I see my title for this video was taken literally by a few. I do have some basic understanding of ground schemes. It generated some excellent comments though! Thanks to all. :D
Unlike most here, I know shit all about electronics at their core. However, being a guitarist for decades now, I find this channel fascinating. Good stuff sir!
I was searching the web to find info about amplifier hum and how to fix it in my first amp build, and what do I find? Yet another great video from Brad that has helped enormously
Really interesting. When modifying amps, you have to be careful that you don’t degrade the frequency response. I use to have a guitar amp that when I plugged in the cable, it picked up the radio. The cable created a tuned circuit.
Some people think ground is magical. It's just a wire like everything else. You put current though it, you get a voltage drop. So, passing the filter cap return though the chassis was a bad idea. Likewise, you may find that the power transformer introduces some hum into the chassis due to stray magnetic fields. So, I'd probably lift the ground at the center tap and run it to the filter cap ground. That way, the power supply is grounded at a point away from the transformer.
I think a lot of thouse people that think its magic generly think that because they dont understand the concept of a relative measurement witch voltage is. and theirs no absolute 0.
Great video and you make a great point. I bet if you twist all the filament wires it would be even better. Grounding is a huge deal when I build my amps.
The other way that the grounding could have been done is to arrange it in what's called the Star-Grounding system, where each ground wire connects to one point only on the chassis, like to a solder tag under one of the power transformer mounting bolts for example, and radiates out from that point like the points of a star.
Agree. Star Grounding is a great way of avoiding hum, which (I think) is a consequence of "ground loops," which in turn result from the fact that even a metal chassis is not perfectly conductive and will exhibit a small, but nevertheless existent resistance between different points. The principal drawback of star grounding is that it is labor intensive and not readily adaptable to mass-produced amps. But for a one-off homebrew or custom job where cost is no object, it works great.
And as a further thought, I think that is what The Guitologist demonstrates here in this great video. By connecting that jumper from the reverb tank chassis to the actual line ground, he is in essence star grounding the tank chassis to the source ground. The difference in hum is dramatic.
There should be only two grounding points in an amp. The safety ground should be connected to the chassis near to the power inlet by a dedicated ground lug. A practical method for grounding the electronics is a multiple star system, where the components in each section of the amp are grounded at a local star at the negative terminal of the filter capacitor which supplies it with current. The local stars are connected by a heavy gauge copper wire ground bus which is connected to the chassis at the input of the amp. The chassis should never be used as a return path for signal currents, its only purpose is to act as a shield from outside interference.
@@cdreid99999 I rarely see any shielding going on inside guitars, either. This stuff isn't that difficult to learn. I figured out the star grounding on my own inside my last guitar via brainstorming why my grounding wasn't working. That worked perfectly and I've been doing it since.
Wow, what timing. Just came across this video and will be working on one. A friend of mine just found one of these at his parents place and is going to be getting it to me so I can go over it. Great info as always. Thanks for another great video.
the builder of that amp didn't think about time ! a steel brad, a plated terminal,a coated chassis +50 years . 1 ohm to open on all ground connections ! fine mecca and replace all grounds with wire ...nice virtual heater ct.. good job !
In my youth I broke the grounding tab off of the plug on a practice amp in order to plug it into a 2 pole cord. I always wondered why it was so noisy after that. Of course this was a much newer model than what you usually mess with. I put it away and all but forgot about all of that until I dug it out and started trying to use it. ended up putting a new cord end on it and it works much better now. I would imagine the same thing might happen in an older home where the ground poles aren't actually wired to anything. After seeing this I am considering adding an additional ground to neutral bridge internally to prevent that in the future.
You should always avoid using the chassis as your ground plane connection, honestly. Rust and other types of deteriorating over time can make these connections go bad and cause these noise issues.
Howdy. One should use a separate wire for grounding as a minus bus. The bus should be connected to the chassis only at the input jack. The connections to the bus should be done in the order the schematics show. The outout jack should be mounted isolated from the chassis using some kind of plastic bushing. The output jack ground should be connected to the bus at the same point as is the last stage cathode. Regards.
