We are on vacation until October 13. All orders placed so far have been shipped.
SAC FET amplifier
• Push–pull Class AB
• Rise time < 2 µs
• Damping factor 3000
• Output with field effect transistors
• Power up to 200 Watt / 8 Ohm (RMS)
• 2x 30 till 2x 70 VDC
• 100 x 50 mm, ~ 30 mm high
• kit mono to solder yourself
• soldered and adjusted
additional heatsink required, e.g. from 75x160x40mm (6506G)
Mounting phalanx (photo) between heat sink and board included
Example transformer 2x37VAC 330VA = 130Watt / 8Ohm with 1kHz sine wave 2V rms
- DXF file of the phalanx
- GIF file of the phalanx
The SAC FET amplifier principle on the smallest possible circuit board.
The small design makes it also ideal as a replacement in defective amplifiers or receivers.
The module can be operated with +- 30 to 70VDC power supply without changes.
Depending on the voltage, outputs of 140 watts into 8 ohms can be easily achieved.
Thanks to a low internal resistance, the sophisticated circuit controls the speakers with a very high damping factor.
The masterpiece of Axel Schäfer, who has developed and improved the design, which can be found at several well-known manufacturers, over decades.
Review 6moons: SAC Il Piccolo
Example with outsourced transformers
Supply amplifier
• longlife Vishay BC capacitors
• 4 x 10.000 µF / 63 Volt
• 4 x Philips MKT foil capacitors
• inline bridge rectifier or single diodes
• 100 x 100 mm, high 44 mm
• kit to solder yourself
• instead with Nippon Chemicon SMH
• 4 x 12.000 µF / 80 Volt
• overall height 66mm
• kit to solder yourself
There is the option of connecting an amplifier module on three sides.
A connection of two amplifier modules is very good in symmetrical operation,
because such a power supply is used very evenly in phase opposition.
It does not matter whether the signal is fed symmetrically using XLR or asynchronously using Cinch and the two amplifier modules are self-symmetrizing using a bridge circuit.
Of course, use in a stereo application with only one power supply is also possible.
When used as a mono block, the transformer, power supply and amplifier can also be connected in a row in a way that is easy to connect and short of cables.
For a suitable transformer, some things should be considered, such as efficiency / power loss.
As the voltage increases, the amperage should also increase.
The smaller the ampere indication on the transformer, the higher the open circuit voltage of the transformer deviates upwards.
The dielectric strength of the capacitors in the power supply should be taken into account - at 10,000µF/63Volt the AC voltage of the transformer should be max. 42 Volt (~ VAC * 1.4 = VDC).
So for lower VA power rather orient at the lower end of the possible voltages.
A conventional transformer with sheet metal laminations can store more magnetic energy than a toroid, but should possibly be shielded laterally with sheet metal.
The advantage of a toroid is only the smaller lateral radiation and thus a renouncement of a structural shielding.
For the operation of both stereo channels, transformers with 2x37VAC and 4.45 Ampere in traditional design have proven themselves well (330 VA).
As potted toroidal cores also e.g. 2x36VAC with 3.5A were used originally.
The manufacturer of the original transformers was Kramer in 32289 Rödinghausen Germany, the first one mentioned was a modification for SAC - a standard 500VA which was unwound to 330VA, this significantly reduced the mechanical hum.
Otherwise, this manufacturer seems to me to be very good value for money: ring core transformers
