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1970s Design Indulgence

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Post Options Post Options   Thanks (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2019 at 3:05pm
Still sounding good after last tweaks. Fingers crossed!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2019 at 6:25am
Originally posted by Graham Slee Graham Slee wrote:

Still sounding good after last tweaks. Fingers crossed!
 

Clap That does sound promising! So you should have a Kit ready by Friday, huh??! 

Another Graham Slee Audio slice of nirvana for mass enjoyment! You're a Star ! 

Knew you'd do it! 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2019 at 3:31am
Originally posted by Graham Slee Graham Slee wrote:

Still sounding good after last tweaks. Fingers crossed!

Fingers crossed!Wink
Bruce
AT-14SA, Pickering XV-15/625, Technics SL-1600MK2, Reflex M, Lautus, Technics SH-8066, Dynaco ST120a, Eminence Beta 8A in custom cabs;; Using Majestic DAC
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jun 2019 at 8:56pm
The day after my last post I disconnected all workshop devices and appliances from the mains because I was on leave with the family. I always think it wise to do this if you're going to be away for a few days.

The amp was powered-up again on Tuesday afternoon and now it's Saturday evening, so it's had approximately 100 hours on-time.

So far it is the best subjective performance I've had out of it, and everything on Bob's YouTube channel sounds good, but as Bob could say, it all has YouTube compression.

So what is it like with a better source? I tried a couple of old Genesis albums: Selling England By The Pound and Foxtrot.

I used the Hana EL on the Technics SL12XX MkIII into the Accession MC/PSU1 Enigma with Majestic as preamp, and using the negative phase of the balanced output to the single-ended input of the power amp.

The tonal balance was pretty good, but I noted the smallest hint of of splash on cymbals and vocal esses.

Otherwise this was one of the best performances of these albums I've heard in recent times. In older times I've heard them a little better, with a bit more "drive" or "oomph" on tracks such as Watcher Of The Skies and Can Utility And The Coastliners.

I gave Queen 1 a try but stopped after a few bars. Whether it's the LS3/5A's or the amp I don't know, but I've heard better from a Rowe AMI jukebox. I have to be honest, both with myself and you, the reader.

Whether this is a burn-in thing or not will only be answered with the passing of time. The 220 pF dominant pole capacitor is a PFR5 type polypropylene and my experience with these suggests 100 hours is nowhere near enough. Those who believe a ceramic in this position will be just as good, ought to try doing my job. Within 50 hours the upper mid distortion they seem to cause is obvious.

Some might think the turnover point of the dominant pole capacitor is too far above audio frequencies to have any effect? Yes, but what about open loop? Negative feedback 'does its best' to reduce distortion but isn't perfect.

Just guessing here rather than opening up the simulator (as the test gear only reaches 80 kHz on frequency response), that if the crossing frequency is 3MHz, then with 77dB open loop gain, the open loop turnover frequency is 424 Hz.

The 25 watt Proprius (lower supply voltage) has a much higher Cdom open loop turnover of about 3 kHz, but stability margin due to this being a higher powered design isn't the same, so requiring a larger Cdom. The ceramic capacitor used in the Proprius has its open-loop turnover nearly 3 octaves away.

Also, we need to bear in mind that the mains transformers (the RS frame type), although being better from a saturation point of view, still draw considerable magnetising current, so saturation still comes into play.

I received an AnTek AS3450 toroidal transformer from the US, but I'm a bit loath to try it. It is 3.4 kg compared to the 2.8 kg of the Amplimo, but it has 2 x 15V additional secondary windings; a GOSS band; and an electrostatic screen; which might be contributing the extra 0.6 kg.

It is also 230V (115 + 115) which on 250V will be more saturated. It all depends on whether it operates at high fux density, and I don't want to make any judgments, but if it was low flux density I would have expected it to be larger, simply because it would need to have more windings. Take off the GOSS band thickness and it's almost exactly the same size as the Amplimo, and that failed to impress.

The AnTek spec includes magnetising current whilst the others don't. At 140V 60Hz it's 34mA which is quite impressive, but what will it be at 50Hz? Looks like I'll have to measure it!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jun 2019 at 9:41pm
And now at 150 hours it has taken on an addictive presentation.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John1479 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jun 2019 at 7:26pm
Originally posted by Graham Slee Graham Slee wrote:

And now at 150 hours it has taken on an addictive presentation.

That's a post I've been waiting to see. I have been following this thread, like many others I'll hazard, from afar with fascinated anticipation. Smile

When John Sampson rebuilt my A1, he was very specific and insistent that 300hrs was the marker for full performance to reveal itself. Somewhere around 307-310 hrs sure enough the sound bloomed into a remarkable cohesive picture, deep and colourful. = Big Smiles. Big smile 

Not wanting to throw a Jinx nor push the bar further. But I reckon, all else being equal, it can only get better.

All the best for a smooth and resounding Triumph. Clap




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jun 2019 at 8:26pm
It is increasingly looking likely to be the transformer type which is dictating the results this early solid-state design is capable of. There is no doubting the configuration's capabilities, but if it is transformer influence it can now be seen how this configuration fell from grace.

1. Styling: slim line cases became the fashion in the 60s and 70s. Laminated frame type transformers simply would not fit in a two inch high case.

2. Profit: easier and cheaper to manufacture once the machines to make toroidals came upon the scene. With the still clean AC supplies prior to all the mains pollution of today there wasn't the problems associated with 'DC offset' there is today.

3. Negative Feedback: with heaps of negative feedback available due to technical advancements in circuit design needed to achieve the best written specs for the marketing departments, transformer influence can be hidden BUT the price has been a considerable increase in brightness, sold as being "better".

4. Noise: hum could be reduced without resorting to regulated power supplies.

5. Increased circuit density: much more can be packed in right up to the edge of the toroidal transformer without suffering ill-effect.

Except, it hasn't really done anyone any favours, except the valve amplifier manufacturers, and alternative solid-state technologies: "digital amplification".

Two simple off the shelf RS transformers have beaten all the toroidals and now my bench looks like a toroidal transformer graveyard.

Further proof is of course required, and that starts with further measurements of transformers, and the commissioning of two prototype higher quality laminated frame transformers.

But what a waste of time it's been. The consensus is that toroidals are better, but valve amp transformers are still frame type...

11 months to get to this realisation.

It could be worth the mention that all these old solid-state amplifier designs used frame transformers, but was that really a clue? After-all, back then that was the only option.

Along the way lots of components may have been falsely blamed, but then again some deserved it. The transformer has not been to blame for everything, just most of it.


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