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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 24th June 2019, 09:46 PM   #111
syn08 is offline syn08  Canada
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Quote:
Originally Posted by Hans Polak View Post
SE is fine and as long as both topologies are using the same Cart, I don't care about the details.
It was your own statement that the JC version had a lot more noise and THD, so it's up to you to.
And yes of course, I have the Spice models for both ZTX models.
And yes measurements with these transistors are within 1 dB with the simulations, see for instance: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851 - Page 44 - Pro Audio Design Forum


Hans
RB =0.025 RE =0.018 RC =0.015

and

RB=0.029 RE=0.020 RC=0.0255

I'm not buying these models
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Old 24th June 2019, 10:02 PM   #112
kgrlee is offline kgrlee
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Quote:
You haven't mentioned if you think NPN and PNP should be matched in pairs or what parameters you personally have found critical other than noise.
Quote:
Originally Posted by kgrlee View Post
No matching is required especially for the battery version where the same current flows through each.

In theory, some Vbe matching might be required for the powered version but I wouldn't bother myself.
I should say a bit more.

There is no need to match a single ZTX851 with its corresponding 951.

If you parallel devices like on Bonsai's page 20, you only need to match if you violate Ic * Pd < 460u for TO92 package which is the cryptic note at the bottom of p6 of my document. Check out the proaudiodesign link for details. My criteria for matching success is that effective rbb' is halved when you double the devices.

But you only need to parallel devices if rbb' is too large for your source resistance and current. That's why the Wireless World 81 version has parallel pairs. I didn't go further cos even that version with old fashioned transistors was better than all commercial step up devices at that time.

Single pair of Olde Hitachi, NEC, Rohm devices becomes rbb' limited at 3mA, 4R3 DC source. ZTX851/951 at about 5mA and 2R6.

If your cartridge has higher DC than 2R6, more ZTX devices & current doesn't help. It would give you a better measured SC noise but not less noise with a real cartridge.

BTW, where is this list of MM generators from George & Hans

Last edited by kgrlee; 24th June 2019 at 10:08 PM.
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Old 24th June 2019, 10:10 PM   #113
billshurv is online now billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
Cartridge dynamic behaviour If I have linked correctly this is the bulk of the information found. George on the following pages did a load of distortion measurements which are also fascinating. As the measurements tally between the two set ups this should be the most accurate model of a cartridge generator yet. When the carts get back to me I need to do some measurements of the motor side.



Pointless and fun, which is the definition of a hobby really
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Old 24th June 2019, 10:14 PM   #114
Bonsai is offline Bonsai  Europe
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JCs circuit with single ZTX devices is siming at 340 pico Volt/rt Hz and 0.09% 20 k THD.
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Old 24th June 2019, 10:17 PM   #115
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by syn08 View Post
RB =0.025 RE =0.018 RC =0.015

and

RB=0.029 RE=0.020 RC=0.0255

I'm not buying these models
These are the official spice models from the manufacturer, Diode.com.


Hans
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Old 24th June 2019, 10:20 PM   #116
kgrlee is offline kgrlee
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Originally Posted by Hans Polak View Post
ZTX.pdf
Thanks for this Hans.

Can you post your LTspice *.ASC so there is no mistake?

Have you actually built one of these?

Hmmm! Some dodgy parameters in those SPICE models but no matter. They will make my winning margin even greater

Quote:
Originally Posted by Bonsai
JC’s circuit with single ZTX devices is siming at 340 pico Volt/rt Hz and 0.09% 20 k THD.
Thanks for this Bonsai. Saves me a lot of work.

This shows more than 3dB noise advantage and more than 2dB better THD. Hans, I'll leave it to you to decide if this is "a lot".

I have also less bits, a single battery and no EVIL 1000uf caps but I'm sure this is of no importance to you ... unless you are building a head amp.

I still want your *.ASC cos this beach bum needs to put on his pre10 LTspice guru hat and try to replicate the 1980 measurements of his circuit in SPICE world .

I haven't updated all my recommendations in the MicBuilders document to take into account ZTX 851/951

Last edited by kgrlee; 24th June 2019 at 10:41 PM.
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Old 24th June 2019, 10:29 PM   #117
syn08 is offline syn08  Canada
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Quote:
Originally Posted by Hans Polak View Post
These are the official spice models from the manufacturer, Diode.com.
Wrong models, since the ZTX devices are not intended for low noise applications.

RB in the model is, for all practical purposes, Rbb in the physical device.
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Old 24th June 2019, 10:47 PM   #118
kgrlee is offline kgrlee
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Originally Posted by syn08 View Post
Wrong models, since the ZTX devices are not intended for low noise applications.

RB in the model is, for all practical purposes, Rbb in the physical device.
Damn you syn08! You've let the secret out.

I was going to get Hans to commit to a little $$$ wager before posting my results

But seriously folks. ZTX 851/951 are about as close to perfect LN BJT devices as any I've encountered ... certainly the lowest rbb' I've ever seen. My estimate is 1R2 or less.

My 'method' is to increase current until Env stops reducing. You can get this from noise contours on the spec sheet ... but there aren't any for ZTX851/951.
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Old 24th June 2019, 10:49 PM   #119
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by Hans Polak View Post
These are the official spice models from the manufacturer, Diode.com.
RC to 4 digits, I've been here the extraction process is very insensitive to series parasitic resistances and the answers are frequently nonsense (even negative). These devices are not characterized for MC pre-amp applications and the values are absurd, a typical single bond is 0.1-0.15 Ohm
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Old 24th June 2019, 10:57 PM   #120
billshurv is online now billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
Quote:
Originally Posted by kgrlee View Post

My 'method' is to increase current until Env stops reducing. You can get this from noise contours on the spec sheet ... but there aren't any for ZTX851/951.

H&H measured it. It's in AoE V3.
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