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  1. #1

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    Hi folks,

    first post here after reading a lot on this great forum.

    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).

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    The Jazz Guitar Chord Dictionary
     
  3. #2

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    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.

  4. #3

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    Not played a JC but my Cube hisses on the JC setting.

    I would expect a JC to hiss as that seems to be the norm. When the volume is turned up does the hiss increase or decrease as you start playing (without earthing the guitar - as that can be another cause of hiss - what pups??)

    There is definately a N/R circuit in action on the Cube 60 as the hiss starts when I start to play and then quickly fades out as I stop.

    My own "hunch" from the sound of the JC stting and from experience of effects/multifx is that the JC setting runs a compressor in the mix, hence the characteristic sound and the hiss.

    I'd be interested to know what other Cube and JC owners think causes the hiss or defines the sound.

  5. #4

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    I think it because it's in stereo you might connecting a hum X to your power cord than to the wall socket works great when I use two amps just plug it to one amp.If not you might NR.

  6. #5
    @ Derek: do the JC's of your friend do the exact same thing? I mean, the hiss increases with volume, right? Or do they just have a basic hiss that doesn't get louder?

    @ FWBO: the hiss stays the same, regardless of whether there's a guitar connected or not and regardless of the type of pickups (tried with humbuckers and single coil)

    @ bluemood: do you use the hum x to get rid of a 'hum' type of noise, like the typical mains hum or is it more of a hiss? And with NR, i suppose you mean a noise reduction pedal, right?

    Thanks for the replies guys, i really appreciate it. Just trying to find out if it's worth spending money on an amp-tech. Because i do like the clean sound very much.

  7. #6

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    The Hum X may not help you I guess I use it to get rid of the 60 cycle hum that you get from two amps in stereo without a dangerous ground lift...Yes NR noise reduction ...Every Roland JC 120 that I have ever heard have had a hiss to them you can hear it in a small room playing by yourself but in a live setting you really can't...I hear that the older ones from the eighties weren't so hissy they had different caps and resistors...I like the JC 120 it gives you a nice BIG clean sound .

  8. #7

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    Yeah the hiss is a problem with the Jazz Chorus and it does get louder as you increase the volume. It's not hum or anything. You're not going to get rid of it.

    I have a JC-160 (the big 4 speaker combo) and the hiss makes the amp pretty much unpleasant and unusable if I'm playing by myself. The chorus on mine is also too noisy to be usable. This used to be my favorite amp eons ago when I played rock, but it doesn't get turned on too much any more these days.

  9. #8

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    Quote Originally Posted by L-vizzz
    @ Derek: do the JC's of your friend do the exact same thing? I mean, the hiss increases with volume, right? Or do they just have a basic hiss that doesn't get louder?

    @ FWBO: the hiss stays the same, regardless of whether there's a guitar connected or not and regardless of the type of pickups (tried with humbuckers and single coil)

    @ bluemood: do you use the hum x to get rid of a 'hum' type of noise, like the typical mains hum or is it more of a hiss? And with NR, i suppose you mean a noise reduction pedal, right?

    Thanks for the replies guys, i really appreciate it. Just trying to find out if it's worth spending money on an amp-tech. Because i do like the clean sound very much.
    Yes, it does get louder as you turn up, but I don't think it is completely a proportional thing (hiss volume staying in same proportion to amp volume) but I might be wrong. Heavy but well built. The hiss and weight has always thrown me off.

  10. #9
    Thanks guys, these are pretty clear answers. I'm taking it to rehearsal tomorrow. Let's see how annoying the hiss is while playing with a full band. If it's a problem, this one will go out the door again. At least i know now it's not worth taking it to a tech.

  11. #10

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    My friends, I have this same problem. No solution?
    Cesar, from Brazil

  12. #11

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    The Roland Cubes were mentioned -- different amps, right? I think they have a built-in noise gate. At least, I've noticed quiet notes trailing off then *snuff*

  13. #12
    in the end i didn't find a way to get rid of the noise. Using the amp with a band though, you don't actually notice the noise, so it's just at home that it's a bit annoying.

  14. #13

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    I have JC-50 [no stereo], and my produce little noise too. But at home I have so little power set that I cannot hear the noise during playing. If I set more power I will hear the noise when I'm not playing only. During gigs or rehearsal [with the band] it doesn't matter.

    Greets,
    asedas
    Last edited by asedas; 04-23-2010 at 06:17 AM.

  15. #14

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    Hi!
    I've got JC-77 too and my problems are similar than yours. I bought my guitar amplifier 15 years ago. I don't remember, that I had notice noise in those days. It was lend for a little time to my friend. After it I had noticed that noise, which disturb me a little bit too. My friend said, that they have JC-120s in their music school (conservatory) and they are noisy too. In the Roland shop the shop assistants suggests me to take it (my guitar amplifier) with me to the shop and then they will monitor and look at it. If I could I will hear/listen the sound/voice of JC-120 guitar amplifiers. I will take it to the Roland shop too. I wonder whether they know about this problem!
    Nikolay

  16. #15

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    Hi!
    I've got JC-77 too and my problems are similar than yours. I bought my guitar amplifier 15 years ago. I don't remember, that I had notice noise in those days. It was lend for a little time to my friend. After it I had noticed that noise, which disturb me a little bit too. My friend said, that they have JC-120s in their music school (conservatory) and they are noisy too. In the Roland shop the shop assistants suggests me to take it (my guitar amplifier) with me to the shop and then they will monitor and look at it. If I could I will hear/listen the sound/voice of JC-120 guitar amplifiers. I will take it to the Roland shop too. I wonder whether they know about this problem!

