Fault-finding hum(s) on a Liverpool - Distress call

[plook]

I made a Liverpool clone a year ago and ran into problems with assorted hums. I used RJ Heyboer and Edcore transformers and these are the hums:

1. Turn power on, and the MT hums. Probably an acceptable level but louder than any amp i have ever built. i will disconnect the secondaries today to see what it is like.

2. Turn standby on and there is classic ground loop or filament style hum

3. Hiss, crackle, fizzle, frying bacon. This one is new and only noticed last night after turning it on for the first time since about last June when i lost all hope and just abandoned it. I'll change all tubes to see if it goes.

Last night i pulled V1 and the hum (apart from MT hum) goes, so this does isolate or narrow it down, but where is it?

Is there a a thread on fault-finding Liverpool hum on here anywhere or some guide notes. many must have been here before. I'm really at my wits end with this, i've made many amps over the years and non have beat me up like this one. i spent 4 hours last night going through everything and i'm close to driving over it with my Land Rover.

Help meeeeeeeeeeee

[Gibsonman63]

It sounds like you have narrowed it down. Pics would help.

On the shielded wire from the input jack V1 are you just grounding one end?

Have you tried different tubes in V1 to see if there is a difference?

Does the hum happen with and without a guitar plugged in? Is it the same if it does?

Did you use a shorting jack for the input? If not, you get the same noise as you would plugging a cable into the amp and not into a guitar when there is nothing plugged into the amp.

[plook]

It sounds like you have narrowed it down. Pics would help.

I'LL POST SOME PICS IN A LITTLE WHILE.

It sounds like you have narrowed it down. Pics would help.

COMING UP

On the shielded wire from the input jack V1 are you just grounding one end?

YES, BUT I MAY REWIRE THE WHOLE OF V1

Have you tried different tubes in V1 to see if there is a difference?

YES, TRIED A FEW, EVEN 12AU7 FOR LESS GAIN, BUT STILL THERE, JUST A TAD LOWER.

Does the hum happen with and without a guitar plugged in? Is it the same if it does?

IT'S WITH THE GUITAR PLUGGED IN. WITHOUT THE GUITAR PLUGGED IN THERE IS THE MT HUM AND THE SIZZLING BACON 'HUM' (MIGHT BE A CAP OR RESISTOR BUT I CAN LOOK AT THAT LATER), BUT WHEN THE GUITAR JACK IS IN THE HUM IS HORRIFIC.

Did you use a shorting jack for the input? If not, you get the same noise as you would plugging a cable into the amp and not into a guitar when there is nothing plugged into the amp.

YES, SHORTING SWITCHCRAFT USED. HUM IS WORSE WHEN JACK CONNECTED TO BOTH AMP AND GUITAR, SLIGHTLY BETTER WHEN PULLED FROM GUITAR AND WHEN BOTH JACKS PULLED YOU JUST HAVE MT HUM AND THE COOKING BREAKFAST 'HUM'

SORRY FOR CAPS, I'M NOT SHOUTING, JUST MAKING IT CLEAR WHO IS WHO BETWEEN YOUR SENTENCES.

PICS COMING UP.

[plook]

Here are the pictures. Happy to take other closer pictures of any area if they will help.

[Gibsonman63]

Plook, it is strange that the hum is louder when you plug in your guitar. Have you tried different guitars? Humbuckers should have much less hum. Maybe try a different guitar cable.

Also, environmental noise can be a bugger. I have a florescent light on my bench. If I forget to turn it off when I fire up an open chassis, it is hum city. Make sure that all sources of noise (Florescent lights, CRT computer monitors, neon lights, dimmers, etc...) are eliminated and try putting the chassis cover on for the shielding.

[plook]

Yes, originally i was testing with a Tele, then i tried a 335 with same results, actually that had howling feedback issues too.

One thing i have noticed is that the amp, wires, chassis, guitar cable (tried another one of them too) is all really microphonic, like an EF86 valve.

Yes, i do hae a tube light in my workshop but i turned that off and sheilded the amp, but same problem.

I re-wired the whole of V1 and i have the same results. I'm really at a loss as to what it could be.

[geetarpicker]

There is no way you should need all that shielded cable! It may actually make things worse. Also you have some oddities in the circuit over near the presence control, your lead dress is not standard plus I see an extra ground terminal over near the phase inverter. Also a ground plate over the bottom is critical for full stability and noise reductionl, but it should play fine at lower volumes without it.

That said, to much deviation from the original KF spec can bite you with these.

Is your guitar cord connected to a guitar with the guitar turned all the way OFF? Does it still hum badly with the guitar connected, amp turned up, but with the guitar turned OFF?

