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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 11th July 2019, 05:52 PM   #601
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by syn08 View Post
Hans, that's for the symmetrical complementary version, calculations are for only half of that.

But in general, I have no idea what you are doing there and where is the discrepancy (if any) is coming from. Since simulation is so much easier, I am sure you could easily figure it out. SNR is by definition the ratio of signal and noise powers at the output, BTW.
You are right that the (dimensionless) SNR normaly is the ratio between input power / output power.
But in audio to my best knowledge it is usually referred to some reference voltage, like 0.4mV for an MC Cart.
That means that it has to be compared to the noise voltage, to keep S/N dimensionless, right ??


This is what Wiki says about SNR in Audio:
Signal-to-noise ratio (SNR), is the ratio between the noise floor and an arbitrary reference level or alignment level.
In "professional" recording equipment, this reference level is usually +4 dBu (IEC 60268-17), though sometimes 0 dBu (UK and Europe - EBU standard Alignment level).


I'll come back to the noise levels of the half version of the preamp.
That was exactly what was unclear in your posting.
May I assume you are using the Maxwell topology ?
If not, could you be so kind to post the circuit diagram.


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Old 11th July 2019, 05:54 PM   #602
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by aboos View Post
The german text on their webpage describes this 'automatic gain adjust' as already mentioned due to the gain dependency from genrator resistance. They had more High output MCs in mind as those have significantly higher Rgen. So the amp is compatible with Low and High output MC carts.

For all reason you mentioned with respect to high variability even between different LOMC cartridges there are different gain settings via jumpers on the board possible (low, medium and high - +12dB, +6dB and +0dB).

So bottom line 'automatic gain adjustment' is marketing blabla
O.K. thanks.


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Old 11th July 2019, 06:21 PM   #603
syn08 is offline syn08  Canada
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Calculations are done in output powers SNR=10*LOG(Psignal/Pnoise)

Not sure what a Maxwell topology has to do here, the model for calculation purposes is a basic AC pi equivalent circuit, no Cbe and Cbc, no output conductance.


Quote:
Originally Posted by Hans Polak View Post
You are right that the (dimensionless) SNR normaly is the ratio between input power / output power.
But in audio to my best knowledge it is usually referred to some reference voltage, like 0.4mV for an MC Cart.
That means that it has to be compared to the noise voltage, to keep S/N dimensionless, right ??


This is what Wiki says about SNR in Audio:
Signal-to-noise ratio (SNR), is the ratio between the noise floor and an arbitrary reference level or alignment level.
In "professional" recording equipment, this reference level is usually +4 dBu (IEC 60268-17), though sometimes 0 dBu (UK and Europe - EBU standard Alignment level).


I'll come back to the noise levels of the half version of the preamp.
That was exactly what was unclear in your posting.
May I assume you are using the Maxwell topology ?
If not, could you be so kind to post the circuit diagram.


Hans
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Old 11th July 2019, 07:09 PM   #604
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by syn08 View Post
Calculations are done in output powers SNR=10*LOG(Psignal/Pnoise)
O.K. accepted. I will stick from now on to S/N as the term that's always used for 20*log(Vref/Vnoise).
That's what I also used in the formula in #541.

But at least its now clear why your SNR calculation differed so much from my S/N calculations in #577 and #581, that was comparing apples to pears.
Problem solved.

Quote:
Not sure what a Maxwell topology has to do here, the model for calculation purposes is a basic AC pi equivalent circuit, no Cbe and Cbc, no output conductance.
Now at last it's clear what model you are using.
Thank you.


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Old 11th July 2019, 09:54 PM   #605
kgrlee is offline kgrlee
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I'm playing hooky from Beach Bum Honey Do issues so bear with me if I'm a little sporadic or miss important stuff.
Quote:
Originally Posted by Hans Polak View Post
To view things from the practical side, I have made a graph in the image below where Rcart and Vcart as inputs are telling how much noise RTI the MC amp may produce to achieve a 75dB-A S/N after Riaa correction.
Perhaps a better practical target is for MC + MCHA to be subjectively quieter than a good MM into a good MM RIAA preamp.

My original document has 1/3 8ve plots of an Ortofon MC + Duraglit vs Ortofon MM into a good MM RIAA preamp.

MC + Duraglit noise measures QUIETER than the MM ... and the noise, being 'redder', is subjectively less yucky than the 'whiter than white' MM noise .. with RIAA etc.

Duraglit + most MC cartridges (certainly the Ortofons) will be quieter than most MMs cos MCs usually have more power output than MMs. MM inductance also prevents them using their full power output except at 1 frequency.

All in my original document .. which also has DBLT results which show Duraglit's advantages for World Peace & your sex life.

