as I haven't posted a single word here (until now) about the SSTART preamp, which isn't tube, isn't hybrid, and doesn't employ any feedback whatsoever (feedback was the point of my post above, since you seem to have overlooked that little detail) and has, as far as I can tell, no relevance to anything whatsoever in this thread. If my writeup on the SSTART and CJ's ART preamp didn't lay out enough differences for you, then get out a few textbooks and ponder on it for a while. I'm sure you'll be able to come up with some more on your own.
Don't get me wrong, I appreciate your plug for the SSTART, but this thread is about Nelson's F5 and I'd just as soon have it remain so.
I repeat: Can I have some of whatever you're smoking?
Grey
P.S.: Who's Fred? Well, that's a looong story. The short version is that he used to be a member here and had a rather unpleasant tendency to want to fight with most everyone about nearly everything, just about all the time. Sometimes even himself. Considering that probably 99.9% of the posts made during his time here were from one or another of his personae (he used a lot of sock puppets), it was like trying to hold an intelligent conversation with someone afflicted with ten personalities that switched at random, sometimes in mid-point. An acquired taste, perhaps, but I confess that I--and many others--never thought he was anywhere near as amusing as he found himself.
wayness_tamm said:
Once upon a time, before I became an author, I used to read the letters to the editor column in Analog and marvel at the things the people said in response to the stories. Mind boggling stuff. Enough so that I often wondered if people had even read the stories at all, or whether they simply made everything up in some drug-induced, stream of consciousness fog of poorly conceived verbiage. Then I became an author and started receiving letters of that sort myself. All I can say is that I still don't understand it.
In post #1990, I said, "Tube folks do this sort of thing all the time, but for some reason it's uncommon in solid state." Somehow, that one sentence appears to have caused such a delicious buzz in your mind that you lost track of all objective reality and decided that the entire post was about tubes vs. solid state.
Hmmmm...
I trust that even a casual read of #1990 will dispel that notion from everyone's mind but yours.
Can I have some of whatever you're smoking?
Now, if I cast a somewhat wider net, I find that perhaps you've conflated a dozen points that I made in a number of disparate threads into some sort of muddled, conflicted, confusing mess. In fact, I have to cast the net wide enough to include another website entirely separate from this one: EnjoyTheMusic.com, as I haven't posted a single word here (until now) about the SSTART preamp, which isn't tube, isn't hybrid, and doesn't employ any feedback whatsoever (feedback was the point of my post above, since you seem to have overlooked that little detail) and has, as far as I can tell, no relevance to anything whatsoever in this thread. If my writeup on the SSTART and CJ's ART preamp didn't lay out enough differences for you, then get out a few textbooks and ponder on it for a while. I'm sure you'll be able to come up with some more on your own.
Don't get me wrong, I appreciate your plug for the SSTART, but this thread is about Nelson's F5 and I'd just as soon have it remain so.
I repeat: Can I have some of whatever you're smoking?
Grey
P.S.: Who's Fred? Well, that's a looong story. The short version is that he used to be a member here and had a rather unpleasant tendency to want to fight with most everyone about nearly everything, just about all the time. Sometimes even himself. Considering that probably 99.9% of the posts made during his time here were from one or another of his personae (he used a lot of sock puppets), it was like trying to hold an intelligent conversation with someone afflicted with ten personalities that switched at random, sometimes in mid-point. An acquired taste, perhaps, but I confess that I--and many others--never thought he was anywhere near as amusing as he found himself.
Nice seeing ya over here again 
Ref. post #1969
There has been some progress; new PCBs are completed and tested with clips on large heatsink and +/- 17.5 V PSU (1.3 A bias). After an hour of listening I couldn't spot a difference compared to standard F5 - although there are some minor component changes:
1. MOSFETs' source resistors were two 1R in parallel, now it's two 0R22 in series
2. 10K resistors in the current limiter circuit are changed to 22k as Mr. Pass recomended
I'll report again after I mount it properly in the case and after some friends lend me their ears (and some of their gear) in listening session to help evaluate further.
There has been some progress; new PCBs are completed and tested with clips on large heatsink and +/- 17.5 V PSU (1.3 A bias). After an hour of listening I couldn't spot a difference compared to standard F5 - although there are some minor component changes:
1. MOSFETs' source resistors were two 1R in parallel, now it's two 0R22 in series
2. 10K resistors in the current limiter circuit are changed to 22k as Mr. Pass recomended
I'll report again after I mount it properly in the case and after some friends lend me their ears (and some of their gear) in listening session to help evaluate further.
Attachments
Re: gerbers?
Hi increek22,
I use Sprint Layout for PCB drawing and in version I have gerber export is not working, so I attach a ziped high res. .JPG (2100 x 500 px) which I hope won't come out fuzzy.
It's a bottom view pic, PCB dimensions are 105 x 25 mm - component placement is self-explanatory for such a simple circuit. Good luck !
increek22 said:
Hi increek22,
I use Sprint Layout for PCB drawing and in version I have gerber export is not working, so I attach a ziped high res. .JPG (2100 x 500 px) which I hope won't come out fuzzy.
It's a bottom view pic, PCB dimensions are 105 x 25 mm - component placement is self-explanatory for such a simple circuit. Good luck !
Thank you Jumo.
If any interest, I posted a layout for the B1 buffer under the B1 Buffer Preamp posts. It is also for single- sided PCB. I drew it in "PCB Artist" which is a free download. So anyone can download PCB Artist or other gerber tool and printed on transparancy for photo sensitive boards, or to a laser printer on toner-transfer film. I have had good luck with the transfer films and etching at home.
Next project is an F5. Thanks to all for this great forum!
Joe
If any interest, I posted a layout for the B1 buffer under the B1 Buffer Preamp posts. It is also for single- sided PCB. I drew it in "PCB Artist" which is a free download. So anyone can download PCB Artist or other gerber tool and printed on transparancy for photo sensitive boards, or to a laser printer on toner-transfer film. I have had good luck with the transfer films and etching at home.
Next project is an F5. Thanks to all for this great forum!
Joe