Random questions....

[cjnuk]

Hi apologies if these have been covered before, couldn't find any references by search and just ignore me if they have!

2 questions which I would love to know other's opinions.

1/ Expensive mains leads. With some of these costing well over £1000 is there really any point to them when, once plugged into to a standard household ring main, are they not then at the mercy of whatever wiring has been used there and are therefore no better than the twin copper and cheapest possible hardware that is normally used? ie no chain is stronger than it's weakest link?

2/ I have a pair of KEL80 monoblocks and re reading the old reviews I hear;

"The output stage is four EL34/6CA7 valves in parallel push pull, class AB. There is a good chunk of Class A available for regular listening levels, with the clout of 80 Watts available for musical peaks and annoying the neighbours."

I always understood Class A meant the output valves were continually conducting and provided all the output rather than just the +ve or -ve parts, so how is this achieved with a push/pull arrangement please?

Thanks for your patience!

Chris

[NickG]

To simply put it, they overlap. If you can understand load lines there is a great Steve Bench series on PP lines. But assuming not.

Imagine the output pair with no signal. both valves are passing (for example) 20ma, the net result at the transformer is 20-20 = 0. Now a signal comes along, on the positive part of the signal, valve one increases conduction, and passes 30ma, a 10ma increase. valve 2, reduces conduction by 10ma so passes 10ma. So the transformer sees 30-10 = 20. But note both valves are still conducting. And on the nagive part of the signal, the same, in reverse, so the transformer sees 10-30 = -20.

Now a bigger signal comes along, valve one now passes 50ma, but this amount of signal will cause valve two to shut off, as it cant go below 0ma. So only one valve is conducting, its out of class A, and the transformer sees 50-0 50. And the same for the negative part of the signal. Now its in class B.

But you note that the point it passes from A to B means that only one valve is providing the output (its not a hard change, the other valve doesn't just stop, it starts to be harder to get it to go to 0v), so the gain is less. in A a signal that produces a 10ma difference in the valve produced 20ma ourput, in class B the 50ma signal produces only 50ma output, so gain is halfed. Also as only one valve is driving the load the valve see's alters, and all sorts of things take place. Thats why this normally has a feedback loop around it to smooth out the change from A to B.

Hope that makes some sort of sense.

I am not going to touch 1. I have some ideas, but not worth repeating :-)

[Scottmoose]

No idea about the amps -not my field. Re the mains cable, I'm with you that a piece of wire is hardly going to have any effect whatsoever on the quality of the mains. OTOH, a shielded mains cable does make sense in that it should stop it introducing a load of hash into unshielded, or weakly shielded interconnects. Although a) they shouldn't have to cost much: £100+ is outrageous. And b) if an interconnect is unshielded, or weakly shielded, then IMO it's not fit for the purpose it's being used for, and should be introduced into my good friend Mr Bin in favour of something worth having. Balanced is best. Semi-balanced better than regular unbalanced.

If you must, don't spend a fortune. Try this: http://www.maplin.co.uk/module.aspx?...4118&doy=10m12 £30 from Maplin. Heavy shielding, decent quality plugs. There are cheaper 'hifi' leads out there, but this is the cheapest I know that actually has something worth having in its construction.

[NickG]

OTOH, a shielded mains cable does make sense in that it should stop it introducing a load of hash into unshielded, or weakly shielded interconnects

In that case, why not just keep them apart?

[Scottmoose]

Not always easy. Hense the reason I hate unshielded wire carrying weak signals. Just my view of course, but I like to minimise potential problems whenever possible. Maybe I should live a little.

[John T]

Originally Posted by NickG

In that case, why not just keep them apart?

Of course!!

The purpose of screened/plaited mains cables is for rejection of RFI.

[cjnuk]

NickG, that makes perfect sense and thank you for taking the trouble to reply, I shall sleep soundly tonight!

Chris

[Deep South]

Scotmoose,
are you talking from theory or practice?

I am conducting an ongoing exercise in wires for i/cs and PCs.

Power cords can most definately have a profound effect on the overall quality of sound from a source. How this happens I don't know.

Many years ago now there was a thread on the WAD forum about making your own homebrew pcs. Being dissappointed in the sound of a newly bought h/amp, I decided to try using one of these homebrew pcs - the difference was incredible AND it was unsheilded.

In fact, on other forums there is definately a majority opinion, from practice that wherever possible unsheilded i/cs and pcs are to be preferred, solely from the one perspective that counts - how they influence or rather how they best let the signal pass through. Those against are almost always theorists, who are too frightened to actually conduct experiments.

I and another user of this forum are exceptionally pleased with the clarity and emotion conveyed by - 20 AWG solid core silver/plated copper i/cs. It maybe that a different gauge wire might be even better, possibly 24 AWG.

I tried using this unsheilded wire as phono outs from my TT but there was just too much hum.Now I am looking for sheilded solid core.

It does seem from my experiments that stranded i/cs just don't have the clarity or emotion of s/core wire.

When it comes to power cords, it would seem that stranded silver/plated copper is very good. I made up one using plaited 20 AWG st/s/plated copper in conjunction with the i/c oulined above with my Badah/amp - a wonderful liquid sound. With instruments sounding just as they should.

I should mention that all the wires used were mil. spec. I don't think you can compare wire bought seperately and sheathed in Teflon tubing, this maybe part of the success using these wires.

When I have found the best combination, I need then to look at power conditioners. However this will not be so important for me once I am producing alt. energy - which of course will not be coming from a utlity company source with all the **** that comes with it.

Black Stuart

[Scottmoose]

Originally Posted by Deep South

Scotmoose,
are you talking from theory or practice?

Both. Never heard a difference between powercords (except in the aforementioned condition when it elimiated interference), never seen any scientific evidence that proves otherwise either. Then again, if you find they make an improvement for whatever reason in your system, then great. Now power-conditioners I can certainly see the merits of. I love the idea of using an alternative home-generated energy source for power though. Best of the lot IMO that, providing you can get sufficient current. Instantly removes the junk that ruins the regular mains source.

Different gagues of wire certainly make a difference in any application -might be worth experimenting with this. If you can find it, try 36AWG in the interconnect. A couple of years back when I was playing with cables that's exactly what I did (semi balanced with triple shield). I was running Nelson Pass Zen amps (Son of Zen with modified Zen line-stage) at the time, so as always YMMV.

Regards
Scott