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Richard Lee's Ultra low Noise MC Head Amp
Richard Lee's Ultra low Noise MC Head Amp
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Old 17th June 2019, 10:58 PM   #11
billshurv is offline billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
Hi Richard,


That saves me the email I was going to write you (mumble) weeks ago . Hope you are keeping well.


Bill
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Old 18th June 2019, 07:17 AM   #12
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by syn08 View Post
Only differential stages come with a 3dB noise penalty, single ended complementary push-pull stages come with a 3dB gain in noise (assuming n/p transistors with the same noise).
All I’m saying is that noise adds stochastically in the ‘push-pull’ versions like Richard’s so you get cancellation, just like you do when you parallel devices. The single ended designs don’t have this benefit unless you parallel input devices.

Last edited by Bonsai; 18th June 2019 at 07:24 AM.
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Old 18th June 2019, 07:24 AM   #13
Bonsai is offline Bonsai  Europe
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Thanks for the feedback Richard -Iíll take a look at the Yahoo site. Trust retirement is treating you well!
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Old 18th June 2019, 04:37 PM   #14
Bonsai is offline Bonsai  Europe
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I've added a slide - slide 9 - showing a single ended design c. 16mA current draw, 0.02% distortion and 350 pico Volt/rt Hz noise. This is a refinement of the slide 8 concept with parallel ZTX851 devices. Its possible to go below 300 pico volt/rt Hz but I need to do a bit more work on it - the main thrust of these SE designs is to get the current consumption down of course.
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Old 18th June 2019, 05:56 PM   #15
syn08 is offline syn08  Canada
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Quote:
Originally Posted by Bonsai View Post
I've added a slide - slide 9 - showing a single ended design c. 16mA current draw, 0.02% distortion and 350 pico Volt/rt Hz noise. This is a refinement of the slide 8 concept with parallel ZTX851 devices. Its possible to go below 300 pico volt/rt Hz but I need to do a bit more work on it - the main thrust of these SE designs is to get the current consumption down of course.
You need to add, for all schematics, an (at least rough) dynamic range analysis. Any flat (frequency range) gain stage before the RIAA correction is prone to severely limit the whole pre dynamic range. That's in particular critical for open loop stages, that may have gains higher than optimum (for the dynamic range purposes). The gain has to be carefully balanced across the gain stages, to avoid early overloading. Call dynamic range "overload margin" if you prefer.

Also be aware that very few devices model correctly model the noise performance. Also, there are much more noise sources beyond the obvious, in particular the power supply noise injection, the electrolytics(which can also be annoyingly microphonic when in the signal path) ESR. Expect a 20%-30% degradation in noise when implementing any design that simulates great.
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Old 18th June 2019, 06:51 PM   #16
Bonsai is offline Bonsai  Europe
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Agreed - these schematics are simply to explore potential ideas and get a discussion going. I've done a 10x overload test (so 20 dB) and none clip - but they really need to handle 30+ dB IMV to cover all eventualities. Job for another day . . .


Cables are also very microphonic - I suspect better quality noes with decent insulators are better in this regard. If you move them around they squeak and make all sorts of popping sounds at these amplification levels.
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Old 18th June 2019, 07:11 PM   #17
syn08 is offline syn08  Canada
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Originally Posted by Bonsai View Post
Agreed - these schematics are simply to explore potential ideas and get a discussion going. I've done a 10x overload test (so 20 dB) and none clip - but they really need to handle 30+ dB IMV to cover all eventualities. Job for another day . . .

Cables are also very microphonic - I suspect better quality noes with decent insulators are better in this regard. If you move them around they squeak and make all sorts of popping sounds at these amplification levels.
Solid state 30+ dB overload margin is probably a stretch to design for (been there, done that) anything over 22-24dB makes sense.
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Old 18th June 2019, 07:18 PM   #18
PMA is offline PMA  Europe
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Originally Posted by Bonsai View Post

Cables are also very microphonic - I suspect better quality noes with decent insulators are better in this regard. If you move them around they squeak and make all sorts of popping sounds at these amplification levels.
Or it is a kind of electrostatic interference in the system?
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Old 18th June 2019, 07:36 PM   #19
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by Bonsai View Post
Agreed - these schematics are simply to explore potential ideas and get a discussion going. I've done a 10x overload test (so 20 dB) and none clip - but they really need to handle 30+ dB IMV to cover all eventualities. Job for another day . . .
IME this problem is grossly overstated. Simply taking a flat G = 100 amp into a decent field recorder will bring some reality into the discussion.
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Old 18th June 2019, 10:29 PM   #20
Bonsai is offline Bonsai  Europe
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Scott, we’ve discussed this before. I don’t think the music coming off a record (or CD) demands huge overload margins and 10-14 dB is sufficient for a given cart and a given LP.

If you are designing for a commercial application then you have to cater for a bigger spread: a hot recording - add 6dB, hot cartridge add another 6dB, space for crackles and pop recovery add 3-6 dB.

That’s why 30 dB OL is required. If you don’t like 30 dB OL, then you need gain switching. Dialing down the volume pot is easier in most cases.
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