Keep in mind these amps have as much gain when on 1/3-1/2 as a fully dimed lead spec 4 input Marshall 50 or 100. Another comparison would be comprable gain to a cranked Fender WITH a cranked Tube Screamer stuck on all the time... Playing a single coil tele will require standing in the room at just the right angle as to minimize ambient hum pickup from the AC wiring of the house. Humbuckers should not be nearly as hard to control, but a 335 might howl simply because the gain is so high. You might need to get some distance between the guitar and the cab to minimize acoustic feedback. Personally I find that potted pickups to be a must with these if you want to crank them much.

[Tillydog]

I'm really at a loss as to what it could be.

There's quite a few solder joints that look like they could do with re-making (mainly looking at the lower row of eyelets in the photos). Likely to be the cause of your crackling, and maybe more.

Andy

Add:

Check your grounding scheme carefully. You might be better grounding V1 cathode resistor (the green wire) to the lug on the input jack, rather than your "ground bus". Have you got photos that cover the PSU end of the chassis, too?

Definitely go over your solder joints carefully with a magnifying glass and re-make any that aren't perfect. If the project has been standing awhile, you might need to get hold of a fiberglass pencil brush to clean the oxidation off the joints before they will take solder properly.

[plook]

I'm really at a loss as to what it could be.

There's quite a few solder joints that look like they could do with re-making (mainly looking at the lower row of eyelets in the photos). Likely to be the cause of your crackling, and maybe more.

Andy

Thanks, i will investigate those joints and re-solder them. Which ones specifically are you referring to?

[plook]

There is no way you should need all that shielded cable! It may actually make things worse. Also you have some oddities in the circuit over near the presence control, your lead dress is not standard plus I see an extra ground terminal over near the phase inverter. Also a ground plate over the bottom is critical for full stability and noise reductionl, but it should play fine at lower volumes without it.

That said, to much deviation from the original KF spec can bite you with these.

Is your guitar cord connected to a guitar with the guitar turned all the way OFF? An open cord will definately hum on these as the gain is very high.

Keep in mind these amps have as much gain when on 1/3-1/2 as a fully dimed lead spec 4 input Marshall 50 or 100. Playing a single coil tele will require standing in the room at just the right angle as to minimize ambient hum pickup from the AC wiring of the house. Humbuckers should not be nearly as bad, but a 335 might howl simply because the gain is so high. You might need to get some distance between the guitar and the cab to minimize acoustic feedback.

All those shielded cables went in one by one as replacements as i was desperately trying to solve the problem.

The ground under the Presence was added yesterday following some advice.

Not sure what the ground plate is, but excuse my ignorance here.

Guitar chord swapped over with same results.

Thanks for the advice on the distance from amp. My workshop is quite small and cramped and i'd say all testing has been within 3 feet.

Can you recommend a layout or pictures to use to try and bring it closer to what it should be. i used a mixture of C@riatone and Ron Worley layouts to do this one.

Appreciate your advice.

[geetarpicker]

The "ground plate" is simply a piece of sheet metal that would be placed over the bottom of the chassis to seal it up. In a stock original Trainwreck there is a full bottom plate scewed on so it's all fully grounded and shielded from the environment. Fenders and Marshalls are the same way but the plate is stapled inside the cab. That said, it should be stable at lower settings without the plate but it's a critical piece to fully get the amp to work well at all volume settings.

I'm pretty sure there are some pics of an original TW (to follow for lead dress) in the files section.

Does the amp hum badly turned up a bit with the guitar plugged in and with the guitar volume knob OFF?

[John_P_WI]

In the last pic, push the yellow heater wire up off of the grid wire.

[plook]

In the last pic, push the yellow heater wire up off of the grid wire.

Ok, will do.

[plook]

The "ground plate" is simply a piece of sheet metal that would be placed over the bottom of the chassis to seal it up. In a stock original Trainwreck there is a full bottom plate scewed on so it's all fully grounded and shielded from the environment. Fenders and Marshalls are the same way but the plate is stapled inside the cab. That said, it should be stable at lower settings without the plate but it's a critical piece to fully get the amp to work well at all volume settings.

I'm pretty sure there are some pics of an original TW (to follow for lead dress) in the files section.

Does the amp hum badly turned up a bit with the guitar plugged in and with the guitar volume knob OFF?

Thanks for the ground plate info. Might come back to that. Will look for pictures in resources for lead dress examples.

I just plugged in and turned the volume pot on the guitar down and all the terrible hum goes (the sizzle is still there but i think that's another issue). if i turn the volume up on the amp the hum starts to come back in around 2pm.

[geetarpicker]

On some builds the ground plate is 100% essential!


Are you saying that IF you keep the guitar turned down the hum is gone?

You say the hum comes back if you raise the amp volume to around 2pm, but is that with the guitar still OFF or ON?