John Curl's Blowtorch preamplifier part II

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Personally, I do not understand why you say such crazy things, Wavebourn.
Perhaps, you do not understand the definition of: NO COMPROMISE
Perhaps a Skoda is your sort of practical 'compromise' and a Porsche is my sort of 'no compromise' design. It is not an impossible design, but a design with a minimum of performance compromises.
Are you trying to impugn my design reputation? This is what you appear to do constantly, and I think that it is to 'sell' yourself to perspective clients, if that is possible. It won't work, and I suspect that this sort of attitude has hurt your job prospects in Silicon Valley as well. They want team players as well as good engineers.
I would normally keep this to myself, but I think that you should know it.
 
Bob, I have a stupid question. How does one wind an air-core toroid? Or more specifically, isn't there a problem removing the form? I'm thinking of this in comparison with the solenoid case where the form might be, say, a dowel which you can just slide out when done winding.

Try a non-magnetic non-conductive former.

I use 10mm diameterTeflon tubing. Then vacuum impregnate the construction with varnish to stop it 'singing'.
 
Then never touch Class D with NFB. This is what it takes: http://eprints.nottingham.ac.uk/501/1/final.pdf

P.S. I have spend only 10 minutes reading this work, so I don't claim understanding more than the basic plot. I don't plan spending more time on it :)

Hi syn08,

Thanks for posting this. It looks like a great reference and an excellent read on a very important aspect of class D amplifiers. When and where was it published?

Thanks,
Bob
 
It never ceases to amaze me, as to why people bring their most fun topic of what they are doing to this thread.

Now, taking a deep breath, I will attempt to remind everyone as to why this thread has grown so 'popular' (in a sick sort of way) and my original intentions of contributing to this thread.

Now, where to go from here? Back to discussing the subtleties of quality preamp design, or continue the aimless diversions that just confuse the issue?

Hi John,

This is indeed a popular thread. It is the "watercooler" thread in this forum. It has touched on many topics of interest to people here, certainly not just the topic of preamplifier design.

Are you complaining about the recent conversations about class D amplification?

I plead guilty to bringing that up, but it was in the context of PIM. The follow-up discussion that occurred seems to reflect some interest on the part of the participants in class D.

Cheers,
Bob
 
Bob, I have a stupid question. How does one wind an air-core toroid? Or more specifically, isn't there a problem removing the form? I'm thinking of this in comparison with the solenoid case where the form might be, say, a dowel which you can just slide out when done winding.

Hi Andy,

Very good question. I first used air core toroids for the output network of my Super Gain Clone amplifier, wishing to minimize possible magnetic field interactions from the coil. It was just a fun thing, and I really don't know whether it made much difference.

I made the coil by winding the turns on a pencil, removing the pencil and then forming the solenoid structure into a toroid by gently bending it by hand.

Cheers,
Bob
 
I have only seen this in a PC SMPS , only a few turns , but it was toroidial (wrapped around a plastic former) . Was PE or a teflon- like plastic.

Try a non-magnetic non-conductive former.

I use 10mm diameterTeflon tubing. Then vacuum impregnate the construction with varnish to stop it 'singing'.

I first used air core toroids for the output network of my Super Gain Clone amplifier, wishing to minimize possible magnetic field interactions from the coil. It was just a fun thing, and I really don't know whether it made much difference.

I made the coil by winding the turns on a pencil, removing the pencil and then forming the solenoid structure into a toroid by gently bending it by hand.

Thanks very much guys.

Love this new multi-quoting feature too :).
 
Hi Bob;

as I asked before;

when eliminating source of PIM we replaced the filter choke by an air core one, then surround the whole thingy by feedback, do we create PIM as the result, since the amp is not ideally linear?

What is better:
to leave an inductor that creates PIM on the place, then reduce PIM using feedback (as you said a negative feedback reduces pre-existing PIM);
or to replace it by an air core one, then generate PIM applying a negative feedback?

Hi Wavebourn,

I may have been unclear in what I was trying to convey in my original post relating the the generation of PIM in class D amplifiers.

As we have noted in many PIM discussions, PIM can be created in two ways (at least). First, it can be created by negative feedback that surrounds an amplifier that does not otherwise have PIM. This is what Otala, myself and Gilbert discussed the most.

