Cacophony Forums
Unofficial Mackie User Forums => DL1608/DL806/DL32R/ProDX Mixers => Topic started by: RoadRanger on March 28, 2013, 02:50:16 PM
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The conclusion of a six page thread on the old forum seems to be that using unbalanced connections (AKA TS or instrument cables) between the DL1608 aux outs and a powered monitor or amp will be noisy. One guy "solved" this by disconnecting the AC ground on the power supply but that's dangerous at best. Has anybody had any luck running unbalanced?
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I suggested disconnecting the earth on the PSU, IIRC it wasn't particularly successful in removing the noise (and as you say removing the safety earth is not recommended though I'm still not convinced it's an issue with a low voltage supply like the DL PSU, most PSU's of this type have only a two conductor mains cable with no safety earth anyway).
I did have success with a custom lead, I tried several variations and I'll check later but I'm pretty sure the one that worked was a TRS to TS with the ring on the TRS left unconnected (i.e. no 'cold' connection). It only works if you use a TRS with the ring unconnected at the DL end not if you strap the ring to earth (or use a TS to TS lead which amounts to the same thing).
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I did have success with a custom lead, I tried several variations and I'll check later but I'm pretty sure the one that worked was a TRS to TS with the ring on the TRS left unconnected (i.e. no 'cold' connection). It only works if you use a TRS with the ring unconnected at the DL end not if you strap the ring to earth (or use a TS to TS lead which amounts to the same thing).
I would have guessed that the "winning" combination would be:
TRS -> TS :
S not connected
R -> S
T -> T
Yes, please check what you did and post it here :) .
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Yes, that's what I thought and tried first but I've checked and the one that works is as above, TRS to TS
T > T
R > unconnected
S > S
Its number 9 on this chart https://dl.dropbox.com/u/15685857/Rane%20chart2.bmp
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Thanks!
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The general rule on balanced to unbalanced is to leave the shield floating at the receiver (amp, instrument etc.) end and to tie return and shield together at the sender end (DL1808). A detailed explanation of grounding and tracing ground issues can be found here and is well worth reading.
http://www.jensen-transformers.com/an/generic%20seminar.pdf
Definitely do not lift AC ground.
TRS end -> TS end
S connected -> not connected
R -> S
T -> T
Not sure if that's what you had in mind RR. This is with a standard 2 wire plus shield audio cable. If the ground currents are significant between equipments a isolator would be needed.
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Agreed but that doesn't solve the aux noise issue on the DL, see my post above.
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The conclusion of a six page thread on the old forum seems to be that using unbalanced connections (AKA TS or instrument cables) between the DL1608 aux outs and a powered monitor or amp will be noisy. One guy "solved" this by disconnecting the AC ground on the power supply but that's dangerous at best. Has anybody had any luck running unbalanced?
I think that you'll find that using unbalanced cables a noisy option using any board. Best solution is to use a TRS to XlR short cable from the Aux outs into an XLR mic cable for the run to the monitor(s).
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The conclusion of a six page thread on the old forum seems to be that using unbalanced connections (AKA TS or instrument cables) between the DL1608 aux outs and a powered monitor or amp will be noisy. One guy "solved" this by disconnecting the AC ground on the power supply but that's dangerous at best. Has anybody had any luck running unbalanced?
I think that you'll find that using unbalanced cables a noisy option using any board. Best solution is to use a TRS to XlR short cable from the Aux outs into an XLR mic cable for the run to the monitor(s).
I suggested trying the DL with the safety earth disconnected, but strictly as a diagnostic (though I did surmise that a safety earth on a low voltage device may not be strictly necessary). In the event it did not solve the problem however the lead detailed above did solve the noise issue on my rig.
to reiterate at the DL end use a TRS plug, leave the Ring unconnected, tip = hot. sleeve = ground
at the unbalanced amp end use a TS plug, tip = hot. sleeve = ground
This works with my DL sending a line signal to my AER Compact 60 (used as a monitor), a TS-TS lead or any other connection scheme generates the high pitched noise.
The DL aux outputs are impedance balanced and an explanation of why this wiring works can be found here http://community.avid.com/forums/t/58612.aspx
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The conclusion of a six page thread on the old forum seems to be that using unbalanced connections (AKA TS or instrument cables) between the DL1608 aux outs and a powered monitor or amp will be noisy. One guy "solved" this by disconnecting the AC ground on the power supply but that's dangerous at best. Has anybody had any luck running unbalanced?
