Altering tone on ceramic pickup?

[Herald1360]

Is there any such beast? Both ceramic/crystal and MM magnetic cartridges have a rising output with frequency type of response into a 47k load and require some form of frequency related compensation circuits to flatten things out.

[HoverJohn]

Hence why I’m a bit stuck and asking for help

[Synchrodyne]

The gram input in question was intended to receive the output from a magnetic cartridge, to which it presents a resistive load of 47k. The preamplifier section provided both gain and equalization, offering three equalization curves, namely “78”, “Hi-Fi” and “LP”. The LP curve is, one would hope, the RIAA curve. The “Hi-Fi” curve might well correspond to the Decca FFRR 78 rev/min curve. And the “78” curve probably corresponds to one or other of the old 78 rev/min curves. As I understand it, the sensitivity of the gram input is something like 15 mV, fine in the mid-1950s, but well away from the 2 mV or thereabouts which has been the norm since the later 1960s. Thus a modern magnetic cartridge is unlikely to be a good match to that input in signal level terms.

The original Tannoy cartridge by no means provide a flat response curve by itself. The flat curves shown in the literature are those after equalization.

You want to use the gram input unmodified, but with a ceramic cartridge. The answer is to insert between the cartridge and the gram input an attenuation and de-equalization network specific to the chosen cartridge. The cartridge makers often published schematics for such networks, as shown upthread for the Decca Deram case. Some makers, such as Sonotone, even offered plug-in adaptor units to match its ceramic cartridges to magnetic cartridge inputs. So it is nothing too complicated, and it has all been done before.

One more thought – I understand that some of the Connoisseur ceramic cartridges (I am not sure which models) differed from the mainstream in not including (essentially mechanical) equalizing for the RIAA curve, something that was otherwise the norm, at least in the stereo era. These were designed to be loaded “low” and used with conventional magnetic cartridge inputs of around 47k input impedance. Apparently their very low capacitance ensured that with typical magnetic input impedances, the turnover point of the differentiation curve was above the AF range, and of course their lack of inbuilt equalization meant that no de-equalization was required.


Cheers,

[Synchrodyne]

Here is a selection of ceramic cartridge matching circuits:

[Synchrodyne]

And here are some Sonotone materials. Sonotone was serious about getting the best preamplifier input matching for its ceramic cartridges, including into "magnetic" inputs.


Cheers,

[HoverJohn]

Cheers for these I did try one similar all crammed into the headshell however it suggests another capacitor i might have another go at that.
The expected input for the Tannoy into the TC10 unit is only 3.5mv and from what ive been led to believe the variluctance is position sensing not velocity I can dig out the diagram of the 3 Dynatron input types I’m just failing how to modify the VR into mag or ceramic.

[HoverJohn]

Ok so having read it all again and got a marginally better grasp on it I realised that I needed to increase the resistance of any circuit that the pickup was attached to. So I’ve drastically increased the resistance before it’s connected to the 47k input. The levels are still on the high side but it has some bass now but it’s tolerable I’ve got some bigger resistors in the post to get it up to closer to 1 Meg.

[PYE 405]

Just to add to the mix of excellent input on this subject already, here is a link to Keith Snook's website with some info on the Quad 22 pre-amp. The item of interest is the phono stage description for various matching, if you scroll down about half way to....
~ QUAD 22 Control Unit Phono or DISC equalisation ~

https://keith-snook.info/quad-22-val...amplifier.html

(I use a Quad 22 with two turntable's, one with a Sonotone 9TAHC (ceramic stereo) wired for mono and the other deck a Shure M75 magnetic cartridge. I play a mix of 78's, 45's and mono LP's with the Sonotone, plus stereo LP's with the Shure.)