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Old 15th Jul 2017, 8:54 pm   #1
Stuvinyl
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Default Connecting Garrard 2025TC DIN to phono RCA amp.

Hi.

I'm new to the forum and have recently purchased an old Garrard turntable. It works perfectly well with the cheap "Hit Parade" amp it came with (din connected) but I have a nice phono stage in my Cambridge Amp and want to use that.
However on purchasing a cheap din to rca converter cable I am getting a lot of hum from the speakers. I presume I need a ground for the amp but can't find a male din cable with an earth/ground cable.
Please could anyone help

Thanks.
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Old 15th Jul 2017, 9:56 pm   #2
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Hello and welcome - the earthing should be taken care of by the interconnect you have bought - but you could try connecting the chassis of the Garrard to the earth point (chassis) of your amp and see if that helps. I assume you have a magnetic cartridge in the 2025? A ceramic cart would overload your phono input. If that's all OK then what you have sounds like an earth loop, which is normally caused by too many earth connections rather than too few.
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Old 16th Jul 2017, 7:46 am   #3
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Way back in the early 1970's my gran had a Garrard 2025 in a separate plinth and cover and Hit Parade receiver with a couple of EMI speakers in tall cabinets. The 2025 was fitted with a ceramic cartridge. A lot of affordable amplifiers/receivers had inputs for ceramic and if you were lucky magnetic cartridge as well.
You may find that you have a ceramic cartridge fitted especially if it has a flip stylus with LP one side and 78 on the other. This won't work properly into the phono stage of the Cambridge.
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Old 16th Jul 2017, 12:14 pm   #4
Edward Huggins
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

No Garrard 2025TC were ever fitted with a Magnetic cartridge, unless someone tried to bodge one on later. They were usually Acos GP96-1 or similar. In this case the OP will need to use the Aux/LIne In socket on his Cambridge amplifier.
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Old 16th Jul 2017, 2:06 pm   #5
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Thank you all for your replies. I'll try the different input asap and then get a new cartridge! Thank you so much again, I thought it would never work!
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Old 17th Jul 2017, 2:00 pm   #6
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

The Garrard 2025 was an entry level turntable that was used in a number of record players and unit audio style music centre. It is not what I would call hifi and so would not spend much on a cartridge for it. I do not know if any magnetic would fit as the Garrard fixed headshell does not accept standard 1\2 inch cartridges like the Audio Technica AT91.
I would look out for something like a Pioneer PL12d, Trio KD1033 or any of the Duals if you want to make the most of your Cambridge's Phono stage.
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Old 17th Jul 2017, 3:34 pm   #7
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

A ceramic cartridge will work quite well direct to an MM input. Post 6 here https://www.vintage-radio.net/forum/...ad.php?t=60957
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Old 17th Jul 2017, 4:19 pm   #8
Edward Huggins
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

This could be misleading to the OP as it is highly unlikely any Ceramic, even low output types such as the Decca DERAM, would work at all well into a typical MM input stage of say, 5mV sensitivity. If it did, then all the rule books will need to be re-written!
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Old 17th Jul 2017, 4:35 pm   #9
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

I agree with Edward and others, this deck is unsuitable for use with anything with hifi pretensions.

It may be just about usable connected to a line level input such as aux or tuner, depending on the input impedance.
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Old 17th Jul 2017, 4:42 pm   #10
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Ah, putting a ceramic (crystal) cartridge into a MM input does work, the low input impedance, it should be zero for a perfect translation, of 47k is so much lower than the 2 or more megohms needed for a 'proper' ceramic input. It can be argued that a ceramic into a low impedance and then via an RIAA correction is better than the classic hi Z input.
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Old 17th Jul 2017, 11:36 pm   #11
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Yes -- that works.

A magnetic cartridge is a velocity sensor with current output. A ceramic / crystal cartridge is a position sensor with voltage output.

Now suppose you had a velocity sensor which produced a current proportional to velocity, followed by an integrator consisting of a resistor and a capacitor in series across the sensor, with the output taken from across the capacitor; recall v = (1 / C) * integral i dt. This would give you an output voltage which depends on the integral of the input velocity with respect to time; which by definition is the input position.