The second way that PIM can be generated is often by passive components whose values change as a function of signal voltage or current. In a linear amplifier a good example of this is variation in the collector base capacitance of the VAS.

In the class D example I was citing primarily the second type of PIM caused by passive components, even in the absence of negative feedback. This was simply due to the output filter inductance varying as a function of the signal current. This can happen in class D amplifiers that have no negative feedback,

There are also class D amplifiers that have negative feedback that is either tapped off ahead of or after the output filter. Those may have PIM created by the negative feedback process as well.

For those where the feedback is tapped off ahead of the output filter, those amplifiers will still be left with the undiminished PIM created in the output filter. This may often be larger than any PIM that is created by the feedback process (that is another point of comparison I was making in the original post).

For those amplifiers that tap the feedback from the far side of the output filter, the negative feedback enclosing the output filter will reduce distortions introduced by the filter, including PIM.

The best solution is to use the highest-quality output inductor in the first place, possibly even an air core inductor. Then negative feedback should be applied around the output filter if possible. Although the use of a high quality inductor will reduce or eliminate the PIM and other filter distortions, it is still desirable to have feedback enclose the output filter to reduce output impedance at high frequencies, retaining damping factor and making the amplifier frequency response less load-dependent. The challenge is to be able to employ a meaningful amount of negative feedback while retaining stability.

Self-oscillating class D modulators are a whole 'nother story.

Cheers,
Bob
 
Hi PMA, I didn't live in the USSR, so I only know Skoda, from the old days. I have seen Russian autos, but I could not know them by name. Stlll, if Skoda does what I think it does, today, then it is still a pretty good example of a good 'compromised' car. Let us compare it to an upscale Mercedes, for example.
 
No problem, just mentioning that Skoda is a Czech, not Russian car :)
 

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Bob, this is a pretty thinly veiled attempt to divert the the thread into something that is 'politically correct', and pushing me into the background, as this is not my area of expertise.
Please everyone, this is the only thread on this website that is directly associated to me, because the title has both my name and my product in it.
Over the years, when I attempted to expand this thread, myself, with amps, microphones, and general ANALOG audio design, all related to the original BLOWTORCH design philosophy and execution, I was resisted by many here as departing from the original intent of the thread. Now, it's to be a free-for-all, just because this thread has been popular?
Of course, there are a number of parallel threads, some of which are concerned with class D design. Do you see me jumping in and inserting analog design techniques in these threads?
It is a fact that this thread attracts a lot of morbid fascination due to the 'hot and heavy' debate about how to design audio products that has gone on here for years. That is most probably why this thread is most popular, rather than any intellectual content, especially recently. For me, the wish, even the 'need' to broadcast what many audio designers have found to be 'successful' audio design philosophy, over the decades, has kept me here, even when the people who first invited me, are either banned or so annoyed with the backtalk, that they do not even bother to contribute on a regular basis.
What a loss it is for this website, but then if you just want to repair your amp, or build your first audio preamp, who cares about the subtle aspects of sophisticated audio design? Now, there is a time and place for beginning in audio, and it is probably best not to start with the expensive stuff, first.
For example, when I was a teenager, I was given a 1954 Chevy to drive. It had a very conventional 6 cylinder engine that was relatively easy to work on. I set forth to add a 2 carburetor arrangement, and dual exhaust. I then learned the tradeoffs of doing these changes, and over the years, learned to modify and work on car engines, myself, to doing engine rebuilds. Had I started with a Mercedes or a Porsche, I might have found my efforts not only wasted, but even destructive, given that these designs are already engineered to relative perfection for their purpose, and leave little room for change without upsetting something, bigtime. I might, then, have been diverted from trying to modify any auto, in future, and lost developing an area of understanding about auto repair and modification.
It can be that same in DIY audio. If you started with a Marantz 9 tube amp and tried to make it more powerful, or lower distortion, you would probably destroy it. However, if you start with a Dyna tube amp, there is lots of room for improvement, yet you don't start with 'junk' so your efforts can be very rewarding. Now, once you get experience in modifying Dynas, or their solid state equivalents, then what? Well, most here, especially engineers, represent the equivalent of General Motors or Ford. They would rather scoff at Mercedes, Porsche, BMW, etc. as overpriced, overengineered, etc.
Now if you are a backyard 'mechanic' or a DIYer, do you want to know what Porsche, Mercedes, etc have learned about improving cars, and what similarly situated high end audio designers have learned, in making hi end designs, or do you want to be told, that it does not make any difference to just get across town, anyway, or that music is recorded lousy, anyway, so why bother with more than an IC in your design?
Everyone, it is your choice.
 
