I'd lose my head if................

[tonequester]

tonequester here.

I've gotten so much from this forum that I've been taking quick notes of all the leads that the great folks have given me, so that I can get to them quickly
at a later time. I note who it was that posted or replied to my post, in order to get back to them if it seems proper. So far, so good, but it had to happen. I was given a couple
of "articles" to check out concerning Harmonic Distortion : www.passdiy.com/pdf/distortion feedback.pdf, and www.passdiy.com/pdf/zealite.pdf. The first article I highly recommend to ANYONE. The problem is, that I can't for the life of me think of who recommended them to me. I forgot to make the note like I had mentioned. Nothing came
up on the second "article". I may have written it down wrong, I just don't know. However, the whole thing lead me to Pass DIY, and a large assortment of great
info, written by Nelson Pass. I'll be spending quite a bit of my time at that site. Still, I don't know just who to thank. I have the feeling that it was Enzo, but I may be wrong on that. WHOEVER it was, thank you. Just the first article was priceless for what I learned about harmonic distortion, intermediate distortion, and the pro's and con's of negative feedback. Whoever the mystery man is(and I,ve covered the forum trying to find out) I wish him all the best,.....and more ! tonequester out.

[pdf64]

Thanks, I missed that thread.
The link in the OP has a problem, try http://www.passdiy.com/pdf/distortion_feedback.pdf

[km6xz]

Interesting, Nelson and I worked together in the 70s as designers for hi-fi and shared a lab. I was doing some projects as consultant and he was an employee. He was developing speakers and had just graduated from UC Davis in Physics. Most of his work was taking a crude patient from a physicist from Austria, Dr Oscar Heil who was the real deal. He had patented a new type of hf transducer that showed a lot of promise and Nelson designed a workable production ready device from the crude version that was the subject of the patent. Nelson was not into electronics at all at that time. I was designing the first digital FM tuner and a RF capacitor phono-cartridge.
Brings back some memories, I went into recording and music production and he went into amp design and manufacturing starting Threshold. There was a lot of tinkering with the new speaker driver to get it working well, and it really turned out great, and was the basis for the company exploding in sales over the next couple years marketing the AMT (Air Motion Transformer ). We had full run of the development woodworking shop and could draw any cabinet up and two days later it would be sitting in the lab ready to experiment with. We were both in our early twenties and had lots of energy to experimenting and testing. A number of the best cabinet designs were for our own use, not being practical for production or home living rooms.

[Steve Conner]

As far as hi-fi audio goes, I'm a follower of Douglas Self and don't have much time for Nelson Pass's stuff.

However, Pass's writings on distortion, and his design philosophy, are arguably more relevant to musical instrument amps. For example, Douglas Self wrote three books and a host of magazine articles on power amps, without ever touching on what happens when his designs are driven into clipping. The answer, as I found out the hard way, is that his "beta-enhanced VAS" circuit saturates and hangs up horribly. The beta-enhanced VAS is also what gives his designs their low distortion performance, so you can't throw it away.

[km6xz]

I really care very little about hi-fi now and do not even have a good system. After recording records so long listening to recorded music is not fun for me. I would much prefer listening to a bad bar band live than a great recording. There are way too many other issues in life to waste a bunch if time chasing sonic phantoms that hi-fi tweakers tend to do.
I've built a number of significant playback systems but got tired of listening passively on a perfectly placed audition chair in a perfect treated acoustic environment of an auditioning room. Being on the dance floor at 4am is much more relevant to my world view now;>) I listen to most music with my feet.

[Enzo]

And I can take no credit for the reference, wasn't me.

[JoeM]

The power amp for my stereo is a Citation 12 that I completely rebuilt from an article in Audio Amateur by Nelson Pass. His design uses power MOSFETs. This was about 1980, I dont even turn it off and it still works perfectly.

[Steve Conner]

Yep. I've seen that article, and his redesign was a real improvement IMO. The MOSFETs were faster than the crappy power BJTs originally used in the Citation, and that probably meant less high frequency distortion and a better-sounding amp. In fact, Pass stated as much in the article and supplied distortion plots to prove his assertion.

However, BJT technology has come forward a lot, and (IMO) Pass Labs have gone backwards. Last I looked, they were making single-ended Class-A amps with silicon carbide power JFETs that cost about $75 each.

I'm going to guess that you don't turn it off because if you ever had to turn it on again, your woofers might not survive the massive turn-on thud.

[Tom Phillips]

...I've been taking quick notes of all the leads that the great folks have given me, so that I can get to them quickly
at a later time. I note who it was that posted or replied to my post, in order to get back to them if it seems proper...

Are you aware of the "Printable View" feature under the thread tools menu? It will give you a nice record of the tread to print or copy and paste into another program. The result is a nice format that records the author and date of each post. It also preserves the live web links. If you save the text in a file you can edit to keep just the information you want, add your own notes, add additional information from other sources etc.
Hope you find this useful.
Cheers,
Tom

[tonequester]

tonequester here.


