Voltage check problem [resolved]

[Hazim_hatta]

Hi all,

I recently build crack for my sennheiser. During build, terminal 2,4,7,9 have higher voltage but similar reading of the pair. An a constant hum even without input when tested with headphone.
My input voltage is 225. Here is my DC voltage reading:

1. 95v
2. 233v
3. 0v
4. 234v
5. 88v
6. 0v
7. 135v
8. 0v
9. 132v
10. 0v

[Paul Birkeland]

What is the AC voltage coming out of your wall and how did you wire the power transformer?

[Hazim_hatta]

Powerline test result is 225v, then I follow instruction in page 26 for 210v to 225v. The official is 240v in my country.

[Paul Birkeland]

I would recheck that line voltage.  I suspect you have closer to 240V coming out of the wall, and that is pushing things up a bit.

[Hazim_hatta]

Should I re-wire the transformer to 240v? I tested power outlet around my house, the reading is 225v

[Paul Birkeland]

You only have to move one connection of one wire to change to the 225-235V, and I would suggest giving that a try. Just move the red wire from power transformer terminal 17 to power transformer terminal 18 and recheck your voltages.

[Hazim_hatta]

I fixed that, the dc voltage drop to 215 - 220 v rage for terminal 2,4 and 125-130v for terminal 7,9

*change to 235-245v setting, the dc voltage on 2,4 reading drop to 195-200vdc and terminal 7, 9 drop to 115 to 120vdc range

[Hazim_hatta]

Is it safe for use? And there is a hum even when not connected to source

[Paul Birkeland]

I would leave it set for 235-245.

With no source connected and the volume pot turned all the way up, there will be noise.  Is there noise with the volume control turned all the way down?  If so, you likely have a loose connection or a solder joint or two that need to be reflowed.

[Hazim_hatta]

With volume all way down, there still hum. Is there certain location that i need to look out for?
And should I proceed with the speedball?

[Paul Birkeland]

If it sounds more like a buzzing noise, that's typically a loose power supply capacitor.  If it's a deep hum, that is more likely to be loose hardware or a loose solder joint.  You can also post some build photos and maybe we can spot something.

[Hazim_hatta]

Here some picture of the build

[Doc B.]

For starters you need to twist the green heater supply wires and braid the red, white and black signal wires from the RCA jacks to the volume pot. The instructions are detailed in the assembly manual. Either of those not being properly dressed could be a reason for excessive hum so they should be corrected first. Once that is done if the hum persists we can start to look at other possibilities.

I have attached a photo of a partially complete Crack amp I am currently assembling so that you can have an idea of what the wiring layout should look like.

[Hazim_hatta]

I braided the wire, but the hum still persist on the right channel only

[Hazim_hatta]

Resolder some point, the Led does not light up. Replace the Led in the speedball kit. The led lights up then turn dark