Express done...need help calming the hisss

[amplifiednation]

nope didn't change the hiss. ha. i'll get back to work on this tomorrow.

now i have to troubleshoot the bright switch too. no biggie. i'll get this puppy to sleep

[M Fowler]

I use colossal's style of bright switch wiring and use short teflon wires.

Mark

[amplifiednation]

Hmm, so powered up the amp tonight, bright switch is fine (?). I'm sure it will come back to haunt me but I'm not fixing anything until then!! I really do like that DPDT wiring though...makes a lot of sense

I'm starting to think the hiss might be pretty normal at those volume levels. Running through my attenuator the hiss is barely noticeable, and that's pretty much the only way I can play the amp! (I am going to VVR soon).

The express sounds really awesome though. I can't wait until it breaks in more. The cleans are nice and bluesy and it is unreal that the volume pretty much stays the same with the guitar control, just adding gain. I guess the magic has been proven. The gain is completely over the top, but I like it.

I might experiment with a MF plate resistor on V1, but I'm gonna leave it alone for a little while, try some new tubes, and see where I'm at after breaking it in a little bit.

Man, those power tubes COOK with the volume at noon!!

Thanks for everyone who helped me with build tips and getting this going! I really appreciate the help and hope I can pay it forward.

Billy, thanks for the paralleled tube idea, it's really cool, it definitely added some tone to the amp, which is always a good thing! There really is no sense in wasting a triode!

Wait until you see what I have planned for a cabinet. I'll see if I can get some clips too if I ever get my recording software working again.

-T

[ampdoc1]

I doubt moving wires, etc will change anything re the hiss problem. The Express is about my favorite amp, and I've built 4 or 5 of them, starting at first with the values/parts/tubes as specified.

But, this is a gain monster, and that's where your problem lies. Try substituting your 12AX7s with 12AU/AT/5751s. My first amp ended up with V1-12AU7, V2-12AT7, V3-12AX7. Still hotter than a pistol, great feel and response,...but a LOT less hiss.

Different tubes/makes etc all adds up. Try out a lower gain tube for V1, as that stage is first in line so any residual hiss there is amplified by the next stages. Then try a few combinations. I guarantee you can bring down the hiss and still keep the sound you want.

a'doc

[amplifiednation]

Y'all were correct. I splurged on some tubes. I got an English mullard and a quad of amperex 12ax7s and they were delivered today. The first tube I tried was that mullard and guess what? No hiss. Unreal!

The amp is nice and quiet...relatively, but the hiss is minimal. Oh...and it sounds awesome!!!! I missed that el34 punch. I am really warming up to the express. I did the tube testing with no attenuator through a 212. Sounded incredible. Its like a Dodge viper at the end of a rope...

So thanks again! I'm still going to try some lower gain tubes but I am pretty happy now!

[ampbldr2]

Glad you resolved the hiss problem. It is funny that a tube can cause this hissing issue. Must be due to the amount of gain in the preamp section.

I had the same issue with my 18trex but have tamed it to a point that it is not there all the time. When money permits I plan to try out 5751 and 7025. http://thetubestore.com/12ax70ectyp.html

[amplifiednation]

That amp is like having the devil by the ballz. It is mind blowing. It is a tone I have never experienced. If i didn't get it right with my build I can't imagine what a good one sounds like...or a real KF. I'm gonna record it soon

I gave myself a nice headache this morning. I have a Gerald Weber attenuator that I built awhile back but I feel like it sucks some tone. I may try an airbrake build, those parts aren't cheap though

[M Fowler]

How long do those expensive NOS tubes last?

In this day and age finding solutions to amp problems using tubes like JJ, EH, or sovtek is how I see the future in the tube amp business.

The new production tubes are getting better while good NOS tubes are getting harder to find, questionable dealers, and way too expensive for me.

Mark

[martin manning]

I'm of the same mind, Mark. Buying the better quality new production, even if they are a bit more expensive, is a good way to encourage movement in that direction. No doubt the current manufacturers have noticed the very high prices being paid for NOS, and recognize that a certain part of that market and pricing (the rational part) is due to the generally higher quality. That should be another indication that people will pay for a better product.

[amplifiednation]

I would love to find some good lines of new production tubes, at least we would know they were legit, they would most likely test good, and they would be available.

But most of the stuff I have that's new production, and I do have a lot of different brands, gets beat by the old glass. Nothing sounds bad, but it just seems like the old stuff sounds better.

How about the genelex stuff with the matched triodes? They are pricey, is it worth it? Do they sound good?

[amplifiednation]

Aahh, my hiss thread almost died. I finally narrowed down the problem.

So i wasn't getting very good (if much of any) response from my tone controls, so I switched my paralleled V1 back to stock values, putting everything back the way it was. The gain was almost too much and I didn't want to mess around with cap and pot values.

I plugged back in the amp to make sure things were working properly, and the hiss was back.

Then I realized that the hiss goes away almost completely when I plug my guitar in! So I guess I'm not sure exactly where that leaves me, but it's not in the plate resistors, right?

The hiss is not the "open jack" sound, but closing the jack definitely silences the hiss.

Thoughts or suggestions?

[selloutrr]

get an alligator clip and experiment with moving the shorting jack at the input to ground closer to the jack.

Also check your grounds loops happen between the chassis and the bus bar.

you could experiment with a cliff jack i.e. undocumented 90's express... so the input jack is floating then ground it back to the bus bar.

[amplifiednation]

It should be some sort of grounding issue, right? I need to take a closer look at that jack. I had the amp back in the cab already when I figured it out. I was getting the hiss with and without the wood faceplate. At least I narrowed it down finally

[selloutrr]

make sure the metal to metal contact is clean between the chassis and pots

[M Fowler]

Most noise I get with the Express is in the presence circuit, touchy focker

I would think that power tube imbalance noise is going to be a problem as well. The preamp we all know is touchy. It just may take an expensive set of NOS tubes to lower the hiss threshold.

Maybe some 7025's might help.


Mark