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LAN_403

HV Enthusiast

Wed Apr 30 2008, 10:44PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Well, if you are looking at pin3 and not getting output, then you obviously must be using an oscillscope. Move your probe over to the trigger input pin of the 555 and you should be able to see thr trigger pulse input. If not there, then just go backwards looking at each point to the output of the comparator.

Also, make sure you max. pulsewidth pot is cranked up (and in the right direction too) - best bets is to set it to 1/2.

Austin

Fri May 02 2008, 03:10AM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

Ok this is what I have found out... After meticulously looking at each resistor in the schematic and matching it to the parts list I noticed that R22 was different than what the schematic called for. The schematic calls for a 22k ohm resistor at R22 but the parts list said R22 was suppose to be a 22ohm resistor. This must have been a typo so I went ahead and put a 22k resistor in its place and I had success, well sort of.

The Tesla seems to respond to the music coming out of my computer however it does not sound anything like the .midi i was playing.

After unhooking the audio jack from the computer, the Tesla went wild with RAGE! it seems I am getting voltage differences out of J2 but still no signal. So I wonder if one of my ICs is toast due to the added stress of not having a 22k resistor in place? just a theory. I will try and put in under a scope tonight to see exactly what is going on.

Daniel you have any suggestions?

HV Enthusiast

Fri May 02 2008, 12:48PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

wrote ...

Ok this is what I have found out... After meticulously looking at each resistor in the schematic and matching it to the parts list I noticed that R22 was different than what the schematic called for. The schematic calls for a 22k ohm resistor at R22 but the parts list said R22 was suppose to be a 22ohm resistor. This must have been a typo so I went ahead and put a 22k resistor in its place and I had success, well sort of.

R22 simply sets the sensitivity of the input comparator. Yep, definitely a typo - i'll have to fix that.

wrote ...

The Tesla seems to respond to the music coming out of my computer however it does not sound anything like the .midi i was playing.

How do you have the output configured? You should be using an output that appears as a sinewave (i.e. flute) for best results. Also, it should be monophonic (single voice), no overlapping voices.

wrote ...

After unhooking the audio jack from the computer, the Tesla went wild with RAGE! it seems I am getting voltage differences out of J2 but still no signal. So I wonder if one of my ICs is toast due to the added stress of not having a 22k resistor in place? just a theory. I will try and put in under a scope tonight to see exactly what is going on.

The R22 should not have damaged anything.

wrote ...

Daniel you have any suggestions?

Definitely use the scope. This will help you identify what the problem is.
I'd use your MIDI output as you have been doing, but use only a single continous tone (say around 500Hz) for troubleshooting.

Austin

Fri May 02 2008, 02:14PM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

I followed the signal all the way from J1 To CR1. I get a signal on the anode side of the diode but not the cathode... Any significance? Also I would like to be more clear on the signal I am inputing to the modulator. I converted the J1 BNC jack to a 1/8 audio cable that I plugged into the headphone jack of my computer. Since I do not have a signal generator I have just been playing single tone .midi files on my computer with the volume cranked all the way up.

Would the 100khz signal generator built from a 555 timer work for a "test" signal for troubleshooting the board?

HV Enthusiast

Fri May 02 2008, 03:31PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

For your case, i wouldn't worry about the volume envelope control path (i.e. CR1 path to pin 5) Simply remove R9 resistor, and concentrate on the primary path.

Input a single tone into J1, and trace through U3 to U4. U3 is a zero cross detector. U4 is a one-shot generator for everytime a pulse passes into the trigger input.

I would suggest the first thing to do is to characterize the output of your computer. Put a 500Hz tone in (or similar) and measure what the amplitude is at R11 vs. volume setting of your MIDI. Also, look to see what the input waveform looks like. You want a sine wave input. If not, adjust your MIDI to an instrument that provides something close to a sinewave.

Austin

Fri May 09 2008, 04:25AM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

Ok I invested in a signal generator to help diagnose this modulator and this is what I have to report.

This is a picture of the 500khz sine wave @ 9.7 volts generated by the signal generator

This is the signal out of pin 1 on U3

This is the signal on pin 2 of U4, however I get no output from pin 3. I have tried several different 555 timers and I get no output of any of them. I also took the Ic out of the socket and shorted it with a wire to test the conectivity of the leads, and everything checked out OK. I am stumped, any ideas Daniel?

HV Enthusiast

Fri May 09 2008, 12:18PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

Ok I invested in a signal generator to help diagnose this modulator and this is what I have to report.

This is a picture of the 500khz sine wave @ 9.7 volts generated by the signal generator

Well, several problems right off the bat.

1. Why are you using 500kHz as a test signal? You should be using 500Hz to 1kHz for testing. 500Khz isn't even a valid signal for this design.

2. Why are you inputting 9.7V at the input?

3. Thats a pretty strange looking sine wave. Possibly because you are overdriving the signal generator.

I think before you do anything else, you need to read the instruction manual a bit more before going further. Maximum input range as stated in the specifications is 9V and frequency range is 50Hz to 5kHz. Inputting 9.7V has the potential to damage some of the ICs.

wrote ...

This is the signal on pin 2 of U4, however I get no output from pin 3. I have tried several different 555 timers and I get no output of any of them. I also took the Ic out of the socket and shorted it with a wire to test the conectivity of the leads, and everything checked out OK. I am stumped, any ideas Daniel?

Its not the 555 timers. See above and also double check the values in your circuits. If you missed some of the key points in the instructions just on testing, you probably missed a bunch of things regarding installation and values etc...

Once you verified everything is installed properly with the correct values, run again using about a 2Vp-p sine wave at 500Hz to 1kHz. I've attached what the waveforms should look like at 1kHz, 2Vp-p input.

]xenosonic_01plots.pdf[/file]

Austin

Sat May 10 2008, 10:32PM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

K Daniel here is another photo of pin 2 at U4. everything seems to be working smoothly up to this point, however I still get nothing out of pin 3. I am going to drive down to frys and pick up another 555 timer, just in case I fried the others. Thank you for your patience with me.

500hz @ 1.4volts

HV Enthusiast

Sat May 10 2008, 11:08PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Okay, good. That looks like a good trigger signal.
Now, did you disconnect everything that was connected to pin 5 of the 555 timer? Basically, the only thing you should have there is the 0.01uF cap to ground. This will disable the envelope control.

Also, make sure your max. pulsewidth potentiometer is set at maximum to get the maximum pulse out of the 555. Check those timing capacitors and resistors.

Austin

Sun May 11 2008, 12:55AM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

I didn't notice this just till now but R10 is open because it said "Not Used" in the parts list however in the schematic it shows a 10k resistor.

I still get nothing out of pin 3 of U4 even after removing R9 and C9 and R10

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