Power supply for K2573

Regarding K2573 - Stereo RIAA Correction preamplifier…

Why is the recommended power supply 1A, and the consumption of the K2573 is only 0.005A? It sounds massively overrated.

Specifications from www.velleman.be

* supply voltage: 10-30VDC / 5mA regulated
* gain (1kHz): 35dB
* input signal: 5 - 10mV
* input impedance: 47Kohm
* PCB dimensions: 44 x 65mm (1.7" x 2.6")
* recommended transformer: 1150007M + K1823

Would I be likely to have any interference problems using this power supply for the pre-amp?

• Switch Mode Power Supply Unit
• Plug In type
• 2.1mm DC Plug
• Input : 100 ~ 240 VAC
• Output : 12V 450mA

This is a guarantee for troubles :slight_smile:

My advice: Use two 9V batteries in series for best results.

Thanks for the warning. What would be the best solution that can be continuously on (no batteries)?

Use a well regulated supply such as the K1823

I made my first attempt using a regulated power supply, but that created massive hum without any input signal.

The second attempt is now using two 9V batteries in serial as recommended, and it appears perfect. I get a single click on the amplifier when i switch this kit on, but I get absolutely nothing coming through. The turntable is running (with Handel’s Messiah); the input leads are connected; the output leads are connected, but there is absolutely no signal coming through.

I’ve tried swapping input and output leads, with no improvement.

What next?

Most likely an assembly problem. Check complete assembly. Check direction of the IC. If necessary, have a friend take a look at your assembly.

I have checked and re-checked. It looks good. No dry joints, IC is correct, all caps and resistors neatly lined up and orientated properly. Shielded wires from connector to RCA jacks.

Next step?

Then it should work :slight_smile:

If you cannot solve the problem yourself, you can return your kit for inspection.
Please return it to:

Velleman Kit Tech Dept.
Legen Heirweg 33
9890 Gavere

Repair is less than price of kit (postage not included)

It would be simpler for me to just rebuild the kit, replacing all discrete components! You don’t know the South African postal system :x

How would I measure the input / output, rather than just “listening for the soundtrack”.

I don’t have an oscilloscope. Only a multimeter I don’t fully trust!

Without the right test equipment, it is almost impossible to check.
Listening to the output is the most simple and most reliable test.
This is a very simple circuit with few components. It cannot be too difficult to get it to work.

I’m not getting much time to solve it… but I’ll get there eventually.

I’ve replaced the IC with no improvement.

Is there any chance that the turntable (Thorens TD-145) has a different requirement, or are they all the same?

The specs of the Thorens original pre-amp and the specs of this kit are almost identical.

Most likely, it is a MM (moving magnet) element, which is fine for this circuit.

If it is a MC (moving coil) element, then this kit is not suited, as MC elements have a very low output and require a different input impedance.

If it was a MC element, what kit would I then use?

Sorry, no such kit…

I found the problem. R11 and R3 were swapped. Apparently there IS a difference between 2k2 and 22k :).

Things are now working properly using the two 9v battery approach.

I’m still a little confused about the power supply though.

If I put a power supply with it’s transformer in the same box as the pre-amp, I get a lot of interference.

So why would it be such a problem to use the power supply in the second post here? The transformer would be located well away from the amp? Or is it the nature of the supply?

It is not regulated and it is switch-mode, two guarantees for noise/hum…
You need a well regulated linear supply. Even then, it will not be as good as batteries.