Power Supply Replacement Kit

About the Stereo 120's Power Supply

The Original Power Supply in the Stereo 120 exemplified Dynaco's design philosophy, to make a little bit of stuff do a lot. Here's a link to a white paper I wrote that goes into a lot of detail about the design of that power supply...Power Supply Circuit Description and FAQs

The bottom line about that design, is that what came out depended a bit more on some hard to control device parameters than we'd like. As a result, while most seemed to work OK, there'd be the occasional one that was pretty finicky, prone to blowing up if looked at sideways. Given the subtleties of the design, you'd be unlikely to find someone who could really repair it correctly.

The design had some features we'd like to preserve:

• slow start
• current limiting
• fold-back
• short-circuit proof
• compatible with original amplifier modules
• compatible with updatemydynaco updated amplifier modules

We'd also like to improve some things:

• better control of slow start current
• predictable current limiting that is independent of transistor parameters
• lower output impedance
• better temperature stability of output voltage
• more accurate output voltage
• lower drop-out voltage (gets more power out of the power supply)

About the Power Supply Replacement Kit

We've updated the design to acheive all the improvements listed above. Many people believe the quality of the power supply influences the quality of the sound. This power supply has definitely moved in all the right directions to make that happen.

The kit you build replaces the original regulator board (PC-15) and pass transistor (Q9) with brand new hardware. It reuses the original transformer, power supply heatsink, and power supply capacitors (although you can choose to replace the caps with our PSRC kit if you're building updated amplifier modules).

Top quality components are used throughout:

• FR-4 PC board
• 1% resistors (except for the output current sense resistor, which is 5%)
• 2% zener diodes
• all components used well within their ratings

The board is easy to build. All the components are through-hole, with clearly marked silk-screen, a detailed assembly manual, and sufficient component spacing to avoid solder bridges.

The board is easy to install. Numbered eyelets on the board correspond to the original PC15 numbers. The mounting arrangement, while compatible with the existing amplifier, actually leaves significantly more room to work inside the amplifier.

Specifications

Here are the specifications for the updated power supply board

• nominal output voltage: 72 Volts
• typical output voltage accuracy: +/-2.5%
• minimum load resistance that allows the power supply to start: 200
• DC load current that triggers protection circuits: 3 Amps, allows more than 60 WPC into 8 Ohm loads
• Output impedance: 17 milli-Ohms at DC, dropping to 3 milli-Ohms above 10 Hz (simulation)
• Noise (0.360 Amp DC load, nominal 120 V 60 Hz AC input): all 60 Hz harmonics have amplitude of 10 uV or less (simulation)

Assembly Manual

Here it is, the detailed assembly manual for the power supply replacement kit. It covers all the applications of the upgrade kit:

• replacing the power supply when standard amplifier modules remain
• replacing the power supply when the amplifier modules have been upgraded
• replacing the power supply when the amplifier modules have been upgraded and the PSRC kit has been installed

Download the Power Supply Replacement Kit assembly manual .

Ordering

Price: $39.00

Click here to purchase the power supply upgrade kit.

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