I think that you'll find that using unbalanced cables a noisy option using any board. Best solution is to use a TRS to XlR short cable from the Aux outs into an XLR mic cable for the run to the monitor(s).
I suggested trying the DL with the safety earth disconnected, but strictly as a diagnostic (though I did surmise that a safety earth on a low voltage device may not be strictly necessary). In the event it did not solve the problem however the lead detailed above did solve the noise issue on my rig.
to reiterate at the DL end use a TRS plug, leave the Ring unconnected, tip = hot. sleeve = ground
at the unbalanced amp end use a TS plug, tip = hot. sleeve = ground
This works with my DL sending a line signal to my AER Compact 60 (used as a monitor), a TS-TS lead or any other connection scheme generates the high pitched noise.
The DL aux outputs are impedance balanced and an explanation of why this wiring works can be found here http://community.avid.com/forums/t/58612.aspx
Most powered monitors I've seen only have XLR inputs anyway. So TRS to XLR is the way to go.
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Cable tie six TRS to XLR cables together for a mini
aux snake and you're done.
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TRS to XLR is undoubtedly the best way to go but for the few people who still have unbalanced inputs to serve (old/budget power amps/speakers or in my case my very expensive AER which, inexplicably, has an unbalanced line input) a simple (but not obvious in terms of wiring scheme, just lifting the earth does not work for example) custom lead solves the problem. 8)
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TRS to XLR is undoubtedly the best way to go but for the few people who still have unbalanced inputs to serve (old/budget power amps/speakers or in my case my very expensive AER which, inexplicably, has an unbalanced line input) a simple (but not obvious in terms of wiring scheme, just lifting the earth does not work for example) custom lead solves the problem. 8)
It's silly that you might need such a lead. Mackie screwed up on their output design to be certain and is refusing to accept blame for such a "Mixing Boards 101" debacle. I mean that should have been one of the first things tested by their QA dept. when they were in the design stage. Really basic stuff. After all, they've probably produced more small format mixers than anyone on the planet. They should know better than to make such an amateur mistake. Can you tell I'm peeved? ;)
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I finally bought a DL1608 after watching it since release. The feature set and form factor are simply uneatable for some of my applications. First thing I did was plug an aux into a powered Hotspot using an unbalanced cable. Hey presto, high frequency noise, slowly cycling and changing. I'd guess I'm eavesdropping on the CPU. Replacing the unbalanced cable with a trs balanced cable eliminated it completely, as excpected.
I built a Jensen Transformer Pin 1 hummer and, much to my surprise, found no indication of a Pin 1 problem whatsoever. See http://pin1problem.com/ for lots of excellent info on this topic. The reported symptoms matched perfectly, but that doesn't seem to be what's wrong.
I carry a ProCo IT-4A 4 channel isolation transformer whenever I'm going into a school or similar venue where things are likely to be dodgy. Unbalanced into and out of that and flip the lift switch and the noise is still there, but very greatly reduced, and quite tolerable. So that's my basic solution. Balanced whenever possible, but keep the IT-4A packed with the DL1608 in case of trouble.
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I don't think the issue is a traditional "pin 1" problem so much as a digital circuit RF infiltration issue. It seems mackie did a poor job keeping the digital RF hash out of the analog domain.
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Yes, that's what the hummer test confirmed.
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I don't think the issue is a traditional "pin 1" problem so much as a digital circuit RF infiltration issue. It seems mackie did a poor job keeping the digital RF hash out of the analog domain.
Actually I seem to remember that the noise goes away if you lift the ground to the power supply. That implies that the problem is that they tied the AC ground to the power supply negative output in the power supply - they really should have brought out three wires from the power supply to the DL1608 :( .
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the noise goes away if you lift the ground to the power supply.
Unfortunately, so does the safety path to ground for the musician with his lips on the microphone.
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My experience running auxs to powered monitor with straight TS to TS 1/4 was unbearable, but fully resolved using TRS to TRS 1/4 cables (expect TRS to XLR would work fine as well). Still working on eliminating high freq noise on synth (Yamaha XS8) input (output from synth is unbalanced). Was hoping to avoid investing in DI box, but doesn't look hopeful. Anyone have recommendation on what has worked?
