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Author Topic: The ultimate JC-120 thread  (Read 42418 times)

petey twofinger

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Re: The ultimate JC-120 thread
« Reply #15 on: August 15, 2011, 10:36:36 PM »
i have one i got in the mid 90's , the reverb stopped working a few years back .  i really had a tough time getting a decent distortion tone using pedals . its interesting in a lot of the boss stuff they always show that amp in the instruction manuals . i have the boss gt6 and it has an output setting for the jc120, although i have never tried that unit on that amp . adrian belew and rob fetters used those amps for a long time , they both got some great tones out of em , you name it ! i saw them live many times and they always really pushed their amps . i seem to remember rob having a proco rat . something about the built in distortion on it i didnt care for , with a usa strat . not sure but i think kurt cobain used this amp a  little , and i know metalica did maybe still does for clean tones (why do i know that?) . i think andy sommers was a fan too . adrian belew used the vibrato/chorus to great effect while feeding back with that amp . they really do have a very distinctive tone . they are pretty solid too , i know mine took a serious beating , i did loose a coupla those rivot thingies , and then the reverb went out , i am guessing it got dropped . going to have to look into that , i am sure it may be an easy repair .
 i used a roland gr-50 guitar synth while i was playing bass in a few cover bands . i would use fretless / acoustic bass patches , or octave down fat bass going thru an eq pedal with no mids and highs to a 250 ys combo eqed low . then the straight guitar sound went thru some reverb or a backwards box and then to the 120 . it was quite a sound ,but i would always switch off to a real bass for most of the night (tracking) . quite a few people would be scratching their heads , "where that bass coming from" ? well , a few anyway .

not sure how the stereo works on it , but i do seem to remember when it was engaged , a distinct sensation of movement , either way they were very deep effects , even on the lower settings . i would just love to know if its possible to get a nice distortion or hard rock tone with that amp . i mean i know its possible , but i never even got close to it .  :(

srry to ramble ! i really do dig that amp . i saw this roland digital amp that looked just like a 120 , it had the 13 pin connector for the gk2 hex pu , it had some cosm and stuff , really cool lookin , used at GC , kinda cheep too , like a vg-8 / jc120 hybrid .  :o
« Last Edit: August 15, 2011, 10:42:57 PM by petey twofinger »

phatt

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Re: The ultimate JC-120 thread
« Reply #16 on: August 16, 2011, 09:10:08 AM »
What makes the chorus and vibrato effects stereo? (other than the obvious, that they have two channels!) Are the left and right channels out of phase when using the chorus effect? If so, how many degrees out of phase? Do both channels change pitch in unison when using the vibrato effect or does the effect use the two channels in a different way somehow? I understand the way the effects are implemented might vary greatly between the different versions of the amp.
-Matt

Hi Matt,
           
Tremolo and Vibrato; 
On most Amps these two words often mean the same thing, Vibrato where the *Output Level* is Vibrated creating a vibe effect.

True Vibrato is not *Pitch related* it is just the level output is turned up and down via a low frequency oscillator circuit (LFO)


True Tremolo is just the fast Chorus, Pitch shifting effect,,
So yeah,, it can get confusing. ???


Chorus effect is often just the dry signal through one speaker and the delayed chorus through the other. Some Amps may have true stereo chorus where one side goes up in pitch while the other side goes down while also mixing the original signal through both sides,, You are more likely to find that in later digital effects units but a couple of really old Valve rigs did have some kind of true tremolo effect.
Sorry names escape me tonight.

Teemu probably knows more,  8)

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armstrom

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Re: The ultimate JC-120 thread
« Reply #17 on: August 16, 2011, 09:35:18 AM »
           
Tremolo and Vibrato; 
On most Amps these two words often mean the same thing, Vibrato where the *Output Level* is Vibrated creating a vibe effect.

True Vibrato is not *Pitch related* it is just the level output is turned up and down via a low frequency oscillator circuit (LFO)

True Tremolo is just the fast Chorus, Pitch shifting effect,,
So yeah,, it can get confusing. ???
Thanks for the reply!

