preamp out instead of MC transformer

Not sure why you said "back into the preamp in." To have any chance of working, it seems to me that the output of the second preamp would have to go to the power amp.

Given that, while it is conceivable to me that the idea might work with certain components, in general there are all kinds of things that could go wrong. Depending on the specific designs significant concerns would be that dc offsets, turn-on transients, and/or turn-off transients produced by the first preamp could be amplified by the second preamp to potentially damaging levels. Low level hum that might arise due to ground loops involving the two preamps could also be amplified to very high levels.

If all of those problems could be avoided, it is probably more likely than not that the signal-to-noise ratio of the first preamp, with respect to its line-level inputs, and/or the gain of that preamp, would be too low, resulting in unacceptable hiss levels.

All in all, it might work under some circumstances with some components, but I don't think it is a promising path to pursue.

Regards,
-- Al

The idea of running it out of the preamp out to the mm preamp and back into the preamp in of the same preamp is to use the MM preamp like an outboard processor, much like people used to do with equalizers and such in the past. I didnt meann to imply using two line preamps.

I don't see how that could even give you a complete signal path. If you have only one preamp, its input select switch will only be able to select EITHER one of its line-level inputs, such as Aux, OR the MM phono input, not both.

If you were to connect the tape output to the MM phono input, you would have to set the input select switch to Aux to get the signal to the tape output. Therefore the output of the MM phono stage would go nowhere. Also, many preamps don't provide any gain between the line-level inputs and the tape outputs.

If you were to connect the main output of the preamp to the MM phono input, and select the Aux input, again the output of the phono stage would go nowhere. If you were to select the MM input instead, with the volume control turned up significantly, you would essentially have put a feedback loop from the output of a high gain amplifier back to its input. A high volume oscillation would occur, that stands a good chance of being destructive.

Apart from the oscillation scenario, btw, it is unlikely that overloading the MM phono input would be among the problems that would be faced. Most preamps provide overall gains from their line-level inputs to their outputs (with the volume control turned all the way up) that are in the rough area of 10 db to 20 db or so. 10 db corresponds to a voltage gain of about 3; 20 db corresponds to a voltage gain of about 10. So the output of a 0.5 mv cartridge would only be stepped up to roughly 1.5 to 5 mv.

So the bottom line, as I see it, is that using one preamp simply won't function, while using two preamps will function but probably in an unacceptable manner.

Regards,
-- Al

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