Question about Lexicon MX200 effects unit (with )

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The unit itself is generating too much noise(hiss). some effects are noisier than others but overall noise level is unacceptable. all the product reviews say how quiet this unit is. tried changing signal path, levels, changing universal parameters etc.

Posted by brian_mimile on


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Fred Yearian

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Check that: You are using BALANCED interconnection lines (TRS or XLR) everywhere. Low quality cables can cause or let in noise and hiss.

Check that ALL, and I mean ALL interconnected equipment is powered from the SAME receptacle or power conditioner.

Check that you are not using a noisy source or recording system like the internal audio of a PC for instance.

Short the inputs to ground and see if the output noise goes away. Some effects are noisy because the inut signal after effects gets added back into the output.

You haven't described your setup and without that information there is not much more I can add. Ferreting out noise is one of my specialties. In general your input level should NOT be too small as this leads to less signal to noise ratio due to digitizing noise. Look at the Lexicon specs to find what the levels should be. Without the description of your setup I can add no more...

Posted on Jul 16, 2011

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  • brian_mimile Jul 16, 2011

    this unit only has 1/4'' inputs-outputs. guitar-Lex input/ Lex output-amp is the signal path (this is acceptable according to Lexicon manual). both plugged in to same power outlet. amp is quiet with guitar. noisy with Lexicon unit plugged in without the guitar. Lexicon input level has no effect on ambient noise.

  • Fred Yearian Jul 16, 2011

    The LEX output to the amp should be a 1/4 inch TRS balanced cable... while they may say that unbalanced connection is OK, that OFTEN doesn't get the job done regarding noise. There is the possibility tthat the LEX has a problem... this is what I want you to do: Using a pair of headphones, plug into the LEX output's one at a time and listen if the hiss is there... Now ONLY the one side of the headphones (left side) will have sound because the outs of the LEX jacks are mono. If you can detect the hiss there objectionably, then the LEX is bad... it happens... and it is likely the CODEC chip in the LEX. Exercize your warranty in this case. Be aware that electronics due to the statistical laws of physics, has a noise floor that we just can't get all the noise out. Unfortunately effects units that massage the sound tend to worsen any noise that is generated in the early stages of the chain within the units.

  • brian_mimile Jul 16, 2011

    I tried the headphone test- it seemed relatively quiet. I bought a balanced TRS cable and tried that on the output to the amp. Didn't have any effect on the noise at all. I may try a different power supply, I don't think the one that came with it is the original (bought used no warranty).
    Thanks for all your help, good suggestions.

  • Fred Yearian Jul 17, 2011

    Oh, oh... some replacement supplies have switching regulators that can leak into the equipment. The fact that headphones seems clean would indicae a ground loop from the LEX to whatever recording system you are using... You haven't told me what this is driving and in analyzing possible causes this is important.

  • brian_mimile Jul 17, 2011

    The signal path is very simple: guitar - Lex mono input/ Lex mono output - guitar amp. The noise I am getting doesn't sound like ground hum so much as it sounds like tape hiss or radio static. I finally was able to verify that the power supply is the model that is specified for the unit. I think your worst-case assessment may be correct - that the Lex has some defective component that is generating noise. Unfortunately I bought the unit used and have no warranty. I have contacted Lexicon re: parts and repair costs and await their response. I opened the unit up and found that replacing individual resistors etc. on such a small scale is going to be beyond my skill level. I could probably fix a jack or pot or replace the whole board without too much trouble. There were quite a few processor type chips on the board and I couldn't see any obvious flaws or hot spots. I think my best option is that a replacement board is not too expensive.

  • Fred Yearian Jul 17, 2011

    I suspect you will find a replacement board is beyond economic repair sense... I would first try some circuit cooler on individual chips. I suspect you will find that the A-D and D-A convertors are the source of the noise... you might get lucky... I have replaced some chips... just did a little 28 legged CODEC chip... not fun the chip is 1/6 the size of a postage stamp. If you can get the thing to show itself with circuit cooler that is a start... use cooler one at a time on the chips and wait a good five seconds for cool to soak in... remember you are looking for a CHANGE... might get better, might get worse...

  • brian_mimile Jul 17, 2011

    Thanks I'll try that.



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There is not enough info here to provide a complete answer, but let me give you some background:

There will always be some hiss. This is due to general amplification where a small amount of noise is amplified along with the general signal. In most cases, the signal is strong enough to overpower any noise that is present (vocals in your example). This noise should not be that noticable in normal cases. If there is an automatic gain control in the line, this could account for it as with "silent" times, the gain will automatically be increased potentially to the degree where the noise is noticable.

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