JP-2C speaker switch not working properly

[Pacho]

Hello everyone! I just got my JP-2C and a Engl E212VB cab (16-ohms). I’ve noticed that with the speaker switch off there’s guitar sound coming from the speakers at very low volume but still. The guitar sound is not supposed to be muted?
The amp is connected from the 16-ohms output to the cab.
Is there something wrong with my amp?
Any help would be greatly appreciated!

 

[bandit2013]

Is there anything plugged into the FX loop? It is possible something is reversed.

Also is this a new amp or a used one? you may have a bad tube like V2. It is probable the switch is at fault though or it could be the 16-ohm jack. Try using the 8-ohm jack instead (it is safe to run a higher cab load on the jack, just do not do it the other way where the cab impedance would be less than the jack rating).

Before jumping to conclusion there is an internal error with components, changing preamp tubes is usually the first thing that a tech will perform to start with and you can do that at home if you have any spare 12AX7 preamp tubes. If that does not work, you need to have a tech look at it. If it is new, report an issue with Mesa customer support or the place you bought it from.

 

[Pacho]

Is there anything plugged into the FX loop? It is possible something is reversed.

Also is this a new amp or a used one? you may have a bad tube like V2. It is probable the switch is at fault though or it could be the 16-ohm jack. Try using the 8-ohm jack instead (it is safe to run a higher cab load on the jack, just do not do it the other way where the cab impedance would be less than the jack rating).

Before jumping to conclusion there is an internal error with components, changing preamp tubes is usually the first thing that a tech will perform to start with and you can do that at home if you have any spare 12AX7 preamp tubes. If that does not work, you need to have a tech look at it. If it is new, report an issue with Mesa customer support or the place you bought it from.

Thank you for your answer.

It’s connected to an Axe Fx 3 using the 4MC so there are cables in the FX loop.

The Amp is new, bought at Thomann.

I will try your suggestion using the 8-ohm jack and disconnecting the cables from the Fx loop. I can’t change tubes because I don’t have any spare but I will try the other suggestions as soon I get home and will let you know.

Thanks again!

 

[Pacho]

Is there anything plugged into the FX loop? It is possible something is reversed.

Also is this a new amp or a used one? you may have a bad tube like V2. It is probable the switch is at fault though or it could be the 16-ohm jack. Try using the 8-ohm jack instead (it is safe to run a higher cab load on the jack, just do not do it the other way where the cab impedance would be less than the jack rating).

Before jumping to conclusion there is an internal error with components, changing preamp tubes is usually the first thing that a tech will perform to start with and you can do that at home if you have any spare 12AX7 preamp tubes. If that does not work, you need to have a tech look at it. If it is new, report an issue with Mesa customer support or the place you bought it from.

I also would like to know if I can use a different brand of 12AX7 preamp tubes along with the Mesa tubes that come with the amp.

Thank you!

 

[Pacho]

Updating the thread:
I've tried again, disconnecting all the cables and using both the 16-ohm and 8-ohm speaker outputs, but the problem persists.

I'm afraid that, although I don't know if it's the cause, there must be a damaged tube because, when increasing the master volume, with the speaker switch in the off position, a kind of metallic click is heard that sounds like hitting glass, so I suppose it must be one of the tubes.

Now I'll find out how to detect which one may be damaged and try to change it, as well as buying new ones because I don't have any spares.

I am very frustrated with this amplifier, which did not arrive in good condition. I don't know whether to return it or change the tube to see if that solves the problem.

Am I missing something else to check? Any suggestions as to the brand of tubes?

Thanks for your help!

 

[bandit2013]

That amp should be under warranty. At least you are covered there. You may have to send it back to the place you bought it from. Before you do, you can change the preamp tubes first. If you can get one or two, that may be all you need.

Since this is a new amp that would rule out it being a limited edition. Tt should have 4 screws on the front panel or face plate just below the control panel. Note that the face plate will be a tight fit due to the piping material on used to surround the face plate. This face plate is removable and there is an access area behind it for ease of preamp tube replacement. The window is rather small but if you place the amp on one side it is easier to get the tube shields off and replace the tubes.

