2. amps-preamps
  3. 138650-117685

Gain setting for both pre-amp and Audio Research power amp w/ high output cart

Greetings.

I just put together an all-analog system consisting of a Rega RP40 TT with an Exact 2 cart, a Spectral DCM-10 pre-amp into an Audio Research Model-115MKII power amp. With a cart that is crazy high-output, my gain settings on the Spectral preamp are set to roughly 10 on dials that goes to 100, and an educated guess that the gain dials on the AR power amp are about 30% from zero.  So low gain.

LPs do sound amazing, really. Better than I ever thought possible in my room. There’s still a good amount of groove noise between tracks and in very quiet passages at hi volumes which is expected with that 6.2mv cart.

Question is, is there a relationship between gain on preamp to power amp in this situation that could alleviate some of the noise? Could I possibly go even lower on the preamp or maybe more preamp gain, even less power amp?

I expect simplest solution is to change to a .4mv MC cart but I’m not going to do that just yet. But is that the only solution?  It's hard to play with the preamp gain on the fly to experiment which is why I'm looking for direction.

 Any advice?

 Thanks much!


thxphotog

Showing 3 responses by brf

brf
1,715 posts
 
Have you tried adjusting the internal Left and Right gain trim pots on the main PC board?
brf
1,715 posts
 
Sorry, I did not equate dials with trim pots in your post. 

Your MM cartridge has an output 6.8mv and your amp's input sensitivity is 0.6v.  The DMC-10 provides 30db MM gain and 10db line level gain, for a total of 40db. 

Gain required to drive you amp to full power can be defined as
20log(0.6 / 0.0068) = 39db

Based on the above calculations, the Rega MM cartridge is an ideal match for your system.  Are you sure you are not using the MC inputs?
brf
1,715 posts
 
You want your phono + preamp to have enough voltage gain to be able to drive your amplifier to full power. Not enough front-end gain, you won’t be maximizing the power amplifier’s maximum output capability. This is often the case when someone purchases an ultra low output MC cartridge. Too much gain, you risk overloading the amp’s input causing potential clipping.

 

In your case, the Audio Research Model-115MKII needs 0.6 volts from your front end to reach full power. Your Rega cartridge produces 0.0068 volts, therefore, your phono section plus preamp must have sufficient gain to produce the required 0.6 volts that your amplifier needs to achieve maximum usable power output when your pre-amp’s volume knob is turned wide open. As previously calculated in the above post, your MM cartridge needs 39db of gain to produce the required 0.6volts required by your amplifier and your DMC-10 produces 40db, therefore, an excellent match.

 

The above exercise is not as important for digital source components as their rated output is typically 2-volt, therefore, most preamps are attenuating the gain downward (that is why many CD player can drive an amplifier directly).

 

Elizabeth’s comment about "Gain required to drive you amp to full power " is very different than the actual amount of power needed or used” is correct, but is a different subject matter that deals with amplifier and speaker matching to determine spl’s required for your room dimensions and listening preference.

 

If this was my system, I would adjust the amplifier’s input sensitivity that gives me the most usable range on the pre-amp’s volume control.
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