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lgvenable
07-11-2008, 10:56 AM
I completed the build of a 2245H subwoofer built according to the 1983 article here on the forum. It has a finished internal volume of 21.1 ft3, and is port tuned to 24.79 HZ (using two 6" ID vents at ~13.67 in long).

I have a subwoofer pre-out signal to the sub. I have a Yamaha YDP-2006 digital EQ (to act as a parametric EQ and low/high pass filter). The inputs are balanced audio inputs. This signal is then sent to a mono bridged Crown PS 400 (660W bridged).

issue 1: ground loop hum> predictably I have a ground loop hum issue:
-Do I need to use a isolation transformer to power the Denon amp and the subwoofer crown amp from the same ground, or just use a isolation transformer to power the sub's Crown power amp?

Do I need to use an audio isolation transformer on the signal as well??

Issue 2: Once I hooked up the map I had like zero output. I got my mp3 player and ripped a few low Hz tones and used it as a head device to power the sub from the Crown amp>>success>> loud and LOW LOW output.

I looked up the pin outs on unbalanced to balanced audio signals (Denon is an RCA unbalanced sub pre-out presumably). Even though I thought I had the pin out connectors made right (soldered up connectors from audio cable pin outs from a sound engineers website) I still got lack luster sound out??

I then got an old Yamaha integrated amp out, and used it to condition the rca pre-out signal. (ie rca pre-out to aux input, pre-out outputs were then wired to the Crown amp inputs ) Success>> got sound (however got ground loop issues again since the two amps Denon and Crown are not isolated or grounded to the same ground)).

Here's my question:
Do I need to isolate both the power and signal using isolation transformers?
Do I need to use some sort of intermediate pre-amp or line level pre-amp to boost the rca pre-out signal strength before it goes to the crown amp?
(Presumably if I need a line level pre-amp to condition the signal it will also need to be isolated to prevent any ground loop from it as well too)

Hopefully some one can set me straight, as when I tested the sub with the mp3 signal>Yamaha pre-amp>crown as a stand alone there was no ground loop issues (as I expected), and the response was pretty good.

Thanks for the help in advance
Larry

1audiohack
07-11-2008, 06:50 PM
I'm having a bit of trouble following your trail, so help me out here.

Have you succesfully driven anything else with the sub out jack from the Dennon? Does it have its own x-over? I assume the Dennon is unballanced.

What if you get the Yam out of the loop so your straight unballanced Dennon to the Crown do you have volume and or hum?

I'm pretty sure you can get through this with out isolation transformers.

lgvenable
07-12-2008, 06:14 PM
heres what I did so far and the results:

1.Hooked up direct from my Denon sub out via RCA to my Crown amp

No signal, but great 60Hz hum! The Denon is setup correctly for signal out at the subwoofer.

2.Connected the denon sub rca out to balanced input to YDP 2006

(with correct bumps to parametric eq (ie +6db boost at 25 hz, +0.5 hz at each: 35 45 55 65 75 100 110 hz LP set to 15HZ 18 db rolloff high pass set to 120 hz 18 db rolloff
(not including all the eq setpoints as I'm on the road not at home)

connected to crown amp via commercial balanced to unbalanced cable.

no joy no signal great hum!

I decided to forgo setting up the eq until I solved the rca to crown issue first. (to simplify the issues).

3.Used an IPOD mp3 player as a head device to power the sub from the Crown amp

No ground loop hum (only 1 device used to aplify signal no hum as expected).

(also did this with the Yamaha amp B4 decoupling the pre-out to amplifir section) it worked perfectly too ( with no ground loop hum )

>>success>> loud and LOW LOW output (with appropriate low hz mp3 tones)

(as a stand alone test of the crown amp and speaker.....no problems indicated as they sounded great.)

4 got out my old Yamaha integrated amp out, first I decoupled the amp from the pre-amp section, then used it to condition the subwoofer (rca) pre-out signal from the Denon amp.

i.e. signal path was = rca pre-out to pre-amp aux input,
pre-out outputs from yamaha pre-amp to the Crown amp inputs )

results: Success>> got sound with ground loop hum

(however as I expected from my initial ground loop hum Google searches >> I had major ground loop issues again since the two amps Denon and Crown are not isolated or grounded to the same ground.

I did this to see if boosting the pre-out sub signal from the line level sub output on the amp was due merely to a signal strength problem, (as I once had with a sub in a car system).

