BHK power and pre amp forum


#1

Group: I just received my preamp beta unit yesterday. It was supposed to be shipped out on May 31 but some production issues (component supplier failure I think) delayed the ship out until June 8. Frustrating only in that I was chomping at the bit to join the party, and experience some of the revelatory sound you all have been reporting!

The good news on the delay is I can confirm the unit does now have a time counter for the tubes. I can’t comment in more detail beyond that right now as I am manual challenged (as in didn’t receive one in the box), but that is the least of my threshold issues…

So last night at 9 pm I finally had the chance to unpack her and begin. I can echo the comment that the trampoline type packaging setup is pretty slick to see, but in my case, opening the box revealed that the system didn’t function as it should. The preamp was twisted in the “hammock” such that the front corner (volume pot) was pushed up against the cardboard frame of the trampoline and not suspended in free space as intended. Lifting the upper trampoline I noticed that the plastic bag covering the unit was torn irregularly at the volume knob (not a clean slit, more like a tear from impact/abrasion) but a quick check for cosmetic damage or wobble or play in the pot was negative, although the plastic bag still kept everything pretty snugged up.

Now I don’t know if anyone else experienced this, but simply removing the preamp from this plastic bag proved unusually challenging. In my case, the vinyl protector for the piano black top plate had peeled up at the edges and adhered itself to the outer bag, so the process entailed gradually pulling the two plastics free enough to allow the tight plastic bag to incrementally slip off. (In the future, I would recommend one of those thin cotton wraps be used between the two plastics to speed this process.) to accomplish this separation I had to (gently) stand the unit alternately on its right and left sides, while separating the plastics and then incrementally inching the outer bag off. And in flipping the unit from left end to right end is when I heard it–loose rattles. Something small is loose inside (first thought) followed by no-- several things are loose inside.

OK. deep breath… work problem #1- remove bag. Finally off, I peeled back the vinyl protector and inverted the unit so anything loose could fall out, and it did–they did. 3 items: a machine screw, a nut and a black washer. Further tips to right and left revealed no more sounds.

I next realized that instead of the manual for the preamp, I received the manual for the BHK amp. No big deal, the other insert said the manual is online at the PS Audio site. Um, no-- its not. At least not yet. great. Lets see what I can figure out using the remote and the front panel button.

So I think-- what to do? Apart from the loose hardware and the bag abrasion at the volume pot, nothing else seems physically imperfect. So I decide to stick to my game plan unless any other issue arises: I will hook up my 3 redbook CD players and my SACD player into the 4 inputs, connect my Little dot Mk. III OTL tube headphone amp to the unbalanced outs, and my pro sound headphone monitor/ distribution amplifier to the balanced outs. That way I let it run in, with music running (alternatively) through all 4 inputs and both outputs driving as well, and I can evaluate the sound of the headphone output of the BHK against the two headphone amps (both driven off the preamp outputs, and also driven by the CD players directly) plus I could compare the BHK to the headphone outs on 2 of the CD players. With 6 different headphones available(Denon, Sennheiser, Beyer, Grado, Goldring, and AT) I’d have plenty of choices.

So over the next 3 hours I do this. couple observations, which I would love to hear feedback on: the volume pot may not be physically loose, but it seems to have right/left “play” in that you can rotate it right or left a click and nothing happens. I also noticed that its a bit finicky-- if you try to just move it one “notch” (say from 60 to 61) occasionally one “click” to the right accomplishes it, but at other times it takes two or 3 clicks to get it to move the one increment up-- a couple times it actually took 5 or 6 clicks for it to respond! also, if you deliberately move the pot up to a predetermined point (say, from 25 to 65) in a smooth rotation, at some point (around the 50s) the sound temporarily drops out-- as if the pot lost its connection or skipped a beat. Is this supposed to happen?

Last mechanical point-- hum. At exactly volume position 85, hum enters the scene from the headphone output. Whether I have the output connected or not, or 4 players on inputs or just one connected, when I stop the CD and turn up the BHK’s volume to 84, its dead quiet, but at 85 the hum jumps in-- prominently. I isolated it to the right channel: if I shift balance to the left to at least 18, the hum is imperceptible (and the unit is dead quite all the way up to 100), but from balance 17 left through zero, to 48 right, the hum is constant and does increase in volume from 85 to 100.

