What's the source of the noise in the Express 5:50?

[GoranS]

Got my Express 5:50 a couple of months ago and while loving the tone I start to get annoyed about the noise level. Purchased mine used in mint condition and my first measure was to put new tubes in V1 and V2 and new power tubes. For the V1&V2 I bought some MESA SPAX7 as they are supposed to be low noise/low micro-phonic.

While searching for the subject I find that it seem like a well known fact that the Express is a bit noisy. If you take channel one the noise is substantially higher in clean mode than in crunch mode. I did not hear it first, but the noise is there and I am somewhat annoyed by the fact that a high quality amp is that noisy.

My question is: Whats the source of the noise. Tubes? Resistors?

Are there any modifications I can do to make it more quiet? For example metal film resistors in the first stages? Since being an old electronics engineer I'm quite handy with the soldering iron...

I'm leaning towards checking the resistors, as I know that thermodynamical noise in some types (carbon) can be a factor especially in higher resistor values in high wattage types. Changing and testing different tubes is another factor but resistors is more likely to produce white noise IMO.

Suggestions? Has anyone done this with success?

/G

 

[Don]

What kind of noise? My 5:50 has a slight hiss, maybe a bit more than my other amps but nothing that has ever been a problem.

Many claim to have tamed the hiss with careful tube selection.

 

[GoranS]

Noise = thermodynamic noise = white noise. Some may call it hiss...

Many claim to have tamed the hiss with careful tube selection

Yes, I know, but I am of the opinion that this should not be necessary, if you choose not to use the most crappy tubes that is or very high gain tubes at the first stage. (V2 I think) I was looking for an answer if anybody knows for sure, first hand, where the noise might be generated. If so I aim to kill it at the source, else I might have to borrow my oscilloscope back and go looking. (I gave it to a friend some months ago..)

/G

 

[GoranS]

On second thought...

Just disassembled the amp. It's very neat. It's so neat I'm having second thought messing with it. Not that I think I couldn't do it, but it's so nicely built, and if I would do a mod I must nail down the source first really knowing it will help.

Tube swapping is simpler, but I do not like the idea of having to buy lots of tubes just to try out.

But just to ask the question: I have a pair of JJ ECC83 S tubes in my drawer. Would they be better in the V1 & V2 pos compared to the MESA SPAX7 tubes I've installed??

/G

 

[THE TUBENATOR]

What type of noise are you hearing? Do you hear that noise with your guitar unplugged and nothing in the FX loop? I installed Mesa SPAX7 tubes in all five pre-amp positions V1 - V5. I did that the first week I received the amp over two years ago. That dramatically reduced the hiss that Express amps are known for. Every single tube in the pre-amp section contributes to the signal or noise so I wanted the lowest microphonic tubes I could get without going to lower gain tubes. I also use the stock Mesa 6L6 output tubes. I know many of the guys on this forum use a mixture of tubes that works very well for them. I'm happy enough with my 5:50 that I haven't looked any further into tube experiments. I can even keep channel two (either blues or burn) at full 5:30 settings on G, T, M, & B without any bass flub or buzzing and fairly high master settings as well and I move th contour setting around. In channel 2 I often use only my guitar's tone and volumn settings to adjust or clean up the tone a little. On channel 1 I keep the gain between 11 ~ 2 o'clock and the Mid at 9 with the T & B set at 5:30 and it sounds great! The extreme settings I sometimes use really makes my 4x12 cab come to life. The purpose of my long explanation is to say I could not use those extreme settings with the regular Mesa 12AX7 tubes shipped from the factory. It was like a run away elephant! I would get bass flub and some light humming/buzzing if I cranked the settings to high. I was thinking of buying a line voltage conditioner/noise filter but decided to start with the pre-amp tubes. I need to add that I only use my amp in the 5 watt setting so I don't know what would happen to my tone or noise level with some of my extreme settings at the 50 watt mode. I should also add that both my guitars have humbuckers and I use no effects pedals and I don't know what my sometimes "extreme" amp settings would sound like with single coil pick-ups.

 

[GoranS]

Thanks Tubenator!

That might be the way to go for me too. I just want to keep it simple not having to have 3 or 4 different tubes in stock.
I would never remember which to put where anyway. :?

The hiss I hear is a white (pink really) noise that is the same whether or not the guitar is plugged in or not. It's of course increasing when increasing the gain or the volume but does not change very much when changing the tone controls. The noise level is significantly higher when in blues mode than in the crunch mode in channel 1. I see the same on channel 2 but haven't investigated enough because I mainly want to use the clean mode. Don't know about the FX loop since I don't use it.

Even at "bedroom level" the noise is audible; clean - gain 11 o'clock - master volume very low.

When I got the amp I switched out the V1 and V2 for Mesa SPAX7 tubes and the power tubes to new stock Mesas since the amp was used. So three tubes is still unchanged, might be that one of them is not okay...?

Getting three more SPAX7 for V3-5 is worth a try and is a solution I like since I just would have to have one type of spare tubes for the preamp section.

cheers!
/G

Edited to add: I do not use the 5W mode at all, since having a damped room in the basement I can crank if I want and I find the tone more pleasing to me in the 50W mode. I still keep it down though to spare the ears.
The noise is the same in both modes, 5W or 50W does not matter.

 

[GoranS]

I've just ordered four Mesa SPAX7 tubes, three for my amp and one spare. (Already have 2 installed)
I'll report back when I've tried. May take a week or so for delivery.
/G

 

[J.J]

I'd be surprised if resistor thermal noise turned out to be the problem. Even a 200KOhm resistor will only generate a few micro volts. The fact that you are getting more noise in clean than crunch indicates a fault somewhere in the amp. I don't know for sure, but would expect that clean mode uses the same gain stages and crunch adds in an additional one(s). The mode switch also does a lot more than it would seem. The Express has a great number of relays in it which are mostly part of the mode and channel switching. These relays change a number of parameters including (but not limited to) cathode bypass caps and resistors, signal routing (adding gain stages) and tone stack components.

