John Curl's Blowtorch preamplifier part II - Page 2404 - diyAudio
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Old 21st June 2012, 05:24 PM   #24031
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Originally Posted by gpapag View Post


May be Scott has something to say on this ( I wish)

George
We have these capabilities but usually you need an expert driver for the tools. Garbage in garbage out. Our modeling folks are now supporting us at up to 50G with some amazing fits to the data. I think they rented a 90G network analyser at the time to verify, I think there are 1050G ones now.
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Old 21st June 2012, 05:31 PM   #24032
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Ah, but the loss of natural tape compression;
They is a lot to be said for tape compression. We used to record very hot, or "pack it on". Kept everything up out of the noise and most tape formulations in the 80s-90s could take it. Some compression does sound good, tape especially.
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Old 21st June 2012, 05:31 PM   #24033
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Well, to continue. I found an approach that is somewhat unusual to 'fix' the 30 ips low frequency head bump problem.
But first, I would like to comment a little on where the 'head bumps' come from, AND the added low frequency roll-off below the head bump peak.
The low frequency response limit of a magnetic head is the WIDTH of the reproduce head, itself. Therefore at 30 ips, a VERY WIDE head keeps the low frequency response from following off. The CONTOUR of the head and how it fits the tape passing by it, is what makes the EXTRA ripples in the low frequency response. Many years ago, Bogen (Germany) and others adapted a contour that had a SINGLE bump, and this was easier to make flat.
The Supermaster (1979) used an AMPEX type head, and had a more complicated head bump structure, so it took MORE to equalize it, but the Ultramaster (1983) that Dave Wilson still owns, uses STUDER heads, and they are the 'single bump' contour, so easier to make a very flat frequency response. Of course, below 15 ips, this head bump business, becomes almost unnecessary to worry about. It only becomes important at high speeds.
Now to describe the 'fix':
Looking at the head bump graphically, I noticed that it looked essentially like a 2 dB (or so) peak, 2 pole Chebyshev hi pass filter. I wondered how I could make its 'complement' in a straightforward way. Of course, gross EQ would sort of work, but would that really give the 'transient response' and the 'best fit' for the problem.
I realized that if I could 'emulate' the head bump with a Chebyshev filter, AND put it in the feedback loop, somehow, I could better flatten out the low frequency characteristic.
So, I tried a number of computer solutions, until I got it pretty close.
This was so much better than the Ampex or the Studer solution to the problem, that it was probably patentable at the time, but that was a long time ago.
Next, I will show a partial solution to the problem.
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Old 21st June 2012, 05:34 PM   #24034
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schematic
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Old 21st June 2012, 05:34 PM   #24035
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Sigh..it was only a matter of time until they started stacking the dice.

After all, most of the silicon is inert anyway. Chips I worked with were 13 mils to 25 mils thick, and the bulk of the device is on the surface.

I wonder how they make the vias?.

jn
Through wafer vias, backside holes, laser drilled alignment holes (connectors directly to the silicon) all available at a price. We don't do it but I even saw someone backgrinding 12" wafers to 10 microns.

BTW have you seen the project to stack a mole of silicon atoms into a perfect cube as a new mass standard?
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Old 21st June 2012, 05:42 PM   #24036
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Through wafer vias, backside holes, laser drilled alignment holes (connectors directly to the silicon) all available at a price. We don't do it but I even saw someone backgrinding 12" wafers to 10 microns.
Sheesh. I'm still trying to figure out how they get the toothpaste in the tube.. perhaps it should be on "How it's made".

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BTW have you seen the project to stack a mole of silicon atoms into a perfect cube as a new mass standard?
I was offered a key position in that project, but I regretfully turned it down. Yes, somebody does have to count to make sure they have exactly 1 mole, but since it involved a number higher than ten, it would have required my removing my shoes.

Scientists think of the weirdest things...I thought I was bad.
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Old 21st June 2012, 05:57 PM   #24037
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Sheesh. I'm still trying to figure out how they get the toothpaste in the tube.. perhaps it should be on "How it's made".



I was offered a key position in that project, but I regretfully turned it down. Yes, somebody does have to count to make sure they have exactly 1 mole, but since it involved a number higher than ten, it would have required my removing my shoes.

Scientists think of the weirdest things...I thought I was bad.
jn
This reminds me of a Trader Joe's brand of guacamole, Avocado's Number. For me the best part of the packaging was a portrait of Avogadro, captioned with his invitation to party.
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Old 21st June 2012, 06:09 PM   #24038
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I realized that if I could 'emulate' the head bump with a Chebyshev filter, AND put it in the feedback loop, somehow, I could better flatten out the low frequency characteristic.
John, that is BRILLIANT !
I've failed to se a HP filter with Chebyshev characteristic there when I looked at your graphs, I have to admit. Now it's obvious.
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Old 21st June 2012, 06:13 PM   #24039
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Trader Joe
Arriba !

(rock me, Amadeo)
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Old 21st June 2012, 06:15 PM   #24040
1audio is online now 1audio  United States
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TeraHertz VNA? That's impressive. And even ADI only rents the stuff. Does anyone actually buy it?
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