To all PS Audio BHK preamp owners *** must read ***

Hey everyone

If you have a PS audio BHK preamp you’re going to want to read this. Before I continue I want you all to know I emailed PS Audio to make sure this was completely safe to try and that it wouldn’t hurt anything or void the warranty. They assured me that it would not void the warranty and it’s completely safe to try. 

It has to do with the bias adjustment for the tubes. The bias adjustment For the 12au7 tubes it comes with is factory set for 4mV. They tell you that you can also use certain 6 volt tubes and the correct bias setting for those tubes is the 5mV setting which is adjusted by moving two jumpers. There is a picture in the owners manual with instructions on how to do this. It’s very east to do, all you really need is a good pair of needle nose pliers. 

I wanted to know if there was any benefit of trying the 5mV setting on the 12au7’s? The gentleman on the phone at PS Audio said he had never been asked that question before and that he would check and get back to me. A couple of days had passed and I opened up my email and there was an email from PS Audio. He said he checked with a few people at PS Audio and they all told him that it was ok to try it and he asked me to get back to him with what I had heard. 

So, I took off the cover over the tubes which is held on with two thumb screws (very clever). I switched jumpers J7 and J8 as per the instructions in the owners manual, put the cover back on and put on the exact same cd I was playing before I changed the jumpers. All I have to say is wow! Right away it was better. There was a slight amount of glare that was now gone. Everything was more coherent. Bass was noticeably better, tighter and more solid. Piano had more weight to it. Massed strings were smoother and more realistic and just more beautiful. All from a 1 mV increase in the bias adjustment. If I didn’t hear it myself on my own system, I never would have believed it. Let’s just say it’s not going back to 4mV ever. I just wanted to share that with BHK pre owners. Take care and stay safe.

Try switching it back. Does it sound worse? Per BHK himself: “The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.“

Hi earthtones

I’ve been listening to the BHK pre for over 2 years now so I know it’s sound well. I’ve always used the 12au7’s. After the first 4-5 months I changed the factory tubes to some nos early 60’s Telefunkens and those tubes transformed that preamp into what almost sounded like a new preamp. I was truly surprised at how much better it made everything sound.

I’ve always had it set at the factory 4mV setting. I’ve put on around 2200 hours on the Telefunkens so I know their sound well. After contacting PS Audio just to make sure what I wanted to try wasn’t going to hurt anything or void any warranties, they assured me that it was completely safe to try and to let them know what I heard. 

One of of my fiends came over a few nights ago and he asked me, do you want to try the 5mV setting, I said sure, we’re never going to know if it’s better if we don’t try it, so we switched the jumpers. 

With regard to earthtones comment of “try switching it back” in this case there is just no reason to do that. The improvements were immeadiatly obvious. We both heard it right away. The slight glare on the flutes was gone. Everything was more coherent. Piano notes had more weight to them. Bass was tighter and more solid. Massed strings sounded smoother and more realistic. I heard all positive and absolutely nothing negative. If you own a BHK preamp and you’ve never tried it before, I recommend you try it, if you don’t like it, you can always switch it back. Based on what I heard, I can’t imagine not leaving it on the 5mV setting. Take care.

Everybody report back. I’m curious. To change tubes, I have to remove tt and top shelf of my rack. I would like to hear from more people before going they the hassle. 

Is your turntable on top of the preamp? Is it not possible for you to just take the preamp off the shelf to access the panel that needs to be removed to get to the tubes and jumpers? If you do have the turntable on top of the preamp this is the first thing I would change. I (hope) must have misunderstood what you said.

I just bought a Shunyata Denali s v2 power conditioner and my same friend is bringing it over on Thursday evening. Two other friends who’ve recently bought one both tell me that it’s amazing and they’ve both told me it’s a significant improvement over the old model which they both had. I’ll report back after it’s installed to let everyone know if it’s as good as they both say it is. Thanks.

Since getting my BHK preamp I have played around with many setting options including the jumpers. I even purchased a 6922 converter to use 6sn7 tubes in the preamp, for that, it is important to keep the jumper at factory setting 4mv. I agree with the rest of the folks on here that when using 6922s/6dj8/7dj8/7308 family of tubes with the 5mv setting it completely transforms the sound, in a good way. I currently have a set of 6922 Telefunken in place-Ironically enough, I have not changed the jumpers back to the 5mV since popping out the Shangaung 6sn7. Perhaps I will later this evening. The one thing I do notice is, if your tubes are not tightly matched and with jumper on the 5mv, they will be more prone to volume pops- I am on the hunt for a set of CCa Siemens for the pre, at that point will roll the Telefunkens over to my BHK power Amp for some expirementation.

