Hi all,
What is the best configuration for those first crucial one or two stages of an audio amplifier? I mean when you're dealing with the very low signal levels you typically get with phono cartridges (anyone remember them? - they're making a comeback!) in particular wrt to minimising noise and distortion? What's best for the front end? Are we talking long-tailed pair or something more involved? I'm well out of date on the subject.
cheers.
** For a regular, moving magnet phono PU, an RIAA pre-amp/equaliser stage using an audio op-amp like the NE5534 is hard to beat. Very low noise, very low THD and easy to use. You get two in the same pack if you buy the NE5532.
Couple of dollars a piece.
.... Phil
Google for "Douglas Self"; he did some good work in the 70s and 80s.
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It's been a few years since I rolled my own preamp, but, IIRC, the first stage (bipolar) should have low VCE and low IC for best noise. ...Jim Thompson
And it's all long-tailed pairs in the input stages.
Very tempting. But this is a personal project/challenge so I don't want it all done for me. Spoils the fun! I've got a stack of old toobz (EL83s?) that are fetching silly money on ebay these days (thanks to the
2nd harmonic distortion revival :)) that I plan to use in the final stages for that "warm toob" sound. Wouldn't seem right using an op amp at the front end under the circumstances. Wanna go retro.
For what it's worth there was a company years ago called PS audio that was renowned for their preamps -- maybe there's a schematic somewhere ?
The guys here are very sharp, but they are not mind readers. Couldn't you have mentioned these requirements in your OP?
Well, a 1960-style solution is a long tailed pair built from both halves of a 12AX7A.
Cheers
Phil Hobbs
Gack! Give me a solid state amplifier any day. But I'm biased, played clarinet in orchestra for many years, so I know what everything should sound like... for example, listen to a Mozart wood-wind ensemble on a toob amp versus a solid state one... the intermod on the toob amp will make the oboe sound just awful. ...Jim Thompson
The 12AX7 (even the "A" variety) is noisy as s*it!
A retro-chic 21st century solution would be to use a JFET and a lower gain and noise medium mu triode like the 12AZ7A, in cascode.
Of course it is. Better than most of its confreres, though, and Cusser wanted retro. ;)
Nuvistors such as the 6CW4 are surprisingly quiet, though. ~2dB NF at 432 MHz iirc.
Cheers
Phil Hobbs
The retro front end is 12AX7 / ECC83.
For the iron-wire 'music' you need the intermod ...
His audio design books are worth reading (just finished Small Signal Audio Design).
Although they wouldn't help the OP (solid state only).
If you can borrow "How to Gain Gain" by Vogel from your local library it'll sort you out.
The closest I get to iron-wire "music" is John Philips Sousa ;-) ...Jim Thompson
You're a punny guy. (biased)
"Small Signal Audio Design" by Doug Self, 2010 is another great reference!
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