The magic of propper grounding, nice video!!....: it´s all about the return current....if you provide a low impedance return path, it´ll be almost dead quiet. But a chassis is *not* a propper return path! Here´s why: the chassis is made out of a aluminium-nickel-steel something (it doesn´t really matter what is it really made of) which has a much higher resistance than copper for example...therefore two major things gonna happen: A - When a current flow through the chassis as it´s used as the return path, it´ll shift its level and "generates" a little voltage across itself. and this voltage is present on all return paths. Even for those which doesn´t carry any current. So lets assume this voltage would be around half a milli volt (a really common voltage) this will be present at the input (first input stage and the input jack) and therefore this voltage will be amplified. B - If the main power supply ground is put on the chassis alone a nice "high impedance" ground loop is built between all the stages and the input/outpt jacks as well. The reason for that is because of its rather high resistance when compared to copper. And because to the remaining ripple on top of the plate voltage the return path also carries this ripple. and as it´s directly and *only* connected to the chassis this ripple noise is also present in every stage of the amp. This is called "hum" and this is what you´re hearing in this video. The reverb tank needs a low impedance ground connection as well, or it´ll hum like crazy...just like you showed here. The best thing you can do is: use a thick solid copper wire and route this to everything that needs to be grounded just *once*. Disconnect (= cut) every wire to the chassis when connected to that copper wire. Only two essential connections to the chassis should be done: the main filter cap(s) ground should be connected to the chassis and the earth wire from the mains plug. If you want to do it about best: don´t solder, instead use screws and clamp it, as a solder joint has about 10 times the impedance than a screwed down solid wire. and please don´t mix these techniques....use soldering thoughout or clamping...not both, as they´re not of equal impedance.
Excellent comment. Thanks for all the helpful tips! I've read a lot of essays on this subject on various sites and in books, but your comment does a good job condensing it down. Ground issues are something I face a lot in these older amps and because so few of them are high gain, bad ground schemes rarely rise to the level they did in this video where something obviously needs doing, but where silence at idle is a must, a total revamp of ground schemes is necessary.
So if the only grounds connected to the chassis are the mains earth wire and the B+ filter caps, where should everything else be grounded? i.e. power tube cathode(s), speaker jack, PT center tap, etc. as shown in Hoffman's grounding scheme: el34world.com/charts/grounds.htm
@@TheGuitologist I have a frontman15 from fender. Even on the clean channel it's noisy with no guitar plugged into it. I opened up the back to have a look around everything looks normal. I have no background in this field please help
I would bet you that half of that hum is being caused by the fluorescent lamp lighting up and directly over the insides of your amp!! It's OK to use such a lamp for a bench light but at some point you gotta turn the lamp off just to check that it is not inducing hum that you'd otherwise chase after, thinking it was from the inside of the amp. Older dimmers, on your circuit or even another part of your house wiring, can also induce hum and noise. The same can be said about the reverb can turned open side up. VERY sensitive to mag fields. You are right fiddling with the reverb driver and recovery wires. If they have been replaced with your typical RCA-RCA hi-fi cables, it's not necessarily the best. Sometimes the return cable does NOT want a ground at the tank end, sometimes it does. This can produce a ground loop. 98% of tube amps will benefit from a synthetic center tap on the heaters. The syn CT is actually a superior method than a real CT from the power transformer, because there are rare conditions where a heater-to-cathode short in one of the output tubes (again, pretty rare but not impossible) can burn out the heater winding. With the syn CT, one or the other or both resistors will blow up, which is much cheaper than a new power tranny. But the thing I would say is that if a tube amp needs a CT on the heaters, not having one will produce 20 times as much hum as you have. It would be intolerable, screaming loud. So...adding the syn CT should not reduce the hum all that much because if it needed a CT, the hum would be brontosaurus-grade. Heater wiring....ehhh. Doesn't make much difference. Seen it done plenty of different ways. No need to knock yourself out re-doing it.
