DetailS on Dynaco 120 Enhanced Custom Solid State Amplifier

 

CUSTOM DYNACO 120 SOLID STATE POWER AMPLIFIER 
60 Watts of Analog Power Per Channel
  • Fully rebuilt and customized, upgraded.
  • Incredible stereo fidelity and "enhanced" for performance, it sounds Amazing  
  • A really special piece of modernized vintage audio equipment. 
  • Painstakingly rebuilt, improved, burned in and tested. 
This is one well built amp that will deliver an exceptional music experience for many years to come. 
So inside this performance “enhanced” amplifier are (2) 10,000uF Supertech capacitors handling the speaker coupling duties. (2) 3,900uF Nichicon and (4) 3,300uF Cornell Dubilier caps at provide the filtering and power supply duties. The replacement circuit boards are very heavy duty and populated with all new components from Panasonic, Murata, WIMA, Nichicon, Vishay, TE Connectivity / Holsworthy, Yaego, Xicon, and Dale. Modern film capacitors in the signal path make this amp fantastic sounding. All metal film resistors provide accurate function and reliable current for the precise and proper operation of the circuit design. 

PERFORMANCE:

In factory stock trim the Stereo 120 has a damping factor of 40 vs. only 10 for the Stereo 70, this is where even the stock Stereo 120 will easily run away with the show. Adding to this advantage is the large increase of capacitance in this particular 120. This amp now provides tight, clean, and sustained bass, surpassing the capability of a stock 120 and well beyond that of the Dynaco model 70. This 120 has a power supply capacitance now rated at 20,400uf. In stock form it was a meager 3,300uf, this enhancement is nearly a 7 fold increase! The output capacitance was originally 3,300uf per channel, it is now 10,000uF per channel. The increased capacitance not only delivers much better response it greatly reduces low frequency distortion. The new high performance power supply board was needed to provide the clean steady power requirements for these capacitance increases and it works wonderfully. Higher output wattage from the Stereo 120 increases the overall performance distance between the Stereo 120 and ST-70 amps. But there’s more, a stock ST-70 has a Frequency response of 10Hz to 40kHz. An ST-120 has a wider rated Frequency response of 5Hz to 100kHz. The 120 has a lower distortion rating of 0.5% vs the 1% rating of the 70. The 120 is 60 watts per channel vs. 35 watts for the model 70. I’m not beating up the 70 here, I love the 70. These are just the hard cold facts and having owned and built multiple variations of each of these amps I am simply relaying to you what I know from first hand experience.

The specifics:

The (4) power transistors are brand new by Motorola. The original stock value of capacitor C12 was just 3,300 uF, not quite enough to get the maximum amount of low frequency power out of a Stereo 120. The new C12 capacitor configuration consists of (3) 6,800 uF 80 Volt Cornell Dubilier electrolytic capacitors. These are wired in a paralleled triple configuration to safely produce an impressive capacitance value of 20,400 uF. The original speaker coupling caps (C7) were also a bit on the small side, at 3300 uF each. This amp now uses (2) 10,000 uF Supertech electrolytic capacitors. These produce better bass by providing more power, and lower distortion. These capacitance increases made necessary the upgrading of the related components (like the power supply) and some other capacitors to make this all work properly, maintain long life and produce higher performance.  

The original speaker coupling caps (C7) were also a bit on the small side, at 3300 uF each. This amp now uses (2) 10,000 uF Supertech electrolytic capacitors. These produce better bass by providing more power, and lower distortion. These capacitance increases made necessary the upgrading of the related components (like the power supply) and some other capacitors to make this all work properly, maintain long life and produce higher performance.

The original Dynaco Stereo 120's power supply performance depended upon unpredictable parameters in the transistors. As such, it has a reputation of being somewhat unreliable and is difficult to repair. This modernized amplifier includes a new fully redesigned regulated power supply. This new PSU discreetly replaces the old PC-15 regulator board and the Q9 pass transistor. It re-uses the original heat sink and is coupled to the new upgraded capacitors at C9 and C12 with their values also being increased from 1,000uF each to 3,900uF each. This improved design and more reliable power supply also provides a soft start, has predictable current limiting, short circuit protection, accurate output voltage, super low output impedance, and low noise. This amp is simply better (and much safer) now than when it was new!

  • Original Dynaco aluminum heat sinks.Cleaned and reinstalled with fresh AAVID thermal paste to provide excellent heat dissipation.

  • 4 brand new feet with steel bushings are installed and the bottom of the chassis

  • The original power switch was cleaned and serviced, the old orange neon bulb was replaced with a nice Blue LED for the illumination

  • Original power cord is replaced with a new black polarized power cord.

  • Input RCA jacks are replaced with brand new high quality jacks. Chrome silver finish too, much nicer looking than the originals were.

  • The speaker terminals are original, cleaned up thoroughly and they're in great shape, these will accommodate either bare wire or banana plugs.

