PT06 current feedback DIY preamplifier.

05 Feb. 2012 by Thanaporn, 208 views.

PT06 Hifi DIY LME49713H based Preamplifier.
PT06 is a preamplifier that was created in the same period of PT05 construction, I want to build this preamplifier to be a part of my main audio system.
In fact, an opamp based preamplifier is not my planned to build before. But after finding and Googled, the LME49713H is a high fidelity opamp for high performance preamplifier. LME49713H are designed and manufactured by National Semiconductor (currently owned by Texas Instuments).

The important keys to my attention the opamp are such:
- High PSRR. (100dB)
- Ultra-low distortion. (THD+N (0.00036%)
- Low noise. (1.9nV/ √ ^Hz)
- Ultra high slew.(±1900V/μs)
- Current feedback circuitry.
- Low Input Offset Voltage.(0.05mV)

Refer to such above features. LME49713H opamp is likely can be a good opamp for my preamplifier in term of excellent sounding. It is an ordinary circuitry designed. Voltage gain of the PT06 preamplifier was set to about 12 times. The power supply unit of the preamplifier is a separate and independent of each other in order to reduce the cross-talk interference between channels. The dual 15VA Toroidal transfermers are used. Because of power supply is very important to sound quality. So same as PT05, the 2.1 voltage regulation power supply is used with the PT06.

From the graph above, we know that when it drives 600ohm load is extremely low distortion even when driven at high frequency.
In exchange of excellent signal amplification features, it consumed more idle current when compare to the others I was knew.

LME49713H power consumption
As we see from the current VS power supply voltage graph, the current consumption is about 7-10mA. But the actual use of my circuit, I get it approximately 12 mA current consumption at 15V power supply.
All devices are hosted in an aluminum chassis. Actually it is the chassis from the other manufacturer. The volume, selector circuit, transformers and main boards are contained within the chassis.
Input signal from unbalanced RCA female connectors are connected by a relays network. They are connected directly with very short length of conductor.
Input signal from the relays network is passed through the red Van Den Hul ThunderLine cable to the 23 steps volume that was assembled by Dale fixed resistance resistors network potentiometer.
The advantages of this volume is no contacting noise such as caused by variable potentiometer. Differences between left and right channel signal level is less than a high grade variable potentiometer because of it is produced from 1% error resistance Dale resistors network. In addition, it is longer lifetime.
The output of the amplifier boards are connected to the output RCA with Van Den Hul ThunderLine cable as well. For more purity signal connection I was using 2 pairs of WBT 0210 MS CU chassis RCA connector.
The estimated power dissipation of each LME49713H opamp is about 360mW, So I chose to install heat sink to make it can working with better stability.

After a PT06 preamplifier was successful constructed. I do not hesitate to experiment with its sound immediately. At that time, Marantz CD5003 is used as a source. Connection between them is JPS SuperConductorQ interconnects cable then the AudioQuest KingCobra is connected to a TH-200se power amplifier.
The sound quality I have heard is totally better than PT03 and PT05, even though I listening it in the first hour. It provides the excellent clarity of sound in every frequency range. The bass quantity may be less than the PT05 but not much. The quality and cleanliness are the major characteristics of the PT06 and LME49713H.

It is my preamplifier that have the value of the cost and time investment. And now it is part of my main sound system.