Greetings Friends. I'd like to add Moving Coil capability to my next Phono Preamp and have a few questions about wiring. I'm following the LencoHeaven LHTR 834p build and there's very little info on the MC portion of the build. For the SUTs, I've opted for a budget set from AliExpress and described as, "1: 10 + 10 Permalloy MC phono transformer, LP vinyl MC phono step-up transformer. Suitable for 3Ω to 100Ω MC cartridges." The item I received is different from the one pictured in the listing. Here's a pic:
As you can see, there's 2 shielded transformers and 3 pins in and out for each. The input side indicates single-ended inputs with 1 as IN and 3 as GND, while the output side seems to offer SE and balanced outputs. I'm a bit confused. If I can make this work, I'll start with an affordable MC cart like the Audio-Technica AT-OC9XEB which requires 100-ohm loading (?)
How would I wire this thang? I'd like to use both MM and MC carts with this pre, so I'll need input jacks for both styles, but what of loading MC carts? Can I wire this to do 1:10 and 1:20? Listing claims so but I can't find any documentation. I don't want to use a switch or add anything that would affect capacitance , I'd rather install as many pairs of input jacks as required and wire em all with the stipulation that only one set is used at a time. Is this the way?
thanks for taking a look.
As you can see, there's 2 shielded transformers and 3 pins in and out for each. The input side indicates single-ended inputs with 1 as IN and 3 as GND, while the output side seems to offer SE and balanced outputs. I'm a bit confused. If I can make this work, I'll start with an affordable MC cart like the Audio-Technica AT-OC9XEB which requires 100-ohm loading (?)
How would I wire this thang? I'd like to use both MM and MC carts with this pre, so I'll need input jacks for both styles, but what of loading MC carts? Can I wire this to do 1:10 and 1:20? Listing claims so but I can't find any documentation. I don't want to use a switch or add anything that would affect capacitance , I'd rather install as many pairs of input jacks as required and wire em all with the stipulation that only one set is used at a time. Is this the way?
thanks for taking a look.
I have tested them few month ago. Not bad - similar to Lundahls 9602 from the wiring perspective as well as some measurement I guess.
Take a look at the Lundahl datasheet and you know how to wire it. Yes it is possible to use it in 1:20 and 1:10, but need an additional switch.
For MM or MC operation you need a switch I guess.
For transformer loading, just put 1 pair of additional input jacks in paralell to the MC input and load it with resistors in the RCA plugs.
Take a look at the Lundahl datasheet and you know how to wire it. Yes it is possible to use it in 1:20 and 1:10, but need an additional switch.
For MM or MC operation you need a switch I guess.
For transformer loading, just put 1 pair of additional input jacks in paralell to the MC input and load it with resistors in the RCA plugs.
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You can build one around a TL072, wall wart and all, for about US $10, it works well enough.
I used it to step up the signal from a Thorens table to line in of a chip amp based amp, which had a pre amp chip feeding the main (uPC1238) chip.
Using transformers can cause slow response, unless ferrites are used.
I used it to step up the signal from a Thorens table to line in of a chip amp based amp, which had a pre amp chip feeding the main (uPC1238) chip.
Using transformers can cause slow response, unless ferrites are used.
Trying to determine how the secondaries are wired...
Can you take resistance readings between -
4+5
5+6
4+6
Thanks!
Can you take resistance readings between -
4+5
5+6
4+6
Thanks!
Why the H-E-double hockey sticks would I ask you to damage your transformers?
Just trying to help you figure out the questions you asked. Your call. The transformers will be fine.
Just trying to help you figure out the questions you asked. Your call. The transformers will be fine.
That seems to be a center tapped transformer, which isn't exactly what they are advertising, but oh well, it's Ali, what do you expect?
Anyway, best guess for output is 5+6 (1:10) or 4+6 (1:20)
I'd just experiment with with of the two sounds best once you get your cartridge and then use the one you prefer.
Anyway, best guess for output is 5+6 (1:10) or 4+6 (1:20)
I'd just experiment with with of the two sounds best once you get your cartridge and then use the one you prefer.
Thanks! And the grounds should be linked across the transformer? There's solder pads on the underside of the board that could be linked to join grounds, I think ..
E the solder pads would link Pin 3 of each side to 5 or 6, as well as pads to link both channels together, and to the PCB ground.
So that certainly makes me think you're right, input on 1, gnd on 3, output on 6, gnd on 5. Soldering the grounds to the PCB would connect to the shields, I assume.
E the solder pads would link Pin 3 of each side to 5 or 6, as well as pads to link both channels together, and to the PCB ground.
So that certainly makes me think you're right, input on 1, gnd on 3, output on 6, gnd on 5. Soldering the grounds to the PCB would connect to the shields, I assume.
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Have to experiment with that as well, to see what's quietest. In theory, yes, but hummm has a way of upending theory...
Ohmmeter currents will not damage a SUT, but could leave a bit of residual magnetism in the metal core. If you are simply checking for continuity and are not interested in the actual ohmic readings, then use the highest range on the meter, where the test current will be a few microamps at best. That amount will not adversely affect the core.
The residual magnetism left in the core is normal and is called remanence.
If the remanence is small enough, the little bit of AC supplied by the phono cart will, over time, demagnetize the SUT's core. If the core is strongly magnetized, then a demagnetizer would be needed. I demagnetized one by placing a 10K resistor in series with it and the 6.3Vac winding of a filament transformer, and placed the transformer on a Variac. I brought up the voltage until I got one mA of current through the SUT, soaked it a bit in that, and then slowly dialed down the Variac to 0Vac. Worked fine. A measly 1mA of current will not damage a SUT.