Premier 16LS2 - HISS

[aldinohiend]

HI!
I have a problem with my pre Premier 16LS2.
An annoying hiss has been heard in the speakers for some time.
It is not continuous. It is random and, when it triggers, lasts a few seconds. It can happen that you do not hear for hours or that you hear many times in an hour.
The technician I turned to told me that the electronics, according to him, is ok. He has replaced the valve sockets but the problem persists.
I replaced the tubes but nothing has changed.
Can you help me, please?
Thanks.

[admin]

Any ground loop issues? Is it a roughly 60 hz hiss? Is there something else in the house that is going on (usually something with a motor) like a fridge or water heater when this happens?

Have you tried swapping the component to see if it's truly the 16LS2?

Does the amplitude change with volume changes?

[aldinohiend]

The hissing was also found by the technician. It is not an "ummmm" but a real hiss at about 1000 Hz. I have no electric water heaters and the fridge is connected to another meter. The air conditioners are also turned off. It's an inherent problem with the preamp that you can't understand why it suddenly came out of nowhere.

[Joe Appierto]

I know you said that the tech ruled out the "electronics" but could it be bad capacitors? The 16LS2 model is just about 20 years old and maybe this is a factor to be considered.

I owned a 16LS2 and ran it together with a Premier 140 and thought it was an awesome combination. Hopefully this problem is resolved quickly and you can get back to enjoying music.

Good luck.

[AnotherJohnson]

Hiss is nearly always a small tube.

Changing tubes is an unreliable test unless you know that the new tube(s) is/are good.

I just went through this with my VVT guitar amp.

One of the replacement tubes turned out to be as noisy as the one it replaced.

[admin]

I would also recheck the tubes. I would look really carefully at the circuit paths that are utilized in both channels (as this is happening in both left/right audio paths) looks for any bulging caps or clear signs of damage. I know you had a professional look at it but even the professionals sometimes miss things.

[roberto]

Hola,
And yes with all the above answers too. 99% of this noise is a bad tube. It looks that one of the 6922 tubes became noisy. How to find the bad one? Simple by doing a replacement only. Have one new 6922 and change V1. Problem solved? No? Leave that tube on V1, and with the old tube in your hand, change V2. Solved? No? Do the same thing until the noise goes away. That's the bad tube and should be resting in the trash can.

Happy listening!

[aldinohiend]

I thank everyone for the answers.
As for the capacitors, the technician assured me that they are all perfect. As for the tubes, I replaced the whole sextet with perfect Telefunken ECC88 and the problem returned.
I honestly don't know what to think anymore .........

[roberto]

Hola.
Is the hissing noise volume dependant? Why are you so sure it is coming from the preamp? Perhaps the noise is coming from other device...I am just guessing.
Are both channels with the hissing noise and have the same intensity or one channel is louder? If the hissing noise has the same intensity on both channels, then you might have a regulator problem at the power supply.

Happy listening!

[AnotherJohnson]

Could be a cable routing issue.

Sometimes cheap resistors are noisy, but CJ does not use cheap resistors.

It could be a first stage small tube in the amp.

It could be a grounding issue somewhere. It does not sound like a ground loop, But it could be stray RF getting in somewhere.

[aldinohiend]

Hola.
Is the hissing noise volume dependant? Why are you so sure it is coming from the preamp? Perhaps the noise is coming from other device...I am just guessing.
Are both channels with the hissing noise and have the same intensity or one channel is louder? If the hissing noise has the same intensity on both channels, then you might have a regulator problem at the power supply.

Happy listening!

The hiss comes from the pre. I excluded all the other devices, leaving only the pre and power amp on. Nothing happens with just the final on. With the preamp you can hear the hiss. And when there is a hiss I hit the MUTE button on the pre and the hiss stopped.
The hiss is heard in both speakers and has the same intensity.

[AnotherJohnson]

I think you’ve been snookered on the idea that all of the replacement tubes are good.

Another possibility is a noisy pot or switch. Were they all cleaned?

In tube gear, hiss troubleshooting begins with the small tubes as the most likely culprit. After that, wear items like switches and pots. Hiss can come from cheap resistors too.

Have you cleaned and sorted the amp to preamp interconnects? Usually these are more likely to produce hum, but it’s free to try.

[roberto]

If you touch the volume knob, does the hiss varies in intensity? I am trying to find from which part of the circuit, the hissing is coming.

[aldinohiend]

If you touch the volume knob, does the hiss varies in intensity? I am trying to find from which part of the circuit, the hissing is coming.

No

[admin]

You mentioned in your for first post that the hiss is not continuous but random. Does it tend to happen "more" when the unit is warmed up or it happens equally in the first minute or so compared to say 30 minutes in?

For experimentation purposes I would also open up the unit, hook it up and run it like usual. With a non-conductive material, I would put pressure and try to wiggle each component in the unit to see if it can induce/stop the hissing. It may be a cold solder joint or some connection issue that was missed with testing as it happens on/off. Make sure you do this with the power supply components as well. I know we are grasping at straws here but worth a try.

[AnotherJohnson]

There are typically DC voltages on the order of 250 V in a tube preamp, even after its unplugged, so if you’re not sure how to discharge it safely, don’t just go probing around inside.

[admin]

There are typically DC voltages on the order of 250 V in a tube preamp, even after its unplugged, so if you’re not sure how to discharge it safely, don’t just go probing around inside.

This is absolutely correct. If you are going to touch the inside with any conductive surface, make sure it is off, unplugged, and you may have to even wait for some time for the caps to discharge. There are large voltages and currents going through some components so safety is #1 and if you don't feel comfortable working on a live circuit, better to leave it to a professional.

However, if you are careful, use a non-conductive probe, it can be helpful to push on components while the unit is on to detect connection issues. I've found cold solder joints that worked "most of the time" and looked ok. However, it is often very difficult to find these without actual signal going through the circuit. I've done this kind of examination a few times and I make sure I'm working in an open setting where I can freely reach into the unit without touching anything else. I have a nice plastic probe that came with a solder kit, I wear gloves and a shirt with tight fitting long sleeves. And I take it really slow.

I agree with AnotherJohnson, there is risk here and safety should come first.

[AnotherJohnson]

Chop sticks can be a good probing device.

Keep one hand in your pocket is a good rule.

If you don’t have a solder sucker or you can’t solder, better to leave the probing to pros.

Best advice - see if CJ would give ideas on the phone.