Finally: I'm convinced that the two amps are not grounded to the same source. I had hum even when each amp was connected to two different power relays, or when they were connected to the same wall outlet (the same relay).

every thing I have googled on ground loop isolation hum agrees with what I have seen, which indicates both amps SHOULD be connected to an isolation transformer to prevent 60HZ hum between the two.

Believe me, if you heard the level of hum you would not believe you could solve the problem ANY other way, especially since my google searches sure discribe EXACTLY what I am hearing.


So once again here's my questions:

Do I need to isolate the amp power inputs using isolation transformers? Has anyone else had to do this??



my initial 4 hour efforts seem to indicate YES.

Do I need to use a balanced to balanced isolation transformer when I use the YDP2006 with balanced inputs/outputs to effectively COMPLETELY isolate the signal from any induced hum in the shielded RCA line coming in from the Denon amp sub out port?

Do I need to use some sort of intermediate pre-amp or line level pre-amp to boost the Denon sub (rca-unbalanced) pre-out signal strength before it goes to the crown amp?


(Just as I did when I used the Yamaha's pre-amp section)

Has anyone else resolved issues like this on the forum?? I cant be the only person using an old school amp to drive my sub >and got ground loop hum can I???

failing all that I'll do a half day off and go to one of the commercial sound suppliers in Milwaukee to see what they'd do.

Larry:D

toddalin
07-12-2008, 06:36 PM
For the ground loop problem, try a "cheater plug" that effectively does away with the ground pin on the wall plug. (I bet that solves the hum problem and as I recall my Crown PSA-2XH also used as a sub amp in mono did this too and it solved the problem for me. Also, I push it from a Yamaha RX-Z9 receiver.) Alternatively, the Crown may have (I think mine does) a ground "jumper" that I think does essentually the same thing and I think I ended up removing it rather than using the cheater.

1audiohack
07-12-2008, 09:07 PM
Hi Larry;


I bet toddalin is right, two different amps with ground pins is usually trouble.

In direct answer to your questions, here is my experiences.



So once again here's my questions:

Do I need to isolate the amp power inputs using isolation transformers? Has anyone else had to do this??


I doubt it, I never have.



Do I need to use a balanced to balanced isolation transformer when I use the YDP2006 with balanced inputs/outputs to effectively COMPLETELY isolate the signal from any induced hum in the shielded RCA line coming in from the Denon amp sub out port?


As long as a component is not self generating noise,I have always managed to eliminate the hum in all my setups without transformers, I don't have a single rig that does not make the ballanced-unballanced jump at least once and I have a setup almost identical to yours in my garage. A very quiet rig at idle is a must for me and something I take pride in. It can be done.



Do I need to use some sort of intermediate pre-amp or line level pre-amp to boost the Denon sub (rca-unbalanced) pre-out signal strength before it goes to the crown amp?


I don't think you should if it is working correctly. Does the Yamaha have gain? I am not familiar with it.


Has anyone else resolved issues like this on the forum?? I cant be the only person using an old school amp to drive my sub >and got ground loop hum can I???


Of course, and of course your not. I think the reason folks don't jump in is there is seldom one easy answer, lots of variables, no one want's to give bad advise, and there is always the probability that you are going to be frustrated before your done is something we all want to avoid.

If your searching has not yet led you to the Rane web site, check out Rane Note 110, in the reference section.

Good luck and let us know how it goes,,, it will work.
Barry.

boputnam
07-12-2008, 09:34 PM
For the ground loop problem, try a "cheater plug" that effectively does away with the ground pin on the wall plug...I'd never do that. Dangerous. You are floating the AC ground - which means that if grounding is needed the device will find another path, possibly through you. Always a bad idea. This may resolve the symptom (stops the hum) but it does not fix the problem.


I'm having a bit of trouble following your trail, so help me out here.Me too.

Can you lay out simply, the signal path you are trying - start to finish?
Is everything on the same AC circuit?


heres what I did so far and the results:

1.Hooked up direct from my Denon sub out via RCA to my Crown amp

No signal, but great 60Hz hum! The Denon is setup correctly for signal out at the subwoofer.I don't understand this - why is there no signal? If there is no signal you may have an open circuit - that can cause hum (increased noise floor).

Too many variables. Let's try one set up at a time. Does this Denon work in other situations?