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jumunius
Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13
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 Posted: Wed May 18, 2011 10:43 am Post subject:
Bass++ troubleshooting, decay pot question |
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So I finally got around to wiring up my Bass++ last night, now onto troubleshooting. I have two boards populated and only one wiring set-up; both appear to work but happen so fast they are little blips.
My main question is about pots: since I have nice 100k Lin pots, I tried modding the decay pot such that I use a 10uf cap (approx 2.2uf*5) and a 100k decay pot (500k/5). Do I have that right in theory? And in practice is that ok to do?
I also used the 100k lins in place of the 10k sweep and main volume pot, adding a 12k resistor between the top and wiper. It's the first time I've done it, and I understand this is how it's supposed to be done but I am slightly confused since the resistance between the wiper and the bottom (ground) doesn't change.
Also, I used a homemade power cable with the + and - reversed in one of the headers -- oof. Really stupid. Might that have fried anything? (It was on for about a minute before I noticed my other modules were failing too and cut power.)
The one bright side so far: the LED works! (The trigger seems to only work when set low, as in CCW, even though I appear to have wired it correctly.) |
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The Peasant
Joined: Nov 13, 2009
Posts: 112
Location: Sunny Alberta
Audio files: 1
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| Posted: Fri May 27, 2011 11:05 am Post subject:
Re: Bass++ troubleshooting, decay pot question |
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| jumunius wrote: | So I finally got around to wiring up my Bass++ last night, now onto troubleshooting. I have two boards populated and only one wiring set-up; both appear to work but happen so fast they are little blips.
My main question is about pots: since I have nice 100k Lin pots, I tried modding the decay pot such that I use a 10uf cap (approx 2.2uf*5) and a 100k decay pot (500k/5). Do I have that right in theory? And in practice is that ok to do? |
In theory this should work, however, the 10uF caps are putting a higher charging load on the TL082 output, which should probably be avoided if possible. If the chip fails after being used for a while or gets warm at all, this would probably be the cause.
| Quote: | | I also used the 100k lins in place of the 10k sweep and main volume pot, adding a 12k resistor between the top and wiper. It's the first time I've done it, and I understand this is how it's supposed to be done but I am slightly confused since the resistance between the wiper and the bottom (ground) doesn't change. |
Other than changing the response curve of the pot, this should present no problems. You may want to try experimenting with leaving out the 12k resistor completely or increasing it to a higher value. No matter what you do here, these parts value changes should not cause the circuit to not function correctly.
| Quote: | | Also, I used a homemade power cable with the + and - reversed in one of the headers -- oof. Really stupid. Might that have fried anything? (It was on for about a minute before I noticed my other modules were failing too and cut power.) |
OTA chips and op amps tend to fry rather easily with reverse voltage, I wouldn't be surprised if you damaged one or more.
Take care,
Doug
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The Electronic Peasant
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jumunius
Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13
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| Posted: Fri May 27, 2011 11:55 am Post subject:
Re: Bass++ troubleshooting, decay pot question |
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| The Peasant wrote: | | In theory this should work, however, the 10uF caps are putting a higher charging load on the TL082 output, which should probably be avoided if possible. If the chip fails after being used for a while or gets warm at all, this would probably be the cause. |
Ahh, this is good to know. Well, I meant to update this post to say that everything's working now, but I haven't powered the unit for more than 10 minutes or so at a time, so it will be interesting to see if it fails with further abuse. In which case I might keep the pot as is but lower the cap to 4.7uf and see if that works -- so long as I'm using this as a kick drum, I usually prefer tighter decays anyways.
| The Peasant wrote: | | Other than changing the response curve of the pot, this should present no problems. You may want to try experimenting with leaving out the 12k resistor completely or increasing it to a higher value. No matter what you do here, these parts value changes should not cause the circuit to not function correctly. |
For what it's worth I ended up changing the 12k to run between wiper and bottom instead of wiper and top -- I preferred the more exponential response to the log one. Should try losing it altogether and see what happens.
| The Peasant wrote: | | OTA chips and op amps tend to fry rather easily with reverse voltage, I wouldn't be surprised if you damaged one or more. |
Fortunately it doesn't seem like it happened this time. My problem was a whisker running to ground on the decay pot. Nevertheless I have learned to be a lot more careful with my power cables in the future!
Thanks for the replies Doug. |
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jumunius
Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13
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| Posted: Thu Jun 02, 2011 4:57 am Post subject:
Re: Bass++ troubleshooting, decay pot question |
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[quote="The Peasant"] | jumunius wrote: | In theory this should work, however, the 10uF caps are putting a higher charging load on the TL082 output, which should probably be avoided if possible. If the chip fails after being used for a while or gets warm at all, this would probably be the cause.
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Ok, I do see where the chip is getting warm, although only moderately. Do I care? Is a little warmth a problem long-term? It didn't appear to get worse with long usage. |
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The Peasant
Joined: Nov 13, 2009
Posts: 112
Location: Sunny Alberta
Audio files: 1
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| Posted: Thu Jun 02, 2011 8:21 am Post subject:
Re: Bass++ troubleshooting, decay pot question |
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| jumunius wrote: | | Ok, I do see where the chip is getting warm, although only moderately. Do I care? Is a little warmth a problem long-term? It didn't appear to get worse with long usage. |
The faster you trigger the circuit the warmer it should get if this is a problem. If the chip eventually fails, then you will know why and how to fix it.
Take care,
Doug
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