Greetings from Kansas, km6xz. I just had to tell you that your post concerning the bringing back of memories made for happy reading. It amazes me that in this "age"
one can be carrying on a "conversation" across half of the world with someone who has played a part in electronics history, and knew others like Dr. Heil who were "making their mark" as well. These days I'll wager that I'd have to search high and low to find anyone of the general public who knows what an Air Motion Transformer is. I can say that A friend I had the pleasure of listening to a pair and examining them in "wonder". This happened in the early 80's. A friend and co-worker purchased a pair for his small apartment. I cannot remember the brand name
of the speaker cabs, but they had the AMT's. He played some Electric Light Orchestra on his rig to impress me, and I must say that I endured one song, fearing that the second story apartment would collapse. Whatever the brand, they handled plenty of power. It must have been rewarding to be right "in the midst" of the electronics revolution?evolution of those days.
Thanks for the interesting posts, and helpfulk advice. May all of your todays, become tomorrows. tonequester.

[tonequester]

Advice on forum details.

tonequester here.

Greetings Tom Phillips. I wish to thank you for the advice concerning the various ways to keep "things" under control on the forum. I'm a newbie of perhaps 2 months, and I haven't mastered my laptop, nor even "computing" yet. I can use all the help that I can get. I appreciate your taking the time. your advice is duly noted !
tonequester.

[tonequester]

tonequester here.


Greetings Steve. I just had a minute to catch up on things here and got the chance to read your replies to the post. I now have quite a few generous souls trying to help
me learn a thing or two about the equipment that has been a big part of my life for 32 years now. I'll get "there", slow but sure. You have been answering my posts from the very first one.
I can't find words to express my good fortune at joining this forum and "meeting" so many good folks that are willing to share, folks like you. I have one question that I've been tempted to ask you and haven';t as yet. I'm going to give it a shot and if you don't want to answer it..........no problem. You seem to be very advanced in theory, and I just can't help but wonder
what your career is. At first I assumed that you were first a musician, and then gifted with electronics knowlege. I,ve read enough of your posts now to re-think that one, not that you aren't a gifted musician as well. As always.....Just curious. tonequester.

[tonequester]

tonequester here


Greetings pdf64. I'm afraid that I don't know what the OP even is ! I couldn't bring up the second thread listed, but the first, the one you named is great. It also led me to
Pass DIY. It has a ton of interesting articles by Nelson Pass. I found out from km6xz that Pass was responsible for bringing Dr. Oscar Heil(inventor,Air M otion Transformer) to
the U.S. I don't know if you've had the time to read the thread yet, but I'm sure you'll probably understand it better than I did, although I think I got the "gist" of it.
Have a "good 'un" ! tonequester.

[Steve Conner]

Who me? I'm an engineer, I design industrial electronics for a living, and I use the money to inflict my musical creations on the world.

[km6xz]

A little clarification. Dr Heil licensed the AMT concept to ESS, ElectroStatic Sound Systems who was Nelson's employer, so Nelson did not bring to the US, but they became close friends and even attended his wedding. Heil was an interesting man, many skills but his main one was the same one that Richard Feynman was best remembered for: being able to get to the heart of complex concepts and be able to explain it so anyone could understand, not by simplifying but by coming up with extremely appropriate analogies that were predictive of future behavior. Most of his work had been in materials and electronics, for example invented the FET.
He came up with a concept that he thought might be useful in transmitting sound through sealed environments passive, but amplifying them. He envisioned a communications port into and out of an sterile operating theater for example. His first crude working models were quickly applied to an active transducer that could be used as a speaker. He only knew one name in hi-fi so he contacted Fisher which was a big name at the time, and he had met Avery Fisher in the day.
The company, he said, were rude to him and dismissed his device as junk. That really angered him, he was going to market it in spite of them, when his offer was simply to give it them for no money, he just thought it was an advance that should be exploited.
He found ESS, a company run by Liberal Arts professors at Sacramento State University who were interested in music but not technology. Nelson and Dr Heil started working on refining it so it sounded better and Nelson was left to polish the design to make it superior to what was available.
In the meantime Dr Heil went back to work on a AMT Woofer. He came back with a strange looking cylinder about 12" in diameter, with cast frame and lots of reinforced Styrofoam disks. It worked, I was there when it was first tried, and it produced deep bass at moderate volumes with great efficiency but would clatter and bottom out when driven to higher levels. The beauty of it was that every part except for the home case aluminum frame was from the hardware store and the main coupling between the many 11" dia disks were paper drinking straws! Elegant! We measured 20hz being down only a couple db from 100hz and very low distortion, unlike any cone speaker and 5 times faster acceleration than a cone speaker so just like the mid-hf AMT was capable of decent looking square waves. Some miniature versions were developed that where intended for headphones also but never released. The woofer never made it out of the lab either. The name ESS went through several hands after the professors proved to not be very good businessmen. They grew the company based on the AMT to be the second largest speaker company but expanded into things that were not good fits so the company imploded, just like Alesis did after taking the industry by storm, mismanagement going on a spending spree brought the whole thing down in a matter of months.