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Annoying Juno 106 chorus - help needed
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radek tymecki



Joined: Mar 22, 2009
Posts: 84
Location: PL

PostPosted: Sun Aug 02, 2009 9:48 am    Post subject: Annoying Juno 106 chorus - help needed Reply with quote  Mark this post and the followings unread

Hi there!

Some say that noise comming outta juno when chorus is switched on is kinda sweet. well it wass sweet sth bout 2 yrs ago but now it's so noisy that i cant stand it anymore!

what parts should I exchange to get it less noisier?

radek
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CJ Miller



Joined: Jan 07, 2007
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PostPosted: Sun Aug 02, 2009 2:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

First thing I would do is check the wiring. IIRC, the 106 chorus is on it's own little PCB... Check the multi-pin connectors to and from this circuit. Also I don't remember how it gets switched in, what the signal path is like. I'll check mine in a few hours.

If you do need to replace anything? It probably uses lame 4558 op-amps, but so does the rest of the synth. They don't seem to get noisier with age.

Wash the cat pee out of your Juno, it seriously helped mine!
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Mooger5



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PostPosted: Sun Aug 02, 2009 5:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

The opamps are M5218 and yes they´re 4558 types, but in SIL-8 package. The lower noise equivalent seems to be the M5238 (J-Fet input). If you think 3-4 dB might make a difference, well...

There´s also IC6 in SIL-9; that´s a wide bandwidth opamp in the final stage. 3MHz? I don´t know why they chose it. You may have trouble in finding a pin-to-pin equivalent...

Transistors are noise sources too. I didn´t search further, but there may be quieter equivalents.

Anyway, that noise in the chorus is independent of whatever signal is fed into, so before swapping opamps you could check if VR2, 7, 12, 17, 22 & 27 were calibrated at all. Turning them clockwise increases the VCA gain in all six voices, achieving a better signal to noise ratio.

Cheers
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Uncle Krunkus
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PostPosted: Mon Aug 03, 2009 3:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Does it use a BBD for the chorus?
Maybe it needs the bias tweaked. Carbon comp. resistors can change value over time, and they may have put the bias out. There may also be a "cancel" trimmer on the way out of a BBD circuit.
Or a dry electrolytic could have a severe effect on the cleanliness of the BBD supply lines.
The only reason I'm thinking of these particular things is because I'm working on a BBD delay/reverb right now, and these issues are clear in my mind.

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Mooger5



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PostPosted: Mon Aug 03, 2009 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, MN3101 and MN3009 and a bias trimmer for each channel. I do the calibration by ear, but anyway rotating the trimmers doesn´t make any change to the ammount of noise.
I don´t know how the BBDs work, but the noise have always resembled what happens when we use too much compression on a signal...
I´m on my second Juno and, like every other I played, all present the "distant shore" the moment you switch them on, even when these synths were brand new. I can live with it, but sometimes it gets really annoying.
So it´s probably not a dead component either, just the OP wanting to minimize an inconvenience.

I wonder how the Juno would sound on analogue tape using NR. Very Happy Weren´t there rackmounting Dolby units? These might be cheap nowadays.
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radek tymecki



Joined: Mar 22, 2009
Posts: 84
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PostPosted: Mon Aug 03, 2009 9:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Mooger5 wrote:
Yes, MN3101 and MN3009 and a bias trimmer for each channel. I do the calibration by ear, but anyway rotating the trimmers doesn´t make any change to the ammount of noise.
I don´t know how the BBDs work, but the noise have always resembled what happens when we use too much compression on a signal...
I´m on my second Juno and, like every other I played, all present the "distant shore" the moment you switch them on, even when these synths were brand new. I can live with it, but sometimes it gets really annoying.
So it´s probably not a dead component either, just the OP wanting to minimize an inconvenience.

I wonder how the Juno would sound on analogue tape using NR. Very Happy Weren´t there rackmounting Dolby units? These might be cheap nowadays.


btw... did You managed to finish Your ssm vcf modification for juno?
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Mooger5



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PostPosted: Mon Aug 03, 2009 11:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I´m working on it, to make it sound cleaner. Just peeled off my last remaining 80017a and measured the capacitors to confirm it´s the same values found in the Juno 6. Smile
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Uncle Krunkus
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PostPosted: Mon Aug 03, 2009 4:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

I wish I had one. The process of getting it quiet would be a great challenge.
If you had a scope, you could trace back fom the output and see what the relative level of the noise to a standard patch is. That may help tie down which section suddenly jumps up in the noise level.
If it was there from new, then it must be a particularly noisy op-amp they used to save money I s'pose. Surely there'd be a quieter replacement for it now?

