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Post by Boomzilla on Jul 7, 2015 5:23:47 GMT -5
I am building an adapter to go from (amplifier) speaker terminal output to (subwoofer) line-level inputs. I have adequate dropping resistors in the R/L channel hots to provide the correct input voltage at the subwoofer. My question has to do with grounding.
From what I've read, only one channel should be connected to the amplifier's ground. At the subwoofer, the R/L grounds will be common, so to connect both grounds would create a loop & induce hum. Is this correct?
Thanks - Boomzilla
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Post by pedrocols on Jul 7, 2015 7:46:27 GMT -5
Rel subwoofers use a similirar device and the connection requires only to connect one of the ground terminals.
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KeithL
Administrator 
Posts: 10,276
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Post by KeithL on Jul 7, 2015 10:13:11 GMT -5
Whether grounding both connections or just one will give you less hum depends on the actual equipment involved. It may also depend on your house wiring, and your power strips, if the two things you're connecting are plugged into two different strips or circuits. If you're building your adapter into a box, you'll get the most flexibility if you put in a "ground lift" switch on one or both connections (they do that on a lot of pro equipment - because sometimes it works better one way and sometimes the other). (Also, if you lift one ground, be sure to always shut the sub off when disconnecting wires, or unplug them in the right order. You'll get a really nasty loud noise if you disconnect the ground while the other wire is still connected if the sub is still on.) I am building an adapter to go from (amplifier) speaker terminal output to (subwoofer) line-level inputs. I have adequate dropping resistors in the R/L channel hots to provide the correct input voltage at the subwoofer. My question has to do with grounding. From what I've read, only one channel should be connected to the amplifier's ground. At the subwoofer, the R/L grounds will be common, so to connect both grounds would create a loop & induce hum. Is this correct? Thanks - Boomzilla |
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Post by Boomzilla on Jul 7, 2015 16:50:47 GMT -5
Thank you kindly @keithl - That's exactly what I wanted to know. Inline ground switches for both channels are easy to fit.
Boom
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Post by novisnick on Jul 7, 2015 18:14:29 GMT -5
Hey guys, how's about a check list of where to start looking for my dang ground loop BUZZ.
I've done some of the basics but I think we should compile a check list to find that bugger!!!
I'll start,
1) dimmer switch
2)
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Post by meldhache on Jul 7, 2015 20:27:42 GMT -5
Ah! Let me think, How to create buzz reasons...
2/ chucklenut....
Mel
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Post by jmilton on Jul 9, 2015 7:21:10 GMT -5
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Post by novisnick on Jul 9, 2015 9:03:07 GMT -5
Thanks, I had already sent the pre-amp back and they said the same,,,,,,it's not our fault, look elsewhere, that's been 8 months ago and I'm still looking for it. |
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Post by 405x5 on Jul 9, 2015 13:11:53 GMT -5
Nothing's more important than SILENCE between the music (and movies).
With all that is invested by the ABOVE AVERAGE enthusiast, one more step that's essential in SOME cases is bringing in a LICENSED ELECTRICAL CONTRACTOR.
Sometimes:
The sump pump circuit can be rewired/properly grounded.
The WELL PUMP can be rewired/ properly grounded.
Those Joe Homeowner hots and neutrals can be reversed and properly grounded.
The faults in gang boxes can be traced.
This is a small list, but you can see where it's going; why go crazy and tear your hair out. Most of the time it can be found out for a very reasonable price. Some things are better left to the PROFESSIONALS.
Typical audio systems tied into properly grounded home circuits actually need NO ADDITIONAL GROUNDING AT ALL, other than what is supplied from each component.
No??
Bill
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Post by Boomzilla on Jul 10, 2015 17:30:17 GMT -5
Well, my parts came in today for the "speaker terminal to line level" adapter. The only parts I don't have (didn't know I needed at the time of order) are a pair of SPST switches for lifting either ground to avoid hum. Radio Shag tomorrow! Once I see how it works, I'll post photos & the "schematic" which is simple enough for your dog to assemble.
Cheers - Boom
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Post by novisnick on Jul 10, 2015 17:35:09 GMT -5
Well, my parts came in today for the "speaker terminal to line level" adapter. The only parts I don't have (didn't know I needed at the time of order) are a pair of SPST switches for lifting either ground to avoid hum. Radio Shag tomorrow! Once I see how it works, I'll post photos & the "schematic" which is simple enough for your dog to assemble. Cheers - Boom  |
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Post by Boomzilla on Jul 10, 2015 18:30:21 GMT -5
Give that pup a soldering iron!
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Post by rocky500 on Jul 10, 2015 20:39:39 GMT -5
Hey guys, how's about a check list of where to start looking for my dang ground loop BUZZ. I've done some of the basics but I think we should compile a check list to find that bugger!!! I'll start, 1) dimmer switch 2) Run a long extension cable from a different outlet in your house. Even from another room. Now use this lead on each component one at a time and see if the hum goes away. Eg. Put the sub power on the lead, then the Preamp etc. 3) If you have multiple power boards, try swapping the order in leads around in them and between them. eg. Sub is on power board 1, move it to power board 2. Swap the order around to on the actual power board. |
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Post by Boomzilla on Jul 11, 2015 13:13:42 GMT -5
Well, this is the absolute antithesis of elegance, but is is functional... I'm not going to show you the guts - my solder joints aren't what they once were due to age and disuse of my soldering skills, but I can promise two things - There are no cold solder joints, and I didn't burn the resistors. So what does this do? It allows you to run a line-level input (such as a subwoofer's) with a full-frequency signal driven off the speaker terminals of an amplifier. Why would you want to do such a thing? Well, you wouldn't if you have a HT receiver or preamp that does bass management for you. You also wouldn't if you had a preamp-out from where you could drive a subwoofer directly. You only need this if your integrated amp or stereo receiver has no line-level, volume-controlled preamplifier outputs. But many integrated amplifiers (such as my Hegel H80) have no preamp outputs. Nor have they any provision for subwoofer outs. So I built this. One set of speaker wires drive the main speakers full range. A second set of speaker wires, connected to speaker terminals on the amplifier, drives this box. The level is dropped via resistors so that line-level stereo outputs can drive the subwoofer's crossover (which you set to whatever frequency the main speakers roll off at). The toggle switch allows the subwoofer to be grounded through either speaker ground wire, or through both - whatever provides the least hum. - Right - Both - Left. Parts, including the plastic project box, probably cost less than $20 (or even less, depending on what you have in your spare parts box...) Simple enough that NovisNick's DOG can put one together!  |
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