If you then connected a resistor across the integrator output that was much smaller than the resistor in the integrator, that would spoil the operation of the integrator; it would discharge through that external resistance much faster than it could ever charge through the integrator resistance.

But it's a fundamental theorem in electronics that you cannot determine, just by manipulating the inputs and taking measurements at the outputs, which of several equivalent circuits you have in front of you. You cannot tell the difference between a velocity-to-current converter followed by an integrator, and a position-to-voltage converter

Which means, if you connect a ceramic cartridge to a low-impedance input, its output will depend on the stylus velocity. And it just so happens that the amperes per (metre per second) you get from this arrangement is close enough to what you would get out of an actual magnetic cartridge to be neither too weak to produce a sensible listening volume without amplifying too much unwanted noise, nor strong enough to drive the preamplifier into distortion.

Which is probably a good thing, really; because it could take some concerted effort to persuade a modern magnetic cartridge with 12.7 mm. mounting centres to fit into that narrow headshell. Could be worth trying with a cheapo magnetic cartridge first before you ruin a posh one.

The 2025TC is basically an SP25 with a different tonearm and a stacking mechanism. It's not bad, subject to the state of the rubber motor mounts and idler wheel, but it falls short of the ideal in ways a good amplifier and speakers could reveal. Still, it's you that's going to be doing the listening .....
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Old 18th Jul 2017, 8:12 am   #12
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

These Posts have given rise to some interesting, yet quite diverse, viewpoints - but by now it may be off-topic. Maybe it needs a new Thread on user's experiences of running ceramic cartridges into RIAA equalised MM inputs. Just because it never worked in my experience, it may not mean that I am correct.
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Old 18th Jul 2017, 9:32 am   #13
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

What often gets missed in all of this is that whilst you can make a ceramic or crystal cartridge essentially velocity responsive by feeding its output into a suitably low impedance, such as a typical magnetic cartridge input, it still does not simulate a magnetic cartridge because the inbuilt step equalizing gets in the way. That is why the makers of ceramic cartridges usually offered matching pad circuits that “undid” the inbuilt equalizing when they were so used, thus avoiding double equalization. It’s non-trivial, in that the step was of 12.5 dB. It’s hard to see that doing it this way – de-equalizing then equalizing – might be better than high impedance loading. But there was another approach – as advocated by Burrows – that used low impedance loading followed by simple integration (rather than RIAA equalization) matched to the combination of cartridge self-capacitance and amplifier input resistance.

Cheers,

Last edited by Synchrodyne; 18th Jul 2017 at 9:38 am.
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Old 18th Jul 2017, 9:58 am   #14
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Here are the Burrows Wireless World articles that provide "chapter and verse" on the topic:

WW 197002 Burrows Ceramic Pickups and Transistor Amplifiers.pdf

WW 197107 Burrows Ceramic Pickup Equalisation - 1.pdf

WW 197108 Burrows Ceramic Pickup Equalisation - 2.pdf


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Old 19th Jul 2017, 7:25 am   #15
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

As though to show the exception to the "rule" of ceramics-only on the Garrard 2025TC, here is one with a Pickering magnetic cartridge in its purpose-built tonearm head. This is apparently a plug-in Pickering, like those that were installed in many Garrard 3000s supplied on contract to makers of better-than-average phonographs.

I would think this particular 2025TC has a four-pole motor, which due to their coils producing AC hum that is out of phase with each other, will hum less than the same record changer with a two-pole motor. From its deep parts bins, Garrard would literally build anything that a record player manufacturer could want.
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Old 19th Jul 2017, 7:39 am   #16
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

At our Uni radio station in 1970/71 we had 2025TC decks fitted with Sonotone 9TAHC carts. Our mixer used 741s wired for Hi-z input. At around that time, Wireless World published an EQed circuit for 47k input from a ceramic. We quickly knocked it up to test and it worked fine but not worth rebuilding the mixer for.
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Old 20th Jul 2017, 8:01 am   #17
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Here is a sheet prepared by Sonotone, with their recommendations for connecting Sonotone cartridges to magnetic and line level inputs. Note that the line level connections are for TUBE amplification, with its high input impedance. Most transistor inputs have a much lower impedance and many ceramic cartridges sound poor when directly fed into such.