  17. #16

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    As you can read from the previous posts, the JC series has always had the annoying hiss. As I pointed out, the Cube series seems to have this solved. If you like the JC sound, but don't want the hiss, my recommendation is the Cube 80 on the JC setting. Good luck

  18. #17

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    Has anyone used anything with chorus that didn't hissssss?

  19. #18

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    I read a lot here those "Nothing to do, the JC series is like that". Well yes and no I suppose. Yes the JC series produces some noise from scratch. But this noise needs to remain reasonable. I am lucky I have two twin amplifiers so I am in a position to compare directly.

    On my best JC-50, when turning it on, volume zero, nothing wired, you have what is know as the "white noise" even if I am not sure it is an appropriate term. I would not describe it as Hum nor as Hiss. I would describe it as a very light Ffff. On this best machine, I have to put my ear very close to the speaker to ear it. Turning the volume knob up, the volume of the Ffff raises until 33% of the course and then stabilizes until 100%. On the second JC-50, when turning it on, volume zero, nothing wired, I also have the Ffff but slightly more audible. Then turning the volume up, it add up a slight Hum and the couple remains stable from 33% to max.

    The Distortion knobs on both Amps, when turned on, add some Ffff to the wet Ffff. This increases while turning the knobs up to 100% but remain acceptable and playable.

    However, on the first JC-50, the reverb knob adds some Hum to the Ffff remaining ok until 33%. From there it increases in a manner that becomes preferably not used. You loose the feature. Strangely, on my second JC-50, the same know does the same but at a much lower volume meaning that the reverb remains useful up to max.

    The bright switch and the Chorus/Vib switch change the nature of the noise. With the Chorus it gets melted in the modulation. With bright on off it is reduced.

    Those Amps are rather old (Jan 1984 for both of mine) and the components inside might loose original performance. Some of them are difficult if not impossible to find (in particular those impacting the sound). However, replacements might exist with about the same delivery. I understand that it would be sad to touch the original Machine. But it might be better to service it and use it instead of keeping it unused in the cellar like the JC-160 of the friend above.

    I have read an announcement from a second hand dealer saying he was happy to have a JC-120 on offer. The post said that the Amp. had been serviced and even the name and address of the service shop was given as "usual partners". The post also said that the JC-120 was absolutely not noisy.

    So, I would say that yes some noise is normal. A Ffff when turning-on climbing up to 33% and then stabilizing; a bigger Ffff with the distortion; and a slight Hum with the spring reverb (should not be the case on a JC-40 with a digital reverb I suppose). But in case of Big Hum and/or disturbing Hiss up to the point that you do not like to play it... I would recommend servicing to keep the pleasure of this nice Amp.

    PS. My experience is with JC-50 only. But the JC-50 (which I use as a "JC-100 Twin" by linking the two amps via the Chorus/Vib backdoor) are 50 Watt RMS amps with 12" 8 ohms Speaker. The JC-120 is a double 60 Watt RMS amp with the same Speaker. I have no reason to think that my experience with the JC-50 would be much different with the JC-120.

  20. #19

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    There is a modification to reduce or eliminate the hiss, at least in the JC-120. I've never tried it and can't vouch for it.


  21. #20

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    Hey folks,

    I've been spending a lot of time on this and found a solution that works for me.
    I'll share it here but know that if it doesn't work for you, please don't blame me.

    I purchased the service note and started to analyze the circuit.
    The hiss I am hearing is from the preamp (because I heard in the DI output), and noticed that one test value didn't match the non-inverting op amp gain values.

    Jazz chorus noise - normal?-screen-shot-2021-02-13-10-34-26-pm-png

    That opamp, IC-3 on this diagram shows a test value going from 135mV to 150mV... that's a gain of 1.11
    However the non-inverting gain using R46 at 100k and R48 at 15k is equal to 1+R46/R48 = 7.67
    That was odd to me, and that could definitely create high hiss especially after all those RC networks used as tone control.
    I replaced R46 with a 1k value and magically, NO MORE HISS.
    One drawback is that now eq is not as effective. But it's passive eq anyways.

    This should work on most 80s JCs if they have this type of preamp gain stage.
    I'll write a bigger post on my trials and findings...

    Let me know if this helps you.

  22. #21

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    Quote Originally Posted by jazzfrog
    Hey folks,

    I've been spending a lot of time on this and found a solution that works for me.
    I'll share it here but know that if it doesn't work for you, please don't blame me.

    I purchased the service note and started to analyze the circuit.
    The hiss I am hearing is from the preamp (because I heard in the DI output), and noticed that one test value didn't match the non-inverting op amp gain values.

    Jazz chorus noise - normal?-screen-shot-2021-02-13-10-34-26-pm-png

    That opamp, IC-3 on this diagram shows a test value going from 135mV to 150mV... that's a gain of 1.11
    However the non-inverting gain using R46 at 100k and R48 at 15k is equal to 1+R46/R48 = 7.67
    That was odd to me, and that could definitely create high hiss especially after all those RC networks used as tone control.
    I replaced R46 with a 1k value and magically, NO MORE HISS.
    One drawback is that now eq is not as effective. But it's passive eq anyways.

    This should work on most 80s JCs if they have this type of preamp gain stage.
    I'll write a bigger post on my trials and findings...

    Let me know if this helps you.
    Electronic expertise comes in handy!

  23. #22

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    Larger post here

    Feedback welcomed.