Stout TMB with a hum

[jly56]

Hi..

I am having some issues with a Stout TMB that I have built.  When I have the speaker connected and the volume at 0, there is a slight hum (60 cycle?) coming from the speakers.  As I turn the volume up, the hum is replaced with the 'normal' speaker noise of an amp with the volume turned up, but nothing in the input. 

I am using Doug's iron and I followed his build, except that I put the on/off switch on the front of the chassis.  The plan was to put it in a combo cabinet and I didn't want to have to reach in the back to power it on.

The original version (picture Stout1) had the filament lines running in the bottom corner of the chassis (like a 5f6a) and I didn't used shielded lines on the pots... Just from the input jack to V1.  Here the hum seemed to be the loudest.

I changed the filament line to flying and used shielded wire for all of the wires going from the pots to the board (and V1).  This seemed to help slightly, but not much.  Pictures Stout 2 and Stout 3 (close up of the board) show it in it current version.  The shielded pot wires are about an inch above the filament power lines.

The hum does get louder when my fingers get close to the PI caps (.01 & .022 going to pin 2 on V2), if that's any help in diagnosing.

I could also make the flying filament lines higher and route the shielded pot lines under them.  Other than that, I am at a loss of what else to do. 

Any suggestions or comments would be greatly appreciated.

Thanks

Edit:  I've also noticed after playing on it for about 1.5 hours this morning that the PT gets rather hot.  Not blistering hot where I cannot hold it, but hotter than other 5f6 and 5F8 amps I've built.  Is this normal with a Stout?  I rechecked the PT wiring and I don't see anything wrong... but I've been looking at the insides of this thing for the last 1.5 weeks and don't know if I would see anything wrong at this stage! 

[Willabe]

This probably wont do anything, but I would rotate the input jacks tip connection away from the heater wire and tube pins.

Lowest signal point in the amp and will take the smallest amount of noise to be injected to upset the whole amp.


                  Brad   

[jly56]

This probably wont do anything, but I would rotate the input jacks tip connection away from the heater wire and tube pins.

Lowest signal point in the amp and will take the smallest amount of noise to be injected to upset the whole amp.


                  Brad   

Thanks Brad....  I'll give it a try! 

[EL34]

I can't see anything wrong in the pics

I have seen several amps built in these chassis and all of them had the heater wires laying flat on the chassis like in my build

Did you try different pre amp tubes?

Negative feedback can reduce hum levels.
Pull the feedback wire away from the speaker jacks?


do a sound clip of the hum

[jly56]

I can't see anything wrong in the pics

I have seen several amps built in these chassis and all of them had the heater wires laying flat on the chassis like in my build

Did you try different pre amp tubes?

Negative feedback can reduce hum levels.
Oull the feedback wire away from the speaker jacks?


do a sound clip of the hum

I started out with the heater wires laying flat (pic 1) and thought that was the culprit, so I changed them to flying.  I have tried different preamp and amp tubes, but not rectifier, as I only have one 5y3.  I moved the feedback wire from over the switch (pic 1) to under the board more and directly to the 8ohm.  I just moved the wire more between the two output jacks... no difference.

I also tried rotating the input jack as Brad suggested.. no difference


Here is a link to my dropbox with a copy of a mp3 of the hum 

https://www.dropbox.com/s/5x48fke2s26o5f0/rec_20150309_182616%20.mp3?dl=0

Hopefully you can hear it.  It's not real loud and the amp sounds great when played. 

Thanks for everybody's assistance.

[EL34]

Sorry, can't hear the sound
Drop box wants me to sign up.


Just post a link to the clip URL here and it will play

[jly56]

Sorry... You have to close the logon screen and then DropBox should let you download it.....

I loaded it to SoundCloud...

https://soundcloud.com/jly56/rec-20150309-182616

Hopefully this will work for you.... just click the play arrow..

Thanks

[shooter]

probably won't help but...when you plug in where does the guitar volume override the hum, 1, 5?.  The build I just finished had hum, pulled each tube, found that V1 was the problem, stuck in a different one and now you can't tell it's on unless the amp gain and volume are around 8 and that's over ridden when the guitar is at 1.