I'd start substituting tubes first, but if that fails without a schematic it will be difficult to find the fault.

 

[vbf]

I had some some hiss in my 5:50 when I purchased it new. I re-tubed with the kit from Doug's Tubes and it quieted the amp significantly.

 

[GoranS]

I had some some hiss in my 5:50 when I purchased it new. I re-tubed with the kit from Doug's Tubes and it quieted the amp significantly.

Thanks vfb. I've read all about it in threads at this forum.

I appreciate the effort being made of buying and testing lots of tubes finding the right combination of tubes. But knowing how my mind works, it's not the right solution for me. As stated in my earlier posts this solution does not appeal to me logistically. I will have to keep 3 or 4 (?) brands of tubes and on top of it remember where to put them. :?

I'll rather buy 5 good quality tubes that will work in any position and keeping one or two spares, even if they are more expensive. Since the Mesa SPAX7's is selected for low noise and low microphonics I'll give them a try as my all purpose Express tube.

I will let you know when my SPAX7 tubes arrives.

 

[StevenL]

Try a 12at7 (slightly lower gain) tube in V4. Made quite a difference with my 5:25. Quieter overall with more volume range in the Master. At7s are cheap too.

 

[vbf]

Does the brand of 12AT7 make a big difference? Doug's has them ranging in price from $9.99 to $30.00 (Mullard).

Also, does V4 function the same in a 5:50 as a 5:25?

 

[StevenL]

I'm sure the quality of the at7 will vary from brand to brand, but the point is the small gain reduction, and thus, the lowering of the noise floor. (It doesn't reduce overall volume that I can tell.) V4 is the tube that splits the signal to the power tubes. If you've got a bad or even a wrong kind of driver tube, the finely processed signal in front of it won't do your power amp section much good after it passes through. It's a very important slot, I'd say arguably, the most important. If you've got some extra cash, hit on the NOS Mullard. It even comes with a little cap on the pins to protect them.

I'm thinking now that an at7 just might work pretty well in V2 in taming the clean channel gain and hiss. Gonna order another one and try it just for the heck of it.

The preamp sections of the 5:25 and the 5:50 are the same. V4 is the phase inverter/driver slot for both. V2 is the first input and the first gain stage for the clean setting/channel 1. So, a slightly lower gain tube (at7 or other) in V2 followed by a nice, quiet, high-gain ax7 in V1 may be just the thing to further tame the clean "hiss."

Man, a clean channel on an Express, working at its optimal level, with no annoying hiss...... one of the wonders of the world!

 

[MrMarkIII]

PREAMP TUBE GAIN FACTORS:

12AX7 = 100
5751 = 70
12AT7 = 60
12AY7 = 45
12AV7 = 41
12AU7 = 19

As you can see, a 12AT7 has 40% less gain than a 12AX7.
If you get "your sound" at a setting of "6", now you're going to get it at "10". Sure it's quieter. 40% less gain should result in less noise.

 

[THE TUBENATOR]

As you can see, a 12AT7 has 40% less gain than a 12AX7.
If you get "your sound" at a setting of "6", now you're going to get it at "10". Sure it's quieter. 40% less gain should result in less noise.

That is the reason I went with the Mesa SPAX7 tubes in V1 - V5. I didn't want to give up any gain but wanted a low noise tube that was actually tested for low noise by a reputable supplier.

 

[GoranS]

Agreed, Tubenator. My thoughts also.

Unfortunately I have to wait for my tubes. A Swedish reseller had a deal on the Mesa SPAX7 tubes, but none in stock.
Since it was a good deal I ordered there, not knowing about the stock situation. I wont expect delivery for at least two weeks.

On the other hand it was a good deal.

 

[GoranS]

When cleaning out old stuff at work today I stumbled across a box with unused tubes.
Sylvania's and RCA's. Even six or seven Nixie tubes.

Anyhow, the only really useful tube I found was a never used Sylvania 12AX7A/ECC83/7025 tube in it's original box.
Might actually give it a try in the V4 position while waiting on my Mesa SPAX7 tubes.
I already have SPAX7's in V1 and V2.

 

[cherbst]

Try a 12at7 (slightly lower gain) tube in V4. Made quite a difference with my 5:25. Quieter overall with more volume range in the Master. At7s are cheap too.

What would this do to the overdrive? I'm thinking with V4 having less headroom I'd get more more preamp distortion, and less power amp? I could use exactly that, a little more preamp distortion in burn mode, and less overall volume (more volume control range). At home I can never run it hard enough to take advantage of power amp distortion anyway

 

[J.J]

Having a lower gain V4 will allow you to run the master higher for a given volume. Running the master higher seems to increase definition and improve the tone in general to my ears. I haven't tried a lower gain tube in that position yet, but I can tell you that V4 is far more sensitive to tube type than expected and can alter the tonal balance significantly. I am using a long plate JJECC83 in V4 which tames down the Tungsol RIs used in V1 V2 and V5 which can be fairly bright.

 

[cherbst]

Well I did try a Groove Tubes 12AT7 in V4. It did allow my a little more range in the master volume control, but still couldn't get past 9:00 for bedroom levels. I also thought it made the amp sound harsh, and was not able to dial it out with the EQ. I went back to the 12AX7 and think it sounds sweeter at low levels, the amount of play in the master volume didn't make up for what it did to the tone for me, and tone is king