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
Cables cannot generate hiss. A bad ground on an interconnect could cause hum, but not hiss. A bad conductor on a speaker cable would result in no sound at all. I would have every tube in my system tested and graded with regard to microphonics and noise. Many tubes are fine in low gain circuits(and can test better than new for transconductance, etc), but noisy as hell if used in phono stage or preamp circuits. In those locations the least amount of noise is dramatically exposed. With the rated S/N ratios of your gear- you should be hearing no noise at all. Actually your amp's 1 volt sensitivity/speaker's high efficiency should allow you to barely crack the volume on your pre to enjoy your music. That should result in less noise from the pre. If you have no hiss with just the McCormack turned on, and the hiss when the pre is on/in the system, with no source connected: It's obviously the pre(probably a tube) that is generating the noise. Kevin Deal would probably be willing to test and grade your tubes: (http://www.upscaleaudio.com/view_category.asp?cat=38), or you could replace them with his "Platinum Graded" tubes(click on "Tube Testing Procedures" on the bottom of the afore mentioned page). I've found Upscale to be an excellent source of tubes, and his testing/burning/grading procedures to be second to none. No connection, outside of being a happy customer.
Hi Rodman99999,

I just had my tubes tested, and also have a brand new batch here just in case. I swapped in the new tubes, and had no change. Tubes were my initial thought as well. My other preamp that I tried also has the background noise, although only at around 2/3 the noise of the Herron.
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.
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.
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.