Details about  high spec Mosfet headphone amplifier - V2.1

Specially optimized for high-end demanding headphones: Outstanding sound, low distortion/noise and excellent load handling characteristics. It can drive pretty much any headphones with ease, regardless of  their impedance or difficulty-level.

DUAL-MONO configuration: Very unique design for this price range! 100% dual-mono design for AMAZING channel separation and stereo performance.

External AC components: For maximum audio + noise performance AC (alternating-current) PSU (power supply) components are kept away from the main amplifier PCB. AC to DC conversion happens inside the amplifier  case very close to the amplifier circuit. This is by far the best method for quality audio.

Twin Power-Supply-Unit: Left and Right amplifier channels have their own dedicated external PSU. Not center- tapped or shared. 100% separate for ultimate dual-mono operation.

Simple IN - OUT design: There are no signal degrading  components. Amplified sound is as close to original source as possible. Very accurate,  high resolution, natural and low noise. Bass, mids and high bands are excellent  and proportional at any volume levels. True audiophile listening experience!

DUAL MONO CONFIGURATION

Built around two separate amplifiers. Each amplifier works independently from each other for powering left and right channels for excellent channel separation and outstanding stereo performance.                                                                                            

MULTI STAGE AMPLIFICATION

Each amplifier has been designed in two stages for maximum performance:                             

•STAGE - 1: IC OPAMP VOLTAGE AMPLIFIER:Sound input stage is an OPA134 or AD8610 voltage amplifier.

•STAGE - 2: DISCRETE CLASS-A MOSFET POWER AMPLIFIER/BUFFER:Outputs of the OpAmps are buffered with Class-A biased pair of complimentary matching high quality, ultra fast switching/response power mosfets. These isolate the headphones load from the opamps for much improved  bandwidth, drive capability, and also reduces the harshness dramatically.                                                                                         

Class A biasing operates Mosfets in more linear region for lesser crossover distortion between positive and negative amplification phases.

DUAL GAIN

Amplifier has 2 gain settings which can be changed with 2 gold-plated jumper links on the PCB. I have set these to as 6.5(gain-1) and 11.5(gain-2).

PSU COMPONENTS                                                                                                                                                                                           

•Amplifier is powered with 2 external high quality 18v ac linear power-supply-units(PSU). PSUs are supplied with this sale.                       

•Internal configuration of high quality Vishay-BC capacitors smoothes the AC voltage. These capacitors are arranged in parallel  configuration for very low ESR/AC ripple current and placed very close to loads to overcome the inductance/resistance of the AC PSU/Wiring.

•Smoothing capacitors are bypassed further with a Wima film capacitor to eliminate higher frequency ripples.                                 

•Low noise Voltage Regulator holds the OpAmp voltage at dead accurate level to stop annoying minor voltage changes and hence continuous stable operation.                                                                                                                                                                                

•Regulated voltage is divided into + - voltages by using precious rail splitter IC TLE2426.                                                                   

•OpAmp circuits have separate multi stage local decoupling capacitors to filter out ripple noise for extremely stable operation.

QUALITY PARTS

•LARGE Polypropylene signal-input capacitors. These capacitors are used only in best quality audio circuits. They are extremely stable, have low inductance and offer highest possible audio quality.                                                                                                                                   

•BurrBrown OPA134 or AnalogDevices AD8610 OpAmps                                                                                                                          

•High quality, low ESR Vishay-BC electrolytic smoothing capacitors                                                                                                       

•Wima DeCoupling capacitors                                                                                                                                                                                 

•ALPS RK27 volume pot                                                                                                                                                                                     

•Low noise metal resistors                                                                                                                                                                                   

•Gold plated IC sockets                                                                                                                                                                              

•TLE2426 precision rail splitter IC                                                                                                                                                                          

•Ultra fast recovery rectifier-diodes.                                                                                                                                                    

•Complimentary matching power mosfets

INPUT

•High quality, audiophile grade, gold plated Neutrik phonos.

