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Old 22nd August 2007, 08:01 PM   #1
Sjef is offline Sjef  Netherlands
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Default UCD700 noise

I'm having a little problem with my ucd700 amps. Well this is the last of many main problems I will not bother you with. It's build dual mono in one case and both channels have a very ignorant high frequency noise, it sounds a bit like a jet engine motor and is allready noticable at the listening position with my small bandor 81db/w/m loudspeakers and is simply unbearable to the ears with my 118db/w/m BMS loudspeakers. This noise started after some 20 to 40 hours of play in time, before they where almost completely quiet, strange

the amps are all made of hypex components, two ucd700hg modules, two hg power supplies one soft starter and two 800VA hypex trannies. everything is connected togeter according to the hypex manual, including earthing layout etc etc.

does anyone else have the same experience with the ucd modules ? and if so what was the cure for it ?

I guess it must have something to do with earthing or Hypex has again delivered a mallfunctioning product
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Old 22nd August 2007, 10:01 PM   #2
BWRX is offline BWRX  United States
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Can you post a picture of the physical layout of parts and wiring inside the chassis? Have you taken standard precautions such as twisting wiring together and keeping power and signal wires as far apart as possible? How close are the modules to each other? It could be that the switching frequencies of each modules are close to each other and are producing a beat frequency. Can you test the amp with only one module powered at a time and see if the noise is still present?
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Old 22nd August 2007, 10:35 PM   #3
Sjef is offline Sjef  Netherlands
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I'll make a picture of it somewhere tomorrow.

Th modules are mounted about 30 to 35 cm apart from each other, one on each side of a 19" enclosure.

I will test the amps seperatly with one channel powered off, thanks for the tip.
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Old 23rd August 2007, 04:23 AM   #4
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OT: Why would anyone put a 700W amp to a pair of 118dB/w/m speakers??? I am a big fan of head room myself but that is just ludicrous. Btw, what speakers do you have? I have never heard of such sensitivity.
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Old 23rd August 2007, 07:22 AM   #5
Sjef is offline Sjef  Netherlands
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The ucd700's are eventually ment for my open baffle woofers, the 118db sensitivity is from my BMS tweeters wich I tried just to hear what the noise sounded like. The noise is also audible on my woofers though, that's why I want to get rid of it. I'm not gonna use them with these tweeters, these are powered by a 300B set amp in a three way active setup. The tube amps are much more quiet than the ucd's, who ever could imagine that.
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Old 23rd August 2007, 07:55 PM   #6
Sjef is offline Sjef  Netherlands
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I have tried hard to spit trough the various UCD topics but it's becoming very hard because they are very large and diverse.

what I was trying to find is a correct earth connection schematics for the modules, power supply, casing, mains input, loudspeaker output etc etc. when using unbalanced inputs.

It seems that the UCD's are very sensitive to this and I can't find anything practical on the Hypex site either.

So in summary, (wich might also be of great help for anyone who want's to build a ucd amp)
what the best place of connection the case to earth ? at the input ? at one or at both? at the output ? at the power transformer ?

What about the mains earth connection when my home doesn't have an earth connection ? It still will be connected to the other equipment via the earth wire (by the way, the noise from the amp is also present when only the mains is connected with shorted inputs)

For the rest everything is allready connected the right way together via the Hypex power supply modules and the amplifier modules.

I have build many amps from scratch in my life and all of them are completely dead quiet as far as my scope can measure but now I'm having troubles with a preassembled kit, that's weird
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Old 23rd August 2007, 08:54 PM   #7
BWRX is offline BWRX  United States
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Have you tried powering only one channel at a time and seeing if the noise is still there (as I suggested yesterday)? How about that picture of your setup too?

You have mentioned that changing the grounding has not changed the noise at all. That could point to a problem that is not related to the power supply, hence my suggestion of powering one channel at a time. If you have a scope, you can measure the switching frequency of the two modules. Do that and subtract the two frequencies. If the sound you're hearing is about that frequency (or some multiple of it) your modules are interacting. Powering down one module will easily tell you if the modules are interacting in some way.
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Old 24th August 2007, 04:04 PM   #8
Eva is offline Eva  Spain
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One or both modules are probably damaged.
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Old 24th August 2007, 06:59 PM   #9
Sjef is offline Sjef  Netherlands
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Hi Brian,

I think you have misread my post. I didn't say that changing the goriunding did not make a difference, I asked for the best grounding scheme for the ucd's. I want to know first before doing any changes over and over again.

I'm gonna try the power down of one channel this weekend, I'm a bit busey at the moment. picture is coming too.

I really have to find some time for it this weekend because it's getting worse every day now.
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Old 25th August 2007, 12:31 PM   #10
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by Sjef
Hi Brian,

I think you have misread my post. I didn't say that changing the goriunding did not make a difference, I asked for the best grounding scheme for the ucd's. I want to know first before doing any changes over and over again.

I'm gonna try the power down of one channel this weekend, I'm a bit busey at the moment. picture is coming too.

I really have to find some time for it this weekend because it's getting worse every day now.

Hi Sjef,

Very strange that you have these issues, the issues suddenly started?

I have been using UcD180 and UcD400 modules for years now, and no issues at all, super silent, they are as silent now as they were right from the start. In fact they are the most silent amps in my house, they easily beat my Tripath based Marantz that produces lots more noise. The ZAPpulses were way more noisier. My Accuphase Class AB amp came close in (low) noise level.

There must be something wrong but can not believe that it is due to some UcD issue.

About earthing. I`m using balanced XLR input with the DEQX PDC as the source. I use UcD180s to drive tweeters and mids directly. No problems related to earthing, I use no safety earth as I do not have that available. XLR pin 1 goes to the UcD modules and to the chassis, power supply is floating from the chassis. I think this is the Hypex recommended setup.

Maybe some of the other Dutch UcD users that are bit closer to you than I am can help you out?

Best regards

Gertjan
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