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Improve, Renew, Restore and Repair your Dynaco Stereo 120, PAT-4, or SCA-80

Side View of a Dynaco Stereo 120 with Super Heatsinks and Updatemydynaco Modules

Make your Dynaco Stereo 120 Power Amplifier Better than New with these Kits

You can bring your Dynaco Stereo 120 Power Amplifier back to life. Even if it's working, you can make it sound better than it ever sounded. You can feel the great feeling of accomplishment that comes from building a kit...You begin with a collection of quality parts, and end with something that sounds great, looks great, and works great. And you built it!

The Dynaco Stereo 120 Power Amp was revolutionary when it came out in the mid 1960's. It had some problems, though, mostly related to under-biasing of the output stage. The result was the cross-over distortion that came to be the unpleasant hallmark of "transistor" sound. Forty years of progress later, we can do a lot better. With our kit, you recycle and reuse the highest quality, timeless parts of the Stereo 120, and replace the parts, e.g. the amplifier and power supply regulator modules, where technology has made the most improvements.

New and Improved!

It's actually true! The updated amplifier modules have been improved. We've included some (but not all) of the improvements of the GT-101 amplifier modules into the TCK modules. The improved version is called Rev B.

click here to order kits and parts

Pick the Parts You Need

Pick just the parts you need at the Updatemydynaco Store to bring your Dynaco Stereo 120 Power Amplifier back to life, to improve it a bit, or to take it about as far as you can go.

See What Our Customers Have to Say

Here are a series of testimonials from our customers.

Kits for Stereo 120 traditionalists

Does your 40+ year old Stereo 120 still have working amplifier modules? Do you want to keep the original modules while still improving your sound? You might want to try:

Make Your PAT-4 Better than New, too!

You'll be just as happy with our kits that make your Dynaco PAT-4 Preamp sound even better than new. These kits are incredible values.

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Reduce Line Level State Distortion by a Factor of 10

At just $5.00, this kit has to be the best value in high-end audio. Every sound in the PAT-4 Preamp goes through the Line-Level (sometimes called High-Level) stages. Improving these stages improves the whole preamp. The 10X distortion reduction brings the PAT-4 to state-of-the art levels. Please have a look at the product and the assembly manual

Switchable Bypass for Tone Controls

You may find tone controls really useful, but perhaps you worry a bit about their effect on the sound. This kit gives you a switched bypass of the tone controls. It replaces the seldom used high-filter. You can instantly compare your sound with and without tone control corrections. Please take a look here at the ordering information and assembly manual for the TCS kit

Electronically Regulated Power Supply for the PAT-4 (PAT4PWR)

This kit produces rock steady, extremely low noise power supply voltages for the PAT-4 Preamp. We think you'll love the way your PAT-4 sounds when you install this new power supply. Has your PAT-4 Preamp always had a hum? The Electronically regulated power supply is often the answer. One customer reports, "I've had my PAT-4 for about 40 years...It always had a low level hum. With the PAT-4PWR kit, the hum is finally gone". Please have a look at the product and the assembly manual

Improve the PAT-4's Phono Preamp (PAT4LP)

Too many improvements to talk about on this page. 4 to 8 dB of SNR improvement is just the start. Check out the PAT4 Phono Preamp Improvement Kit here.

Make Your SCA-80 Better than New, too!

Our newest kits make and SCA-80 better than new.

Build a Power Amplifier Kit

Let's say you don't have a Stereo 120 to update, but you still want to build a power amplifier kit...One that puts out more than 50 Watts per channel into 8 Ohms, and nearly twice that into 4 Ohms. It sounds great, and uses top-notch components. Visit Akitika's website and look at the GT-101 stereo power amplifier kit.

