Weber 5F6A Noise

[bluesky636]

I recently completed a build of the Weber 5F6A. The build went great, with only a couple of problems, and the amp sounds Fantastic. Hiss levels are just slightly greater than the hiss from my Fender Blues Deluxe Reissue and hum is almost nonexistant. I have documented the entire build here:

http://www.fender.com/community/forums/ ... f786f167cf

I do have one bug that is bothering me.

I am getting a scratchy sound while the amp is sitting idle with everything plugged in but not being played. It is sort of a crackling/scratchy sound that is distinct from the normal background hiss. It also appears to get slightly worse as time goes on. You can't hear the noise while actually playing, though.

I do know that the Presence circuit design allows a DC path to ground through the pot which causes a scratchy noise when the Presence pot is turned. The idle noise sounds just like that. I have the parts on order to convert the old Presence pot circuit to that of the 59 Reissue Presence circuit which blocks the DC path to ground. You can see the difference in the two schematics.

https://taweber.powweb.com/store/5f6a_schem.jpg

http://ampwares.com/schematics/59_bassman_manual.pdf

I am thinking that this noise is also a DC noise (Maybe caused by power supply ripple?) and if changing the Presence circuit doesn't cure it, I'll check the coupling and bypass caps for any DC where it shouldn't be. Oh, and before anyone asks, I did swap each preamp tube with a second set of tubes with no difference. I don't have a spare set of power tubes (except those in my BDRI).

Does anyone have any other suggestions as to what the cause of the noise might be and how to troubleshoot it? Thanks.

[statorvane]

I have built a 5F6-A and several other pups-pull amps w/NFB, and I don't think your sound has anything to do with DC voltage on the NFB / presence circuit. I have had the identical symptoms you describe that were caused by bad solder joints. As the amp warmed up the noise got worse. IIRC the last time was particularly nasty and hard to track down. By chopsticking I was able to find a loose connection on a preamp tube.

[martin manning]

Looks like you've received some good advice here and at the other forum. Re there being a poor connection somewhere, this includes tube pin-socket connections, so you might try gently wiggling the tubes to see if there is any change. You also have four input jacks with grounding contacts that might not be up to par. Does it matter which input you're plugged into? A noisy resistor or bad coupling cap is a posibility too. You might isolate the problem by first unplugging the guitar and then the preamp tubes one at a time beginning with V1. When the noise stops, you'll know which area it's coming from. I can't see the presence pot causing this when you're not touching it, unless the pot is bad.

Sorry to say I really don't like the idea of attaching the cap board and the doghouse to the chassis with "velcro"... lots of vibration, and high voltage there. Painful as it might be, I'd fix that.

[tubeswell]

Maybe a loose connection (like Martin suggests) or another possibility is DC leakage somewhere like a bad pot (like a presence pot) if (say) solder or flux got into the pot (in which case change the pot). Or excessive solder flux between eyelets on the board (in which case, try scrapping it away)

[Structo]

I've had bad preamp tubes sound like that.

Try substituting one known good tube one at a time and listen.

[NickC]

I've had crackling/scratchy noise attributable to poor lead dress. I chop-sticked the wires, found the offending culprits and moved them. A few millimeters here-and-there can make a world of difference.

[bluesky636]

OK. I tapped every single component, solder joint, tube, wire, etc. that I could get to without taking the amp apart. Here is what I found:

The only point in the amp that reacted to my tapping were the input jacks. Particularly, it seems, the Bright input.

[img:356:430]http://inlinethumb30.webshots.com/43165/2482425990090987409S600x600Q85.jpg[/img]

[img:357:600]http://inlinethumb07.webshots.com/46534/2416063810090987409S600x600Q85.jpg[/img]

Side note: I just noticed that the schematic and the wiring diagram differ as far as which set of input jacks the 1M resistor is wired to. I wired mine per the schematic which appears to be correct as far as which jack is high level and which is the low level input.

Anyway, I found that tapping lightly on the tip terminal of both normal inputs did not result in any significant noise. However, tapping lightly on the tip terminal of the Bright input jacks, and in particular, the High level input, would result in a loud, crackling noise. Pushing on the tip terminal to cause it to break contact with the switch contact caused the same noise. Also, tapping on the 1M resistor on the high level Bright input would cause the same noise. It was interesting to note that once the noise started, tapping on the tip terminal of the high level Normal input would cause the noise to occur with that input. Tapping the Bright jack tip terminal or 1 M resistor would cause the noise to stop.

So, it would appear that I MIGHT have a bad 1M resistor on the Bright input, or the tip and switch terminals are not making good contact. I can squeeze the terminals together more tightly (easy to do) or change the 1M resistor. So before I do either (after dinner) which seems to be the most likely cause of the noise? I should note that the amp has been on for almost 2 hours and is making a very slight crackling noise which gets worse if I tap on the Bright input tip terminal.

I'll be back after dinner.

[bluesky636]

Guys, I have done everything suggested (documented in my build thread) except the "tap" test.

OK. I tapped every single component, solder joint, tube, wire, etc. that I could get to without taking the amp apart. Here is what I found:

The only point in the amp that reacted to my tapping were the input jacks. Particularly, it seems, the Bright input.

