Reverb Hum-How to get rid of it

[Willabe]

It seemed to me, apparently incorrectly however, that if you connect Filter Cap ground node A, to the Node A star ground which is attached to the BUSS, that when all the Filter caps get connected on their separate stars which are all wired on the same BUSS, that the grounds would all be picking up all of the nodes of the star points since everything is connected to the same BUSS.  And that's what I assumed was causing the ground loops.

How is that any different then how you have it wired now? All the grounds are connected.

All the component grounds, including the pots go to 1 or the other ground buss and the daisy chained filter caps all go to the upper ground buss, so do all the jacks and ft sw. 

[Willabe]

...... that the grounds would all be picking up all of the nodes of the star points since everything is connected to the same BUSS.  And that's what I assumed was causing the ground loops.

If you ground both ends of the shield on a shielded cable, that's a ground loop.

Signal runs down the shield, to the chassis, through the chassis over to the other end of the shield, runs back down the shield, to the chassis, through the chassis, over to......

And round and round it goes. That's a ground loop.

Same thing happens if you ground both ends of the ground buss to the chassis. It makes a ground loop.

Signal runs down the buss, to the chassis, through the chassis over to the other end of the buss, runs back down the buss, to the chassis, through the chassis, over to......

Round and round it goes.

[wsscott]

Good explanation.

[wsscott]

Finished it up, and the hum seems much better.  It's still there but much improved.

However, now I've got a problem with the 6.3VAC filaments not heating up.

The amp had been running fine, and I let it run for awhile and turned it on and off several times with no issues.

Then I turned it on to check my guitar's sound, and now I'm not getting any sound. The filaments are not heating up.  The pilot light is on, and the filaments get their power from there.  There is continuity from the pilot light wiring to all of the filaments.

The filament voltage seems high however at 6.9VAC.  The only thing I noticed is that the wiring on the 2 tabs on the pilot light socket appeared to be touching, ie. 1 wire on one tab was touching the other tab.  So maybe a short.  I was adjusting the pilot light bulb holder this weekend and maybe it got into a position that caused a short.  Could that have damaged the transformer's filament windings?  But could the pilot light still illuminate if there was a short/damage in the secondary filament supply?

The caps are all getting proper voltages, so I think the Secondary winding is okay.

[Willabe]

The filament voltage seems high however at 6.9VAC.

You have heater acv, so the PT's heater wind should be good.

If a PT secondary has no load on it it's acv will be high.

Being very careful, put the amp in a room where you can turn out the lights, black out drapes over the windows, so it's totally dark. Turn the amp on, then black out the room, look to see if every tubes heater is lighting up. Some tubes heaters light might be just barely visible, look closely.

Also check the 2 @ 100 ohm faux CT R's. Might have burned up. 

This should tell you what's wrong.   

When you measure heater acv, use alligator clips on your meter leads, clip 1 lead on 1 tube socket heater pin and clip the other lead to the other tube socket heater pin. Do not clip 1 meter lead to a socket pin and the other meter lead to ground.

[wsscott]

Ok, looks like it's either with the Reverb F/S  Jack, or the switched style Output Jack, or the Output cable.  Whewww!

Hopefully a much easier fix.

[Willabe]

Well???

[wsscott]

I haven't had a chance to get to it yet.  I want to re-solder the wiring at the pilot light to make sure there are no dry joints.  That was what I re-positioned in doing the ground wiring, and since at one point I didn't have any voltage at the tube heaters but had continuity between them and the pilot light, I thought best to start there.

The reason I mentioned the jacks was thinking it was a sound output issue, and of course the jacks wouldn't prevent voltage getting to the filaments.

I'll keep you posted.  Thanks.

[wsscott]

Interesting development.  I was reviewing the circuit on the Reverb Intensity pot and found an issue.  Currently the Reverb jack is, and has been, isolated from the chassis, and its Ground point is only connected to the #1 far left tab on the Reverb Intensity pot.  That tab is not connected to any ground point. The schematic shows that it should be, but it's not.  I had previously disconnected its ground, but it still functioned, mysteriously. The pot is not isolated from the chassis, and there is continuity between the chassis and back of the pot.  If no plug is plugged into the Reverb jack, there is no continuity between the jack's ground point and the chassis or the BUSS--as it should be.  BUT, if I plug in the plug that connects to the footswitch, there is continuity between the jack's ground lug and chassis.  There shouldn't be any continuity.  If I take just an un-wired 1/4" plug, and plug it into the reverb footswitch jack, there is NO continuity between the jack's ground lug and the chassis or the BUSS, as I think it should be.  The footswitch is a dual switch for Reverb and Vibrato.  It has a stereo 1/4" plug.  Since I'm using 2 separate isolated, non-switched, 1/4" jacks, I have a stereo to mono adapter that connects the stereo plug on the footswitch, to the mono adapter, which then plugs into the jacks.