Now I realize that this might be normal, or due to several possible factors, but I wanted to ask my beta teammates to check this if they can and let me know what they find. I am in the mode of trying to determine if my unit is faulty or not; at this point I don’t think its fair to provide sonic observations or comments if I don’t have a properly functioning unit. Obviously, parts falling out of a statement/signature/$6000 component is cause enough for pause; but these volume pot and hum issues may be additional symptoms that something’s not right. As you might have guessed, my first 3 hours of listening was in some respects satisfying and impressive, but not in all ways, and I don’t want to indict the design before giving due consideration that this particular execution isn’t what it should be. I will call PS Audio to consult with them later this AM about next steps.

One last question–the unit was supposed to have switchable phase, but the phase buttons on the remote are labelled for DAC and PHONO, and neither functions. Is there some trick in the manual to enable phase inversion anywhere (hopefully on the remote, as it was described?)

Thanks, and I’ll keep everyone updated-- John


#2

I suspect the nut and washer are for one of the RCA jacks on the back – check and see if any one of those fell off.

The machine screw stumps me, can you send a picture? Is it a flat-head screw or a rounded pan-head screw? (Or no head, suggesting a setscrew for the volume knob?) It may have been just a cover screw, so check under the unit at the bottom of the chassis for any obvious locations where the screw came from.

You may have a bad encoder for the volume control. I don’t think they’re using a potentiometer directly, but it doesn’t seem to be working right.

I’ll have to let the experts (Paul or BHK) chime in on that one.

Hope it sounds good, at least . . .

–SSW


#3

Sounds to me like the knob might have gotten bashed in and there’s a mechanical rub. That and the loose screws make me think this one may need to come back home - but let’s use it for a while and see what it sounds like and how it performs.


#4
Paul McGowan said Sounds to me like the knob might have gotten bashed in and there's a mechanical rub. That and the loose screws make me think this one may need to come back home - but let's use it for a while and see what it sounds like and how it performs.
It's possible the hum at volume level 85 may be from switching in the passive component at that volume setting, so there may be a bad cap or resistor there for the coarse volume setting. (The tube gain seems to be working fine, but just at that coarse setting those parts may have a bad component)

But John, this is the reason you guys do the beta testing, so you can find out all these problems before final production starts.

Thanks for volunteering, but as Paul says, it will most likely have to go back to Boulder.

–SSW


#5

Paul,

And if John’s unit rotated in the plastic ‘hammock’ it means that the packaging doesn’t fully constrain the unit during shipping, i.e., it’s ‘weak’ along the vertical rotational axis and allows the unit to rotate. This is bad, especially if the volume knob is used as a rotational stop (very bad).

You may need to think about putting some cardboard under the unit before it goes into the ‘hammock’ with proper cutouts such that the cardboard uses the plastic sheets of the hammock to constrain the rotation, or put a protector over the volume knob such that the knob itself can’t be used as a mechanical ‘hardpoint’ during shipping.

I’m surprised this happened, but then again, the PWD/DS packaging is the same but there’s no volume knob on those units, unlike the BHK preamp.

Anyway, it looks like you may need to noodle this a little more.

–SSW


#6

Streets still Works and Paul: thanks for the quick replies! Streets, I couldn’t agree more that this is just the thing the beta testing program is designed to ferret out, so it is to be expected (even welcome). That said, I have utmost respect for Paul, Bascom and the team so, given the lack of similar issues from other Betas, I don’t want to dive in fully and offer observations or conclusions unfair under the circumstances. I will do as Paul suggested and soldier on, listen to it in the main system and look for any other issues. Hopefully this experience will assist in future decisions (like the packaging), and I know that in the end, Paul and company will make sure everything is right. As promised, i will offer unvarnished views, but at least the context is now known so if my listening observations in the end amount to data outliers, we have a possible explanation (beyond my own peculiar system or tastes).

Streets, I do have a picture of the loose parts on my Iphone-- attached (first pic the parts are above the amp photo on the manual (for scale), in the second it’s a close-up in my hand.)IMG_0422.JPGIMG_0423.JPG. Meanwhile, Paul-- can I get a copy of the manual? And is there switchable phase?


#7

Uh oh. I think those came from inside the preamp. (I’m pretty sure all external fasteners are black).

Paul, methinks there may be a QC step missing that ensures all fasteners are torqued down. This could have caused a massive short inside the unit and an unhappy customer (and smoke). Possible shock hazard to the customer, also, albeit remote.

May need to have one more pass through the assembly procedures to ensure everything is fastened down properly.

Just a suggestion.

–SSW


#8

Yeah, not good. We’re on it. Thanks for the help.


#9

FWIW, the front display on my DS DAC is loose (when I press lightly on it to change inputs it moves, been like that since new), and when I purchased a brand new Bridge II in Feb, the nut was almost off of the screw holding the bracket to the panel.