New Posts New Posts RSS Feed - 1970s Design Indulgence
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Welcome to the Graham Slee Audio Products Owners Forum

 

Open to all owners plus those contemplating the purchase of a Graham Slee HiFi System Components audio product and wishing to use this forum's loaner program: join here (Rules on posting can be found here)

This website along with trade marks Graham Slee and HiFi System Components are owned by Cadman Enterprises Ltd

1970s Design Indulgence
 Post Reply Post Reply Page  <1 236237238239240 345>
Author
  Topic Search Topic Search  Topic Options Topic Options
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2022 at 9:59am
The first watt theory seems quite elegant until analysed.

Using my old trusty (and dusty) SPL meter - the cheap looking one most PA system installers used - I measured the average music level from my speakers and from the manufacturer's specified sensitivity, found it was 1/4 watt.

It just so happened that the "optim-meters" on the amplifier said the same thing.

So then I played a same level referenced continuous tone (1.2kHz because I lost my 1kHz file), and it measured 13dB more.

13dBSPL is 20 times more output, so are the loud bits of the music really 20 times 1/4 watt?

And if so, it suggests that 5 watts is where the optimum distortion should be adjusted to.

So this is my 5 watts hypothesis for the 11th October 2022, and I will spend some time with the amplifier on the analyser and see if it makes any sense.
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2022 at 8:33am
Wires do in fact have magnetic fields surrounding them, but they're not the shape of fields like the ones that grow crops or cows roam in.

Or are these electrical fields or "I" fields, or "H" fields?

Unfortunately for those who think they can separate out all these fields, physics gets in their way.

A circuit contains all these fields and to prevent one interfering with another and another interfering with one, and all the rest of them, would probably require the circuit to be expanded to the size of a real field!

Then you'd have carloads of other problems like resistance and inductance defeating the circuit's operation.

And if not shut out, there's all the other magnetic fields happy to induce themselves into these resistances and inductances.

However, once shut out by surrounding the circuit we want, using electrical shielding that serves the purpose, and extends out to its signal source by using common-sense (which seems awfully rare these days), we then investigate how connections inside the box can muck things about.

Edward. M. Cherry (Dr.), studied and explained mutual inductance within circuits, but there are other ways of understanding inductance, and hearing aid users have a switch which lets them pick up audio provided by a hearing loop.

This amplifier's circuit boards use Dr Cherry's layout principles to separate high and low current sections, using its supply rails, such that currents flow with the least mutual inductance of other currents.

But then, wires must convey signals, power, and outputs.

Plonking a mains transformer inside the loop formed by the stereo ground circuit has a profound negative effect, at least on measured results. Things like that dictate a particular placement of the mains transformer.

Once correct, it matters little whether it's an E-I laminated transformer or one of toroidal construction.

It then becomes a matter of the routing of wires. Shall we screen the 3 inches between input sockets and the PCB? What beast inside the box could grab hold of the signal and do it much damage?

The input ground is taken to chassis, period. No other ground point should be taken to chassis, as it would create a ground loop producing the most dominant frequency, that of the mains, plus any oscillatory artefacts.

That ground therefore carries the corrective influences of the amplifier's negative feedback, intended to prevent all kinds of nasties. Should we really induce that into the fresh input signal?

Obviously not, but obviously not all that obvious to those who would insist on screening that link! Measurement soon puts paid to that notion as you see a not nice mains ripple on the signal.

A little knowledge is a dangerous thing because a little knowledge is insufficient knowledge.

Not that I know it all. There is forgetfulness, which is why some fools fear to rush in and jump to jumping conclusions. The better fools, that is.

And so I came to the bundling of the three ground wires and the HT wire, which seems to make sense, yet it didn't. I mean, they're one and the same to a.c. - they're actually joined at a.c. through the reservoir capacitors.

But here, you see, the reservoir capacitors are "point source", inducing one into another further away, adds a stray capacitance, due to the electrical fields around wires.

Separating them reduced the 2nd harmonic distortion by 5dB. Hardly surprising really, as the power supply in a single rail a.c.-coupled amplifier carries half wave class-B currents - which are asymmetrical - and asymmetry leads to second harmonics.

But, you see, there is still so much to learn, and a lot to try and remember.
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2022 at 10:05am
Yes, at least even I can understand with my gratitude for your considerate less technical terminology. 
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Oct 2022 at 10:36am
Originally posted by Sylvain Sylvain wrote:

Yes, at least even I can understand with my gratitude for your considerate less technical terminology. 

Dear Sylvain, your comment is very helpful in guiding the writing style I need to adopt.
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 15 Oct 2022 at 10:16am
It's been a week of nearly no progress yet again.

However, a manufacturer of old fashioned transformers reasoned that if you mount an E-I transformer on anti-vibration mounts, it should quieten things down.

I'm sure some will hear the magnetostriction noise, but I need a stethoscope - very quiet indeed!

So, by the looks of things, we'll end up with all our power supplies using old fashioned E-I laminated transformers.

What's that? Huh! Yes, you'll never buy anything from Graham Slee that's ultra-low noise. Beware sinad freaks, don't dare to venture anywhere near - you might be converted to music!

This sojourn has cost another delay of who knows how long. We only have three enclosure makers supposedly there to help us - by that I mean paid help - they make the money if only they could be bothered.

The main one we really need is so busy on tax payer funded projects, and this super simple enclosure design is too difficult for anybody else.

So today, let us pray for a Skype design meeting opportunity so as to place the holes in their new positions. Let us also pray for the miracles of 1. the machines then being available to turn out the two pre-production enclosures, and 2. that the crippled single remaining case finisher can produce an acceptable finish for us.

Because prayer is all we have left in the new Venezuela.
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 15 Oct 2022 at 3:51pm
Amen
Back to Top
Sylvain View Drop Down
Senior Member
Senior Member


Joined: 18 Jan 2010
Status: Offline
Points: 481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 15 Oct 2022 at 5:22pm
A further thought .....i still have a dense rubber material that was advertised as '' used to contain vibration in US submarine wall panels" and without naming the Manufacturer,  introduce the substance material denser to Sorbothane to support Ampfliers and large speakers. Could be useful to mount E-I transformer if heat does not degrade it's characteristics  
Back to Top
 Post Reply Post Reply Page  <1 236237238239240 345>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.156 seconds.