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Old 27th Oct 2010, 4:29 pm   #1
D_S_J_R
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Default Using a ceramic cartridge with modern electronics...

All this recent rekindled interest in vintage record players got me going a bit I must admit and I've been buying inexpensive bits and bobs to fuel it. One of these bits is an ACOS GP104, which was a late addidion to the ceramic cartridge portfolio (late 60's if I remember correctly) and I'd like to use it with my current hifi system to see just how good/bad it is. Mine came with several styli and I've fitted a new diamond single "Transcription" stylus as I don't need the 78 option on this one. I'm currently using a rather nice old Thorens TD125 turntable (from 1971) and Rega R200 tonearm (from the late 70's/early 80's) with it to good effect with the lower output cartridges I'm normally using.

The 104 has an output capacitance of 200pF according to the spec and the output into 2M test loading is around 350mV at 3cm/s. Acos claimed that this model could be used into a 47K magnetic phono input, which I've tried, but obviously the gain is much too high. On low level music, the sound shows great promise, being quite well balanced, but even my Croft valve equipped RIAA phono stage overloads on anything with bass.

There's another excellent but closed thread here concerning optimum loading and how this was changed/adapted when record players went from valve to transistor amplification. I was was wondering what sort of L pads I should make up to bring the levels down to a usable level so that the 104 could feed the "magnetic" cartridge input? As this model was apparently intended for such a role I'm hoping that mechanical stress within the cartridge will be minimised. Certainly, at 3grammes tracking force and with a little ballast in the headshell enabling me to balance the arm out, there's no obvious mistracking.

Can anyone do the maths for me and suggest a suitable attenuator pad? I suppose the optimum output level to aim for is around 0.8 to 1mV per cm/s into the RIAA phono input.

P.S. I also have an Acos GP96-1 cartridge coming in a Hacker M7 headshell and also a Sonotone 9TAHC. Any thoughts on whether these would also be compatible - I don't know how different their characteristics are I'm afraid, but I remember a 104 sounding better in a Hacker GP42 record player, this with a 1M loading?
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Old 27th Oct 2010, 9:06 pm   #2
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Default Re: Using a ceramic cartridge with modern electronics...

Hi,
I don't think an L-pad is the way to go. I guess you have in mind for the cart to see a MegOhm or so and then feed into an equalised mag input. A meg or so input on an amp would normally be flat.
I'd be inclined to add parallel resistors across the mag input until the cart is loaded down enough. I think this may be "velocity mode".
Graham
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Old 27th Oct 2010, 9:53 pm   #3
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Default Re: Using a ceramic cartridge with modern electronics...

That's what I meant - apologies. I just need to reduce the level going into the mag phono stage and apparently the cartridge will give a flat(ish) response in this mode. Any ideas of resistor values please? I thought an L pad would reduce the level as well as maintaining a "seen" 47K.....
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Old 28th Oct 2010, 12:37 am   #4
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Default Re: Using a ceramic cartridge with modern electronics...

If I read the OP correctly, the intent is to use a ceramic cartridge into an RIAA-equalised magnetic pickup input. Once I read that a ceramic (or crystal) cartridge could feed an RIAA equalised magnetic pickup input if loaded with 10 K ohms. You might give that a try.
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Old 28th Oct 2010, 9:00 am   #5
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Default Re: Using a ceramic cartridge with modern electronics...

Frankly it would be a lot easier to make yourself a little amplifier circuit to use as a standalone ceramic cartridge phono stage that would then feed a line input. I made one years ago and it worked superbly - some of the old ceramics were surprisingly capable (if I remember, correctly, the Sonotone 9TA was the best of all those I had!).

I'm sure I've still got the circuit at home somewhere - I'll have a root round for you!
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Old 28th Oct 2010, 9:20 am   #6
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Default Re: Using a ceramic cartridge with modern electronics...

The "proper" way to run a ceramic cartridge is into a high-impedance input (several hundred K to 1MΩ) with a flat response. An EL84 / UL84 or an op-amp work great.

