April 1, 2012 at 6:04 pm #15293
I’m sure you’ve been asked this but is there a fix for the extreme imbalance between left and right signal.
There is easily a 9db difference.
How does this get repaired????
This is way too extreme.
I may like to sell this piece eventually and want it working right.
HarleyApril 2, 2012 at 8:39 am #15862
As you can imagine, I take a dim view of your comment about wanting to sell it!! 😯
As for a 9dB difference, the usual reason for L/R level difference is the linearity of the input and output potentiometers…. they are never perfect and when new they are often as much as 1dB adrift at certain parts of the scale. However, a 9dB difference is virtually impossible and I would look elsewhere for the reason. The most likely cause is an incorrect connection on the input…. For balanced connections 2 is +ve, 3 is -ve and 1 is ground. All must be connected. For unbalanced connection 2 is hot and both 3 and 1 must be grounded…… if pin 3 is left hanging then the level will be at least 6dB low.
So check both input and output connections!
On the earlier V1.05 versions, we sometimes had problems with the output stage going ‘one legged’, but the later V1.07 versions did not suffer from this.
If there is a real electronic fault, I’m happy to let you have the circuit information for that model, or if you would like me to fix it, the deal is that I charge US$50 plus the cost of returning it to you. (I’m assuming you are in the US.)
BTW, when sending equipment to me for fixing, be sure to give it a low value for customs….. the risk of getting it impounded is much higher than the risk of losing it; a $25 valuation ensures it gets here without problems!April 2, 2012 at 1:08 pm #15861
I said “ MAY WANT TO SELL”….just leaving my options open..lol.
Hi Ted I took it out of the rack and will test it more thoroughly and get back to you with the results.
I’m going to see my tech guy on wed and he can take care of repairs…Philadelphia is a little closer to NYC than England.
So I could use the circuit info.
HarleyApril 2, 2012 at 2:51 pm #15860
I was just winding you up!!
I have emailed the circuits to your ‘studio’ address.April 2, 2012 at 6:41 pm #15859
Yes I realized and that’s why I wound you right back!!!
thanks for the info got your e-mail
Going to check the outputs…could be the problem there.
When running a test tone in and just looking at the meter it seems it’s compressing exactly the same left and right
I’ll have to listen to the output now both xlr and 1/4″
HApril 2, 2012 at 7:02 pm #15858
Ok testing done and It seems to be the wiring on the xlr output. The volume is lower on one side and then intermittently comes back. So we will have that checked out and all should be well.April 3, 2012 at 9:47 am #15857 That’s good! I do get numbers of engineers with those JM compressors worried about level differences and it’s often a wiring or connector problem. I’m glad yours is OK again. That’s quite a rare piece you have; the very early ones had no output gain control, then I added a control on the back as a temporary measure while we redesigned the fronts to take the new layout. There were probably only about 10 units made like yours.April 3, 2012 at 11:38 am #15856 Rare?? I thought the v1.07 with the rear output gain knob was common. If so that’s very good news. ThanksAugust 23, 2012 at 11:13 pm #15855 Hey Ted
I know Jim Kay has been in touch but he said you sent him a flow chart for the sc2 and not the full schematic and it’s still not fixed
one side is compressing more than the other and it’s not the input knob and the chips aren’t over heating
Really need your help on this.August 24, 2012 at 8:00 am #15854
Ah! So the problem is over-compression on one side….. That is always caused by one of the opto resistors being more sensitive than the other, it can be an ‘ageing ‘ problem.
Under the lightproof box there are two light cells (type ORP12) and a pair of LEDs. Physically moving the light cells will give different compression results.
Pls email me separately at
email@example.com I will be sure that you have the schematic.February 14, 2013 at 1:17 am #15851 Hi Ted it’s many months later and still no joy. My tech guy hasn’t been able to figure out why one side is compressing more than the other.
So in a last ditch attempt to get this back in service I think i want to send it off to you.
Unless you think there’s some one in the USA who can fix it…
harleyFebruary 15, 2013 at 6:09 pm #15852
OK, send it to me at the Sound House, Hunsdon Road, Torquay TQ1 1QB, UK, and I will fix it…. The fault is bound to be a faulty compression cell and I do have stocks of the original cells.February 15, 2013 at 7:44 pm #15853 Many thanks in advance!!November 2, 2013 at 4:07 pm #15863 Hi Ted
I’m getting closer to sending this unit back to you…it’s still 6 db lower on the left side. Could there be any other reason we’ve over looked??
I am going to ask some questions of my new tech to see if there’s anything else he can check out
Are you planning a trip to the states any time soon?
HarleyNovember 6, 2013 at 10:37 am #15864
I don’t have any trips planned at the moment….
Looking back over this thread, if the compressor is working at all on both channels then the problem is certain to be either one of the gain cells is faulty, or, more likely, that it has taken a knock and the relationship between the LEDs and the gain cells has been changed…. one of the gain cells has moved away from the LEDs.
It’s worth removing the plastic covers (on the gain cells); one plastic cover is over a single cell and LED, that one controls the compression meter.
The other cover is over 2 gain cells which are set close to the pair of orange LEDs (you will see when you get the cover off) The gain cells should be close to the LEDs , the closeness controls the amount of compression so compression imbalance can be corrected by moving the cells.
If you are sure you have a faulty cell, I can supply replacement gain cells as they are difficult to get. The price is $5.50 each plus $5 for shipping. (I need to confirm that shipping cost)
It’s worth giving the above a try as sending it back to the UK will take time and effort and shipping is expensive.
If you do decide to send it to me be sure to mark it clearly as being sent for repair otherwise we do get problems with customs.
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