Thanks, Hugh.
Let's see what how the next try goes. If I fail with that ... is it possible to use a pair of NPN & PNP bi-polars instead of JFETs, for a zero DC offset buffer? So:
* signal comes into the bases
* emitters are joined with a pot, and
* collectors are at +25v for the NPN and -25v for the PNP?
Or would the:
* signal come into the collectors
* emitters are joined with a pot, and
* bases are at +25v for the NPN and -25v for the PNP?
Regards,
Andy
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Because of the invariant 0.65V Vbe on a npn and pnp, you are unable to drive them with conjoined bases; you have to separate them, and drive each base with a DC separation.
No, I'd stay with your jfet, but there may be something else that is wrong, since joining the two fet gates is very easy to achieve bias - then the adjustment to quiescent is done with the source resistors - a pot as you suggest. That should work fine, though you can adjust offset there with a reference voltage - only millivolts - applied to the gates even though that needs a DC blocking cap.
Cheers,
Hugh
No, I'd stay with your jfet, but there may be something else that is wrong, since joining the two fet gates is very easy to achieve bias - then the adjustment to quiescent is done with the source resistors - a pot as you suggest. That should work fine, though you can adjust offset there with a reference voltage - only millivolts - applied to the gates even though that needs a DC blocking cap.
Cheers,
Hugh
Thanks for that info. Pity!
Interesting - perhaps we can discuss this over kafe in a coupla weeks? Meanwhile, as I said, I will check what I've done, in case I connected up the 2SJ103 the wrong way round.
Thanks,
Andy
AS,
I haven't spoken to Grey for five years, however, many people get sick of the carping and bullying and walk away. It's nothing to do with the forum per se, just the personalities who post, and the mods do a very good job, but as you know any forum is a form of addictive behaviour, and therefore takes over one's life to a degree. I try to restrict my input so that I have some balance in my life; for example every day I visit a café and meet and chat with people over coffee. I have found that it's difficult to have a genuine friendship with virtual people; you need to talk to real people, in face to face.
Could it be that Grey, who was a pungent, strong personality, feels the same way?
Hugh
I haven't spoken to Grey for five years, however, many people get sick of the carping and bullying and walk away. It's nothing to do with the forum per se, just the personalities who post, and the mods do a very good job, but as you know any forum is a form of addictive behaviour, and therefore takes over one's life to a degree. I try to restrict my input so that I have some balance in my life; for example every day I visit a café and meet and chat with people over coffee. I have found that it's difficult to have a genuine friendship with virtual people; you need to talk to real people, in face to face.
Could it be that Grey, who was a pungent, strong personality, feels the same way?
Hugh
Teflon baby Teflon. Ronald Reagan was the Teflon President because criticism never seemed to stick. I believe in free speech. In the world of hi fi there will be heated disagreements and personal attacks. ignore them, words cannot kill you. they can make you angry but they cannot kill you. do not let words chase you away from diyAudio forum or any forum. Be strong not weak of mind. Be Teflon.
Ah yes, but we all get old and tired........ in Reagan's case however he developed dementia; in that situation words eventually lose meaning. Then we consider risk and reward; people risk much in forums as they start out, a lot of disclosure and strong comments, but after a time they often ask themselves what the rewards (or downsides!) really are.
In my situation, I stay on because I run a business. It's largely instrumental. I enjoy many of the people I talk on the forum, but I remind myself that I'm not here to demonstrate how clever I am, hell, there are lots of people that are smarter than me, but the abilities of a human are myriad. Many have huge academic and maths backgrounds and can agree anything very cogently, but a few are intensely practical and they have huge value on this forum. A very good example is Tubelab, George, who is the most experienced tube designer and builder I have ever seen. A couple of years he developed a scaleable push pull pentode amp with plentiful TV tubes which can be built out to more than 500W. This is an astonishing design. He has always offered an exceptional, elegant cathode follower 25W SE amp with 50% plate efficiency. He never professes philosophy or ideology - he simple builds an idea he has and then lists the pros and cons. Recently he suffered the decline of US manufacturer and lost his job. Very sad. These guys are worth gold. Another fascinating and well educated fellow is Bigun, who is very active and offers full on, well developed amps. And he has a marvellous persona on this forum, very pleasant to everyone.
There is a long thread discussing current v. voltage feedback. Most are interested only in the ideas and concepts; but very few actually build these two topologies, otherwise identical, and compares the sound quality. This is hard work, not the sort of thing most hobbyist do. It's very interesting, but I'd always try to build the amps and then compare the sound quality. To me this is the definitive outcome of our fascinating hobby.
Cheers,
Hugh
In my situation, I stay on because I run a business. It's largely instrumental. I enjoy many of the people I talk on the forum, but I remind myself that I'm not here to demonstrate how clever I am, hell, there are lots of people that are smarter than me, but the abilities of a human are myriad. Many have huge academic and maths backgrounds and can agree anything very cogently, but a few are intensely practical and they have huge value on this forum. A very good example is Tubelab, George, who is the most experienced tube designer and builder I have ever seen. A couple of years he developed a scaleable push pull pentode amp with plentiful TV tubes which can be built out to more than 500W. This is an astonishing design. He has always offered an exceptional, elegant cathode follower 25W SE amp with 50% plate efficiency. He never professes philosophy or ideology - he simple builds an idea he has and then lists the pros and cons. Recently he suffered the decline of US manufacturer and lost his job. Very sad. These guys are worth gold. Another fascinating and well educated fellow is Bigun, who is very active and offers full on, well developed amps. And he has a marvellous persona on this forum, very pleasant to everyone.
