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Old 30th Apr 2023, 9:06 pm   #1
Michael Maurice
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Default Using a ceramic cartridge with a modern amplifier.

I am repairing a Goldring GL68 turntable that is fitted with a BSR SX6M cartridge.

The owner wants to keep that cartridge and the turntable because she loves playing both 78’s and 33/45’s so the flip under cartridge suits her well.

However she has a receiver that has either a magnetic PU input or line level Aux/tape.

It wont work as is with the PU input as the output is far too high, I can plug it into the Aux or Tape sockets but the output is too low and severely lacking in bass.

I can tackle this two ways: I can build a little preamplifier with a 1M input impedance/resistance and a gain of around 4, the output going to the tape or aux input.

Or I could load the cartridge with say 100K + 1K in series then take the output from across the 1K resistor into the PU input.

Which would be the best way to go? Obviously the 2nd option is the easiest.
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Old 30th Apr 2023, 9:27 pm   #2
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Default Re: Using a creaming cartridge with a modern amplifier.

Dynatron advocated putting 100k in series with each “hot” connection.
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Old 30th Apr 2023, 9:53 pm   #3
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Default Re: Using a creaming cartridge with a modern amplifier.

That might work up to a point, but is an awful solution.

The only way to make a ceramic cartridge work with an amp designed for magnetics is to substitute a magnetic cartridge. The AT91 series has 78 styluses available, though these are less convenient than a turnover type.

If the customer really wants to keep the ceramic cart, the only solution that I can think of is to use a buffer preamp. The TL71 can be configured to present a high impedance.
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Old 30th Apr 2023, 10:12 pm   #4
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Default Re: Using a ceramic cartridge with a modern amplifier.

I would have assumed that the magnetic i/p would be equalised for the rising characteristic of the pickup, due to V = L (dI*dT) in which case the output fom a ceramic would appear bassy. Given that a ceramic cartridge is equivalent to a capacitor, perhaps it would be better to shunt its output, rather than the series resistor proposed? Paul's preamp solution would be best, and it coulde easily be powered/fitted into the set.
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Old 30th Apr 2023, 10:42 pm   #5
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Default Re: Using a ceramic cartridge with a modern amplifier.

The cartridge would be shunted by the 101K, the junction of the 1K resistor makes the whole thing look like a potential divider.

I do agree that Paul’s idea is probably the best way forward.
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Old 30th Apr 2023, 10:48 pm   #6
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Default Re: Using a ceramic cartridge with a modern amplifier.

This maybe of interest, it is from a few years ago.

The last ceramic cartridge I had in my system was back in the sixties. I upgraded this to a moving magnet and this type has been my preferred choice ever since.
I have two ceramic cartridges. A Sonotone 9ta and a Decca Deram. Ceramic cartridges require a special input. A moving magnet (mm) cartridge input is unsuitable. A ceramic cartridge requires no RIAA equalisation, in theory it requires no equalisation at all. It requires a high input impedance, the typical 47k of a mm is far too low. The 300 plus millivolts of a ceramic cartridge's output is also far higher than the few millivolts a mm cartridge puts out.
I therefore required a ceramic phono pre-amp. After some thought and research I came up with this very simple circuit based around the INA217 integrated circuit. The exact requirements a ceramic cartridge need are tailored for in this phono pre-amp.
I was surprised at how good these ceramic cartridges sounded, having read mainly derogatory things about them. Both of mine were a pleasure to listen to. The thing that struck me most about them was that they did not cause me any listening fatigue. The highs, middle and lows were good. OK fair enough they do not reach the extremes of some of the better designed mm cartridges, but I feel also that they should not be over looked. I have for far too long.

For stereo you require two of these circuits. This circuit has zero gain. No equalisation correction. It also has the correct input impedance. It is designed to plug into the line input of a solid state amplifier. It is not required for valve amplifiers.





https://www.vintage-radio.net/forum/...1&d=1682890674



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Old 30th Apr 2023, 11:52 pm   #7
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Default Re: Using a ceramic cartridge with a modern amplifier.

I was very impressed with the sound of a ceramic cartridge connected to my Philips N4515 tape machine in preamp mode. This uses a sensitive low impedance input of about 2k ohms. It is probably the best performance I have ever heard from a ceramic cartridge although the cartridge in question was also made by Philips and had seen little use. I don't know whether a non-Philips cartridge would produce such good results.
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Old 1st May 2023, 6:03 am   #8
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Default Re: Using a ceramic cartridge with a modern amplifier.

Hi,

Hopefully you can open the file I attached, and hopefully I am not stepping on anyone's copyrights by uploading it. If in doubt, please feel free to delete it, and I will make a hand drawn schematic for you to convert the signal from a ceramic cartridge to suit an MM phono input.

In the attached file, go down to page 11 and read from there. You will see a simple network that converts the signal from constant amplitude to a constant velocity input. It is very simple and it works well. I have used it several times myself.

