suitable power supply for dozen opamps? - Page 8 - diyAudio
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Old 18th July 2014, 02:25 PM   #71
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Ok,

15-0-15 of PSU connects to POS-GND-NEG of xo PCBs.
These circuits are dual polarity, therefore need 3 lines.

HPF is not a dual polarity circuit, therefor only needs two lines and associated common should be secured to return line.

Thanks
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Old 14th August 2014, 06:41 PM   #72
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Quote:
Originally Posted by Speedskater View Post
The drawing in post #60 is missing an important connection from the signal return/shield to the internal circuit common.
hi again dA, back with update:
I've connected hpf circuit to jacks as illustrated below, following instructions from quote above.

However I'm getting an odd sound through the hpf section. I doubt it's PSU related because it is not present in the XO circuits (including 0hz-87hz crossover band).

Meaning the hum is strictly limited to HPF circuit- it largely resembles the sound of a guitar amp when the jack is absent (?)... drrrrrrr droning sound (if that rings a bell).

It may well be ground loop.

I'm confused because I was advised the simpest solution would be to remove the one (or more) connection(s) from outer ring (of jack) to the internal circuits common - but this contradicts speed skaters post quote above. So I'm after some re-assurance please...

This is the current configuration.
Click the image to open in full size.

Many Thanks
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Old 14th August 2014, 08:03 PM   #73
Mooly is online now Mooly  United Kingdom
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Try shorting the junction of C1... you have a lot of C1's , of each pair of C1's to ground which will kill any signal. Try the last opamp stage first. Make the short to the correct ground point. You should have silence. If you have then do the same for the first pair.
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Old 16th August 2014, 11:25 AM   #74
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Hi mooley, I'm unsure what you mean exactly, here is my guess?
Click the image to open in full size.
I noticed my circuit lacks the provision I think exists on all amplifiers/ line level devices. (example below), where an additional cap is in place separating common from circuit. So would adding caps to common line help (unless this is what you're already suggesting)? a 10nF ceramic disc is all I have here.

Click the image to open in full size.

I'm sure this is very trivial to most peeps on here, tbt I have no idea..
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Old 16th August 2014, 03:30 PM   #75
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It was yes. You just have to try and find where the problem is. You could also try lifting (might be a better option) the cap directly after the first opamp to isolate the signal chain.

The caps are very application specific and tbh its something I've never done on anything of mine. It would have no effect for ground loop issues, more for RF problems.
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Old 17th August 2014, 08:32 AM   #76
AndrewT is offline AndrewT  Scotland
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the single polarity power has a virtual earth created at rail voltage.
This becomes the "ground" for all the signal levels.

Any components that gets connected to "ground" in a dual polarity sch must now be connected to the virtual ground.

This keeps the +IN and -IN at the same DC voltage.
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Old 23rd August 2014, 11:48 AM   #77
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Ah

Because the HPF circuit has an op amp with + and - pins - I assumed and connected it up as if it were a dual polarity circuit. :doh:

The neg pin of the op-amp is currently connected to the negative terminal of the PSU - it should be connected to the 0v of the PSU, i think...

I will amend and return with feedback - no web access at home.
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Old 30th August 2014, 10:37 AM   #78
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Hi all back once more with some R&D...lol

unfortunately re arranging the hpf to single polarity did not eliminate humming problem i'm experiencing.

The hum is still present when the whole project is OFF (no mains input) and while both signal returns are isolated - I think this is a feedback issue.

The test amp i'm using to detect the hum is definitely not the source of hum,
The interconnect protruding from the test amp, when unconnected causes no hum while test amp is on, I switch test amp off - connect rca to HPF out-jack and switch test amp on, hum is present.

The hum is present on both IN and OUT jacks.
I find this strange because the signal return of both jacks are separated from hpf circuit - a loop is impossible, yet hum still occurs.
Anybody seen this before? As I said definitely not PSU issue because, a)PSU voltage readings are spot on and b) the crossover section works splendidly with no hum what so ever.
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Last edited by giro1991; 30th August 2014 at 10:43 AM.
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Old 30th August 2014, 11:19 AM   #79
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Short the input of the test. You should have no hum. Keeping it shorted, connect the grounds of the test amp and filter together. Hum or no hum ?
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Old 30th August 2014, 11:24 AM   #80
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Is your Xover located near to a mains field such as radiated by a transformer?

Mik
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