Noise Problems in BHK Pre with 6V or 7V Tubes

The preamp clearly sounds best - significantly best - with 6 or 7 volt tubes, but I have tried NOS and new production tubes and always have noise problems. I have tried perhaps half dozen different tubes, but always the same: NOISE. I particularly like 7DJ8/PCC88 and have tried several pairs of them. It is nice and quiet with 12V tubes, but the sound is degraded. Currently 12AU7WA/6189 French Mil.

PS Audio says that if it works properly with the stock 12V tubes that is the end of their responsibility.

Does anyone know of a 12V tube that works well in the preamp that approaches the sound quality of a decent 6 or 7V tube? This is my last gasp with this thing before I replace it. Otherwise I think this is a very thoughtful design of excellent quality.

Thanks in advance.

What are the attributes you think sound best with 6v tubes?

Edit: it would also help to know exact tubes you’ve tried.

Try true NOS Telefunken tubes. Try Brent Jesse. None of the new manufacturers can equal the quality of the old tubes.

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I’ve had no noise problems with my BHK Pre using: NOS Telefunken 6922s, NOS Siemens 6922s, NOS Siemens 7308s, NOS Valvo CCAs. I’ve purchased my best NOS tubes from Brendan Biever @ tubeworld.com. Always buy tubes, NOS or new production, specifically graded for low noise. I agree btw the BHK sounds brilliant with 6-7 V tubes, but it wants the best low noise valves or like any other high performance pre it won’t sound it’s best. One other tip be sure to set the bias correctly when you switch between 6-7 V tubes and 12 V tubes. See the dedicated tube rolling thread for instructions.

“What are the attributes you think sound best with 6v tubes?”

Thought someone would ask, and it is not easy to answer. Laid back yet with more definition; more dimensionality; individual instruments are more clearly defined in space; more depth to the image. In short. and I know this is not specific, more like music and less like hi fi.

I haven’t tried any of those specific tubes yet. Had the Tele 6922’s on order for months, then finally cancelled.

I am familiar with and following the recommendations for voltage and current jumpers for all tubes.

All the tubes I purchased were tested, balanced, and matched, and all from reputable dealers. I even tried purchasing the same tubes from different sources, but without exception I had noise problems with all 6 or 7 volt tubes, and none with 12 volt tubes. I do think something is not quite right in my unit. Do you know if the gain can be lowered in this unit? I am using big mono blocks (Jeff Rowland) with very efficient speakers (Spatial X-5), which I know is making the problem worse. But at 12 volt, nada.

All my NOS 6JD8 equivalent tubes had about 4-6dB higher noise floor than the stock Psvane 12AU7 with 99dB efficient speakers.

Have you tried a fresh set of Gold Lion 6922s or similar?

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Just to get a sense of the rest of your system, what speakers are you using? Are they high sensitivity? Also not sure how many 12 volt tubes you’ve tried, but there are quite large variations in their sound quality. There are some very fine 12au7 tubes that are more “musical” sounding than any 6 or 7 volt tubes I’ve tried, including 7d8 Telefunkens (although those are excellent.) A long black plate square getter RCA 12au7 comes to mind as a possibility. Brent Jesse (Audiotubes.com) has an excellent rundown of the sound of many tubes in both families. Another good source for really well screened tubes for noise is Andy @ Vintage Tube Services in Rockford, Mi. It’s much better to touch base with him by telephone than email. I don’t know anyone that screens tubes more carefully for noise than he does.

Yes, Gold Lion 6922’s. Didn’t get pulsing or volume control noise with them, but definite background ‘rush’ sound.

I am using big mono blocks (Jeff Rowland) with very efficient speakers (Spatial X-5 - 98dB), which I know is making the problem worse. But at 12 volt, nada. That is why I was wondering if the gain in the pre can be reduced. Not likely, I assume.

Thanks for the tube and source recommendations.

Have you tried using Rothwell attenuators? Might be just the ticket for your issues. I used them when I had a gain mismatch issue between and amp and preamp. Some people find they affect the sound negatively, some don’t. I didn’t. Lots of reviews and info about them online.

Rothwell Attenuators (Pair) -15dB | eBay

I’m all balanced. I did find some balanced attenuators (-20dB), not Rothwell. They are pretty cheap. But I wonder what they will do to the impedance. I’m usually in the ‘less is more’ camp.

I think I will wait to try this. Fairly narrow bandwidth. Will hustle up some good 12v tubes per your recommendation.

Try these and enjoy…

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If you can…locate some Amperex 7316’s. These are the quietest 12au7’s I have ever heard. And they sound heavenly…

I’ll try a set of 6922 gold lions I have in storage, but based on my experience with the 6xxx NOS tubes, I believe the +4-6dB added noise floor is normal.

Photon mentioned the Rothwell attenuators and I find them to be very good. I use a pair to level match my SPP and DSD inputs since the SPP runs high even at low gain.

Just ordered a pair of -20dB Rothwell XLR attenuators.

I have the same experience as far as noise from 6 or 7 volt tubes. I am currently enjoying NOS Conn (Slyvania) 12AU7 which sound wonderful without the noise issue. I also have the Gold Lion 12AU7 but I prefer the Conn to them.

If you can you might want to change your order to the -10db version as 20db is an awful lot and I found the -10db models to work just fine with 93db speakers. I own an earlier version of Clayton’s speakers that also claimed efficiency in that range and found in reality that was not actually the case.

Thanks, Dawkins, made the change.

I can confirm my newish Gold Lion 6922 have similarly higher noise floor to my other 6JD8 NOS tubes, so the higher noise floor is likely a design element.

Measuring dbA 1-inch from tweeter at volume 1 with a Reed R8060.

Running at 5mv, 47dB left / 49dB right

Running at 4mv, 46dB left / 48dB right

With the Gold Lion 12AU7 at 4mv, 42dB left / 44dB right

I was doing a bunch of sweeps and tweaks today, so here’s a frequency sweep of the two tubes. I might read it as the 6922s being warmer and the 12AU7 more sparkly.