Seems to me that somehow, the mono reverb plug on the adapter is grounding out somehow, even if the adapter is not plugged into the stereo footswitch plug.

If I'm correct then this grounding is probably also affecting the Hum.  So I need to deal with this plug.  Thoughts.

[Willabe]

Interesting development.  ......

If I'm correct then this grounding is probably also affecting the Hum.  So I need to deal with this plug.  Thoughts.

Before we go chasing rabbits, you last said the build was not working at all, no output.

Is it now working?

If it's working, is the humm gone, mostly gone?

[wsscott]

Yes, it started working.  I think it was a cold solder joint at the pilot light.  I re-soldered that connection just to be sure.

The hum is certainly improved.  When I was trying to fix the above problem when the heaters weren't getting power, I was plugging and unplugging jacks, and noticed that I had gotten the power to the filaments back and it was making sound, but the reverb jack/plug was acting erratically and there was some feedback.

So I think we're dealing with 2 different issues.  The power to the filaments, which I think is resolved.  And now the reverb jack issue I have described.

I'm thinking that maybe if I fix the plug that is shorting to ground somehow internally, then I can properly wire the #1 lug on the Intensity pot to the ground BUSS.  By fixing the plug, that will eliminate the Intensity pot grounding to the chassis, which may be causing a ground loop.  And by wiring #1 lug on that pot like is shown on the schematic to the BUSS it won't have 2 ground points to create a ground loop.

[Willabe]

and its Ground point is only connected to the #1 far left tab on the Reverb Intensity pot.  That tab is not connected to any ground point. The schematic shows that it should be, but it's not.

Hook up that ground connection to the buss. Do this 1st.

I had previously disconnected its ground, but it still functioned, mysteriously.

See below for why it still worked.

If I take just an un-wired 1/4" plug, and plug it into the reverb footswitch jack, there is NO continuity between the jack's ground lug and the chassis or the BUSS,

This is a big clue. ^^^^^^^^^^^^^^^^^   

The footswitch is a dual switch for Reverb and Vibrato.  It has a stereo 1/4" plug.  Since I'm using 2 separate isolated, non-switched, 1/4" jacks, I have a stereo to mono adapter that connects the stereo plug on the footswitch, to the mono adapter, which then plugs into the jacks.

The stereo to mono adapter is isolating the tips/hot but sharing the ground. So your picking up the vibrato ft sw jacks ground.

If I'm correct then this grounding is probably also affecting the Hum.

No it's not affecting the humm.

[Willabe]

You said the chassis verb jack is a stereo TRS, yes? That's why you need a stereo to mono adapter to use with the verb/vib ft sw. Which has 2 separate jacks.

Right now on the chassis stereo TRS isolated ft sw jack, do you have any wires hooked to it's ground?

You said you have a wire from that ft sw jacks ground lug going to the far left verb pots lug. (Yes I know it's not wired to the buss.)

But did you also hook up any other wire to that verb/vib ft sw ground lug? Like maybe you ran a wire from the verb/vib ft sw ground lug over to the B node filter cap that feeds the vib osc/driver? 

[Willabe]

If you stay here for a little while I think we can finish this.

[wsscott]

I connected the wire from the #1 lug on the Intensity pot to the Ground BUSS, and I would say the HUM is fixed!

In my post #88 I measured the noise difference between Reverb On/OFF at about 4 db.  Now it's down to a difference of 1.2db.  Really very quiet.

Also, I get no increase in Hum when I change Volume, Reverb Intensity, or Output Level.  Before I was getting louder hum when I increased the Output Level.  So that's great.  I think the Output Level can now be adjusted to get unity gain with the input signal and no increase in noise.

I think the little bit of hum that's left is normal and expected with a tube amp.

So I'm very happy!

As to your question, the chassis reverb jack is Mono, but the plug on the cable from the dual Reverb/Vibrato F/S to the Reverb and Vibrato mono jacks is Stereo.  So that's why I needed the adapter.

So I think it's time for a drink!!  Thanks everyone for your help and patience.  The re-wiring of the grounds to match up with the Filter Cap Nodes really seemed to be the trick.  Thanks again.

[Willabe]

I connected the wire from the #1 lug on the Intensity pot to the Ground BUSS, and I would say the HUM is fixed!

        

Now put a 3 prong to 2 prong adapter on the verb/vib units power cord plug.

Any better? Does it lower the last little bit of humm any?

[Willabe]

As to your question, the chassis reverb jack is Mono, but the plug on the cable from the dual Reverb/Vibrato F/S to the Reverb and Vibrato mono jacks is Stereo.  So that's why I needed the adapter.

Ok, my mistake, got it backwards, there's 2 chassis mono ft sw jacks. The ft sw cable has stereo TRS jack on it's cable end.

