[snaimpally]

I recently purchased a used T10RB serial no. 18829-0421. I swapped out my SP14 preamp and put the T10RB in and immediately I heard a low level, but audible hiss. I used the same RCA cables from my CD player (Marantz CD6007) to the preamp and I used the same RCA to XLR cables from the preamp to the power amp (DIY ClassD Nilai). The system is totally quiet with the SP14 but hiss is present when the T10RB is present.

I used the input selector to change the input but the hiss does not change regardless of the input selected. I opened it, removed the tubes, and re-seated them, but it didn't change anything. I tried futzing with the ground lift switch but that didn't make any difference either.

Suggestions?

[Chazz5]

Does the appearance of the tubes have anything to suggest they have a lot of mileage on them?

[ArthurDent]

First thing that comes to mind is the tubes. Found this with a quick search from an Absolute Sound review in 2019 -   
When I got everything up and running, I did encounter some very loud hissing noises that got louder as the preamp warmed up. After a little troubleshooting, I figured out that it was a bad tube in the left channel. After a quick email, AVA sent out new tubes, and once I swapped those in, everything worked as it should. AVA has a three-month replacement policy for tubes in new equipment. The thing is, tubes don’t last forever. They have to be replaced sooner or later, and it’s not uncommon to get a faulty tube, or to have a tube go bad, off the bat. When you get into the tube game, you basically accept this limitation as a given, and I think AVA’s policy is reasonable, if not generous

If you have spares try swapping one at a time to isolate the weak one(s). You can always give Frank a call, or I'd guess he or Larry will respond with more knowledgeable info when they see your post.

[Stercom]

Probably too much gain with the T10RB. Depending on how loud the hiss is try using some 10db, 15db or 20db attenuators on the input to your power amp.

[ArthurDent]

Probably too much gain with the T10RB. Depending on how loud the hiss is try using some 10db, 15db or 20db attenuators on the input to your power amp.

 That was my second thought, but from what I can find online both are 20 dB gain, so should be no change. I'm sure I've seen Larry or Dean post what the AVA std gain is, but haven't been able to find the post. And of course as we all know, everything you read on the internet is true. 

[snaimpally]

First thing that comes to mind is the tubes. Found this with a quick search from an Absolute Sound review in 2019 -   
When I got everything up and running, I did encounter some very loud hissing noises that got louder as the preamp warmed up. After a little troubleshooting, I figured out that it was a bad tube in the left channel. After a quick email, AVA sent out new tubes, and once I swapped those in, everything worked as it should. AVA has a three-month replacement policy for tubes in new equipment. The thing is, tubes don’t last forever. They have to be replaced sooner or later, and it’s not uncommon to get a faulty tube, or to have a tube go bad, off the bat. When you get into the tube game, you basically accept this limitation as a given, and I think AVA’s policy is reasonable, if not generous

If you have spares try swapping one at a time to isolate the weak one(s). You can always give Frank a call, or I'd guess he or Larry will respond with more knowledgeable info when they see your post.

I don't have spares unfortunately. I'll call AVA or place an order with Viva Tubes.

[snaimpally]

That was my second thought, but from what I can find online both are 20 dB gain, so should be no change. I'm sure I've seen Larry or Dean post what the AVA std gain is, but haven't been able to find the post. And of course as we all know, everything you read on the internet is true. 

The Nilai amps do have adjustable gain - I left it at medium, which is the default/factory setting. It can be set via a jumper so I could set it to a lower setting.
The SP14 I have is a Don Sachs Model 2 and when I swap that back, everything sounds fine.

[ArthurDent]

The Nilai amps do have adjustable gain - I left it at medium, which is the default/factory setting. It can be set via a jumper so I could set it to a lower setting.
The SP14 I have is a Don Sachs Model 2 and when I swap that back, everything sounds fine.

Sweet unit, I run his Kootenay amp, in winter now. The 'gain' search I did was for a generic SP14, which yielded the 20 dB figure. Just searched for Don's SP14 and comes up with 18 dB. So there is a little more gain with the T10RB if the numbers I found are correct.

Spare tubes are pretty much a must, and Frank's prices are fair if you're looking for solid no frills replacements. If you go down the NOS rabbit hole, it can get expensive real quick. Don generally recommends whatever make/brand the unit was voiced with, as does Frank, but NOS & high end reissue replacements can make a big difference.

[G E]

Agreed about bad tubes possibility.  Hissing is one of the symptoms of one going south.

Ground wire might alert help

Unlikely to be too much gain.

[danielgk]

If all else has failed, you might try this (no guarantees):

With preamp off and unplugged from line voltage, remove top and loosen transformer bolt enough to allow transformer rotation.  If transformer wiring is tight due to multiple wire ties that make wiring look "neat", cut wire ties.  Plug preamp back in, turn on, and get it to where you hear the hiss.  Rotate transformer to find the null spot where the hiss is the quietest...there should be 2 null spots, 180 degrees of transformer rotation apart from each other (either that or the transformer rotation just doesn't do anything at all).  Turn preamp off, disconnect from line voltage, tighten transformer bolt, "pretty" up wiring if you want, put top on, re-install in system.


Good luck


Dan

[Stercom]

If all else has failed, you might try this (no guarantees):

With preamp off and unplugged from line voltage, remove top and loosen transformer bolt enough to allow transformer rotation.  If transformer wiring is tight due to multiple wire ties that make wiring look "neat", cut wire ties.  Plug preamp back in, turn on, and get it to where you hear the hiss.  Rotate transformer to find the null spot where the hiss is the quietest...there should be 2 null spots, 180 degrees of transformer rotation apart from each other (either that or the transformer rotation just doesn't do anything at all).  Turn preamp off, disconnect from line voltage, tighten transformer bolt, "pretty" up wiring if you want, put top on, re-install in system.


Good luck


Dan

Dan, very interesting. Why would positioning of the transformer cause a low level hiss through the speakers? (that would make sense to me if its transformer hum though) Thanks, Scott

[ceylon]

Suggestions?

replace the tubes with a pair you know are phono quality dead quiet.

i have 2 questions:

how sensitive are your speakers?

does the volume of hiss follow the volume control?