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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
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?
Post removed 
thxphotog OP
6 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?
No worries. And thanks very much for the research and replies. "MC inputs"? There are MC inputs? I’m confused. :-) The DMC-10 has a single phone input, and two options for output (not counting tape) DC Coupled and AC coupled. I’m using DC Coupled.
thxphotog OP
6 posts
 
Thank you for this reply!  I will continue to play, but want to reiterate, it's sounds amazing right now.  I just have a feeling it could be better w/ a lower noise floor.
10-03-2018 8:20amMy Bryston BP-26 to Bryston 4B-SST² used with a typical CD player allows me a ’range’ of volume from 7 O’Clock to 8 O’Clock, zero to too loud is all in that space.
So I use two preamps in various ways all the time (have four in the system at once), partly to have some volume control flexibility.
All that was to explain I use multiple volume gain and multiple equipment gain all the time.
In all my puttering around, I have found no magic combination, ever. More on one or another, maybe for ONE ALBUM, but usually it is always a tossup. The main problem is too much gain all around*. But I am not going to buy other equipment just to cure this.
* maybe if I played music at higher SPL, but I like it at lower levels.                              
What I would say is find out the zero gain point on the controls. Set one at that point. For example my Conrad Johnson ACT2 zero gain, attenuation is at ’77’ (out of 100) on the volume control. The zero gain/attenuation for my Bryston BP-26 is at 1 O’Clock on the volume knob (as it is set now, it can be changed, since it is just a set screw)See how it sounds with each in turn set to zero gain/attenuation. One combination may sound better than the other.

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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