[jelt2359]

For those who have modded the mutec 3+ USB, can it take a 7V power supply? Or just 6.3v?

 

[jabbr]

For those who have modded the mutec 3+ USB, can it take a 7V power supply? Or just 6.3v?

https://www.head-fi.org/f/threads/the-diyrs-cookbook.781268/page-76#post-13531120

 

[jelt2359]

https://www.head-fi.org/f/threads/the-diyrs-cookbook.781268/page-76#post-13531120

Thanks!! Oops. I have been using the LPS-1 at 7v.

 

[johnjen]

Perspectives and Techniques on ‘tuning’ an audio playback system.

I tune my system NOT to fix acoustic problems but to improve SQ.
This is a subtle difference that ultimately makes a significant cumulative difference in the long run.
IOW the tweaks I make aren’t meant to compensate for deficiencies but to mitigate choke points.
Put another way…
By removing technical, electrical and electronic limitations that exist in the entire system, what can be sometimes described as glaring deficiencies are removed, or at least reduced, and not simply patched.
This is as much a perspective on What is being tweaked, as well as Why.
Sorta like how you approach improving your system.
Is the glass half empty/half full?
Are you fixing a problem or making the system better?

This leads to a concurrent and consequential thought.
Who and Why do some experiment with our audio systems?
This is a rarely asked question with no simple answer and certainly a no consensus end result.
It is a rare mix of overall technical understanding and abilities, materials sciences, acoustics, electronics and electrical expertise, among many other talents, all in an effort to engage us with a whole other realm (Music and all that is involved with this entire topic).

To that end I use the process detailed below to ‘evaluate’ and refine the structure of what areas of the system to work on next, based upon all previous experiments and knowledge gained therefrom.

1. Is there something to want or desire?
For example a new kid on the block (e.g. AOIP) pops up on the scene is it something that answers a need, or is curiosity alone enough to want to pursue the avenue of experimentation?

2. What (as in defined or at least adequately described) is wanted or desired
Are there specific technical or functional enhancements that can be explored and what would be considered as yielding ‘Better’?

3. How to achieve - plan of action and budget
Details concerning ‘resource allocation’ (what , when, how much…)
3b. What h/w and/or s/w solutions exist.
Research of gear, solutions, factors involving the integration into the existing system, these endeavors are, or at least can be, a big portion of the fun.

4. Implementation of $ and integration into the rest of system/setup interface
This entails the procurement and physical tasks required to set it all up and plug it all in, then get it all to work.

5. Noticed changes - what outcome was achieved?
This is where the feedback loop of experience kicks in, where implementing further refinements to the basic (proof of performance) implementation, allows for a test for scaleability and adds to the overall evaluation of this avenue of experimentation.

What was learned usually can lead to additional ideas for further refinement and experimentation.
And if the results do contribute to an improvement in overall SQ (ie. it’s a keeper) it can also be combined with other ‘related’ tweaks as a ‘standard’ refinement.

Also note, if any step is missing or fails to complete, the process halts at that point.

These techniques and evaluatory steps have proven themselves to me over time and the cumulative results tend to reinforce each other.
And sometimes in unexpected ways with the total being far greater than the mere sum of the new individual tweaks.

This series of techniques has been applied to several completely different areas of interest and with similar end results.

JJ

 

[mourip]

Perspectives and Techniques on ‘tuning’ an audio playback system.

I tune my system NOT to fix acoustic problems but to improve SQ.
This is a subtle difference that ultimately makes a significant cumulative difference in the long run.
IOW the tweaks I make aren’t meant to compensate for deficiencies but to mitigate choke points.
Put another way…
By removing technical, electrical and electronic limitations that exist in the entire system, what can be sometimes described as glaring deficiencies are removed, or at least reduced, and not simply patched.
This is as much a perspective on What is being tweaked, as well as Why.
Sorta like how you approach improving your system.
Is the glass half empty/half full?
Are you fixing a problem or making the system better?

Thanks for posting your personal outlook on tweaking. You are right. It is seldom discussed as a topic on its own.

I did find myself wondering what prompted "Is the glass half empty/half full? Are you fixing a problem or making the system better?" Where you addressing the previous posts of others?

