Lowering Noise and Microphonics

[JammyDodger]

Hey All,

I've just completed my TW Express (mostly Ceriatone parts). Fired up on the first try! Arm hurting a little from patting myself on the back.

While there is zero hum from the amp, the noise (hiss) seems a bit higher then I would have thought. Also the first stage is very microphonic. I have new Mullard 12AX7's in the preamp sections. I was wondering if dropping the gain in the first stage would help?

I have a couple of other tubes to play around with including a 12AU7, 12AX7LPS and a ECC832 (two different gains).

Any suggestions?

Cheers, Mike

[Lonely Raven]

I just finished my Ceriatone build as well. I noticed how sensitive the v1 is. If you *breath* on it you hear it! LOL

I'm trying out a 5751 in that position which quieted it down a bunch, but I think the 5751 tubes might be a hair less gain then your typical 12AX7. (correct me if I'm wrong).

I think I've read in the forums that the CV4004 are also a good quality v1 if you can find one!

I also have quite a bit of hiss. I'm not sure how I can improve on that, so I'm searching the forums in hopes of some info. Maybe someone can save us both the searching and scouring and offer some suggestions?

Also, question for you since we are on the same page...does the treble boost switch drastically boost the volume as well? When I switch mine up it's GOBS louder then middle and a little louder then the down position.

[drhulsey]

Also the first stage is very microphonic.

V1 in my Express clone was microphonic with a JJ 12AX7. That ceased with a NOS SyLvania. That stage is very tube sensitive. Don't give up on the 12AX7's just yet
BTW, Biofreeze should help that arm. It sure did mine

does the treble boost switch drastically boost the volume as well?

My bright switch doesn't add much volume, but the treble pot really pumps it up

[nickt]

BTW, Biofreeze should help that arm. It sure did mine

Hey Tim

are you saying you froze your tube? "Cryo" treated? Liquid nitrogen kinda thing? I know you're a plastic surgeon so could have easy access to a cryotank.

Just curious if it makes a big difference.

cheers
Nick

[drhulsey]

are you saying you froze your tube? "Cryo" treated? Liquid nitrogen kinda thing?

Haven't you heard of BioFreeze It's a topical pain reliever. I thought it was invented in Australia– prepared from Goanna semen
There are about as many hokey treatments out there for tube electronics as there are in plastic surgery. I can envision a Star Trek episode where the crew travels back in time to the early 21st century, and Scotty says, "I wonder why they di'no' cryotreat all their tubes? And what are those rubber O-rings for?"
Whatever works

[nickt]

are you saying you froze your tube? "Cryo" treated? Liquid nitrogen kinda thing?

Haven't you heard of BioFreeze It's a topical pain reliever. I thought it was invented in Australia– prepared from Goanna semen
There are about as many hokey treatments out there for tube electronics as there are in plastic surgery. I can envision a Star Trek episode where the crew travels back in time to the early 21st century, and Scotty says, "I wonder why the di'no' cryotreat all their tubes? And what are those rubber O-rings for?"
Whatever works

No I haven't heard of BioFreeze and I'm Australian! - lots of stuff gets invented in Australia (then gets exploited elsewhere for huge profits) Why just last night I heard the local natives invented the manually reversable vasectomny (they call it the "whistle dick" of course) but like cryo treatment I've yet to confirm the truth of this claim.

I suspect that cryo treatment isn't hokum though. I used to work with mass spectrometers and there was a bunch of stuff that had to be done to quiet the things down. Of course cryo treating a tube with poor vacuum and poor quality/dirty internals is probably a waste of time.

[drhulsey]

... the local natives invented the manually reversable vasectomny

We have one here, too. It costs $5000 up front, a month in advance, requires 2 hours of surgery, a 2 day hospitalization, and you walk funny for a few weeks

I suspect that cryo treatment isn't hokum though.

