The intermittent noise I've been hearing I think might best be described as tube "ringing", a high pitched microphonic whistlelike sound. I thought I had the noise licked, but it resurfaced today. It can only be heard at moderate to high volumes. I'm expecting 4 NOS Telefunken 12AX7s this week so I hoping that will wipe out the problem. Any ideas gentlemen? |
Rushton:
Thanks for your thoughtful and detailed response. Oddly enough, the noise I was hearing was not present last evening. I would not think this so strange, except the hissing sound was heard on at least three consecutive days before that. I'm almost scared to go home tonight and see whether it has emerged again. Of course, the noise did not go away before I ordered a quad of Telefunken 12AX7s off ebay. I haven't decided whether I'll swap them out as soon as I receive them or if I'll wait for the problem to present itself again. I'm beginning to wonder whether the problem is with the unit and not the tubes, since I can't imagine a tube going bad then miraculously repairing itself. I did not listen for very long last night, so the problem may be heat or thermal sensitive. I should have a chance this evening to give the Rhea a decent workout. I am curious to see what change the Telefunkens will bring. BTW, the people at Musical Surroundings wrote back to me indicating that some people have had good results replacing the 12AX7LPs with GE 5751s. Might try that if the Teles don't do the trick. Anyway, I'll keep you "posted". |
Rushton, still don't have the new tubes but perhaps you can explain why I would be getting ringing in both channels on some days but not others. For example, last night I had a few friends over to listen to the system. Of course, the ringing was present when I turned the system on and stayed all night without abating. Tonight I'm alone and I turn on the system and other than the usual tube rush one might expect to hear, all is quiet. The night before last quiet too. Like you say, the only way we'll know if its the tubes is to swap 'em out. At the moment, I only plan to swap out the 12AX7s in the first gain stage. Any reason to think these might not be the culprits? This is just too strange. |
I have the Rhea plugged into a PS Audio P500 power regenerator, as I do virtually all of my components. I tried going directly into the wall receptacle, but that did not kill the noise either. I guess the Rhea, which is my only piece of tube equipment, might be more susceptible than the others to RF, but I have my RPTV plugged into the P500 and it plays fine. Hopefully the tubes come tommorow and we will know more. If its any help, the ringing when it comes is present even when I switch inputs, gain settings, load settings, mute, and when I power up/down the unit. Would you agree with me, since the unit performs flawlessly on certain nights, like tonight, it is something external to the unit itself? |
Patrickamory, I had earlier spoke with Jim White about the power regenerator and he simply suggested I try listening to the unit plugged directly into the wall because of the size of the transformer. I do not have it plugged into one of the regenerated ports and, in any event, I tried to go directly into the wall, but it did not solve the problem. Also, the Rear Projection TV does not seem to have any effect on the unit. The other night when I had friends over, the TV stayed off. I intend I calling Jim White if the replacement tubes don't do the trick. |
OK, the Telefunkens arrived today. Now mind you, the Rhea has been consistently quiet so it came as no surprise that I did not hear the ringing which I had been hearing when the Telefunkens went in. What I'm a little disappointed with is the fact that in terms of tube rush, I do not find the Telefunkens any quieter. At a certain volume level, which I consider moderate, at the listening position, I can hear the rush of air coming from the speakers. Its not a ringing and I accept this noise as being entirely normal. I never thought tubes would be silent or even whisper quiet, but I did think from all I read and heard that the Telefunkens would be quieter. Not so. I understand that Jim White hand selects the Sovtek 12AX7s he puts into the Rhea for low noise so either he does a very good job, or the design of the Rhea is just a high gain unit which is prone to a fair amount of tube rush. Anyway, my question is this: I replaced the 4 12ax7s in the first input gain stage. I'm still aclimating myself to the Telefunkens, and at most I hear a slight warm and bloom in the midband. Rhea tube complement (each channel) is V1 & V2 (12AX7LP—factory graded low noise), V3 & V4 (12AX7WB) and V5 (6922). Do you think I can get the unit to run quieter by swaping out the 12ax7WBs or the 6922. The folks at Musical Surroundings which distributes the Rhea said some people have had good luck with GE 5751s. I'm wondering if I go with 5751s in V1 & V2 and the Telefunkens in V4 & V5, do you think it will lower the noise floor. Should I swap the Sovtek 6922 with a Telefunken or Mullard 6DJ8? Any ideas where to go from here in terms of improving the performance of the Rhea be it to have it run quieter or richer? Thanks. |
Rushton:
I am pleased to report that I have lowered the noise floor significantly by replacing the stock Sovtek 6922s with Siemens 7308s. I was able to raise the gain setting from 50 to 62 on the Rhea, which is a two-step jump and at this higher setting I can now listen virtually as loud as I dare to without hearing any tube noise from the sitting position. The ringing is gone as well. Before receiving the Siemens I had swapped out the Sovteks with a second set of Sovteks I had in an old Audible Illusions Modulus and the noise was still present. So I'm quite certain the Siemens are responsible for the improvement. The 6922s in the Rhea operate as an output buffer. I encourage all Rhea users to try a vintage NOS 6922 or a 7308 in lieu of the stock Sovtek if you are experiencing excessive tube noise as I was. I am very happy at this moment. |
No, Dan. The first thing I swapped out was the 12AX7LPs which are at the first gain stage (V1 & V2 in each channel). The improvement in soundstaging and three dimensional layering was nothing short of spectacular. The swap did not, however, kill the tube rush. Next I swapped out the Sovtek 12AX7WBs for EH 12AX7 gold pins. Perhaps slightly warmer sound, but still no improvement in tube noise. The last tubes to go were the Sovtek 6922s in favor of the Siemens 7308s. Thats where I lowered the noise floor considerably. I can now listen virtually as loud as I dare and tube noise, although still present, is not audible from the listening position and that is at two gain settings higher. |
Foo:
Its been awhile, but to the best of my recollection I replaced V1,2,3,4 with Telefunkens (12ax7) & V5,6 with Siemens (6922). Noise floor dropped considerably and sound was much warmer and more natural. A worthwhile upgrade in my opinion. |
