Need help... my tubed pre is making small explosion noises!!!

[fjhuerta]

Well, I would have thought tubes weren't so easy to get into...

My sister just came from the States for my wedding. She brought me the ASL 2004 DT preamp (with the 2 12AX7's and 1 12AU7). I was ecstatic...

Sadly, the preamp is incredibly noisy. I can listen to it humming everywhere. This wouldn't be as bad if...

Well, I turned it on, then turned on my power amp, then played with the volume level. Out of my left speaker, a small "explosion" was heard. I thought it was lightning. Then, out of the right speaker another "explosion" started. Before I knew it, a HUGE explosion sound came out of both speakers. It was really, really strong. I turned off the power amp. I was 100% sure my speakers were damaged...

I waited for a while, turned on the power amp. Sure enough, the hum was there, as strong as ever. But the "explosions" were gone. I listened for around 4 hours. No trace of them.

1) Should I just throw the pre-amp away and never bought another "made or designed" in China product ever again?

2) Is it possible that one tube is defective?

3) Any chance that I damaged the speakers? I listened to them for a long time afterwards... tweeter is fine, woofers are fine. I played them as loud as my amp could go. No distortion whatsoever. I'd expect they are OK.

4) ... is this normal in tube equipment? I wouldn't think so - my Margules ACRH-1 has never misbehaved like this... :(

[Clay]

One idea is to lift the ground on any three pronged equipment you have.
If using a 3 pronged amp, I need to list the ground to eliminate the ground loop hum.
I have blown up (not exploded) a EL34 and as I remember it was a very loud noise.
I always keep the volume down for 5 minutes while the tube pre amp and Dynaco ST70 amp warm up.
I also have a sequence to turn stuff on.
Pre amp first
tuner to provide input while it warms up (volume down below audible)
amp.
My tube amp does not like to be on without input (At all) - I think it wrecks something
I have had some loud noises, yet it is usually a dirty volume control on a 40 year old pot.
I used to switch tubes around to trouble shoot then I got a tube tester.

[fjhuerta]

Clay, thanks for your input. It's not as if the tube itself exploded - the speaker itself was making the noise.

The first thing I did was to "float" the preamp. It didn't work... hum went down, but not by a significant amount.

I think it's an excellent idea to warm up the equipment before serious listening, to avoid the "explosion" noises.

I'll try your sequence tomorrow morning. Also, I left on the pre-amp. Is it a good idea never to turn it off? At least this way, I think I won't get the "BOOM!" noises.

Thanks again for your input. It's really appreciated.

[Dave]

Originally posted by fjhuerta
Clay, thanks for your input. It's not as if the tube itself exploded - the speaker itself was making the noise.

The first thing I did was to "float" the preamp. It didn't work... hum went down, but not by a significant amount.

I think it's an excellent idea to warm up the equipment before serious listening, to avoid the "explosion" noises.

I'll try your sequence tomorrow morning. Also, I left on the pre-amp. Is it a good idea never to turn it off? At least this way, I think I won't get the "BOOM!" noises.

Thanks again for your input. It's really appreciated.
Javier, the way I understand it you shouldn't leave tube equipment on continuously. At least this seemed to be the general consensus of forum members a year or so ago.

[Clay]

I left on the pre-amp
Thinking about it, most new equipment requires burn in like Grovers :)
So leaving on the pre-amp for a few days that you are at home to prevent fires should be a good idea for bran new stuff. I would even leave the radio on at a low volume so it is a system on.


Some folks think it is ok to leave tube pre amps on for continuous listening days.
I never do. I also never leave tubes on if I go out even for a short trip due to a fire hazard.

IMO Also remember tubes like to be in action when they are on. I read somewhere not to just leave tubes running it they are not working at all.
That's why I always use the sequence and have the volume with an input like radio at a inaudible (50dB) or so level for at least 5 minutes so the tube temp can equalize and get up to operating temp (at 350 degrees for my EL34s. I used my heat sensing gun on it. I have the heat gun to tune my gas rc car. :) )

[Metralla]

Javier,

I doubt that the amp had ever been fired up before you did so, and I bet the tubes never had. I think the loud noises you heard are signs of the amplifier settling down, the caps charging, the dielectric forming and displaying some instability in the B+ voltage (the high tension circuit) between cathode and anode. It's certainly possible that you won't hear these again.

It's also pretty certain that those budget Chinese tubes are quite ordinary - as you would expect for the price.

Hum is a different situation. You may want to check the layout of leads and see if you can maintain distance between power cord, line level wires etc. Careful dressing of the connections may lower the hum, and then again - you could have a problem with the valves. Better valves may work.

Regards,
Geoff

[fjhuerta]

Geoff, the valves are not chinese... they are... well, what are they? :D JJ's, actually.

The power cord is away from the RCA interconnects, so I don't think organizing the cables is the answer...

All I can think of right now is moving the valves around, see if it helps. :(

This will teach me to buy local or locally serviceable stuff.

[Damián]

Originally posted by fjhuerta
This will teach me to buy local or locally serviceable stuff.
Can't really help you with the technicalities Javier, but don't despair. Just take it one thing at a time, don't rush it and you'll find a way around it sooner or later.

I know this just sounds like pep talk, but I really do believe that approaching stuff like this with patience is the key to working problems out.

Just use common sense, try one thing at a time so you know what the problem was once you find it and come here for help, it's clear that many/most people here do know their way around [audio] electronics.

In the end it'll probably all boil down to some $0.25 faulty cap or a loose solder joint, and once you get that out of the way you'll have an enjoyable piece of gear to listen to.

I do second the advice of whoever it was that said that leaving tube gear on could be a bit of a fire hazard, so please pay close attention to it if you do.

