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Identity and Product Position

Historical Facts (Short)

• The A-8670 appears in the late-1980s transition period before remote/motorized control became standard in many integrated amplifiers.
• Contemporary German press mentions in the research set include:
• Stereoplay (Nov 1989): Spitzenklasse I class mention.
• HiFiVision (Apr 1990): Spitzenklasse ranking entry.
• In the compiled notes, A-8670 is repeatedly treated as an analog-centric model in the line because it avoids later remote-control switching complexity.

Production details (field-backed)

• No SMD components — entirely through-hole construction.
• Modular plug-in boards for each functional section (preamp, power amp, protection, PSU, switching).
• All-metal chassis with no noticeable plastic structural parts.
• Gold-plated connectors on phono and CD inputs.

Complete Electrical Spec Sheet (Manual-Backed)

Power and distortion

Parameter	Value
Continuous output (RMS, both channels driven)	105 W/ch min, 8 ohm, 20 Hz-20 kHz
THD at rated output	0.008%
DIN output	2 x 115 W @ 8 ohm, 1 kHz
DIN output	2 x 160 W @ 4 ohm, 1 kHz
Dynamic power	303 W @ 2 ohm
Dynamic power	235 W @ 4 ohm
THD at 1 W output	0.008%
IMD at rated output	0.005%
Damping factor	150 @ 8 ohm (1 kHz)

Frequency, equalization, and tone

Parameter	Value
Frequency response (CD/Tuner)	2 Hz-50 kHz (+0, -1 dB)
RIAA deviation (phono MM)	+0.3 dB, 20 Hz-20 kHz
High-cut	6 kHz (6 dB/oct, treble minimum)
Subsonic filter (MM/MC subsonic modes)	20 Hz (-3 dB, 6 dB/oct)
Bass range	+/-8 dB @ 100 Hz
Treble range	+/-8 dB @ 10 kHz
Muting	-20 dB

Input sensitivity and impedance

Input	Sensitivity	Input impedance
Phono MM	2.5 mV	50 kohm
Phono MC	160 uV	130 ohm
CD	150 mV	30 kohm
Tuner	150 mV	30 kohm
Tape Play	150 mV	30 kohm

Output, overload, and noise (IHF-A)

Parameter	Value
Tape Rec output level/impedance	150 mV / 1.0 kohm (phono)
Phono MM overload	200 mV RMS @ 1 kHz
Phono MM overload THD	0.012%
S/N — Phono MM (5.0 mV input)	94 dB
S/N — Phono MC (0.5 mV input)	75 dB
S/N — CD Direct	107 dB

Mains and physical

Parameter	Value
Europe models	AC 220 V, 50 Hz
USA/Canada models	AC 120 V, 60 Hz
UK/Australia models	AC 240 V, 50 Hz
Worldwide models	AC 120/220 V switchable, 50/60 Hz
Dimensions	435 x 157 x 391 mm
Weight	13.5 kg (29.8 lb)

Front Panel and Control Map (Manual-Backed)

Controls and functions

No.	Control	Function
1	Power switch	Main on/off
2	Servo operation indicator	Servo status LED
3	Muting switch	Signal attenuation mode
4	Mode selector	Stereo/Mono
5	Volume control	Main level
6	Input selector + indicators	Phono, Tuner, CD-2, CD-1, Source, Tape-2, Tape-1/Video, DAT
7	Speaker selector	Off / A / B / A+B
8	Headphone jack	Phones output
9	Bass control	Tone network low band
10	Treble control	Tone network high band
11	Balance control	L/R level trim
12	Source Direct switch	Tone path bypass / direct path
13	Recording source selector	Routes recording source among tape/dat/source options
14	Cartridge selector	MC subsonic / MC / MM / MM subsonic

Signal routing implications

• Input selector and record selector are not the same path; recording source routing can be independent.
• Source Direct changes where tone network is inserted in the signal path.
• Cartridge mode selector changes phono front-end operating path (MM/MC and subsonic configurations).

Connectivity and Load Rules

Rear panel I/O summary

• Inputs: Phono, CD-1, CD-2, Tuner, Tape-1/Video, Tape-2, DAT.
• Recording/playback loops: Tape-1, Tape-2, DAT (depending on selector mode).
• Speaker terminals: A and B sets.
• Headphones: front panel jack.

Proprietary Technology Names

Name	Japanese	Function
Delta-Turbo Power Supply	デルタターボ電源	Secondary filtering topology to keep charging pulses out of audio ground; reduces supply-rail IMD.
Super-Servo	スーパーサーボ	Servo circuit applied throughout the signal path to eliminate time-difference IMD and maintain DC offset stability without coupling capacitors.
Opto-Drive	オプトドライブ	Optocoupler-based drive system in the power amplifier; optically isolates control circuits from the audio signal path.
Source Direct	ソースダイレクト	Bypasses the Super-Servo tone network, routing the signal directly from the preamp to the power amp.

