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[Andrew Hamilton]

Hi Folks, I was wondering why my Massive Passive is showing a slight phase distortion for sine wave frequencies above 3 kHz.  When I watch the recaptured signal on a DK Audio meter, the left/right levels remain the same for each frequency step on the oscillator, but the line which indicates phase correlation becomes more and more "bowed" in the middle when the oscillator is switched to higher and higher frequencies.  The cables are good (can pass the freq.s from the same oscillator to 23 kHz without "bowing" effect).  The other equipment in the chain is immune to this abnormality only if the Massive is physically removed from the chain.  Merely bypassing the Massive with it still connected introduces the same symptom.  A friend said, "What about a cap going bad?"  I asked, "But there is no gain loss on either side.  The phase rotation occurs to both channels."  He speculated that something in the monolithic power supply might introduce this frequency-dependent, symmetrical disorder.  Any ideas or moral support would be appreciated.  Manley's tech support are on holiday, starting today.    


_andrew

[Brian Roth]

Hmmm...I'm not familiar with your exact test setup...

If you suspect a phase shift through the gear, then I'd try multing the signal through both the Manley as well into an oscilliscope.  Either use "XY" or dual traces to see whazzup.

Bri

[bushwick]

Please post back here. I am interested in what you find.

Thanks,
josh

[Andrew Hamilton]

I've seen it on the 465M in XY mode - that same "bowing" of phase.  As before, the bow shape is symmetrical about the 45 deg XY line of coherence...   Another list member has informed me that, ...

"In "bypass" (unlit) the tubes are not in circuit but the input amplifier and balanced output transformer are in circuit.
note the input tranformer, input amp and output transformer are still in while in "bypass " mode.

That would be a good place to look. (like a broken switch/relay that still connects to something else and acts like an RC circuit "warping" the HF of one of the channels. Or just a funky transformer or bad input amp."




Thanks,
    _andrew

[Andrew Hamilton]

I spoke with two techs at Manley today, who are filling in for Paul Fargo.  They suggested that I try using the unbalanced outputs, first, to see if the issue goes away, having bypassed the output x-formers.  Then try the unbalanced inputs also, if the outputs, alone, don't fix it.  If it's still there, then the issue might be the active input stage (buffer).  All three are in the chain, as quoted above, when the unit is [not hard-] bypassed.    One of the techs - the more knowledgable sounding - said that the "bowing" effect of the X-Y pattern at higher frequencies must be due to one channel losing gain compared to the other.  But if that were the case, I should think that the direction of the bowed line would also shift in the direction of the louder channel.  However, the directiion of the line (which on the DK Audio meter is vertical, rather than at 45 deg.) doesn't change as I raise the frequency from the oscillator - nor does the level going out of either channel of the EQ.   Only the upper phase is bending - symmetrically - about the coherent center, without changing direction or height.






(Will follow up with results)

_andrew

[jazzius]

How does it sound?

(i often get stange X/Y things going on when using various permutations of my analog chain, but tend not to worry about it if sound sweet!)

[Andrew Hamilton]

Good point.  However, I had not even gotten to the point of hearing the session files through the chain when I noticed the phase anomaly while calibrating with an oscillator.  I am transferring some rock music from 88.2 to tape (at customer request) [ATR-102 0.5" 456, 30ips...]    and have the use of two EQs - the MEA-2 and the Passive.   We ended up quitting early after preparing the process EDL  because I wanted to be able to use the Passive in a repeatable condition.  I figured, if it's functioning properly, and hf phase distortion is what it is supposed to add, then cool, let's try it.  But if it's something broken, like that the trannies are funky and will sound different when fixed, better is almost worse!   (j/k)...  I realize that this is a little bit insane, since the tape machine is going to introduce enough distortion to swamp what the Passive was doing, especially since his mixes are from tracks off a 2" 16 track and have been Smarted and Chandlerized to a very "warm"  degree by the previous studio...  But if something is broken I'll be too distracted worrying over it to give it an objective chance.  Happily my client is very understanding of this voodoo and insists on letting me sort this out before we proceed.


The good news is...
Per Manley's tech's advice, as soon as I switched to the unbalanced outputs, the
problem went away. So, apparently, one of the output x-formers is not passing high frequencies at the same level as the other.   But its effect is extremely subtle. It is minute enough a difference so as not to pull the direction of the X-Y trace away from 45 degrees in any noticeable way. The trace only begins to swell in the middle - this ultra thin line that starts to become almond-shaped as F is raised.   For now I am now using the 1/4" I/Os - which are balanced in and unbalanced out.  



_andrew