The footswitch is a dual switch for Reverb and Vibrato.  It has a stereo 1/4" plug.  Since I'm using 2 separate isolated, non-switched, 1/4" jacks, I have a stereo to mono adapter that connects the stereo plug on the footswitch, to the mono adapter, which then plugs into the jacks.

The stereo to mono adapter is isolating the tips/hot but sharing the ground. So your picking up the vibrato ft sw jacks ground.

That's where it was picking up the ground for the verb intensity pot. But it didn't like it and hummed. 

When you wired the verb pot ground, which also has the ft sw ground wire connected to it, to the buss at the C node, it liked it, and most/a lot of the last remaining humm went away. This was after all the other re-grounding making a bussed multi star ground system, had already killed a great deal of the humm. 

Bussed multi star ground, nice.

[Willabe]

2 last humm level tests;

Because that ft sw jack has a shared ground on it's stereo to mono adapter, try this;

1. With the reverb and output volume where you normally will use it, turn off the vibrato with the ft sw, listen for humm, now turn on the vibrato with the ft sw, listen for humm, any difference?

2. How about with the ft sw unplugged, any difference in humm? 

And do both the verb and vibrato work with the ft sw unplugged?

[wsscott]

I wired that Reverb Ground to the Node E connection and not Node C.  I guess I could change that wiring if you think it might make a difference.

Using the 3 prong to 2 prong converter for the power plug, I really can't notice any difference.  If there is any, its really really a small amount of decrease.

The answer is No to both of your questions.  The hum is very minor but not affected by those changes.

Yes, with both Reverb and Vibrato unplugged, both are running.

The Output jack I'm using is a switched style, but I'm not wiring in the switch leg.  So the middle leg of the jack is not wired, just the 2 outer legs go to input source and ground BUSS.

Should I wire the middle one into the circuit with the left side leg, or just leave it be?  Should I just use a regular 2 leg jack for the Output jack?  And finally should I isolate that jack from the chassis?

[wsscott]

I just checked and the main Output jack that connects to the amp is already isolated from the chassis.

[Willabe]

I wired that Reverb Ground to the Node E connection and not Node C.  I guess I could change that wiring if you think it might make a difference.

Yes, I would, that was the whole point of all this. Just un-solder it, and use a gator clip cable to try the C node ground star. It might be a little better, if not put it back where it was. E node verb recovery triode is directly before and drives the C node output triode.

It seems that the verb intensity pot liked being grounded to the buss E node better than sharing the vibrato B node ground star through the stereo to mono adapter ground.

The Output jack I'm using is a switched style, but I'm not wiring in the switch leg.  So the middle leg of the jack is not wired, just the 2 outer legs go to input source and ground BUSS.

I think the vib jack's switch grounds the oscillator which turns it on so the vib works without the ft ws. Take a short gator clip cable and with the ft sw unplugged short the vib ft sw tip to ground.

Does the vib work now? 

If so wire up the jacks switch if you want the vib to work without the ft sw plugged in.

[wsscott]

Sorry, you misunderstood.  The Vibrato works fine.  I was talking about the output jack from the revive to the amp, not the vibrato output jack.  I was wondering if I should wire the main output jack so it is functioning as a switched jack, or change it out for a normal jack, ie. not a switching jack.

[Willabe]

I don't know why Sluckey drew that output jack with a tip switch.

I can't think of a reason you would want to kill the output if nothings plugged in? Nothing would burn up with nothing plugged in.

You can use that jack, but I'd leave it, just don't wire up that switch, you don't need it.

[wsscott]

Thanks for the confirmation.

[Willabe]

Also, I get no increase in Hum when I change Volume, Reverb Intensity, or Output Level.  Before I was getting louder hum when I increased the Output Level.  So that's great.  I think the Output Level can now be adjusted to get unity gain with the input signal and no increase in noise.

After you get that last ground wire from the verb intensity pot to the right node, try below; 

Test it for unity gain, and see if there's any noticable humm. You couldn't do that before, at unity gain it had too much humm to run at that setting. I know you said you think you could now, but lets see for sure.

Then see if you can push it past unity gain some, any humm increase. Sometimes guys will use a unit like this for a little boost to push the amps front end a little. Comes in handy for some things.   

[Willabe]

I think the little bit of hum that's left is normal and expected with a tube amp.

Are you testing with Hummbuckers or single coil PUP's?

[Willabe]

I think the little bit of hum that's left is normal and expected with a tube amp.

Are you testing with Hummbuckers or single coil PUP's?