OUTPUT

•Silver plated 6.35mm headphone socket. Can drive headphones in range of 32 - 600 ohms.

EXTERIOR

•Very high quality black aluminium enclosure. Dimensions:  45mm x 108mm x 160mm (H-W-D).

•Solid Aluminium volume knob

•Chrome plated on/off switch.

•Blue power-on led.

HIGH BANDWITH

•Amplifier circuit is capable of very high slew rates and has very fast response to the rapidly changing input signal hence minimum  

error/ degradation occurs to the amplified source.

•Perfect flat frequency response within the 5Hz - 20000Hz audible spectrum and effective bandwidth is in excess of 500000Hz.

BUILD PROCESS

•All soldering are done by hand to perfection with 4% silver solder.

•Printed circuit board is fiberglass (glass epoxy) type for better performance.

•Components are installed very closely to the OpAmp ICs and Mosfets for minimum noise and better sound.

POWER SOURCE

•Amplifier is powered with 2 external 18v ac power-supply-units (PSU). PSUs  supplied with this sale.

ACCESSORIES

•Supplied with very high quality UK type power-supply-unit. Adaptor is given for Euro or Australia type mains sockets. You will receive the correct type according to your region.

Listed below are upgrade and modification options available during purchase.

OpAmp Upgrade:

Standard design is based on high performance OPA134 opamps. AD8610 opamp upgrade option is available.

These opamps are of the highest audio pedigree.

Additional fee of £15

Above option may add 1 – 2 days of delay for ordering/fitting. (I do have limited spares in-stock, please check).
If you want to upgrade, please request  the total from me before paying and I will modify your invoice

•United Kingdom:
-First class recorded: £6.50
-Special Delivery: £13.50

•Europe:
-Air sure : £14.50
-Internationally signed for: £14.50

Orders will be posted within 3 - 4 working days of payment. I will keep you informed ASAP

Thanks for looking

* * * * * * *

NEW PCB v7 is best sounding design yet! See the upgrades history below.

Each amplifier is constructed slowly from scratch, by hand, and myself only to the highest audiophile quality standards.

No external costs so you  are sure to get a good deal!

Buy with confidence. Good audio reproduction comes from good engineering. I have two Electronics Engineering University Degrees and currently working as a full-time professional Electronics Engineer.

1 year written guarantee. It is very unlikely but if you have any problems within a year of purchase,
I will take care of repair and additional costs.

* * * * * * *

I manufacture my own printed-circuit-boards (PCB). Design is continuously upgraded for better performance.

NEW PCB v7: Best sounding design yet! Now fitted with twin sets of AC-to-DC conversion circuit and ground-reference ICs

(one for each channel).

Having the design like this improves the following:

•Results in better crosstalk performance between left/right channels.

•Improved supply regulation.

•Completely stops power sharing between left and right channels.

•Momentary current demand in one channel may not affect the other channel

•Improvement in sound quality especially in case of big bass notes. Better,  deeper bass!

PCB v6: Dual gain

Fitted with 2 gain settings. Gain can be changed by removing/inserting of  2 gold-plated jumper links on the PCB. Additional gain setting is suited for  low sources and headphones which require more voltage drive.

PCB v5: New opamp supply capacitors

Larger value, lower esr opamp supply capacitors for better , stable performance.

PCB v4: Fitted with RK27 volume POT

Designed the circuit layout around this outstanding volume POT. By far the best POT you can buy at this price range. These pots are of the highest possible audiophile quality offering superb operational feel and accuracy and unlike many other  types of pots, volume increase is smoother,  most of the volume control is usable.

PCB v3: Replaced the signal input capacitors to  large Polypropylene type.

These capacitors are only used  in best quality audio circuits. They are extremely stable, have low inductance and offer highest possible audio quality.                                                                                                                                

PCB v2: Fitted with ultra fast recovery rectifier-diodes.