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1970s Design Indulgence

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2021 at 10:23pm
Originally posted by peterb peterb wrote:

Apologise, I was too brief with my post ....... Manufacturing Kit?

Even with the manufacturing equipment (even if I had the space), I doubt I'd be able to make a suitable transformer. I think it takes considerable skill and knowledge, or a lot of trial and error. It also needs a lot of materials, and willing suppliers. My experience in electronics manufacturing is such that I can guess the costs, then at least double it. The reel sizes are not what you'd buy from RS, and how many gauges of wire? The wrapping insulation tapes? The cores?

I'd rather somebody who does it for a living to benefit. Did I tell you what happened late '70s when I had difficulties getting printed circuits made? The cost to do the job right was £40K then! I ended up making PCBs for a living instead of doing what I wanted, which was amps. It was a waste of 7 years of my life. Mind you, these days, my board specs impress my PCB supplier! I wish I'd kept a photographic record of it all, you wouldn't believe it otherwise.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2021 at 9:39am
If you can't illustrate what you had, borrow somebody else's

pcb mfr

The brown and cream Dorniver Micromat CNC driller router, the under stairs position, and the "window wall" onto the processing section, are almost an exact match. The Micromat was £18,000 in the mid '80s. My extractors and compressor were piped to an external brick shed, to keep the noise down. Most of the "carcase" remains at Bridge Electrical, who took over the building. This image is courtesy of our current UK PCB supplier.

Making stuff commercially is quite costly in real estate, machinery and labour. The image shows about one fifth of the plant used to make a printed circuit board, and such a set up would be geared to making between one and three hundred boards - perhaps a thousand at a push.

Now add a few other processes that are required to manufacture amplifiers: the metalworking plant for making the enclosures for example. I think there's an image of a press brake somewhere in this topic. How about an anodising line? Oh, and the screen printing department (done that!) with all the photographic gear to transfer the artwork to the panels - and so on. A factory visit to a plant in Wetherby (used to be Farnell Instruments) would be an eye opener for the hifi enthusiast.

So to transformers, and the number of winding machines. Not something easily plonked in the garage. Every part of the process to make amplifiers and such requires an incredible number of processes. Now, I'm not one to boast, but my career has taken me through just about every part of the manufacturing process, either I did it myself on the industrial scale required, or subbed it to other factories. And when times got hard, I did it for Audionics, and since they went bust, I'm free to say so, because before they went bust, they threatened me with legal action never to say anything (nice people? NOT). And there's a witness to all this: John C.

The reason for including the Rotel transformer video, was to illustrate the complexities of amplifier manufacturing. To be able to do the entire manufacturing process such as the likes of Rotel, means you have to sell an awful lot of amplifiers! Now, we make 3,600 items a year, so in comparison we're "table top". So our rag tag combined square footage might total 500 sq ft., and that by comparison is "table top" and after a career that walked through the reality of industrial processes, where I had to make it financially viable, I think I've a better idea than most in how these things work.

To make quality hi-fi gear in the UK is hard work, and it's hard work because the politicians and the radical left lobby have made it that way. I have lived through the destruction from within - now everything is made in China. We're capable of doing it all in the UK, but not with the addiction to globalisation we have today.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 2021 at 11:55am
Thank you for the education .....and it is valued.

There is much talk to return  '' Re processing or repairing culture  from the Establishment. I have email some Transformer manufacturers in United Kingdom, most around the North East to tempt their enthusiasm to re-contruct my existing  ROTEL transformer with your specs.....when it is clearer.   
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 14 Oct 2021 at 8:46am
Terry's Transtronic-made toroidal transformer (TTTT) is now powering the amplifier. I will write to Terry at some point to discuss things further, if he's still willing to help.

You'll have heard of rotating toroidal transformers to obtain the lowest noise? Well, you have now.

With the aid of a noise meter, or if you saved your pennies and got a FFT trace (audio frequency spectrum analyser), like I did, you can usually see that the transformer interferes less with your electronics if you rotate it one way or another. This is because the stray field is not uniform within the transformer (as you've been made to believe), and it shoots out some stray fields from different points around its circumference.

Usually there isn't too much difference, and here, as it's for DIY, you can't be expected to own a £15 grand audio analyser, to be able to get the best results. I think, however, that Terry's design might not have been implemented to the nth degree (trying to put it mildly).

