Onkyo TX-2500

Onkyo TX-2500MKII

Circa
1 9 7 6 c.1976
1 9 7 8 1978

Pioneer's original forte and original business was loudspeakers, Onkyo made it with receivers : properly integrating three separates into one enclosure.
Onkyo is nowadays only working around mini-components, integration toward reduction, and home-theater, the latter being integration pushed to the limit : intergalactic battleships, earthquakes and super-heroes all in one room !

Whatever the brand, most receivers made in Japan were export-only : Japan never really cared for receivers although integration would've been practical for most japanese audiophiles and their... small rooms.


The TX-2500 hides behind its very conservative front what was beginning to be common features in 1976 : PLL MPX decoder, tuning servo-locking and "Accutouch" tuning knob.
Accutouch temporarily inhibits the locking circuits for manual, large-scale, tuning : hands-on ; when released, hands-off, the locking function clicks back in and fine-tunes on its own the locked station until the TUNED indicator lights up.

A variant of Accutouch was also used by Luxman at the time for temporary volume muting.

The TX-2500 tunes in AM or FM with a 3-gang varicap, two IF amp stages, 4-elements ceramic filters and an Onkyo-made low-pass filter.
One-step on/off muting is at hand, just like a (potential) Dolby FM adaptor (in the future) for the (upcoming) Dolby FM (maybe) broadcasts which reduces deemphasis to 25µs instead of 50µs.
The latter feature was removed from the 1978 MKII version but the actual 25µs / 50µs function was still there ; it just wasn't labeled DOLBY anymore and the back loop was scrapped.

The main section of the 2500 boasts a beefy transformer (we're in 1976, not 1979), fairly low distortion, and square-wave response worthy of an H/K product : only 5% tilt at 50Hz.

The preamp section had two RCA & DIN tape loops, the Dolby FM loop, one phono MM input, hookups for two loudspeaker pairs and dubbing from tape 1 to tape 2. It is simple, it works, it makes music.


The TX-2500MKII is a visual redesign in 1978 style with however much better specifications for the preamp and tuner sections and quite a bit more output power, too. So the inside of the two versions must be rather different...


A TX-2500MKII restoration here.

Onkyo TX-2500, image 1 Onkyo TX-2500, image 2 Onkyo TX-2500, image 3
Onkyo TX-2500 specifications
Title Value
(TX-2500MKII variants are noted in BLUE)
MAIN section MAIN section
Output : 120W (dynamic output) 2x 100W (DIN)
2x 40W (4 Ohm, 1Khz, 0,5% THD) 2x 70W (DIN)
2x 30W (8 Ohm, 1Khz, 0,5% THD) 2x 50W (DIN)
2x 34W (4 Ohm, 40Hz...20Khz, 0,5% THD)
2x 27W (8 Ohm, 40Hz...20Khz, 0,5% THD)
THD : 0,5% at rated power 0,1%
0,2% at 1W output
IMD : 0,5% at rated power
0,3% at 1W output
Damping factor : 40 (8 Ohm, 1Khz, 10W output)
Power bandwidth : 2Hz...60Khz (± 1dB
Square-wave tilt : < 5% at 50Hz
PRE section PRE section
Inputs : 2,5mV / 50kOhm (phono)
150mV / 50kOhm (tape RCA)
30mV / 50kOhm (tape DIN)
350mV (30%) / 50kOhm (Dolby in)
150mV / 50kOhm (tape out, Dolby out)
Maximum phono input : 150mV (1Khz ; 0,5% THD)
Bass control : ± 12dB at 100Hz
Treble control : ± 10dB at 10Khz
High filter : 6Khz
S/N ratio : 65dB (phono ; IHF-C) 85dB
80dB (tape ; IHF-C)
TUNER section TUNER section
Tuning range : 87,5...108MHz (FM)
530...1605Khz (AM)
Usable sensitivity : 2µV (11,2dBf, mono, FM) 1,6µV
5µV (19,2dBf, mono, FM)
25µV (AM)
Sensitivity at 50dB s/n : 4µV (17,2dBf, mono, FM) 4,5µV
40µV (37,2dBf, stereo, FM) 45µV
IF frequency : 10,7MHz
Capture ratio : 2dB 1,5dB
Image rejection : 45dB (FM)
40dB (AM)
IF rejection : 80dB (FM)
30dB (AM)
S/N ratio : 65dB (FM mono)
60dB (FM stereo)
40dB (AM)
Adjacent channel attenuation : 60dB (FM)
Selectivity : 42dB (FM ; DIN ; ±300Khz ; 40Khz hub)
AM suppression : 50dB
THD : 0,2% (FM mono)
0,4% (FM stereo)
0,8% (AM)
Frequency response : 30Hz...15Khz (+0,5 / -2dB)
Stereo separation : 37dB (1Khz, FM)
30dB (100Hz...10Khz, FM)
Muting threshold : 4µV
Stereo threshold : 4µV
Servo-Lock threshold : 4µV
Pilot cancellation : 60dB
General General
Componentry : 1 FET
54 transistors
6 ICs
47 diodes
Dimensions : 48,8 x 16,3 x 40cm
48,3 x 16 x 37,1cm
Weight : 12kg.
Onkyo TX-2500 : 0 topic
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page online since : august 2010
page updated : august 2010
page type : LGT / KNB
page weight : 245.98 Kb / 0 b

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