Regards,

Jan
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Old 1st May 2023, 7:58 am   #9
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Default Re: Using a ceramic cartridge with a modern amplifier.

Re this from p.11 of the R. Miller document:

“But nearly all records from 1954 were cut requiring RIAA filters for replay, so ceramic play is not flat. Manufacturers of inexpensive players saved the cost of EQ filters, feeding the amplifier directly with the ceramic cartridge output, so reproduction is tone-colored by the resulting non-flat frequency and phase response errors. Below, tilting the RIAA groove curve enough to approximate a horizontal line, reveals the deviations from flat, audible as distorted timbre of voices & instruments. On a full-range speaker, it sounds weak in the bass, honky in low-mids, lacks presence in high-mids, and is too bright. Deemed acceptable for low-end record players, it falls short in audiophile quality.

“An easily made adapter converts the ceramic’s constant amplitude output to a quite good-enough approximation of constant velocity response for feeding a common magnetic RIAA preamp.”


I don’t think that that explanation is quite right, although the end result probably is. In the right circumstances, ceramic cartridges do not require any external equalization at all for best performance. In such cases the non-use of equalization is not a cost-saving exercise, but simply good engineering.

Most ceramic cartridges – since the later 1950s at least – have inbuilt RIAA equalization, usually achieved by mechanical means. Thus however loaded by an amplifier input, they do not require RIAA equalization per se. (Although they might require correction for poorly implemented internal equalization.)

There seem to be three common ways of (electronically) loading (self-equalized) ceramic cartridges.

One is to have them looking into a sufficiently high resistance (say 2M2) that the CR network formed by the combination of the cartridge self-capacitance and the amplifier input resistance has a time constant that puts the turnover frequency (between the 6 dB/8ve bass downslope and flat) below the audio range, or at least below about 50 Hz. This produces a flat response that requires no equalization in the amplifier. I have seen it said that 2M loading with a flat response is the way to get the best results from e.g. the Decca Deram.

Another is to use a moderate load resistance, say in the 100k to 200k range, which will put the turnover frequency somewhere in the audio range. This can be compensated by a (simple) complementary bass boost filter in the amplifier. The filter turnover frequency required will depend upon both cartridge self-capacitance and the actual load resistance, but in practice the former is sometimes taken as being around 600 pF. This was essentially the method advocated by Burrows, and was also used commercially (e.g. see the Quad 33, C1 input setting.) The lower the load resistance, the higher the turnover frequency.

The third is to condition the cartridge output, using an RC network, so that it is suitable for feeding into a standard moving magnetic cartridge input with RIAA equalization. This requires three things: (1) de-equalization to cancel the inbuilt RIAA equalization. Essentially this requires a 12.5 dB step between 500 and 2120 Hz; (2) attenuation to a level suitable for the MM input; and (3) provision of a sufficiently low net resistive loading on the cartridge that ensures that the turnover frequency is above, or at least close to the top end of the audio range. Thus the whole response is tilted upwards by 6 dB/8ve, as well as being modified by de-equalization. Many ceramic cartridge makers published the circuits required to do this, and they tended to vary somewhat. Some, such as Sonotone, also offered plug-in adaptors that contained this kind of network.

As far as I can see, the circuit offered by R. Miller was of the third kind above, but he seems to be a little uncertain as to how it actually achieves the desired result and/or what the starting conditions are.


Cheers,
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Old 1st May 2023, 3:57 pm   #10
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Default Re: Using a ceramic cartridge with a modern amplifier.

Well it always depends on the starting point, and also the cartridge itself, either it's a magnetic or piezo.
I don't agree that ceramic carts has "built in RIAA's". It is explained very well why the 2 octave flat part of the curve between 500Hz and 2kHz had to be made. This requires a network at both recording and playback of course. The ceramic transducers don't have that built in flat part, just as magnetic types doesn't. So some kind of network is necessary if the resulting frequency curve has to be flat on reproduction, both on magnetic and ceramic carts.
Yes, running the ceramic cart into a high impedance input, will give the lift in the low end and roll of at the top, but it definetely goes wrong at the 2 octave flat part. I have experimented with that several times.
As stated in the article, ceramic/crystal carts were considered cheap and non hifi, so adding a network for compensation was probably ignored for economical reasons rather than brilliant engineering.

I tried out the simple network for ceramic carts on several occations, and it does flatten the frequency curve as he states. But few wants a ceramic cartridge to fit a normal MM phono input. But it is doable and it works quite well.

I agree that some cartridges can sound close to decent with no correction, simply fed into a high impedance high level input. It still does not sound correct in the middle of the curve though. But it can be corrected to sound pretty good, but with loss of signal of course, so again it's a compromise.

In Michaels case, where a ceramic cart has to be used with a normal MM input, the shown network will give great results.

Jan
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Old 9th May 2023, 8:27 am   #11
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Default Re: Using a ceramic cartridge with a modern amplifier.