There is a long thread discussing current v. voltage feedback. Most are interested only in the ideas and concepts; but very few actually build these two topologies, otherwise identical, and compares the sound quality. This is hard work, not the sort of thing most hobbyist do. It's very interesting, but I'd always try to build the amps and then compare the sound quality. To me this is the definitive outcome of our fascinating hobby.
Cheers,
Hugh
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no talking about politics and religion. no talking about abortion. But discussing stereo is like talking about politics. Some people think tubes are stupid to use and ancient, that those who believe in cables are nuts. Your opinions and facts are going to upset some or a lot of people. As a result some people are going to be banned for what they say. Is it possible to have a civil discussion about stereo? I think Hi Fi brings out the best and worst in us. Before the internet you could not offer your opinions to the world. The internet gives you a voice. I wish there was a Hi Fi forum with no censorship. anything goes. This is true of sports forum. Guys there are opinionated and very mean and critical. I don't believe in censorship. I want to hear both sides and make up my own mind. My posts are usually very short but even then some people think my postings are dumb, ignorant and stupid. but I am Teflon. do not get discouraged about the rudeness. Life is adversity. it would be very dull if somebody agreed with you all the time! You guys need to post and pass on your knowledge and passion to the next generation.
Problem solved! Yes, Hugh, it does work fine!
I inserted a 1Mohm resistor between the joined bases & the PS 0v - the JFETs need an earth reference! This would've happened as a matter of course in the real build but in my "test rig" (which I created to be able to measure the Source resistor values required to achieve zero DC offset for each complementary pair, so I can order the appropriate combination of fixed res and parallel pot), I had left this off.
So, with the earth-reference resistor in place, now I can get down to <1mV DC offset for the 3 pairs I've tried so far. (If I hadn't been able to get a <2mV DC offset with the first complementary pair I tried I would've figured out this earth-reference resistor was required, long ago!
)So now to measure the remaining 11 complementary pairs and then order the resistors & pots.
Regards,
Andy
Thanks Jens,
Folks,
Steve and I have finished the R&D on the next two amplifiers from Aspen - large ones.
NAKSA 125
This amp uses 52V rails and is rated to 125W into 8R and 190W into 4R. Extremely and unusual rail efficiency. Bipolar design with a single pair of large mosfet output devices. Clip into 8R is 140W, this is a very large scale amplifier and supernatural quiet.
Quality: Up to the NAKSA 80, but a sense of large sense just as you'd expect. It uses low global feedback and exhibits the N80 qualities of musicality and image and resolution.
NAKSA 200
This amp uses 65V rails and is rated to 200W into 8R and 300W into 4R. This amp is very similar to the N125 but uses some dimensional changes and very powerful output mosfet devices. Again, quote output is extremely conservative. Bipolar design with a single pair of 480W mosfet rated output devices. Steve has built the first example; clip is not known yet but expected to be stupendous. This is Aspen's version of a very powerful amplifier with all the usual audiophile qualities and should be able to cope with absurdly difficult loads.
Quality: Up to the NAKSA 125, with no expected reduction of sonic qualities at all. Similarly the N200 uses low global feedback and exhibits the N125 qualities of musicality and image and resolution.
I am moving slowly with production, although I now have numbers of N125 stock. My health is OK but slowing me down as I try to force my weight now as the Docs get my meds correct. As my situation is pleasure rather than work, I do not keep my clients as happy as I should, my delays are infuriating but I'm not prepared to compromise my work output at this point.
I am delighted to talk to people over coffee at any time of the day!!
This has been a wonderful six months, and I thank Steve, Paul and Jon for their help more than than they know. The designs are rolling off the PC at present; I am even surprised myself that the creative thoughts are coming even late in my life.
My big issue now is my website. I have lost any ability to edit it; I was bad with software before, since my illness I'm a complete idiot, but I find it hilarious......... the only way to confront our demons!
Cheers,
Hugh
Folks,
Steve and I have finished the R&D on the next two amplifiers from Aspen - large ones.
NAKSA 125
This amp uses 52V rails and is rated to 125W into 8R and 190W into 4R. Extremely and unusual rail efficiency. Bipolar design with a single pair of large mosfet output devices. Clip into 8R is 140W, this is a very large scale amplifier and supernatural quiet.
Quality: Up to the NAKSA 80, but a sense of large sense just as you'd expect. It uses low global feedback and exhibits the N80 qualities of musicality and image and resolution.
NAKSA 200
This amp uses 65V rails and is rated to 200W into 8R and 300W into 4R. This amp is very similar to the N125 but uses some dimensional changes and very powerful output mosfet devices. Again, quote output is extremely conservative. Bipolar design with a single pair of 480W mosfet rated output devices. Steve has built the first example; clip is not known yet but expected to be stupendous. This is Aspen's version of a very powerful amplifier with all the usual audiophile qualities and should be able to cope with absurdly difficult loads.
Quality: Up to the NAKSA 125, with no expected reduction of sonic qualities at all. Similarly the N200 uses low global feedback and exhibits the N125 qualities of musicality and image and resolution.
I am moving slowly with production, although I now have numbers of N125 stock. My health is OK but slowing me down as I try to force my weight now as the Docs get my meds correct. As my situation is pleasure rather than work, I do not keep my clients as happy as I should, my delays are infuriating but I'm not prepared to compromise my work output at this point.
I am delighted to talk to people over coffee at any time of the day!!
This has been a wonderful six months, and I thank Steve, Paul and Jon for their help more than than they know. The designs are rolling off the PC at present; I am even surprised myself that the creative thoughts are coming even late in my life.
My big issue now is my website. I have lost any ability to edit it; I was bad with software before, since my illness I'm a complete idiot, but I find it hilarious......... the only way to confront our demons!
Cheers,
Hugh
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