I used to have an HP3000 (for no good reason). The disk drive was the
same size as a washing machine.
Hi Jan,
We used to use the OPA-660 in some video products that had zero feedback. The '860 was essentially the same except that the buffer section was a closed loop buffer instead of the open-loop diamond of the '660. ±5 V was fine for analog video work, but everything is digital now!
You can buy the front half of the '860 as the '861 and add your own open loop diamond buffer, either from TI or National, but the ±5 volt limitation of the front end isn't very useful except maybe as a zero-feedback I-V for a DAC. You still need some buffers, and now you have twice as many packages as you did with the OPA-660. They just keep going backwards, one step at a time...
The AD844 and LME49713 are rated to ±18, which is much nicer for analog work. But without access to pin 5, you can't adjust the open loop gain and you lose out sonically in a big way. The AD844 also has a built-in DC offset that just requires one external 10 kohm trimpot, so it was great from a low parts count standpoint. Oh well...
Thanks,
Charlie
Ayre
That was when I worked at Dysan making the disk packs (up to 11 14" platters for all of 200 MB) and the machinery to make the disks. The drives were large used 5 HP motors and voice coil actuators that could move a head stack 4" in 2 mS. It was amazing what was possible when money was not a problem.
I started my working life as a glorified mechanic for ICL, British computing - start at the bottom, my son! - and one of the exercises was maintaining disk drives, of the washing machine size. These were the glory days - oil hydraulics, slippery fluids everywhere! And one of the you beaut efforts was checking alignment, by manually moving the heads to the correct track of the calibration disk. While working - pull ratchet away from cog with one hand and with the other slowly, slowly allow the head to self propel across the disk. But!! Be careful, very careful ... once the head got to a certain transverse speed a valve in the hydaulics would trigger, and the hydraulics then drove at a much higher pressure, the heads would take off like a wild animal.
Needless to say, sweaty palms and bruised knuckles were the order of the day - rodeo for the grease monkeys ...
Needless to say, sweaty palms and bruised knuckles were the order of the day - rodeo for the grease monkeys ...
I this case I start a new thread concerning a question to the exactly differences:
http://www.diyaudio.com/forums/anal...n-mark-levinsons-jc-1-jc-1dc.html#post3655508
Additional I am looking for faulty modules of all JC1 variantes - therefore I start this thread:
http://www.diyaudio.com/forums/anal...ed-modules-mark-levinson-jc1-resp-ro-iii.html
thank you very much in advance for advices there.
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I started my working life as a glorified mechanic for ICL, British computing - start at the bottom, my son! - and one of the exercises was maintaining disk drives, of the washing machine size. These were the glory days - oil hydraulics, slippery fluids everywhere! And one of the you beaut efforts was checking alignment, by manually moving the heads to the correct track of the calibration disk. While working - pull ratchet away from cog with one hand and with the other slowly, slowly allow the head to self propel across the disk. But!! Be careful, very careful ... once the head got to a certain transverse speed a valve in the hydaulics would trigger, and the hydraulics then drove at a much higher pressure, the heads would take off like a wild animal.
Needless to say, sweaty palms and bruised knuckles were the order of the day - rodeo for the grease monkeys ...
I hate to say this but my very first foray into the real world was a 3 month placement as part of my course at ICL Wakefield (UK) repairing colour monitor scan boards and setting up the 5" disk drives, with an offset screw, a setup disk and a scope with the eye diagram on...
I don't think so, but I do remember they were neurotic about static damage, it was 1983 and as you can imagine, the first view of reality after the classroom was quite illuminating, your bright eyed enthusiasm of new and exciting world soon dulled by the 20+ year stalwarts who had to nursemaid another student. 30 years on and I know how he felt
Tief, there is a lot of confusion here:
The JC-1 looks like the post that I originally put up recently with multiple complementary bipolar transistors.
You know about the JC-1 DC, the JC-1 AC is similar.
The McKinnie RO-3 is a clone of the Vendetta Research SCP-1. Reza Oskoui used to be a technician for me for several years in Switzerland, and I shared the circuit with him.
The 'reason' that the JC-1 worked and the JC-1 DC was a 'disappointment' did not as well, was because it had a common base input, instead of a common emitter input. I had Reza, in 1976, modify a JC-1 to be either type of input with a switch. We ran a listening test. I hope this answers your question.
The JC-1 looks like the post that I originally put up recently with multiple complementary bipolar transistors.
You know about the JC-1 DC, the JC-1 AC is similar.
The McKinnie RO-3 is a clone of the Vendetta Research SCP-1. Reza Oskoui used to be a technician for me for several years in Switzerland, and I shared the circuit with him.
The 'reason' that the JC-1 worked and the JC-1 DC was a 'disappointment' did not as well, was because it had a common base input, instead of a common emitter input. I had Reza, in 1976, modify a JC-1 to be either type of input with a switch. We ran a listening test. I hope this answers your question.
Not to give the wrong impression here, either --- a modern version using a common-gate MC circuit has just been published in Linear Audio #6 -- the design was done by Erno Borbely. As was noted in his excellent article at least one cartridge mfr recommends lower Z and some have uncovered several patents related to this approach to reduce the distortion of the cartridge. Certainly worth a try especially if some cartridge makers think so as well...
[but like any amp circuit, the results also depends on the design details of implementation.]
Thx-RNMarsh
[but like any amp circuit, the results also depends on the design details of implementation.]
Thx-RNMarsh
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Can you provide one of those patent numbers? It seems counter-intuitive to reduce the distortion of a magnetic transducer by loading it. Unloaded its a voltage generator. Once you load it you are drawing current from the device. That then involves the magnetic circuit which will probably be pretty nonlinear.
Well, everyone is welcome to try common gate input. VDH also thought that low Z input improved distortion. I just repaired a Vendetta configured with summing input (Low Z) and I left it that way for the customer.
However, with the JC-1 series, it failed, sonically. It was MY idea to change the next generation of JC-1 to common base input, so it was extra painful to realize that it did not work right.
However, with the JC-1 series, it failed, sonically. It was MY idea to change the next generation of JC-1 to common base input, so it was extra painful to realize that it did not work right.
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They often mention electromechanical coupling and cantilever damping as contributing to the distortion reduction. I have seen no evidence that these claims have any merit and I have seen no test LP with better than several percent distortion at higer modulations.
A friend of mine (who knows what he's doing) has been able to measure -40dB at 300Hz from HFS-75, a test record from the now-defunct HiFi Sound sold in the mid-1970s; he didn't specify recording level. He's bringing a copy with him next month for us to try with my setup- perhaps we can get some data which will support the hypothesis or not.
It seems odd to me, but data are everything. Presumably, since we're a couple decades above the fundamental resonance and the arm he uses (and mine as well) are quite well damped, the distortion would be originating from the cartridge mechanical end- the suspension compliance, needle/vinyl compliance... A few frequency sweeps should confirm this. The nice thing about this test record is the 300Hz bands at beginning, middle, and end, so that the alignment can be set to try to minimize distortion across the disk, useful for us benighted souls who don't have linear tracking arms.
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