BHK Amplifier Issue

After Dirk’s revelations, and my stupid denials of the problem, I finally pulled my head out of my ass and got to the bottom of this. Thanks for all the help.

The problem is simple rust from water trapped between two steel plates.

Way back in 2015, when we first launched BHK, the bottom plate for the amplifier was built in two pieces. There was the main steel bottom piece and attached to it, in the middle, another steel piece used as a stiffener so the big toroidal transformer didn’t deform the bottom plate during shipping.

To build this assembly, each piece was separately fabricated using laser cutters, then attached to each other with a spot welder. That assembly was then sent out to the platers where it was zinc plated. As part of that plating process the assemblies are washed and dried, then baked to remove any moisture that might eventually cause some rust.

For the first two months of production, the platers neglected to bake the assemblies. Our quality control people caught the issue and returned all the inventory to be rebuilt. Unfortunately, two months of production got out the door and Dirk’s BHKs were among those. He first noticed a discoloration around the outside edges and, when he drilled out the spot welds and separated the two plates he saw the rust inside.

We are still investigating how many amps were affected and then trying to figure out what to do about it. Of course, anyone with an affected amp can get a new bottom plate. It doesn’t look like there’s actually anything other than ugliness to be concerned with as the stiffeners we’ve looked at were more ugly than non functional. There’s likely not enough water inside to cause more ugliness than what we saw but I cannot be sure of that. They certainly aren’t right.

If you want to check your serial numbers, look at the last block. Dirk’s ended in 5G0032 so they were right in the first month. The way to read the serial number, BTW, is simple. The first is the year, so 2015. The G corresponds with the month in alphabetical order. G is the 7th month (counting up from A), and then the last two are the unit ID. So, Dirk’s was number 32, built in July of 2015.

Anything built starting in August of 2015 is fine.

As a side note, not long after this we changed entirely the way those plates are assembled. Instead of spot welding our metal vendor now separately plates each piece and then assembles them together using some sort of viciously strong glue.

My apologies, again, to anyone affected with this issue and thanks to our loyal PS customers for the help.


Does this just affect BHK 300’s or also 250’s? My 250 was a beta unit so definitely early production for that series.

In the redacted @Dirk report he mentioned he had BHK250 and BHK300 and the photos showed they were both affected by corrosion to about the same extent.


That is correct. My BHK250 serial number: 5G0060


Thanks guys. Mine is 5D0013. Where is the best place to look to see if there is a problem? Does the unit need to be opened up?

You should definitely have your amplifier inspected with your BHK250 being such an early model… The top has to be removed. You’d be better of letting PS Audio inspect it.

Thanks Dirk (and Brodric).

I don’t have any BHK amps so I don’t have a dog in the fight but I would think the risk to the unit shipping back and forth would be greater than the impact of surface corrosion on/between the bottom plate.

Without the present of water and oxygen and/or electrolyte the corrosion won’t get very far, very quickly. I don’t think I’d ship mine back unless Paul says they’ve found them corroding through and no longer doing the job of holding up the transformer and guts. It can’t have any impact on the amplifiers primary job.

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Well, just on that. @Dirk was having on-going operational issues with his BHK amplifiers. Not just with one, with all three. Now that he’s done the repair, if the operational issues are now found to be cured, that would tend to confirm the corrosion did have an impact on the amplifiers primary job.

p.s. you obviously didn’t see the photos of how much metal was corroded.

No, I didn’t and then clearly the bottom plate is used for more than simple physical support.

Glad to hear the issue has been identified and will be solved.


Yes, the bottom plate, in addition to carrying the weight of the transformer, is the common grounding point for the amplifier internals (several ground wires attach directly to that plate).

As a follow up to this Dirk has been taken care of and happy.

If any of you want help or advice email me directly.



Good for Dirk and good for PSA. The right thing has to be done in the end. It’s a big reason why we stick around!


Maybe he was appointed the PS Audio repair agent for Scotland? He seems quite capable in that line of work.


An impressive presentation all around!

Congratulations all around.

Presumably those owners with affected BHK amps who don’t know about the issue because they don’t follow the forums (and we know that is a big number of customers), they will be found and looked after as well.


“Presumably those owners with affected BHK amps who don’t know about the issue because they don’t follow the forums (and we know that is a big number of customers), they will be found and looked after as well.”


Why what? You saw the photos didn’t you? It should be self evident why.

Not only that, Paul advised the affected serial numbers here on the forum to contact him via email about it. If owners don’t follow the forum, how would they know to contact him?

i also saw all the answers that Paul gave on the topic (topics if you include all the PUFFING and recasting of the topics to all parts of the forum…)

my confidence is broken also now…