Summary of Alchemist Forseti APD15A RC Integrated amplifier
This article details the repair of a 1990s Alchemist Forseti integrated amplifier suffering from a DC fault on its loudspeaker outputs. The unit features a robust dual mono design with extensive heatsinking, two pairs of output transistors per channel (2SA1302 and 2SC3281), and dedicated power supplies including 200VA toroidal transformers and large capacitors. Access requires removing the top panel with an Allen key.
Parts used in the Alchemist Forseti Integrated Amplifier:
- Top panel secured by 13 cap head screws
- Allen key for screw removal
- Printed circuit boards
- Power supplies
- Output transistors (2SA1302 PNP and 2SC3281 NPN)
- 200VA toroidal mains transformer
- Bridge rectifier
- Four 10000uF/50V reservoir capacitors
- Electronic switching relays
- Heatsinks
- Rear panel connectors
We recently had a customer present this faulty Alchemist Forseti integrated amp for repair – I’d guess this dates from the 1990’s and has been well looked after. It’s a bit of a bruiser as you can see from the extensive heatsinking!
Unfortunately it developed a DC fault on the loudspeaker outputs and destroyed the customers speakers, so it’s now in the naughty corner awaiting surgery.
Access to the internal circuitry is via the top panel, which is secured by 13 cap head screws.
There are 13 screws to remove in total, an allen key is needed.
The rear panel has good connectivity for analogue sources (all line level, no phono input but there are two pre-outputs to drive extra power amps should you need even more power.
Once the top panel is removed, this is the view of the printed circuit boards and power supplies – it’s very nicely laid out.
The Forseti is constructed as a dual mono design, which should give better channel separation and therefore improved stereo image – here is one channel’s output stage which employs two pairs of output transistors per channel – 2SA1302 are the PNP transistors and 2SC3281 are the NPN making a class B push pull output stage.
Each amplifier channel is fed power from it’s own dedicated power supply comprising 200VA toroidal mains transformer, bridge rectifier and four 10000uF/ 50V resevoir capacitors.
All of the the inputs are electronically switched by relay to keep signal paths extremely short for best possible sound quality.
The Forseti is a very well constructed amplifier which promises excellent performance – we will have to wait to hear this until we have diagosed and fixed any issues.
For more detail: Alchemist Forseti APD15A RC Integrated amplifier
- What caused the need for repair?
A DC fault on the loudspeaker outputs destroyed the customer's speakers. - How do you access the internal circuitry?
Remove the top panel which is secured by 13 cap head screws. - What tool is required for disassembly?
An Allen key is needed to remove the 13 screws holding the top panel. - Does the amplifier have a phono input?
No, it has good connectivity for analogue sources but no phono input. - Can this amplifier drive extra power amps?
Yes, there are two pre-outputs available to drive additional power amplifiers. - What type of output stage does it use?
It uses a class B push pull output stage with two pairs of output transistors per channel. - What specific transistors are used in the output stage?
The unit employs 2SA1302 PNP transistors and 2SC3281 NPN transistors. - How many capacitors are in each power supply?
Each dedicated power supply comprises four 10000uF/50V reservoir capacitors. - Why are relays used for inputs?
Relays electronically switch all inputs to keep signal paths extremely short for best sound quality.