[img:356:430]http://inlinethumb30.webshots.com/43165/2482425990090987409S600x600Q85.jpg[/img]

[img:357:600]http://inlinethumb07.webshots.com/46534/2416063810090987409S600x600Q85.jpg[/img]

Side note: I just noticed that the schematic and the wiring diagram differ as far as which set of input jacks the 1M resistor is wired to. I wired mine per the schematic which appears to be correct as far as which jack is high level and which is the low level input.

Anyway, I found that tapping lightly on the tip terminal of both normal inputs did not result in any significant noise. However, tapping lightly on the tip terminal of the Bright input jacks, and in particular, the High level input, would result in a loud, crackling noise. Pushing on the tip terminal to cause it to break contact with the switch contact caused the same noise. Also, tapping on the 1M resistor on the high level Bright input would cause the same noise. It was interesting to note that once the noise started, tapping on the tip terminal of the high level Normal input would cause the noise to occur with that input. Tapping the Bright jack tip terminal or 1 M resistor would cause the noise to stop.

So, it would appear that I MIGHT have a bad 1M resistor on the Bright input, or the tip and switch terminals are not making good contact. I can squeeze the terminals together more tightly (easy to do) or change the 1M resistor. So before I do either (after dinner) which seems to be the most likely cause of the noise? I should note that the acrackling noise which gets worse if I tap on the Bright input tip terminalmp has been on for almost 2 hours and is making a very slight .

I'll be back after dinner.

[martin manning]

Tip and switch terminals not making good contact is not too uncommon... bend them a bit to tighten them up and/or clean them by drawing a piece of paper soaked in contact cleaner through (Jelle's trick).

[bluesky636]

Tip and switch terminals not making good contact is not too uncommon... bend them a bit to tighten them up and/or clean them by drawing a piece of paper soaked in contact cleaner through (Jelle's trick).

I'm going to do that. I am all out of contact cleaner right now and have more on order. I'm also going to reflow the solder on the resistors and wires on all the jacks.

[bluesky636]

Ok. I have reflowed the solder on all of the connections of all four input jacks. I have also tried to tighten the contact between the tip and switch terminals of all four jacks. I also redressd a couple of wires to get get them away from the soldered eyelets.

The amp has been sitting idling for about 2 hours now. There is still a very slight crackle/scratchy noise riding on the background hiss, but both the crackle and the hiss seem to be reduced and the crackle is not occurring with as great a frequency as it was before. I'm not sure what else I can do inside the amp to improve things or if I should just declare victory and live with the slight noise. The parts for the presence pot mod arrive next Tuesday and I will install them next weekend. I'll see if that has any impact on the noise and take a look around inside the amp again. I'm also going to plug the amp into a different outlet to see if possibly my power conditioner is causing the noise.

Any other suggestions?

[bluesky636]

Plugging directly into the wall outlet insead of my power conditioner made no difference.

[Cliff Schecht]

I just finished up a 5F6A build recently and have been using it a lot at band practice. It's one of the quietest amps I've built, even dimed. I used the stock 0.1uF coupling caps so it does fart out when distorting the power amp but I run it clean with a 12AY7 in V1 anyways. With that said, I do get a hiss with the occasional light popping like what you describe. It's nowhere near enough to be bothersome, in a room that's anything other than dead silent you have to put your ear up to the speaker to hear it, but it's there.

To be honest, most of my old Fender builds do this. My Express does it, my Rocket does it when dimed. Maybe I've just gotten used to this sound. Once you kill all of the hum in a high gain tube circuit there is still an appreciably high noise floor usually. This is sort of the nature of the beast, we are relying on electrons blasting around in a vacuum sealed glass envelope at light speeds. Sometimes electrons bump into other electrons and make it to the plate when they aren't supposed to. I haven't studied the exact mechanism in depth enough to give a fully informed answer but like I said, it's to be expected when using such an archaic way of amplifying a signal.

In an amp like the 5F6A that has quite a bit of gain on tap, more than needed to reproduce a clean output wave, and so the noise floor in the first stage becomes especially critical. I usually will roll a few tubes to find the lowest noise one in a higher gain amp. In an amp like the tweed Bassman the choice is easy, a 5-star GE 6072A (black plate) is about as good as it gets noise-wise IME with this circuit.

[statorvane]

Okay, I remember something else. I had a situation a few years ago where I was getting some weird effects that I thought were in the amplifier, and eventually found the culprit was my new, $25 Hosa cable. A real piece of junk - it was microphonic! Have you tried a different cable?

I'll never buy Hosa products again. Pure junk.

Also, I'm not sure what jacks are included in the Weber kits, but I recall when I was building my clone there was a good bit of grumbling about the jacks that were included with the kit. Virtually every forum post suggested upgrading to Switchcraft jacks. I isolated the jacks from the chassis. If you've wired it up, and you have a wire from switch ground to a grounding point, you may want to try isolating yours too. I used black electrical tape around the chassis where the inputs jacks are.

[johnnyreece]

Weber says they're shipping with Neutrik jacks now. Doesn't guarantee quality, but it gives a much better shot than what they used to have.