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Furman RV-1 spring reverb... how to add balanced XLR's?
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Marlowe
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10th March 2008
Old 10th March 2008
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Furman RV-1 spring reverb... how to add balanced XLR's?

I just picked up a Furman RV-1 and it comes with unbalanced 1/4 ins & outs but has holes cut in the chassis for mounting balanced XLR ins & outs.

Has anyone here added the balanced jacks? How easy a job is it to do?

Thanks,

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10th March 2008
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I have one also and was wondering the same thing, have you opened it yet?
Please post pics if you do,
Cheers,
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13th March 2008
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13th March 2008
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Marlowe
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13th March 2008
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Thanks Kiwi, but the other half of the question for me is: how is it done on the rv-1 specifically? I opened it up and, as an electronics novice, I couldn't figure out what's what in there.
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13th March 2008
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how many springs are actually in the rv-1, 3?
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13th March 2008
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Quote:
Originally Posted by Marlowe View Post
Thanks Kiwi, but the other half of the question for me is: how is it done on the rv-1 specifically? I opened it up and, as an electronics novice, I couldn't figure out what's what in there.

I don't have an RV-1, but the basic principles of connecting unbalanced to balanced is covered in that Jensen pdf. You can see that there are various methods, and some are better than others. I would be inclined to buy the best Jensen transformer for the job and wire it up as suggested.

If you aren't confident with a soldering iron, you could simply buy an Ebtech Line Level Shifter with XLR's and connect it with short cables. Or maybe remove the transformers and XLRs and install them inside the RV-1.

You could do the pseudo balanced trick, as mentioned by Jensen, which doesn't require transformers, but could be subject to noise.

Get an audio electronics repair guy to do it if you aren't sure.
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13th March 2008
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Furman are good about giving schematics to their gear, provided they can find them. They sent me schematics for the PQ3 EQ, also sold in balanced and unbalanced configurations. The schematics they sent had both configurations detailed. The balanced version of the PQ3 (about the same vintage as the RV-1) was not transformer balanced. Give them a call. Their number's listed on their website.
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14th March 2008
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What's wrong with unbalanced? Are you getting hum or buzz? Are your line lengths really long? If not, unbalanced (as long as the cables are properly wired) is a more direct and cleaner signal path. If you purposely want a transformer color to the sound that's another story, but otherwise you might be better off as it is.
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14th March 2008
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Quote:
Originally Posted by Zep Dude View Post
What's wrong with unbalanced? Are you getting hum or buzz? Are your line lengths really long? If not, unbalanced (as long as the cables are properly wired) is a more direct and cleaner signal path. If you purposely want a transformer color to the sound that's another story, but otherwise you might be better off as it is.
The Rv-1 is a great sounding albeit noisy unit, hence trying to improve the signal path by balancing it. As noted, there are already sockets cut into the frame for XLR connectors...
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14th March 2008
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Good point, but I agree with the poster above, I am trying to cut out as much noise as possible and take advantage of the holes already punched in the chassis.

Why do you say unbalanced is more 'direct and cleaner'?

Quote:
Originally Posted by Zep Dude View Post
If not, unbalanced (as long as the cables are properly wired) is a more direct and cleaner signal path.
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14th March 2008
Old 14th March 2008
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Quote:
Originally Posted by lozion View Post
The Rv-1 is a great sounding albeit noisy unit, hence trying to improve the signal path by balancing it. As noted, there are already sockets cut into the frame for XLR connectors...
Most (all?) Furman gear of this era (late '70s to mid '80s ish) is pretty noisy internally. You may not see much improvement in the noise floor by balancing the I/O, especially if your cable runs are already short.

You might try swapping the opamps (most likely 4558s stock) for something quieter (burr brown opa2132?). On the PQ3 and PQ6 at least, and probably the RV-1, these chips are already socketed, so the swap is very easy to do.

Three things I did/do to my pair of EQs to quiet them:
1) swapping the original power transformers for new ones. In my case, both transformers were mechanically resonating @ 60Hz, inducing this into the signal. (~$25)
2) replacing the electrolytic caps in the box (all four of them!). This further reduced the mains hum in the units. (~$4)
3) I drive them as hot as possible.

Do contact Furman for the schematics though. IIRC, their balanced versions have more opamps in the circuit than their unbalanced versions, so it might not be as easy as just a few wires. Don't know if they used the same PBC or not either. Ignore this if you're just going to slap a couple of transformers inside.
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15th March 2008
Old 15th March 2008
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Quote:
Originally Posted by Marlowe View Post
Good point, but I agree with the poster above, I am trying to cut out as much noise as possible and take advantage of the holes already punched in the chassis.

Why do you say unbalanced is more 'direct and cleaner'?
Think about it. Why do we balance gear? It's a set of electronics at the output and another set of electronics at the input designed to get your signal to the next piece of gear with minimal line loss and minimal hum and noise (via the noise cancelling aspect of the hot and cold). The insides of your gear are unbalanced so the balancing is an extra process your signal goes through at the input and output. No matter how you cut it, it messes with the sound. If you balance with transformers that may be a sound you want. If you balance electronically, well, have you ever heard anyone say they want the "sound" of electronic balancing? No.

Some mastering engineers, like Doug Sax use an unbalanced signal path for this reason -less electronics = cleaner signal path. With a recording studio you are leaving yourself more susceptible to hum and RF and with snakes running in every direction running unbalanced might become a nightmare (not to mention issues with line loss).

If you run unbalanced you have to be aware of a few things: listen for line noise (if there is none, you're ok), make sure you're cable is wired correctly if it's recieving or feeding balanced gear (depending on how the gear is balanced you may have to lift the cold or tie it to ground), don't use very long runs (line loss, more potential for RF and hum). The upside is a cleaner signal path and a sound you might prefer.
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3rd February 2010
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Its interesting.. I just bought an RV-1 off of craigslist. The unit was was the old green-faced model. From the 70's. and its just dead quiet. And sound great. Such an immediate improvement over plugs. I'm happy that I haven't had the noise issues that others hint at.
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3rd February 2010
Old 3rd February 2010
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Quote:
Originally Posted by lozion View Post
The Rv-1 is a great sounding albeit noisy unit, hence trying to improve the signal path by balancing it. As noted, there are already sockets cut into the frame for XLR connectors...
Going balanced is probably not going to improve the noise by much, if at all. The noise almost certainly comes from the cheap chips that Furman used. Rechipping with newer, lower noise ICs with the same pinout will probably improve it significantly. Fortunately most Furman stuff I've seen has the chips conveniently moujnted in sockets, which makes the job pretty easy.

If you DO balance it I'd go the transformer route. However the cost of decent transformers is most likely going to be as much or more than you paid for the unit.
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