PRODUCTS AND SERVICES
  - VINTAGE TUBE AMPLIFIER REPAIR AND RESTORATION:  MARANTZ, McINTOSH, SCOTT, FISHER, HARMAN-KARDON AND OTHERS
  - FIRST GENERATION SOLID STATE McINTOSH AMPLIFIER REPAIR, RESTORATION AND MODIFICATION
  - AMPLIFIER AND CROSSOVER PC BOARD DESIGN AND PROTOTYPING
  - CUSTOM LOUDSPEAKER CROSSOVER NETWORKS BOTH ACTIVE AND PASSIVE
  - AMPLIFIER MODIFICATIONS:  NEW POWER SUPPLY TRANSFORMERS, OUTPUT TRANSFORMERS, CUSTOM WINDINGS

Contact North Reading Engineering at: audio@northreadingeng.com

WELCOME TO NORTH READING ENGINEERING

North Reading Engineering is all about audio amplifier engineering and can design, prototype and restore just about any vintage classic tube or solid state amplifier made.  Repairs and restorations, once complete, are characterized on calibrated analyzers and response plots provided to the customer.  If you're an audio OEM, North Reading Engineering can provide you with prototype amplifier, passive and active filter hardware including BOMs, Gerbers and suppliers.   

HH SCOTT LK-72A/299C 2-CHANNEL BASIC AMPLIFIER FOR BUILDERS
With excellent, high quality exact replacement power supply transformers available for this vintage amplifier, North Reading Engineering has redesigned and "modernized" the amplifier.  With either Hammond or premium Lundahl C-core output transformers the reproduction of the amplifier is remarkable using currently manufactured tubes.  A detailed description of the the design process and testing can be found HERE

THE SCOTT 299C DEMONSTRATOR SHOWN BELOW IS GOING THROUGH A MECHANICAL REDESIGN AND WILL BE AVAILABLE WITH A NEW CHASSIS DESIGN AND CHOICE OF EITHER SOLID-STATE OR VACUUM TUBE HIGH VOLTAGE RECTIFICATION.  STAY TUNED! 

SALLEN-KEY, 2-CH, BAND-PASS FILTER MODULE
For amplifier builders, the Sallen-Key module provides two, 4th order, band-pass small signals to amplifier inputs.  Designed to accept a wide range of capacitor values to implement band-pass filtering for woofer, midrange and tweeter applications.  On-board +/-15VDC regulated on-board supply, Sallen-Key filter topology USA made, through-hole PC boards with clear, bright silk screened component IDs are also available to allow amp builders to evaluate and modify the design to suit specific filter requirements.  For more information including performance data and ways to use this module is found HERE.

   

BALANCED 2-CHANNEL, BUFFER / 3-WAY ACTIVE SPLITTER AMPLIFIER FRONT END MODULE
EMI/RFI hardened amplifier front-end, XLR/TRS combination inputs, +/-15VDC regulated on-board supply, ultra-low distortion, super quiet buffer/splitter accepts inputs from any small signal source and splits them into three independent signals, each capable of driving (for example) an amplifier in a bi- or tri-amplified loudspeaker system.  Op-amp sockets enable users to evaluate different packages or replace a blown device.  High quality, USA made, through-hole PC boards with clear, bright silk screened component IDs are also available to allow amp builders to evaluate and modify the design to suit specific buffering requirements.  For more information including performance data and ways to use this module is found HERE (webpage) and HERE (video).

   

CUSTOM ENGINEERED PASSIVE LOUDSPEAKER CROSSOVER NETWORKS
Networks are designed and their performance verified using a wide range of tools including analog circuit simulators, high sampling rate acoustic analyzers, distortion analyzers and precision measurement microphones.  Acoustic measurements are taken in quasi-anechoic conditions using near and far-field techniques.  Designs can be implemented using custom wound autotransformers, PC board layouts and active filters.  

NETWORK REBUILDS, MODS, MEASUREMENTS
Do you have an old JBL, KLIPSCH, EV or other network that you would like updated or duplicated?  Pricing is quite competitive and performance data demonstrating network behavior is provided to the customer.

VINTAGE McINTOSH AMPLIFIER SERVICING AND RESTORATIONS
North Reading Engineering has the experience, tools and test instrumentation to properly assess the condition of your vintage, first gen solid state amplifier and make it a whole lot better. More information on amp servicing can be found HERE A complete rework of an MC2100 amplifier is shown on the forum website HERE

MC2105/2100, 2505/250 and 2300 PREAMP BOARD UPGRADE
First generation McIntosh solid state amps can be upgraded to make better sound.  This isn't a "re-cap" or "update" of the original design.  It's a re-engineered preamplifier section, designed as a direct swap for the 043-795 and 044-331 preamplifier boards (lower left).  The new preamplifier board (lower right) provides a significant, measureable performance upgrade to these vintage classics.  More information on the preamplifier section can be found HERE A beautifully done customer MC2105 install HERE.  (Note: Bare PC boards are no longer sold for customer assembly, only fully assembled and tested boards are available.)

