John Curl's Blowtorch preamplifier part II

[john curl]

PS folks, Jack Bybee has 651 HP, as measured by dynamometer by special upgrade house, in his Bentley. Car is still heavy, however, great touring car.

[Bob Cordell]

Originally Posted by john curl

Hi Wavebourn, going to Denver to drum up business. I am being sent by one of my business partners. Good place to go, I hear. Never went there, myself, before. We will be showing our new amp, but my new business partner has lots of new stuff to show. How about all digital from phono cartridge to loudspeaker? That company is Behold. It will be interesting to compare it to other stuff.

Hi John,

Will Behold have an exhibit room of their own? Is that where your new amp will be shown? I'll look forward to seeing it (and you).

Cheers,
Bob

[Bob Cordell]

Originally Posted by anatech

Hi John,

Being ignorant of each designer's preference, I can only reply to what I see "out there". The most popular input stage is the single differential pair, and for a good reason.

The complimentary diff pair may work extremely well, if and only if (IFF) all the NPN and PNP (or N channel and P channel) transistors are closely matched together. I know this from working on several examples of this design from several different brands of audio components. Matched by hand, they very audibly out perform the exact same circuit the way factories generally put them out the door. In other words, the performance of a single differential pair exceeds that of a complimentary diff pair in normal manufacturing. This means that using a complimentary diff pair is not a good idea for any line of amplifiers with higher production numbers than custom, low volume brands. It simply takes far too much care (=time + labour) to put out high numbers using the complimentary diff pair.

I think one of the earlier attractions of the complimentary diff pair was that it enabled the designer to run the input stages at far higher current levels, more easily than could be done with a single differential pair. Of course, by making the DC resistance seen by each base equal, the DC offset issue would not be an issue as long as the single pair was matched. Of course, the single pair was far easier to match and they even came out with matched pairs in a single package (like 2SA798 for an inexpensive solution). Once the J-FET came into widespread use, the problems with current vs. DC offset pretty much evaporated, again as long as they were matched (uPA68H as an example).

I still see the complimentary diff pair design as a liability rather than a plus for most manufacturers.

Other interesting input stages are the old single, which I really don't care for. It's an ancient design as far as a time line is concerned. They already had tube differential pairs, so why did the single transistor input stage appear? Later on, a more interesting input stage appeared using complimentary devices - one of each. These could be BJTs or J-FETs. Rotel had one example, and there must be more. These are sufficiently weird enough to throw most technicians off.

-Chris

Hi Chris,

Interesting observations about the input stages, especially with regard to base current in the BJT designs. I always favor the JFET input stages for this among several reasons, even though the input-referred voltage offset is typically greater. DC servos fix this quite well.

Given that one likes JFETs at the front, and given the poor availability of dual p-channel devices, the way I naturally lean is toward the unipolar JFET input stage.

The complementary input stage was also attractive because it was visually symmetrical AND because it made it straightforward to drive a push-pull complementary VAS. With the unipolar input stage, you have to do rail-rail level shifting in some way to drive a push pull VAS. This is not that difficult and does not compromise the sound quality if it is done right, but some attention to detail is needed.

Of course, there are many who just plain forego the push-pull VAS and use one with a current source load. I think this approach is inferior, although it can be made to work well.

Cheers,
Bob

[john curl]

Well, I made 2 separate attempts to input earlier, but I just gave up trying to convey something about input stages or the use of output coils.
For me, it is just too difficult, if every word is parsed, every design idea is challenged, every 'fact' either in the present, or in the past is thought to be a product of my imagination.
I do wish to point out what I find here, on this thread.
I find that most of my critics have little real experience with amplifier design that has actually been accepted in the audio marketplace.
I also find that many here have little or no understanding of the history of audio design, and the tradeoffs made over the decades, and why. Heck, most of you don't know where most of the designs that you play with, were developed, or why.
Now, if you want to know more about where these designs came from, and what we are working on, today, I'm your man. However, if I can't make any headway due to parsing and quibbling, then so be it.

[PMA]

Do you believe in a virtual persuasion? I do not think so. Those who criticize have usually absolutely no experience with high end. They can never be persuaded in a virtual space, and they will not have a possibility of serious comparisons. This is all useless. There is the one and only big advantage - the virtual space enables people from different parts of the world to communicate. On expense of problems we can see every day.

[Wavebourn]

Originally Posted by PMA

Do you believe in a virtual persuasion? I do not think so. Those who criticize have usually absolutely no experience with high end. They can never be persuaded in a virtual space, and they will not have a possibility of serious comparisons. This is all useless. There is the one and only big advantage - the virtual space enables people from different parts of the world to communicate. On expense of problems we can see every day.

Which thread are you talking about PMA?
I do not see here, in this thread, any criticism regarding design ideas. What I saw, and what I participated in, was some idea as if PIM is visible on the picture as a non-harmonic content, that is totally wrong. However, there were some tiny creeks of discussions, by Bob Cordell, Jan Didden, Andy__C, and others, but I did not see any input John contributed to this technical discussion.

[PMA]

This is a Blowtorch thread, Wavebourn, and it has been continuing for several years (before you have joined). Mods splitted it into 2. I am not very interested in a PIM war, I am very interested in a high end preamp design. And John is the one from whom I have learnt most.

[Wavebourn]

Originally Posted by PMA

This is a Blowtorch thread, Wavebourn, and it has been continuing for several years (before you have joined). Mods splitted it into 2. I am not very interested in a PIM war, I am very interested in a high end preamp design. And John is the one from whom I have learnt most.

I know PMA how this thread is called, but can you show me something about Blowtorch and it's criticism? It is good that you've learned John Curl's design preferences, we have 2 John Curls now, that is better than one. But who is criticizing that, at least last half of the year, in this particular thread? Why John is crying that the whole community is against his great ideas, why an ensemble of yourself and Joshua sing the same song regardless of what is going on in the thread, as if you are singing from some parallel reality absolutely irrelevant to the discussion?

What do you smoke, guys? I want to try the same.

[Wavebourn]

Originally Posted by stinius

Hi John

Why don’t you mention other Czech cars like the TATRA?
A very nice car, but it’s obsolete.

Drivers in Siberia liked Tatra trucks. They had an air cooling system, also their suspension was very good to drive through a forest.

[Wavebourn]

Originally Posted by Zen Mod

certainly ; you are using ГУ50

Now, wait till they accuse me in stealing it's design from Telefunken.