Here is an article to show how I designed my 6SN7 preamp with CCS based on DN2540N5 or IXCP10M45S D-MOS transistors. The article is an addition to my design which showed a 6SN7 tube in parallel connection. Here I will continue to develop the schematic. I will introduce a popular solution for a reliable constant current source.
Here is my design of a 6SN7 (6N8S) based preamp with parallel sections of the tubes. I plan to use just two tubes, one for each channel. As we all know 6SN7 is a double triode and for my design I will tie the two sections in parallel. The main design parameters fall into three points – low-distortion, low-gain and low output impedance without using a output buffer/cathode follower. In order to achieve some of these goals I will be using an active load – constant current source(CCS).
Setting the bias point
First of all lets begin with the obvious – setting the tubes into the desired operation point. Lets consider a fairly typical power supply voltage of around 300V and a 30kohm plate resistor which results in a plate current of 10mA. From these three values it’s easy to draw the load line, so here’s what it looks like:
The Tektronix SG505 instrument is an ultra-low distortion and low-nose oscillator intended for testing of audio grade electronic products. This one came to my possession as a non-working unit and I set-out to fix it.
The DIY LPRO-101 ruibidioum clock generator. This box together with some additional electronics on a separate PCB will transform this LPRO unit into stand alone equipment. I’ve always wanted a good and affordable frequency standard for my home lab. Searching the eBay one might find quite a lot of solutions. The good thing is that nowadays we have plenty of options.
Here is a quick article describing a low-noise power supply for low current applications. It’s simple, and easy to build. All parts are widely available and cheap. I’m using this power supply to power-up my RIAA preamplifier. It’s more that capable of delivering excellent results. Build one and try it for yourself.
First of all lets see the basic functional diagram of the regulator.