The way I look at it all changes that we make to our system are made in the hope of improving sound quality and meant for promoting our personal enjoyment. Otherwise what would be the point? Every system has limitations, "choke points" as you describe them. Some we make ourselves due to a lack of understanding of our equipment and how it works and interacts, some are due to limitations built into our equipment as a product of being built to a certain price point. It seems to me that system building will always be a bit like cooking. It involves science and art. Success will always be determined by our own personal and subjective satisfaction with the outcome. It seems to me that doing DIY comes from either a desire to learn, a form of self-enabling, or else a way of getting personally satisfying sound on a limited budget. I also think that spending a lot of money does not ensure good sound unless you understand system interaction ...so learning always needs to be involved.

As an aside. In reading other forums it always amazes me how much contention develops between the self proclaimed objectivists and those who are described by them as subjectivists. At the end of the day all that matters is that one is satisfied with the sound one is getting.

 

[johnjen]

Thanks for posting your personal outlook on tweaking. You are right. It is seldom discussed as a topic on its own.

Yeah this is a highly individualistic question/answer, which is why I presented it in this way.

I did find myself wondering what prompted "Is the glass half empty/half full? Are you fixing a problem or making the system better?" Where you addressing the previous posts of others?

No, that perspective hadn't crossed my mind.
But I can see where it might with some.
I WAS thinking that often times the orientation is to wanna make a change based upon the individuals audio experience and how it could be 'better', if only…
This is the glass half empty orientation, because there is a perception of 'a problem or lack' of some sort.
And of course the 'half full' is about, as I put it, 'getting the system out of its own way', such that more of the actual music is allowed to be presented to our ears, ie being screwed with less and less.

The way I look at it all changes that we make to our system are made in the hope of improving sound quality and meant for promoting our personal enjoyment. Otherwise what would be the point? Every system has limitations, "choke points" as you describe them. Some we make ourselves due to a lack of understanding of our equipment and how it works and interacts, some are due to limitations built into our equipment as a product of being built to a certain price point. It seems to me that system building will always be a bit like cooking. It involves science and art. Success will always be determined by our own personal and subjective satisfaction with the outcome. It seems to me that doing DIY comes from either a desire to learn, a form of self-enabling, or else a way of getting personally satisfying sound on a limited budget. I also think that spending a lot of money does not ensure good sound unless you understand system interaction ...so learning always needs to be involved.

Those CP's (choke points) are 'built into' not just the gear but the entire set and setting (AC power delivery, EM level of 'noise', ground modulation, etc).
The gear is made by a manufacturer who HAS TO meet certain requirements and expectations, some of which can be 'improved' and only by the owner themselves (called tweaking).
The delivery of the AC power distribution system, which includes the ground connection, to our gear can be VERY compromised.
And once again it's only the owner who can deal with this, for the obvious reasons.
And I agree that a good portion of this focused attention is to learn AND enjoy the results there from, in ALL of it's manifestations.

IOW, for me purchasing the gear after doing all the research, is but one of the initial 1st steps.
THEN the fun REALLY begins as optimizing the system by removing CP's and tweaking and dialing in those variables that can be addressed are experimented with.

As an aside. In reading other forums it always amazes me how much contention develops between the self proclaimed objectivists and those who are described by them as subjectivists. At the end of the day all that matters is that one is satisfied with the sound one is getting.

Earlier in this thread I wrote a post about this dichotomy of the subjectivists vs the objectivists.
My point was that it will always come down to what do you like 'Better', which is a purely subjective orientation.
Now what makes up the criteria that constitutes 'Better' is also purely subjective as well, even though one may use an objective means of quantifying those 'preferences'.
It will always boil down to what is 'Better', based upon each one's subjective preferences.
And in all actuality we need both sides of this dichotomy TOGETHER, not at logger heads against each other.

That is if the goal is to achieve the best we are able.

JJ

 

[johnjen]

So here it's been a month since my last post and there is news to report.

The system continues to push that 100% ceiling ever higher, and even when the system isn't operating at peak SQ the HDSuperDuperGlue effect is still grabbing me and not letting go.
The last several nights I have seen the early dawn rise at 5am.

And finally after 1Khrs the system peaked and set new all time 100% SQ levels.

But then BigPoppa said, again, Hey JJ, ya gotta try this, it REALLY helped…
And remember his ac power delivery is about as opposite from mine as you can get.
His power distribution is completely ungrounded and old, as in decrepit.
While mine is a dedicated short run that has been dialed in.

