Common Ground Amps

[rubin]

What do you look for to identify a common grd amp?

[ben62670]

Do you have the amp yet? Do you have an ohm meter?

[rubin]

Do you have the amp yet? Do you have an ohm meter?

Yes it's a nad c270 I don't have an ohm meter

[Lasareath]

Here's the Manual:

http://www.adnm.com/pdfs/nad_c272_manual.pdf

[ben62670]

The manual won't tell you if it is common ground. Either someone will chime in, or you will need a multi meter. They are $20 for a decent cheap one. They are very handle for testing batteries and outlets. An mm should be in every mans home;)

[headrott]

Ben, I take it that the resistance of the negative binding posts should be low if they are common ground? Or how would you test this with a VOM?

[ben62670]

You got it. If the resistance is low tie the negative amp posts together. Some amps use different internal feedback schemes that can be damaged if a jumper wire is not used. Some disagree. I have learned by blowing 4 internal resistors. Its free insurance to jump them. also fire up the amp with the jumper wire in place with the speakers not hooked up. The amp will have issues (like possible death), but at least your speakers will not blow if they are not hooked up. I had a friend kill his amp and a bunch of drivers:(

[headrott]

Ouch, both the amp and the drivers. I certainly do not want that to happen.

So if the resitance between my negative binding posts is 20.5 ohms on my Aragon 8008bb amp, this would mean it is not common ground, correct? If it is not common ground, then how can I see if a jumper could be used? I've had some tell me that some amps are not designed to have a jumper used with them. How can you tell if this is the case?

[ben62670]

If you are getting 20 ohms you need to use a jumper.

[headrott]

Or an AI-1 cable correct?

[ben62670]

Correct.

[headrott]

Do you know for a fact that the Aragon 8008bb amp can use a jumper without damaging anything? I just don't want to blow up an amp I just bought.

[ben62670]

Did you measure 20 ohms?

[headrott]

Yes, on both sets of binding posts (they're bi-wireable) they measure 20.5 ohms between the 2 negative binding posts.

[ben62670]

Jump the grounds and you are set;)

[headrott]

Although, an AI-1 gives better sound (i.e SDA effect and lower noise) correct?

[ben62670]

Some say so. I personally like a good cable upgrade. I seem to be the minority on that opinion. When all is said and done an A-1 will cost you about $300 with cables. I charge $350 to build one.
Ben

[ben62670]

Double post.

[headrott]

Yeah, I have been finding out they are not cheap at all to build. I feel comfortable about building one and (sort of) have the money to do it. I just don't want to build it and find out that that's not the problem (that the amp is actually common ground).

[Lasareath]

Buy some Carver TFM-35X's, 45X's or 55X's they are common ground. :D

[rubin]

I have read that amplifiers that are NOT! common ground CANNOT! be bridged. Is that correct?

[ben62670]

Bridging amps is not the way to fly except in some Pro Audio apps.