Architecture and Signal Topology

High-level signal path

Interactive Front Panel Replica

Power up, wait for servo LED, set speakers to A/A+B, then raise volume

ONKYO Integra INTEGRATED STEREO AMPLIFIER

Power ON / OFF Servo Operation 4 Blocks Separate Construction Anti Electromagnetic Interference Transformer Muting
-20dB / OFF Mode A MONO B STEREO Volume Input Selector OFF A B A+B Direct Tone Defeat Defeat High Cut Filter 0 Low Impedance Drive
Discrete Amplifier Tone Direct DAT->TAPE-1+2 OFF SOURCE TAPE-1->DAT+2 DUBBING MC SUBSONIC MC MM MM SUBSONIC Speakers Phones Bass Treble Balance Source Direct Rec Selector Cartridge A-8670

Phono Tuner CD-2 CD-1

Source Tape-2 Tape-1/Video DAT

A

0

0

C

Tone

Off

MM

Rail map exposed in the block diagram

Rail	Approximate value
+B1	+55 V
-B1	-54 V
+B3	+22 V
-B3	-22 V
+B4	+22 V
-B4	-22 V
+B5	+13 V

Supply/regulator chain elements called out in the manual

• Transformer: T901 (NPT-1040 family designation in manual).
• Rectification branches: D921, D931, D932.
• Constant-voltage blocks tied to Q109/Q110 and Q901/Q902/Q903/Q904 domains.

PCB and Sub-Assembly Map

The chassis/parts pages show a strongly modular multi-board design.

Assembly ID	Board name
U001	NAAF-3601-2 main circuit board
U003	NATEC-3603-2 speaker terminal board
U004	NASW-3604-x power switch board
U005	NATEC-3605-x fuse board
U006	NASW-3607-2 input selector switch board
U007	NADIS-3608-2 input LED board
U008	NASW-3609-2 source direct switch board
U009	NAAF-3616-1 volume control board
U010	NAAF-3611-2 tone control board
U011	NASW-3612-2 muting/mode switch board
U012	NADIS-3613-2 power LED board
U013	NADIS-3614-2 servo LED board
U014	NAAF-3617-2 equalizer board
U015	NAPS-3620-2 power supply board
U016	NASW-3602-2 speaker switch board

Why this matters for service:

• faults can often be isolated to specific control boards instead of probing the entire unit blindly
• switch-related intermittent faults are physically distributed across several boards

Board-Level Component Facts

Main board (NAAF-3601-2) — selected components

Designator	Device / Value
Q519, Q520	NJM4560DX
Q585	NJM2902N
Q851	TA7317P (protection IC)
Q586	TLP-531 (photo coupler)
Q501, Q502	2SK389GR or 2SK389BL
Q613, Q614	2SC3855 (power output NPN)
Q615, Q616	2SA1491 (power output PNP)
Q903, Q904	2SK246GR
R615-R618	0.47 ohm, 5 W, metal plate
RL851, RL852	NRL-2P7A-DC12-43 (relay)
C913/C914	1000 uF, 6.3 V electrolytic
C915	0.047 uF, 50 V film
C934	220 pF, 16 V electrolytic

Equalizer board (NAAF-3617-2) active devices

Designator	Device
Q105, Q106	NJM5532D
Q109	M527M20L
Q101, Q102	2SK146GR or 2SK146BL
Q107, Q108	2SC1815GR
D101-D104	TLR112

Equalizer board passives: mixed styrene/film/electrolytic values, consistent with low-level phono equalization design.

Power-supply board (NAPS-3620-2) key items

Item	Value/type
C921, C922	15000 uF, 71 V electrolytic (see variant note below)
D921	PB102F
D925, D926	1NS402F
D931, D932	RDF02F
R923	51 ohm, 1/2 W metal oxide
R932, R933	0.22 ohm, 1/2 W metal oxide

Switch/control boards with notable part families

Board	Notable components
NASW-3607-2 input selector	NPS-442-L575 switch family
NASW-3609-2 source direct	NRSF-142-2SS switch
NASW-3612-2 muting/mode	NPS-222-L56 switch family
NAAF-3611-2 tone control	variable resistor network for tone control

Protection Circuit and Bench-Test Behavior

Protection IC context

• Protection logic is centered on Q851 = TA7317P.
• Relay and speaker switching stages are downstream of main amp output block.

