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.

Scot
scothurwitz
Thanks for the tip.  I'll give it a try.
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.“
https://forum.psaudio.com/t/bhk-preamp-tube-rolling/3403/8

Thank you for this post. Will have to give this a try. 
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.

Scot
Well now I’m really curious so I guess I’ll try it.
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. 
Aberyclark

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.

Scot
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.
Scothurwitz

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


Aberyclark

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?

Scot