Noise Floor Question
Mar 22, 2006 at 9:48 PM Thread Starter Post #1 of 7

replytoken

500+ Head-Fier
Joined
Jul 6, 2004
Posts
753
Likes
10
I am trying to solve a noise floor issue that has come up in my home system. I have been using a Rega Mira3 integrated amp to power my 2 ch. home system. Its a wonderful solid state amp that puts out a very smooth and silky sound. When used as an integrated amp, the speakers are dead silent when the source is off. I recently purchased a Mapletree Audio EAR++ to use as both a tube headphone amp and as a preamp with the Mira3. In order to do so, there are two switches inside the Mira 3 that "uncouple" its preamp from its amp. Throwing these switches allows the EAR++ to connect directly to the Mira3's amplifier. Here's where things get a bit complicated.
eek.gif


When I power up the Mira3 in this configuration (amp and preamp uncoupled), my speakers have a slight, but constant, white noise sound (floor noise?). When a preamp is attached to the Mira3 and powered up, the noise is more pronounced. It is not specifically the EAR that is causing the noise, because I hooked up a HR Total Airhead as a substitute and I still had noise. Why would the Mira3 be absolutely silent when its preamp and amp are integrated, but it generates white (floor) noise when the amp and preamp are uncoupled? I do not believe it is a ground loop hum because it does not sound like a hum. I unplugged my other pieces of audio equipment (one at a time) to see if they were the cause, but had no success. I really like the Rega and the EAR, but I am at a loss as to how to eliminate this noise. Any suggestions?
 
Mar 22, 2006 at 10:03 PM Post #2 of 7

familyman

500+ Head-Fier
Joined
Jan 14, 2006
Posts
939
Likes
13
do you have a power conditioner? i hear the Furman power factor pro does a good job of lowering the noise floor.
 
Mar 22, 2006 at 10:10 PM Post #3 of 7

replytoken

500+ Head-Fier
Joined
Jul 6, 2004
Posts
753
Likes
10
Quote:

Originally Posted by familyman
do you have a power conditioner? i hear the Furman power factor pro does a good job of lowering the noise floor.


I do not. I am using the Wiremold power stick recommended by Naim. I would consider using a conditioner, but that still does not explain why the amp is silent when its integrated, but not when it is uncoupled.
 
Mar 23, 2006 at 12:08 AM Post #4 of 7

sacd lover

Headphoneus Supremus
Joined
Aug 31, 2002
Posts
8,190
Likes
33
Quote:

Originally Posted by replytoken
Why would the Mira3 be absolutely silent when its preamp and amp are integrated, but it generates white (floor) noise when the amp and preamp are uncoupled? I do not believe it is a ground loop hum because it does not sound like a hum. I unplugged my other pieces of audio equipment (one at a time) to see if they were the cause, but had no success. I really like the Rega and the EAR, but I am at a loss as to how to eliminate this noise. Any suggestions?


I suspect the preamp gain for the ear+ is much higher than the preamp gain stage of the Rega. Remember the Rega, designed as an intergrated, is perfectly level matched for the gain of the preamp section to mate with the power section. The ear's higher output causes, what I suspect is "tube rush" to be amplified to the point of audibility by the Rega's sensitive input stage. Tube rush is a term used to describe the tubes inherent thermal noise .... which sounds very similar to white noise. The use of something like Rothwell inline attenuators may back off the gain enough to remove this noise .... otherwise I know of no other solution except having the gain of the ear lowered internally. This is a guess, so I could be totally wrong.
 
Mar 23, 2006 at 12:31 AM Post #5 of 7

replytoken

500+ Head-Fier
Joined
Jul 6, 2004
Posts
753
Likes
10
Quote:

Originally Posted by sacd lover
I suspect the preamp gain for the ear+ is much higher than the preamp gain stage of the Rega. Remember the Rega, designed as an intergrated, is perfectly level matched for the gain of the preamp section to mate with the power section. The ear's higher output causes, what I suspect is "tube rush" to be amplified to the point of audibility by the Rega's sensitive input stage. Tube rush is a term used to describe the tubes inherent thermal noise .... which sounds very similar to white noise. The use of something like Rothwell inline attenuators may back off the gain enough to remove this noise .... otherwise I know of no other solution except having the gain of the ear lowered internally. This is a guess, so I could be totally wrong.


Your guess is probably correct in that I am probably hearing tube rush from the EAR, and I probably should have ordered it with unity gain as the lowest setting rather than 5 dB. But, there is still noise in the speakers when the EAR is not even attached! It is much less, but it is still present. This is what I cannot figure out, much less solve. (Also, the gain issue probably can be addressed with a 12AY7 instead of the 5751.)
 
Mar 23, 2006 at 5:17 AM Post #6 of 7

replytoken

500+ Head-Fier
Joined
Jul 6, 2004
Posts
753
Likes
10
Well, I stand partially corrected. I spent some time with the Rega amp tonight, and it appears that the small amount of noise was also present in the integrated mode. Its a pretty small amount, and you have to have your ear up to the speaker to hear it, but its is there. So, unless I want to purchase a new amp,
evil_smiley.gif
, I guess I am going to learn to live with it. Also, a 12AY7 should bring the gain down in the EAR++ from the 5751 (and minimize the floor noise), so I am open to suggestions about good sounding 12AY7's.
 
Mar 23, 2006 at 5:53 AM Post #7 of 7

familyman

500+ Head-Fier
Joined
Jan 14, 2006
Posts
939
Likes
13
or you could just not put your ear right up the the speaker
tongue.gif
 

Users who are viewing this thread

Top