So as a consequence BigPoppa and I are 'exploring' using a Chinese made torroidal based 500VA isolation transformers.
Its $125 (+$60 shipping), fairly compact and has an on/off switch, built in fuse, and 2 duplex receptacles.

And of course since it's me, it didn't stay 'stock' very long.
Thus far I've added a WAQy chip to the fuse and played around with using several different short ac power cables to feed it.
So far I like my gen-4 DIY cable the best, even over shorter larger gauge 'stubby' cables.

That is until I re-configured my direct ac run from my breaker panel.
A short while back I added a short piece of 10gauge romex to the end of my dedicated run and soldered it to the pre-existing romex (12gauge).
Originally I had terminated it with 2 more duplex receptacles in a box for additional gear to plug in.

So I re-terminated that 10gauge romex run into an IEC connector which then plugs only into the Iso-Xfrmr.
It delivers 1.09/1.75 KA to my iso-xfrmr (according to my ASCC tester).
Yes that's 1,090/1,750 Amps (depending upon if the ground wire is used in the test).
These numbers are among the best I have measured in my system.

The fuse, and I'll be replacing (at least) one of the duplex receptacles, along with another WAQy chip, will be upgraded before to long as well.

Thus far I can confirm Musiqboys observations when he added his Iso-Xfrmrs to his system.
More impact and 'slam', better mid range definition and resolution, added tinkle (a technical term if ever there was one) on top, and yet another 'veil' has been lifted.
And I suspect all of these contributions to become more pronounced as I continue to mod this unit.
Oh, and my body simply can't stay still, even on speakers. HB&W and T3 big time…

So far I'm only using the Iso-Xfrmr to power my amp and dac, while the rest of the digital gear is being fed by the dedicated audio ac power feed.
This provides an added degree of isolation between the digital gear and the amp and dac, except for the ground connection.
I will probably reverse this just to see if the digital gear will respond to this balanced power delivery as well.

I've even tweaked the shape of the wires used in connecting to the IEC connector for maximal contact patch.
And there is another related tweak inbound as well, along these same lines.

This series of experiments has led to some additional insights that I'll write up and post after I gather a few more observations.

But the SQ is just amazing, no matter if it's peaked or not.
IDMA (It Doesn’t Matter Anymore) continues to be amazing as the non peak SQ continues to rise.
But when it peaks,
well it's one of those things that really is only understood from direct experience,
as in words just fail to convey the experience.

JJ

 

[astrostar59]

Hi John
I agree. I got a PS Audio P10 2 years back and never looked back. Before I got it I noticed I preferred the sound of my system in the early hours, about 1am-2am. I eventually realised it was mains noise from heavier use in my district during the day, and also stuff on in my house or block such as AC, Hairdryer, Power Tools, Wash Machines. The P10 regenerates the AC from AC - DC - AC. It is about 75% efficient, so not save the planet, but I only need 20% of it's capacity most of the time.

Noise again John, it is like the SMPS thing we went through on the Rednet and LPS's. It seems to me the audio manufacturers know this stuff, but don't tell us.... because they don't make a regenerator.

 

[Golfnutz]

"So I re-terminated that 10gauge romex run into an IEC connector which then plugs only into the Iso-Xfrmr.
It delivers 1.09/1.75 KA to my iso-xfrmr (according to my ASCC tester).
Yes that's 1,090/1,750 Amps (depending upon if the ground wire is used in the test)."

JJ, I hope you mean KVA (as in 1750 watts).

Like you, I have a 10gauge wire direct from the panel into my listening room, connected via Hubble twist lock. The iso comes standard with the Hubble twist lock and Hubble receptacle - medical grade (2.4kva/20A). I also have another iso for my digital equipment in the back room (1.5kva/15A), with Hubble IEC and Hubble receptacle plugged directly into panel receptacle, which is also 10gauge and Hubble receptacle (distance of receptacle to panel is less than 6"). Iso's are ECA.

I wouldn't say the differences with and without are night and day, but having them does seem to make my system sound somewhat smoother.

 

[johnjen]

"So I re-terminated that 10gauge romex run into an IEC connector which then plugs only into the Iso-Xfrmr.
It delivers 1.09/1.75 KA to my iso-xfrmr (according to my ASCC tester).
Yes that's 1,090/1,750 Amps (depending upon if the ground wire is used in the test)."

JJ, I hope you mean KVA (as in 1750 watts).

