Sujet Les différents modèles de JC120

Ma contribution :

Earlier models JC120 is easily identified by the look of the rear panel. JC120 started producing  1975 and had a footswitch connection for reverb at rear side then at January 1976 chorus/vibrato footswitch was added.
In October 1976 JC120 gets new connection for distortion and 1978 new jack for ext speaker. 1979 there is two main in jacks and jacks for footswitches and ext speakers are changing place  until 1984 when JC120 gets modern design of rear plate.

JC-120 serial:
380100 - 415099 input stage BJTs+FETs
420600 - 471649 input stage similar
481650 - 502499 input stage IC TA7122
512500 - 779499 input stage similar
789500 - 248099  input stage FETs
(950100 - 283149 USA) same
258100 - up input stage FETs+BJTs
(293150 - up USA) same

Ici, un descriptif des différents modèles avec les changements

Citation de https://www.ssguitar.com/index.php?topic=2243.0 :

3rd Edition (1979) - applicable to
JC-120  S/N  380100 - 415099

- Gain stages are discrete, combinations of BJTs and FETs
- Distortion circuit is an overdriven FET+BJT stage permanently in circuit
- Features a FET-differential -based "pre-limiter" preventing power amp hard clipping
- Discrete BBD oscillator driver
- Separate LF oscillators for vibrato and tremolo. Vibrato /w. depth and speed control in front panel.
- Line out tap at speaker output

JC-120   S/N   420600 – 471649
JC-160   S/N   440100 – 470549

- Pretty much similar to revision described above
- Separate LF oscillators for vibrato and tremolo. Vibrato /w. depth and speed control in front panel. Also includes a trimmer for chorus adjust in rear panel.


JC-120   S/N   481650 – 502499
JC-160   S/N   480550 – 500849

- Gain stages are TA-7122AP, low noise integrated preamp ICs
- Distortion circuit is a switched on cascade of two BJT+FET based gain stages
- FET-differential pre-limiter preventing power amp hard clipping
- Current feedback power amplifier (meaning, the output frequency response is not linear but instead varies in interaction to speaker's impedance, similarly to many tube amps)
- Discrete BBD oscillator driver
- Separate LF oscillators for vibrato and tremolo. Vibrato /w. depth and speed control in front panel. Trimmer for chorus adjust in rear panel.
- Line out tap at speaker output
- LDR-based muter for the chorus/tremolo

JC-120   S/N   512500 – 779499
JC-160   S/N   510850 – 282918

- Pretty much similar to one described above

4th Edition (1979) – applicable to
JC-120                 S/N   789500 – 248099 or 950100 – 283149 (USA versions)
JC-120A and R&P    S/N   810600 - 001099
JC-160                 S/N   782921 - 244509

- Gain stages are discrete, FET -based
- Pre-limiter circuit omitted, will be omitted from following versions
- Distortion circuit is an overdriven FET stage switched into the circuit
- “Main In” external inputs
- Current feedback used in the power amplifier
- BBD now with driver, pre driver made out of digital logic and discrete circuits
- Separate LF oscillators for vibrato and tremolo. Normal vibrato controls in front panel, chorus adjust trimmer in rear panel.
- Line out tap at speaker output


5th Edition (ca. 1982) – applicable to
JC-120   S/N   258100 and up or 293150 and up (USA versions)
JC-160   S/N   254510 and up

- Gain stages are discrete, FETs or combinations of FETs and BJTs
- Current feedback from PA is omitted and no longer featured in following versions
- Includes a bright switch
- Distortion circuit is a switched in FET gain stage with diode clippers in feedback loop
- “Main In” external inputs
- BBD + BBD driver setup
- LF oscillators for chorus and tremolo now combined to a single circuit. Chorus mode has fixed settings for vibrato speed & depth
- Line out tap at speaker output

Note : Cette version aurait un chorus plus proche du CE-2 que du CE-1, mais ça reste à vérifier.
 
JC-120H - the head unit (1984) – applicable to
100/117V      70126811
220/240V      70126814

- Gain stages are OpAmp –based
- “Single channel”
- Distortion circuit is a switched on combination of two parallel shunting diode clippers + switched in gain control in the preceding stage
- Revised reverb circuit with BJT drivers and current feedback
- “Hi-Treble” potentiometer control
- “Sub In”, external mono input
- “Normal/Mixed” and “Effect” line outs preceding power amp
- Four speaker out jacks (this is a head)
- BBD and LFO setup similar to 5th edition of the circuit


JC-120 UT / JT (2nd Edition - these are the newest JC-120 amps)

- Gain stages are discrete, FETs or combinations of FETs and BJTs. FX loop circuitry also uses OpAmps
- Distortion circuit is a switched in FET gain stage with diode clippers in feedback loop, very similar to circuit of "5th ed". but some component values are different
- Modern FX loop with loop level selector and all other goodies
- BBD and LFO setup similar to 5th edition of the circuit
- Revised reverb circuit, similar to JC-120H model
- Output –tapped “Line out” feature omitted

 A propos des haut parleurs

 Another important difference are the speakers. I'm not too familiar with this topic, barely I know that speakers used in Roland JC-120's (and JC-series amps in general) have also changed throughout the years, a variable also having quite big impact on the overall tone of the amp.

