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Discussion Starter · #1 ·
Has any Lexicon MC-12B owner experienced a *dramatic* amount of hiss through their balanced outputs? I'm not talking about "normal" hiss levels--this is 60+ dB at 1 meter hiss! I'm trying to track down the culprit of the hiss (processor, amps, etc.) and am just looking for any feedback. It could be operator error, the Lex, my cabling, or the amps.


Here's the situation:


1. Lexicon MC-12B using 4 balanced/XLR outs (FL, FR, RL, RR) and 3 unbalanced/RCA outs (C, SL, SR)

2. Llano Trinity 300-2 amp using balanced/XLR ins (FL, FR)

3. Llano Trinity 300-2 amp using balanced/XLR ins (RL, RR)

4. Llano Trinity 300-3 amp using unbalanced/RCA ins (C, SL, SR)

5. Each balanced cable is 10' of AVCable's LC-1



The Trinity 300-3 using unbalanced/RCA ins is whisper quiet, even with cheap cables--no hiss from the three attached speakers under any conditions. I'm using this amp waiting for three 300-1 mono balanced replacements--misery loves company, I guess!


The remaining four speakers in the "balanced chain" produce a HUGE amount of hiss under all conditions (no input, internal calibration noise, any source). I don't have any balanced out gear that I could hook into the balanced-in Llanos to take the Lex out fo the equation, so I can't tell if the amps are the problem (what are the odds that both are messed up?) or if the Lex's balanced output circuitry is messed up. Or if it's my cabling. Yanking the unbalanced outs out of the Lex doesn't change the hiss levels at all.


I'm new to balanced and I must say I'm not impressed so far :). I'm on my second MC-12B (first one was DOA) and would hate to find out that the replacement is messed up too. I realize that I haven't done any scientific testing, but these amps are a bear to get out of the rack to switch out cables, etc.


Any thoughts/help?
 

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Alex,


Find out the pin out of the balanced input on your Trinity amps. They may suffer the Pin 1 problem.


Shawn
 

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Discussion Starter · #3 ·
Wow, that didn't take long...I'm checking with Randy White at Llano as we speak.


Can you elaborate on the "Pin 1 Problem"? It sounds evil.
 

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Discussion Starter · #5 ·
Shawn...thanks. I await news from Randy on this--I can't imagine that he'd break protocol on something like this, though.
 

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Alex,


"-I can't imagine that he'd break protocol on something like this, though."


Actually, a fair number of high end companies get it wrong. And I think once they make one product with it wrong they keep going so they don't have compatibility problems within their products.


Shawn
 

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Discussion Starter · #7 ·
Per Randy:


Pin 1 = Ground

Pin 2 = In Phase

Pin 3 = Out of Phase


As far as I can tell, that's normal, so I'll keep searching for a cause.
 

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Alex,


Yes, that is proper. If you have a multi-meter verify the pin out of your cables are wired straight through. Those PDFs I linked to above will give more tips on determining where the noise is coming from too. Good luck!


Shawn
 

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Discussion Starter · #9 ·
Thanks...so far, the amp guy says it's the cables or the Lex, the cable people say it's the amps or the Lex and Lex says it's the cables or the amps. I don't have a multi-meter but I guess I'll buy one...although I have 14 balanced cables (2 sets of 7) and they all produce the same result. My guess is that I've gotten a second Lex lemon or there's something "wrong" with the amp design. Ugh.
 

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Pin-1 refers to when pin 1 of an XLR is connected to the audio ground and chassis ground, leading to ground loops. So you should find out how the Llano amps implement their pin 1, because it's not clear from their response which ground it's hooked up to. Ideally, pin 1 should be tied only to chassis ground. Sometimes lack of grounding or improper grounding can lead to excessive hiss as well.


--Andre
 

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Discussion Starter · #12 ·
Thanks for the additional responses--I believe that there is a rational solution staring me in the face, but I had to rule out a problem with the Lexicon before moving to the amps.
 

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Discussion Starter · #13 ·
Here is the response from Randy at Llano--it sounds like I've got a problem, in that his amp design doesn't jibe with Lexicon's balanced topology. Thoughts?


------------------------

Pin 1 is audio ground only it is 10 ohms above chassis ground. We have never had a hiss problem before with XLR, but we have also never had XLR used with a home processor like this one before either.

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amillians,


Saw your post about the hiss in another thread, didn't realize until this one you were talking about Llano Trinity amps. I'm having exactly the same problem; MC12B w/Llano Trinities. The Llanos worked fine via balanced connections to my Proceed AVP, so it's hard to know exactly where and with who the problem lies. Got a feeling there is no solution available to us, but let's stay in touch. I gather Randy thinks the issue is with the Lex.
 

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Discussion Starter · #15 ·
Misery loves company! :)


Randy is a stand-up guy, so I'm sure we'll reach a peaceful conclusion. I have a pretty large investment in his amps (2 x 300-2, 1 x 300-3 with 3 x 300-1 replacements on the way) so I am definitely not going to live with this hiss...it is 100% intolerable and intrudes into every movie scene.
 

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Just sent Randy an email -- hopefully I'll hear something today or I'll give him a call when I have a minute. I've spoken w/Jeremy at Lexicon who is looking into the hiss issue. I'm supposed to hear back from him. Just moved, so I'll be hooking it all up w/single ended until the issue is resolved. Hopefully I won't get any noise (which is why I went with balanced in the first place), and I will miss the 6db or so of gain that balanced affords.


My email is [email protected] -- let's compare notes as things evolve.
 

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Where can I find out about Jensen Transformers, and how much are they? Will they alter the sound quality?


Any info. appreciated.
 

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"Where can I find out about Jensen Transformers, and how much are they?"


Look up in the thread... earlier I linked to some of their infomation about 'Pin 1' problems.


Shawn
 
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