I know how to set up an audio system thank you, I’ve been doing this for 40 years.  Yes, I know how to access tube panel. No my TT is not sitting directly on top of the preamp. Lots of unhooking to access tubes due to rack. 
Stop assuming everyone is stupid

geee wiz


I never once implied that you don’t know how to set up a system, I was simply asking a question. If you go back and read your original post on this subject (you know, the one I noticed you deleted) that’s what it sounded like based on your vague description. The comment about the tube panel was not directed at you either, how could it be, I don’t know you and have never met you, it was simply letting everyone know how easy it was to do. I don’t assume anything about anyone, especially if I have never met them and don’t know them. Again, I was simply asking a question. I still don’t understand why you can’t just reach behind your preamp and unplug the power cord and disconnect the cables and just pull it forward off the shelf?
The only thing I found stupid was your reply, are you always this angry?

Hi Scot, I just wanted to let you know that I tried setting the bias to 5mv with my Amperex 7316 tubes. I didn’t notice a big change in the sound. However, I am probably one of the worst people for this experiment. I have really bad aural memory and as a result I dislike doing A-B tests.

I may try it again, after all, it’s free. I don’t doubt that you heard a big improvement, there are just so many variables involved with different systems and ears, that I’m more surprised when people agree.

If you get a chance to try the 7316 tube, do it. I really like this tube in my BHK preamp.

It’s cool that you at least tried it. I was using some early 1960 Telefunkens and I heard the improvements right away. I recently had some Amperex nos 7308’s from the early 60’s I’ve been dying to try so I put those in and changed the voltage jumpers to the 6 volt setting and my initial impression of those tubes is very positive. They seem to be a little warmer and a little more full bodied than the Telefunkens.

I normally also do not believe in a quick a/b comparison, it’s just too easy to be fooled into thinking something is “better” when after a few weeks of carefull listening, you realize that the change was just different but not necessarily better. In the case of the 4 to 5mv when I changed the bias jumper and put on the same cd we were listening to when it was set to 4mv we both noticed that the slight glare on the flutes was completely gone. We also both noticed that when the massed strings started playing they sounded more realistic. You know the old saying, ymmv. I would suggest changing it back to the 5mv setting and listening to it for a few weeks, like you said, it’s free and if you decide you don’t like it you could always put it back. 

Try it with other tubes. Your Teles may be getting tired and the increased bias current is giving them a boost.
I tried it and it’s no better and possibly somewhat worse. I may have detected a slight thinning of the lower mids and flattening of the soundstage. I’m not sure really but I’m keeping at the designed 4mv spec. I don’t understand Bascom’s rationale. For him to have stated a few years ago on the PS Audio forum that you simply chose 4ma for 12v and 5ma for 6-7v, end of story, then to purportedly suggest later on that you should experiment with it makes me wonder what exactly were the design parameters under consideration. In other words, what does he really think about these choices? Also, I would think running higher bias is going to burn out 12v tubes faster.
".....I would think running higher bias is going to burn out 12v tubes faster."                                                                    +1
Earth tones & rodman99999

I agree with both of you, I think it probably reduce the life expectancy of the 12 volt tubes. My goal was to see if I heard enough improvement in sound quality to warrant leaving it at the 5ma setting and I did. I don’t know how much shorter the tube life will be but the improvement in sound quality, in my system and in my opinion, was worth finding out. 

I also tried a 6 volt tube to hear the difference. I had bought some Amperex nos 7308’s from the early 1960’s and changed the voltage jumpers to the 6 volt setting and left the bias jumpers in the 5ma settings as this is what it calls for in the manual. I have read on several forums that Bascom himself prefers these and feels that his favorite tube is a nos 6 volt tube from the 1960’s. I forgot exactly which one. 

I must admit, I like the 6 volt tube as well. To my ears, the resolution is the same but it’s a little more full bodied and a little warmer. I don’t like to make quick judgements, it’s too easy to be fooled. I’m going to give it a few weeks and go back the the 12au7’s and listen to those again. Either way, I think for the Monet, this preamp is amazing.

@Scot- KUDOS, on your experimentation.      To me; sound quality is also paramount.       My intention for posting was to inform, per the shortened life expectancy of an over-biased tube.      It’s beneficial, for everyone to be aware of the facts/possibilities, in order to make such value judgments, for themselves.      Happy listening!
Tried it, didn't like it at all.Phillips Ecc82 tubes, my favorite out of 8 or so vintage tries.The Aja SACD sounded bloated and slow. Heavy big thick mid-range and very little high end. Ride cymbals were gone, forget the triangle.Very holographic, but unnaturally so.Switched back after the first 2 tracks, and felt I had to chime in with my 2 cents. But hey, everyone should give it a go. If you like it - good for you! If not, it's a 30 second swap back. Awesome preamp!
I'm sure different tubes react differently. I suspect that's why we like tubes...