Phono stage and preamp overload

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.

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.

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.

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!

Or on the other hand, let’s over think things a bit too :)

Yes, 66dB gain on top of 0.5mV results in exactly 1.0 Volt output. You did the math correctly! In reality, there are some additional factors to account for:

1. Loading a cartridge (increasingly lower load resistances on the phono stage) will start to lose some of that source signal as the load resistance approaches the cartridge’s DC coil resistance. This is because of Ohm’s law. For example, if you had a 5 ohm coil cartridge (e.g. your Dyna is 5 ohms) and you fed it into a phono stage loaded at 10 ohms, the voltage would be divided such that only 10 / (10 + 5), or two-thirds of the cartridge’s voltage, would be available to your phono stage. That represents a loss of -20 * log(2 / 3) = 3.5 dB of signal from your loading, which is reasonably significant. It’s also why there’s a rule of thumb "load resistance should be AT LEAST 10x your coils" so that this loss is limited to well under 1 dB. In your case, 10x would be a 50 ohms loading. However I’ve gone lower than 10x, and it can sound fine in certain situations until you start going below 5x (other bad things start to happen besides the signal loss, like a changing frequency response). This is also the reason why stacking a SUT (step-up transformer) into another SUT won't get you anywhere - the net gain starts to move backwards from the loading losses.
2. It’s hard to represent the output level of any analog device with just one number. Your cartridge will be able to put out much greater peaks than that 0.5mV. Some say up to 10x more. That’s why it’s OK to do the cartridge & phono math, but you need to leave a lot of room for overhead. MC is right that for preamps you generally have the volume control guarding the input stage, which helps protect its circuitry from overload (i.e. you just set the volume lower as necessary). However some preamps could be configured differently, with an input stage and THEN a volume control - these would be susceptible to overload.

In your case, a 1V "typical" output from phono stage is fine. Usually your concern should be overload margins within the phono stage itself, not the downstream preamp. But sliced a different way, your 66dB gain on 0.5mV is LIKE 20dB + 46dB which is analogous to a 5mV MM cartridge (20 dB is 10x which takes 0.5mV to 5mV) into a 46dB MM stage, which is quite normal. Either 66dB or 60dB is likely to be optimal for your system.

I also agree with MC that most cartridges over $1K these days can sound excellent. Proper installation and system matching are crucial, as always. And Koetsus are particularly lovely. And for the money, I’ve also become a particular fan of the current Benz lineup (Zebrawood L, Ebony L).

Well the stuff you have listed there is excellent. I would lean Koetsu but in truth once you get much over a grand it is hard to find a bad cartridge and a good one at this level is really good. They do keep getting better but already you are at a level where it pays big time to put that cart on a top flight arm and table. Frankly the table and arm are more important. Especially once you have an excellent phono stage, which you do.

(I’m not sure if this is what you have or what you’re considering?)

What table and arm are you using?

Thanks, millercarbon.  Truth be known, your passion for analog and distaste for digital factored in to me going down this path.  Your input/insight is much appreciated.  Best,

You are seriously over thinking it. Especially since overload is much less likely than having too much. Your typical phono stage with 45 to 65 dB gain will output a normal 3 or so, right in the sweet spot of your preamp input range.

The volume range on virtually all preamps is so wide it just isn't a problem. Almost always, the worst that will happen is you have to turn the knob a lot more, or a lot less, than with your line level sources. This is where you stop and remind yourself, the position of the volume knob means nothing. It is nice if all the sources are at about the same level, because then you don't have to fiddle around as much. But that is pure convenience and nothing to do with sound quality. Do it a time or two, you will see.