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My experience running auxs to powered monitor with straight TS to TS 1/4 was unbearable, but fully resolved using TRS to TRS 1/4 cables (expect TRS to XLR would work fine as well). Still working on eliminating high freq noise on synth (Yamaha XS8) input (output from synth is unbalanced). Was hoping to avoid investing in DI box, but doesn't look hopeful. Anyone have recommendation on what has worked?
Is it the same noise as patching the monitor with an unbalanced cable? IOW, it the synth generating the noise or is it the mixer once again dumping ground path noise into it's own input?
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My experience running auxs to powered monitor with straight TS to TS 1/4 was unbearable, but fully resolved using TRS to TRS 1/4 cables (expect TRS to XLR would work fine as well). Still working on eliminating high freq noise on synth (Yamaha XS8) input (output from synth is unbalanced). Was hoping to avoid investing in DI box, but doesn't look hopeful. Anyone have recommendation on what has worked?
Is it the same noise as patching the monitor with an unbalanced cable? IOW, it the synth generating the noise or is it the mixer once again dumping ground path noise into it's own input?
The two problems are totally different as well as the solutions. One is a unbalanced output ( consumer level XS8) into a balanced pro level input of the DL. The Monitor hookup ( unknown monitor pro or consumer?) from the balanced aux output of the DL into the monitor. There is no magic fix-it solution that would properly handle all cases. For the XS8 I would use a ISOMAX DB2PX from Jensen Transformers or something equivalent. Not inexpensive but worth while addition to your toolbox. It's a two channel unit. For the monitor it could be a ISOMAX PC2XR if the monitor is consumer level. There are a lot cheaper DI boxes out there but in the end you get what you pay for. Read AN003 from Bill Whitlock at http://www.jensen-transformers.com/apps_wp.html
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The safety earth is indeed tied to the low voltage -ve. Removing the safety earth does not remove the noise (at least not on my system, see earlier post). Have you tried jack inputs with a TS-TS lead? If they are noisy then you almost certainly need a DI box, if you're in the UK buy one of these http://www.soundonsound.com/sos/may12/articles/orchid-di-boxes.htm Micro DI is only £25 posted, brilliant!
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The two problems are totally different as well as the solutions.
Not necessarily. It depends on how the noise is coupled to the audio circuity. My suspicion is that the noise is riding on DL's internal audio ground bus. If you use an unbalanced connector that shorts ground to cold, which is exactly what happens in a 1/4" TRS connector when you plug in a TS cable, noise riding on the ground would then be introduced to the cold input on a differentially balanced input. Since the noise would not be common mode on the hot connection, it would not cancel. In the case of plugging in the unbalanced cable on on the input, the noise would be introduced into the the DL's channel input as opposed to the self powered monitor scenario where the noise would not be cancelled at the monitor's input using an unbalanced cable. In both cases though, the source of the noise would be the DL's signal ground bus. When using a balanced cable in both instances, the cold connection is never tied to ground and the non-common mode noise would not be injected into the balanced input though the noise would still be coupled to the upstream or downstream device's audio ground. So long as said device has proper isolation to prevent that noise from coupling within it's circuitry, you wouldn't know it's there. Of course, this is just a theory, but it seems logical based on reports. At my day job, we design a variety of FPGA based digital A/V equipment and go through great pains to ensure that switching PSU noise and various digital clock circuits don't get into the analog audio circuity. It's not always easy & I suspect Mackie didn't do their due diligence in that regard. FWIW, this isn't the first time I've noticed a whine in Mackie digital mixers. Their d8b board also had a whine on the control room outputs of a similar nature, though it may not have been as bad.
As for line level transformer isolation, I agree that the Jensens are the way to go if you can afford it. In lieu of those, I'd recommend the Whirlwind ISO1 or ISO2 transformers for line levels as they have very good specs for a lot less money. They can take fairly hot signals (+20dBu @ 20Hz) without saturating and are pretty flat to that point. The devices come with both 1/4" and XLR connectors on inputs and outputs so you can balance and unbalanced lines as needed along with the isolation.
