Crackling Noise in DT25

[the29band]

I get this hum and crackle noise in my DT25 head/cab amp. The noise starts a few minutes after the amp has been turned on and even when the amp's volume is all the way down. The noise is there with or without a guitar plugged in. Anyone know what might be causing this? Attached is a sample I recorded. 

DT25.mp3

[BillBee]

Shot in the dark here but when was the last time the tubes were changed?

[Palico]

Put money on a tube, probably red plating. That sounded pretty much like mine did. 

 

Okay probably not a good idea, but on mine I just lightly tapped the tube with the back of my finger nail and you could hear my taping almost like it was microphonic. Get a set of EH tubes for it and bias it. Willing to bet the bias is high on the bad tube.

[the29band]

I have not changed the tubes on it since I got it about 1.5 years ago but I have also rarely used the amp during this time. I will go ahead an get the tubes changed. Thanks. 

[ChrisOe]

Please report back if it helped, because mine is doing the exact same thing.

 

Thanks

Chris

[mpeskett]

I had also experienced this exact problem for a long time until recently. It was really frustrating. I even took it to an authorized repair centre who said they had fixed it and said all it needed was a cleaning of the internal connectors which can become oxidized after a while. However I brought it home, fired it up and the noise was still there.

 

The issue is something to do with the tubes and not necessarily 'bad' or 'microphonic' tubes. I replaced my tubes with a matched pair of EL84s and a new 12AX7 from JJ Electronics. This brand seems to be especially recommended for DT25 amps. I then biased the EL84s to 25-26mV. Problem solved.

 

So it could simply be a case of biasing the tubes you already have. Or, it might be worth buying new tubes altogether AND biasing them. JJ Electronics highly recommended. I was so relieved to have finally solved the problem myself.

 

One other thing to note is that you will probably only hear this crackling noise in Class A/B mode and not in Class A.

[psarkissian]

1.5 years,... 18 months, time to change the tubes (valves).

 

Red Plating typically sounds worse, but yes, maybe that or a failing grid element.

 

Do not use JJ, Mesa or Groove Tube. This is not an all analog tube amp. You can't get away with the

same kinds of tube swaps as you can with an all analog tube amp. When I service DT series amps with

tubes that are other than the specified tubes, it's because they came back for servicing for that reason.

 

Use the specified Electro-Harmonix versions, they are optimal for this product. Can't put other tubes in,

bias to the specified bias volts without problems down the road. It's a digital/analog (hybrid) amp. Can't

treat it the same as an all analog amp.

 

[the29band]

I had also experienced this exact problem for a long time until recently. It was really frustrating. I even took it to an authorized repair centre who said they had fixed it and said all it needed was a cleaning of the internal connectors which can become oxidized after a while. However I brought it home, fired it up and the noise was still there. The issue is something to do with the tubes and not necessarily 'bad' or 'microphonic' tubes. I replaced my tubes with a matched pair of EL84s and a new 12AX7 from JJ Electronics. This brand seems to be especially recommended for DT25 amps. I then biased the EL84s to 25-26mV. Problem solved. So it could simply be a case of biasing the tubes you already have. Or, it might be worth buying new tubes altogether AND biasing them. JJ Electronics highly recommended. I was so relieved to have finally solved the problem myself. One other thing to note is that you will probably only hear this crackling noise in Class A/B mode and not in Class A.

 

I hear this in Class A as well

[the29band]

1.5 years,... 18 months, time to change the tubes (valves).

 

Red Plating typically sounds worse, but yes, maybe that or a failing grid element.

 

Do not use JJ, Mesa or Groove Tube. This is not an all analog tube amp. You can't get away with the

same kinds of tube swaps as you can with an all analog tube amp. When I service DT series amps with

tubes that are other than the specified tubes, it's because they came back for servicing for that reason.

 

Use the specified Electro-Harmonix versions, they are optimal for this product. Can't put other tubes in,

bias to the specified bias volts without problems down the road. It's a digital/analog (hybrid) amp. Can't

treat it the same as an all analog amp.

 

 

These good?

 

http://www.musiciansfriend.com/accessories/electro-harmonix-el84-matched-power-tubes/210092000118185

 

http://www.musiciansfriend.com/accessories/electro-harmonix-12ax7eh-preamp-tube

 

Thanks! 

[Palico]

These good?

 

http://www.musiciansfriend.com/accessories/electro-harmonix-el84-matched-power-tubes/210092000118185

 

http://www.musiciansfriend.com/accessories/electro-harmonix-12ax7eh-preamp-tube

 

Thanks! 

 

Yep that's the ones.

[psarkissian]

EH Matched Set Mediums,... yes.

EH Mediums for the pre-amps,... yes.

 

For those who say that EH's are just Sovtek Russian tubes with EH painted on it,

let me remind,... EH owns the Sovtek factory in Russia. The EH's go through further

scrutiny and sorting, which is why we use them, and are better suited for this amp.

 

I chat with Mike Matthews (owner of EH) about this every year at the trade shows here,

to stay current with what they are doing.

 

As for grades, this is determined by the proportion of vacuum vs gas,...

Soft--- more gas (a gassy tube), less vacuum, saturates more easily, so it distorts more easily.

Hard--- less gas, more vacuum, higher saturation point, harder to distort and so more headroom.

Medium--- in between, has good headroom, but will distort if you push it.

 

It's not an all analog tube amp of old, so stay with the mediums on these.

[spaceatl]

It's New Sensor Bro....They make them all...

[psarkissian]

Apparently also owned by Mike Matthews. Wasn't aware of that as we usually

chat about EH and Sovtek, since we get tubes from his EH firm. I'll have to remember

to ask him about that when I see him at the next NAMM here. Cool.

 

And we chat about his stompboxes,... I run two Small Stones at different rates,

gets a nice stereo swirl effect in the headphones when I record guitar. With an

electric 12-string, it's even better. He's amused by that, thinks it's cool.

[marco3253]

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