Wow ! No way. Id never seen another one of these. My friend back in high schools dad gave him one of these. I hadnt seen one since. That was about 23 years ago LOL!. Cool video as always and thanks for all that you do and continue to do. :-)
Oh and by the way, wow. That amp quieted down big time with what you did. Whenever I watch your videos and a few other peoples, i take notes on some of these tricks and discoveries you guys find. That way if i run into something like this I have a few ideas to try and usually it ends up being one of these types of things that help me figure it out. Greatly appreciated. :-) Rock on !
Has anyone heard from Uncle Doug? I have missed him. He has some great tips for hum problems (aka death capacitor). Hope he's okay. Good catch on the reverb tank. Liked and subbed.
Someone said he is responding to comments on his channel still, so he's around. Maybe Texas has been dry of tube goodies of late. Thanks for subbing, love the username! \m/
I really like these types of grounding repair videos much more because they are are to reduce the S/N ratio down to not hear any buzzing noises, RF interferences, lights interferences, magnetic fields, cell phone interferences, etc. I read in a guitar magazine of Eric Johnson recording his album at A&M studios in hollywood because he made every one remove the Fax machine, coffee machine, soda machine, etc because he would hear all types of noises and interferences coming up through the grounds which is a S/N ratio. If you put your Oscilloscope and measure the noise floor or better use a Spectrum Analyzer which I hope you get soon on your bench to measure amplifiers S/N ratio and noise floor dbm and dBa levels. Grounding Schemes are very interesting to me because you can measure the "leakage current" on the green earth ground of how much leakage current the amplifier is leaking into the earth ground which is considered BAD.
Filament wires don’t have to be twisted. As long as they are cable-tied together and remain tight together, this will yield the same result as twisting.
I've never done an actual experiment myself to A/B all the various claims with regard to filament wires. Maybe this will be the subject of a future video.
Great video. I read the comments, and don't have much to add, except, I wonder if you intentionally raise subjects so as to read what people will respond to in the comments! You might as well have some entertainment for yourself! I learn from every one of your videos! Thankz
Your hum is front end cathode earthing, move the cathode earth lead around and find a null spot. It`s done. Reverb Hum ! Something probably the same problem on the reverb recovery side. Move earth points around.
Lots to learn in these videos! There are some ugly solder joints coming off that transformer! Red ground wire, slight difference. With wire to reverb tank, huge diff! Even with that what else can be done to clean things up? That 60 HZ hum drives me nuts, no matter how slight it is.
My champ developed a hum and I changed the main filter caps and noise went away and it got real clean. THat was cool but then my Musicman RD50 got t hum after touching to of the tube sockets leads with a screw driver. THe amp guy said he would change "7" filter caps for a buck and a half and I can't feel that right now and will try it myself. Fingers crossed. Yup hear the noise. I fixed a bunch of old tube noisy/humming amps by changing the filter caps and "SWEET" clean sounds came out.
@ Russel Hltn. Yes you are right! The Guitologist you building more ground loops into the amp with those wires, some of them might cancel out the hum, but you really need to redo the whole grounding scheme..
You are right, but this repair was really about the reverb. I didn't bother to film all the work done on that. It involved tedious unwrapping of the reverb transformer to find broken leads and re-solder the terminals, among other things. It was only after fixing the reverb that I noticed how noisy everything really was, particularly the reverb when on. The easy fix was a ground wire from the tank housing to the CT. Ideally, these late 60s Gibsons need total rethink of the entire ground scheme, I agree. The problem is, the reverb return ground is to the chassis through an RCA jack, so that would need to either be hard-wired or isolated somehow from chassis.
I didn't see how the reverb is connected. It might be the hum is due to a ground loop between the two audio leads. Either way, there's two tactics I've seen to deal with hum. The first is to do grounding right. However, with 3rd pin power ground, it's not always possible to avoid ground loop. Especially when you start connecting different pieces of equipment together. So the other way is to run massive grounding straps to minimize the voltage drop due to the current.
The reverb return comes in at the far left side of the chassis, near the inputs. That's where the return is grounded to the chassis with an RCA jack. It's not well thought out at all. It needed to be isolated from chassis and a wire run for grounding.