And to the OP, get a decent quality passive DI for the keys and be done with it. As long as the transformers are good, it will sound great and you won't have to worry about noise problems. I generally use Radial JDIs for keys and other line level devices. They have Jensen transformers in them and sound great. If you can't afford the JDI, the Whirlwind Directors work ok.
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Read Bill Whitlock's explanation AN003 it's too long to repeat here but has valuable info on the subject. I also considered the signal differences (pro vs. consumer level) which you never touched on which clearly makes for different solutions. Some of the solutions you proposed (low $) use an output transformer, a clearly inferior solution compared to a input transformer as used in the ISOMAX . As to noise on the signal return in the DL, that would cause balanced to balanced (XLR) to react as well and it doesn't. A quick check of the DL indicates no direct connection of chassis ground and signal return. The power supply on the other-hand has safety ground tied to the power supply's ground output as opposed to a more direct path from the chassis. Clearly a poor design. Since it takes two kits to make noise we can't exclude the interaction of that design either. The DL chassis leakage current should be drained by a different more direct path. We are also getting into an area where schematics are a must.
To the OP buy the best solution that you can afford not the cheapest. Ask what kind of transformer is used and stay away from output transformers.
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Read Bill Whitlock's explanation AN003 it's too long to repeat here but has valuable info on the subject. I also considered the signal differences (pro vs. consumer level) which you never touched on which clearly makes for different solutions. Some of the solutions you proposed (low $) use an output transformer, a clearly inferior solution compared to a input transformer as used in the ISOMAX.
I'm very familiar with Bill's writings and often refer folks to them myself. I've had email conversations with him on various grounding subjects. He's a smart cookie. And I agree that input transformers generally offer better CMMR. However, there are cases where using an input transformer isn't always possible to accomplish certain tasks. For instance, if you need to balance an unbalanced line level output for a relatively long run and maintain line levels rather than step down to mic levels. You cannot use an input transformer for that task due to the inherent issue of input transformers requiring close physical connection of their output to the input they're feeding due to capacitive loading. And while Bill's method of isolation does offer more noise rejection on paper, output transformers have worked in pretty much every application I've ever used them in to get rid of ground noise usually caused by loops from running gear over distance on different branch circuits in given venue. By all means, use the ISO-MAX stuff. It's great (except the dip switches suck to deal with on dark stages in tense situations) but not readily available or affordable for everyone.
As far as consumer vs. pro levels not being addressed, I'm not sure what you're talking about. The DIs referred to are designed to handle a variety of levels from weak consumer signals to hot "pro" levels. Yes, they must drive a mic input rather than line input which is par for the course. The ISO1 can handle most line levels as well.
As to noise on the signal return in the DL, that would cause balanced to balanced (XLR) to react as well and it doesn't. A quick check of the DL indicates no direct connection of chassis ground and signal return.
Why would a balanced to balanced connection cause noise? And I'm not sure what you mean by "no direct connection between chassis ground and signal return." The chassis is connected to the sleeve connection on the input, no?
The power supply on the other-hand has safety ground tied to the power supply's ground output as opposed to a more direct path from the chassis. Clearly a poor design. Since it takes two kits to make noise we can't exclude the interaction of that design either. The DL chassis leakage current should be drained by a different more direct path.
Agreed.
To the OP buy the best solution that you can afford not the cheapest. Ask what kind of transformer is used and stay away from output transformers.
While I will always agree that you should always purchase as much as you can afford, output transformers are not as bad as you make them out to be and have applications that can't be addressed with input transformers. A decent quality output transformer is far superior to having no transformer at all and will provide one key element regardless of it's lesser CMRR as compared to an input transformer - you can still completely isolate the ground between devices which is the root of most noise issues.
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I was addressing the specific OP issue about the Yamaha XS8 not a bunch of other hypothetical situations. I try not to comment on situations that have little to no useful information ie. powered monitor (no model # or other helpful info.). I can give lots of scenarios were I would use much different solutions such as optical or wireless. I'm guessing his distance is quite short (Keyboard to mixer ~10 ft.). Input transformers are named that way because their location is near the input so why would I locate them near the output? In fact Jensen had a mod for the Cr1604 that located the transformers in the unit where they really belong (unfortunately it doubled the cost of the Cr1604). Bill's solutions work and not just on paper that's why he is one of the Worlds foremost authorities on the subject. He is one Valley away and I have attended his seminars and spoken to him on several occasions at AES meetings and at his shop. I try not to find myself in situations that require last minute panic setup changes of this order. The pro to consumer level of 12dBu is what I was referring to which is not always handled by the mixer. As to the noise issue on unbalanced external kit I will try to reproduce the noise condition and see if there is a simple solution such as a more direct chasis ground. I agree that output transformers give you the isolation and in most cases solve the noise problem but give you little further protection against other noise sources especially with long runs of unbalanced 2 wire cable. I did measure the DL leakage and remember somewhere around 400uv or -64 dBu for the unbalanced cable use. That would be the noise floor which is not good. I will revisit that measurement.