Like you, I have a 10gauge wire direct from the panel into my listening room, connected via Hubble twist lock. The iso comes standard with the Hubble twist lock and Hubble receptacle - medical grade (2.4kva/20A). I also have another iso for my digital equipment in the back room (1.5kva/15A), with Hubble IEC and Hubble receptacle plugged directly into panel receptacle, which is also 10gauge and Hubble receptacle (distance of receptacle to panel is less than 6"). Iso's are ECA.

I wouldn't say the differences with and without are night and day, but having them does seem to make my system sound somewhat smoother.

The ASCC tester calculates current. So those readings are in amps not watts.
But keep in mind that those are peak amps in an 8ms time window as per the ASCC test.
I wrote about this 8ms time window in my posts about fuses and how they are rated.

That 8ms time window is most significant and is tied into our (US) AC mains line frequency.
And granted if your line frequency is 50Hz then that 8ms 'window' becomes 10ms so the potential for even greater peak current exists.
And if you have 220-40 VAC as your primary line voltage (which cuts the amount of current needed by ≈ 1/2 given the same load) these amounts of available peak current become even less critical.

I have even thought of using a Iso-Xfrmr as a step up to 240VAC and modifying the wiring in my amp and dac for this voltage, which would drop the peak current demand by ≈ 1/2 as well. But performing this series of mods would have 'consequences' some of which could have 'consequences' of their own.

And yeah the sonic results aren't a night and day, OMG slap you upside the head sort a change, but when the system has had lots of CP's removed, these sorts of improvements can be heard as VERY meaningful.
More so than one might expect.

JJ

 

[johnjen]

Hi John
I agree. I got a PS Audio P10 2 years back and never looked back. Before I got it I noticed I preferred the sound of my system in the early hours, about 1am-2am. I eventually realised it was mains noise from heavier use in my district during the day, and also stuff on in my house or block such as AC, Hairdryer, Power Tools, Wash Machines. The P10 regenerates the AC from AC - DC - AC. It is about 75% efficient, so not save the planet, but I only need 20% of it's capacity most of the time.

Noise again John, it is like the SMPS thing we went through on the Rednet and LPS's. It seems to me the audio manufacturers know this stuff, but don't tell us.... because they don't make a regenerator.

I too hear 'better' SQ late at night, but some of this is due to the house being quieter both acoustically and electrically, not to mention my mind is also quieter then.

I have wondered about using an AC power regen unit.
And perhaps I might try one at some future point, but the power we have here in the PNW and specifically Seattle is remarkably stable and free from 'noise'.
And my house is ≈ 50' away from a brand new step down transformer on the pole outside.
And my audio system, which is powered by a dedicated line from my panel, is ≈ 35' away, so my 'setup' is nearly ideal in terms of power delivery.

And I have wondered what these regen units can provide in terms of short duration peak current delivery, which seems to be a rather important factor in attaining optimal SQ.

And I do agree that if noise that is created and is present in sufficient quantity in our gear, it does impact the SQ, and by quite a bit.
But our gear generates (especially digital circuits) a fair amount of noise, and I'm thinking this self generated noise has a greater impact on our SQ than much of the external ac power noise that 'comes in on the power line'. Much of which is taken into account by the input power circuitry of the gear itself (mov's, caps, inductors, even the transformer).

And a regen unit can't really address this gear created noise.
And neither can these Iso-Xfrmrs, but they can help to isolate one group of gear (digital) from another (analog), by using several of them, with the sole exception of the common ground that ties them all together.

Besides all of this fussing with wires and such is grist for the mill of this hobby and can tend to keep us out of trouble…
Well except for our bank accounts and spousal approval anyway…

JJ

 

[Golfnutz]

OK, now it makes sense (*not the peak amps), but the iso xfmr you bought. I wasn't sure if it you purchased a 500VA or 1.75KVA iso xfmr.

*I'm not sure how relevant peak amps are in this type of application. I would think 500watts on a 15amp circuit would be what most people would be interested in.

 

[johnjen]

Yeah a 500VA Iso-Xfrmr is more than enough for headphone gear.
In fact I'm using all of ≈ 120VA for my amp and dac.
And if I were to add all of my digital gear, it would only add ≈ 30-45VA, max.

In my research the ability to deliver peak amps seems to be way more significant than mere watts, especially for our low powered HP systems.
For high powered speaker systems it is also important but their 'need' for big current pulses can easily out strip the branch circuits ability to not limit these short high current demands.

