LA2A drip electronics opto 4 troubleshoot question

[ToonDP]

Hi, my name is Toon,

I'm a student audio engineering and for my final paper/project I'm building an LA2A clone. I know the basics of electronics but i'm fairly new to all this DIY stuff so thats why i thought it was best to build the drip electronics opto 4 clone.

I just finished the build, did the power up / power down test and installed the tubes. According to the manual the next step is to do a pass audio test. So I hooked up my interface (focusrite liquid saffire 56) and connected the line out of my interface to the input of my LA2A and the output of my LA2A to the line input of my interface. I sent out a sine wave and well… nothing really happened.
Only when I put the gain at 100 i got a little bit of input signal back into my interface.

could somebody help me with this? What is the best way to troubleshoot something like this?

Thanks for helping me out.

 

[ruffrecords]

You first need to do 2 things.

1. Check the dc voltages on al the tubes are correct. If not, then check the components around each one for errors.

2. trace your signal through the unit. First check there is a signal on the secondary of the input transformr, and then that there is one after the opto and so on until you find where the signal stops.

Cheers

Ian

 

[ToonDP]

Thanks for helping a newbie like me out Ian! Really appreciate it!

 

[gemini86]

With ANY project, the best way to troubleshoot low/no audio is to just poke through the signal path with a voltmeter. (keep one hand in your back pocket, and don't lean against the work bench, tube voltages kill.) I found a small practice guitar amp at the second hand store that I use for a little circuit sniffer. Just wire a .1uF cap onto a shielded cable and use it as a probe, it will quickly tell you where you loose signal, then you can pull out the volt meter to get specifics.

 

[Hank Dussen]

Here's the LA2A beta with loads of links to different threats: http://www.groupdiy.com/index.php?topic=21908.0 Many hints all over.
But in general: first check (and double check) all the components. As well as the wiring, solder joints, etc
And then what Ruffrecords and Gemini said.

 

[Hank Dussen]

And also check the threat on drips site...

 

[ToonDP]

Thanks again for all the tips.

I checked my DC voltages over the tubes/components and they appear to be fine

I wanted to trace my audio signal throughout the unit, but because I am a newbie, I am not sure how to do this right.
Starting with the output of my interface: how can I measure this signal correctly so I know what is actually going into my unit?
I want to send a simple line signal (+4dBu) through my unit. What is the best way of doing this? According to the manual of my interface, 0dBFS = +16dBu. Is it correct that when I send -12dBFS to the output it equals +4dBu? And if so, should I measure 1,22V?

 

[gemini86]

Just measure the output with a voltmeter and adjust until it's where you want it. Measure the signal voltage at each component, see where is changes and determine if it's correct.