Browse the Store

We've got the stuff that lets you make your Dynaco Stereo 120 Power Amp and PAT-4 Preamp better than new. It's right here in the store. Amplifier modules, super heatsinks, replacement capacitors, power supply replacements, beautiful blue lights and even new feet! It's all here.

click here to order kits and parts

Search the Website

The website has grown so much, it's easy to miss something that you're looking for. Use this search box to find what you need.

only search the updatemydynaco web site

Super Heatsink Option

The original UpdateMyDynaco kit recycled the original Dynaco heatsinks. Those heatsinks were perfectly adequate for music listening, but a bit marginal for heavy duty use. That's why we've introduced the Super Heatsink Option. The Super Heatsinks are direct replacements for the originals, but are 3 times as thick, at 3/8" versus the original's 1/8" thickness. The result allows the LM3886 to deliver significant 4 Ohm power, more than 100 Watts!

Ordering the Super Heatsink Option has added benefits:

Order the Super Heatsink Option from the UpdateMyDynaco store.

original heat sink is 1/3 the thickness of the Super Heat Sink

the original black heat sink (on the left) is only 1/3 as thick as the super heat sink (on the right)

Super Heat Sink Modification Applied to Dynaco Stereo 120

update kit with the super heat sink option

A Bit of Kit History

Lots of people used to build electronic kits. Heathkit, Eico, and Dynaco let anyone assemble great stuff and save a lot of money. On top of that, building the kits was relaxing, educational, and rewarding. Weíre here to say that the good times are back! UpdateMyDynaco has designed a high performance amplifier replacement module kit that lets you make your Stereo 120 better than new.

The Dynaco Stereo 120 was the first powerful (60 Watts/Channel) transistorized stereo power amplifier in wide production. My uncle had the Stereo 120, PAT-4 Preamp, FM-3 tuner, and A-25 Loudspeakers. In 1968, that was the good life! I always liked the look of the amp, its size and its shape. The neon-illuminated crystal clear rocker switch promised power with its orange glow in a darkened room. As I studied engineering and analog design, Iíd marvel at all the function the Dynaco guys crammed into those few transistors.

Original Amplifier Module, 40+ years old

Amplifier Improvements

Forty years of technological progress allows us to bring you lower distortion and greater efficiency, along with protection circuits that make your amp nearly bullet-proof. Our Update Kit for the Dynaco Stereo 120 lets you rescue your Dynaco from demise in the dumpster and make it better than new! Many old Stereo 120ís have dead or dying amplifier modules. The update kit consists of new amplifier modules that you build. You recycle the power supply and chassis, and replace the old amplifier modules with the new. In a few short hours youíre ready to listen to tunes on equipment built by you!

New Module reuses old heatsink

You can buy the modules in kit form, or assembled. Youíll need an old Dynaco Stereo 120, as you will re-use its chassis, power transformer, and power supply. Our detailed construction manual guides you step-by-step through the process. Itís easier than a jig-saw puzzle, and a lot more fun.

Inside of an updated amplifier

Buy the Kit (or Assembled and Tested)

The kit costs $89. That gets you two 60 Watt Amplifier module kits, and for a limited time, free shipping in the USA. A pair of assembled and tested circuit boards costs $139. The assembled and tested version is currently built to order, so you'll have to wait a little bit to get one. You can buy all the variations here. Either form still leaves a lot of fun for you ripping out the old stuff and putting in the new.

