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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

Showing 5 responses by mlsstl

mlsstl
1,459 posts
 
The specs on the McCormack show a 98 dB S/N ratio with a 1 volt input sensitivity for full output. The Herron has an 80 dB S/N ratio (for moving coil input) and the speakers show a sensitivity of 92 dB.

The rushing noise you hear is white noise and is typical of the residual background noise you get from gain circuits. All electronics produce this noise, but it is usually inaudible.

Since all the electronics have been checked or recently upgraded, the assumption is they are working correctly. (You also didn't mention any channel imbalance with the noise which could indicate an aging or faulty tube in one channel.)

That leaves the strong suspicion that you have a gain mismatch at work. Speakers a bit more sensitive than usual. A relatively powerful amp. A tube preamp (which often tend to have a bit more residual noise than solid states).

Are there any internal gain setting switches in either the preamp or amp? If there are, try some different settings. If that doesn't help, I'd simply try some different preamps and see if the noise disappears. You'd also want to try some different power amps with the Herron. (Looks like you've already tried different music sources.)

While each piece of equipment you listed is good stuff and has excellent reviews, it may be they are just not suited for each other.
mlsstl
1,459 posts
 
Actually, 80 dB for the Herron is a pretty good noise figure (just reading from their spec sheet). That was for the moving coil input option and that circuit has a lot of gain. I would think that figure would improve with a line level input.

And a 1 volt input sensitivity on the power amp is perhaps a shade low, but certainly not an unusual figure.

Really, there is nothing about those numbers that suggests your setup should have the level of white noise you indicate. (You didn't say, but I gather you checked both amp and preamp for any additional gain-setting switches?)

If I were you, I think I'd have the preamp tested for output noise. I think I'd also contact the manufacturer and ask them if they have any insight. And, have you tried this preamp in another system? That might be revealing.
mlsstl
1,459 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.
mlsstl
1,459 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.
mlsstl
1,459 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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