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A trip to the dark side?

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Lucabeer View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Lucabeer Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2023 at 2:18pm
Originally posted by Graham Slee Graham Slee wrote:

In an (ICE) car you have a small nominal 12VDC. Maximum power is reached when the load equals the battery internal resistance (possibly at cranking), so the voltage there is 6VDC. But then there is the charging current plus the regulation required for the F-V converter known as the alternator. Therefore your sensors and comparators have a hard time of it, but they expect you to do fantastic things.

I learned the hard way through making plug in temperature controls for plating lines, and the demands for process chemicals were often +/- 1.5C. If the installation electrician did not comprehend cable power losses, I'd end up the other end of the country trying to combat relay chatter and subsequent burn-out.



Yes, and the battery voltage severely drops according to loads, and to age of the battery due to increased internal resistance. So we have to compensate in the software for every sensor reading and every PWM actuator command, to take into account for voltage fluctuations. That's one advantage of doing things all digital, at least.

For sure, we have the advantage of dealing with much slower slewrates: usually we are dealing with 5-10ms sample rates, very often even with slower ones such as 100ms. Much easier than the bandwidth required by audio!

Controlling a temperature with such a small error? Crazy. The sensors themselves usually have a precision of +/- 1 degrees. And then you have cables, disturbances, and quantization. I would consider myself lucky with a global precision of +/- 2!!!!



Edited by Lucabeer - 26 Mar 2023 at 2:18pm
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 27 Mar 2023 at 11:35am
Ceramic stuff again...

The difficulty in EQ'ing a ceramic cartridge preamp is that nobody documented the "gain curve" as meticulously as they've done for magnetic cartridge equalisation.

We know that somewhere there is a 12dB difference between the bass region and the highs. That appears on every RIAA recording and is nothing to do with the cartridge response (there is also boost below 50Hz).

The +/-6dB, or half of the 12dB delta appears at 1kHz, so it should be easy to determine the +/-3dB points of inflection by drawing the slope on log-lin graph paper. That's true.

However, there cannot be a 6dB/octave (or 20dB per decade) slope in such a short range of frequencies that cover only two octaves.

Neither can it be that way on the RIAA recording.

But we definitely need the "best fit" or we'll have phasing problems which sound like distortion.

The commonly shown graph of RIAA EQ for a magnetic cartridge has slopes and flats that are a result of the cartridge's constant velocity output. The ceramic output has constant amplitude.

What's required is some mathematical formula to convert from CV levels to CA levels, and there is such a thing, but it's quite complicated for my old grey matter to get around.

The Sonotone response pen plot came off a test record. The result supposedly was via one of the circuits inlaid onto the graph. Both are pre-input passive networks which rely on the input stage loading (input impedance), and also rely on the cartridge capacitance itself.

We have a choice of where to put the EQ:

1. input network
2. NFB network
3. output network

So far, in my simulations it appears that the "network for ceramic input" is the most easily workable (http://www.roger-russell.com/sonopg/sonopc.htm).

However, the simulation I ran for the values shown gave an early bass roll off, and the values I obtained for a much closer frequency response were a "mile" different.

The cartridge can be modelled by an a.c. voltage source in series with a 600pf capacitor.

Some might find the 600uuF etc, notation confusing, but a micro-micro farad is simply a pico-farad.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 28 Mar 2023 at 10:18am
This is the input network: the cartridge is modelled by V1 and C1; C2 is arm wire capacitance; R5 is the op-amp bias resistor followed by R2 and C4 RFI filter; and R6, C3 and C5 EQ the mid-range 12dB.

I must point out that this isn't universal for all ceramic cartridges - it just suits a 9TA - and a 9TA that has 600uuF (600pF) capacitance, because 10% either way will offset the bass +/-1dB between channels.

I'm having second thoughts about the input network.

9TA input network

9TA constant amplitude anti-RIAA response

The 12dB mid range "shelf"

9TA bass turnover

The 50Hz bass cut compensation for the 50Kz RIAA bass boost

9TA between lower &quot;flat&quot; and 1kHz

The response between the lower "flat" and the shelf centred on 1kHz

9TA between 1kHz and upper &quot;flat&quot;

The response of the RIAA shelf between 1kHz and upper frequencies

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 28 Mar 2023 at 5:08pm
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