Our Products and Prices
Part Number DescriptionCost
TCK Two single channel amplifier update kits$89.00
TCA Two Assembled and Tested single channel
amplifier update kits
$139.00
SHS Two Super Heat Sinks$20.00
FFT Set of four vinyl feet. The original ones
tend to disintegrate after 40 years.
$4.99
PSRC Power Supply Replacement Capacitors,
for use with the Updatemydynaco kits
$15.00
PSUG Power Supply Upgrade for Regulator,
for use with either original Dynaco or Updatemydynaco kits
$39.00
PSUGA Assembled and Tested Power Supply Upgrade for Regulator,
for use with either original Dynaco or Updatemydynaco kits
$79.00
BLUE Blue Light Kit,
for Stereo 120, PAT-4, Stereo 80, or SCA-80 Power Switches
$7.95
DRD4 Distortion Reduction Kit for PAT-4, an unbelievably economical
way to reduce distortion by 10X
$5.00
TCS Tone Control Switch for PAT-4, replaces the HI FILTER that
no one ever uses with a tone control defeat switch
$10.00
C12XX Take C12 from stock 3300 uF to 20,400 uF for better Bass$21.00
PAT4PWR Improve the sound of your PAT-4 Preamp with an electronically Regulated Power Supply$39.00
PAT4PWRA Assembled and Tested electronically Regulated PAT-4 Power Supply$79.00
PAT4LP Makes a huge difference to the sound of the phono preamp$24.00
C7X2 Better bass for original Dynaco amplifier modules.$25.00
RY301 Replacement Speaker Relay assembly for Stereo 400 Power Amp$24.00
SCA80C9 Replacement C9 for the SCA80, doubles capacitance for lower noise and better bass$14.00
SCA80C11 Replacement C11 for the SCA80, tighter, quieter regulated supply for the preamp sections$29.00

click here to order kits and parts

About the Kits

Component Quality

The amplifier modules are built on high quality 2-layer FR-4 PC Boards. Critical signal path capacitors have high linearity NPO or poly-film dielectrics. The output capacitor stays very linear owing to the constant bias voltage. The resistors are metal film, mostly 1% tolerance.

About Assembly

Kit construction has three steps:

  1. Removing the old amplifier modules, saving some parts for re-use.
  2. Stuffing and soldering the new PC boards.
  3. Mounting the new PC boards, and completing final assembly.

The kit uses all through-hole components. The circuit board has been specially designed with generous spacing between all the soldered points, making assembly easy.Check out our YouTube video, where we summarize the assembly process.

Assembly Manuals

To keep the assembly process simple, we've written manuals tailored to each kit. Click on the links to download the described item.

If you're having trouble viewing the manuals in Firefox, the following tip may be helpful. Go to Tools=>Options, pick the "Applications" tab. Scroll down and look in the left ("Content Type") column until you see any entries that include the words "Adobe Acrobat". In the adjoining space in the right ("Action") column, select "Use Adobe Reader (default)".

Obsolete Assembly Manuals

We've been doing this long enough that some products and/or PCB revisions are obsolete, e.g. no longer shipping. Typically, this involves subtle design improvements or increased ease of assembly. Don't refer to these manuals unless you have an older product.

Specifications

FAQS

Q. How long does it take to assemble?
A. Probably less than 5 hours of work. Disassembly takes about 1 hour. Building the new amplifier boards takes about 90 minutes each. Reassembly takes another 90 minutes.

Q. How much of the old Stereo 120 has to work?
A. Just the power transformer.

Q. What tools do I need?
A. At the minimum, youíll need:

  1. 30 Watt pencil style soldering iron
  2. Wire cutters and strippers
  3. Phillips and straight blade screwdrivers
  4. Needle nose and/or regular pliers
  5. Paper towels and Isopropryl alcohol (to clean thermal compound off old heat sinks)

Itís also handy, but not necessary, to have:

  1. Nut drivers
  2. A multi-meter

Q. I haven't soldered for a while. Is there somewhere I can get a refresher?
A. This youtube video reviews soldering technique.

Q. Do I have to be an electronics genius to build it?
A. Not at all. If you can stay calm and follow directions, you shouldnít have any trouble.

Q. Do I need any supplies that arenít in the kit?
A. Just isopropyl alcohol and some paper towels for clean-up. Just be careful about paper towels and isopropyl alcohol...they are a flammable combination. We supply solder and all the hardware youíll need. Youíll recover the wire and screws youíll need from the old Stereo 120. We recycle a number of the bits into the updated design. We even supply the thermal compound you need.

