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.