The circuit for magnetic input shows a tube, too; but the impedance seen by the cartridge is dependent on a shunt (load) resistor, so this circuit would work with either a tube amplifier or most transistorized ones.
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Old 20th Jul 2017, 9:27 am   #18
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Not quite sure where the OP is with this now? It seems that if he wishes to play a ceramic cartridge into the MM input of his Cambridge amplifier, then some kind of passive network will need to be inserted. I still think the neatest solution would be to use the Aux/Line in sockets or go get a half-decent turntable with an entry level MM cartridge and enjoy what the Cambridge can really offer.
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Old 20th Jul 2017, 10:09 pm   #19
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Well, the Sonotone data sheet kindly provided by GP49000 is quite explicit – kudos to Sonotone for providing good product literature. Whilst the network details would be cartridge-specific, the same principles would apply generally.

For direct connection, an amplifier with a 2M input impedance is required. Such high impedance inputs are/were scarce on solid-state amplifiers. For example, the radio and auxiliary inputs of the Cambridge P40 and P50 were specified as 100k, 100 mV, so unsuitable for the purpose.

In the case where an equalized magnetic cartridge input is to be used, a de-equalizing network is needed. That shown would, I think, provide an upstep curve that cancelled the equalization built into seem to have missed the cartridge. Kudos to Sonotone again for offering a plug-in adaptor that contained de-equalizing network. Clearly it anticipated the problem caused by the scarcity of high-impedance inputs on the one hand and on the other hand, in their absence, the likelihood that some users might default to direct connection of self-equalized ceramic cartridges to magnetic inputs.

The Cambridge P40 and P50 both had “ceramic cartridge” inputs of 100k, 100 mV. From the P50 schematic, it looks as if RIAA equalization was applied to this input, using the same network as for the magnetic cartridge input. Use of such an input with a self-equalized ceramic cartridge would result in double equalization, so that a de-equalization network would still be required, as with the magnetic input case. This kind of input would be right for a non-self equalized ceramic cartridge. But this was a minority type, with about one, the Connoisseur SCU1, extant in the late 1960s. All of the others were self-equalized. But the Cambridge approach was not atypical of amplifier makers of the time, many of whom seem to have missed the mark when it came to using low-impedance loading for ceramic cartridges. Quad was one of the few who attended to the detail in this regard; the C1 disc input on the 33 was tailored for self-equalized ceramic cartridges of a specified self-capacitance range (which covered most of them). One or two did offer solid-state amplifiers with high-impedance inputs, notably Tripletone, who, operating at the “budget” end of the market, had a particular need to get right the issue of ceramic cartridge matching. Another was Ferrograph, with its F307. In this case the high impedance input looked to have been a carryover from the Series 7 tape recorder, whose high impedance line input may have been motivated less by the need to match ceramic cartridges than to provide an input suitable for connecting to valve amplifiers, many of whose (unbuffered) tape outputs needed to look into impedances of at least 500k, sometimes as much as 1M.

Anyway, in the case at interest, as the amplifier is unlikely to have a high impedance “flat” input, then connection to the magnetic cartridge input via an appropriate de-equalizing network is the best answer.

Here is a sampling of several such networks, additional to the Sonotone case already covered.


Cheers,
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Old 21st Jul 2017, 2:41 pm   #20
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Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

The 2025TC isn't the easiest turntable to fit a magnetic cartridge to, and you need that 4 pole motor to make it worthwhile. I've got a USA model and have a 50Hz 4 pole motor spare so I'm giving it a try.

Two cartridges spring to mind, the Shure M71/M74/M75/M81 slimline, the mounting bracket has a centre hole that can be enlarged to take the 6BA screw. The half inch screw "ears" will need cutting back to fit the slimline headshell. The other is the Pickering V15HB with a single mounting hole, again it needs enlarging. I'm going for the Pickering as it's more robust for exchanging LP and 78 styli. Both cartridges will be too far back in the Garrard headshell, so an additional 6BA threaded hole is needed.

I've just tried a very quick and dirty adaptation on a scrap 2025TC arm, the pictures show the result. You have to bend the bracket on the V15 to get the screw to fit, and then bend it back. It is possible to break the weld if you're heavy handed. When I do the USA model I'll drill the additional hole a little further forward - and more precisely .

The Pickering V15HB isn't common, but they do show up and I've just bought a couple quite cheaply.
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