JJ 828 Stereo Röhrenverstärker

The basic design criteria for amplifier JJ 828 were as follows:

• - integrated amplifier with remote control
• - minimum 50W output power per channel
• - sufficient damping factor at minimal global feedback
• - great sound

Our designers have chosen this solution:

• - high quality components
• - inputs switched by signal relays
• - independent power source for each channel
• - ultra linear circuitry with KT 88 tube
• - high operational current of KT 88 (75mA)
• - KT88 cathodes feedback (CFB) via output transformers
• - output transformer unique design

For the first time, tube ECC 99 is used as a driver for KT 88. This is a tube specifically developed by JJ Electronics for application as a unique linear driver for high power tubes KT88 and 300B. Concertina with ECC 82 parallel was chosen as a phase inverter in front of the ECC 99.

There are two feedbacks in this design: one is a global feedback from OT (–6dB) and the second is from the KT88 cathodes through OT (5dB).

Output transformer is based on C-core made from 0.13-0.15 mm sheets, with air distance 2 x 0.05 mm. The air distance provides linearization of electrical parameters within the entire power range. The manufacturing of C-core, similarly as in the case of the JJ 322 amplifier, is under complete control of JJ Electronic. There are two OT coils: each has four primary, four bifilar secondary and two feedback windings. This OT design yields 3mH at Lp 35H lsp.