[sluckey]

There's a simple test you can do to determine if the hum is caused by the heater circuit. Disconnect the PT heater wires from the heater string. Temporarily connect a 6V lantern battery to the heater string so the heaters will be powered by pure DC. Does this eliminate the hum?

[EL34]

Just curious what happens when you ground points A,B,C and D on my diagram below


Ground them one at a time and then unground them before doing the next one

[jly56]

Just curious what happens when you ground points A,B,C and D on my diagram below


Ground them one at a time and then unground them before doing the next one

A - much louder buzzing sound
B - HUM GOES AWAY!!!!! Amp sounds like a 'normal' amp
C & D - nothing


What did I do wrong at those caps? 


Thanks!!

[EL34]

A is the wiper on the Volume pot and that is what you grounded, correct?
Take a good clear picture of the back of the pots and the tube sockets in the same pic

Like this pic

[EL34]

It's hard for me to see what's going on in the tone section here
Your big blue caps are covering up the wiring

[hardhead]

There's a simple test you can do to determine if the hum is caused by the heater circuit. Disconnect the PT heater wires from the heater string. Temporarily connect a 6V lantern battery to the heater string so the heaters will be powered by pure DC. Does this eliminate the hum?

Very useful tip....Thank's Steve

[jly56]

A is the wiper on the Volume pot and that is what you grounded, correct?
Take a good clear picture of the back of the pots and the tube sockets in the same pic

Like this pic

Yes... grounding the middle tab on the vol pot gave a different, louder buzzing sound.  The line that goes to pin 7 on v1.  Am working on getting pictures of the pots and the tone section...

[jly56]

Sorry about the caps... had some Sozo's left from a previous build... they were a real PITA to fit in..  Pic 1 is the tone section.  Pic 2 are the pots and pins....  Sorry that my photo skills are not very good.  My wife is the photographer in the house and she is at work!  The wiring was cleaner before I started moving the heaters and everything (yea sure!)

I rechecked the wiring and don't see anything wrong, but like I said earlier... I've been looking at this thing for almost two weeks and don't think I would even see a mistake...

I verified that there is a 470K below test point B.  What does it mean that it became silent when I grounded at that point?

Thanks for looking!!!!

[jly56]

It's hard for me to see what's going on in the tone section here
Your big blue caps are covering up the wiring

I put the 100K under the caps (as opposed to above the caps, like your diagram)..... could that be causing a problem?

[EL34]

No, grounding point A, middle wiper on the volume pot, make the amp hum louder?

[jly56]

yes... Hum became much louder...

[EL34]

I would try Steve's suggestion for now
Just get one of those 6 volt lantern batteries at Walmart and do what he says
It will be a bit of a pain, but you have already spent 1.5 weeks chasing this issue


I just turned my TMB on and it is pretty quiet
There is a small amount of background hum, but not bad at all


If I have time tomorrow, I can open mine up and ground the volume pot to see what happens on mine

[jly56]

Will do... I have to run down the hill anyway, so I can pick up a battery and give that a try.

Like I posted earlier... the amp sounds great when played... maybe I'm expecting too much silence 

I did think it was interesting that the hum went almost completely away when I grounded your test point B.  It then sounded like what I would expect.  Just a very little bit of hum. 

THANK YOU for all of your and everybody else's assistance!  Will keep you posted!

[EL34]

I suspect a volume pot issue or something at this point


I'll try and do the same grounding points on mine tomorrow

[jly56]

Well....I know when I've been licked   

I tried the 6V batteries for DC heaters... still hums... I even replaced the vol pot with a fresh 500KA pot... still hums... (maybe it's me?)

At this point the wiring and soldering (and sockets) looks like Frankenstout's TMB  ( ) and I wouldn't want to sell it to anybody....  This was going into a combo cab for resale...... oh well.. it can wait

Guess I'll put it on the shelf for a week and then rewire with new sockets and heater lines....(laying flat... like rev 1.0).... I didn't like the flying heater lines when everything is so close together (between tubes and pots)...  I've got something else to work on anyway!

a BIG THANKK YOU for everybody's suggestions... especially the 6v battery suggestion...  now I have a nice setup for test heater lines with DC.

