Phono stage and preamp overload

Thanks you for the responses.  Always knew I could count on veteran Agoners for help.  

mulveling — Thanks for the details and additional considerations.  Every but helps, as I learn more about analog.

millercarbon — I have the x250.8, pre3, and xp-17 already.  Also have a pair of salon2’s, which I love.  I went a little on the lower (affordable?) end for table and tonearm but do plan to upgrade down the road, as funds allow.  For the table, I am awaiting delivery of an Avid Diva sp 2 and will start with an rb330 tonearm (likely the weak spot, but short’ish term).  Also awaiting delivery of the DV 20x2L.  Just getting my feet wet in the analog realm, so I’m sure mistakes will be made but I’ll learn.

Thanks again!

I am wondering how the attenuators on a linestage protect its inputs from overload. That doesn’t happen, because the attenuators enter the circuit after the signal. Any distortion produced by overload will be audible (if it’s of sufficient magnitude) regardless of the attenuators setting. It might be less objectionable at lower volume levels but it’s no less a part of the signal fed to the amplifier and speakers.

Upon further thought, I may be wrong. In a full function preamplifier (phono and line inputs) the line level inputs connect to the attenuators. So depending upon the type of attenuator, there would be an effect on overload. Sorry. For phono, the attenuators do not affect phono overload, is what I was thinking.

It sounds like you have solid info above ( a rarity!)

In general, people struggle with too little photo stage gain, especially from low output moving coils where the max may be something like 1/2 mV, rather than too much.

In the good old days, manufacturer’s targeted a nominal interface at the preamp line of 1V rms = 2.83V peak to peak. Today this has been obliterated, mostly by DAC manufacturers wanting to have their products double as preamps. 2.2 and even 6 and 10 (!)V rms are not unheard of. Yes, i’m talking to you Theta., Rant off.

But 1V is still a solid target. So a MM cartridge that has, say an 5mV peak output might require a phono stage with 1/.005 > 200X gain (@ 1 kHz) or 46 dB. Bingo. A MC with 0.5mV peak output would similarly require 10X more, or 2000X (beginning to see why moving coil amps must be low noise???) or 66dB.

A 10V overload (rms or peak?) is huge.

As noted, in the vast majority of preamps, the first thing the RIAA stage output signal sees is the (passive?) volume control. So the point becomes moot. EXCEPT!!!!! for those that first:

a) hit a buffer

b) have monolithic resistor arrays as a volume control (like my prototype*)

c) have other similar circuitry first

In high end, which values simplicity and a pure signal path these are rare.

* note: the monolithic chip has been a learning experience. As a postulated it is in fact superior to most conventional volume controls with huge UI benefits, but it also carries lots of pitfalls, this being but one.

Upon further thought, I may be wrong. In a full function preamplifier (phono and line inputs) the line level inputs connect to the attenuators. So depending upon the type of attenuator, there would be an effect on overload. Sorry. For phono, the attenuators do not affect phono overload, is what I was thinking.

Right ( I think i understand your point). Most of the time the flow is:

1. Phono stage with lots of gain and equalization -->
   100X -> 2000X @ 1 kHz
2. volume attenuators, which will lower this level commensurate with your desired volume level, and always therefore within the overload range
3. active line stage with a little amplification/gain, maybe 2-6X.

Its very rare to have too much phono gain. Its hard to get without noise and distortion, so most of the time one struggles for enough

Note there also may be a transformer at the very front end. Those are some fancy, expensive transformers.