Manual procedure facts

The adjustment/protection page provides explicit expected behavior:

1. Relay should engage about 5 seconds after power-on.
2. Servo indicator LED should light at the same time.
3. Relay should drop shortly after power-off (about 0.5 s in procedure text).
4. Applying +200 mV DC at CD input test condition should force relay off.
5. Applying -200 mV DC under same condition should also force relay off.
6. With the procedure test fixture and no load baseline:
7. 2 ohm load at ~35 V p-p should not trip relay in that specific test setup.
8. 1 ohm load may make relay chatter then latch off.
9. off-state should clear within roughly 1 minute, or by power-cycle.

Bias / Idle Current Adjustment (Manual)

Failure Patterns with Practical Diagnostics

#	Fault	Key symptoms
1	Input selector oxidation	Intermittent channel drop, crackle on switching
2	Source Direct switch contamination	Dropout in direct path only
3	Relay/contact aging	No relay click, low-level dropouts
4	Regulator-area heat stress	Unstable logic rails, random protect triggers
4a	TA7317P phantom triggers	Overlaps with (4); passive drift around Q851
5	Bias drift / trimmer aging	Idle current won't settle near target
6	Load misuse heating events	Excessive heatsink temp under A+B

1) Input selector oxidation (very common in field notes)

Symptoms:

• intermittent channel drop
• crackle when switching sources
• source-dependent no-audio states

First checks:

• reproduce while cycling selector positions repeatedly
• inspect/clean selector board and contacts
• verify that issue is upstream of relay by checking phones/speaker behavior consistency

Fixes (Field-backed):

• Temporary: DeoxIT D5 spray into the switch body, cycle 30-50 times with unit powered off.
• Permanent: desolder entire switch block from PCB, disassemble spring contacts, burnish silver-plated rails/forks with fiberglass pen or metal polish (Simichrome/Brasso), rinse with 99% IPA, re-lubricate with dielectric grease (DeoxIT FaderLube or clear silicone), reassemble, verify continuity on all pin combinations before resoldering.

2) Source Direct switch contamination

Symptoms:

• normal output in tone path, dropout in direct path only

First checks:

• A/B test tone vs direct repeatedly
• treat as separate switch-domain fault, not automatically as relay failure

Full rebuild procedure (Field-backed):

1. Desolder multi-pin Source Direct switch from front panel PCB. Use copper braid or vacuum pump to protect pads.
2. Straighten bent metal tabs holding the casing together.
3. Extract plastic slider assembly from metal housing. Watch for spring-loaded ball detent — microscopic springs will escape if dropped.
4. Clean oxidized silver-plated fork sliders and static rails with fiberglass pen or metal polish. Do not use sandpaper (strips plating).
5. Rinse with 99% IPA to remove all residue.
6. Apply minimal dielectric grease to rails (DeoxIT FaderLube or clear silicone).
7. Reassemble slider, re-engage spring/latching pin mechanism, bend tabs back.
8. Verify continuity on every pin combination in both latched states before resoldering.

3) Relay/contact aging or relay-drive path faults

Symptoms:

• no relay click on startup
• low-level dropouts that recover at higher volume
• intermittent one-channel output

First checks:

• protection state timing vs manual expectations
• coil voltage and relay drive path
• contact resistance/pitting under load

Replacement cross-references (Field-backed):

• Finder 40.52 series
• Omron G2R-2 (check 5mm vs 3.5mm pin pitch; may require bending pins or drilling PCB)

4) Regulator-area heat stress

Symptoms:

• unstable control logic rails
• random protect triggers
• thermal intermittence

First checks:

• inspect/reflow around regulator transistors and hot resistors
• verify +/-B3, +/-B4, +B5 stability under idle and signal conditions

4a) TA7317P protection IC phantom triggers

Symptoms overlap with (4) but root cause is passive drift around Q851 rather than rail instability.

5) Bias drift / trimmer aging

Symptoms:

• idle current cannot settle near 15 mV target
• excessive idle heat or crossover distortion

First checks:

• verify trimmer integrity
• verify thermal coupling and nearby transistor pair health
• verify emitter resistor values in-circuit and out-of-circuit where needed

6) Load misuse heating events

Symptoms:

• excessive heatsink temperature under A+B usage
• protection triggering with mixed low-impedance loads

First checks:

• confirm real load per channel and A+B effective load
• enforce 8 ohm minimum for A+B mode

Service Workflow That Minimizes Rework

Step	Phase	Focus
1	Visual / safety	Fuses, burns, cracked solder, damaged connectors
2	Power baseline	Confirm major rails and regulated rails before audio tracing
3	Protection path	Startup delay, relay action, DC detect response
4	Switch isolation	Input, source-direct, mode/muting, record selector
5	Main amp	Bias trim range, emitter resistor integrity, output pair behavior
6	Phono / equalizer	Only after line-level and protection are stable
7	Final matrix	All inputs, tape loops, direct/tone, A/B outputs, phones

Parts Strategy (Reality-Based)

Recap priorities (if doing full restoration)

Highest impact/age risk first:

1. Power-supply electrolytics (including main reservoirs and rail decoupling).
2. Control/logic rail electrolytics in regulator-adjacent zones.
3. Phono/equalizer electrolytics (noise-sensitive path).
4. Only then consider broad signal-path capacitor substitution experiments.