A magnetic cartridge is a velocity sensor. A ceramic (or crystal; the former being artificial, the latter a naturally-occurring substance) cartridge is a position sensor. There is electrically no way to distinguish between an actual position sensor, and a velocity sensor followed by an integrator. This "phantom" integrator and the stray capacitance of the amp input combine to give a crude approximation to the RIAA equalisation, which can be neatened using the tone controls always found on record players with ceramic cartridges.

Running a ceramic cartridge into a low impedance magnetic input sort-of works because the low input impedance breaks the implicit integrator in the same way as it would break a real one. Not to do so would violate the principle of equivalence, with dire consequences for the stability of the universe
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Old 28th Oct 2010, 9:25 am   #7
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Default Re: Using a ceramic cartridge with modern electronics...

If you choose to run the ceramic cart into a 47K load (standard for magnetic carts) all you need is an attenuator pad. Just a simple Y or T pad, calculated for 47K and with as much attenuation as you think you will need, should work OK. A quick google produced several online calculators which will do all the arithmetic. An example:
http://www.random-science-tools.com/...ttenuator.html

Suggest quickly knocking together a (say) 20dB attenuator and see how it goes. You can easily go up or down a bit in the light of experience.
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Old 28th Oct 2010, 10:39 am   #8
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Default Re: Using a ceramic cartridge with modern electronics...

+1 for Beobloke. When I was a skint teenager in the late 70s / V early 80s my budget only ran to non-magnetic cartridges. To this day the *biggest* single improvement I have ever made in my audio system was the switch from a crystal cartridge to a ceramic. I built a little two transistor pre-amp (one per channel) from a circuit in Practical Wireless and fed it into a line level input on my B&O 900. Music poured forth and I was hooked. I subsequently went magnetic and built an Amtron kit Riaa preamp (which also picked up radio Moscow!). It was a slight step up as all upgrades tend to be. Over the years I've reached the heady heights of Garrard 301, moving coil cartridge etc, etc, but the Crystal to Ceramic upgrade remains the biggest step change.

I'm afraid I don't have the pre-amp circuit, but there was very little to it as no RIAA compensation is required (the cartridge effectively does this for you). Maybe start with a non-inverting FET op-amp and experiment with how much gain you need. With the figures you quote maybe a gain of 1 is sufficient. Then either just listen to music or build a valve version using ecc83 or similar.

Have fun!

Paul
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Old 28th Oct 2010, 11:21 am   #9
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Default Re: Using a ceramic cartridge with modern electronics...

The circuit I used was something along these lines:

http://users.belgacom.net/hamradio/s...ystal%20PU.gif

I suspect you would need to tweak some of values depending on the cartridge in use.

Regards,

Paul
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Old 28th Oct 2010, 6:42 pm   #10
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Default Re: Using a ceramic cartridge with modern electronics...

Back in the mists of time I had a belt-driven turntable fitted with a Sonotone 9TAHC cartridge whose output fed nicely into the 1 M Ohm line level inputs of a Ferrograph 724 tape-recorder, which had built in power-amps, bass & treble controls and even speakers. So I had, very compactly, a way of playing records as well as the recording functionality. I eventually moved to a moving magnet cartridge which involved an external RIAA unit, power supply etc - a lot messier as I could not use the Ferrograph's 'external' power supply line. When I finally moved up to the Shure M75 cartridge I decided that I could finally notice an improvment over the Sonotone.

Otherwise, I also have read of connecting a ceramic cartridge straight to the input of a 47k RIAA unit, but have never have had to try it out.

I wonder how well these elderly designs of ceramic cartridge can handle the wide groove deviations of later LPs?
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Old 28th Oct 2010, 7:33 pm   #11
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Default Re: Using a ceramic cartridge with modern electronics...

Hi,
A book I have somewhere mentions that if a ceramic cartridge, such as a GP104, is "loaded low" by the input impedance of the likes of a Phono input on an amplifier (which includes the RIAA equalizing stage) the output of the cartridge should be forced close to velocity characteristics.
I am not personally too convinced about this statement however.

