MiniWave Problems

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neilbaldwin
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MiniWave Problems

Post by neilbaldwin » Sat Mar 17, 2018 1:48 pm

I have two MiniWaves here, one built by Blacet (I believe) and the second one that I recently built.

The second one is misbehaving. Have a look at the photos. The first one the the output of Bank 0 / Wave 0 fed by a triangle wave. You can see it's outputting a decent sine wave as it's supposed to. The second one is the output from the problem one, same input etc. You can see there's some distortion/interference and you can also hear this in the output. It's not a trimming/calibration issue. I've compared every component between the two modules and they're identical (the older one is a first revision, the second one is a newer revision). I've reflowed all the joints and checked it over for shorts. Nothing so far.

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Image
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Navs
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Post by Navs » Sun Mar 18, 2018 3:42 am

The distortion is regular between the cycles - could it be the ROM itself? I remember reading a thread about a discontinuity on the Megawave. Can you swap the relevant chip?

Obviously, if the other waveforms display a similar distortion then maybe the problem lies elsewhere. There are a couple of other sines you could try.

Image

Side issue: I only know the Megawave so maybe the banks are arranged differently, but on the Wiard/Malekko module one has to drive the table with a saw, rather than a triangle to get the sine from Bank 0/ Wave 0.
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tIB
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Post by tIB » Sun Mar 18, 2018 3:48 am

The blacet miniwave wants a saw too. Feed it a saw and swap the roms over would be my suggestion - are you sure both roms are the same? There were a number of variants.
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neilbaldwin
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Post by neilbaldwin » Sun Mar 18, 2018 5:54 am

Thanks gents.

Sorry, focusing on the sine output was probably misleading. I only used that as it was the clearest illustration of the output issue. It happens on all waveforms, some worse than others.

I've tried swapping the ROMs and the problem persists. I think my next strategy is going to be swapping all the ICs to eliminate the possibility of a dodgy chip somewhere.

Something else I noticed last night too: the noise appears on the output regardless of whether I have an input connected. It it much worse in +/-5V mode than 10V mode too. Bizarre. I thought it would a grounding problem but all tests so far don't turn up anything.
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tIB
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Post by tIB » Sun Mar 18, 2018 7:54 am

Have you tried Jon Blacet? He's very helpful in a minimal amount of words type way!
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neilbaldwin
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Post by neilbaldwin » Sun Mar 18, 2018 8:02 am

I haven't so far. An email to him seems inevitable at this point. :D
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neilbaldwin
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Post by neilbaldwin » Sat Mar 24, 2018 10:15 am

Turns out one of the A-to-D ICs was faulty. Replaced and now working!
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Navs
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Post by Navs » Sat Mar 24, 2018 11:20 am

result :beer:
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