My tube pre is "hissing" at me!

[dbaldus]

I recently picked up a tube pre-amp here on the forum, the Conrad Johnson PV-7, and swapped out my Parasound PL/D 1100 (solid state) pre for the CJ. I was expecting a major improvement in soundstage and sound character (warmth, dynamics, etc.), some of which is there, but what I did not expect was the hissing noise that emanates from the speakers are soon as the pre is powered up. When I plug the Parasound back in, the hissing is gone and the room is dead silent, but as soon as the CJ goes back in, the hiss comes back.

Turning the volume up does not cause any differences in the volume of the hissing and the hissing itself is covered up completely by any music. However, when there's no music going, I can hear it very clearly from my listening position - its annoying and is really starting to take away from my enjoyment of the pre

I'm guess I'm just wondering if maybe this is something inherent in tube gear or maybe I have a "bad tube" that needs to be replaced? Has anyone else had an issue similar to this?

Any insight from the tube gurus here would be much appreciated - thanks!

[cstmar01]

Tubes can be noisy upon first firing it up. Best thing to normally do is fire it up and let it sit in standby mode then play something. Can also be due to having a SS amp hooked up to a tubed pre. Also could mean a bad tube or the tube is starting to go ect.

I would first try having it on for awhile then playing music.

[dbaldus]

Tubes can be noisy upon first firing it up. Best thing to normally do is fire it up and let it sit in standby mode then play something. Can also be due to having a SS amp hooked up to a tubed pre. Also could mean a bad tube or the tube is starting to go ect.

I would first try having it on for awhile then playing music.

Do all tube pre's just go into "standby mode" when first powered up? I've noticed that when I fire it up, nothing happens. But once I play music, I hear a "clicking noise" (like a relay or something) and then the hiss starts immediately afterwards.

I'll let it "warm up" for a few minutes in standby mode first and see if that helps.

Also, why would it matter that I have a SS amp hooked up to it? Just curious... thanks!

[thsmith]

Sounds like a tube or cap issue.

[JAC]

Never hear a tube component that didn't have some tube noise. Some have far less than others, but most all (I have heard) have it.

[Toolfan66]

My tube pre has a little hiss nothing major. But I let my pre warm up for at least 15 min.

[dbaldus]

My tube pre has a little hiss nothing major. But I let my pre warm up for at least 15 min.

Does that reduce the hissing?

[dbaldus]

Never hear a tube component that didn't have some tube noise. Some have far less than others, but most all (I have heard) have it.

Is the hissing that I'm describing (i.e., faint hissing coming from the speakers that does not vary when the volume knob is adjusted) sound like the tube noise that you've had?

[kawizx9r]

Had an extremely minor hiss in my system before when I ran a hybrid ss/tube amp and tube pre but I had to be close to my speakers to hear it (it was consistent though as you describe).

Did you get other tubes with the pre? I'd say roll in some other tubes and check to see if the hiss goes away. Another thing, let it warm up for a good while before you play anything through it. For awhile, I had never shut off my amp unless I wasn't going to listen to music for at least 4+days.

[JAC]

Is the hissing that I'm describing (i.e., faint hissing coming from the speakers that does not vary when the volume knob is adjusted) sound like the tube noise that you've had?

Yes, it is a fixed noise (white noise sounding hiss) in general but does reduce after warm up.

It shouldn't bother you when the music is playing except if you are sensitive to "noise floor".

The absense of noise is the "blackness" people describe when they get better systems with low noise floors.

Absence of noise is "sonic blackness"

[newbie308]

You are hearing the sound of millions of supercharged electrons. That's what tubes do. When it stops completely you have a dead tube because the emitter has no more electrons to give up. Enjoy!

The fidelity is unmatched, but the noise is unavoidable. At least not without filtering out the frequency it is producing, but that will affect the music as well.

[dbaldus]

Thanks for the input, guys. It's difficult for me to know if something is "wrong" because I'm new to tubes, but I didn't think it should be making so much noise that it is audible from the listening position (9 feet away). I suppose I'll have to get the SPL meter out and get some readings on the hissing and report back :)

Also, out of curiosity, are some tubes known to be "quieter" than others?

[doctorcilantro]

You said you could hear the tube rush from the listening position. That doesn't sound right to me. I've honestly had to play around with cheater plugs and floating the ground on some of my gear which dropped the noise floor to only be audible at 6" from the speaker.

I assume it's coming from each channel with equal amplitude as you didn't mention just one channel being problematic. Do you have a set of shorting plugs to use on your amp to get a benchmark? Or spare tubes to roll in?

[dbaldus]

You said you could hear the tube rush from the listening position. That doesn't sound right to me. I've honestly had to play around with cheater plugs and floating the ground on some of my gear which dropped the noise floor to only be audible at 6" from the speaker.

I assume it's coming from each channel with equal amplitude as you didn't mention just one channel being problematic. Do you have a set of shorting plugs to use on your amp to get a benchmark? Or spare tubes to roll in?

Yes, the hissing is balanced on each speaker.

I have some spare tubes to roll in, so I'll try that.

What do you mean by a "set of shorting plugs to use on your amp"?

Also, the CJ is a 2-prong outlet, so I won't be able to use a cheater on it, right? I'm thinking of a cheater as a 3 prong to 2 prong adapter, but maybe you're talking about something different?

[F1nut]

You've got a bad tube or tubes, period.

[Big Dawg]

I had something like that with the tubes that came with my (used) tube pre. Switched them out for some NOS Amperex, and the noise was gone (and the music was sweeter).

[doctor r]

You will need 3 - 12AX7 tubes and 2 - 12AU7 to fully retube the PV-7. That should take care of your issue.

[schwarcw]

You will need 3 - 12AX7 tubes and 2 - 12AU7 to fully retube the PV-7. That should take care of your issue.

Welcome to the world of tubes!! Buy the 7025 tubes instead of the 12AX7, they are definitely lower noise. They may cost a little more but they are worth it. Speakers connected out of phase will sometimes make a peculiar noise similar to a hiss.

Good luck!

[ShinAce]

Turning the volume up does not cause any differences in the volume of the hissing and the hissing itself is covered up completely by any music. However, when there's no music going, I can hear it very clearly from my listening position - its annoying and is really starting to take away from my enjoyment of the pre

Wait a minute! Is the amp on a fixed volume level and you're changing the volume from the pre? If you're using the amp's volume, then it's not the pre that's hissing, it would be the amp's output stage. If you're using the pre's volume, then it very well is the pre.

[dbaldus]

Welcome to the world of tubes!! Buy the 7025 tubes instead of the 12AX7, they are definitely lower noise. They may cost a little more but they are worth it. Speakers connected out of phase will sometimes make a peculiar noise similar to a hiss.

Good luck!

Can 7025's always fit into a 12AX7 socket? Just curious if it would even work in my situation.

Also, I have some 12AU7's in the circuit as well, so wouldn't I need to replace those with something "quieter"?

[doctor r]

12AX7s and 7025 are both 9 pin tubes that will physically fit the same socket. All the small 9 pin variants can fit so you need to match the electrical characteristics not the physical. There are low noise 12AX7s as well as the 7052s (a premium version) and low noise 12AU7s. Forum members or quality tube dealers would be your best sources. You might try the wanted section here and see what is offered. You do not really know which tubes may be giving you problems so replacing all might be worthwhile.