[mstef]

My MC cartridge is a .3MV output. Am looking for advice on the amount of phono stage gain I should be looking for. Why is too little or too much gain bad? or is it? Thanks for any help.

[Wayner]

You need a LOMC (low output moving coil) preamp that will produce about 60db of gain. Not enough gain, like putting this cartridge into a standard MM (40 db gain) phono-stage will be almost unheard. If you were to put a 5mv MM into a LOMC preamp set for 60db of gain, it would be way overdriven, resulting in huge amounts of distortion, caused by (a, too high of an input voltage, and (b, to high of drive current).

Wayner

[mstef]

Thanks Wayner. Would 55db be enough?

[Wayner]

Probably. Who's phono stage are you looking at?

W

[mstef]

Vista Phono 1

Mstef

[Wayner]

Vista website says it's got 60db of gain.

Wayner

[mstef]

Vista builds them with gain based on the cartridge output and recommended 55db for mine. I was just unsure about that number. Thanks for your advice! I think I should go for 60db.

Mstef

[BobM]

55 or 60db of gain would be minimal for a LOMC. I would suggest you need a tad more optimally, perhaps 65 or 70db to get those dynamics and kep the noise floor low.

[toobluvr]

55 or 60db of gain would be minimal for a LOMC. I would suggest you need a tad more optimally, perhaps 65 or 70db to get those dynamics and kep the noise floor low.

Isn't it kindof hard to recommend a fixed number?    Doesn't it depend on the gain in the rest of the system -- line stage gain, amp voltage gain, and speaker sensitivity?

For example, all other things being the same, a 20 db line stage might need 50 or 55 on the phono, while a 10 db line stage would need 60 db or more with the same cartridge.

Also,  if you have 103 db horn speakers,  don't you need less phono stage gain than with less sensitive speakers?

[BobM]

Well, for his .3mV cartridge you will need about 60-65db of gain to get you to a reasonable @2.0V output line level. For a 3.0mv output you probably only need 40-50db of gain. So it's all about the cartridge output level and the gain needed to reach a standard 2.0V line level signal.

At least that's how I understand it.

[mstef]

Thanks guys! I get it, not one shoe fits all. So if I'm manufacturing a  phono stage to a specific gain for a customer, I should be asking; what is your preamp gain and speaker sensitivity? Not just your cartridge specs.

There's got to be a practical lower limit on preamp voltage input regardless of  line stage gain / speaker sensitivity.

[toobluvr]

Well, for his .3mV cartridge you will need about 60-65db of gain to get you to a reasonable @2.0V output line level. For a 3.0mv output you probably only need 40-50db of gain. So it's all about the cartridge output level and the gain needed to reach a standard 2.0V line level signal.

At least that's how I understand it.

Ahhhhh!    I got it Bob.  I never looked at it that way.

Makes complete sense, but let me ask you this....
If you have a line stage with tons of gain.....or an amp that swings a lot of voltage (ie: sensitive on the input) .....or super sensitive speakers......can't you get away with less than a 2V source?

I could be mistaken, but I always thought that if the system is really sensitive or gutsy downstream from the source, then the source could be less robust than 2V.  Kindof like a tradeoff.

[Wayner]

Ahhhhh!    I got it Bob.  I never looked at it that way.

Makes complete sense, but let me ask you this....
If you have a line stage with tons of gain.....or an amp that swings a lot of voltage (ie: sensitive on the input) .....or super sensitive speakers......can't you get away with less than a 2V source?

I could be mistaken, but I always thought that if the system is really sensitive or gutsy downstream from the source, then the source could be less robust than 2V.  Kindof like a tradeoff.

You must first make the phono stage happy with the preamp. Too low an output on the phono stage means higher noise floor, loss of dynamics, regardless if the amp/speaker combo is high efficiency or not. Too much gain from the phono stage and the preamp overloads on dynamic passages. A small target window must be found that is a balance between noise floor and overdriving the preamp. His ideal gain window might be something like 62.5db, who knows. He obviously is having problems with it set at 55db and a higher gain setting is required. I'd start at 60 and work my way up. BTW, if the phono stage is clipping or having lots of noise because the gain is insufficient, the preamp will happily magnify those problems, cause it's job is to take little signal and make it into bigger signal. Shit in = shit out, only louder.

Wayner 

[mstef]

That's some excellent advice guys! Thanks.

Mstef

[Charles Calkins]

Wayner:
 Please try to explain something to me. I'm seeing that the cheaper Grado cartridges have something like 5mv
 The more expensive Grado cartridges in the wooden box have 0.5mv. The cheaper Grado cartridges in the wooden box have 0.4mv/5mv. I don't get it! I would think 5mv is better than 0.5mv. Sure is confusing!