MA6100 INTEGRATED AMPLIFIER COMPLETE RESTORATION
New Power Supply Assembly
The MA6100 restoration package replaces the thermally distressed, old school, turret board supply (lower left) with a completely new, drop-in, PC board fabricated from a high current capacity, dual-trace, USA manufactured board (R1.1).  The board and component selection have been engineered to manage the excessive heat generated by regular amplifier use.  The supply section has demonstrated superior heat management and excellent reliability.  The assembled and tested power supply board is also available for purchase for installation by the customer.  A high resolution image of the board top shown HERE and bottom HERE.  The development process of the power supply board showing the prototype R1.0 and final R1.1 version with installations shown HERE.  (Note: Bare PC boards are not sold for customer assembly, only fully assembled and tested boards are available.)

 

MA6100 Preamp, Power Output, Phase Inverter and Voltage Regulator PB Board Reworks
EVOX MMK polyesters in preamp, phase inverter and voltage regulator boards are replaced with WIMA, AC pulse, polyethylene MKP (photo lower right).  Small-signal by-pass caps are replaced with low DC leakage, solid Tantalum electrolytics.  The power output driver complimentary pair and voltage amplifier stage heat sinks and mica insulators cleaned and thermal compound applied, output stage power transistors replaced.  The amplifier is dismantled and chassis cleaned and polished (lower left).  Previous repairs are identified, reworked as required.  Blown transistors can be matched and installed.  Chassis fasteners replaced with stainless steel, new plastic chassis feet attached, panel lamps replaced with LEDs, glass faceplates, NLA Amphenol card edge connectors and multi-can caps can be sourced and installed (pending inventory).  Reworking MA6100 PC boards is shown HERE.

 

MC250/2505 RESTORATIONS
Preamplifier, Power Supply and Output Stages

Factory preamplifier replaced with the R2.3 preamplifier assembly.  Power supply and output power board capacitors replaced, output transistors replaced, potentiometers, RCA jacks, rockers switches replaced, chassis stainless steel cleaned, polished with new stainless steel chassis hardware.  Chassis bottom, prepped and painted (lower right).   A reworked MC250 is shown HERE.

 

VINTAGE VACUUM TUBE RESTORATIONS
MARANTZ, McINTOSH, SCOTT, FISHER, HARMAN-KARDON AND OTHERS

Power supply rebuilds, power supply transformers replaced with new units (lower left, HH Scott 299C), recaps, board replacements, RCA jacks replaced, chassis stainless steel cleaned, polished (McIntosh).  New stainless steel fasteners.  Chassis bottoms, prepped and painted (McIntosh). 

 

CROWN AMPLIFIERS
XLi Series, Tri-amped, 2-Channel, Actively Filtered "Stacks"

If you want to go 3-way active using Class AB amplifiers there is now no need to spend a small fortune on amps, networks and cabling.  With the active filter inserts developed by North Reading Engineering a 3-way amplifier stack for the Klipschorn, Jubilee or any 3-way audio system can be had for reasonable cost.  North Reading Engineering can design and install active, steep slope filters in an XLi stack to accommodate either a 2 or 3-way system.  Amps run cooler, no passive network losses and an independent volume control for each driver.  A detailed description of the filter assembly is shown HERE.

Mod the D45-75A Amplifiers Into Actively Filtered Power Amps
Crown D45-75A series of amplifiers, converts CHANNEL 1 of the amplifier to a (steep slope) 24dB/octave band-pass filter and CHANNEL 2 to a 24dB/octave high-pass amplifier.  More information on this modification HERE.

Vintage Crown Solid State Amplifier Repairs -
Contact North Reading Engineering

NORTH READING ENGINEERING PAGES
MODELING THE KLIPSCHORN BASS HORN (Part I) - The Beranek Model, LTSPICE and a slew of measurements.
MODELING THE KLIPSCHORN BASS HORN (Part II) - Extending the model to simulate factory filter responses.
PHOTOGALLERY OF A KLIPSCHORN REPLICA BUILD - Building a Klipschorn is not for the faint of heart!
A KLIPSCHORN NETWORK FOR BUILDERS - A measured design you can build yourself.
UNDERSTANDING IMPEDANCE - Resistance, Reactance, Nyquist and Excel all in one place.

NORTH READING ENGINEERING VIDEOS
BALANCED 2-CHANNEL BUFFER / 3-WAY ACTIVE SPLITTER (R4.0) - Module overview and selected analyzer results.

PLACES TO VISIT
LTSPICE DOWNLOAD PAGE
KROHN-HITE

       

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Contact: audio@northreadingeng.com
Phone: (978).795.7172
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