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View Full Version : Is THIS the Achilles heel of changing to UK spec the power supply of USA-gear?



Neil McCauley
14-07-2008, 10:48
Good morning colleagues.

Every now and then, as a temporary ‘civilian’ I buy equipment from North America, via eBay. Depending on the time available, either I use a heavy duty step-down mains transformer, or I get the power supply replaced. Items that I’ve done this to have been the STAX CA-X preamp, various Levinson preamps and so on. And a US-spec Meridian 601 digital preamp.

I didn’t realise until very recently - catalysed by a passing comment by a UK audio engineer with over 30 years of hands-on sleeves rolled up experience to date, that all of the US made items were somehow disappointing whereas as European units which had been sold into the US and then imported by me had, as best I could tell, worked precisely as they should.

The passing comment he made, and I should point out that this was in relation to vintage US-made kit, was that changing the power supply to UK spec was all very well, but because every component after that point was “expecting 110v” is was not sensible to automatically assume all would be well. His implication being is that while it would work, e.g. no hum, etc, it just would not perform as it was originally intended.

If indeed this is the case, and I have no knowledge in this area with which to contradict him, then not only does this explain my consistent disappointment with all converted US-made vintage items, but that this is a useful point to note for prospective buyers.

Any observations, comments or thoughts on this? These would be most welcome. Thanks. H


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Prince of Darkness
14-07-2008, 11:03
The passing comment he made, and I should point out that this was in relation to vintage US-made kit, was that changing the power supply to UK spec was all very well, but because every component after that point was “expecting 110v” is was not sensible to automatically assume all would be well. His implication being is that while it would work, e.g. no hum, etc, it just would not perform as it was originally intended.


Not sure where he's coming from here, the components after the power supply don't get 110V anyway (unless that is the specified HT). If the PSU is properly specified for the mains supply then the output voltages and currents will be the same. In practice we do see wrongly specified transformers which will effect the voltages to some extent. I wonder if the different A.C. frequency will have an effect on the performance of filtering components (60Hz U.S.A. 50Hz Europe)?

Neil McCauley
14-07-2008, 17:32
The previous issues of the PS Audio Mains Regenerators did have a facility to switch frequencies by increments up to 100Hz. They told me that this was abandoned after considerable in-the-field experience in that while in the short term noticeable improvements in the sonics could be achieved by increasing the frequency, long-term the disadvantages (odd bass characteristics for example) meant that there was no overall improvement.

Meanwhile Helmut Brinkmann told me that some of his customers with very sophisticated German amplification were using devices that brought the frequency up to 120Hz with no unfortunate effects.


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MartinT
15-07-2008, 18:49
I think the point being made is based around how the transformer is switched between 115VAC and 230VAC. Voltages after the transformer should be the same, with a caveat. When a transformer is designed for both markets, there are two windings which can be connected in series or in parallel. Commonly, the windings are connected in parallel for the US market and in series for the European market. The mains current draw for US equipment is therefore twice that of European equipment, but of course at half the voltage (so the power input remains largely constant).

The caveat is this: the best transformers are designed for a single job, a single frequency and with a magnetic flux range in mind. It is entirely possible that a dual-voltage transformer is a compromise and not ideal in one or both regions. The solution would be to replace the transformer in American-sourced equipment with a dedicated 230VAC unit providing the correct output voltages at the necessary rated current.

None of this should matter with more modern switched mode power supplies.

By the way, the problem with European spec PS Audio P-300 regenerators was that they included an additional step-up transformer to derive the 230VAC output, thus compromising regulation. I have one, but the Premier is much, much better.

MartinT
15-07-2008, 18:54
They told me that this was abandoned after considerable in-the-field experience in that while in the short term noticeable improvements in the sonics could be achieved by increasing the frequency

The Premier works completely differently by tracking the mains waveform and constructing a perfect replica. It can therefore only create a 50Hz waveform in Europe (or 60Hz in the USA). The big win over the P-300 and similar, though, is efficiency since they make the power supply rails track this waveform closely. That makes for low heat output and high efficiency.

Neil McCauley
15-07-2008, 21:41
The Premier works completely differently by tracking the mains waveform and constructing a perfect replica. It can therefore only create a 50Hz waveform in Europe (or 60Hz in the USA). The big win over the P-300 and similar, though, is efficiency since they make the power supply rails track this waveform closely. That makes for low heat output and high efficiency.
Agreed!


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StanleyB
16-07-2008, 11:34
I didn’t realise until very recently - catalysed by a passing comment by a UK audio engineer with over 30 years of hands-on sleeves rolled up experience to date, that all of the US made items were somehow disappointing whereas as European units which had been sold into the US and then imported by me had, as best I could tell, worked precisely as they should.

The passing comment he made, and I should point out that this was in relation to vintage US-made kit, was that changing the power supply to UK spec was all very well, but because every component after that point was “expecting 110v” is was not sensible to automatically assume all would be well. His implication being is that while it would work, e.g. no hum, etc, it just would not perform as it was originally intended.


The poor chap needs to cut off those sleeves and go and lie down for a while. He has been working too hard.
The reality is that the transformer is there to convert from a high primary mains supply to a low secondary mains supply. That secondary supply is then rectified and fed to the various parts of the circuit.
What is important is to note that 220V/2 = 110V/ and 240V/2 = 120V. That's roughly a 10% difference between 220V and 240V. If you fit a 240V transformer that then raises the rectified supply by 10%, some equipment might fail to work properly. An amplifier would have to have its bias and voltage offset re-adjusted. A phono stage on a higher DC line might no longer follow the RIAA curve, especially if it is an opamp design.

Neil McCauley
17-07-2008, 17:00
I wonder if the different A.C. frequency will have an effect on the performance of filtering components (60Hz U.S.A. 50Hz Europe)?

Apparently yes - according to a well known valve amp engineer of my acquaintance who wishes to remain anonymous because of unfortunate rude and ignorant comments on the PFM forum. Tried to persuade him that this forum was composed of civilised and far from Neanderthal contributors who rarely mention Naim. He remains currently unconvinced.

Anyway, he believes that the different frequency is quite probably the major contribution to transformer saturation in imported valve amps from the USA. So … we might be getting somewhere.

He then exited, leaving me (us?) with the following conundrum. Logically, any piece of audio equipment will perform best at one specific mains frequency – and not necessarily the one is was designed to accommodate. (he’s talking here of step variables between 50Hz up to 100Hz). Other than carefully listening, how might one predict which optimum frequency that is? To date, he has been unable to develop an algorithm to solve this.


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StanleyB
17-07-2008, 18:39
Anyway, he believes that the different frequency is quite probably the major contribution to transformer saturation in imported valve amps from the USA. So … we might be getting somewhere.

Which transformer? There are more than one in a valve amp.

Mike
17-07-2008, 18:49
This is becoming absolutely FASCINATING!.... I am becoming more and more interested in trying some form of mains regenerator! :scratch:

Any volunteers around who would be willing to let me have a go? :eyebrows:

MartinT
17-07-2008, 19:22
Which transformer? There are more than one in a valve amp.

We are discussing the mains transformer. The output transformers in a valve amp perform a very different role and are called upon to be flat in response from 20Hz - 20kHz, so their design (to couple the high voltage / low current output from the output valves to current hungy speakers) make quite different demands.

Mike
17-07-2008, 19:41
Or how about interstage transformers?