I recently obtained a current probe that I will use to measure actual current flow in real time of these current pulses.
I figure that these results will provide some deeper insights into all of this and help put much of this in a better perspective.

JJ

 

[johnjen]

Balanced VS. Singled Ended Means of Signal/Energy Transfer

In the mean time while I gather further observations and, as this Iso-Xfrmr continues to settle in (along with 2 more mods to add), this subject has ‘popped’ out as a consequence of these latest experiments.
And this missive presents my answers in more detail, why I prefer the balanced signal/energy transfer mode of operation vs. the single ended approach.

When I first looked into the idea of using an isolation transformer, which creates a true balanced power feed for the gear plugged into it, I wondered about current dump ability, as per the ASCC tests I had performed and posted previously.

These ASCC testers require that both the Neutral and Ground be at ground potential.
And since balanced power uses both the ‘hot’ and ‘neutral’ equally to provide 120VAC to the load, this essentially means the hot is only 1/2 hot and the neutral is also 1/2 hot, as such this arrangement of ac power delivery is not going to work with the ASCC testers I have.
Which would leave me with only being able to listen for results and not be able to measure them.
But I have a plan…

But this is getting slightly ahead of myself.

There has been an ongoing ‘debate’ about the benefits (or lack of same) of using a Balanced (Bal) vs. ‘Single Ended’ (SE) means of transferring electrical signals/energy from one device to another.
Not to mention any benefits of the gear itself due to ‘handling’ a balanced signal vs SE signals.

‘Normal’ Bal circuits are more ‘complicated’ and thus usually require more complex designs which usually equals more parts and thus more cost.
Whereas SE circuits are (or can be) much simpler and so usually less costly.
There are exceptions of course.

So why are Bal circuit designs considered ‘better’ by some?
And if they are going to be more expensive to purchase, does this mean it necessarily results in ‘better’ SQ for the entire system, to help justify the added cost?
The short and simple answer is no, not always, not necessarily.
There are some excellent SE designs just as there are some excellent Bal based devices.

So why is Bal still widely used, and for some, the preferred means of passing the signal along?
For me it comes down to my approach for the entire system, and is not just based upon which device is better at a specific function.

Passing signals/energy in a Bal mode has inherent advantages over SE methods.
Some of which really don’t apply, such as being able to deal with much longer runs of cable.

But then there is the whole concept of using 2 wires to actively pass the signal along, instead of using one active and one passive wire to perform the same task.
And there are significant differences in the connectors themselves which are used between these 2 methods of signal transfer.

The ‘standard’ SE connector is the ubiquitous ‘RCA’ connector which started life as a quick and dirty solution as a means of providing signals for testing and calibrating. And by my way of thinking they are a poorly designed connector and in multiple ways. And yes the implementation has improved remarkably over the years, but still the basic design is weak.

The ‘standard’ Bal connector is the 3 pin XLR connector. This is a robust and well designed connector meant for pro audio use, which means it will hold up to abuse and the rigors of prolonged use.

But the biggest single advantage that Bal has over SE is the use of 2 ‘active’ wires vs, SE’s use of one ‘active’ & 1 ‘passive’ wire.

So what do I mean by ‘active’ vs ‘passive’?
Just this, an active wire has EMF ‘behind’ it to ‘drive’/induce the voltage and current thru the wire.
In contrast, a ‘passive’ wire (usually a ground) has no (or Very little) motive force to ‘drive’/induce the voltage and current thru the wire.

The ground while being defined as 0 volts usually has ‘residual’ voltage riding on it, but it has very little EMF to provide a voltage potential to ‘drive’ the voltage and current thru the wire.
In addition ground is itself being modulated from a variety of sources, such as the power supplies themselves, not to mention all other circuits that dump ‘noise’ onto the ground plane.
Which means ground, supposedly at 0 volts, is subject to various other voltage influences, this is a source of variability since SE circuits ‘stand on ground’ so to speak.

So in SE mode the hot circuit pushes and pulls the signal/energy, while the neutral/ground is used as a reference or sink to ‘ground’ that the voltage from the hot/signal/energy circuit can push and pull against.
It is purely passive and provides no additional ‘power’ to help control the circuit itself, and so only 1/2 of the circuit is available to provide power, and thus its name, Single Ended.
But in Bal mode both wires are equally ‘driven’ in a complimentary and synchronized fashion. Which in turn means that ‘full’ power is available to drive the circuit under load.