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Thank you all for the great insights and recommendations. Sincerely appreciated. The powered stage monitor I am using is a Behringer Eurolive 205D and with balanced TRS cable from DL1608 aux to main input the noise level is greatly reduced and satisfactory. With regards to the my main synth, a Yamaha Motif XS8, I do think it is a contributor to noise (FYI, I am not using the FireWire connection for connection to a PC). I do get some lower frequency noise/hum when using an analog mixer as well - Yamaha MG16/6FX, just not the same magnitude. I have two other keys that plug into the DL1608 as well (Yamaha MO6 and a DSI Prophet 08) and they are clean. I am using 15 and 20 foot cables into the mixing board.
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I am using 15 and 20 foot cables into the mixing board.
15-20 feet can be problematic for unbalanced cables in a RF and ground loop hostile environment, especially since that model of keyboard uses a 3 pin AC cord. I would suggest purchasing a quality passive DI and using a shorter run of unbalanced cable to the DI, then use regular XLR cables between the DI and mixer. When using a DI, you will need to use mic inputs rather than line inputs. If you plan on providing stereo feeds for various venues, you might consider a stereo DI or 2 single DIs. If for some reason you must use the line inputs on the DL, then get line level isolation transformers instead. Get the ISO-MAX units for the best possible quality. Get the Whirlwind units if you're on a tighter budget.
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I decided to go with the Radial Pro D2 to address the synth noise since my primary application is live sound as opposed to studio. I will say the Radial JDI looks to be the top of the line solution, but hoping my choice will be satisfactory. Will provide an update on how things work out when I receive the unit. Thanks again for the excellent advice.
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That DI will work great. They rate maximum input at 20Hz at +18dBu which is pretty good. That means it will handle even more input at higher frequencies and it's doubtful the keyboard's output is anywhere near that hot anyway.
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I'm happy to report back that the Radial Pro D2 cleaned up all the noise (high frequency and hum) that was getting into the DL1608 from my Motif XS8 synth. The best results required using the pin 1 ground lift feature the Radial box provides. It's constructed like a tank and gets the job done :)
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Nice! Glad to hear it.
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Having read all the guesses and theories about what causes the hum and high pitched noise on Aux's I decided to go back to basics which this mixer seems to lack. From Aliens to RF to cables etc. the guessers of "it's the power supply" pat your self's on the back. The obvious problem is the power supply all $3.99 worth of it. Mackie's new innovation after Greg and I'll coin the word "Bean Counter Engineering" is in full bloom. Onyx mixer are notorious for their power supply problems as is now the DL. Fortunately there is a simple solution.
For $9.00 and $8.00 shipping and handling from Amazon you too can be rid of the noise issues on all unbalanced lines. The problem stems from a pass thru of the safety ground to the power supply ground. This imparts a power supply generated ripple onto the shield and pin one connections to the tune of 450uV or -65 dBu (its actually chassis ground current in uA but my measuring setup measures uV ). It's also distorted accounting for the higher pitch sound along with hum. The general opinion for tolerable noise levels is -80 dBu or less (~80uV). This cannot be achieved with the current supply even with the additional chassis to safety ground wire that is also needed to get below -80dBu. In defense of the manufacturer APX, they do have the correct non pass thru supply if Mackie would only order it. Back to the solution.
The supply I ordered 6 amp max @ 12V isolates the power supply ground from safety ground (CE approved). Murphy of course was in the picture. I ordered a two prong plug supply as pictured and received a three prong version instead. It did however isolate safety ground from signal ground. I would have preferred the two prong variety since it would also have given me the added protection from miss-wired AC outlets. Yes they do exist along with poor or non-existing safety grounds in the real world. I always carry a Multimeter with me on a new environment for just that reason.