OK. I confess DBLTs are almost impossible with a vinyl playback system though good 'Blind' is possible with some (?!) organisation.
___________

There are also some noise plots of various MMs with RIAA & Awt which show why you shouldn't use Awt to determine subjective noise if the spectrums are very different. Even if you have a spectrum analyser (easy today) you should LISTEN to the noise to determine subjective offense.
___________

I think we are almost there with the various Duraglit Specials. I need to sort out the subsonic LF issues and update my recommendations taking into account ZTX851/951. Also, there's a bit more work to be done on syn08's Solar Panel stuff.

For our next trick, MUCH HARDER, we should attempt getting MM noise to better Duraglit. This would involve smashing even more Golden Pinnae myths than Duraglit. Any takers? Guru Wurcer? ... though that should be in a separate thread.

This has been a fantastic thread. First, some beach bum improved JC's supadupa design by 4.4 dB for noise & 2dB for THD. But this pales into significance compared with syn08 & Guru Wurcer taking Duraglit to even greater heights of S/N & THD
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Old 11th July 2019, 10:10 PM   #606
kgrlee is offline kgrlee
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Quote:
Originally Posted by stocktrader200 View Post
how does the noise of the pre compare to an inline x10 transformer.
Circa 1980, the best transformer I found was the VERY expensive Denon for DL103. But even the unmatched WW 1981 Duraglit beat that for noise.

The quietest competing active device was the Stan Curtis designed, Ortofon MCA10 which IIRC, used JCs circuit. Stan claimed to have designed all good British electronics .. like JC claimed to have designed all good US electronics. This was better all round than the mains powered Ortofon headamp.

Duraglit's advantage over these two, the best of the rest, wasn't small .. 6-10dB depending on your chosen noise weighting.

The best I have ever achieved with a transformer was 1.7dB NF for a Calrec microphone preamp with either a large Lundahl or Sowter. In a different forum, I discuss using an even larger core
STEVENS AND BILLINGTON TX 103 MOVING COIL STEP UP TRANSFORMER | eBay
This would give 1.5dB NF if matched to the MC cartridge.

Duraglit, with its original matching recommendations, gives 3dB NF. With syn08 & Guru Wurcer's findings, we can beat 1.5dB NF
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Quote:
Originally Posted by macka
In practice reducing the resistive loading of LMCC over a range of Cart Rs x 10 has a non linear effect versus frequency. This is also dependent of the Cart impedance. With suitable test record this can be verified. The take away is that the resistance loading should be adjustable for a flat response.
Got any real-life evidence ? In da previous Millenium I looked at a lot of MC responses with loading and have yet to see any effect .. even into a virtual earth .. ie short circuit.
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Old 11th July 2019, 10:23 PM   #607
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by kgrlee View Post

MC + Duraglit noise measures QUIETER than the MM ... and the noise, being 'redder', is subjectively less yucky than the 'whiter than white' MM noise .. with RIAA etc.

Duraglit + most MC cartridges (certainly the Ortofons) will be quieter than most MMs cos MCs usually have more power output than MMs. MM inductance also prevents them using their full power output except at 1 frequency.
Power has nothing to do with it just like the impedance matching had nothing to do with it, BTW no power is transferred to a virtual ground. You will have to explain your spectral terminology preferably with pictures. If you read the link from Hans, the guy measuring with an accelerometer show just how much mechanical energy is lost in the arm from the cart, the DL103R was particularly bad.

Checking the Stereophile website typical specs are more like this.

Quote:
Signal/noise (A-weighted): 80dB (MM), 66dB (MC)
The ultimate limit contains a term sensitivity/sqrt(coil-R) and MC looses.
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Old 11th July 2019, 10:24 PM   #608
kgrlee is offline kgrlee
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Gotta go back to Beach Bum stuff but ..

syn08. Yes. I did ASSume Duraglit would behave like a common or garden common base. Too good stuff to digest, ponder & reply in a short post.

Guru Wurcer, where did you get DL103 at 12R? I've got 40R from my Jurassic notes. Spectral pics in my original document.

Last edited by kgrlee; 11th July 2019 at 10:27 PM.
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Old 11th July 2019, 10:39 PM   #609
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by kgrlee View Post

Guru Wurcer, where did you get DL103 at 12R? I've got 40R from my Jurassic notes. Spectral pics in my original document.
Quote:
Output Voltage
0.25 mV

Frequency Range
20 Hz to 45 kHz

Output Impedance
14 ohms
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Old 11th July 2019, 10:43 PM   #610
billshurv is offline billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
DL-103 did have a coil R change at some point in its 50 year life.
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