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Old 20th December 2006, 02:10 PM   #1
tmblack is offline tmblack  United Kingdom
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Default Any good Output Transformers from China?

Good enough for hi fi and cheap!
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Old 20th December 2006, 02:39 PM   #2
Klimon is offline Klimon  Belgium
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Definitely - there are some cheap Chinese amps with quite good opts (e.g. dynavox vr-70e), certainly considering the low prices. I bet there are lots of offerings on seperate Chinese opts in places like ebay. The shipping cost to the UK would defeat the purpose though.

www.die-wuestens.de is an excellent address for high quality/low price opts in Europe, shipping to Belgium is remarkably low so the UK might be cheap too.

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Old 21st December 2006, 10:02 AM   #3
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Mind some of the transformers sold for SE, some aren't gapped! I have a few here I ended up restacking...
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Old 21st December 2006, 02:49 PM   #4
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Default Re: Any good Output Transformers from China?

Quote:
Originally posted by tmblack
Good enough for hi fi and cheap!
You really mean the "worse for hi-fi" ?? Welded gaps isn't a proper technical solution for true SE as it bridges the gaps.

richj
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Old 21st December 2006, 03:19 PM   #5
rdf is offline rdf  Canada
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Quote:
Originally posted by Klimon
I bet there are lots of offerings on seperate Chinese opts in places like ebay.
Careful though, I just won an auction for a pair of beautifully built Asian no-name toroidal 5K SE OPTs. They were the last the seller had and won't come up again. He used them in at least two of his home amps, including a nice looking 300b. Nor did he ever hear complaints about those sold in the past. Since many don't measure what they build however no one seems the have noticed the trannies were improperly designed and can't seem to withstand any DC current. Bass was 2 dB down at 100 Hz with standing biases as low as 20 ma. Parafeed they work fine.
The brand name printed on the side is a company specializing in power transformers and custom work. My guess is someone fancied themselves an OPT designer and commissioned a run, selling them off when they realized the error (or not!) This seemed like an ideal auction win. Many pairs were sold in the past, typically for 2.5x what I paid, the seller's rating is top notch and yet the product is hooped.
Before going this route I recommend searching for prior experience with the product on this and other DIY forums.
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Old 21st December 2006, 03:51 PM   #6
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Quote:
Originally posted by rdf


My guess is someone fancied themselves an OPT designer and commissioned a run, selling them off when they realized the error (or not!)
Before going this route I recommend searching for prior experience with the product on this and other DIY forums.

Cutting between the lines.....the above this is buyers horror story to catchout the unexperienced.

Over 40 years I've fixed perhaps too many first time experimentor 10-20W kits which came with crappy output transformers.....still the most critical single item.

The UK has by far the most time-served and experienced audio transformer designers around still in their winding houses. History says it. The drawback is they want too much for their product.......BUT it is good quality.

richj
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Old 21st December 2006, 04:30 PM   #7
EC8010 is offline EC8010  United Kingdom
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You get what you pay for. A decent output transformer requires quite a bit of interleaving of primary and secondary sections. In other words, you wind a bit of primary, stop, bring out the wires, and wrap a bit of polyester tape over it. Then, using a different gauge of wire, you wind a bit of secondary, stop, bring out the wires, and wind a bit of polyester tape over it. And you keep on going like that, stopping and starting. That's a lot of work for a push-pull output transformer, with four secondary sections and three primaries in each half. Then, of course, you connect all your primary sections together to make the centre-tapped winding that the constructor expected and connect them to something more robust for the constructor (tagstrip or multicore flying leads). Having wound the bobbin, you need to stack the core, alternately for push-pull, one on top of the other for single-ended. If it's single ended, some tape needs to be added to define the gap. Now the shrouds can go on.

As you can see, making an audio transformer is labour-intensive, so paying cheap labour in China might make sense, but they would need to know how to wind the transformer and to exercise proper quality control (and use proper materials). The production runs are short so you can't save production costs by bulk buying materials.

Oh, and what about the cost of designing the transformer in the first place? Power transformer manufacturers generally haven't a clue about audio. There are so many variables in designing an output transformer that making good output transformers is an art, and it's partly gained by experience, so when you buy a good output transformer, you're benefiting from years of that company making and testing audio transformers.

The bottom line is that once the knowledge of how to make good audio transformers is lost, it is highly unlikely to be regained. So support your national audio transformer company and don't sell them down the river...
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Old 21st December 2006, 05:42 PM   #8
rdf is offline rdf  Canada
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Confirmed on all counts. Not only did the designer not understand the special requirements of DC current in a toroid, the finer details of winding seemed to have slipped through the cracks as well. Parafeed it was flat to 20 kHz but began rolling off soon afterwards, nothing special in general and fairly poor for this type of transformer. To be fair to the manufacturer, I'm sure they did an excellent job of building exactly what they were asked.
Still, at under $90 pair they'll probably make a real nice 6CW5 or 6BQ5 SE parafeed.
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Old 21st December 2006, 07:10 PM   #9
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This is interesting because I tookup a local designer (here in Switzerland) who said he could design a good quality p-p tube o/p tranny for me. (Never assume the person who one is dealing with has any clue) unless it's the designer himself and if you know something about making a spec; youv'e got him on hanging on the ropes). That's where the problem lies.
The company website claimed any transformer or choke could be designed.
SO I took them on. I provided a spec and within a couple of weeks heard no reply. So I was sure they were sweating over it. Then I got reply, "sorry I'm after isn't on the program",-> implying can't do it.
Same time I also submitted spec to a UK house down south and got same day reply and spec haggling started. The trade off is obvious, a 18 sect design takes more time than a 3 section and one has to justify specified leakage inductance v.s b/w and other winding issues.
Some designers still work all out with slide rules and maths. Others use a prepared computer program so the end product is prettywell anticipated and production reliable but can lead to cutting corners, i.e less iron, higher thd at LF cutoff freq and anticipated throughput power.
If the design justifies...a good designer who knows his salt will instruct self healing paper not polyester for interlayer insulation (lower dielectric capacitance)
Magnetics has always been portrayed as a black art when it needn't be. It's a pity that so many of today's science graduates lack the imagination of magnetics knowledge when SMPS is so closeby. Creating a specification is the single most challenging aspect for any engineer.

richj
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Old 2nd March 2007, 10:59 AM   #10
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I saw a bunch of beauties at VT4C .
Two different barnds, different prices (cheaper/dearer). I bought some parafarnelia from them but the Xformers look nice.
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