Vintage NAD Equipment

[HangtownMatt]

Today, just on a lark, I stopped in a local Thrift store. Low and behold they had two NAD 2240-PE amplifiers and one NAD 5220 CD player. This stuff is 1988 vintage, made in Japan, and I scored the whole lot for $24 in perfect condition.

My question is about the amplifiers. They are two channel with 40 watts per channel and a true high-current design with THD <0.03%. OK... Enough gloating :>) I would like to use these in my system for home theater. I currently have a Yamaha RX-V661 that I would like to use as just a pre-amp as much as possible. Connected to the Yamaha pre-outs is a Conrad Johnson MF-80 external amplifier (Solid State early 90's vintage w/ 2-channel, 80 watts per channel) to drive my Vandersteen Model 2 CE front left and right speakers. The in-wall surround speakers can be driven by the Yamaha, but I would like to incorporate one of the NAD amplifiers to drive a center channel. My questions are (1) Should I simply connect one channel of the amplifier to the CC and leave the other channel connected to nothing? or (2) can I connect both amplifier channels to the same CC ? My concern is that both of these scenarios could damage either the amplifier or speakers. So I'm consulting the experts !

Matt

 

[TLS Guy]

Today, just on a lark, I stopped in a local Thrift store. Low and behold they had two NAD 2240-PE amplifiers and one NAD 5220 CD player. This stuff is 1988 vintage, made in Japan, and I scored the whole lot for $24 in perfect condition.

My question is about the amplifiers. They are two channel with 40 watts per channel and a true high-current design with THD <0.03%. OK... Enough gloating :>) I would like to use these in my system for home theater. I currently have a Yamaha RX-V661 that I would like to use as just a pre-amp as much as possible. Connected to the Yamaha pre-outs is a Conrad Johnson MF-80 external amplifier (Solid State early 90's vintage w/ 2-channel, 80 watts per channel) to drive my Vandersteen Model 2 CE front left and right speakers. The in-wall surround speakers can be driven by the Yamaha, but I would like to incorporate one of the NAD amplifiers to drive a center channel. My questions are (1) Should I simply connect one channel of the amplifier to the CC and leave the other channel connected to nothing? or (2) can I connect both amplifier channels to the same CC ? My concern is that both of these scenarios could damage either the amplifier or speakers. So I'm consulting the experts !

Matt

Do NOT connect both speaker outputs to the SAME speaker. Your NAD will blow up INSTANTLY and be DEAD FOR EVER. Only use one channel.

Now you have another problem you have not considered, and a lot of people don't when using different amps in HT. That is phasing. On a lot of amps, especially from that era they are phase inverting. That is to say the speaker output is 180 degrees out of phase with the input. If my memory serves me correctly, and it may not, I believe your NAD is a phase inverting amp. Your Conrad Johnson and your receiver I don't know. Now if your Conrad Johnson is non phase inverting and you NAD is phase inverting, you mains and center will be exactly out of phase even if wired correctly.

Now it is a funny thing but owners manuals seldom state if an amp is phase inverting or not.

The only way you can tell for sure is to put an audio oscillator to one channel of an amp and connect the oscillator output also to the x plates of an oscilloscope and the speaker output of the channel connected to the oscillator to the Y. If the pattern is a straight vertical line the amp is non phase inverting. If it is a circle it is phase inverting.

Now this is a very common error when using different amp brands. I have inverting and non inverting amps in my rig, and they are from the same company and designer. The manuals are silent on the issue. I can tell you if you are using different amps this has to be done to know for sure. You can try by listening, but with the scope test tells you for certain. Obviously an out of phase condition, commonly caused by this problem is disastrous to the audio results.

If you have a phase inverting amp being used with a non inverting amp, then the speaker connections to the inverting amp should be reversed.

I hope you or anybody else reading this really understands this. It is really important.

 

[HangtownMatt]

Awesome advice TLS Guy ! Thank You for taking the time. I think I understand what you are talking about. When I was running the CJ with the Vandersteens as a 2-channel stereo I did have the speaker cables (red/black) flipped for exactly the same reason you stated. Not that I really understood why, but just because that's what the owner ' manual stated to do. Interestingly though, after having just checked the owner's manuals, the CJ amp has correct phase but the CJ pre-amp is phase inverting. So I would assume that when I connect the CJ amp to the Yamaha I should connect red-to-red and black-to-black. Correct?

I never even considered the NAD could be phase inverting. I may have to get me one of those scopes.

Thanks again,

Matt

 

[TLS Guy]

Awesome advice TLS Guy ! Thank You for taking the time. I think I understand what you are talking about. When I was running the CJ with the Vandersteens as a 2-channel stereo I did have the speaker cables (red/black) flipped for exactly the same reason you stated. Not that I really understood why, but just because that's what the owner ' manual stated to do. Interestingly though, after having just checked the owner's manuals, the CJ amp has correct phase but the CJ pre-amp is phase inverting. So I would assume that when I connect the CJ amp to the Yamaha I should connect red-to-red and black-to-black. Correct?

I never even considered the NAD could be phase inverting. I may have to get me one of those scopes.

Thanks again,

Matt

Yes, that would be correct. I assume you are not using the CJ preamp, correct? So the issue is, is the NAD phase inverting or not?

But may be you have a way to find out. Set up your Yammy to two channel stereo. Connect one channel of the NAD to a pre out on the Yammy. , the other to the CJ amp. Connect one stereo speaker to the Yammy and the other to the CJ amp. See if the channels are in phase or not. You probably have a test disc with a phase test. It is best to listen in mono with a program with a good bass content if you don't have a disc with a phase check.

Now if you are using just one two channel amp whether it is phase inverting or not is immaterial. The loony crowd starting saying that absolute phase was important years ago. That is nonsense, especially as you have no idea of the phasing of your source material. However when it comes to mixing amps it becomes a vital issue. Before the loony hullabaloo most amps were phase inverting. Since the hullabaloo it is lees common. Now with the advent of the HT scene I think it is even less common, but I'm by no means certain of that, so you have to check. Your NAD is before the hullabaloo.