Isolation transformers - where do I start?

I use Equitech and www.b-p-t.com products

Storytime: Interesting update on the issue Sean raised above concerning my use of the API PW Ultra 116 PLC (although it admittedly doesn't have to do with isolation transformers). To recap briefly, I have everything plugged into this one unit, the source components into the individual isolation transformers, the VTL MB-185 tube monoblocks into the filtered but non-isolated high-power outlets. The 116 Ultra is then plugged into a single wall outlet via its own cord (and a grounded 3-prong adaptor). Sean mentioned that running everything from this one AC cord could be choking off the whole system's power somewhat, and suggested that I run the power amps to the wall separately. The thought had occurred to me before, but as I explained I don't have the outlets near the system to accomplish this, in addition to which API recommends plugging everything into their unit (VTL doesn't agree, FWIW).

Tonight, I was doing some lowish-volume comparisions between my old C-J MV-55 amp and the VTL's, as part of some auditioning I've been doing over the past few days just to get a handle on where I am with the new amps, now that their re-tube complement is fully burned in and I've installed a pair of Shunyata Sidewinders PC's on them, and before I decide to either send the VTL's away for a while to be upgraded and/or sell the C-J after 3 1/2 great years. Both the VTL's and the C-J were plugged into the Ultra's amp outlets (it has four), but of course were not all powered up at the same time, since one or the other was without a speaker load until I switched the cables over.

Listening to several audition cuts while A/B'ing the amps had me feeling pretty good about my upgrade once again, after not having heard the old amp for a while. The C-J obviously doesn't have the power to go loud like the VTL's (which was the main instigator for my upgrading, because I moved to a larger listening room), but it held its own on transient articulation and freedom from sounding mechanical or hard. Overall though, even at these late-night levels, it could not match the new amps in terms of frequency extension both up and down the spectrum, transparency to fine detail, resolution of images' spatial context, image separation, relative lack of imposed timbral colorations, bass authority and tautness, dynamic independence of images from one another throughout the soundstage, depth of field, and the smooth cleanliness that indicates relative freedom from noise and distortion artifacts. Next to the VTL's (at about 2 1/2 times its price when new), the C-J sounded smaller, flatter, coarser, more colored, more veiled, more congested and prone to glare, looser, more sonically changeable in the face of its input signal and load demands, less extended spectrally at both ends of the scale, and also dynamically at the small-scale end (didn't get into high level dynamics during this session, but of course the VTL's rule there as well). Don't get me wrong, the MV-55 was still enjoyable in its own right (and represented a huge improvement over my previous Classe Seventy SS amp at the time that I got it), but in short it was confirmed once again as sounding less natural and imposing more of its own character on the sound than the much more powerful mono's that are replacing it.

About the only possible negative on the side of the VTL's that I could find in these direct comparisions was a slight suspicion that they might be just a tad lean tonally through the midrange, but I couldn't be sure whether this might seem to be so simply because in A/B'ing the two amps, they were more extended and present at both frequency extremes, with less thickening congestion through the center. When I had last done comparitive auditioning on the VTL's, it was with the Sidewinders vs. the stock cords, and though I generally found the Sidewinders were a pretty universal improvement in terms of laying bare the soundstage and improving dynamic liveliness, I did wonder whether they could be just a little too bright-sounding in my setup. I chose not to get overly concerned about this for the time being however, since the VTL 'sound' had struck me as having been just a smidge dark and lacking in sparkle before replacing the cords. But now, I was wondering about the cords again, when Sean's admonition came back to me. Maybe if the amps were plugged into their own outlets, they might sound slightly heartier in balance.

That's when I suddenly remembered something I had forgotten before - I still had my old original, non-'Ultra' Power Wedge downstairs somewhere. This smaller model didn't have the balanced AC option on the isolated source outlets like the current version, but I could use its filtered amp outlets. I went and found it, and with its power cord I could stretch far enough to reach the AC duplex on the adjacent wall, and then use it for plugging in the monoblocks alone. The mono's would still have to share one main AC cord to the wall, but not in addition to the source components. The outlet in question was also on a different circuit breaker, something confirmed when the amps' turn-on current in-rush dimmed the lights on that side of the room much more than when they're plugged into the Ultra along with everything else as usual.