The (4) power transistors are brand new by Motorola. The original stock value of capacitor C12 was just 3,300 uF, not quite enough to get the maximum amount of low frequency power out of a Stereo 120. The new C12 capacitor configuration consists of (3) 6,800 uF 80 Volt Cornell Dubilier electrolytic capacitors. These are wired in a paralleled triple configuration to safely produce an impressive capacitance value of 20,400 uF. The original speaker coupling caps (C7) were also a bit on the small side, at 3300 uF each. This amp now uses (2) 10,000 uF Supertech electrolytic capacitors. These produce better bass by providing more power, and lower distortion. These capacitance increases made necessary the upgrading of the related components (like the power supply) and some other capacitors to make this all work properly, maintain long life and produce higher performance.  
The original Dynaco Stereo 120's power supply performance depended upon unpredictable parameters in the transistors. As such, it has a reputation of being somewhat unreliable and is difficult to repair. This modernized amplifier includes a new fully redesigned regulated power supply. This new PSU discreetly replaces the old PC-15 regulator board and the Q9 pass transistor. It re-uses the original heat sink and is coupled to the new upgraded capacitors at C9 and C12 with their values also being increased from 1,000uF each to 3,900uF each. This improved design and more reliable power supply also provides a soft start, has predictable current limiting, short circuit protection, accurate output voltage, super low output impedance, and low noise. 
  • This amp is simply better (and much safer) now than when it was new! 
  • Original Dynaco aluminum heat sinks.Cleaned and reinstalled with fresh AAVID thermal paste to provide excellent heat dissipation. 
  • 4 brand new feet with steel bushings are installed and the bottom of the chassis 
  • The original power switch was cleaned and serviced, the old orange neon bulb was replaced with a nice Blue LED for the illumination 
  • Original power cord is replaced with a new black polarized power cord.
  • Input RCA jacks were replaced with brand new high quality jacks. Chrome silver finish, much nicer looking than the originals were.  
  • The speaker terminals are original, cleaned up thoroughly and they're in great shape, these will accommodate either bare wire or banana plugs.  
  • The chassis is nice and straight. It was slightly oxidized with rust spots from dust/dirt mixed with ambient moisture over the years. This is typical of most of these units. Carefully cleaned the chassis using a high grade metal cleaner and specially treated to prevent further/future oxidation. The entire chassis was then hand polished to a decent shine, as you can see. The are always a few bad spots that remain, they're cosmetic only and very light. Some scarring and stains from previous use and neglect will always remain and must simply be accepted, consider it as "character". After all, these are nearly 50+ year old chassis! As you can see, it is now very presentable. 
  • The chrome chassis had 2 holes drilled in it when I got it so these were blacked off using metal hole plugs (see photo)
  • The cover is refinished in Dark metallic Grey and has a custom made solid aluminum identification badge with a dye sublimated image. 
  • The cover is straight, no dents, dings or warpage. 
This amp is now fully reconditioned into a fine state of appearance with super fantastic performance.
Idles and operates dead quiet, no hum or hiss, no popping or speaker thump when powering it on or off. 
  • Amazing output quality and has plenty of low end punch. Incredible sonics! 
  • A discreet and compact design, both clever and convenient, allows the amp to be placed where space is limited. 
  • Everything inside is in the same location as was originally and uses the original brackets and mounting locations. 
  • Run any speakers rated from 4Ω up to 16Ω (Ohms), simply hook them up. Just be sure they are rated and ready for the 60 watts per channel this amp produces.  
  • Rated at 100K ohms (100,000 ohms) of input resistance, be sure your preamp impedance is appropriate for use with this solid state slugger. (under 10K ohms) 

Description:  (from original Dynaco literature referring to a stock unit)  
"The Dynaco Stereo 120 is an all silicon transistor basic power amplifier for use with separate preamplifiers which have their own volume controls. The unit contains two 60 watt amplifiers on one chassis with a common power supply. Although the Stereo 120 is a solid state device, containing transistors and similar semiconductors, it has been designed to be used under normal conditions without special safety precautions, just as if it were a high grade tube amplifier. Thus it can be connected to source and speaker components and used with confidence in all conventional arrangements. There are no circuit breakers, speaker fuses, or other resettable devices to impede the use of the Stereo 120 under any reasonable conditions of use or abuse. This is achieved by using novel circuits (on which patents are pending) which automatically and instantly protect the amplifier. 
Specifications (from original Dynaco literature referring to a stock unit) 
Power output: 60 watts per channel into 8Ω (stereo)
Frequency response: 5Hz to 100kHz 
Total harmonic distortion: 0.5% 
Damping factor: 40 
Input sensitivity: 1.5V 
Signal to noise ratio: 95dB 
Speaker load impedance: 4Ω to 16Ω 
Semiconductors: 15 x transistors, 15 x diodes 
Dimensions: 13 x 10.5 x 4 inches 
Weight: 20lbs 
More about this amplifier: 
This amplifier is completely rebuilt, obviously. All replacement components / parts that were used are common, modern, and readily available components. Included in the sale is a CD-Rom with a copy of an original Dynaco 120 owners manual that includes the original assembly instructions, original part numbers and schematics. I am also including the manuals / instructions used for the upgrades that include parts lists and numbers with the values for the components used in this specific build. All diagrams and information I gathered and used for the project will be included for reference or any future service needs. 
Feedback posts from some of my amplifier customers: 
 "Thanks for a superior sounding system!!!" 
 “Okay, so now I’ve hooked up the stereo 120. OMG again! 
 "The sound of this defies logic! STUNNING!” 
 "Stunning build quality. Very happy with my new amp. Thanks again!"
 "There aren’t enough positives I can add here! The tube amp was a work of art!!" 
 "Great seller. The rebuild he did to the amp I bought from him was amazing. WOW"
 "Superbly packaged! Great back and forth convo, a true all-star, awesome seller!" 
 “Now I can’t darn well sleep because I can’t stop listening to this thing! You were right. This is definitely a giant killer!” 
"A+ seller. Excellent restored amp, accurately described. Great packing, communication, too."
 
Included with your shipment: 
The manuals, instructions, pictorials, diagrams, schematics and supplemental documentation are all included on a CD-ROM.

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