Doug, don't worry about opening up your TMB (unless you want too!).. and thanks for your input...

I'll post back to this thread when Rev 48 is finished!

Thanks

[Toxophilite]

I think if you grounded it at 'B' and the hum stopped it's likely the problem is in your preamp (is that right Doug?)


Try yanking V1 and see if the hum goes away


I had this sort of problem and it was because I hadn't separated the preamp and input grounds from the rest of the grounds (PI power amp filer caps etc)


What's your grounding setup like?


I meant to post this earlier. but forgot hit the post button!

[EL34]

I think if you grounded it at 'B' and the hum stopped it's likely the problem is in your preamp (is that right Doug?)

That's what I am thinking but I don't don't where at this point


I still want to open mine up and poke around


In the mean time, jly56, can you post the voltages of your first two preamp tubes?


pins 1-2-3-6-7-8

[jly56]

I think if you grounded it at 'B' and the hum stopped it's likely the problem is in your preamp (is that right Doug?)

That's what I am thinking but I don't don't where at this point


I still want to open mine up and poke around


In the mean time, jly56, can you post the voltages of your first two preamp tubes?


pins 1-2-3-6-7-8

Luckily, I decided to take a nap (instead of work), so Frankenstout was still on the bench!

Pulled V1 and the hum is still there!?! (I would have bet anything that it would have gone away!)
Edit:  No hum with V2 pulled.... nice and quiet! 

Pin     V1           V2
1        208.7      232.2
2        0             61.7
3        2.1           89.6

6         204.6       225.7
7         0              60.9

8         2.1           89.6

Heater lines were all 3.3v

All within 10% of the V listed on your build PDF, aren't they?

Edit:  FYI  the sockets used in V1 and V2 are high quality QQQ sockets that I love to use (but expensive).  V3 and V4 are cheapo ceramic sockets.. would have figured that these would have been a problem.

Thanks

[jly56]

I think if you grounded it at 'B' and the hum stopped it's likely the problem is in your preamp (is that right Doug?)


Try yanking V1 and see if the hum goes away


I had this sort of problem and it was because I hadn't separated the preamp and input grounds from the rest of the grounds (PI power amp filer caps etc)


What's your grounding setup like?


I meant to post this earlier. but forgot hit the post button!

Hi Toxophilite....


The hum did not go away when V1 was pulled...  I would have bet anything that it would have, but it didn't.


The grounding configuration follows Doug's layout for the Stout TMB. The power caps only have a single ground, so they could not be separated.  The preamp is grounded at the input Jack and pots. The amp section and the OT are grounded at the PT.


Thanks

[shooter]

You can try swapping v1 and v2, no soldering required.  Also double your NFB resistor , does require soldering.  The big guy's will have to help on the PI, I cheat and use a transformer!

[EL34]

The hum stops when grounding the input grid on V2, so something is up before that stage.
Not sure what it is yet

[sluckey]

See pic. Put a ground strap on the indicated turret. Does this affect the hum?

[jly56]

See pic. Put a ground strap on the indicated turret. Does this affect the hum?

Yes, the hum becomes louder.

[sluckey]

OK. Now disconnect the feedback wire that connects to that same turret. Does that affect the hum?

Measure resistance from V2-8 to chassis. Should be about 52K. What have you?

[jly56]

OK. Now disconnect the feedback wire that connects to that same turret. Does that affect the hum?

Measure resistance from V2-8 to chassis. Should be about 52K. What have you?

Hum became louder with fb disconnected.   V2-8 to chassis is 53.8k.


Edit:  I have to go to my old job and do some work ( ) for them today, so I will not be able to test anything until this evening.  Thank you to everyone who is helping me with this!

