BHK Preamp - New Tubes & Speaker Hiss

Audio Components Amplifiers
41

If I understand, you are hearing a hissing from your speakers. And you changed tubes and no difference. So how do you know that the preamp is producing the hiss?

42

Because when I redirect my DAC directly to the amp there is no hiss.

43

Dead equal.

44

Again, was this a sudden change? The preamp was quiet previously?

45

It was sudden. The small hiss I could hear when I pressed my ear against the speakers suddenly became amplified. Again, the ear-against-the-speaker white noise is perfectly acceptable; this however is annoying.

46

The fact it came on suddenly and is present with two different sets of tubes suggests to me something has happened to the preamp, but I remain suspicious of the tubes themselves.

What tubes do you have?

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47

Hey Jim, call PS Audio. If it is happening equally in both channels, it is very unlikely to be a tube issue. Having had this issue with a BHK preamp myself, it was an internal preamp issue. Others have made similar comments.

Hope the DS DAC is serving you well as the Cubans! Good luck brother.

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48

And please let us know what you learn/how the issue is resolved.

Good luck!

49

I replaced the originals with a pair of 1964 6922 gold pin Amperex ECC88s.

50

For what it’s worth, those have quite a bit more gain than 12AU7s, so you will inherently have more noise with them. I’d recommend giving a new pair of 12AU7s from us a shot and see if you still get the same level of noise.

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51

Brother Kevin. The DAC is a pure sonic joy. I am fortunate to have crossed your path at the right time. You indeed too good care of the unit. All I did was adjust the output a bit and it was good to go. This hiss from the preamp is annoying, and it is present regardless of upstream feeds and active channels. Most frustrating is the I have no clue what it could be from. I still enjoy a Cuban or two a week. Maybe when the pandemic subsides we can get together for a cigar of your choice (I have a humidor list). Jim

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52

The hiss volume is identical between the two sets of tubes. When you say “from us” do you mean PS Audio? I would give it a shot.

53

PS to my last message: the hiss does not get louder or less loud when I change the preamp’s volume. With no signal from any other component feeding the preamp, the hiss is the same at volume level 1 as at volume level 85.

54

Hi @jimkiely1960 you may have shared elsewhere, but what jumper settings are you using with the 6922 tubes?

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55

I didn’t change the jumper settings; they are presumably at the factory’s default level. Again this problem didn’t start when I put in the new tubes. It started when the ECC88s we led in it and remained unchanged after the tube switch. I just switched back and the problem is still there.

56

Are you saying that you’ve been switching back and forth between 12 volt and 6 volt tubes without changing jumper settings?

57

The voltage is identical at 6.3, so I’m not saying that.

58

Exactly what tubes were in the BHK when the problem started?

59

The BHK Preamp is shipped from the factory with 12 volt tubes. So the “factory’s default level” jumper settings are for 12 volt and 4 amps
The EC88/ 6922 tubes that you mentioned are 6 volt.

2 Likes
60

So if there were two ECC88 tubes in the preamp when I bought it from the dealer in Chicago, it was not the factory that placed them in the unit? Is that the logical deduction here?F##k. I’ll check the bias settings. What I did was simply replace what was there. I owe you a thank you.