Re: 30 Hz > 15KHz , 8 W rms , only £ 2477 for 2 .. Valve of course

[Spike]

Interesting comments.

It might be worth noting that that hum-dinger was invented in order to get round a problem that noticeable at the time.

Modern low-noise systems can be expected to be very much more sensitive than those of ~75 years ago, and might be subjected to effects that were undetectable back in those days. Could it be that bonding the neutral line to earth unbalances the mains wiring, leading to residual effects that could be detected?

The ADSL broadband system works as it does because the two-wire system is balanced. Adding imbalance at the consumer end, an all-too-often occurrence, can lead to severe MW pickup at night, and during the day if close enough to a MW transmitter, leading to some combination of lowered noise margins or connection speeds.

[Brian Gaff]

When I were a lad, this was the cheapest way to get full wave rectification.

Only two diodes needed, but wait, maybe these are special Russ low noise matched diodes?

Brian

[Brian Gaff]

Is this not the latter day equivalent of selling dodgy medication off the back of a handcart? Brian

[Brian Gaff]

But we went through this when the op amp principal was used and then one accident with an input and bang goes a speaker coil and possible half the power devices in that side of the amp.

Brian

[David Looser]

Do you actually mean "sensitive"? (i.e.. the input signal necessary for full output) in which case modern domestic audio systems are no more sensitive than those of the 1970s. Or are you saying that, being low-noise, hum will be more apparent? But amplifier noise levels have more than adequate for decades too, it's the background acoustic noise levels in homes which matter here, and they have, in general, got worse in the last 50 years or so due to higher levels of traffic noise etc.

Well of course it unbalances it! That's the very definition of unbalanced!

What "residual effects" did you have in mind?

The telephone system has used balanced wiring since the 1880s, for very good reasons. But here we are talking about a power supply. Mains transformers inherently reject common-mode noise so it's hard to see what benefit running balanced mains to an amplifier could have.

If you can come up with either a properly thought through theory as to the benefits of balanced mains (not a "could it be... residual effects" kind of half-baked hypothesis) or, better still, real evidence of an audible improvement I'd be interested to see it. But if not.......

David.

[Spike]

I meant 'sensitive' as 'being able to detect ever smaller signals and any previously unrecognised effects'.

I know that. The 'could be' was a bland way of leading on the main point, which was:

E/m fields affecting electron flow in valves (seen that enough times) and perhaps conduction processes in semiconductors (not a field I'm interested in). Doubtless there are others.

I am, like you I suspect, not an expert in low noise audio systems.

I've no intention of coming up with 'a properly thought through theory', and I suspect that if you could, you would have done so before now. But to take the line that because you can't think of something that has not yet been detected simply isn't a viable methodology. The reverse is usually true: LHC, anyone?

[David Looser]

Funnily enough many of the *real* audiphools will tell you how much better audio is with the technology of the past. Not just valves, but directly heated triodes, real 1930s technology.

As for "smaller signals", the dynamic range of audio really hasn't changed that much. The limits on "smaller signals" is set by the limits of human hearing and the acoustic environment in which we live. And, "unrecognised effects"?, when was the last occasion a previously "unrecognised effect" was found to matter in audio?

Care to elaborate?

I thought not :-) But if you think there's something in it give it a go, buy a mains isolating transformer with a centre-tapped secondary and try it out. Let us know how you get on.

The whole field of audio is simply crawling with half-baked nonsense There are audiphools who fall for this crap and shysters like Russ Andrews prepared to fleece the gullible in order to make a quick buck.

Not in the case of audio it isn't. Real advances are few and far between, bogus claims like this are ten a penny.

What on earth has the LHC got to do with it?

David.

>

[Woody]

Ah, so what. I still have a copy of the Radio and TV valve and transistor data book which has page headers for Geranium transistors!

Maybe an early version of flower power?

[Brian Reay]

If you rectify AC you replace the 50Hz sinusoidal "hum" with a 100Hz "rasp". True, you can regulate and filter but anything left will be more "hash" and probably more in the hearing range of the ear.

As the audio guys who have joined this thread have generally acknowledged, a lot of this "noise reduction" is in the sphere of counting angels dancing on pin heads.

[Lordgnome]

Ah, I did that many years ago - it was a hybrid. The unit was a microphone mixer and I used cascode triodes for the front end - decent low noise transistors had yet to be invented. I fed the heaters via a stabilised DC supply, using an OC35 and a zener. The result was great. Absolutely no hum and the noise figure was within 3dB of the theoretical. That was in the sixties. The unit is still in service.

Les.

[Jim Lesurf]

Yes. And in addition to that, much of recorded/broadcast music in recent years has become level-compressed, etc, to occupy far smaller dynamic ranges that even half-decent home electronics can handle. Then stir into the mix the use of methods like mp3... Chances are that most people are listening to music that never needs anything like the dynamic range that their hearing could handle, let alone that of a decent audio amp.

Slainte,

Jim

[Jim Lesurf]

IIUC yes some valve amps have used dc heating to avoid 50 Hz injection.

However in some designs/devices that means that more of the cathode current may come from one part of the cathode than another. So IIRC some then have to alter the polarity every now and then to even up cathode aging.

Yes, IIRC some designs still use direct heated cathode valves. Although I'm no expert on 'modern' valve audio amp design so someone else can perhaps fill in these details who knows more about the designs.

Slainte,

Jim

[Brian Reay]

I'd be curious how "bad" the hum would have been without the DC feed in Les's design.

I used to work with a "HiFi nut". He'd buy almost anything to get the sound right. He spent more time listening to test sounds than he did to music.

I saw (or perhaps heard) the same when someone should me some flash Bose system. It came with a CD which was, essentially, birds in a jungle. The sound was impressive- the birds seemed very real, almost to the point if being disconcerting.

Personally, I prefer to listen to music and, while we've a pretty good set up (Creek amp), it isn't "top of the range" and I confess I'd struggle to claim it was better than a cheaper system (from Richer) in the dinning room.

[David Looser]

That has been done, much pro-audio kit made in the valve era used d.c. to feed the heaters of valves in the early stages of microphone amps, tape recorders etc.

Big power valves with directly heated filaments have heavy filaments and were intended to be a.c. heated. If you run them on d.c. then the characteristics change as one end of the filament is more negative (w.r.t. the grid) than the other, and so carries most of the current. With a.c. the most negative point changes over the mains cycle from one end to the other distributing the current flow much more evenly over the filament. At the sort of signal level these valves run at induced hum from the filament wiring isn't a problem.

Of course d-h valves intended for battery operation *must* have d.c. filament supplies.

David.

[Clive George]

If he's got any nous, said electrician will charge you special audiophile rates and ensure he uses degaussed pliers, cutters aligned with the local magnetic field and balanced consumer unit labels.

[Laurence Payne]

Oh, I don't know. You could be getting on with something intellectually stimulating in the next room rather than having to actually TALK to the bitch!

[Jim on the crappy lappy ...]

like at a glory hole then? .......

[Jimbo Jones ...]

he has the cheap model ? .....

[Arny Krueger]

DC filaments were not uncommon on tubed preamplifiers. Even fairly basic gear like the Dyna PAS-3 had a rectifier and a filter cap for the filaments.

Many other vendors did this as well here's an archive of H H Scott equipment with several examples:

examples.

In the old days the rectifiers were selenium, and therefore physically large.

[David Looser]

"Frank Turner-Smith G3VKI" wrote

Are you asking whether the filament pins of battery DH valves are marked "+" and "-" on the data sheet? If so the answer is yes.

David.