An update: I tried the circuit as suggested by Jan, it did work, but I felt it too loud for the amplifier so I may well try a 120K resistor instead of a 68K and see how that goes.
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Old 9th May 2023, 8:44 am   #12
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Default Re: Using a ceramic cartridge with a modern amplifier.

Many years ago Sonotone sold a velocity compensator that allowed the use of such as the 9TA into a magnetic input. I think they published the circuit too.
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Old 9th May 2023, 12:11 pm   #13
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Default Re: Using a ceramic cartridge with a modern amplifier.

Further on the Sonotone "velocity equalizer":

https://hex.ro/wp/blog/sonotone-netw...tic-input-diy/
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Old 10th May 2023, 7:31 pm   #14
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Default Re: Using a ceramic cartridge with a modern amplifier.

Sorry to ask this but I don’t understand “… constant amplitude device..”
I’d appreciate simply explanation, thanks.
John
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Old 10th May 2023, 9:42 pm   #15
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Default Re: Using a ceramic cartridge with a modern amplifier.

A piezo-electric cartridge produces an output voltage proportional to the DEFLECTION of the stylus.

A magnetic cartridge produces an output voltage proportional to the VELOCITY of the stylus.

Disc-cutting engineers have to think in terms of the width of modulation of the groove, and how to fit all the music on one side of a record. Records are best thought of in terms of stylus deflection. So a ceramic cartridge requires no great amount of frequency response shaping and into a load impedance which doesn't upset it, can get away with none.

If we made tracks on a record with constant width of modulation, representing a scale of increasing frequencies, the piezo-electric cartridge will give similar output voltages on them all.

In order to track higher and higher frequencies at the same peak deflections, the stylus has to move faster and faster making an output voltage increasing proportionately to the frequency. This is light in bass and over-strong in treble. A frequency response in the amplifier is needed to correct this.

The RIAA response is designed to correct this, and also to handle some effects in the recording process.

So piezo cartridges may need a little response twiddling, but magnetic cartridges need something much more dramatic.



There was a preamp design in WW, Bailey-Burrows-Quilter series where rather than bust a gut to make a very high Z input for ceramics, the designer chose to badly load the cartridge in such a way that RIAA frequency response correction was pretty much just right for what the loading did to the cartridge. This works though it shocked some people at the time. It's what those conversion networks do. And if the signal is still too strong, you can always attenuate. It's easy to throw away gain!

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Old 10th May 2023, 10:29 pm   #16
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Default Re: Using a ceramic cartridge with a modern amplifier.

Thank you David, I’m thinking about your reply, hopefully it will sink in. It was the thought of a “constant amplitude ” of the ceramic pickup that got me puzzled.
John

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Old 11th May 2023, 12:20 am   #17
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Default Re: Using a ceramic cartridge with a modern amplifier.

Yeah, it's just a direct consequence of a fixed level of signal having been chosen to be cut on the disc as a fixed amplitude of stylus movement irrespective of frequency, and the position-to-voltage ceramic cartridge producing therefore a fixed output voltage irrespective of frequency.

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Old 11th May 2023, 10:12 am   #18
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Default Re: Using a ceramic cartridge with a modern amplifier.

Once again thank you David. Would I be right in saying a ceramic transducer cannot be designed as a “ constant amplitude “ device, leaving aside its use for record reproduction?
John
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Old 11th May 2023, 11:51 am   #19
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Default Re: Using a ceramic cartridge with a modern amplifier.

Sorry should have said “ described “ not “ designed “.
John
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Old 11th May 2023, 12:10 pm   #20
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Default Re: Using a ceramic cartridge with a modern amplifier.

Given a constant amplitude of wiggle of the groove, the ceramic cartridge IS the one which gives constant amplitude of its output voltage.

Under the same circumstances, the magnetic cartridge gives a rising output voltage at higher frequencies.

You have to keep tabs on what being described as constant and why, else it all gets confusing.

It's safer to just think of a piezo cartridge reading the distance its stylus is deflected by the groove to make voltage, and the magnetic cartridge reading the velocity its stylus is deflected at to make voltage.

Cartridges are transducers, converting one physical property into electric potential difference. They differ in just which physical property is converted.

Ceramics convert simple distance. Magnetics convert the rate=of-change-of-distance-with-time.

For a sinawave signal, there is only one frequency present at any one time, and there is a mathematical relationship between deflection and instantaneous rate of change of deflection. Sinewaves slow down towards their positive and negative peaks, and move quickest in the zero crossing sections. So there is a 90 degree phase shift in the outputs of the two sorts of cartridges. The mechanism creating this also gives the non-flat response of the magnetic cartridge if the recording is constant amplitude of wiggle. It's easy to grasp if you're comfy with calculus, but difficult to explain without it. It comes out of differentiating a time-varying sine function and getting a cosine function (of the same frequency as the sine) but scaled in amplitude by the frequency of the sine.

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