A simple circuit to reduce the ceramic cartridges level to that suitable to Phono level inputs and also make the output something closer to RIAA can be seen here

Regards
Andrew
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Old 30th Oct 2010, 5:38 am   #12
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Default Re: Using a ceramic cartridge with modern electronics...

As mentioned in the thread: https://www.vintage-radio.net/forum/...251#post300251, ceramic cartridge matching and equalization was well-covered in several books by the late and great Gordon J. King, some under his pseudonym John Earl.

Whilst much is duplicated across these books, nevertheless it is worth looking at them all to get a reasonably complete picture.

I have attached a couple of scans that are illustrative. One shows the pad required to match the Acos Hi-Light ceramic cartridge to an RIAA-equalized input.

The other is more general, and shows a simple attenuation pad. The curves on page 84 show why the RIAA curve works, after a fashion, to equalize ceramic cartridges when they are looking into a relatively low impedance. But is also shows why the step in the RIAA curve creates errors, avoidance of which requires “pre-correction” by way of cartridge-specific R-C networks of the type shown for the Acos Hi-Light.

I imagine that Acos (and likewise others) provided technical information on suitable matching pads for its various models. I am not sure how easy it would be to find such material these days. Savoy Hill might be worth a try. According to an old catalogue (going back to the days when it was owned by Gwilliam Tudor-Rees) if offered packages of assorted Acos technical data.

DSJR – please send me a PM if you would like more scans of the pertinent pages from the GJK books. I thinking it would be stretching things a bit on the copyright front to attach them all to this thread.

Cheers,
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Old 31st Oct 2010, 9:11 pm   #13
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Default Re: Using a ceramic cartridge with modern electronics...

Thank you all so much for your help in something that many of you may not feel at all necessary these days. I shall try both ways, an attenuator/impedance matching arrangement and also a little J-FET circuit I found for matching a high impedance-needing source to a modern lower impedance amp input.

I'll keep you posted. Mr Synchrodyne, expect a PM soon
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Old 14th Nov 2010, 6:23 am   #14
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Default Re: Using a ceramic cartridge with modern electronics...

Ceramic (piezo-electric) cartridge matching is a curious little corner that became an issue with the transition from valve to solid sate electronics in the late 1960s. Provision of a high impedance input (1M or more) of sensitivity appropriate for (self-equalized) ceramic cartridges was not a problem with valve amplifiers. But it seems to have been a headache for the designers of transistor amplifiers. By the late 1960s the use of ceramic cartridges in domestic audio systems was fading anyway, so some manufacturers may have felt that it wasn’t worth much expenditure of effort, and that minimal accommodation would do. On the one hand the “business case” for such action is evident, but on the other hand it could result in an otherwise high quality and generally high performance product that had relatively poor performance in one particular area, not consistent with its general positioning.

Using RIAA-equalized magnetic cartridge inputs, sometimes with reduced sensitivity and/or different input impedances seems to have been the most common approach to providing ceramic cartridge inputs. This brings with it the previously-mentioned conflict with the self-equalization, and so the desirability of using matching pads, although I suspect that in practice that didn’t happen all that often.

That said, effectively differentiating piezo-electric cartridge outputs by feeding them into a relatively low impedance (say 100k or less) input and then using equalization as for magnetic (velocity-sensitive) cartridges was well established practice in the valve days. Before the arrival of the RIAA curve, it enabled the use of multiple equalization curves as easily with piezo as with magnetic cartridges. The various Leak valve control units from the RC/PA/U onwards seem to have done it this way, for example.

A reasonable inference is that the practice of differentiating piezo cartridge outputs originated at a time when such cartridges typically did not have built-in equalization. Then subsequently built-in equalization was adopted. What is not readily apparent is when this transition to built-in equalization happened, and whether or not it was universal. Was it facilitated by the arrival of the RIAA curve? Or did it happen with the advent of stereo? Or perhaps it came with the widespread adoption of ceramic rather than crystal elements, at least where better quality was concerned. With valve amplifiers, it was easy enough to provide high impedance (1M or more) “flat” inputs that would accept the output of self-equalized piezo cartridges, and this seemed to happen at the lower priced end of the amplifier market. Such inputs were more-or-less the same as those used for radio tuners and the like, so were economic fitments.

