SUT Problem - Help needed

[martinswimmer]

Hi everyone,

I've been having troubles with this home made SUT - I'm using 2 EMI BBC 1:30 input transformers with resistance of 12.47 KOhms and 42.4 Ohms but can't get any sound out of low output (0.2Mv) Entre 1 cartridge.

The cartridge is fine - I'm running it straight into gain adjustable phono stage and it plays great.
The transformers seem fine - I've used them in the past with Denon DL103 and AT-OC05 and 09 and just today I ran the sound out of cassette player into them and checked on multimeter and got correct voltage.

I can't get any measurable signal out of it when connecting this LOMC. Is there anything like not enough current from the cartridge to overpower the impedence of the coils of the SUT or any other aspect that I might be underestimating?

I've got a few other home made SUTs and they all work fine. I've found Tamura input transformers from Otari reel to reel to be particularly good.

Thanks!

[anubisgrau]

did you connect correctly?

[martinswimmer]

did you connect correctly?

Yes, connected properly and verified on multimeter that it's working fine with higher output from cassette player.
Uzgred, i ja sam iz Beograda, Dorcol.

[Barry]

Have you connected the output of the SUT to the disc input of an amplifier? Was there no audible output?

Assuming an input impedance of 47KOhm for the disc input, and with the figures you provide for the SUT, the impedance presented to the Entré MC cartridge will be 108.5Ohm. Given the 3.5Ohm coil impedance of the cartridge this loading impedance ought to be quite satisfactory (Entré recommend > 30Ohm).

Again given the coil winding resistances and the nominal turns-ratio of 1:30, the 0.2mV output from the cartridge will be boosted to 4.3mV: an acceptable figure.

How did you measure the winding resistances?

[martinswimmer]

Have you connected the output of the SUT to the disc input of an amplifier? Was there no audible output?

Assuming an input impedance of 47KOhm for the disc input, and with the figures you provide for the SUT, the impedance presented to the Entré MC cartridge will be 108.5Ohm. Given the 3.5Ohm coil impedance of the cartridge this loading impedance ought to be quite satisfactory (Entré recommend > 30Ohm).

Again given the coil winding resistances and the nominal turns-ratio of 1:30, the 0.2mV output from the cartridge will be boosted to 4.3mV: an acceptable figure.

How did you measure the winding resistances?

Hi Barry, I've got it connected to phono stage, but the input impedence is not 47Kohm - i've got the jumpers to present less of a load - around 100 ohms (if I'm correct). I measured winding resistances with a multimeter.
I'll try connecting it directly into an ampifier - phono stage might be tripping or something?

[Barry]

If you're loading the output of your SUT with 100Ohms, I'm not surprised you can't hear anything.

Change the input impedance of your phonostage back to 47KOhm.

[martinswimmer]

If you're loading the output of your SUT with 100Ohms, I'm not surprised you can't hear anything.

Change the input impedance of your phonostage back to 47KOhm.

LOL - thanks, I'll try that.

[disarmamant]

I measured winding resistances with a multimeter.

It’s never a good idea to measure the winding resistance with a multimeter, you could end up magnetising the core of the transformer.


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[RothwellAudio]

Hi Barry, I've got it connected to phono stage, but the input impedence is not 47Kohm - i've got the jumpers to present less of a load - around 100 ohms (if I'm correct).

If you're loading the output of your SUT with 100Ohms, I'm not surprised you can't hear anything.
Change the input impedance of your phonostage back to 47KOhm.

No, I'm not surprised either. 100 ohms on the secondary and a 1:30 turns ratio will present the cartridge with a load of just 0.1 ohms - near as damn it a dead short.

It’s never a good idea to measure the winding resistance with a multimeter, you could end up magnetising the core of the transformer.

Yes, that's true. It's tempting to do because it's an easy way of identifying windings and checking there are no breaks in the windings but it can magnetise the core. Fortunately it's easy to demagnetise the core with a signal generator.

[martinswimmer]

No, I'm not surprised either. 100 ohms on the secondary and a 1:30 turns ratio will present the cartridge with a load of just 0.1 ohms - near as damn it a dead short.


Yes, that's true. It's tempting to do because it's an easy way of identifying windings and checking there are no breaks in the windings but it can magnetise the core. Fortunately it's easy to demagnetise the core with a signal generator.

Thanks for this. Unfortunately, I need to measure resistance to find out what are these transformers.