I think you have the terms backwards. Vibrato is periodic variation in frequency, tremolo is periodic variation in amplitude.
http://en.wikipedia.org/wiki/Vibrato

I believe guitar and amp manufacturers have created much of the confusion between these two terms. A "tremolo bar" (or whammy bar, if you must) is really a vibrato bar since it changes the frequency of the signal. The "Vibrato" effect found on most Fender amps is really a tremolo effect since it simply varies the output volume.

Now, the question remains... Is the vibrato on the JC120 real vibrato, or did they use it in the Fender sense to mean tremolo (I've never heard a good clip of the vibrato effect being used on a JC120... if I could find one it would be instantly obvious which effect they really use). As for the chorus, I'm aware of the different ways to achieve a stereo chorus, my question was which one (or ones, if it varied between revisions) were used by Roland in the JC series of amps.

-Matt

teemuk

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Re: The ultimate JC-120 thread
« Reply #18 on: August 16, 2011, 09:54:26 AM »
The effect's (whether its chorus or vibrato) mechanics itself lie in delaying the signal by very short time periods, furthermore the lenght of these time periods constantly being modulated by a low-frequency oscillator. This "wet" delayed signal is then mixed in with the untreated "dry" signal and the phase shifts will do their thing.

I guess that makes the effect a true vibrato since it's not based on plain amplitude modulation.

In JC-120's (and as far as I know in every JC-series stereo amp) the effect (whether it's the vibrato or the chorus) created that way is only added to one of the channels, the other channel  always remains totally uneffected. I guess you could call that "stereo", seems to be at least what Roland is doing. I guess you can also call it "true stereo" when the effect is actually added on both channels. Yeh, kinda confusing...

The way how the effect is mixed in that "stereo" configuration does not (in my experience) vary from one JC-120 to another but the circuitry driving the bucket brigade delay chip (the heart of the time-based effects like chorus and vibrato) does: In the early JC-120 versions there were two separate low frequency oscillators to modulate the variable delay circuit; one generating a sawtooth wave, another one generating a sine wave. Sine wave was switched in for the "vibrato" effect, sawtooth for the "chorus", giving each a unique tone and vibe.

In about the 5th edition of that amp Roland, however, simply started to use a single sawtooth oscillator for both of those effects and just made the oscillator's frequency ("Speed") and its output signal's magnitude "fixed" for one effect, user adjustable for the other. (They had been this way all along but the important thing is that they started to use just a single LFO waveshape for both effects). Now both modes actually generated the very same output, though one of them was user adjustable. You could also dial the "chorus" mode to produce the very same effect as "vibrato" mode.

To reflect this, Roland changed labelling in JC-120H (and some other JC-series amps) to simply state: "Chorus (Manual-Off-Fixed)" instead of the older "Vib-Off-Chorus", which was getting to be somewhat misleading. However, I think people actually thought Roland had removed the "Vibrato" feature (and some could with good reason argue that they actually did) so the older style of labelling was kept unchanged in all the JC-120 combos.
« Last Edit: August 16, 2011, 10:02:28 AM by teemuk »

joecool85

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Re: The ultimate JC-120 thread
« Reply #19 on: August 16, 2011, 10:29:20 AM »
       
I think you have the terms backwards. Vibrato is periodic variation in frequency, tremolo is periodic variation in amplitude.

I agree, I played cello for 8 years and vibrato is when you rotate/wiggle your finger on the fingerboard and it moves the pitch quickly up and down ever so slightly, almost a "warble" sound.
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armstrom

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Re: The ultimate JC-120 thread
« Reply #20 on: August 16, 2011, 01:16:08 PM »
Ok, so there's nothing special going on.. If you were to put the two speakers from a JC120 in two different rooms you would only hear the effect in one of the speakers and not the other... interesting. Doesn't sound like something I want to emulate. I think I'll just stick to my plan of using a mono chorus effect that later gets split to two LM3886 power amps driving individual speakers. It's easier that way :)

Kaz Kylheku

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Re: The ultimate JC-120 thread
« Reply #21 on: August 17, 2011, 12:55:26 AM »
Personally, I was always fascinated by the "rivets".  I wasn't sure if it was supposed to look like fancy upholstery or kind of medieval theme, but distinctive, nonetheless.