Provision of high impedance inputs on transistor amplifiers was certainly possible, but involved complications that were generally not otherwise beneficial, and so tended to be avoided. There were some exceptions, though. Tripletone, at the low cost end of the amplifier market where use of its units with ceramic cartridges was highly likely, used a bootstrapped emitter follower to obtain 2M input impedance, later moving to a FET input (Mullard TA320 IC, I think.) Ferrograph also used a FET source-follower in its F307 amplifier, following practice earlier established with its Series 7 tape recorders.

The use of high impedance, flat inputs assumed self-equalized cartridges, which by the later 1960s seemed at least to be in the majority. Thus it was technically a better approach to the problem than differentiating and using RIAA equalization, although the latter usually won on convenience grounds, so was more common. So it is not so surprising that in order to ensure that their wares gave a reasonable proportion of their designed-in performance, the ceramic cartridge makers developed their ad hoc matching and equalization pads. There were other approaches that the amplifier makers could use, the Quad 33 C1 input providing an example, but these were not common.

But it is not clear that all of the cartridge makers embraced self-equalization. The matching pads for the Goldring CS91 and CS91/E shown in the King excerpt I posted earlier are of the attenuating but not of the equalizing type, unlike those shown for other makes and models, including the Decca Deram, elsewhere in the same book. The curves shown suggest that these Goldring cartridges might not be self-equalized. As a corollary, one may wonder what their frequency responses might look like when fed into a 2M flat input. Linsley-Hood seems to have covered this possibility in his 1969 Wireless World Modular Pre-amplifier design, as it has provision for step-equalization of a high impedance ceramic cartridge input. In this case the reason for such is given as failure of self-equalization rather than lack of it.

Anyway, one might say that the amplifier makers, faced with the difficulties of providing high impedance inputs for piezo cartridges in their solid date designs, more often than not took the path of avoidance, and were probably looking towards a future in which provision for these could be neglected. But the tape recorder makers faced a similar problem, and one that was less easily avoided. As well as an expectation that self-equalized piezo cartridges could be used directly with tape recorders, most valve amplifiers had tape outputs that were taken from the anode of an early pre-amplifier stage and which needed to look into a high impedance, typically 500k or greater. Cathode followers for the tape outputs were very rare in British amplifier practice; Dynatron must have been one of the very few to use these. With valve tape recorders, provision of high impedance line inputs was not a problem. Insofar as early solid state tape recorders might be used with valve amplifiers that did not have DIN-style “constant current” tape outputs, high impedance line inputs were necessary, and ways and means to provide them had to be found. As mentioned earlier, Ferrograph used a FET source follower line input for its Series 7 range, allowing a 2M impedance. For its A77 model, Revox used a bootstrapped input stage for its bipolar input amplifier. The bootstrapping must have been quite “tight”, as the 1M auxiliary input impedance is, as far as I know, defined by a parallel 1M input resistor, indicating negligible shunting by the amplifier input itself. Uher I think used input an input potential divider with an 1M upper leg, probably taking the signal down towards microphone level. Solid state amplifiers were less demanding. Tape outputs were often buffered by emitter followers, and even where not, did not require to look into particularly high impedances. After a few years the tape recorder makers could ignore the need to match older valve amplifiers or ceramic cartridges. By the time cassette decks arrived as legitimate hi fi components, line input impedances of around 47k sufficed.

Cheers,
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Old 22nd Jan 2011, 7:12 am   #15
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Default Re: Using a ceramic cartridge with modern electronics...

It’s probably worth cross-referencing this later thread: https://www.vintage-radio.net/forum/...814#post399814 which adds materially to this discussion.

I’ve attached a couple of items, including the pertinent pages from Walton, which show the natural frequency response for an amplitude-sensitive cartridge and include the comment that equalization is a cartridge design issue. There is also an HFN (via Classic Hi-Fi) review of the Acos GP81 which shows frequency response with both 1M and 2M loads, the results pointing to 2M as being the desirable number.

