My Express Build with some problems

[jaxx]

hi guys,

i done a lot of other boutique amps, so i decided to do an express too.
before do it, i red all the informations here, watched photos excetera..


my express have some problems:

i have a constant white noise in background, and i try several solutions to delete it but without success.
i've got to remove bypass caps switch cause it make selfoscillation.
when i turn the presence pot it makes some scratches.

it do not sound bad but it's and incredible harsh sounding, i also put in parallel to the 47pf a 250pF between PI plates to reduce harshness.

i tried NFB to 4 8 and 16 ohm but i have always the same poroblems.

withenoise disappear only if i remove the connection from PI kathode resistor 10k to presence pot. i tried also to remove the pot and go to ground from PI 10K res with a 5K res, but i have the same noise.

i also tried different grounding solutions but nothing done.


the only mod i've done from original circuit is to put into two multicap can.
a 50+50uF FeT to sobstitute the first 80uF el.cap and a 40+20+20+20uF JJ to replace the other.
i did a unique star ground to prevent ground loops.

someone can help me?


many thanx in advance.

[paulster]

That sounds quite normal in an Express build.

You'll notice that there's no inter-stage attenuation so the noise from V1 is going to get massively amplified throughout the amp.

Careful tube selection, particularly for V1, is the solution.

[jaxx]

thank you paulster,


i changed many tubes in v1 position (also in v2 and v3), but nothing change.

i used t.sol selected tubes and i comparate them with normal sovtek 12ax7.

no differences in hum. this make me think there were something else that generate hum.

do you think there are some circuit mods to do to attenuate hum?

also i noticed if i beat with a pen on 2n2 interstage cap it generate an effect similar to beating on a microfone.

a changed that cap, but nothing changed too.

[geetarpicker]

Harshness and excessive noise is typical of many TW clone builds, due to parts choice and layout changes. What parts did you use? Any pics? Transformer placement and layout issues can cause hum. Also, the bright switch will typically be way too intense unless the volume is up high like 1/2 to 1pm. Also what speakers are you running with this amp? I use the 2 long cord trick going in with Mogami cable. George L is typically harsh with my amp.

Noise to a point is still an issue with these however check out this video link. I'm playing an Express with all the knobs on 1/2 (+500pf bright switch on) and the guitar on only about 2 to keep the amp clean as the Gretsch pots come on quick. That's a worst case scenario for noise (guitar low, amp cranked) but it's still not bad even during a such a delicate sparse song. I did mute the mic before the very first note is played, but after that the mic is on an never noise gated or anything.

Keep in mind these are high gain amps, but compared to say a dimed Marshall 50, JTM45 or similar they are actually quieter in noise spec. That said are you used to playing such amps with all the knobs on TEN? Playing such amps fully dimed is like a wreck only on about half. Coming from the EVH school of thought (my prior amp was a '68 Plexi 100 which I played fully dimed, an attenuated) an Express is actually a quieter amp in noise spec. Also with a TW there should only be hiss, but very little actual hum.

Listen to this track>

http://www.youtube.com/watch?v=-U36UxwiHaI

[jaxx]

hi Glen!!!

i used Fisher and Tauche multicap can electrolityc and a JJ multicap can el. for filtering, sozo caps, all carbon film Kiwame 2w and 5W resistors, Alpha pots and switchcraft jacks.

trannies are ruoted about 90°, and i use the headphones method to find the best position, in fact thare is a minimal electromagnetic induction hum from speackers.

trannies are hand made by an italian artisan that do transformers about 30-40 years. i always buy trannies by him, they sound very good and are not expensive too. i never had a problem with their ones.

chassis is an alluminium 1444 hammond series.
i used 3 t.sol 12ax7 and two t.sol el34b.

my speackers are not a good ones, but with others amp that i do don't sound so bad.

i had to take out brite switch cause it make oscillation and extremely harsh sound.

hum is like an air blow, a constant one.

i know all your videos, is for that sound that i decided to do an express.

