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New to me McCormack DNA-225

vintageadict

vintageadict

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So I just got a McCormack DNA-225 (Platinum + level upgrades from Smcaudio) in the house. Hooked it up last night for a listen. I'm really impressed! My pre is a CJ PV-12 and I am driving some ADS-L1290's. I had Richard So refurbish the tweets, mids and crossovers so they are as close to spec as I can get them. Difference in sound? Better lower end (especially at lower volumes), tube like sound that envelopes you, soundstage like I have not experienced making the speakers almost disappear. I still have a lot of critical listening to do but after only a few hours I am thoroughly impressed. I couldn't get my previous amp/pre dialed in so I put a Shcitt Loki tone control in but I don't see the need with this amp. Great synergy with my pre and speakers. This is what I was hoping for along with improved bass at lower volumes.

Now some not so great news and a question.

1) I am getting a low level hum. I can hear it in the listening position at fairly low volume levels but at normal listening it's tough to hear. I am going to work on my cord management and connections to see if I can get rid of this but any advice would be appreciated.

2) This is just a question. The amp has xlr inputs but my pre only has rca outputs. Is there any reason to use interconnects that have an rca/xlr plug? I am thinking no but if anyone has done this or has insight to any benefits I would appreciate it.

Thanks and as always, really appreciate the wealth of knowledge this forum provides.
 
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Here is a little more information. The hum is there regardless of other components being turned on. As soon as the amp is powered up the hum starts. It is not volume dependent and remains constant in both speakers. It can be heard while playing music at low levels. Rearranging wiring has no effect. Also, I can run another amp through the preamp. The hum comes through those speakers as well if the McCormack amp is on. It does not if it is off. It slowly dies down but is audible for a few seconds after the amp is turned off.

I'm pretty familiar with hum. This is much more than your normal audible hiss unfortunately. I'll try to attach a short video of the sound. I have a feeling this is going to someone's bench or going back to the seller worst case (unfortunately).
 
Yes. No hum coming from the amp that i have noticed. Very audible through the speakers. The seller thinks it could be a ground issue and wants me to test it with no other components connected. I plan to try that tonight.
 
I am working through it now. If i disconnect everything from the amp except the speakers then it is quiet. Assuming it is a ground loop. I can’t figure out if it is one of my input components or something else. My CJ pre has a two prong plug so no ground. Could that possibly be the problem?

It is quieter than before but still there.

I am using a two furman power conditioners to hook everything up. They are daisy chained.
 
I would try plugging the power conditioners into the wall independently of each other. Worth a shot.

Another thing worth trying is to install a cheater plug on the amp's power cord. Probably not ideal to run it that way all the time, but could help pinpoint the source of your hum.
 
Sounds like a ground loop. Add back components one at a time. This will tell you the culprit. You can put a Hum X on it and take care of the issue.
 
I was able to reduce the component count down so I could get by with one power conditioner. The amp is plugged directly into the wall. The hum is greatly reduced. It’s still there but i have to be next to the speaker to hear it well.

Tried to isolate the component to no avail. That is why I am wondering if it is the preamp. I still get zero hum out of my old marantz amp.

I’ll try a cheater plug and see what that does. I looked at the hum-x. They have a long list of “do not use with” and it includes amplifiers. No experience with those.

Thanks for the effort and suggestions. Ground loops are a pain in the arse! Lol.
 
I’ve used a Hum-X with a power amp and it worked perfectly. Just say’in. YMMV.

There is a right way and a wrong way to plug in your CJ pre. Without anything else plugged into it, plug the CJ in, turn it on. With a meter measure the ground plain voltage. One probe to the phono ground and the other to the ground of the outlet. Now reverse the plug and measure again. Which ever way produces the least voltage is the proper way for it to be plugged in. The power conditioner may complicate this. I’d check the ground plain voltage between it and the power conditioner too. I don’t think this will solve your hum problem, but when the CJ‘s power cord is properly oriented it will sound better. This goes for all components with a two prong plug.

Good Luck!
 
Stereodiver said:
I’ve used a Hum-X with a power amp and it worked perfectly. Just say’in. YMMV.

There is a right way and a wrong way to plug in your CJ pre. Without anything else plugged into it, plug the CJ in, turn it on. With a meter measure the ground plain voltage. One probe to the phono ground and the other to the ground of the outlet. Now reverse the plug and measure again. Which ever way produces the least voltage is the proper way for it to be plugged in. The power conditioner may complicate this. I’d check the ground plain voltage between it and the power conditioner too. I don’t think this will solve your hum problem, but when the CJ‘s power cord is properly oriented it will sound better. This goes for all components with a two prong plug.

Good Luck!
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I thought there might be something to orienting that plug. I’ll definitely test this.

The only thing that I don’t get is why this ground loop occurs with the McCormack amp. I had another amp in its place and it was dead quiet. Older amp with a 2 prong plug though.

Thanks for the tip on the CJ. Continuing to learn here.
 
Yea, when I had my H K Citation 16 I couldn’t get rid of the hum either. That’s why I bought the Hum X and it work perfectly!

Good Luck!
 
I tried the Hum-x. The hum is still there. I don’t think it’s a ground loop. I can disconnect all inputs except main out from pre to the amp and it still hums. I even tried a different pre and it was still there. My other amps are quiet when connected.

Also tried an extension cord to another room on a different circuit with same result.

Has to be something with the amp. I have a 30 day return window. I’d like to work it out though. Amp sounds awesome with some volume. I just don’t want to be in a situation where it gets worse and I kick myself for not addressing it right now.

I attached a video of the sound. This one is public.

 
One more bit of info. If i turn the amp on by itself (preamp off) the hum/buzz is there. It’s faint enough that I have to have my ear close to a speaker but it is there in both channels. It gets louder when the pre is energized.
 
If all this is the amp humming the amp needs some work.

The amp alone should not hum unless it is a mechanical hum of the transformer which it should not but could have.
 
Thanks for confirming Blue Shadow. I agree.

I learned more about trouble shooting a ground loop than I ever thought I would. :rflmao:

I'll see if I can get them to take care of the amp issues. If that gets taken care of I think it could sound amazing. Par for the course with vintage equipment. Not the first and won't be the last.

Thanks to everyone who tried to help
 
IF it’s a mechanical hum, sometimes,,, you can tighten the mounting bolts to get rid of it. Putting rubber gaskets, o-rings, or grommets could work too.

Most times I find the above to be an exercise in frustration.

Good luck!
 
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