Projects' Details

How it is built

Image 1: Power Supply

Image 3: PCB of Power Supply

Image 4: Input Dual-FET

Image 6: PCB of Input Dual-FET

Image 7: Driver Stage

Image 9: PCB of Driver Stage

Image 10: Chassis Overview

Image 11: Front Chassis View

Image 12: Toroid Overview

Image 13: Sockets on Rear Wall

Image 14: Sockets Inside View

Image 15: Front Glass Plate

Image 16: Sides/Top Plates

--------------------------------------- Datasheets of parts:

Datasheet 1: 2SA1015L

Datasheet 2: 2SC1815L

Datasheet 3: 2SJ109

Datasheet 4: 2SK389

Datasheet 5: EYN

Datasheet 6: PHE426

Datasheet 7: X7R

Datasheet 8: NMJ6HC-S

Datasheet 9: NXJXXX

Datasheet 10: HLMP-D150-K150

Datasheet 11: LM117-317A-317

Datasheet 12: LM137-337

Datasheet 13: OP27

Datasheet 14: OPA548

Datasheet 15: 67W-Y-X-Z

Datasheet 16: 540M-100K X2

Datasheet 17: REF02

Datasheet 18: H4P-H4-H8

Datasheet 19: PR4-5

Datasheet 20: RC55-65-70

Datasheet 21: MK132


...My DIY audio world...
Chassis Overview


How the Pure HeadAmp was born? For few years I used fantastic HeadPhone Amplifier v1.0. It was A class headamp made by AudioAlchemy. But one day left channel silenced. The AudioAlchemy used old power transistors marked specially for the manufacturer so it was too difficult to recognize what is genuine type transistors used there. I decided to sell the headamp and built new one from scratch. Of course, new headamp should to work in pure A class. I have just started to search over an internet and found: A Pure Class A Dynamic Headphone Amplifier by Kevin Gilmore. Author designed the headamp to drive Grado headphones particulary. I have/love Grado headphones - I am owner of SR-225. I have just known: this project had been created for me. The article includes not only cleary and simply description of the head amplifier and ultra-regulated power supply. And there was a value added part: ballanced bridge output version of the head amplifier. In the articles the author wrote: The balanced bridge output version of the amplifier is for those headphones that can be wired as dual mono. It has twice the voltage swing, twice the slew rate and 4 times the output power. Just it was my Pure HeadAmp - pur and strong device dedicated for pure and strong Grado headphones.

How it was made

The Pure HeadAmp is dual mono amp from power supply to output sockets. It consist 5 circuits placed on 9 pcb: double Ultra-Reg Power Supply, double Input Dual-FET Preamp, quadruple Driver Stages and single Attenuation. The Ultra-Reg Power Supply is powered by two big audio type toroids 50VA each with 8 x 7,5A Schottky diodes + pair LM317/337 + 2x 4700uF Roederstein electrolytic oversized Snap-In capacitors and is based on REF02 voltage source with two power operational amplifiers from Burr-Brown OPA548T to get stabilized symetric +/-16VDC. The power supply works in dual mono configuration too. The input amp works as a dual-FET fully-differential fully-balanced front-end amplifier based on matched pairs of 2SJ109/2SK389 Toshiba transistors. The driver stage is a standard A Class voltage amplifier (used as a voltage shifter) based on 5 matched pairs of 2SC1815/2SA1015 Toshiba transistors. The double driver stages work in balanced bridge. Motorized blue ALPS potentiometer works as an attenuator. I used resistors: Caddock MK-132, Mills MRB-5, Welwyn RC55Y, Holco H4 and capacitors: WIMA MKS 02, Rubycon ZL, Vishay ERO, Roederstein EYN, AVX X7R and Evox Rifa PHE426. As a DC Servo works operational amplifier from Analog Device - OP27. Input/Output and Phones Sockets are made by Neutrik, Amphenol and Clifford. Internal signal cables are made of pure Cu solid core of Neotech and AC power conection is made of 3-wire shielded cord. All electronic components are soldered on 70um Cu stiff and thick pcb. Soldering was made by high quality 0,032" dia. Johnson's IA-423 "ternary eutectic" alloy - composition comprising its three component elements (tin, silver and copper). Audiophiles also claim that IA-423 is the best sounding solder they've ever heard. All details of basic project you can find on A Pure Class A Dynamic Headphone Amplifier website and on Addendum: A Pure Class A Dynamic Headphone Amplifier (Kevin Gilmore) website.

A housing of the Pure HeadAmp is made of Alu, steel, glass and MDF. Bottom and rear plates are made of 3mm Alu plates, internal plates are made of 2mm steel sheet, front plate are made of 4mm grafhite glass and both side plates are made of 19mm one-side laminated MDF. All Alu and steel plates are painted by black mat varnish. Both side MDF plates are painted by grey polished varnish. The front glass plate has natural graphite colour. A top plate has cut rectangular holes covered by Alu net. In front glass plate are drilling holes for potentiometer's axle, 3 Jack 6,3mm sockets and for 4 screws to fit the plate to housing. Jack sockets have a 1mm Cu shield to decrease trafos' brum in output.
Sockets Side View
In rear plate are drilled holes for sockets: 4x BNC, 4x RCA, 2x XLR Female, 2x XLR Male, 1x PowerCon, 1x Power Switch, 1x Mic Male, 1x Ground Switch, 1x Out Trafo Switch and few holes for screws.
Sockets Overview
The AC power socket and switch are shielded by Cu pipe. Between power supply pcb and amplifier pcb is fitted 1mm Cu shield. All plates are screwed by Alu square slates and by 3mmm dia. non-magnetic stainless steel screws. The housing of the Pure HeadAmp is stands on 4 rubber feet. The housing is solid, heavy and stiff. I am satisfied of my project but ... BUT as you can see on the photos the project is not finshed yet. BUT I will finish it till of the end of this year. At the moment I have finished project of all audio pcb and I had to sent Gerber's files to workshop to order they make these pcb. Totally I need 7 pcb: 2 pcs of Input Dual-FET Preamp, 4 pcs of Driver Stages and 1 pcb of Attenuation (both pcb of Ultra-Reg Power Supply I ordered few months before and now they wait to soldering yet).

Now the device has only housing and is ready to put inside electronics. Of course, updated photos will be placed in the site asap. Be patient as me the Pure HeadAmp will come in one complete piece soon.