[Ed_Chambley]

May not have anything to do with your noise, but I would check it.  I had a ton of SoZo caps I received for nothing and have been using them.  I say that to bring your attention to your very last coupling cap.  Blue SoZo caps always have a dome on the foil side.  All if yours do except the last one.  It looks from the photo the cap is marked backwards and while that in itself may not cause any noise, but I would check it.  It just looks funky.

I have had luck in reducing noise by using spaghetti tubing where plate R's cross over the preamp ground.

Your hookup wire looks like cloth covered PVC.  Have you been using this wire?

Did you try bypassing the tone stack?  Just thinking out loud.

I know Doug asked, but just want to make sure.  I cannot see how your slope resistor is wired.  Confirm you have connected on the Pot side of the 500pf to your Bass cap only.  In one photo I can barley see what may be the slope resistor.  I cant tell how it is wired.

[EL34]

I would swap out the tone caps to go along with what Ed said
Try another brand just as a test


I don't think the cloth wire is a problem, I used cloth on both of my builds in that chassis

[Ed_Chambley]

I would swap out the tone caps to go along with what Ed said
Try another brand just as a test


I don't think the cloth wire is a problem, I used cloth on both of my builds in that chassis

Doug, I don't think the cloth wire is a problem, but what he is using is different I think.  It is not pushback as far as I can tell.

[jly56]

I would swap out the tone caps to go along with what Ed said
Try another brand just as a test


I don't think the cloth wire is a problem, I used cloth on both of my builds in that chassis

Doug, I don't think the cloth wire is a problem, but what he is using is different I think.  It is not pushback as far as I can tell.

Hi... Still at work, but saw the messages...

Yes... the one Sozo looks 'backwards'.. at least with how I like to orient them...  The wire is not push-back, but a cloth cover 20G solid wire (600v) that is a lacquered cotton braid that is bonded to the pvc insulator.... it doesn't push back (you have to strip), but it doesn't get so fuzzy, especially when you have soldered/unsoldered a connection as many times as I have with this project.  I have used this wire for a couple of years and a number of other amps without problems.

I will try everybody's suggestions when I get home tonight... I'm meeting the better half for dinner, so it will be late.... but not working tomorrow!!!!

Thanks to everybody who has posted!!!!!!!
 

[jly56]

Hi all who have been helping me...

I had a chance to work on the Stout this afternoon and this is what I have done.

Ed_Chambley reminded me that the Sozo's like to be connected a certain way... outside foil vs inside foil.  I began by reversing each Sozo caps direction.  The only difference that made was when I reversed the cap that the feedback was connected to, the hum became louder.

I decided to pull all of the Sozo caps and replaced with some Sprague caps.  That did NOT make any difference in the hum.. but it is now easier to see the wiring and the slope resistor, which was going from the pot side of the 500P to the Bass cap.

I would like to try Ed's suggestion of bypassing the entire tone stack, but would like somebody's (Doug?) direction on how to do this.  My theoretical skills are not that strong and I don't want to cause more problems.

One thing I noticed a few days back was with the treble control.  I'm not sure if it did this at the beginning or if this happened somewhere with all of the heater rewiring, but...  When the treble gets to around 7, then I actually start loosing volume until it is almost completely gone when treble is at 10.  Also, the treble pot doesn't seem to affect the sound as much as the mid or the bass. 

Doug, did you get a chance to see if grounding the wiper of the volume pot caused a louder hum, on your amp?

I have attached the latest picture of the pots with V1 and V2.

Thanks for your comments and suggestions!

[EL34]

I didn't open mine up.
I was waiting for you to do the other things first


I still think it is in one of the pots at this point


I see pot tabs that are bent and lots of solder
Possibly flux on the carbon traces or a tab that is not making contact with the carbon traces?

[jly56]

I didn't open mine up.
I was waiting for you to do the other things first


I still think it is in one of the pots at this point


I see pot tabs that are bent and lots of solder
Possibly flux on the carbon traces or a tab that is not making contact with the carbon traces?

Yes...  Everything has become a mess with all of the soldering/unsoldering/resoldering trying to trace down the hum. 


Don't worry about opening up you amp.  At this point I'm just going to put it on the shelf and rebuild it from scratch at some later time.


Thanks for all of you help.