Best of luck, regards

Damián

[fjhuerta]

Hola Damián! Thanks for your help!

Well. I tried moving the valves around. It didn't help much. I then left the pre on for a couple of minutes and played with it. The hum is so loud it can be heard all around the house.

I decided I didn't want anything to do with a piece of equipment that could potentially damage my new speakers. So I unplugged it, and replaced it with my old passive.

The speakers are apparently OK. No damage can be seen or heard. Which is good. The old passive - amp combo sounds terrific - no hiss, no hum, no nothing. Now I have a nice little system.

I'll be calling my local tube guru today. Since I have the schematic of the thing, I'll ask him to try and find out whether the thing is damaged or not.

Still - I knew about ASL's bad reputation, and bought stuff from them hoping they would have fixed their issues. No luck - so I will never buy from them again (as tempting as their products are - their $99 tube monoblocks look sweet!).

[-=Rudy=-]

Loose tube in the socket? (Maybe a loose contact on one or more of the pins?) I remember a similar loud noise when I bumped a couple of tubes in an ancient amp I pulled out of an old console hi-fi system.

[-=Rudy=-]

...bump...

[fjhuerta]

Rudy, no loose tube that I could find. The tubes are firmly placed on their sockets. I also tapped lightly the tubes, to see if there was any noise. No such luck :( Thanks for the advice, though.

The passive is a bit lifeless, but at least it doesn't make weird noises... :(

[DanG]

Javier, I have been following this thread with great interest.

I am running a Dynaco pas and st70.

I normally have the st70 plugged into the back of the pas, using the switched socket. Turn on the pas, both the pre and the amp light up at the same time. No explosions.

HOWEVER. When I plugged the st70 directly into the power strip, and turned on the pas and st70 separately, POW, POW. As you said, an explosion on one side, then an explosion on the other. VERY unnerving.

I have since been keeping the st70 plugged into the pas, and everything seems OK. Sounds great, speakers are fine.

I have a buzz in the system, not too loud. It is clearly affected by a halogen floor lamp. I have purchased an inverter and plan to run all the line equipment off battery power. The amp itself sucks too much power, and will have to remain on house current. So I will once again be turning on the pas and the st70 separately.

The inverter should arrive this week. I will keep you posted.

[fjhuerta]

Dan, sounds like both of us have exactly the same problem.

I hadn't thought about using an inverter, but that sounds like an excellent idea. I don't think there was any RF-producing equipment around the tubed pre when I made my tests. That, and I physically moved the unit from one house to another to be able to test it on another piece of equipment. The same hum was there.

I'll be writing the tube guru around here, and ask him for his opinion. Please keep us posted on your prgress - I'll do the same :)

Javier.

[fjhuerta]

Found a fix for my problems.

It's ugly, it's messy, it should not have to be done, but... hey, it works!

I plugged everything into the tubed pre. Then, I sent the pre's outputs to my passive, and from there, to the amp.

Apparently, the gain level on the 2004 is set absurdly high. By using the passive, I can lower its gain level, and thus get rid of almost all of the hum and hiss. Even then, I can easily get full volume out of my amplifier - except now, the thing has zero noise.

I wish someone at ASL could be paying more attention to their products. I don't think this should be a necessary thing to do. But at least I have tubes back up on my system. :)

[-=Rudy=-]

Originally posted by fjhuerta

Apparently, the gain level on the 2004 is set absurdly high. By using the passive, I can lower its gain level, and thus get rid of almost all of the hum and hiss. Even then, I can easily get full volume out of my amplifier - except now, the thing has zero noise.


Jeez...I'll bet someone could wire a pair of high-quality resistors to the output of your tubed preamp to do the same thing for you. A potentiometer is nothing more than a variable resistor. If you could duplicate the setting you're making in your passive unit, it should have the same effect.

[DanG]

I've been making a lot of changes, but but I seem to have stopped the explosion problem.

When I've got the st70 amp plugged into the back of the pas-3 pre-amp, power on, power off, everything's fine.

When they're plugged in separately I was still experiencing small explosions. But now I've figured that out, too, I switch the pre-amp on first, and off first.

I'll post on my experience with the inverter in a new thread. Initial response is positive, but I want to do some A/B comparison.

[Tony Plachy]

Javier, The hum could be due to many things, check both your grounds and your cables. The popping when you first turn things on is probably just normal warm up of the pre amp. Better pre amps stay in mute for about a minute while every thing warms up and then feed signal to the power amps. Does your pre amp have a mute switch? If so put it on before you turn the pre amp on.

[fjhuerta]

Hi Rudy,

I might just get the resistors myself and wire them to the hot tip of the RCA jacks. If that's indeed the problem. I have heard from other people at AudioAsylum that the 2004 DT is dead quiet - something my sample is definitely not! I'll just open the thing and check if something is wrong. Maybe I'll find a ground cable disconnected, or something obvious inside.

From what I've read, ASL is not the best company regarding quality issues. Argh.

Dan, if I ever get to take my pre to the tube guy around here, I'll ask him about the inverters. He sells a couple of models...

[fjhuerta]

Made a new test today.

I played a cut, then turned off the power to the preamp.

The noise is gone, and the preamp plays for a couple of seconds before shutting up.

I think it's the power source the noisy one.

I'll have to take the pre for a check-up...

[fjhuerta]

Done. After talking to my local tube guru, the preamp was shipped to him. He told me that, depending on the problem, he might be able to fix it by Wednesday.

RA! I say :)

[fjhuerta]

Update:

The pre's power source is shot. It'll take an extra week to fix, plus quite some $$$.

I won't ever buy another ASL product again. Buyers, beware!!!