Losen the screws on the faceplate but do not fully remove them. The two on the bottom can be used as leverage or pulls to get the face plate to swing out from the bottom. If you have a limited edition model, you literally have to pull the chassis out as the faceplate of that version is not removable. Trying to reach the preamp tubes from the rear of the amp is very difficult since the cooling fan and a few of the chokes and one small transformer for the reverb is difficult to get around from the back side.

With just one good tube, you can start with V1, turn on the amp and see if any changes occurred. If yes, you found the culprit. If no, put the original back in and move to the next tube. The signal path for CH2, CH3 is as follows (without listing the individual triodes) V1-> V3->V4-> V2-> V5.

It should be possible to use any 12AX7 tube in the JP2C. However, sticking with the Mesa branded tube may be best as it is a new amp.
Note: I did try some Russian preamp tubes, EH, Mullard, and Tung Sol but had issues with a motor-boating sound. Not sure what caused that to occur but it was some form of self-oscillation. The tubes I tried did have some use on them. That issue never occurred with the Mesa branded JJ tube. The other is the JJ ECC83s (same tube) as that used by Mesa.

If you cannot find the Mesa branded tubes, you can get them from TAD but will not have the Mesa logo on it.

Frame grid JJ 12AX7, E83CC. These tubes are of good quality and are a step up from the JJ ECC83s. Much less noise floor and nice sonic characteristics. They look the same as the ECC83s but have different internal control grid structure. I have run these in the JP2C.

https://www.tubeampdoctor.com/en/7025/e83cc-jj-highgrade-tad-premium-selected?c=138

The following are much the same as the Mesa 12AX7 tube. JJ ECC83s.

https://www.tubeampdoctor.com/en/ecc83-jj-tad-premium-selected?c=138
https://www.tubeampdoctor.com/en/ecc83-jj-tad-balanced-phase-driver-selection?c=138

If you cannot find what preamp tube is at fault, make sure you have all of the original tubes in the amp if you have to go back to the place you bought it from. They may be able to help you get the issue resolved or may end up replacing the amp with another one if the amp was damaged during shipping. Something inside may have become disconnected. There are some ribbon cables to connect some parts of the preamp. This is not something you want to go poking around in if you have no clue what you are doing. Tube amps run on a high voltage power supply in the range of 450VDC. The capacitors used in the power supply may still have stored energy at that voltage or within lethal levels so last thing you want to do is find out with your fingers that it does. That may be the last thing you do in your life, so keep your hands out. I am just showing you the inside. The likelihood of a connection becoming loose is very low. The speaker on/off switch is soldered directly to the rear board. Leave that for a tech to service under warranty. Besides that, getting the chassis out of the head shell is not as bad as trying to get it back in.

 

[Pacho]

Thank you so much for the detailed explanation.

I can assume then that changing preamp tubes won’t void the warranty, right?

I’ll order the JJ tubes you are suggesting and try to find the broken one, if there’s any, before contacting Thomann and send it back to them.

Again, thank you so much for taking the time to help me!

 

[bandit2013]

If you cannot get a resolve on the issue with change in preamp tubes, I would put the originals back in before you send it to Thomann if that is the course of action. Preamp tubes should not void the warranty but it depends on how it is worded. There is more at risk when using non-Mesa tested power tubes if they result in damage to the amp which can happen. Unlikely a preamp tube will cause any issues. I would not use Russian preamp tubes in the JP2C as I tried them with some abnormal results.

Another trick you can try once you remove the faceplate, you can check to see if the preamp tubes are seated properly. Remove the shields and inspect the tubes one at a time. If the glass no longer has the silver coating or it if has turned white, that would be the tube at fault. The white getter flash is an indication the glass envelope has lost vacuum and the pure barium coating will react with oxygen and turn white if that is the case. Once you have the shields off, you can turn the amp on, check to see if the two heaters are active in each tube. That is about as much observation you can see. If one of the tubes is not working or may be lacking an internal connection that will result in low output levels. The reseating process, remove one tube at a time, look at it, make sure all 9 pins are present and insert it back into the socket. If for some reason you have a bent pin (not likely but if someone forced the tube into the socket it could be possible).

