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Author Topic: Alesis HD24/D&R Dayner Ground Loop  (Read 3249 times)

cymatics

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Alesis HD24/D&R Dayner Ground Loop
« on: May 12, 2004, 11:23:58 AM »

Apologies in advance for the crosspost to Gearslutz

I have a D&R Dayner that I have been running with 3 ADAT XT20s for the last few years. In order to get the ADATs connected to the console free of ground loops, I had to telescope the ground at the channel inputs. The wiring schems was as follows:

ADAT OUT ---> Dayner IN

TIP--------------------RING
RING----------------SLEEVE
GROUND---------x

I was using the Elco +4 outputs of the ADAT. The Channel inputs on the Dayner are unbalanced +4 & -10 on the same TRS connector (-10 on the tip & +4 on the ring)

I recently purchased an Alesis HD24 that I have been totally unable to connect to the Dayner with out creating a ground loop. At this point, I'm just about out of ideas for trouble shooting. I have disconnected every single connection from the console except one output from the HD24. I have attempted every conceivable method of custom cable assembly to connect the HD24 to the console to no avail. I have confirmed that both devices are plugged into an outlet that is referenced to the same ground.

I have a cheap (low quality) isolation transformer that successfully broke the loop. However, 24 channels of high quality isolation transformers is out of my budget right now.

The only other success I have had in breaking the loop is plugging the power cable of the HD24 into a grounded-to-ungrounded outlet adapter. While this successfully broke the loop, I am wary of implementing it as a long term solution.

Is there anything else I can do other than lifting the earth ground of the HD24?

If there is any other info I can provide that may be helpful in solving this problem, please let me know.

- jon

ssltech

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #1 on: May 12, 2004, 04:21:03 PM »

First thing to do is to reconnect the power ground. Next thing to do is to lift ALL of the grounds on the input AND output cables.

Then report back.

-In simple terms, lifting the grounds on the returns alone still leaves the possibility of a loop if the sends have a through ground connection.

The idea of -10 on one leg of the signal and +4 on the other is a wierd one to me... most manufacturers that I've dealt with use jumpers inside to set the gain of the send/return buffers... Soundcraft and Allen&Heath are examples which spring to mind. -I've never installed a Dayner, and you seem to be fairly intelligent so I won't presume to question your post, but if the two legs have different gains (and presumably some sort of polarity reversal, otherwise connecting both legs of a differential signal would cause cancellation rather than addition!) means that CMRR figures are going to be laughable, unless I'm missing something... -You're quite certain that there aren't any internal jumpers to set the gains from +4 to -10, right? -If there were, then the sensing gain of each leg could be equal, and some more usable noise rejection figures could be expected... with some 12dB or so of gain defference between the legs, I'd expect that noise rejection would be lamentably poor...

-So try the "All audio grounds lifted" route. I expect that should do what you need.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

cymatics

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #2 on: May 12, 2004, 11:24:44 PM »

ssltech wrote on Wed, 12 May 2004 21:21

First thing to do is to reconnect the power ground. Next thing to do is to lift ALL of the grounds on the input AND output cables.

Then report back.



I had actually tried that (and every other imaginable permutation of connecting the available conductors between the devices) and still had a ground loop.
Quote:

The idea of -10 on one leg of the signal and +4 on the other is a wierd one to me...

It is unusual, but that's exactly how it's setup.  I always get funny looks when I tell people about it.

Quote:

and you seem to be fairly intelligent


Thanks for giving me the benefit of the doubt, but I know more than a few pople who would dispute that  Smile

I actually just discovered that what I assumed was a balanced output from the HD24 is actually a pseudo-balanced output!!! Mad  The version of the HD24 with the 'hi-def' converters has a true balanced output.  I'm inclined to believe that a telescoped ground arrangement like I had with the ADAT XT20s will work just fine once I get the upgrade card for the HD24.  For some reason, the Dayner does not like the 'impedance matched' fake balanced setup.

I should be getting the 'hi-def' converter card Monday, so I'm going to cross my fingers and just run it for the weekend with the earth ground to the HD24 lifted.  Hopefully I won't blow myself or any equipment up.

Oh well... live and learn.

Thanks for your help.

- jon

Mysterytrain

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #3 on: May 13, 2004, 10:06:58 AM »

I had been using a soundcraft ghost and 3 ADAT's with no grounding problems. Like you I have sold off my ADATs and replaced them with an HD24XR..still no problems with ground loops. I would look at the console as the source of the problem. Remove all inserts, powered speakers mic inputs and try the isolate the problem that way.
Peace, Ron
www.mysterytrain.org
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cymatics

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #4 on: May 13, 2004, 11:18:31 AM »

Mysterytrain wrote on Thu, 13 May 2004 15:06

Remove all inserts, powered speakers mic inputs and try the isolate the problem that way.

Been there, done that (see my 1st post).  The seemingly omnipresent ground loop occurs with only a single output from the HD24 to the Dayner.
Quote:

I would look at the console as the source of the problem.

Since installing the Dayner, I have become painfully aware of its unusual sensitivity to differences in ground potential.  In my relatively short career as an AE (about 7 years) it is probably the most 'picky' peice of gear I have encountered in this capacity.  While this has proven to be a royal pain in my ass when installing new equipment, everything else about the console makes it well worth my time.  FWIW, once it is playing nice with all the gear connected to it, it puts a great big smile on my face.

- jon

Mysterytrain

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #5 on: May 17, 2004, 09:30:43 AM »

Hmmmmmmmmm, I've had a problem like this with older crown amps and any sort of preamp. I've had to lift the AC ground on the amp to make everybody happy. I did some searching online for the D&R and didn't find much info. Is the power supply mounted in a metal rack? You might be getting some chassis ground looping that way. How old is the unit? there might be some leaky caps. I'm guessing you have tried to contact D&R. Ground loops suck..I have a mystery loop these days with my PA rig when we do gigs..small A&H GL2 and a Crown PB2..seems to work fine during rehearsals with one monitor going. but when I'm using two mains and two monitors I get a nasty hum. Been thru all the cabling too
Sorry I could be more help
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Mysterytrain

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Re: Alesis HD24/D&R Dayner Ground Loop
« Reply #6 on: May 17, 2004, 09:46:23 AM »

Just re-read your first post...and I also don't like the -10 at the tip and +4 on the ring configuration. The HD24 can go balanced or unbalanced but the + signal is on the tip..have you tried a mono 1/4" cable so that signal is on the tip and ground is on the sleave or a TRS with the -sig (hd24 ring) going to the sleave at the console and ground wire lifted at the console? or both tied together on the sleave at the console. If the jacks on the D&R are configured as you say then you need to send the tip of the HD24 to the ring of the dayner if you are going +4 sounds very strange to me.
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