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Background noise problems

Hi,

I posted around 2 months ago on this issue, but like an idiot, I was due for vacation in Bali a few days after I posted and missed most of the conversation. Anyways, I have tried a few more things and was hoping for some feedback....

Here is my situation: I am getting upper-frequency "snow" coming out of my speakers. My current setup is a Gold-level McCormack DNA-125 amp, Herron VTSP-1a/166 preamp, and Sony 9000es CDP that has been upgraded to VSE Level 6, with Tyler Acoustics Linbrook Signature speakers. Except for the snow that I am getting (sounds like a snowy TV) the system sounds great. Unfortunately, I am hearing the hiss around 20 feet away.

Here is what I have tried so far:
1) substituting a Eastern Electric Minimax preamp for the Herron: less of the hiss sound, but still present. I am assuming the preamp has less gain?
2) Substitute a Consonance CDP for the Sony. Not much change in background hiss
3) substitute a Jolida integrated amp for the Herron/McCormack combo, input from the Sony: this virtually eliminated the hiss

I have had the Herron checked over by Keith, replaced tubes, and everything has checked out. The McCormack was recently upgraded, but it is possible something is wrong there. The Sony unit was also recently upgraded from Level 5 to Level 6, but the hiss was there before the upgrade and still remains.

A few notes: I hear the hiss as soon as the Herron is engaged, whether or not it is receiving an input. The hiss is the same on all inputs, whether or not they have an active input or are not connected. The speakers are basically dead silent when only the amp is engaged.

It makes me think that I have some issue with compatibility in my system with the Herron, but as I am still getting some background noise on the substitute preamp, I am wondering where to go from here. The Jolida intergrated was basically quiet, which is a good sign.

Where should I go from here? I have the makings of a superb-sounding system, but need to get rid of this background noise. It can be heard easily in the music. Thanks in advance!
dawgcatching
mlsstl
1,391 posts
 
Just had another thought. Why don't you call the power amp manufacturer and see if there is a simple mod to reduce the input sensitivity of the McCormack? This would reduce the amp's gain and reduce the hiss. You'd have to run the preamp's volume control at a higher level to reach listening volume.

This is based on my impression that you get the hiss when the preamp is on, even if the volume control is turned down.
dawgcatching OP
139 posts
 
Well, I called McCormack (talked with Kris I believe) and he gave me a tip that I hadn't thought of (and I don't know why it would even matter). But it did. His idea was to turn the preamp on, with IC's connected to the input, but not to the pre. As mentioned earlier, the amp was dead quiet with IC's connected to the pre (but the preamp was off) and would get noisy as soon as the output tubes were active on the preamp.

Well, with the IC's connected to the amp only, that loud white noise came out of the speakers, but as soon as I plugged in the IC's to the pre and turned it on again, it was quiet.

So, it seems that there is something going on with the amp. As it is under warranty by SMC, I will call Kris tomorrow and see if he has any ideas.

Any reason the amp would be noisy only with the IC's not connected on the preamp side? It made the problem very difficult to diagnose.
mlsstl
1,391 posts
 
It almost sounds like the McCormack has some type of auto-sensing gain control, but their web site and the reviews mention nothing about that. The noise doesn't really behave like any defect I've seen before, but maybe that's what is going on. Only further investigation will tell.

However, Stereophile's review of the DNA-225 did have an interesting comment
"The voltage gain into 8 ohms was higher than usual, at 30.5dB. Both of these factors will make the McCormack a good choice for use with a passive volume control, though pairing it with a typical tube preamplifier will result in too much system gain."

Too much system gain can aggravate noise problems. Stereophile also tested the amp's S/N ratio (though not your model) and it wasn't as good as published specs.

If no defects are found, it is looking more and more like you have two wonderful pieces of equipment that simply may not be suited for each other.
dawgcatching OP
139 posts
 
Thanks for the note. I will call McCormack again and see what they say. Another user (4yanx) has my McCormack/Herron setup and loves it. I sent him an email to see if he had any of these issues.

I also saw that Stereophile bit about the high voltage gain on the 225. I don't know if the 125 is the same, but I will ask.
mlsstl
1,391 posts
 
The reports I found gave the same voltage gain (30 dB) for both the DNA-125 and the DNA-225.

It will be interesting to see what you eventually find.
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