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By JC - Bob, this is a pretty thinly veiled attempt to divert the the thread into something that is 'politically correct', and pushing me into the background, as this is not my area of expertise.

I think mr. Cordells example could be applied to BOTH analog and class D , so It might be premature to call it "offtopic" . It has me interested in trying different NFB takeoffs and possibly using a air core toriod at my main OP. :cool:

By JC - It is a fact that this thread attracts a lot of morbid fascination due to the 'hot and heavy' debate about how to design audio products that has gone on here for years. That is most probably why this thread is most popular, rather than any intellectual content, especially recently. For me, the wish, even the 'need' to broadcast what many audio designers have found to be 'successful' audio design philosophy, over the decades, has kept me here

The "morbid fascination" can be a good thing , it keeps them coming (and reading/learning). So , in the end , at least some knowledge is disseminated.

By JC - What a loss it is for this website, but then if you just want to repair your amp, or build your first audio preamp, who cares about the subtle aspects of sophisticated audio design?

This might apply to most newcomers , who post to beg for help with their latest EBAY audio acquisitions. For others "who are hooked" :spin: , "subtle aspects" are vigorously debated (all aspects of component choice , layout styles) we constantly search for either a better OP stage (look at the "hoopla" :mad::mad: the krill thread caused :eek: ) or whatever will make for more reliability , lower THD , faster ... an on and on.

If this was not true , DIYA would just have the DX amp (a good amp for new members) ... no variety , but instead , every flavor of every topology is here and most designs are in a constant state of "evolution".
PS - I hate IC's - I just repaired a bass guitar amp with an STK-4050 , I a/b'ed it with one of my discrete DIY amps and there is no competition.
OS
 
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OK John, I usually don't put people down, but in your case, I'll do it anyway, as you refused to play with carbon, even offered to do it for free.

A Mercedes is not engineered even close to it's max., take a look at Kleemann for example.

I have had the pleasure of driving one of those Kleemancars, and it is in just about any way, waaaay above a Mercedes.

So is RUF, in the exact same way......so stick to talking about something you know something about.

I happen to be developing carbon disc brakes for performance cars, which has given me a chance to see much of the top stuff.

Magura :)
 
Give me a break, Magura. Of course, an expert can modify a Porsche and make it into a RUF Porsche, but a novice can't. That was my point. Personally I usually don't use output coils, (remember that debate?) so 20uH output coils don't mean much to me. In fact, in analog, more that 2uH is too much, and that is invariably air coil, unless you are a 'General Motors type' designer. Now, if I told you that when I have even made a 2uH coil or less that I like to use 14 ga oxygen free wire, half my critics here would hit the roof, and tell me to prove its worth, or forever hold my peace, wouldn't they?
Now we are 'dancing around' toroids, for some reason. Not that there is any good reason in ANALOG to consider them seriously.
Take my word for it, it is a diversion from further addressing more painful subject matter.
 
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Hi John,
Now, if you, Anatech, were a well known designer, with design credits that I would know about, maybe I would take you more seriously, but frankly, I don't know what you are talking about, half the time, except when you are attacking me directly. This is how I see it.
Actually John, I can accept that I am not a well known designer. This doesn't bother me at all. To my credit, many engineers who I have worked with tell me I have good solid instincts and the changes I have suggested in their designs have worked well. These are people who really do not want to be front and center as you like to be. They would rather work and go home like everyone else. They are happy and well adjusted people. ;) They recognize me for what I'm worth, and they do listen when I make a suggestion. I'm not always right, but I learn like most other people around here.

Good information is available all around you, it's up to you to recognize it for what it is. I'm talking about everyone here, not just me.

I think the only reason you say you don't understand what I'm saying is due to two things. One, you don't pay attention when anyone who is not a "name" talks to you. You also see only your viewpoint and generally assume the worst in people. I'll bet that's why you attack members for no particular reason. That's even when they support you!

