The Bellari RP503 microphone preamp channel strip is low cost and surprisingly customizable. Just what we like... Read further to find out what gear modifications can be done to this unit.

There's nothing that we like better than a "cheap" piece of recording equipment that can be hot-rodded to perform much better.  The Bellari RP503 fits the bill.

Before getting into mod details, let's take a look at the product specs for this microphone preamp - channel strip. 

The Bellari RP503 Tube Mic has a great-sounding preamp section with phase reversal and +48 phantom power. A gain potentiometer allows you to add just the right amount of drive for the tubes and a clip LED indicates overload. The compressor section sports Threshold and Ratio controls for dialing-in perfect dynamics. A handy gain-reduction meter indicates the amount of signal compression and the circuitry may be completely bypassed. The EQ portion features low- and high-shelving filters for the lowest and highest frequencies, while a sweepable mid section allows for precise tailoring. Both XLR and 1/4" inputs and outputs provided.

Bellari RP503 Tube Mic Pre Channel Strip Features:

• Phase reversal
• +48 phantom power
• Gain potentiometer
• LED indicates overload
• Compressor section with threshold and ratio controls
• EQ low- and high-shelving filters for the lowest and highest frequencies
• Sweepable mid section allows for precise tailoring
• XLR and 1/4" inputs

Great right? All at a price less than $200. You are basically getting one channel of preamp, compressor and EQ.

Searching around the Internet, the general concensus is that the stock preamp isn't THAT great sounding, but decent for the price. For $180 what do you expect, right? This preamp can be EASILY modified in two ways.

The stock opamps can be replaced in this preamp.  There are 5 opamps to replace in the channel strip. One possible substitute is Burr Brown OPA2604 opamps or OPA2134PA.

There is also a stock tube in the preamp that can be replaced with something better, such as a NOS Telefunken 12AU7 tube.

After swapping the opamps and tube, many people have turned from mediocre reviews to great reviews of this preamp.

Here's a great thread with some discussion on this preamp mod 

Make sure to have a professionaly do the mods - there is always a chance of breaking the unit or hurting yourself if you don't know what you are doing.