mV output from cartridge, please explain

The rated output of a cartridge (such as 3.0 mV, or 0.5 mV) is the voltage of the output signal, usually based on the stylus tracking at a specific rate (for example, 5 cm per second). Moving coil cartridges usually have voltage output of less than 1.0 mV (although there are a few "high output" MC cartridges with output of 1.5 mV or so). Moving magnet cartridges usually have output levels in the 3-6 mV range (although a few may run higher).

The output level of the cartridge will determine how much gain, measured in dB, that must be provided by the phono preamp or step-up transformer. Usually, moving coil cartridges need about 60dB of gain from the phono preamp (before the signal goes to the main preamp), and moving magnet cartridges usually need around 35-40 dB of gain from the phono preamp.

The voltage needed to drive your main power amp is determined by the output voltage of the linestage preamp, not the output of the cartridge / phono preamp combo.

How it relates to real life is related to the output voltage times the amount of gain that it is subjected to all along the signal path. It starts out at, say 1mv, and then goes into a phono section. It then goes thru the gain stages of amplification and the voltage is increased by whatever value of gain those amplification stages have.

That's where the rubber hits the road. You have to have enough gain to bring the voltage up to the point where you can drive the input of the amplifier to full volume. This spec is called the input sensitivity of the amp. If the input sensitivity of the amp is 2v, then the maximum output of the preamp must be at least 2v in order to drive the amp to maximum output. If the gain in the phono stage and linestage added together do not generate the full 2v, then the preamp will not be able to drive the amp to max level. This could happen when the cartridge output is lower than the gain stages can increase to the 2v level. So you have to have enough cartridge output to supply to the preamp to allow it to amplify it enough to drive the amp to max. If it is too low, then you have to crank the volume wide open to get decent listening levels. If it is too high, then you can barely crack the volume controls and it gets real loud. Also, if it is really too high, then you can overload the phono section inputs and cause distortion.

The reasons that it is hard to just give a flat figure for this, is that all phono stages and linestages have different gain specs. Some are high, and some are low. In addition, many amps have different input sensitivities, so a front end that may work perfectly on an amp with 2v input sensitivity would be way to hot for an amp with 0.3v input sensitivity.

The best way to calculate this is to take your cartridge output voltage, and figure out what gain amount is needed to provide the necessary output voltage to match, or slightly exceed the input sensitivity voltage of your amp. This way you will know that you will be capable of driving your amp to full volume with the voltage that comes from your preamp output. Then compare this gain figure with the specs for gain in your phono stage and linestage combined.

Thanks guys. I understand all that but it still doesn't answer the question. It is impossible to do the math (peak output voltage of system = peak voltage from cartridge times total gain of system) unless you know the value of all three variables. To calculate the peak voltage out of the amp I need to know the peak voltage I can expect from the cartridge.

I know how much voltage my amp puts out at full power, or I can easily figure it's sensitivity if you want to go that route.

I can add together the gains of the different components I am interested in to get the total gain of the system.

What I don't know is the peak output of the cartridge. I know it is rated to put out a specific voltage (say 1 mV)when playing a certain test record. I know some records are cut hotter than others, but:

1. is this 1 mV the average it will normally put out when playing a typical record and the peaks are higher?

2. or is 1 mV the maximum voltage I can expect from that cartridge when playing a typical record?

3. or is it somewhere in between?

Herman, I don't know if it is peak or average, and I did a thorough web search, and couldn't find the answer. I think it is the peak output at a certain level of stylus excursion, but it don't know if that is the maximum level of excursion or not.

What I would do(and have done) is to use the given output spec for the cartridge, and use that as a max. If it is averaged and you get a little more out of it, that's no problem. The main problem is falling short.

I have my system set up right now with a little too much gain, so I have to carefully use the volume control. I'm not overloading my phono section, and it sounds good. I think I could cut 6db without any problem. I'd say better to have too much gain than too little, within reason.

If the cartridge were a Shure product very detailed specs are available on the Shure website. I don't know what your cartridge is so I don't know how they spec it.

Shure specs output as millivolts RMS, with sinusoidal groove modulation at 1000 Hz having a PEAK velocity of 5 cm/sec. Other manufacturers probably follow Shure's example.

Twl speaks of having the volume "wide open" as if this were a bad thing. Actually, the amplification circuits are always wide open, and the volume control cuts the ouput voltage down to the level you want. Ideally you would have just enough gain to fully drive the power amplifier with the volume control maxed out (which really means it is having minimum effect). Most rigs end up with the volume control between 12 and 2 o'clock when playing loud, which means that there is unnecessary gain in the system.