[redshark]

Jaxx, I just saw the picture of your build. My experience is not even close to all the guys around here since I had just built one express, but I have to say that when I built it I followed the layout really close. I have no hum, not even playing single coils and very little hiss level which is expected with this amps.
What I could see is that the hum could be coming from the grounds of your pots, I would check them again, I would also check the input jack.
I see some of the wires that go to the preamp tubes are a little bit longer than they should be , that could make it noisy too and seems to me that they don't follow the correct layout so as a starting point I would use a chopstick with the amp on and start moving wires around the preamp tube pins, see if you could decrease the hum at least doing that. Good luck with it!!

[passfan]

I notice you're using the fender style switchcraft jacks. Are they the shorting type ? I just had a problem with a brand new set on a fender deluxe build. The shorting contact arm was weak and I got intermitent crackling and every now and then a high pitched wooshing sound out of them. It got so bad I left the back off so I could tap them with a chopstick to get them to stop just so I could play. I changed them out to cliff jacks. Also, they are metal bodied so if you wire a ground up to them it could create a ground loop. I had a slight hum until I removed the ground and used a star washer in between the jack and the chassis. Good luck.

[geetarpicker]

Sadly I think this is yet another example that if you change the layout from what Ken did it can really bite you. These amps are one of the most finicky ever designed in regards to layout, grounding, parts choice, wire choice, tube choice, etc.

Sadly just following the schematic is only half the battle. Best to stick to Ken's plan on these IMHO, at least if you are building your first. I hope this one can be fixed, but it might take alot and/or never quite sound like it should.

[passfan]

In this pick a cliff jack is used on the input. Cliff jacks are isolated from the chassis and require a seperate ground wire , which the builder installed. The metal switchcraft style jacks are grounded through the frame and do not require a seperate ground. If you refer to the amp layout in the files section you will see the omission of any ground buss connection here using the metal input jacks. Also notice the same ommission on the second output jack as well.
https://tubeamparchive.com/download/file.php?id=11171

[redshark]

I agree with Glen here, schematic is I don't think even half. The appropiate layout basicly provides a safe platform to develop a design that in diferent circumstances could be UNSTABLE and very noisy. I had seen pictures of clones that use cap cans but still they keep the location of the components and matches the layout and that is why I think they can get away with that. Good luck but keeping this layout could be the source of problems besides the things pointed by others here.

[jaxx]

hi at all!

at first i would to thanks all of you for your response.

@redshark:
i noticed what you mean only after building. i think this is true without compromises!!! only now i understand what ken mean..''just a trainwreck suond like a trainwreck''
i hope to fix it.

@geetarpicker:
you have the reason. but only now i noticed that.


i'll do some changes in layout, and i hope to fix all problems.
thank a lot to all of you, and if someone else have other suggestions...tell me!!!


thanks




Eddie

[dartanion]

Layout makes a huge difference, so does lead dress. I have built Wreck style amps with different layouts, but lead dress is not something to ignore, especially if you vary from the original. If you look at photos of original Express amps, and the many well done clones here, you'll see how tidy they are in lead dress. Pay close attention to the photos and clean up the lead dress. I would wager than there is induced hum because of this issue.

Congrats on the build and that it works! Now it's just cleanup time.

[jaxx]

all these modes will be done!!!

thanks a lot




Eddie

[Mont]

I just finished my first express and I was having the same problem. this is what fixed it for me. the earth ground should have it's own ground. the 6.3v center tap I wrapped around the heater wires and then grounded it right next to the first out put tube, V5. you might have to drill a hole. I hope this helps..

[jaxx]

you fixed it with this mod? wow!!!

i tried several and different changes but nothing done..


so i've got to do a star ground only for the heart connection, and place the heather earth next the first output tube.

i'll try it!!!


thankx


this is my heart connections, one star ground only on the chassis.

massa=gnd
terra=earth