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xrk971 26th September 2019 06:34 AM

Sometimes an amp designed for +/-24v when operated at higher voltages will exhibit a change in the harmonic distortion profile. It may have lower overall distortion but higher relative H3/H2. Lower voltage may have higher H2/H3, hence sweeter sound. Zman01 is right, the way to get to the bottom of this is to measure.

Here’s how:
Howto - Distortion Measurements with REW

meanie 26th September 2019 06:39 AM

Now that i m happy with how the M2X sounded, i will proceed to house it into a proper chassis. Then i will pull out the Focusrite and log some readings.

Thanks X for the thread on Distortion Measurement with REW.

Dadbeh 29th September 2019 05:22 PM

If the filter caps are 50v, is a transformer with 38v output, safe to use?

Shawnstium 29th September 2019 05:59 PM

Is that 38v (ac or dc?) measured or the rated rms at no load?

xrk971 29th September 2019 07:55 PM

A 38vac trafo makes 53vdc no load. Probably 49v under load, so with zero safety margin it might work but you might also get a big explosion at some point.

But 38vdc is fine for 50v caps. I think you need 64v caps for a 38vac trafo.

Dadbeh 29th September 2019 11:41 PM

I actually misread the panel on the Trans. It was 36 vac that the transformer outputs. This :

I connected it to power supply with 50 vdc volt 10000 micro farad power supply and smoke went up. I am ordering 63vdc ones.

Imgur: The magic of the Internet

Vunce 30th September 2019 03:33 AM


Originally Posted by Dadbeh (
I connected it to power supply with 50 vdc volt 10000 micro farad power supply and smoke went up. I am ordering 63vdc ones.

Something doesnít sound right, if hooked up correctly I donít think you should see any smoke with a 36vac trafo and 50vdc capacitors. Could there be a short somewhere?

gaborbela 30th September 2019 06:13 AM

With 36VAC transformer very much you push those 50V caps to their limit. Also, it depends on who produced those capacitors. You should have at that voltage min 10V or so extra tolerance.

Shawnstium 30th September 2019 11:01 AM

Double check how the primary side is wired up and measure your mains voltage. Was a cap wired up with its polarity reversed?

Using a variac to slowly ramp up the voltage while monitoring the output is the safest method to start up a new design. There is also the incandescent lightbulb method and the use of current limiting resistor for slow/safety start ups.

My final PSA would be to wear eye protection when your first fire up a new power supply. Explosions of hot electrolyte in the face won’t be pleasant...

Dadbeh 7th October 2019 11:30 AM

. There are two primary windings. red/black is primary. which is the correct way to wire it for a bipolar power supply like SLB?
1 - to use only one of the primary winding and leave the other pair of red/black loose
2 - to connect the two reds together and connect the two black together and then to connect them to the 115v mains?

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