                                                             Cheers
                                                            Charlie

[BobM]

The difference between 5.0mv and .5mv output are the number of windings on the coil. More windings = higher output. For a moving coil, where the coil is attached to the cantilever, this equates to more or less mass on the moving part. It is easy to understand that less mass on the cantilever equates to more speed and detail and likely finesse out of the cartridge, but at the cost of gain.

For a moving magnet or a moving iron cartridge the coils are not attached to the cantilever. So I'm not sure that there is anything to be gained or lost with a higher or lower output level, unless the magnet attached to the cantilever is itself different betwen the two. Can someone who understands these designs better chirp in here?

As I understand the 2 designs: MM carts use a tiny magnet moving between fixed coils to generate output. In a MI cart, both the coils and the magnet are fixed and a soft iron cantilever with the stylus attached at the end generates current by virtue of varying the distance between fixed coils and magnets. This I guess allows the whole cantilever assembly to be of much lighter construction, something that Decca reckoned was responsible for their claim of producing "highly musical cartridges" allowing faster dynamic response times and in the early days, less record wear than other designs. I guess that less damping needs to be applied and because coils can be fixed, higher outputs can be generated compared with either MM or MC designs.

So perhaps a lower output MI design shares the same speed and moving mass issue as a LOMC, vs. higher outputs in both designs. I'm guessing you don't see low output MM's because you just can't generate sufficient current with a smaller magnet (or put another way, a stonger field will result in finer degredations and better sound).

Another point to consider, the mass that moves on an MM is farther away from the fulcrum than with an MC (or a MI perhaps) and likely is heavier, making a MM slower due to a higher effective mass cantilever and requiring more inertia to move it. The effective mass needs to take in the whole length of the cantilever, not just the tip mass. It's the inertia of all the moving parts that equates to speed. This same principle applies to the tonearm's effetive mass. If the counterweight is closer to the pivot point the tonearm will be able to react faster than if it is farther away all the way at the end. So a tonearm with a higher effective mass could conceivably sound faster than a lighter tonearm with a weight farther away from the pivot point.

[mstef]

As a newbie to the circle, I want to thank all for your help. This audio community is so helpful and sharing. For that I am most grateful.

Mstef

[neobop]

I'm not an expert on Grados, but the LO ones will benefit from the "purer" sound associated with low resistance and inductance, assuming you can amplify it cleanly. They say all the wood bodied ones are better because of the fixed cantilever. Not sure about the moving mass, but it sounds plausible.

Stanton and Pickering made LOMMs. It can be done, but I've never taken mine apart. On the other hand, Audio Technica is said to make the only true MMs. You can see the 2 tiny magnets attached to the cantilever. The better ones certainly don't sound slow.

RE: Gain. Yes a satisfactory amount does depend on your system. There's not only a dramatic difference between speakers, but how about line stages? Some have 20dB, some 10dB, and a passive has 0. There's no 1 right answer. As Wayner said, you need enough not to compromise the S/N, and not too much that will overload your input.

[blakep]

You must first make the phono stage happy with the preamp. Too low an output on the phono stage means higher noise floor, loss of dynamics, regardless if the amp/speaker combo is high efficiency or not. Too much gain from the phono stage and the preamp overloads on dynamic passages. A small target window must be found that is a balance between noise floor and overdriving the preamp. His ideal gain window might be something like 62.5db, who knows. He obviously is having problems with it set at 55db and a higher gain setting is required. I'd start at 60 and work my way up. BTW, if the phono stage is clipping or having lots of noise because the gain is insufficient, the preamp will happily magnify those problems, cause it's job is to take little signal and make it into bigger signal. Shit in = shit out, only louder.

Wayner 

Bingo.

I've been using 103R's for about 4 years now. 2 of them-well actually 2 1/2 as my current 103R has actually been retipped.

Denon sends an individual test spec sheet and both my 103R's spec'd slightly  higher in output (about .29 or .30 mV) than the stated .25 mV output. So it's possible that you could have a cartridge that might output a bit more than it's spec'd but I'd say you have to proceed based on stated spec unless you have the individual spec sheet for your cartridge already.

What I can tell you from experience is that my 103R's work best with about 60 db of gain. Your equipment might be different but that's what works here based on experience and I can tell you that 55 would be not enough and 65 would be too much.

Coincidentally, FWIW, that is exactly the number that the KAB phono gain calculator (bottom page of phono preamps page on the KAB website) on the kabusa.com site gives you. It has been virtually dead on with any cartridge I've ever used.

[BobM]

I've solved the correct gain problem by using a Hagerman Piccolo step up. There are 3 gain settings you can choose from. Sometimes I find the 20db boost to be sufficient and sometimes I use the 26db boost. So I guess my optimal setting is probably somewhere between the two, but it's only an extra click & a half on the volume control one way or the other.