Arm cable RCAs into mic pre XLRs

[boXem]

Usually star quad cables do not shine on the capacitance side, and splitting the shield to the two xlr will not be easy either.
Just think about what solution feels the most comfortable for you (split 1 cable or fit 2 cables in 1 connector) and go with it.

 

[sergeauckland]

Thanks, for the latter option something like a single run of Van Damme star quad?

Possibly, but star-quad isn't two runs of twisted-pair, it's one run of twisted-four, so there's no attempt to keep the two circuits separate, and crosstalk will be high. You could try one length of screened Cat 5 cable, as that should be thin enough. It has four twisted pairs, so just use any two and ignore the other two.

S

 

[Jas0_0]

I believe the MC cartridge has 4 wires for the left and right channels. Each channel needs to be connected to its own input on the preamp, so you would need two RCA to XLR cables.

The single ended input impedance of the TRP is about 16k ohms. The typical source impedance of a MC cartridge is around 100 ohms so using the 10x rule the ideal preamp input impedance would be around 1k ohm. You could try adding a 1k ohm resistor between pins 2 and 1 on the XLR to load the MC cartridge and help reduce the rise in response above 10kHz. You might want to look at what the cartridge manufacturer recommends for input impedance loading.

Let me know how the TRP works out, James. I've used it with ribbon mics and it was excellent.

Thanks, Dave

Hi Dave,

I wonder if you could help. The AEA TRP has arrived and I've plugged it into my RME ADI-2 Pro FS. I'm getting a really large amount of hiss/noise on both channels when I turn up the Output Level controls. Is that normal?

I've not yet got my cart or tonearm cable sorted so nothing is plugged into the TRP's inputs - is it possible the hiss will go away when something is plugged in?

Many thanks,

James

 

[sergeauckland]

A MC cartridge presents a very low impedance to the amplifier, typically something like 10 ohms, so you will get a lot of hiss with an open-circuit mic input. Try shorting out the inputs of the mic pre, that should give you a close approximation to what you'll get with the cartridge connected.

S.

 

[Jas0_0]

A MC cartridge presents a very low impedance to the amplifier, typically something like 10 ohms, so you will get a lot of hiss with an open-circuit mic input. Try shorting out the inputs of the mic pre, that should give you a close approximation to what you'll get with the cartridge connected.

S.

Thanks Serge - how do I short the inputs?

 

[intaud]

Serge is correct regarding noise with an open-circuit mic input. Short pins 2 and 3 on the preamp input XLR with a paper clip just to test that the noise is reduced.

Dave

 

[intaud]

Make sure its off or your volume is turned down before you do it.

 

[Jas0_0]

Thanks Dave. Just to double check before I do any damage, I open out a paper clip and stick one end in the pin 2 hole and the other end in the pin three hole, and repeat for the other channel?

I actually have some spare male XLR cables with the other ends unterminated. Presumably if I plugged those in and twisted together the cables from pin 2 and 3 this would have the same effect?

James

 

[sergeauckland]

Thanks Dave. Just to double check before I do any damage, I open out a paper clip and stick one end in the pin 2 hole and the other end in the pin three hole, and repeat for the other channel?

I actually have some spare male XLR cables with the other ends unterminated. Presumably if I plugged those in and twisted together the cables from pin 2 and 3 this would have the same effect?

James

Yes, that'll do the same job. If the cables are much longer than your turntable to pre-amp cables, you might get a bit more hum, but it'll give you a fair idea of how much noise you should get with a cartridge connected.

S.

 

[Jas0_0]

Great - thanks, will give that a go
J

 

[somebodyelse]

Scott Wurcer's Linear Audio article is mostly about the digital riaa eq, but there's a section on interfacing cartridge output to mic inputs, including schematics if you can do the DIY.
https://linearaudio.net/article-detail/2240

 

[Jas0_0]

Yes, that'll do the same job. If the cables are much longer than your turntable to pre-amp cables, you might get a bit more hum, but it'll give you a fair idea of how much noise you should get with a cartridge connected.

S.

Serge is correct regarding noise with an open-circuit mic input. Short pins 2 and 3 on the preamp input XLR with a paper clip just to test that the noise is reduced.

Dave

Thanks Serge and Dave. This evening I tried as you suggested, using the spare XLR cable to connect pins 2 and 3. The result was a dramatic reduction in hiss for both channels. I could still hear hum through the speakers if I turned the mic preamp gain right up, and set the ADI-2 Pro volume to 0dB, but this will be far more gain and volume than I will ever need. At what will be very loud listening levels there was nothing to hear.

I noticed also that if I touched the exposed cable shield, there was a notable drop in hum, so I will need to work out how to ground this setup properly. Still haven't go my head around how to do this. Linn declined to tell me - suggested I go to a Linn dealer and buy a cable instead. Perhaps I shouldn't be surprised.

Here is the noise profile with the mic pre at max gain 84dB (one channel only) once digital RIAA had been applied.