After switch on, and viewing the harmonics of a 1kHz fundamental, I saw the third harmonic had mostly disappeared into the noise. Wow, I thought, until I realised the noise had come up, and the third harmonic was drowning in it.

Out came the box spanner and, after loosening it, the transformer was gripped and turned clockwise and anti-clockwise by increments, while viewing the FFT. Like some "It's a Knockout" game, the amount of adjustment is limited by the terminations of the transformer's leads. Ultimately, I was able to get between 10 and 20 dB noise improvement, but not immediately.

Initially I could get a useful improvement to one channel, but not the other, and when I got them both the same, it was nothing to write home about. I eyed up the removable GOSS band another manufacturer had provided me with, and wondered if it might fit the TTTT. It was a bit of a faff, but it did fit quite snugly, and so I began again.

Back, forth, and back and forth, and the eventual result was 79/81dB S/N with the L and R FFT noise wiggles at roughly the same level. And then I put the lid on, and it was 77/82dB, so off came the lid, and back and forth - lid on and lid off, and eventually 81/81dB S/N was obtained 
(A wtd., but with a good FFT noise match).

As the DC operating point had been optimised several times before (and the A stage now has the voltage regulator), I left it untouched, and went through the motions of studying the harmonics at different output wattages.

I'd say that 0.022% THD at 44 watts, and 0.034% THD at one watt should be inaudible, so I was happy with that. Oh, and by the way, all the above was tried on the 240V primary tap, as well as the 250V primary tap, and differed very little.

I did have to micro-adjust the Vq and it's now 24mV emitter to emitter, which means it's on the cusp between class B and class AB.

So, onto the listening. Joe Walsh's Songs For A Dying Planet didn't sound so strident anymore, and his typically "forced" lyrical delivery seemed more relaxed. The bass was impressive. Next up was the new Yes Quest CD on the laptop style transport on my PC via Foobar 2000. The start of Ice Bridge was not very impressive, with bass boom hiding the instrumentation right at the beginning. Otherwise I was totally immersed, picking out nuances as you do when listening to a new album, on the umpteenth play - what joy!

Will it remain that way? With all my experience, I still cannot say, and time will tell.

As for the mucking about rotating the transformer, that is not on for the DIYer, and I think it best that I copy and paste this post as an email to Terry, and that we maybe get somebody else to build the next transformer?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 14 Oct 2021 at 7:30pm
Eye opening post. Trivially compared to Graham's work, some years back I rotated the output transformer in one of my guitar amps after a tip and it cut the induced hum. But I had no idea toroidals did anything like this.

Edited by Fatmangolf - 14 Oct 2021 at 9:08pm
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote discrete badger Quote  Post ReplyReply Direct Link To This Post Posted: 14 Oct 2021 at 9:13pm
Is there any practicality in using some sort of shielding within the case, to try to contain the fields? Or will that just lead to more problems than it solves?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 15 Oct 2021 at 7:11am
Originally posted by Fatmangolf Fatmangolf wrote:

Eye opening post. Trivially compared to Graham's work, some years back I rotated the output transformer in one of my guitar amps after a tip and it cut the induced hum. But I had no idea toroidals did anything like this.

I think the clue here should have been the third harmonic. Amplifier people generally measure using a 1kHz fundamental (for starters) and the third harmonic is therefore 3kHz.

Please note, I said field without qualifying what sort of field. So, what are the other frequencies other than 50Hz?

OK, let's ask another question: how pure is tap water (bearing in mind that purity is a concept)?

I was never educated in transformer design, the HNC taught transformers as being "perfect machines," but you can take that with a pinch of salt.

Terry specified evenly distributed windings, and I spent a few minutes peering through the insulation wrap, looking for them, and scratching my head.

Wires have inductance (20nH per inch), and I remember doing the "right hand rule" in Electrical Science, even though it's getting close to 50 years ago.

I'm sure I previously mentioned my incredibly large single-turn audio transformer? It used to be the Boots' beagle-smoking building - the ground floor was a lecture hall - and I had to oversee the afterthought hearing-aid loop installation. Even though it had a shorted turn (an architects steel monstrosity behind the rear seats) it worked perfectly all the way to the fuel station...

So, I'm in the hands of the transformer winder's mind, and if that mind is empty, then God help me!

TTTT noise

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