Cheers,
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Old 22nd Jan 2011, 9:30 am   #16
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Default Re: Using a ceramic cartridge with modern electronics...

For a contemporary viewpoint, the experiences of science broadcaster Arthur Garratt may be useful. I slightly pararphrase here, as I don't have the original in front of me, but:

"for discs, I use a Decca Deram straight into 2M. If you try to be clever and treat it like a magnetic, correcting it as such, it won't work, You get yourself involved in the most complicated circuitry for no reason at all. As it is, I am flat to 20k within 2dB on the EMI test disc and can see no distortion feeding sine to the CRO."
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Old 22nd Jan 2011, 2:12 pm   #17
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Default Re: Using a ceramic cartridge with modern electronics...

Thank you all so much for your info

A brief update - I did some Googling and found a good website dealing with simple circuits to do with music pickups as much as anything else -

http://www.muzique.com/schem/multi.htm



The chap there sold me a couple of general boards, which come with extra circuit ideas not on the site, clearly labelled and easy to build, the high impedance buffer only requiring a 9V supply, which I already had, one J-FET, five resistors plus a wire link and three capacitors per channel, which were quite easy to obtain and fit. I've fitted the boards, hard wired with phono leads, into a little ABS box and it worked first time, with no hum, noise and basically a very clear and stable sound for such a very simple circuit. I optimised the input impedance at 2M and sat down to listen..

The Acos GP96 I have, sounded a little too soft and I get the feeling the "Stereo" side of the flip-under stylus is actually a 78 tip (incorrect stylus fitted). The Sonotone 9TAHC clone was a disaster and I suspect it's faulty, although I'll have to check the wiring on the little rear plug. The biggest surprise was what I thought was a clapped out Ronette 105 I bought from the US in filthy condition (plenty of photos, so I knew what I was getting), which sounded really good indeed to me once scrubbed up.

Lastly, a NOS Acos GP104 "transcription" - single stylus - was suffering from old age, the stylus decoupling needing some "exercise" to free off properly and the internal rubber coupling to the ceramic elements seemingly stiffer than I remember from 1971. I had high hopes for this one, so fitted it to my Thorens 125/Rega R200 and played it through the HiFi at 3 grammes playing weight. The upper bass and male-vocal region was truly sublime, although the upper midrange was recessed. Deep bass and very high treble was ok, if a little recessed but tracking overall was fine with no nasssssty ssssssibilance at all. In this case, I wonder if reducing the impedance to 1M may tilt the balance enough to lift the upper mid a touch?

To conclude, a wonderful experience and great fun to build this little circuit. I wonder if this latter needs to be any more complex as there are several circuits this board can take?

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Old 11th Feb 2011, 7:56 pm   #18
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Default Re: Using a ceramic cartridge with modern electronics...

Deram + Device + Delight. PW Jan1971
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Old 13th Feb 2011, 12:43 am   #19
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Default Re: Using a ceramic cartridge with modern electronics...

The PW circuit shown seems to be a high input impedance “flat” amplifier, a variation on the fet input theme.

Thus I think that there might be a typo in this statement in the article:

“The device shown in Fig. 1 enables an R.I.A.A. corrected, high impedance loading, 50 mV output, high compliance ceramic cartridge to be used successfully with an R.I.A.A. equalized, stereo preamplifier having a 100-300 mV gramophone input.”

Perhaps it was intended to be:

“The device shown in Fig. 1 enables an R.I.A.A. corrected, high impedance loading, 50 mV output, high compliance ceramic cartridge to be used successfully with a non-R.I.A.A. equalized, stereo preamplifier having a 100-300 mV gramophone input.”

That would make more sense, as a self-equalized ceramic cartridge looking into a high impedance does not require further equalization.

RIAA-equalized amplifier inputs with sensitivities in the 100 to 300 mV range were probably not too common, as to suit magnetic cartridges somewhere in the 2 to 5 mV range was more normal. Still, some amplifier makers did offer reduced sensitivity on their RIAA inputs to cater for ceramic cartridges installed on the “loaded low and equalized” method. Rogers comes to mind with its Ravensbourne and Ravensbrook models.

Cheers,
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