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elektro80
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PostPosted: Mon Aug 03, 2009 4:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

If it can be of any help, factory new 106s often had a noisy chorus pretty much the way you describe it. This could be fixed under warranty. This probably means that someone out there should know a lot about what caused this problem and it is likely that it could be the same thing you are looking at now.

?

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Mooger5



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PostPosted: Mon Aug 17, 2009 5:03 am    Post subject: Reply with quote  Mark this post and the followings unread

I think I found a solution: by switching the output level to "medium" (there´s the switch on the back, with h-m-l positions) the noise seems to quiet down significantly in relation to the music signal.

Uncle Krunkus and Elektro80, you think this noise is not a compromise typical of BBD efects, but a repairable malfunction? I´ll definitely ask the vintage synth forum about the factory fix and let you guys know. It might be worth salvaging the chorus board from a dead Juno and rack it. Smile
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Mooger5



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PostPosted: Mon Aug 17, 2009 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, I used the search function and didn´t find a specific cure for the noise, but found this page. http://techtone.me/Roland-Juno6-JU6-Noisy-Chorus-Repair.aspx which is intriguing. So BBD chips wear out this badly over time?
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Uncle Krunkus
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PostPosted: Mon Aug 17, 2009 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm,....
Very interesting.
I didn't realise they would get noisier with age, but I s'pose it makes sense, as keeping the noise floor down across thousands of cap transfers is a difficult thing to get right in the first place. The biggest descrepancy I've noticed across all the MN32XXs and MN30XXs is the signal to noise ratio. Some are better than others, (usually the shorter ones).
You may be able to get MN3009s from Smallbear.

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beatncore



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PostPosted: Mon Aug 17, 2009 1:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi all!
Maybe this is not the right place and I should open a new topic, but as this topic isn't old, I decided to ask here.

The chorus on my Juno is sounding like "on-off-on-off.....", instead of the noticeable LFO effect. It sounds like the chorus is not been modulated.
Could it be something with the calibration?
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Sebo



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PostPosted: Mon Aug 17, 2009 1:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi:
I have a Juno-106 and the chorus is a little noisy (noisier than my Juno-1, but Juno-1 is know to be quieter).
But when I switch the level from the back, the noise has the same level in relation to
the synth sound.

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Mooger5



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PostPosted: Wed Aug 19, 2009 2:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Hmmm,....
Very interesting.
I didn't realise they would get noisier with age, but I s'pose it makes sense, as keeping the noise floor down across thousands of cap transfers is a difficult thing to get right in the first place. The biggest descrepancy I've noticed across all the MN32XXs and MN30XXs is the signal to noise ratio. Some are better than others, (usually the shorter ones).
You may be able to get MN3009s from Smallbear.


Well I couldn´t find MN3009s anywhere, not even in the local market. There´s the 3209, but they don´t seem 100% compatible, at least one uses N-channel triggering or something while the other uses P-channel. Anyway the 3209 has poorer SN ratio.
And the chips getting noisier with age somehow contradicts the fact the noise could be fixed under warranty. I think I´ll leave mine as it is...
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Mooger5



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PostPosted: Wed Aug 19, 2009 2:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
Hi:
I have a Juno-106 and the chorus is a little noisy (noisier than my Juno-1, but Juno-1 is know to be quieter).
But when I switch the level from the back, the noise has the same level in relation to
the synth sound.


Yes, what I´ve found doesn´t make much sense, although the chorus runs in paralel with the dry signal. The switch in the back sets the output level for both. It must be the modest soundcard I´m using; works best with moderate levels.
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magman



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PostPosted: Thu Aug 20, 2009 1:39 am    Post subject: Reply with quote  Mark this post and the followings unread

A quick search on the web found MN3009's at the following stores:

http://www.dalbani.co.uk/forums.html

http://www.vintageplanet.nl/semiconductors.html

Nikko looks to be your best bet, but Vintage Planet is an excellent place for all thinks old synth.

Good hunting

Magman
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Mooger5



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PostPosted: Mon Aug 24, 2009 1:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

magman wrote:
A quick search on the web found MN3009's at the following stores:

http://www.dalbani.co.uk/forums.html

http://www.vintageplanet.nl/semiconductors.html

Nikko looks to be your best bet, but Vintage Planet is an excellent place for all thinks old synth.

Good hunting

Magman


Oh, thanks for the link to Nikko. And I´ve bought from Senso before. You´re right about it.

Cheers!
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calande



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PostPosted: Fri Jul 24, 2015 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

I replaced both MN3009 chips from the jack board, but no change. Chorus is still noisy when turned on Sad
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