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[Mark McFarlane]

...
PS: If the product used thru hole parts, the rework should be reasonably easy. If it was built using SMD parts, the rework will be much harder than soldering wires and I wouldn't advise it without proper tools.   

If they're SMD I'll just move the rack and unplug the cables

[Darren Scaresbrook]

If they're SMD I'll just move the rack and unplug the cables

C'mon Mark, where's your sense of adventure?

Seriously though, I think you will find that they are smd. The speaker sockets look like standard pcb mounting through hole types, which should make it simple to add a .002uF cap from left and right of each output to ground. You could do this on the back of the board under the socket.

If you have no joy from other avenues, it may be worth trying this on one channel.

Darren

[John Roberts {JR}]

I did lots of SMD rework using my old Weller iron, before buying a hot air station, but I don't recommend it, especially if not very experienced at soldering small thingees.

If the only difference is adding some parts you can tack leaded parts onto the PCB.. You can even remove SMD parts with an iron (careful you don't lift foil). Changing values, might not be so easy. 

JR

[Keith Broughton]

Just for fun, try soldering  500 (ish) ohm  resistors at the end of the "un used" cable, (one from shield to tip and one from shield to ring) and see if that bit of load clears the distortion.
If it does, then you should be able to leave the unit wired to the patch bay and still get enough level to phones that get plugged in on the studio side of the patch.

[Tim Padrick]

If your extension cables are shielded, try an unshielded extension.

[Mark McFarlane]

No response in 3 days from Rane after they suggested unplugging the extension cables and I suggested maybe the design change would was a result of the problem I am seeing.  Not sure if I'll write the guy back or not, I think I'll chalk it up to one overworked guy who doesn't want to deal with me.  My studio rack is actually on wheels on a tile floor so I can unplug without too much difficulty.

If your extension cables are shielded, try an unshielded extension.

Unfortunately I don't have any unshielded cable handy, but I guess I could wire up some zip cord...

Just for fun, try soldering  500 (ish) ohm  resistors at the end of the "un used" cable, (one from shield to tip and one from shield to ring) and see if that bit of load clears the distortion.
If it does, then you should be able to leave the unit wired to the patch bay and still get enough level to phones that get plugged in on the studio side of the patch.

A good idea, thanks.  I could just make up some 1/4" jacks with the resistors and leave 'em in the live room.

I guess I need to schedule a  trip to the electronics store for unshielded cable and some resistors.  I'll be in San Francisco over Christmas, maybe I'll do it there.

[John Roberts {JR}]

No response in 3 days from Rane after they suggested unplugging the extension cables and I suggested maybe the design change would was a result of the problem I am seeing.  Not sure if I'll write the guy back or not, I think I'll chalk it up to one overworked guy who doesn't want to deal with me.  My studio rack is actually on wheels on a tile floor so I can unplug without too much difficulty.

Unfortunately I don't have any unshielded cable handy, but I guess I could wire up some zip cord...

A good idea, thanks.  I could just make up some 1/4" jacks with the resistors and leave 'em in the live room.

I guess I need to schedule a  trip to the electronics store for unshielded cable and some resistors.  I'll be in San Francisco over Christmas, maybe I'll do it there.

Yup, both good suggestions, while I prefer making the internal tweaks, one or both external band-aids could do the trick less invasively.

Arguably you could leave a pair of cheap cans plugged in, too.

JR

PS: Zip cord is roughly 18 pF a foot, to get really low capacitance you need to use something like 300 ohm twin lead (old TV/FM antenna wire) as low as 5 pF per foot. 

[Steve Macatee]

Agreed that this sounds like the added capacitance is presenting a problem to the HC 6 output stage when connected in this way. Kind of surprising since this is a very typical use of the product. But dung occurs.

I like the "add a load resistor at the end of the unterminated cable" idea best. Once I'm back in the office, I can try to simulate this added capacitance. (I'm out until Nov 16 with spotty phone/email/web access - vacation)

And agreed that we would be glad to send the resistors - heck I'd solder up a fix for - maybe a female switching jack at the end of the long cable that auto terminates when unplugged.

But in the end the product should not have this problem. I'll look back and try to figure out the capacitance per foot of the two cable types you have used and have our test department load it this way to see if we can duplicate the problem.

Sorry for the trouble.

Steve

[Mark McFarlane]

...
But in the end the product should not have this problem. I'll look back and try to figure out the capacitance per foot of the two cable types you have used and have our test department load it this way to see if we can duplicate the problem.

Sorry for the trouble.

Steve

Thanks Steve for considering this issue. I look forward to hearing back from you some weeks in the future.

Historically it has't been a big problem for me because I usually monitor the headphone mixes using a software switch and a dedicated headphone amp instead of jacking into the front of the HC-6S, but I have had a few people complain of distortion when they were working in the control room space. I never tried to reproduce the problem until a few weeks ago when I was making some other system changes and ran some tests....

[Steve Macatee]

Hey, I'm back and getting caught up from vacation. Indeed, there was an ECN (Engineering Change Notice) in 2009 that removed the output stage feedback capacitors since certain loads (like your excess unterminated cable) can cause a low-level noise with certain positions of the front panel knobs and certain impedance headphones connected in front. Fascinating.

I was able to duplicate your problem here today by adding these caps back in to a new HC6S and duplicating your set up. The solution is to remove these two caps on each of the 6 output stages. We can of course remove these for you here at the factory since these are surface mount parts. Alternately, if you're handy and you've got a soldering iron (and good eyes or a magnifying glass) or a small sharp pair of cutters, you can remove the parts yourself.

As you found, they are in the schematic as feedback around the op amp output stages - but are omitted these days. Here's a photo
http://www.rane.com/jpg/hc6sboard.jpg
In the photo they are C22 and C33 to the upper left and upper right of the 8 pin 4580 IC "U2" (they are kind of a pink color in this photo but your color may vary. I think the green ones sound the best. Just kidding of course.)

Here are all the designators for the twelve parts to remove: C22,C33,C18,C35,C20,C37,C62,C97,C68,C99,C74,C101

Sorry for the trouble. Let us know how it turns out or if you want to send it in, we'll get it fixed up for you. Service unit turn around time is usually 2 or 3 days here in the building.

[ProSoundWeb Community]