Onkyo Integra P-308
Onkyo Integra M-508
(1986 - 1991)

Later, more affordable siblings to the Grand Integra M-510, but bearing the same basic audio engineering design - with a build quality a few of kilos down...

The Integra P-308 sports a Subsonic Feedback Loop between its inputs and outputs to cancel spurious DC, ELF (no Jenna Elfman here, alas, only Extremely Low Frequency) signal components along DC drift and intermodulation distortion - without using coupling caps.
Cardans are set inside to keep short signal paths, and regulated, separate, trafo windings feed each block independently : phono EQ, linear gain, headphone. Eight inputs are available, with two dedicated to Phono MM cartridges or Phono MC cartridges, each with two-position trims. A contra-bass switch is added for those in need of more (light) guts down below - but only at 200Hz.
The export models had the Line 2 inputs located front, below the attenuator - strange move. The Tape 1 button was however (worldwide) labeled D.A.T. - Onkyo was one year ahead. Albeit adorned with many a dispensable function, build-quality of the P-308 is tremendously clean.

As in the Grand Integra M-510, Signal In-Phase Filters and Charging Noise Filters iron out differences in current and load between the P-308 and the amplifier - the Integra M-508. Click the buttons below for the clearly explained graphs representing these circuits.

The Integra M-508 is a miniature M-510 : same technology, same Real-Phase circuit. However, the box dwindles from 62kg to a mere 25 (still quite healthy !) and the overall build-quality goes with the price - not with the 950,000¥ of the M-510. Dual-transformers, too, but only one power cord and the eight caps amount to 80,000µF. The two Real Phase transformers are outlined in white on the image below.
Mostly, inside, is the Linear Switching circuit, also used in the M-510 : high-bias and wide-bandwidth (20MHz) power transistors to prevent crossover distortion and increase the Class A operating range without a sliding bias system.

Simulated wood sideburns for all and Onkyo's typical (of the times) tiny flashy LEDs indicating the P-308's state of mind : Servo Operation and Recording Output. Bar the lamp dimmer, the M-508's functions are identical to those of the M-510.
Both units have gold-plated terminals and a Grand Integra badge. Said badge in the original japanese versions was however placed elsewhere and only said... Integra :)

The M-508 at Onkyo.
The P-308 at Onkyo.
The P-308 with better inside images.
A real japanese P-308.