An analogy.
Take a piece of string and tie a rubber band to one end and thumbtack it down on a table.
Now grab the other end and pull on the string.
You are both pulling and pushing on the string while the rubber band is passively allowing itself to be pulled and pushed solely based upon what you are doing.
And to take this one step further, lets imagine the thumb tack is stuck to a chunk of wood which can move.
This can induce ‘stray’ or extraneous changes in the accuracy of the input (our arm) and output (where the string is located), which can result in a lack of precision.

Now remove the rubber band and hold both ends of that string and keep it taut.
Now you have 2 hands that can actively pull and push that string with more than just twice the power and control.
There are 2 active sources of power that are balanced with relation to each other, which yields much greater precision and control over the delivery of that signal/energy.

This is the advantage that Bal has over SE in terms of delivery of that signal/energy.
There is much greater control and potential EMF behind ALL of that control in delivering the signal/energy.

And as I stated above “When I first looked into the idea of using an isolation transformer, which creates a true balanced power feed for the gear plugged into it, I wondered about current dump ability, as per the ASCC tests I had performed and posted about previously.”
And thus far my early observations are that I need not worry about current dumping capability, as it’s not a problem, at all.
And like my analogy of using the string, when the power is delivered with an equal (balanced) amount of power behind both wires, being able to dump current is enhanced.

So by using a simple (and fairly cheap) isolation transformer, the delivery of the ac power is enhanced in such a way that results in changes to the SQ which are very similar to using a dedicated branch circuit.
And when used together the best of both worlds can be realized.

This is a demonstrable demonstration of how, when well implemented, a balanced circuit can make a significant increase in overall SQ.

And to top all of this off, and to help provide some deeper insights into all of this, my plan is to use a rather special contact based current probe with my scope to actually see and measure the current pulses inside the power supply of an amp.

With this capability I’ll be able to compare different power delivery setups directly to each other.
I’ll use a wimpy appliance cord, a DIY reference G-4 power cable, among other cables on both SE and Bal ac power feeds.
I’ll also be able to look at different portions of the power supply of the amps demand for power, namely at the primary and secondary of the power transformer.
And I’ll be able to test fuses as well, in fact I have several types of tests I plan on investigating to see if I can observe differences in current draw by changing a single parameter, one at a time.

I’ll use my old Schiit 1st generation Mojo amp as a test bed with shorted inputs and fixed resistive load on the outputs.
I’m figur’n this setup will provide an even better measure of the current behavior and demands than my hand held ASCC tester, albeit with increased resolution comes added complexity.

And all of this testing will be done on a low current draw, test bed amp, that draws ≈ 40 watts at idle.
This set of conditions is probably very close to the edge of even being able to differentiate what subtle changes in cables, fuses, and power delivery schemes can make to the current demand and flow inside the test amp, in the first place.

So hopefully I’ll be able to focus in on some changes that correlate well with the changes in the DUT (device under test) and the draw some conclusions after factoring in the resultant changes to the SQ I hear.

Oh Yeah I’m hav’n some fun now…!!!

JJ

 

[BIG POPPA]

So Yeah I got the Iso transformer. Have a SR Black receptacle on one side, Cardas Rhodium on other. Furutech Rhodium IEC inlet with fuse holder/ with SR Black fuse w WA Qu chip. And Transformer WA Qu chip> My cables are tweaked, gear is tweaked. Always in a state of improvement.

So here it's been a month since my last post and there is news to report.

The system continues to push that 100% ceiling ever higher, and even when the system isn't operating at peak SQ the HDSuperDuperGlue effect is still grabbing me and not letting go.
The last several nights I have seen the early dawn rise at 5am.

And finally after 1Khrs the system peaked and set new all time 100% SQ levels.

But then BigPoppa said, again, Hey JJ, ya gotta try this, it REALLY helped…

So as a consequence BigPoppa and I are 'exploring' using a Chinese made torroidal based 500VA isolation transformers.
Its $125 (+$60 shipping), fairly compact and has an on/off switch, built in fuse, and 2 duplex receptacles.

And of course since it's me, it didn't stay 'stock' very long.
Thus far I've added a WAQy chip to the fuse and played around with using several different short ac power cables to feed it.
So far I like my gen-4 DIY cable the best, even over shorter larger gauge 'stubby' cables.