Output transistor replacement rule

• Replace NPN/PNP output devices as matched complementary sets.
• Always re-check bias and protection behavior immediately after replacement.

Pairings and Use Cases (Factual, Not Marketing)

What the electrical profile implies

• Damping factor 150 and strong dynamic power numbers generally favor good woofer control with conventional dynamic speakers.
• Stable high-current behavior is useful for difficult loads, but this does not remove the A+B impedance rule.

These are repeatedly mentioned pairings in the research set; treat as reported experience, not universal truth.

Documented pairing examples

Speaker model/family	Reported outcome
Acoustic Energy Aelite One	strong bass control from compact cabinet
Vintage Jamo (Power 330, D365)	high-output, dynamic playback pairing
Technics SB-3670	period-correct late-80s pairing in EU
Nubert NuLine/NuVero	well-controlled and effortless drive
Older KEF / older B&W	often cited as good tonal match

Polish community pairings (Field-backed)

IQ sat, MB Quart 802, Visonik Expuls 2, Philips FB820, ELAC EL 75, New Mildton 170, Bolero 200, Mission 703/773, Onkyo SC-550.

Pairing cautions

• Bright/forward speakers can become fatiguing for some users at high SPL.
• Repeated field notes mention audible strain/coloration when volume is pushed very high (around/above 12 o'clock region on dial).

Reported Sonic Character (Compiled, Cross-Language)

This is field-backed, not bench-measured.

Range	Character
Bass	tight, punchy, controlled
Mids	slightly forward/present
Treble	generally clean; harder when pushed
Macrodynamics	strong

Cross-brand comparisons that repeat in notes

Compared to	Assessment
Same-era Yamaha	Often described as less aggressive, more fluid
A-8650	A-8650 reported as softer; A-8670 as more forceful/dynamic
A-8690	A-8670 favored by users who prefer a purely analog path with external modern DAC
Kenwood KA-1100SD	Similar power class; AudioKarma consensus is "can't go wrong with either." Kenwood has adjustable phono stage but uses hard-to-source output transistors. Onkyo typically ~$100 cheaper on secondary market. Field-backed
Sansui AU-X501	German reviews note the Sansui maintains better control at high volumes despite lower specified power; softer midrange character. Field-backed

Intra-Series Comparison Snapshot

Item	A-8650 (compiled)	A-8670	A-8690 (compiled)
Position	Lower sibling	Upper-tier analog	Flagship in family branch
Power class @ 8 ohm	~80 W/ch	105 W/ch min RMS	~100 W/ch
Damping factor	lower than 8670 in compiled notes	150	~100 in compiled notes
Digital section	none	none	includes onboard DAC
Common preference split	softer presentation	stronger drive/control	feature-rich but older digital stage

High-Value Facts for Fast Recall

Recap Reference (Field-backed)

Recommended cap types by board section. Use 105°C rated capacitors throughout.

Board section	Recommended types	Notes
Power supply main reservoirs	Nichicon KG Gold Tune (15,000-18,000 uF, 63-80 V)	Highest aging risk; replace first
Regulator-adjacent electrolytics	Nichicon KG Gold Tune	Heat-stressed zone
Phono/equalizer electrolytics	Elna Silmic II	Noise-sensitive path; lowest-noise caps available
Signal-path coupling (under 4.7 uF)	WIMA MKS (film)	Film replacement for dried electrolytic coupling caps
Broad signal-path electrolytics	Elna Silmic II or Nichicon KG Gold Tune	Lower priority; only after PSU and phono are done

Do not touch ceramic or mica capacitors unless physically damaged.

Modifications (Field-backed)

Modification	Details
Bridge rectifier upgrade	Replace stock rectifiers with Schottky or fast-recovery diodes for tighter supply rail behavior
Audiophile recap	Nichicon KG Gold Tune for PSU, Elna Silmic II for signal path, WIMA MKS for film positions (see Recap Reference above)
Binding post upgrade	Replace original speaker terminals with WBT-style or quality banana-compatible posts
Op-amp rolling	Stock NE5532 (phono/preamp) → OPA2134 (smooth FET-input) or LM4562 (lowest distortion). Install DIP-8 sockets if soldered. Verify operating voltages before rolling
Input selector replacement	ELMA Type 04 (2x6, non-shorting) or Cole S3900 rotary switch retrofit. Requires significant modification work to fit original panel cutout