preamp out instead of MC transformer

It's not a stupid question. Actually I think it's quite inventive.

Almarg should be nominated for sainthood for taking the time to give such a detailed answer.

I don't see gain/overloading as the biggest issue here. Head amps generally add 20-30 dB of voltage gain, and there are many line stages that add 20dB and a few more than that. The real issue is proper resistance loading of the cartridge. While you could use Y connectors to add a loading resistor, it would be in parallel with the input impedance of the preamp. This may or may not be a known quantity, and might vary greatly with frequency. Real head amps are designed to minimize these issues.

As long as you keep the volume down on the initial run, I doubt you can hurt anything by trying. If you've overloaded at any point in the chain it will become obvious in short order.

Ok, in my scenario, there is a line preamp and a MM phono preamp, 2 seperate preamps. In the old days, signal processors where used by hooking a loop into the line preamp. However, now that you mention it, I dont remember if it was from the preamp out to preamp in, or record out to record in. I am envisioning the MM phono preamp in the same location as the processor would have been, mainly to add RIAA equalization and gain. So the line would go from cartridge to aux input to line preamp out to MM phono preamp in to mm phono preamp out to line preamp in.

Actually, as I wrote this I realized I was thinking of an integrated amplifier that had a preamp in. I guess I would have to go from the MM phono preamp out to the amp.

The idea is to get the line gain and the mm gain to cumulatively be enough for a MC cartridge, but writing this has made me tired. too tired to think about it anymore.

Equalizers and other processors were, and sometimes still are, generally inserted into tape loops, which places them "before" the volume control. In some situations it might also be appropriate to insert a processor between preamp and power amp, or in the case of an integrated amplifier between the output of the preamp section and the input of the power amp section. That of course would put the processor "after" the volume control.

So the line would go from cartridge to aux input to line preamp out to MM phono preamp in to mm phono preamp out to line preamp in.

If the MM phono preamp is inserted into a tape loop of the other preamp, as I indicated earlier preamps often do not provide much if any gain between their line-level inputs and their tape outputs.

If the main output of the first preamp is connected into the MM input of the second preamp, then as you now appear to realize the output of the second preamp would have to go to the power amp, not back to the first preamp.

That arrangement would function, but it would also create the risks and sonic issues that I described in my first post above. As well as the loading issue that Armstrod pointed out.

The same cumulative gain could be realized, without most or all of the risks that I described, by simply connecting the turntable into the MM phono stage, connecting the output of that preamp into a line-level input of the other preamp, and connecting the output of that preamp into the power amp. The result, though, would probably be totally unacceptable hiss levels, because chances are that the signal-to-noise ratio of the MM phono stage would be inadequate for LOMC's.

Onhwy61, thanks for the nomination!

Regards,
-- Al

Seems to me, your question is not "stupid", but there are some factors to consider.

In concept, you just want a buffer amplifier with about 20 dB of gain (because that is the average difference bewteen MM outputs and MC outputs, a factor of ten) to put between the MC cartrigde and your MM phono input.

In theory, a line stage amp will give you this, depending on the design, and you would probably need to use its power amp outputs, because line level outputs like TAPE out will not have enough gain.

But, in reality:
(1) You need a second linestage amp to go from your phono preamp to the power amplifiers, unless its already got a gain control built in;
(2) You cannot use the same linestage amp for both functions as explained above;
(3) You will have noise problems because the noise floor on most linestage amplifiers is much higher that what is desirable for MC inputs;
(4) You cannot load the MC cartridge correctly if it is a cartrigde that requires a low input impedance such as 100 ohms. That being said, there are some high output MCs that can be loaded at 47K.

So if you have two linestage amps of execptional low noise performance, its possible, depending on the cartridge. But probably not practical.