[wsscott]

I'm using single coils and also a 1khz signal injector.  I didn't notice any real difference in hum level changing the ground on the Reverb Intensity from Node E to Node C.  The hum with the Reverb On is still very minor, and it barely changes at all with increase in Output Volume or Reverb Intensity or Master Input Volume.  I am also able to get unity gain now of a 1khz, 150 Vrms, signal where before I couldn't take it past about 26 Vrms due to the hum.  So this is great.  I can take the Output Volume all the way up and exceed unity by just a little bit, but then I can increase the Master Input Volume and push it further, but the scope shows the signal getting some distortion at that point.  So all of this is great.  I don't think there's anything left to do.

[Willabe]

The hum with the Reverb On is still very minor, and it barely changes at all with increase in Output Volume or Reverb Intensity or Master Input Volume.  I am also able to get unity gain now of a 1khz, 150 Vrms, signal where before I couldn't take it past about 26 Vrms due to the hum.  So this is great.  I can take the Output Volume all the way up and exceed unity by just a little bit, but then I can increase the Master Input Volume and push it further, but the scope shows the signal getting some distortion at that point.  So all of this is great.  I don't think there's anything left to do.

Agree, that's great, very happy for you. You did a good job!

How does the Maggie pitch shift vibrato sound? I love my Maggie's vibrato.

I didn't notice any real difference in hum level changing the ground on the Reverb Intensity from Node E to Node C.

That was worth trying, now you know.   

I'm using single coils.... 

That's great, even with single coils it's very quite. Might even loose the last of that humm with Humbuckers.

[wsscott]

Yea, the Varistors in the Maggies for the true pitch shifting Vibrato are really cool.  Love them.  This mod was based on the M10A circuit.  I have a 1964 Gretsch Country Gentleman that I got in high school, so its humbuckers really give a nice sound too.

I haven't seen Sluckey on the Forum recently.  Is he still active, or .... ?

Thanks again for all your help.

[Willabe]

I haven't seen Sluckey on the Forum recently.  Is he still active, or .... ?

No, not here;

https://el34world.com/Forum/index.php?topic=31909.msg351724#msg351724

[Willabe]

Yea, the Varistors in the Maggies for the true pitch shifting Vibrato are really cool.  Love them. This mod was based on the M10A circuit.

Probably sounds best driving the varistor's harder by turning up the input volume and using the output volume for just enough output to get unity sound. The more you push those varistor's the more intense the vibrato should be.

Should be able to get a much fuller vibrato now. And that was part of the problem with having to turn down the output control to keep the humm tolerable. 

I have a 1964 Gretsch Country Gentleman that I got in high school, so its humbuckers really give a nice sound too.

I'm sure it sounds great!

[Willabe]

Yea, the Varistors in the Maggies for the true pitch shifting Vibrato are really cool.  Love them. This mod was based on the M10A circuit.

Probably sounds best driving the varistor's harder by turning up the input volume and using the output volume for just enough output to get unity sound. The more you push those varistor's the more intense the vibrato should be.

Should be able to get a much fuller, richer, stronger vibrato now. And that was part of the problem with having to turn down the output control to keep the humm tolerable. 

I have a 1964 Gretsch Country Gentleman that I got in high school, so its humbuckers really give a nice sound too.

I'm sure it sounds great!

[wsscott]

Yes, I love the CG.  Just wish I could play a lot better.  I'm better with rhythm than lead.  I use round wound strings most of the time on the CG, and flat wounds on the Warmoth Strat I built.  The flats give it a much more mellow tone.

As to the vibrato, yea the varistors really give it a different sound than tremolo.  I built a mod of the new Magnatone Twilighter amp, which has both tremolo and vibrato, but I decided just to build it with tremolo since I had this unit for Vibrato. The tech at Magnatone share their schematic with me which hadn't circulated on the internet a couple of years ago. What I've found that's really neat is to have both the Vibrato and the Tremolo on together.  You really get a great effect, a lot like an Echo effect.

Anyway, nice to have this much improved and pretty damn quiet.  The biggest change is how the Output Level is now much more useable.  I don't know how the grounding was affecting the Output Level pot's "sensitivity", and maybe you know what was happening, but it now seems to have the range of a 100K pot vs. what it was like before.

[Willabe]

Is the vibrato stronger now that you can turn it up?

[wsscott]

I never had a problem with the Vibrato.  Always very quiet, no hum.  So it's great.  The Reverb can go all the way without being an issue.  The hum might increase a very minor amount but that's only when its Intensity gets 90-95% fully turned up.  Its pretty consistently quiet all the way up.

[wsscott]

I got the "Revibe" reinstalled into its cabinet, and hooked it up to my amp, and it's incredible!  It's even quieter now than when the chassis was out of the cabinet and on the work bench when I was testing it.  The "hum", and I don't even think it would be appropriate to use that word anymore, is almost totally gone.  I would say I should use the Italian word "Perfetto"! to describe it.

This has been a long journey over the years!  A Long and Winding Road.  But finally got there! And I learned so much along the way. Thanks so much for everyone's help.  Best.