I hope you find the issue with a tube swap or if anything get a resolve on the issue. You are missing out on some really nice tones if you cannot get it to operate. Also double check all of the dip switches. If you are using the Footswitch with the amp, make sure the channel switch is set to the FS position (usually CH2). If you are not using the footswitch, it should not matter. That could be another test to try, disconnect the footswitch and use the mini toggle to select the channel. The only thing that could result in an issue with the amp would be the strobe mute circuit as that will short out sections of the preamp so the configuration changes does not make a huge pop or static noise. Either that or a DC blocking cap between stages is leaking DC voltage as that will also shut down the control grid. Not something you want to poke around to find. That is what the Tech service is for. They have all of the information from Mesa if they are certified tech for them. I would assume Thomann would have such as they are a Mesa dealer. As for preamp tubes, that is more of a trivial thing. Just use a good quality tube. No need to go for any NOS tubes. I felt the JP2C sounded really good with the Mesa branded JJ ECC83s. Nothing is bullet proof and issues can happen during shipping. I have had to change out a few preamp tubes on a new amp a few times. They were either crappy tubes (microphonic) or just made the typical pop-corn noises. That is why I got in the habit to order replacement tubes when I get an amp.

 

[Pacho]

If you cannot get a resolve on the issue with change in preamp tubes, I would put the originals back in before you send it to Thomann if that is the course of action. Preamp tubes should not void the warranty but it depends on how it is worded. There is more at risk when using non-Mesa tested power tubes if they result in damage to the amp which can happen. Unlikely a preamp tube will cause any issues. I would not use Russian preamp tubes in the JP2C as I tried them with some abnormal results.

Another trick you can try once you remove the faceplate, you can check to see if the preamp tubes are seated properly. Remove the shields and inspect the tubes one at a time. If the glass no longer has the silver coating or it if has turned white, that would be the tube at fault. The white getter flash is an indication the glass envelope has lost vacuum and the pure barium coating will react with oxygen and turn white if that is the case. Once you have the shields off, you can turn the amp on, check to see if the two heaters are active in each tube. That is about as much observation you can see. If one of the tubes is not working or may be lacking an internal connection that will result in low output levels. The reseating process, remove one tube at a time, look at it, make sure all 9 pins are present and insert it back into the socket. If for some reason you have a bent pin (not likely but if someone forced the tube into the socket it could be possible).

I hope you find the issue with a tube swap or if anything get a resolve on the issue. You are missing out on some really nice tones if you cannot get it to operate. Also double check all of the dip switches. If you are using the Footswitch with the amp, make sure the channel switch is set to the FS position (usually CH2). If you are not using the footswitch, it should not matter. That could be another test to try, disconnect the footswitch and use the mini toggle to select the channel. The only thing that could result in an issue with the amp would be the strobe mute circuit as that will short out sections of the preamp so the configuration changes does not make a huge pop or static noise. Either that or a DC blocking cap between stages is leaking DC voltage as that will also shut down the control grid. Not something you want to poke around to find. That is what the Tech service is for. They have all of the information from Mesa if they are certified tech for them. I would assume Thomann would have such as they are a Mesa dealer. As for preamp tubes, that is more of a trivial thing. Just use a good quality tube. No need to go for any NOS tubes. I felt the JP2C sounded really good with the Mesa branded JJ ECC83s. Nothing is bullet proof and issues can happen during shipping. I have had to change out a few preamp tubes on a new amp a few times. They were either crappy tubes (microphonic) or just made the typical pop-corn noises. That is why I got in the habit to order replacement tubes when I get an amp.

Thanks again.

I just ordered a couple of tubes replacements to try to fix it following your instructions, so I have to wait until next week. In the meantime I contacted Thomann and explained the issue to them.

I’ll keep you posted!