john curl said:
Speaking about low noise: John, your Vendetta SCP-2 MC is now history
With the attached MC input stage I got 0.3nV/rtHz using regular K170BL/J74BL with Idss=11+/-0.5mA and 0.25nV/rtHz with selected (for noise) devices. It is also rock solid stable.
The complete MC uses a few more high voltage opamps (OPA552), has servo (OPA445, hence no film or electrolytic caps in the signal path, except for decouplings and the output optional 10uF polypropylene). 28dB headroom (+/-24V supplies, +/-16V for the input stage), 64dB gain, 0.01% distortion mostly 2nd harmonic, RIAA better than +/-0.1dB.
All the above measured and consistently confirmed. BTW, it's a dual mono construction hosted (preliminary) in a single 6 x 6 x 2 inch 0.1" aluminum case with two magnetically shielded 25VA toroids on board. 108dB channel separation, if somebody cares about.
It's part of HPS 3.0 soon to be finished and posted in the HPS thread. Don't worry, it sounds amazing even with that much feedback.
I'm not planning to get into business and sell this stuff so your old SCP-2 record is safe from a commercial perspective
Next, down to under 0.2nV/rtHz with BF862, SMD parts (including inductors), etc... Hard to find good SMD parts (in particular resistors), but not impossible.
Your next step should be to replace the monolithic 797 op-amp with a discrete high performance op-amp. May I suggest the Forssell 993...Its all FET, runs on up to 24 volt rails, and sounds terrific. I know what the 797 sounds like, as well as a lot of other op-amps. The only monolithic op-amp I can even tolerate are the new LM4562 family in the metal can...and most of the discrete op-amps on the market, largely unknown to the home audio world, and well known in the pro audio and recording world, sound better than the best of the monolithics.
As John has said, you have done pretty well on this from the look of it. Have you actually measured the noise figure from a functioning amplifier, or just Spiced it?
Just for fun....Here are some links to the discrete op-amp world...
I have tried most of what is out there, and find the Forssell 993 to be my favorite of the current commercial offerings. It is all FET. I'm working on a hybred J-FET/BJT design of my own, but I'm not ready to chat about it yet, still working out topology variations, like whether to go with Diamond output or conventional complimentary PP topology.
Fred Forssell 993, but also check out the 992....
http://www.forsselltech.com/main.shtml
http://www.forsselltech.com/jfet993.shtml
http://www.forsselltech.com/downloa...estData/jfet993_specificationsAndTestData.pdf
Great River publishes a schematic of their op-amp...
http://recording.org/users/kev/Great River Opamp2.pdf
The John Hardy version of the bipolar 990
http://www.johnhardyco.com/pdf/990.pdf a complete chat with schematic and applications
API clone pages
http://web.qx.net/jgreenlee/
Anyway, this is just a start....Discrete op-amps should have their own pages on DIY...I have not looked, there might be! Aside from some discussion of theory, I'm not sure that they really fit on the blowtorch thread, as most applications of any op-amp are based on making use of feedback, but then again, a lot off nearly off topic, and way off topic stuff ends up here anyway....
Woof!
Cheers
As John has said, you have done pretty well on this from the look of it. Have you actually measured the noise figure from a functioning amplifier, or just Spiced it?
Just for fun....Here are some links to the discrete op-amp world...
I have tried most of what is out there, and find the Forssell 993 to be my favorite of the current commercial offerings. It is all FET. I'm working on a hybred J-FET/BJT design of my own, but I'm not ready to chat about it yet, still working out topology variations, like whether to go with Diamond output or conventional complimentary PP topology.
Fred Forssell 993, but also check out the 992....
http://www.forsselltech.com/main.shtml
http://www.forsselltech.com/jfet993.shtml
http://www.forsselltech.com/downloa...estData/jfet993_specificationsAndTestData.pdf
Great River publishes a schematic of their op-amp...
http://recording.org/users/kev/Great River Opamp2.pdf
The John Hardy version of the bipolar 990
http://www.johnhardyco.com/pdf/990.pdf a complete chat with schematic and applications
API clone pages
http://web.qx.net/jgreenlee/
Anyway, this is just a start....Discrete op-amps should have their own pages on DIY...I have not looked, there might be! Aside from some discussion of theory, I'm not sure that they really fit on the blowtorch thread, as most applications of any op-amp are based on making use of feedback, but then again, a lot off nearly off topic, and way off topic stuff ends up here anyway....
Woof!
Cheers
Joshua_G said:
Joshua,
This test feeds the 60Hz test signal in *series* with an 8 ohms resistor into the amp output. It is a specific protocol to measure IIM and compare different amps. As such, it doesn't have a direct relation to a real speaker.
If you want I can send you some literature on this, I think I have something in my library.
Edit: The attached is the way Jean Hiraga did this test. It looks like I was wrong, he does include either an 8 ohms load or speaker load, and feeds the test signal through 250 ohms. In a perfect amp you would only see the 1kHz at the output, not the 50 (or 60) Hz external signal.
But this may be a slightly different test than Bob alluded to.
Jan Didden
Attachments
courage said:
The schematic is attached as a link to my web site. You may be one of those that have lately strange connectivity issues to www.synaesthesia.ca Can you access my web site?
Better say he displayed image directly from web addres, no need to be logged (img). Maybe syn08 would like to write the link in a plain html text, for those who have higher security settings.
http://www.synaesthesia.ca/files/input_stage.JPG
http://www.synaesthesia.ca/files/input_stage.JPG
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