LED does not light up but everything works [resolved]

[hpleung]

Hi,

I am doing a check on my crack before moving on to the speedball. One thing i have noticed is that little LED does not light up but the headphone amplifier itself works fine with excellent sound.

I am posting some pictures if anyone can take a look at why the little LED does not light up. Does it matter - are there any obvious mistakes?

Thanks,

 

[Paul Birkeland]

What are the voltages on terminals 1-10?

 

[hpleung]

I seem to get 2.00 volt - I am a newbie. So i used the Volt-Meter in AC measurement mode - selecting "max".

 

[hpleung]

I forgot to mention - for measurement - 1 probe on terminal 1 and 1 probe on terminal 10.

 

[Paul Birkeland]

OK, you have not passed your voltage checks since it appears that you haven't done them.  You should not listen to an amp that hasn't passed its voltage checks.

The voltages specified in the manual are DC voltages, so you need to set your meter to DC, not AC.  You do not want to select min/max/hold, as those functions aren't necessary for a voltage check.

The manual gives some instructions on how to perform the voltage checks, so you may want to revisit those so we can get a better picture of what's going on with your amp.

 

[hpleung]

Good suggestion. Here is my measurements for 1 and 10 after following the instructions.

1 = 130v
10 = 0.07mv

Voltage at terminal 1 seems much higher than the value in the manual (>10% more than 100v)

 

[Paul Birkeland]

Can you provide the DC voltages for terminals 1-10?  1-10 means 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.

If you have 130V at terminal 1 you absolutely must not attempt to use your Crack.

 

[hpleung]

1 = 130.0
2 = 153.6
3 = 0.06mv
4 = 153.5
5 = 138.3
6 = 0.06mv
7 = 137.2
8 = 0.12mv
9 = 137.6
10 = 0.07mv

Any suspicion on which connection i should maybe redo the soldering?

 

[Paul Birkeland]

Is your 12AU7 glowing?

You are missing a connection in your amp. See step 2 page 35.

 

[hpleung]

Yes they are both glowing.

Let me fix that missing connection. Thank you for spotting that.

 

[hpleung]

The LED lights up now. Thanks - it was the missing wire.

Also, the weird stuff i was observing with using the headphone output from my laptop as line input; i.e. if you pull out the laptop charger, sounds on the crack stops; is now also fixed. All of my sources work now. Thanks.