So, with the mono's on their own cord and circuit, I powered them back up, expecting to hear at the very least sound that was merely equally good as before, and hopefully better in some way. But when I played the last cut over again, I was startled to discover that it sounded as if something had broken. The VTL's were now rendered as sounding much closer in almost all ways to the old amp, losing most of their considerable advantage at the flick of a switch. I couldn't believe it. How could amps that should by rights be so easily superior suddenly sound not all that much different in a head-to-head, no matter where I plugged them in? In some ways, like smaller image and stage sizes, and sounding pinched and glarey on unision horn charts, they now sounded worse if anything. Feeling freshly vulnerable to the whims of fate, I started the track again from the beginning, but could only get halfway through it before I needed to jump up and put things back the way they had been.

With the MB-185's restored to drawing juice from the 116 Ultra with the rest of the system, I again heard the sound they ought to have, no problem. Whew! I checked both outlets with a voltmeter, both read 120v. I'm not gonna dwell on this episode too extensively right now, either concerning its possible causes, or to extrapolate it to when (or if) I decide to get new multiple dedicated lines and outlets installed. Although I believe the old Power Wedge isn't supposed to have quite as good an AC filter as the Ultra does, I really don't think that this could account for everything I heard. I tend to think that either it's because of something having to do with the way the outlets are wired, or because API is right about the advantages of plugging everything in centrally, but I can't know for sure. All I know is that for now, I'm sticking to the one main AC cord for the system, even if Sean is technically correct (and he always is), and am not going to lose any sleep over it. Good night. :-)

Zaikesman: I'm human and make mistakes too. Wanna see some threads and posts to prove it ? : )

As such, most of my comments are based on either first hand experience, common electrical / electronic theory, logical deductions and / or any combo of the above. With that in mind, nothing in audio is set in stone and one REALLY needs to try things out for themselves within the confines of their own system to see what works best. I have seen / heard components and cables sound like hell in one system and really compliment the performance of another system. You really don't know until you try it.

Having said that, i would be curious to see if the outlets that you plugged the amp into were on the same breaker and circuit that the line level gear was plugged into. Can you verify this and let us know ? It is possible that one set of outlets was on one leg of the circuit and the other outlet was on the other leg of the circuit. The fact that you have also introduced a completely new device and source of filtration into the system could also introduce another variable into the equation.

Is there any way to plug the amps directly into the same outlet as the line level gear is plugged into using one heavy duty extension cord with some type of outlet splitter ? I would be curious to see what happened in such a situation. Sean
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Sean: Your first two paragraphs are a given of course - I was jes' funnin' (and am not one to talk when it comes to freely dispensing 'authoritative advice' that amounts to little more than my take on common sense, bountious caveats included gratis :-). You may still well be correct in your basic presumption here, I just may not be able to take advantage of it.

As I say, the possibility of the second PLC tossing a spanner in the works does exist, but I could test this by plugging it in to same wall duplex as my regular one and trying this hook-up again, and then doing what you suggest in the last paragraph. The outlets in question are confirmed as being on separate breakers, but on the same side of the box.

I did notice something else today though - the two outlets are oriented 180deg. upside-down from one another, so that the polarized wide plug-blade slots are on the left with one duplex, on the right with the other. Since the adaptors I'm using are also polarized, and I am grounding them at the center screws in each case, this means that by necessity, both the 3-prong PLC wall plugs were plugged in oriented in opposite directions. I don't know how wiring behind the outlets looks, so I don't know for sure if this really resulted in the two PLC's being plugged in with reversed respective polarities, but the evidence is suggestive.

Reverse AC polarity within a system can play a lot of games. One may not realize these "problems" exist until the situation is corrected. Once that takes place, the "sonic haze" has been lifted and you can now hear things that were previously not noticed.

I'm sure that you've seen this before, but take a look at this thread about Noise, Hum and AC Polarity to really sort through what's going on with your system. Don't forget that you have to remove ALL interconnects from the system as you can't have any of the component's chassis' tied together. Sean
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