John Curl's Blowtorch preamplifier part II

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If you have the drawings for the test fixtures for the 5173 that would be great. The manual doesn't include the test fixtures. I have made some but I'm sure there are more details I'm missing.

And a manual for the Quantech 315C. Its very different from the 315B which I have a manual for.

Let me know.
 
I have a full set of QuanTech schematics, including the test fixtures. I now can pdf/email them from our copy machines.

Yeah, I love those machines. We have to insert our badge, to use them. But then it knows who I am and can send a color PDF (or other format) straight from the machine to my personal network folder. And they're fast, when only scanning; like a couple of pages a second (I've never actually made paper copies with one.). What's not to love?
 
Some of us are still designing analog audio circuitry, and we still need testers such as the QuanTech to sort out the good from the marginal.
It is unfortunate that QuanTech went out of business, many years ago, but this one instrument gave me the ability to make breakthroughs in low noise design, starting 45 years ago. Without it, I would never have discovered the low noise properties of the 2N4403, 2N4405, and even the 2N4401, in 1968.
The 2N4401-4403 push pull parallel combination was the basis of the Levinson JC-1 that we introduced at the NY AES, 40 years ago having a noise spec of 0.4nV/rt Hz without an input transformer. Some people did not believe it was possible at the time.
Today, with selected modern devices, it is easier to do, but back then, it seemed almost impossible, at room temperature.
The QuanTech noise analyzer allowed me to get real feedback as to what the real tradeoffs were in bipolar transistors, and also jfets, especially as they got better.
I will always be grateful for being assigned to it, back in 1967, when I was with the Ampex Instrumentation Recorder group, and given this assignment to find the lowest noise bipolars in our inventory, because it could be tedious and I was the new kid in the group. It just so happened that I liked comparing transistor noise, so when I moved to the Audio Division, 6mo later, I got samples from every manufacturer I could and I tested them on the QuanTech, finding surprising breakthroughs in both bipolars and jfets over the years, AND eliminating expensive, but noisy jfets, that were batch sensitive.
 
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Hopefully, today's up-in-coming audio designers will make their own 'discoveries' that will allow 'breakthroughs' based on their open mindedness and passion for the subject.
The test equipment will, of course, be different, but if one is fortunate to have access to something that gives a real 'breakthrough'.
For example, in low temperature physics, the guy who used lasers to 'cool' almost to absolute Zero comes to mind. Anybody see the program on low temp physics showing this a few years ago?
 
If you have the drawings for the test fixtures for the 5173 that would be great. The manual doesn't include the test fixtures. I have made some but I'm sure there are more details I'm missing.

And a manual for the Quantech 315C. Its very different from the 315B which I have a manual for.

Let me know.

I'm not sure I can find the more recent 5173 literature but we do have two of them. One of our calibration engineers flew out there to get help with repair, they offered instead to sell us the company lock, stock, and barrel.
 
I would like to further comment on what is necessary to make an 'exceptional' audio design. As I said before, knowing your 'building blocks' can be very useful, even giving someone an engineering 'edge', over the competition, until they can find out what you know and do the same. And 'Thus it is always so!' '-)
However, I achieved 0.4nV/rt Hz capability in 1968, but the JC-1 did not come out until 5 years later. Much of the difference between early discovery, and proper implementation came before finding an OPTIMUM TOPOLOGY to utilize. This took me several more years to develop.
Now what is the problem? Well, it is a matter of distortion, cost, and low noise, and these requirements can be contradictory at first application.

For example: One could just use a single transistor, or even better, parallel a bunch of them, and then use an op amp for rest of the gain. This could have been done with four paralleled 2n4405 devices and a uA709, back in 1968 and we would have had ultra low noise and low distortion too! Yet, what are the 'drawbacks'? Cost might be one, because a low noise +/- 15V power supply could be expensive, and any IC op amp was not 'dirt cheap' in those days. Another design decision was whether to cap couple or not. The input bias current could be somewhat high, was it too much for a MC cartridge to bear?
If so, what relatively high value of input C would be necessary to not add excessive 1/f noise to the equation?
What about the optimum input impedance range? I would think 100 ohms or less would be best in this design. That sort of leaves out a making general purpose test amp this way. In other words, to get the BEST low noise performance, you have to direct couple the input, if possible, and keep the useful impedance range limited to perhaps 100 ohms, to get the lowest noise with this method.
Now, should the discrete transistor array be cap coupled to the IC? Here, there is a trade-off between size, voltage rating, and value of the cap. Cap quality might be important too. Of course, even in 1968, we could DIRECT COUPLE the discrete input stage to the op amp, BUT we would have to offset voltage in both op amp input terminals. This could be done, even then. So then what? We make something that meets a noise and a general distortion spec. for a MC input, but is it worth doing? We have replaced a very cheap and compromised input transformer, with a solid state gain stage, but will it be really better, and worth it? Why not just use a better input transformer? (more later)
 
again
 

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Hopefully, today's up-in-coming audio designers will make their own 'discoveries' that will allow 'breakthroughs' based on their open mindedness and passion for the subject.
Just backtracking for a sec, a very important breakthrough will be in people's thinking: the realisation that "big sound" is possible without all the usual negatives. I was inspired by wandering around Kenrick Sound's videos, which shows the best, and worst of what happens. Obviously, bigness is often accompanied by over the top glare, a sound which is in your face, and impossible to live with - however, when it's right then the sound is magic, the real deal.

People need to get past the idea that achieving that sort of sound is only possible with monster horn systems, equipment that's dropped off the back of the pro music guys' truck. Why PA systems are usually atrocious to listen to in domestic environments is because when listening at high levels there's no room to hide for the remainder distortion, the defects which are barely noticeable at the usual home listening levels are now enormously magnified, the problems in the system are screaming at you - such a setup is a complete non-starter.

It's all about attitude - good, big sound is possible, but it won't fall off the back of a truck, into your lap ...
 
I've pointed to a couple of videos over here, http://www.diyaudio.com/forums/everything-else/242996-i-thought-interesting.html. They've managed to capture some of the essence of what I'm looking for - Kenrick has gone mad recently, taking huge numbers of videos over the last months or so. The THE BEST JBL HARTSFIELD IN THE WORLD restored by KENRICK SOUND ???????????? #7 - YouTubehttp://www.youtube.com/watch?v=3PQRT_O4IMU has a huge series with different tracks played - this still has problems with vocals but does some things very well ...
 
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PNP transistors are always quieter than NPN transistors. This is because the BASE of the PNP is N material. The Rbb' of the PNP is usually about 1/2 the value compared to NPN transistors with similar construction.
Demian, please look up the part numbers that I spoke about. 2 types are the 2N4403 and the 2N4405.
 
I've pointed to a couple of videos over here, http://www.diyaudio.com/forums/everything-else/242996-i-thought-interesting.html. They've managed to capture some of the essence of what I'm looking for - Kenrick has gone mad recently, taking huge numbers of videos over the last months or so. The THE BEST JBL HARTSFIELD IN THE WORLD restored by KENRICK SOUND ???????????? #7 - YouTubehttp://www.youtube.com/watch?v=3PQRT_O4IMU has a huge series with different tracks played - this still has problems with vocals but does some things very well ...

Ok , so you have never personally heard any of them , nor have you ever heard the sound you speak off ..
 
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