Hiss, hum and lag

[Deijavoo]

Just got a used Mark V two weeks ago and while I'm really into the sounds I'm getting from my guitar I'm having a few small teething problems.

Hiss and hum on channel 1 and 3 is not unbearable but it definitely annoys me next to the almost silent operation from my Dual Rec. Channel 2 is actually lower for this noise too.

Changing channels also seems to have a split second lag in actually changing too. Is this normal?

It's still under warranty, it's only been bought 11 months ago but where I am in the UK is a pain to get to an authorised tech, my local one would do an awesome job but again would that cause an issue with my warranty?

Thanks guys.

 

[Deijavoo]

I should point out that this noise is there no matter if jacks are plugged in or not and it only goes away with the mute button or standby mode.

 

[bandit2013]

The hiss is more than likely preamp tube related. It will be more noticeable in CH1 clean as well as Mark IV mode in CH3. I have yet to have any noticeable noise in CH2 due to the additional gain stage. There is not one tube that CH2 bypasses that is not used by both CH1 and CH3. I have had various hiss or hum issues depending on tube used. Tung Sol, EH, or similar type like Mullard (12AX7 or CV4004) seem to have a low frequency hum that can be annoying. I found that Mesa branded JJ tubes will make a considerable hiss or white noise. Easy way to find the noisy tube is to pull the chassis out, reconnect all the cables (especially speaker load) and remove all of the tube shields. Remove one of the preamp tubes and turn it on, usually start with v1 and work your way down the chain. V2 may not be the contributor since it is only used in CH2 but try it anyway. Fist find the which channel is worse, Ch1 or CH3. Leave it there and remove preamp tubes one at a time but first put back what you removed. Also do not try to insert the preamp tubes with the amp powered on in case you miss alignment of the pins. If nothing seems to make a difference it helps to use a known good tube and swap it in for one to remove and move it down the line of tubes. Usually the culprit is V1 or V3 Also turn on and off the effects loop (hard bypass or active) as well as turn on and off the EQ which may help in defining where the noise is coming from if not tube related.

An SPAX7 (basically a low noise 12AX7) may fix the issue if you can find the tube location responsible for the noise. The best tubes I ever had in the Mark V that were whisper quiet were the vintage Mesa tubes (Chinese 12AX7A) from 1990's.

The lag is a delay that Mesa has used on many of the amps with reverb. I bought the Mark V and Roadster New and they both have the delay of the reverb. The Mark V does seem to have channel lag in response to signal but will go away if you turn off the reverb or use a lower setting of reverb (similar with the Roadster, sounds like a whoosh or sweep effect as it rings in after channel changing form a high gain to low gain channel). The RA100 on the other hand does not do this nor does the Mark IV. I believe the engineer felt that attenuating the reverb and allowing it to return to the signal path at some rate was better than banging the tank with a sudden change in amplitude. Too bad they did not make that a selectable option. This lag is normal.

 

[Deijavoo]

Thanks Bandit, yeah I assume preamp tube, but on a less than year old amp? Saying that I suppose it could of been used heavily in the store before purchase.

In terms of pulling out the chassis I'll have to take it to my tech, I'm just so not confident in doing that. I really hope it is an easy preamp tube that's causing it, I'll swap out every single one if it helps but I'd rather save on that £200+ if I can. I'll just get SPAX7s if they are the quietest, thanks for that mate.

In terms of the lag, my reverb is always off as I use a Big Sky in the loop so if I'm left with no fix on the issue I may end up leaving the club pretty soon. :-(


Thanks though dude, I really appreciate the help.

 

[bandit2013]

It is not uncommon to get a noisy tube. I have had a few that just make pops with static then it goes away only to return (depending on what channel I am using). I have had a few Mesa tubes do this as well as other brands too. Hiss on the other hand is similar but may be a factor of gain of the tube. Tubes will make noise but there are some that will be quiet. I generally found the Mesa branded JJ tubes to be more prone for the hiss or crackle + pop issue. Other tubes I have used generally are prone to low frequency hum. A mild hiss I can tolerate but a low hum or buzz is not fun.

You should not have to pull the chassis to change a preamp tube. It can be difficult getting the shield off of V1 and getting it back in place. The shorter shield is much easier than the long one. You can swap one of the short shields for the long one ( I had damaged the aluminum bumps on the long shield so I bought a quantity of the short shields from Mesa) Also you need to pull two or three of the power tubes to gain easy access to the preamp tubes. You can leave the rectifier in place. The only issue with finding the noisy tube with everything in place, time to wait for the power tubes to cool down. Best not to jar them when they are hot, also prevents getting burned. When I am in a rush I use an insulated glove to remove one of the power tubes if I need to just access V1. Note: if you remove the power tubes, keep them in order so you can return them to the proper spot. You could also pull the inner pair and set them aside from the others that way the match pair stays together.

When I do tube rolling or debug (finding the noisy tube) I will generally pull the chassis out. If you do it, you need to loosen the support bolt under the power transformer first before removing the mounting bolts on top of the amp. Hint, if you leave the power tubes in place, keep the protective cage in place. Perhaps for the first time attempt, it would be best to remove the power tubes so they do not get broken. Keep in mind that the rectifier tube is closer to the power input transformer and the line in plug. Take a picture of the back of the amp with the tubes in place for reference if needed. Last thing you would want to do is install the rectifier in the wrong socket.

If you have a combo, not to worry, preamp tube are easy to access so removal of the chassis is not necessary. Installing the chassis in a combo is more difficult than the head but it is the same process due to the larger cavity of the comob, do not let go of the chassis or it may drop on you. Note, the amp chassis is the bulk of the weight of the amp. If you attempt, remember to remove the reverb cables before sliding the amp chassis fully out.

 

[Deijavoo]

Thanks again bandit.

removed it, and swapped the V1 with a regular JJ. The noise is certainly less, not silent but I'm thinking of replacing the lot with s type valves now. Tomorrow will be super high volume so time will tell.

Ended up removing the chassis, what an astounding sight seeing inside of that amp, just wow!

 

[bandit2013]

I overlooked the LAG issue and commonly mistake that for reverb roll in after channel switching.

There should be literally no delay between channel switching. Perhaps 15ms to 30ms. If it is actually 1 second then there could be some issues. Have you experienced this lately. If the Lag time increases with long play times. There may be a slight increase in switch time when operating at 45W if tube rectification is used vs diode rectification on CH1 and CH2 but the increase should be negligible. The dry signal should be there almost immediately (within 30ms at best).

 

[Deijavoo]

It's not quite a second, definitely less than that but I have no idea how I would test that. It must be milliseconds like you said but I'm just not used to that yet. The amount of time the amps been on makes no difference.

In terms of the hum, it's certainly a lot less but still there a little bit. Everyone assures me it's normal, it must just be me.

 

[bandit2013]

There will be some amount of hum associated with how high the gain is set too. Sometimes it is noise on the power line not getting filtered properly. Could be from lights in the room or other sources. Most of the time if it is associated to the amp even with the gain dialed down some, it is a preamp tube. Tubes that I have encountered that can be sensitive the to the common hum issue would be of the 12AX7 family (Russian made) Tung Sol, EH, Mullard, Svetlana, Sovtek, etc.. do a search on New sensor (US broker for Reflektor tubes). JJ are notorious for Hiss or white noise, however that can happen with any tube. I have found that some of the vintage Chinese Mesa tubes are extremely quiet. Most of the current Mesa tubes are also good but generally speaking, tubes are not as good as they used to be. If the noise is dominant and suddenly goes away when you play, it may or may not be tube related.