Thanks, I have a Gibson GA17RVT that does the same thing when you put on the reverb on. Are you planning to permanently run a ground wire from the reverb tank to the chassis?
Have the exact same problem with the exact same noise on a Gibson Falcon amp I just recapped. Will try a wire from the reverb tank to different ground points and see how it goes.
Try placing the artificial center tap to the cathode of the power tubes. Separating the pre and power sections and giving each their own ground helps too. Maybe adding a larger value grid resistor on the reverb in tube. 1meg might seem like a bit too much but the output signal is mixed with a wet signal and the high frequencies are still there Good luck!
So, I don't know how far back you read the comments on these things but a question for you... How did you know to check the reverb tank grounding for the noise on that amp? Did you re-rout the ground? Is it common to the Gibson amps or is it a common problem generally? Okay, so that was 3 questions. Reason I ask--I've got a noisy (I think) Fender SFDR and it has chassis grounds all over the place. And the brass bus bar under all the pots has certainly seen better days.
Thanks for making these videos about amps. I'd would like to send you an english tube amp I got with tremolo and reverb. The tremolo do not work. When I turn it on, it kind of works, but the speaker throbs in an out with the speed of the tremolo and sort of cancels the sound out. I like your thoroughness, but I am on the other side of the planet.. Anyway, I'll keep on enyoing your uploads.
I have one of those amps, & I've noticed that the reverb is slightly noisy, although not quite as bad as yours. I think the reverb on those sounds a lot more shrill & intense than a typical fender amp, otherwise, i've got absolutely no complaints about it tonewise. I wouldn't mind finding some way to actually improve the reverb tone, rather than having to use a reverb pedal. I guess in that way, it is what it is.
Man I hate havin to tear down my windsor studio again. But when it warms up its got the hum. I guess ill have to check the chassis grounds lug. The standby switch seems to not work too. It all started when I retubed from amplified parts. I kt88 in and let it sit for 20 minutes then turned off standby. For 5 minutes it played fine then the hum started . the volume would compress. Go soft then louder. And the standby switch quit to off. Now everytime I turn it on theres that hum. The hum is the same no matter what. Volume no volume unplugged and plugged in cord. Returns no difference. Man and I thought it was a studio amp?
I've always avoided Gibson amps (actually my first amp I got in 1969 was a Gibson though) even though I like the looks and sound of some of them because I've always heard that they didn't stick to the scats and instead used whatever components they had on-hand even if they weren't the exact values the scats called for and that sort of thing, and it seems to be true judging by all the YT repair videos of them. It seems like no two of them are alike. For the record, I think the newer GA-40RVT is the most beautiful amp ever made, and I love that it has a handle on both sides. All larger amps should do that.
I have the Epiphone Maxima ea 600 rvt with power issues it blows fuse when powered on im pretty sure it's as blown rectifier Diode a Motorola mr1033b diode that's hard to find it has a separate part number of IN3253. It is a 750mA lout and 200volt vrrm. It has other reverb and weak signal output issues. I would love to get you opinion on where to start on repairing it. I know the skills to have to work on electronics. Can you shoot me a reply brother on what you would do first to troubleshoot it. It's a beautiful amp. Also i have the Schematic for it as well.
I even unplugged my Reverb tank & the hum is still there, nothing changed. trioed HumX in the wall outlet, unplugged all effects, hooked up Noise gate in the effects loop............... noise gate is able to roll down the noise but doing that also chokes out my guitar signal. So the noise gate isnt my solution. any ideas? the same guitar is quiet on a different amp so I dont think its the guitar.
Hi brad , I just bought a crapy Princeton 65. solid state. I fix a broken connector at the reverb tank. i was noticing how much noisier that is with the reverb on. If I run a ground wire from the tank to the chassis would that help.? that would be to easy huh?
I have problem with one small 10W amp, suddenly overdrive channel started to (literally) farts on each string pick, totally unusable, while clean channel is ok...btw there is only 1 switch for overdrive on/off, no any pots at all..What might be problem here?
