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!
I thought you pretty much had your answer after try #3. It's based around the McCormack and the connection w/ the Herron. Sorry, but I don't know enough of the details on input & output of those two, but the easy approach would simply be "how did you like the sound with that Jolida?", 'cause that gave you the lack of hiss you wanted.
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.
Thanks for the replies. I also suspect it is related to the preamp, as I have pretty much tried everything else. Keith noted the gain may be an issue, but he couldn't put his finger on a "this is definitely causing the noise" problem. I checked all of the tubes (as did Keith when he had it in) and they have all checked out.
Thorman: I did try changing interconnects, so that wasn't it.
Tvad: The system sounds great except for the hiss, which is so loud that is audible at least 15 feet away. It really detracts from the music, which is why it is really bothering me. It is like looking outside through a really dirty window. My old system used to have a minor hiss, which was slightly annoying but not a deal breaker, but this can be heard through the music at all times.
Mr_hosehead: well, the Jolida was quiet, which was terrific. With regard to musicality, it was really flat and lacking detail. My current components are great, except for that loud hiss that I can't seem to get rid of.
MIsstl: If I need to look at a different preamp, what range would I be looking at for a gain to reduce the noise? If the Herron is 80db, then what would be better, or ideal? Is there a general rule, or is it something I will just have to try and compare? The EE Minimax I tried again last night (which got a bit quieter after I swapped the rectifier tube, and wasn't bad) actually looks higher at a 96db s/n ratio, but that may not compare directly with the 80db you were speaking of (I wasn't familiar with the moving coil input term) .
Also, is there an input resistance mismatch that could be causing this?
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.
Yes, I didn't see any gain-setting switches to play around with. I just got the preamp back from Keith at Herron, where he tested the preamp and didn't find anything out of the ordinary. He gave me some things to try (which I did) and it didn't solve the problem). He was very helpful, but in the end, couldn't figure out what was happening, except that it wasn't a faulty preamp, which leads me to believe there is a compatiblity issue with the amp.
Perhaps another thought: does anyone think there could be an issue with speaker cable? I don't see why there would be (I am using Signal Cable bi-wire) but thought I would throw that out there as something I hadn't yet pondered.
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.
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.
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.
Thanks. I spoke again with SMC, and they said I was doing the IC test incorrectly. What he suggested instead was that I take the units to my workplace (out in the woods, a resort that has very clean power most likely, as there is power to vacation houses that are empty this time of year). I wanted to try it away from town and any RFI interference that perhaps would be an issue, and this area is pretty remote.
End result was that running through my monitors at work, I had the same issues with the preamp and amp engaged. So, I know it isn't my house electrical nor is it RFI.
As a test, I took my work amplifier home and hooked it up (Arcam A75). It is DEAD quiet, and I am listening to it right now. And, the Arcam has pre-outs, so I hooked those up to the McCormack again. Voila-dead silent.
There is some incompatiblity issue going on here between the amp and preamp. I have had the unit checked out by Keith Herron 2 times in the past 6 months (including the 1a/166 upgrade) and he couldn't find anything wrong. I will give him a ring and see if there is something else that he can think of, some reason why this pre isn't working with the amp. I have picked both his brain and the guys at SMC, and nobody has yet figured out a reason why I would be having this issue.
Thanks again for everyone's help. I will let you know if I ever do find out what is wrong with my pre-amp combo.
Well, I have more or less figured it out. Due to the sensitivity of my speakers and amp, combined with some noise induced by tubes in general (something ambient in this area that tubes are picking up) a tube preamp is basically out of the question. Every tube pre I have tried just hasn't worked out. I am extremely frustrated right now, but at this point, it is time to step back and look for a good SS pre, or a dead-quiet tube pre (I hear the Dehavilland Ultraverve qualifies on this front).
Thanks to the forum for helping me out, and Keith at Herron and Steve and Kris at SMC Audio for helping me to isolate the problem.
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