Projects' Details

How it is built

My inspiration: astonishingly beautiful inside darTZeel NHB-18NS remebers me luxury Swiss watch.

Image 1: Battery Power Supply

Image 2: Batteries

The.Preamplifier

...My DIY audio world...
mbl 6010 Black

About

This is my dream about great design. The Preamplifier® will be build as a copy the mbl 6010 Der Vorverstarker®. It will be a copy of housing only. But my device will get a

mbl 6010 Silver

silver housing like silver version of mbl device. Inside it will be completly different. My inspiration is darTZeel - battery powered dual mono preamplifier model NHB-18NS manufactured in Geneva, Switzerland. In housing similar to mbl 6010 will be enclosed "Diammond Buffer" powered by batteries and big capacitors reservoir. It will be dual mono configuration from input to output and from mains to output of power supply. There will be three power supplies: first for battery charger, second for traditional regulators (to supply during chargering of batteries) and third for mirocontroller of input selector/attenuator/display. Each input socket and output socket will be switched on-off by small relays. The attenuator will be built on digitally controled relays. Programmable controller will be equiped with IR (infrared remote) receiver and two-digits display. All other functions will be switched on-off by rotary switches. On rear panel will be placed many sockets (XLR, RCA, BNC, Jack, mini XLR, DIN, D-Sub and PowerCon) to assure all possibility connections in my system. I intend to build big, heavy, universal and good looking machine. And what is important: I want to enjoy the sound.

How it was made

The Preamplifier® is designed around the "Diammond Buffer". The circuit I found on Sjostrom Audio named as Sjöström Super Buffers: SSB01 An ultra high performance diamond buffer with a 4-layer board, gold pads and with surface mounted parts on both sides. I made 2-layers pcb with thru-holes parts. I gave up the surface mounted parts because I use better resistors than in Sjostrom buffer. I use a Caddock's resistors type MK-132 and MP915. The Preamplifier® is build in dual mono configuration. So two mono buffers are powered by two symetric battery power supplies. Additionally each channel of battery power supply has separated battery charger. Two mono attenuators are build on ladders of resistors driving by relays. The attenuator and source selector are drive by two programmed PIC16F819-I/P microcontrollers. One of the PIC drives two-digits display to show level of attenuate. The controller has an infrared receiver. Volume controller and input selector is built on 2 x BCD Coders

Designing The Preamplifier® I had an idea to build device powered by batteries. I use four 12V 5Ah sealed lead acid rechargeable batteries. Batteries give energy to buffer via bank of large electrolityc capacitors (in one channel: 4 x 22000uF BC Components and 2 x 270uF Sanyo OS-CON and 2 x 47nF Vishay ERO). Maybe such big capacity need something like soft-start. At this moment I do not know if it will be necessary. I do it, I will build it. The batteries (each channel) have chargers build on UC3906 and LM339. Chargering process is switched on manually thanks to the LED voltage indicator. There are two "classic" power supplies built on typical LM regulators to give energy during chargering process to both buffers. The "classic" powers supply is in dual mono configuration too. Third power supply built on typical 3-legs regulators gives various voltages for: both PIC microcontrollers, LED drivers ULN2003A and miniature 12V relays Siemens and Takamisawa. This is a complete set of three power supplies. Mode of operation is switched by rotary 4-position ALPS switch.

The microcontroller of The Preamplifier® is based on RelaiXed -- Balanced pre-amplifier built by Jos van Eijndhoven. First annotation about the microcontroller for audio volume
Elector Audio Special German magazine
control is published in Elector Audio Special German magazine The basic circuit was modified by me to get more LEDs to indicate more operations like: active input of the source selector, muting on/off, mono mode, inverting channels, active power supply which is just powering the "Diammond Buffer", mode of charging batteries status (Bulk-Charge/Over-Charge), stand-by on/off and 2-digital level of volume (total: 20 x LED). The microcontroller is conjoined with two rotary ALPS switches and two small toggle switches. One of the rotary switch is used to select type of input (group of inputs) and second to select power supply and batteries charger. One of the toggle switch is used to change mode of play (mono/stereo) and second to invert channels (L+P to P+L). A schematic of the circuit is still underconstruction, but I publish in shortly after it will be finished. Of course, layout of pcb will be different than basic pcb.

What about inputs/outputs switches and attenuator? These are two important parts of The Preamplifier®. They have significant influence on sound. First input/output switches: all pins of sockets (signals and ground) are connected or disconnected to "Diammond Buffer" by miniature relays made by Takamisawa. Resistors of the attenuator ladders are switched by Takamisawa relays too. I chose these relays because they are made in high quality way. Up till now I did not choose type of resistorst for attenuator. The best choice is foil resistor from Vishay (TX2352) or wire wound resistors from Mills (MRA-5), eventually foil ones from Caddock (MK-132, MP915/930) but they are very expensive. Maybe I use metal film resistors from Holco H4). The choice depends on my incomes. Digital signal of volume position and active input for microcontroler is provide by 2 x Bourns PEC11-4125F-S0018 BCD Coders.

All components will be enclosed in Alu housing with internal Alu walls. All walls will be made of 5 mm thick Alu plates. Front panel will be made of 10 mm thick brushed Alu plate. More details, schematics and picture I will be publishing step by step during construction process. At this moment The Preamplifier® consist of few pcb, some of them soldered yet and many drawings.