audio-talk

cressy wrote:being having a good read of this
http://www.platenspeler.com/background/ ... und_1.html

Apologies to all but apart from being difficult to see, the first part at least sounds like cobblers. The Wikipedia page is pretty vague as well. The low frequencies are NOT attenuated to "prevent the needle jumping out the groove" :

"The RIAA (Record Industry Association of America) characteristic, which is [also] embodied in British Standard 1928:1955, specifies that a record groove is cut [initially] with constant amplitude modulation, from 20 Hz to 500 Hz. Played back by a magnetic pick-up cartridge, the output signal voltage amplitude then rises at the rate of 6dB per octave, or 20dB per decade. After 500 Hz it is cut at constant velocity - [for which the cartridge output voltage is constant at all frequencies above 500 Hz. This is the original EMI standard. The superceding Decca standard is the same, but with the addition of] - "treble pre-emphasis, which comes in at about 2123 Hz. The net result is a replay curve with an average rise of just below 6dB/octave over the entire spectrum, with a small 'step' at the middle frequencies."
- Gordon J. King, Audio Equipment Tests

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well the gain should be 63 for both stages, id say slightly less as i upped the cathode resistor on them to run them at about 5ma rather than the 6.5 it shows for class a1 so probably a gain of about 60

didnt read that bit myself, i was looking at the spice models he'd done on his circuits. does sound odd though, the needle jumping out of the groove. cant see that happening. i thought is was so that they could actually fit a reasonable amount of music on the disc.

Well, I don't know if its the result of constant amplitude or low end cut, the result would be that without the curve the HF signal would either be so quiet it would disappear below the noise level, or the grove displacement would restrict the number of turns you could fit on a side. And I think the stylus would have trouble tracking the excursion.

As Nick says the RIAA is an attempt at a constant amplitude cut or a close approximation to one.

There was a Stereophile? article, that was very good.

-- Andrew

Third attempt at saving this post!

Yes I think so, aided by that the faster the stylus moves, the more output signal Voltage.

As for the constant amplitude part, it's exactly that as far as I can interpret. Don't forget most cartridges the ornary bod in the street was using would've been crystal, (or 'ceramic') having not had much to do with any for years but IIRC it doesn't slope off below 500 Hz like a mag one does. Or not as much ~ as I say can't remember!

Well the old integrated amps of yore while they had phono inputs for mag pick-up, if it were a crystal pick-up it'd be shoved straight in the high impedance sockets, at least 1 megohm, which were flat response. Same basic input as for other inputs. You then trimmed it a bit with the tone controls if necessary.

The Decca pre-emphasis bit is simply to improve signal to noise ratio, but that's the bit you gotta take off even for a mag cart. Hence the smaller of the two caps in the EQ network.

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got my nuvistors today, very very tiny, theyre only about 15mm tall by about 8mm across. got my jbe slate turntable too, but got the bestest thing at 4.15 in the morning, my little baby boy!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

elliott andrew cresswell

luckily we were home in tome for the postie.

no sleep though since 5.30 am sunday when i got woken up by my other lad. need sleeeeeeeeeep

Well done Ant ! (not that you did the hard work. )

Which of our two Andrews has the honour of sharing his name with Elliott ?

Why is it always at night

Great news, hope all are well (or as well as can be expected).

Congratulations...

congrats Ant, all the very best to you all......

ps Elliot is top of our list of boys names at the mo...good call!

cheers guys, the andrew is after my best mate who i built the el84 amp for, elliott wasnt my choice, i wanted luke, but who cares, hes got all the right bits in the right places and elliott seems to suit.

all three of them were born at stupid o'clock in the morning for some reason

Congrats !

I too have an Elliot - (first name Leo after Mr Fender ) , and his Mum chose Elliot

I like it ...

All the best to your family..

Rgds
Pete

cressy wrote:.....but got the bestest thing at 4.15 in the morning, my little baby boy!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

......luckily we were home in time for the postie.

The postman brings likkle baybees? I'm sure MrI told me it was a stork.....

Congratulations to all the Cresswells

DTB

I thought we were talking about valves!

Still, maybe there is something more important. Well done to Mrs Creswell; you had it easy, young man.

Congrats to the pair of you!