Q. Can I see schematics of the updated amplifier module?
A. Click here for a schematic of the amplifier module.

Q. What are the shipping options?
A. All shipments are by USPS Priority mail. This makes it easy for us, and gives you free shipping. The only exception is if the value of your order is less than $89.00, we charge $5.00 shipping.

Q. How is the new design different or better than the original design?
A. There are a number of ways. Here's a short list:

Video Above shows the upgrade process using
Updatemydynaco modules

Q. What IC is the design based on?
A. The design is based on National Semiconductor's LM3886.

Q. What wire gauge did Dynaco typically supply for hook-up wire?
A. The general hook-up wire used within the amps was typically 20 AWG, with a nominal conductor diameter of 32 mils. However, the speaker wire used in the amps and for the output inductors was 16 AWG, with a nominal conductor diameter of 50 mils. That was necessary because the original inductors used about 6 feet of wire.

Q. I don't see the answer to my question here. What can I do?
A. Submit a Technical Question

Old Versus New

The following plot compares 1 kHz THD+N versus output power for the old (original) and new (UpdateMyDynaco) designs. Note that the old design distortion increases a bit at first, indicating crossover distortion. The new design's distortion and noise is about 1/10 as much, and decreases smoothly as the level increases. This indicates a relative absence of crossover distortion. (Note...the absolute power numbers may be off by a few percent) The overall decrease in THD+Noise for both amps with increasing power just reflects that noise is a smaller part of the output as the input level increases.

Comparison of Distortion of New and Old Amplifiers

The original Stereo 120 had significant crossover distortion, visible as extended numbers of high harmonics at small output signal levels, like half a Watt. That crossover distortion was one of the most recognizable shortcomings of early transistor amps. The figure below shows the dB relative amplitude of the harmonics in the original Stereo 120:

half watt crossover distortion spectrum of original amp

Notice that the second harmonic is down about 60 dB, with 20 harmonics visible, indicative of classic crossover distortion.

The UpdateMyDynaco Stereo 120 has almost no distortion at a half Watt of output:

half watt crossover distortion spectrum of updatemydynaco amp

The second harmonic is down 92 dB, while the few other harmonics are more than 110 dB below the fundamental!

At 6.25 mW of output power, the differences are even larger. The original Stereo 120 crossover distortion harmonics are down 60-70 dB:

6.25 milli-watt crossover distortion spectrum of original amp

The UpdateMyDynaco Stereo 120 has harmonics in the noise floor, more than 100 dB below the signal.

6.25 milli-watt crossover distortion spectrum of UPdatemydynaco amp

More Stereo 120 Resources

Stereo 120 Data Sheet and Test Reports

Here are some scans of historic documents about the Stereo 120

Stereo 120 Original Assembly Manual

The updatemydynaco assembly manuals typically have all the information you need to make your Stereo 120 better than new. Still, some people like to keep their Stereo 120 original. Hereís a set of pdf files with high resolution scans of an original Stereo 120 assembly manual, plus a sheet with revisions.

Understanding the Stereo 120 Design

Weíve written a few documents, in case you want to repair your old Stereo 120, or just learn more about power amplifier design.

The Classic link for lots of Dynaco stuff is here:

Tubes 4 hifi specializes in tubes and tube based mods for Dynaco equipment, but they
keep a great page with all the Dynaco Solid State Schematics

Links for Audio Do-It-Yourself (DIY) Enthusiasts

If you're visiting this web site, you probably enjoy Audio DIY as a hobby. Here are some links you may find interesting:

Articles on Historically Interesting Solid State Amplifiers

The Stereo 120 wasn't the only history making amplifier, here are a few others:

Articles on Historically Interesting Vacuum Tube Amplifiers

These tube amps were designed by Hafler and Keroes before there was a Dynaco:

An older Audio Research and Mcintosh Design:

Old Dynaco Catalogs, Big Files, Beautiful Color Scans

I found some lovely old brochures in my files...a short (4 page) brochure, and a long (16 page) brochure. The scans are in color, and the 16 page brochure has 5 pdf files of about 6 Mbps each.

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