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Author: Ventsislav Simonov Page 1 of 10

6SN7 Preamp With DN2540N5 or IXCP10M45S

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.

6SN7 PREAMP. DN2540N5, IXCP10M45S. PCB_3D
6SN7 preamp. DN2540N5 or IXCP10M45S. PCB 3D rendering.

6SN7 Preamp With Parallel Sections + CCS

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:

6SN7 Load line and biasing
6SN7 Load line and biasing

Tektronix SG505 low-distortion audio oscillator

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.

Front view. Tektronix SG505
Front view

The LPRO-101 DIY Rubidium Clock Generator

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.

Low-noise Power Supply


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.

Positive voltage regulator:

Error Amplifier Low-Noise

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