The early amps feature Roland Corporation "Musical Speaker" drivers, made in Japan. These have a distinctive metal dustcap and either a black&blue or black&white label.

R&P speakers were developed in collaboration with Pioneer in the late 1970's, they basically appear in circa 1979 amp revisions. These drivers featured some fancy innovation but I'm not entirely sure what it was; basically they seemed to have a wider and HiFi'er response than generic Roland speakers of the time and the new technology was marketed keenly. The Roland amplifiers featuring these speakers were marketed as a unique top notch line, either indicated by "A" or "R&P" in the model number. Some amps even featured R&P insignia but I'm not sure if JC-series ever had that. These speakers again had metal dustcaps.

In the early 1980's Roland started to manufacture some of the speakers in California, USA. These Roland AD "Audio Development" Heavy-Duty Transducers seem to be featured in the newer JC-120's. These speakers also seem to lack the metal dust cap

A propos de la tête

Citation de https://www.ssguitar.com/index.php?topic=2243.0 :

This is actually the model of which's schematics are most commonly referenced when people request for a JC-120 schematic. An important point is that the schematic (often passed on with nickname "1984") doesn't match ANY of the JC-120 combo designs by a long shot. First and foremost, the gain stages are based in opamps only, unlike in JC-120 combos. Unique features incommon to combo versions also include:

- The amp is single-channel design
- "Hi-Treble" control, which is basically a bright switch replaced by a potentiometer
- Effect line out, which is basically a mono line output for the wet chorus effect only
- A more accurate labelling of the revised chorus effect: Manual/Off/Fixed
- Sub In jack, a line in jack that basically bypasses most of the preamp, excluding chorus
- Line out jack, a line out that mixes both channels (wet and dry) to a single mono output. The difference to certain combos that had line out jacks is the take off point. In combos the take off point is at the speaker output, in the head version the takeoff poinr is before power amp.

Rear panel arrangement from left to right: Fuse holder, two speaker out jacks (left), two speaker out jacks (right), Sub In jack, three footswitch jacks for chorus, reverb and distortion, effect line out jack, normal/mixed line out jack.

Un avis sur les premières éditions du JC-120...

Citation de https://www.gearslutz.com/board/so-many-guitars-so-little-time/181432-roland-jc-120-tough-date-2.html :

The differences are not that huge. 

Personally I've not enjoyed the early ones I've had (three) as they were noisy and the much vaunted analog chorus wasn't sounding that great. The 4th and 5th editions do have a different chorus sound but they are a bit quieter and sound superb.

... et sur les dernières ;)

Citation de http://www.tdpri.com/forum/amp-central-station/275955-roland-jc-120-jazz-chorus-old-vs-new-difference-2.html :

 

Very noisy (hiss), and running anything through the FX loop made the noise problem worse. I called Roland, I tried different pedals, guitars, cables. The thing was just noisy. I returned it for a Fender Twin. No FX loop, but a sweet clean tone. I just run my fx through the front, and I'm happy. 

Ampli souffrant à priori d'un bruit de fond élevé, plutôt surprenant pour un transistor, a vérifier lors d'un achat...

Citation de https://www.jazzguitar.be/forum/guitar-amps-gizmos/4185-jazz-chorus-noise-normal.html :

I recently bought a used Roland jazz chorus 77 and have a question about the infamous noise these things make. When switched on with volume on 0, the amp makes some white noise that's bearable (similar to what my peavey delta blues does, i guess). What does bother me is that when you turn the volume up, another type of hiss comes up and this one gets louder as you turn the volume further up.

Are there any JC owners here that can tell me if this is normal. I've already read a lot about the typical hiss but i'm not sure if this second type of hiss should be there (the amp is pretty beat up).    

Every JC I have ever played thru or seen (many) have this same issue. A good friend of mine has 3, and they all do the same thing. The Cube series seems to have a much better handle on the problem.    

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https://taweber.powweb.com/weber/cali12f.htm

http://www.electrovoice.com/product.php?id=410

 Pour ceux qui pense que les GT75 sont des HP pourris : Cliquez ic

Et puis pour tout savoir sur la marque

https://www.soundonsound.com/sos/nov04/articles/roland.htm