The needed chassis ground to safety ground wire (I used 16ga wire 14 or 12 would be better) was attached above the power supply plug with a spade lug. Loosen the two screws and place the spade lug between the plastic and the main body. There is a chassis ground flashing behind the plastic. Re tighten the screws and run the wire to the safety ground the mixer supply is plugged into. This configuration gave me 20 - 30uV ( -92 to -88dBu) without the ground wire you would get 350uV. You will never eliminate the noise but you will make it irrelevant in the system. This beats spending $60-$70 per Aux on a DI box.
One word about safety ground. If the ground is noisy or non-existent you will still have problems the severity of which I can't predict. There will also be poor designs that will impart noise on the mixer and for those you will most likely need a DI box. Most well designed kit will be fine. My test setup was a Behringer C50 self powered speaker using the RCA input driven from Aux3. Definitely unbalanced and yes I could hear the Hum and high pitched noise with the Mackie supply. For giggles I also ran a 50 foot cable from the mixer to the speaker with no additional noise (coiled and thrown on top of my AC cables). Other environments may not be so kind. I will get my lab supply next week for low noise power and will see that the poor safety/chassis ground are the cause behind all the noise. I'm also near the lower limit of my meter (10uV).
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Maybe a link to said power supply on Amazon? :)
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RR: How about leaving my posts where I put them!!! It's not about high frequency noise on aux's it's about the power and grounding system of the DL. Also restore the post from BlendedMix since that is far from over and the information in that post would have been very useful. It's starting to feel like the Mackie forum!!
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If you lose track of where someone's posts are you can click on their name and choose "Show Posts" over on the left. BlendedMix's post can be found here:
http://cacophony.aspinock.com/index.php?action=profile;area=showposts;u=4412
I didn't delete any of his that I remember?
I do move posts into FAQ's so folks can find answers to their questions without folks asking the same questions over-and-over like on most forums (Kudos to Mike Rivers for that suggestion). Looking at the number of folks who just stop by to lurk here vs those that post would indicate I could increase the message volume here 10x by eliminating the FAQ list but the goal here is to help folks out, not stoke our own personal egos I think? Perhaps if that's your goal also you'll post a link to the actual supply you are using? Thanks! :)
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Maybe a link to said power supply on Amazon? :)
+1 plz
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At the least I'm sure most of us would like a cheap spare PS to carry in case we misplace the original or it goes teats up on us at a gig x( . I'd rather buy one that someone else has already tested rather than play "guinea pig" with a new one :eek:.
If folks do want to run a safety ground I'd suggest running it to the chassis of one of the grounded devices in your rack. If your DL1608 doesn't live in a rack a short pigtail at the DL1608 with a spade lug to male faston would let you easily disconnect it from the ground wire. None of that is Kosher of course. The "right" solution as I posted earlier is to have designed the DL1608 to take a three contact power plug so a separate ground could be used. I believe I have a Behringer mixer or two that do this - guess Mackie should have copied them ;).
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The reason I haven't posted a link should have been clear, I was dissatisfied with the Amazon purchase. I like to get what I order don't you? As far as it not being "kosher" is clearly incorrect. Since the DL1608 that we all have is not going to be changed by Mackie gratis this is a solution for those that want to lower the noise. I thought the purpose of going with the DL was to eliminate the rack? Parts of the BlendeMix posts are missing. I'm also not finished with my investigation for a recommendation.
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The reason I haven't posted a link should have been clear, I was dissatisfied with the Amazon purchase. I like to get what I order don't you? [...]I'm also not finished with my investigation for a recommendation.
Cool, please let us know which one you settle on. Personally I'd rather have the one you received than a two wire.
I still have an amp rack for subs and monitors so running the ground wire to that rack would make sense to me, YMMV :) . OTOH I'm not having the "problem" so...
I may have "split" one of BlendedMix's posts between two threads if half of it applied to a FAQ and half was about something else. I also sometimes go through and "split out" stuff posted in (or moved to) the FAQ threads that isn't directly relevant. Didn't mean to freak you out ;) .
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Splitting makes things hard to find. As to the Amazon PWS I'm not sure you'd get the same one if you order so hold your horses. Sound like I'm announcing the release of V1.5. Going to the LA Opera, Bye.