PSU11/Phono11 - voltage drop

[NickG]

The blue trace in this graph is the 39k2 value, the other 39k. Maybe you could hear the difference.

http://www.lurcher.org/nick/images/phono-2k.jpg

[Paul Barker]

imhe the 39k2 is far superior 39k is awfully shrill, can't listen tuit for long, unless it's through a cd player when I'd have left the room already.

[NickG]

What have you been doing today Paul? It seems to have made you morose and lacking in humor. Maybe lead poisoning from two many bathroom jobs?

:-)

And yes, it was intentional.

[Black Stuart]

Hi NickG,
that's what I thought and said to Adrian. I think I will get some Rodersteins which are exact ratings.

Black Stuart

[JerryT]

Hello black stuart

If the tolerance on the resistors is 1% then nominal 39k resistors will have values that lie between 39.39k and 38.61k. 1% 39k2 resistors will lie between 39.59k and 38.81k. In theory 39k2 will give the 'correct' response - in practice the difference between 39k and 39k2 is likely to be very small. If you want to be that precise then you need to measure all of the components in the RIAA network to ensure the values in both channels are the same, and that they are all (capacitors included) at the calculated value.

I know what I'd do - but you must make your own choice!

Jerry

[Black Stuart]

Hi Jerry,
I measured the 3 series resistors (Tantalums) and they had drifted quite a bit. I have posted that I think bigger wattage resistors seem to drift far less. I would really like to find some 1W exact resistors. Why do designers bother to specify exact values if they are not important - are they, or not?

Black Stuart

[NickG]

The last think you need in the RIAA stage is resistors that drift, I would suggest that even more important than having a exact value, is having matched chans. Personally I have had good results using RC55Y metal film resistors from RS in the RIAA stages, they do the values you need and are 0.1% parts

[Paul Barker]

No my humour got so dark you didn't recognise it.

[NickG]

Despite the origins of the word, there is a difference between humor and psychosis

:-)

[Black Stuart]

Nick,
I had a look and could'nt see any 39.2 or 316, I'll have to have another look and yes you make an important point about channel matching.

Incidentally, RS used to be so easy to navigate and find what you wanted and some wally has changed everything just like BBC radio - if it ai'nt broke don't fix it - yes but new egos in control don't want to hear that.

Black Stuart