Now, about this bit where you say I attack you directly. Not once have I attacked your designs - ever. The only thing I have spoken up about is the way you behave and the way you treat others around you. That's it, your poor behavior around other people.

Please everyone, this is the only thread on this website that is directly associated to me, because the title has both my name and my product in it.
Big whoop!
The name is the "Blowtorch" originally, someone added your name to this title. I wonder who that could have been? Anyway John, you had two partners, so it's really about 1/3 of you at best.

You are more than capable of beginning a new thread on any subject, and I think you should have treated some things you brought up here in it's own thread. That way you couldn't accuse people of being off topic.

It is amazing to me to be called a liar, a blowhard, etc.
Well, I have never called you anything. I have pointed out how you are acting from time to time. Concentrate on acting professionally.

My friend got very upset with me, and told me to keep my mouth shut, at least for several months. He has HIS reasons, and I have a big mouth.
That would be your personal problem, not ours. Why would you be telling us these things?

You do not have a big mouth John, you never share anything of value unless you are using it as an example to gloat over "your" achievements. Every single subject you have mentioned has never been expanded upon by you. Mind you, all you have to do is claim something and you will learn all about these things from other members.

That is how many companies cheat people by finding patents and actively attempting to break them. So, I shut up about that venue of measuring PIM.
Please John, this is the American system after all. It's well known, and I have pointed out many times that your competitors search patents in order to figure these things out. Heck, I'll bet you do the same. Search patents to see if you can get around them in order to claim something as your own.

Perhaps, you do not understand the definition of: NO COMPROMISE
John, you really crack me up sometimes!
Don't you understand that engineering is all about compromise? Ever design is the end result of balancing several requirements and price isn't the only one. From what I have seen, your definition of "no compromise" only means expensive. If you optimize any one thing, other characteristics will suffer for it. Engineering is all about defining an acceptable mix and designing towards that end. The only other things you can then play with is reliability, the user interface and appearance.

Please, correct me (the non-engineer) if I'm wrong about this.

Hey Joshua,
Once you agree you are self-appointed righteous, it means my point is taken.
Man, you are comic relief!
Most of your posts are not technical in nature and typically only exist to support John's comments. Completely pointless.

In fact, what you do not realize is that a post from you typically puts a smile on my face.

-Chris
 
I'll let you off the hook, with a little something.

Look for the Kleeman.

That's the one with more engine power than you could ever want, and more than comfortable braking power.

http://www.watt.dk/?id=5

Look under "galleri"

Magura :)

EDIT:

Actually, you're not really right here. I made my first set of brakes for that particular car, so I'm not really an expert.
 
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Hi John,
In fact, in analog, more that 2uH is too much, and that is invariably air coil, unless you are a 'General Motors type' designer.
Depends on the design. The great majority of audio designs quite rightly do use a choke in order to make sure an amplifier does not become unstable. It is in fact good engineering practice. If it wasn't, most manufacturers would not expend the money to install them.

What you mean to say is that since your designs do not require a choke, you (quite rightly) do not use them. Just a different design John, that's all.

What we didn't need to hear was a put-down of all other designs that do use a choke in the output. Your open statement is actually technically in error.

Not that there is any good reason in ANALOG to consider them seriously.
Well, again this is from your viewpoint only. I don't like toroid power transformers myself, but they make dandy inductors at higher frequencies. They exist because they are in fact - useful.

Open you mind to other approaches John, and remember ...
"Condemnation without Examination is Prejudice"

-Chris
 
Bob, this is a pretty thinly veiled attempt to divert the the thread into something that is 'politically correct', and pushing me into the background, as this is not my area of expertise.

Hi John,

You are delusional. Stop whining and start making real technical contributions.

I brought up class D amplifiers in the context of PIM. That is all. Others asked some very good questions and I answered them. I will continue to do so to the best of my ability, sharing my knowledge.

Cheers,
Bob
 
By anatech - Depends on the design. The great majority of audio designs quite rightly do use a choke in order to make sure an amplifier does not become unstable. It is in fact good engineering practice. If it wasn't, most manufacturers would not expend the money to install them.

For thrills , I have run abusive tests without my 2uh OP coils. BUT , just in case (and for more "margin")... ,the coils go in. Everybody might not have my speakers. :)
OS
 
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