You're right. It probably won't make a NOS Mullard out of a sow's ear

[gcenker]

Jammy & lonely,
FWIW, I was going nuts trying all types of preamp tubes to try and get rid of the microphonics. I was always blaming the tubes because I'd inevitably get self oscillation with the volume up around 1o'clock (unfortunately that's the amps 'sweet spot' as well). What worked for me was to wire a 33k grid stopper resistor directly on pin 2 of V1 AND take the solid copper wire leading from the volume pot to pin 7 of V1 and replacing it with this:

http://store.haveinc.com/Ebus30/Parts/P ... de=CURRENT

It's solid core, shielded coax so it stays where you put it! Ensure it touches nothing and ground only one side. After installing it I realized I suddenly had a box of "good" tubes which were mysteriously no longer microphonic.

Since KF designed the Komet, I noticed an interesting coincidence:

[Lonely Raven]

I finally got to crank my 'wreck last night (apartment living sucks). I got home before my neighbors and had about 15 minutes to give it a little push.

I started out with the volume and 9'Oclock, just thumping a few chords and listening for anything wrong (new build you realize). After about 5 minutes of that, I dialed it up to 1 O'clock and started riffing out a bit.

I get no oscillation, no unhappy noises, but the hissing is bad and the tone clearly needs to be dialed in. Changing V1 out a few times in that 15 minutes I heard drastic differences in tone, but nothing I liked.

I'd really like to snub the hiss a bit, and dial in the tone...but with my limited high volume time since I'm in an apartment...I'm beginning to realize that maybe this wasn't the best amp for me to build.

That said...it was fun to roll back the guitar volume and hear things clean up, but the apparent volume not change! I love tube compression! I'm just not sure this is the amp for me yet. I'll have to do some dialing in to see if I can get it more like Glen's tones before I give up on her.

[geetarpicker]

I can see how the noise of an Express might seem too much when playing at home. On stage however I've never found it to be an issue.
In the studio I actually found the amp's signal to noise ratio is actually pretty decent when you consider the volume and gain levels. I remember back in the day (in a recording session) diming my old '68 Superlead and then comparing that noise to that of my Express set to a similar gain. At that point the Marshall was actually noisier when I played both recordings back at similar playback levels. However the Express is a high gain amp basically stuck on the high gain setting and played that way most of the time. If you play the amp at home an attenuator will reduce the volume but ALSO the noise too, something to consider. If you check out my Youtube clip (the one with the studio audio, not the camcorder ones) those recordings show how much noise there is during the cleans which isn't too bad. I did mute the audio right up until I hit the first notes, but from then on the audio is left turned up until the end of the clip.

Glen

[drhulsey]

What worked for me was to wire a 33k grid stopper resistor directly on pin 2 of V1 AND take the solid copper wire leading from the volume pot to pin 7 of V1 and replacing it with this...

I got by with shielded cable only from the input, but a lot of folks have used it on the volume control, as well. I do like your choice of solid core shielded cable. I'll have to get me some of that

[gcenker]

I got by with shielded cable only from the input, but a lot of folks have used it on the volume control, as well. I do like your choice of solid core shielded cable. I'll have to get me some of that

You won't be dissapointed. It's VERY high quality, teflon/foil/shielded SOLID coax ... and the price is right $0.30 per foot! Made life a LOT easier for me when dealing with an untamed express!

-Greg

[Lonely Raven]

I got by with shielded cable only from the input, but a lot of folks have used it on the volume control, as well. I do like your choice of solid core shielded cable. I'll have to get me some of that

You won't be dissapointed. It's VERY high quality, teflon/foil/shielded SOLID coax ... and the price is right $0.30 per foot! Made life a LOT easier for me when dealing with an untamed express!

-Greg

Maybe mines just not wild enough?

[briane]

well were all talking tubes....but the original post asked about hiss.

I have zero hiss in my TW express.

I suspect resistor choices. What kind of resistors did you use?

[JammyDodger]

Briane,

Hey - I used the carbon film resistors that came in the kit from Nik. No Carbon Comps in the circuit at all.

Mike