Pre amp for low output cartridge

cotter SUT

The real question here is what is your amplifiers input sensitivity...that determines your most fundamental gain equation.

While 40 db of phono stage gain is in typical situations inadequate for a 0.28 mv cartridge, in this case you will have enough gain, due to the unusually high gain of the preamp's line stage (selectable to either 30 or 36 db).

However, an ambiguity in the specs leaves me not completely certain as to whether you will have adequately low hiss levels, although I suspect that will be ok too.

Did you mean "DMA-90" when you said "DMC 90"? Assuming the answer is yes, I'm basing the following on the specs shown here for the amp, and here for the preamp.

Concerning gain:

Assuming that the phono stage and line stage gains are set to their maximum positions, with the volume control turned all the way up the total gain of the preamp is 40 + 36 = 76 db. That corresponds to a voltage gain of 6310 times, based on the relation db = 20 times the logarithm of the ratio of two voltages. That will boost the rated nominal output of the cartridge to 0.28 mv x 6310 = 1.77 volts, which is more than the 1.5 volts that is spec'd as being required to drive the amp to full power. And particularly high volume musical peaks will cause the cartridge to put out significantly more than 0.28 mv. Therefore you won't find yourself running out of range on the volume control.

Concerning noise:

Phono section noise performance is specified as "95 dB A Weighted, ref 100 mV @ 1 KHz." I suspect that the 100 mv level refers to the output of the phono section, rather than the input, but I'm not 100% certain of that. 100 mv is of course way more than the input would ever see from a moving coil or moving magnet phono cartridge, but that doesn't necessarily mean that the noise level is not spec'd based on a hypothetical input of 100 mv.

If, as I suspect, the 100 mv refers to the output of the phono section, since 40 db corresponds to a voltage gain of 100, the A-weighted noise level referenced to the input would be 95 db below 1 mv, which is 84 db below 0.28 mv. That represents exceptionally good performance, and would almost certainly assure acceptably low hiss levels.

In the event that the 100 mv refers to the input of the phono section (which I doubt), it would imply an A-weighted noise level of 95 - 40 = 55 db below 1 mv, or 44 db below 0.28 mv, which would most likely be unacceptable. In that case you would probably want to add a moving coil step-up transformer, ahead of the preamp's inputs.

Regards,
-- Al

The cartridge has .28mv output. Spectral DMC 12 pre amp.
Spectral DMC 90's running in bridged mode. 180 wpc into 8ohm.

40 db may or may not be enough gain, depending on how much gain your preamp and amp have as noted by Swampwalker.

Here is a link to the KAB Calculator

There is a gain calculator on the KAB web site. It will tell you total system gain recommended; phono stage + line stage+ amp.

How low is the output of the cartridge?
What is the preamp line section's gain?
Most of the time I hate carts <.25mV because they require SUT that may add another same amount to the purchased cartridge. For ones .25mV I have total gain in my set up 70 dB where 60dB is transformerless MC section +10dB of low-gain line section'n love it a lot!