What would be a list of recommended things to do when wiring a ground circuit in an amp as well as no-no's? I'm having noise problems on a tweed deluxe clone that I bought new, developed a noise which turned out to be from a bad ground and the useless idiot to whom I took it to did a terrible job of fixing that. After tinkering a bit the amp has lowered substantially on it's noise level but it's still noisier than it was when new.
Wow! I have a 1965 Gibson Explorer amp and it's the same amp as far as I know.. not a lot of stuff about them.. been cool if you'd have played it some so I could compare it to mine.. certainly shrill.. been debating on if I should modify it or what. plus the reverb doesn't produce reverb.. instead just makes this crappy distortion the more you turn it up! Anyhow, cool videos.. cool I'm not far from there in Seymour Indiana.. I just hit subscribe! keep em comin'!
Great video.I have a Fender UL 135 watt with the same noise.Brand new filter caps and power tubes biased to 33 ma.I was measuring pin 3 on the power tube socket and the probe slipped and shorted to pin 2 and blew the fuse ,now theres noise with the master volume turned up.Any thoughts.
My Fender Supersonic 22 makes a loud pop when switching from the clean to the gain channel. It seems to be a common problem with this amp. Any ideas on what's causing the pop and how it might be fixed?
Hi Brad how are you doing? I have a problem like that with a marshall VS100R. Im in europe and Im getting the same hum as the power transformer on all the channels, all the time no matter of the volume, even with no cable plugged in. Where would you start looking? Thanks man, I appreciate your help
No. Ironically, the better the connection, the more it will hum in this case because of the places on the chassis where the various things were grounded, it was setting up some pronounced ground loops.
Did the noise decrease when lowering volume? I have a Marshall amp that has a 50hz hum even in standby, yet to find the cause, noise is coming from the speaker. Amp is Silver Jubilee 2550, I have also a 2554 (combo version) and it's dead silent
Yes and no. Sometimes a 3-prong affixed to an amp that originally had a 3-prong can hum WORSE if a ground loop was inadvertently set up in doing so, or if polarity was reverse from what it should have been.
As there is AC on the filament wires, the currents in each wire at any time are moving in opposite directions. By keeping them in close proximity, the electromagnetic fields around each should, in theory, cancel, leaving no net 60 Hz field around the pair. As Electrofrying D points out above, you can get the same effect by keeping them parallel and close together. Twisting them, however, kind of ensures that this is the case, regardless of your best intentions, and is a technique that goes back the better part of a century. If nothing else, it looks cool and results in what many consider a neater installation.
More like its noizy tube in preamp.. This heappends when tube lovers dont want to buy new production tubes and old one brakes hum from glow wire to main B+, and then hummmmmmbzzźzzzzzz..
With all due respect...it can only be one or the other. It can be an Epiphone EA-32RVT Comet or a Gibson GA-32RVT Lancer....but it can't be Gibson Epiphone EA-32RVT Comet.....No more than your Volkswagen Touareg is a Porsche Cayenne. Platform sharing buy Epiphone does not a Gibson make...just saying
Maybe because solid state amps break less? I had a tube amp that basically needed repairs on a yearly basis, but have had solid state amps I've never opened in a decade or more.
Trust me, that is certainly not true of all solid state amps. I have had two Marshals now that have both exhibited problems. My Son's Marshall is sitting here right now being a bitch.
I got some issues here: original problem was bad rectifier tube and fuse. Replaced All tubes and fuse, not its has this crazy sound. Could you give me advise? Here is video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-eHGmKMvTxB4.html
Sounds like it's going into a motorboating oscillation. Sometimes that can happen if a preamp tube stage loses its bias or it could be in the power supply. Check solder on the board. If that's a modern Vox, I wouldn't trust the soldering on that board as far as I could throw it.
it looks as though there Are a lot of people in here watching your videos that knows what there talking about.i think my grandson knows more. about electronics than I do and he's in kindergarten so don't take any advice from me other than ask someone else 😁
The Guitologist I love to joke around in the comment section at times.but when it comes to the technical stuff I'm watching and taking in as much as my prayers brain can absorb.
