5E3 clone build has low level hum

[mazzbob]

I am pretty sure it is a grounding issue at this point. I just haven't found where it is. The sound is surely is a 60hz hum. I have used a a good ground where I did a continuity check and then grounded all the accessible grounds as pots jacks board grounds among others which resulted in no changes at all. So I have to keep looking where that ground fault is. It may be a solder joint under the board as well, actually anywhere. I must have missed something somewhere but I haven't found it yet.

[Cliff Schecht]

Isolating the input jack makes a HUGE difference on some amps, others it makes worse. Really the name of the game is knowing where your return currents are going to flow and controlling them properly. High current return paths carry a lot of hash that, if not connected directly to the decoupling capacitors ground, can easily get introduced into other parts of the circuit. Physical separation is the best way to prevent circuits from crosstalking and amplifying unwanted noise, but this isn't always possible. Strategically moving one ground can make a world of difference.

There are different methods for grounding an amp and obviously more than one scheme can work and perform nearly identical to other schemes. Some people have their preferences for one reason or another but you have to look at the circuit and see where possible interactions occur. I like chassis grounding but this can become a problem in steel chassis where there are higher return currents. Aluminum is usually a better performer but isn't always what one has available.

[orrong65]

I'm probably covering old ground (ha ha) here, but I spend a lot of time getting vintage amps quiet so they can record. I have worked on a lot of small amps like 5b3s and champs, many of which have BIG noise issues.

I agree with the earlier posters that these smaller amps tend to be "noisier" because they use the chassis for the circuit connection for several different elements: for the heater circuit, for the speaker-OT circuit, and for the pre-amp/power amp. And these can interfere with each other. Remember that Fender built these amps to a price, so they didnt put in all the best circuitry.

I start on the noise reduction process by adding a second heater wire all the way from V1 back to the pilot light, lifting the each tube's heater earth from the chassis. This makes the heater circuit a discrete circuit just like in Princetons and larger amps. Making sure all the tubes are phased the same, and twist the two heater wires together all the way. Without a heater OT center tap to earth, you should add two 100ohm resistors off the pilot light to earth. This should result in a noticeable reduction in hum - it works very well on VibroChamps.

If that doesnt reduce noise enough, lift the speaker connection from the chassis and directly wire it back to the OT, without earthing it. Like the heater circuit, make this a discrete circuit that does not use the chassis.

If you still have unacceptable noise - from here on I usually start to test individual components - starting with the power resistors, then the plate resistors etc.

[mazzbob]

I want to thank you all for your help and knowledge. I will be working on the ground issue and looking at all the ground connections. Probably will install a buss. If I still have an issue I will then isolate the jacks as this was a problem I had to deal with before on the other build. I know I'll find the problem I just will go one item at a time. It will show up. I have to take some pics of the unit and post them.

[mazzbob]

I did some checking with the amp last night and found that the volume pots are not working as they should. At less than 1/4 of a turn the amp seems to be at almost full power there is really no loudness tapering at all. At less than 1/2 way it is at full power. I'm going to have to look and see if I made some errors in the pot connections ( but I don't think so). I may have installed the wrong type pots because I didn't double check them.

I'll probably install different pots and make sure they are analog. I may also at that time I'll probably isolate the input jacks as well as add a ground buss that is separate than all the other grounds and utilize that if necessary.

Thanks tubeswell that is a great article on grounding it gave me lots of ideas on my next build.

I would like to THANK everyone on their thoughts and knowledge. I will post some pics as soon as I can and let you all know how things work out.

[alanp]

I did some checking with the amp last night and found that the volume pots are not working as they should. At less than 1/4 of a turn the amp seems to be at almost full power there is really no loudness tapering at all. At less than 1/2 way it is at full power. I'm going to have to look and see if I made some errors in the pot connections ( but I don't think so). I may have installed the wrong type pots because I didn't double check them.

The volume on my 5e3 does the same thing, twitchy like that. I've been told that it's a fault in the original design, along with the interactive volumes.

[Structo]

When I was having some hum problems in my D'lite, I ordered the isolating washers for the jacks.
Isolated all of them, input, FX loop, speaker.

Didn't really notice much improvement and later found an issue that resolved it.

I like the logic behind it though and it just makes sense to eliminate the chance of it at not much of a cost.

[Aaron Howell]

I recently built a 5e3 which had an ever-present hum. Turned out to be one of the shorting jacks not doing its job.