Their job was to be ... riveting. As you can see, it worked.

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phatt

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Re: The ultimate JC-120 thread
« Reply #22 on: August 19, 2011, 06:41:20 AM »
           
Tremolo and Vibrato; 
On most Amps these two words often mean the same thing, Vibrato where the *Output Level* is Vibrated creating a vibe effect.

True Vibrato is not *Pitch related* it is just the level output is turned up and down via a low frequency oscillator circuit (LFO)

True Tremolo is just the fast Chorus, Pitch shifting effect,,
So yeah,, it can get confusing. ???
Thanks for the reply!

I think you have the terms backwards. Vibrato is periodic variation in frequency, tremolo is periodic variation in amplitude.
http://en.wikipedia.org/wiki/Vibrato

I believe guitar and amp manufacturers have created much of the confusion between these two terms. A "tremolo bar" (or whammy bar, if you must) is really a vibrato bar since it changes the frequency of the signal. The "Vibrato" effect found on most Fender amps is really a tremolo effect since it simply varies the output volume.

Now, the question remains... Is the vibrato on the JC120 real vibrato, or did they use it in the Fender sense to mean tremolo (I've never heard a good clip of the vibrato effect being used on a JC120... if I could find one it would be instantly obvious which effect they really use). As for the chorus, I'm aware of the different ways to achieve a stereo chorus, my question was which one (or ones, if it varied between revisions) were used by Roland in the JC series of amps.

-Matt

Thanks for the correction Matt. :-[

Trust me to get it back to front.
Must make a note to myself to check my brain is on the right way before I type :duh
Phil.

phatt

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Re: The ultimate JC-120 thread
« Reply #23 on: August 19, 2011, 07:00:01 AM »
Ok, so there's nothing special going on.. If you were to put the two speakers from a JC120 in two different rooms you would only hear the effect in one of the speakers and not the other... interesting. Doesn't sound like something I want to emulate. I think I'll just stick to my plan of using a mono chorus effect that later gets split to two LM3886 power amps driving individual speakers. It's easier that way :)

Yep I'd agree with that, no need to make things needlessly complex for little benefit.

My Nobels Sound Studio 1 (SST1, a little red headphone box of tricks) had the chorus ONLY on one channel and dry on the other.
Turn off the *dry signal* and all you got was an up/down warble that was not very musical.
IME, Live stereo efx is overkill and hard to define in a live mix and you may end up worse off but in recording it can be very useful.
Phil.

madstereoman

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Re: The ultimate JC-120 thread
« Reply #24 on: August 09, 2012, 09:06:43 AM »
Hi:
Does anyone know how to remove the front grille from the JC-120?
Thanks

vin97

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Re: The ultimate JC-120 thread
« Reply #25 on: November 07, 2016, 11:11:22 AM »
Is there any way of knowing whether it is the old Chorus/Vibrato circuit or the new one apart from getting a guitar and testing it (even then I'm not really sure how you would know)?
There are a lot of '81 and '82 models for sale online that may or may not have the old circuit and I don't know for sure.

J M Fahey

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Re: The ultimate JC-120 thread
« Reply #26 on: November 08, 2016, 11:42:25 AM »
Only by opening it and looking, way too many different versions out thyere.

MAYBE a very dedicated collector knows just by looking at the extension cord or smelling it, but us mere mortals need to look and compare with known schematics.

vin97

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Re: The ultimate JC-120 thread
« Reply #27 on: November 08, 2016, 08:03:32 PM »
Ah damn.
That makes getting one of the old models online very difficult.

J M Fahey

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Re: The ultimate JC-120 thread
« Reply #28 on: November 11, 2016, 08:48:37 AM »
Maybe Teemuk can chime in, he knows *a lot*  about SS amps (you might say he wrote the book ;) ), including JC120 , so maybe he can tell you to look at knob type or exact name on the label or, preferrably, a range of serial numbers.

vin97

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Re: The ultimate JC-120 thread
« Reply #29 on: November 12, 2016, 01:36:28 PM »
Ok, slightly different question: What is the maximum delay time for the chorus and could it be increased by simply adding more memory?