Electronics 4 Final

1-5. You have built a Urei 1176 limiter but are not getting any sound out of it. Describe how you would troubleshoot the problem. Go through the first three steps including at least two different outcomes from each test you will complete. Be sure to list your steps and describe any procedures or tests in detail. Also describe all test equipment you would use (anything other than the 1176). A schematic is attached.

• Turn it on with a VariAC

  • If it turns on, run and test audio

  • If it doesn’t turn on, you would go to the power supply portion of the circuit and split the circuit in half

• Test specific components based on the circuit’s function at different points of the schematic

• Replace components based on what is not functioning correctly

6-10. A Neumann KM140 into MAC floor pocket A12 is not working. It is running through a Hardy M-2 and then into the RedNet A16R to Dante and then to the Avantis. Describe how you would troubleshoot the problem. Describe how you would troubleshoot the problem, describing (in detail) your first three steps with an overview of how each would be undertaken and where the results would lead you.

• Look at the Hardy to see if there is signal, also check phantom power, routing, and preamp gain

  • If there is signal, the problem is after the Hardy in the signal chain

    • Check the LEDs on the RedNet monitor

    • Check signal in Dante

      • If there is signal in Dante, it’s a routing problem from the Avantis to Dante

  • If there is no signal, the problem is occurring before the Hardy in the signal chain

11. Inside a piece of equipment with a grounded 120V AC power cord, where should the green wire of the power cord be connected?

• Chassis

12. What is the purpose of connection in the question above?

• So you don’t die/get electrocuted

13. Your job this semester is to repair equipment that fails in the department. When you come to work there is a mic preamp with a note that says “dead”. What would you do first? You have all the equipment in the Electronics Lab (M257) to work with.

• Power up with variac

  • Check fuse - blown

  • Replace fuse

  • Try power again

    • Works - check function

14. What are the most typical connections for a 3 pin XLR running a balanced line.

1. Earth

2. Hot

3. Cold

15-16. For some reason all the mic cables are missing from the Simon building and you need to record a concert. Your recording device has mic preamps and needs to be 20ft. Away from the stereo mic pair. You are using ribbon mics (non active) in an ORTF configuration. Describe in precise detail how you would make cable(s) to make the recording happen. You have:

-2 male XLR connections

-2 female XLR connections

-50ft. Of unbalanced/shielded cables

-25ft. Of Ethernet (cat5e) cable (4 twisted pairs inside an outer jack)

-solder and soldering iron

-you A111 toolkit

-no connection to the internet

• You need two 20 ft cables for the stereo mic pair

• Ethernet has 8 wires, 4 pairs of twisted pairs

• Use two pairs for two XLRs  

• Solder each wire to one male and one female XLR connector

• Use the leftover ethernet cables for ground to create balanced lines

17. You have found that when you connect the XLR output of your 1176 (schematic on the last page) to a flash recorder with unbalanced (RCA) inputs (I have no idea why you are using consumer gear) that you get no audio. However, when you connect the 1176 to your Stucker! Computer audio IO (balanced TRS input) you get audio, and it sounds fine. You can also connect the outputs of the Stucker! (balanced XLR) to the flash recorder and it works fine. What is the problem?

Cold isn’t shorted to ground

1176 is active balanced and Stucker! Audio is not active balanced. 

For moving between balanced and unbalanced lines, transformers’ must have cold shorted to ground so that the signal path is completed. So if cold is not shorted to ground for the 1176 to the flash recorder, then there can be no audio.

You only want to see hot if you’re reading signal

If you don’t short cold to ground you are not finishing your transformer connection

18. How would you fix the problem above (give specific details if there is a wiring involved).

 RCA to XLR problem

• Short cold to ground

19-24?. Audio PCB layout. Draw it out bitch.

25. You have 2 options that will correctly convert an unbalanced RCA output to a balanced XLR input, for both options you will use an adapter that properly (for this equipment) converts the RCA to XLR. You then have an extension cable, either XLR-male to XLR-female or RCA-male to RCA-female. Both cables are of the highest quality. Which of the following is true?

1. The RCA extension will be quieter

2. The XLR extension will be quieter

3. There will be no difference

2. The XLR extension will be quieter

26. What is the problem with the outlet?

• Flip black and white wire, and then add a green wire for the earth connection due too there being none in the photo

27-28. Describe the audible differences between a Hum and a Buzz. 

• Hum is 60 hertz sine wave generally and a buzz is a more complex waveform with higher frequency content

29. There is something you can disconnect to solve a hum problem but in another situation connect to solve a buzz problem. What is it?

ground