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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 (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2021 at 12:02pm
The weighting of tonal balance is proportional to magnetising current.

The best results without resorting to other design mitigations were from a 80mA I-mag laminated transformer, which buzzed like crazy.

The best results after resorting to numerous design mitigations were from a 14mA I-mag toroidal transformer.

When the mains voltage falls by only 10V with the 14mA I-mag transformer, the weighting of tonal balance is upset cutting the bass end. This is because the magnetising current has fallen (considerably) along with the voltage drop.

Now, if we add the mains offset caused by Candy washing machines (we've had two, so I know it's them) to the fluctuating mains voltage that seems to happen on Sundays (240V instead of 250V - the workshop mains comes from the meter tails, so the only impedance is the 100A meter shunt).

I am pleased I now know, by measurement, exactly what's going on. It isn't very nice, considering that an EU implementing measure says the Candy group mustn't do it, but I will do my best to work around it.

There is no such thing as DC offset. What happens is that the current on one half cycle is offset by half wave rectified heavy current demands by reluctance devices such as washing machine motors.

Arguably, neither is there any such thing as DC. It is either from an AC derived rectifier, or from a battery. The latter discharges!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2021 at 10:55pm
After further transformer studies, I decided to try an RS 2 x 50V secondary, 100VA laminated transformer that was surplus to earlier adventures in this topic.

One of the first things I managed to do was kill one channel's meter and blow the channel fuse, by not looking what I was doing. The fuse was replaced and the amp was set up on the analyser and the abused channel was no different to the other, and so no damage - apart from the meter - was apparent.

The reason for trying the transformer was because it measured a large magnetising current compared with the toroids. I expected the case to really hum, but without getting my ear up to it, I can't hear any.

S/N was obviously compromised by 5 or 6 dB, but at listening distance it's unheard.

Insufficient transformer watts (VA) was demonstrated by the amp only reaching 35WPC. By rough calculation, I think it would only require 120VA to reach more than 40WPC. The problem here is the size of standard laminations and going up in size means the transformer would be too large to fit the case.

So, I will run the amp like this for a while, and then vary the mains supply voltage down via the Variac to see if the SQ worsens. My aim is to secure good SQ at any voltage between 230V and 250V, and if that is so, then I could try and find somebody to make a more suitable laminated transformer - that fits the case!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Nov 2021 at 8:39am
It would seem that all our transformer manufacturers are having such a lovely time winding things for the green revolution, that 20 weeks for a prototype is becoming the norm.

I suspect that I will be unable to complete this design, due to my eventual death, which looks more likely to happen before the transformer is finalised, based on the number of prototypes that tend to be required due to human error, and then there's the lead-time for them making a batch for production.

Silly me, I should have considered the three score and ten before embarking on this project, having started it at the age of 63! Now 66, I don't think I have sufficient time left!!!

By the way, it can be made to work with RS Stock No. 504-111, provided circuit modifications are made such that it only reaches 35WPC.

I try to imagine this situation in 1976, when a trip just across the county line, led to Mr AC Ainsley pointing me to his pal just down the road, who made a lovely 5A EI laminated for him, enabling me to complete my disco amp, while disco was still in fashion!

At least then I lived in the age of can do - will do, sadly no more. Angry


Edited by Graham Slee - 25 Nov 2021 at 8:41am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 2021 at 10:13pm
vector diagram
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 27 Nov 2021 at 3:19pm
Please explain the significance ...am lost 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 27 Nov 2021 at 3:44pm
Current flow in Dual rail is symmetrical, in single rail it is asymmetrical with regard to positive and negative flow.
Just listen, if it sounds good to you, enjoy it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 27 Nov 2021 at 7:13pm
I love the analogy and respect the work done to get there. The scientific method.
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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