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Post by Deleted on Jul 30, 2014 22:07:36 GMT -6
Not truly DIY but seemed the best fit.
I bought a used Chameleon Labs 7802. I find it has a ground type, 60hz hum on both channels. I have tried dropping the ground, different cables, different connections to my interface, in the rack and out of the rack and the hum persists. Before I return it or take it to a local shop, is there anything external or internal you may suggest I check out? I'm not an electrician but am handy and teachable.
Thanks
Rob
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Post by svart on Jul 30, 2014 22:26:34 GMT -6
First place to look is always the power supply. Look for capacitors with puffy tops first. They are the black cylinders on the board on the right side.  |
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Post by Deleted on Jul 31, 2014 9:23:35 GMT -6
Thanks for the reply. I will check the caps. I experienced that with a mic power supply. In the end, the transformer was toast and had to be replaced. With what you suggested and what that may represent, maybe I should return this thing.
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Post by svart on Jul 31, 2014 11:06:24 GMT -6
If it's just hum issues, then I doubt it's the transformer. Dried up/old caps are the most likely culprit in something like this.
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Post by Deleted on Jul 31, 2014 11:35:10 GMT -6
I see. Ok. I won't give up yet.
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Post by Deleted on Aug 2, 2014 15:34:41 GMT -6
Got back home and popped the cover. Here is what I found. It seems three of the caps have what seems to the uneducated to be glue or epoxy. Did this come out of the caps svart? Does this mean that 3 went bad? |
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Post by Deleted on Aug 2, 2014 15:42:17 GMT -6
a better pic
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Post by mulmany on Aug 2, 2014 16:29:07 GMT -6
Those look fine... that stuff on the bottom looks like a silicon to stabilize the caps from vibrations. If the caps had blown, the tops would be puffed out, normally.
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Post by Deleted on Aug 2, 2014 17:00:41 GMT -6
Ok. Thanks for that. That's good but still no good with the hum. Guess I have to decide to take it to a shop or return it.
What would you do? They are a bit hard to find and are a stereo optical.
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Post by mulmany on Aug 3, 2014 18:00:47 GMT -6
Ok. Thanks for that. That's good but still no good with the hum. Guess I have to decide to take it to a shop or return it. What would you do? They are a bit hard to find and are a stereo optical. I would look at the connector wiring, are the grounds good? Disconnect and reseat all of the molex connectors. If you short the input, do you still have hum on the output? |
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Post by Deleted on Aug 8, 2014 10:37:57 GMT -6
OK, I was able to get ahold of Chameleon labs. They suggest I try a new tube to see if it helps.
Do you think I can get a cheap 12ax7 at GC just to trouble shoot?
And, if it works, where should I turn for a quality tube for usage?
Thanks
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Post by kcatthedog on Aug 8, 2014 18:23:36 GMT -6
A cheap tube will probably create more problems than solve any.
I would contact Christian at proaudiotubes . He will set you straight and could test your current tube.
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Post by Deleted on Aug 8, 2014 19:58:59 GMT -6
I should have been clearer. I'm just trying the cheap tube to see if the ground type hum stops. I won't operate with it as I know you are right.
Thanks.
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Post by jcoutu1 on Aug 8, 2014 20:00:45 GMT -6
I should have been clearer. I'm just trying the cheap tube to see if the ground type hum stops. I won't operate with it as I know you are right. Thanks. Do you have this plugged in on the same circuit as the rest of your gear? Is it possible that it's actually a ground loop causing the hum? |
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Post by kcatthedog on Aug 9, 2014 5:37:12 GMT -6
understood, I did the c12 diy build last summer and have the chinese new tube left over, happy to send it along if you pm me your address btw as I have 2 WA76's here now and my cl7802 with mullard onboard, yesterday I did some fool around with comp on (dbox sum>comp>burl b2>apollo print) master buss clips a bit apples and oranges given the differences 4:1 to 2:1, non tube vs tube optal ect., but I ended up , pushing the drive control ( tube) up past 12 to 1-3 territory of 50-75%,WOW; it was like adding air on an eq just opening up the mid to high mid range, very nice on the vocals and the acoustic guitar in the mix but not compromising the rest of the mix. I was using the HPF too as I recall cowboy commenting on that. So, yes I expected even order harmonics and I like the sweet smoothness of the NOS military spec mullard but I wasn't expecting an almost EQ like result. So, just sharing that to encourage you to keep diagnosing your cl7802. if you want a listen: www.gearslutz.com/board/product-alerts-older-than-2-months/712858-ua-apollo-first-look-user-review-461.htmlpost 13829 at bottom of screen |
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Post by jimwilliams on Aug 10, 2014 12:02:48 GMT -6
Got scope? Look at the power rails.
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Post by Deleted on Aug 10, 2014 21:59:57 GMT -6
Thanks kcatthedog!
Jim, no I don't - thanks though.
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Post by kcatthedog on Aug 11, 2014 16:33:00 GMT -6
do u need a tube ?
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Post by Deleted on Aug 12, 2014 6:41:54 GMT -6
Got one. Will test tonight.
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Post by Deleted on Aug 13, 2014 11:44:32 GMT -6
Ok. Ground loop after all. The questions is why is this unit susceptible and my other units are not. Hmm.
None the less, it is work with a ground lift. Any ideas for a long term solution?
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