Vibrolux reverb custom issue

[daz]

I have this amp with a issue where theres some intermittent noise and i think it may be related to another issue which is NOT intermittent. So i want to focus on that. And that would be that the volume control on the normal channel is making noise where it shouldn't. If you turn it up with nothing plugged in it makes hiss, and it's NOT the jack switching. I can even put dummy plugs in both of the normal channel's inputs and ground the hot tabs and nothing changes. (plus i checked the jack switching too) I've tried a number of things like new tubes, checkin solder joints and re-tensioning the sockets. Even with a guitar plugged in it does it regardless of the volume on the guitar being down of up. The way i see it it must be between the pot (which is fine plus i cleaned it) and the place where the channels are combined, but theres nothing much i can see that would cause this. It's one of those issues that i can't wrap my head around so i'm really stumped. heres the 2 channel inputs....



Also, it may be worth mentioning that as you turn it up, hiss increases in a linear fashion peaking at 10, but at about 4 a low mid hum starts that increases then tapers off and is gone by the time i hit 8.

Another hint....the hum seems to be from somewhere after the volume pot and the hiss from before. I determined this, right or wrong, by grounding the wiper of the treble pot. When i did that the hiss as i turn up stops but the hum that starts at 4 then out at 8 is still happening. By the way, the hiss that increases in a linear fashion also happens with the bright channel volume, but only a tiny fraction as much. Maybe 10% as loud, just enough to be able to hear it.

[pdf64]

Have you ruled out the normal channel plate resistor R4 being bad?
Pete

[daz]

Have you ruled out the normal channel plate resistor R4 being bad?
Pete

I didn't check the resistor's value, but i checked the voltages and that seemed fine. So just now i checked the value, albeit in circuit. But it does measure about 100k. Unless it'd driftiing way out under load or some such thing, i think it's ok.

[JoeM]

daz,

I've had newer Fenders with noisy plate resistors, don't recall if the value had changed, but it could be the source of your noise.

[daz]

Ok, i'll give it a shot and post back in a minute.

edit: clipped one leg and tacked in a new 100k but no joy.

[Enzo]

Forget the hum, if it is a problem after the hiss is fixed, we can look at it then, otherwise, let's look at one problem at a time.

SO you aren't really telling us the volumne control is making hiss, you are really telling us there is hiss, and the volume controls the level of it, yes?

The normal channel and the bright channel are identical except for the littl brightness cap on the volume control of the bright channel. SO are you reporting that the bright channel does NOT hiss like the normal? Oh wait, I see later you tell us this.

it must be between the pot (which is fine plus i cleaned it) and the place where the channels are combined

hum seems to be from somewhere after the volume pot and the hiss from before.

Pick one, the hiss is coming from before the pot or after it, I'd agree, but not both. If the pot turns the level of it up and down, then the pot is after the source. If the treble pot can kill the hiss it is before that too. A little hiss is normal from gain, but I'd expect more of that from the bright channel. SO regardless, we have somewhere between the input jack and the treble control so far. Grounding the inputs doesn;t stop it, but does grounding the tube grid? I'd short pin 2 to pin 3 with a screwdriver to see.

DC voltages like on the plate can get in the way of grounding certain points in the circuit, but you can still do it using a cap. The value is not important, I reach of a 0.047uf because I have a ton of them handy. Ground one end of the cap, and a clip wire to the other end. Use that cap to "ground" points in the signal path. You can thus ground the plate with the cap and see if the noise is killed. DOn't freak out when it makes a pop as the cap charges.. And don't forget to discharge teh cap to chassis before touching a grid, as that will make a loud pop also. The cap will shunt a lot of signal to ground. If it has no efect, the hiss is coming in later. If it kills or seriously dulls the sound of it, then the hiss is coming through the point you shunted.


And warm up your scope. You know the hiss is at certain points like the volume and treble controls, so go ther and see what it looks like. Now go back to like the plate of the first tube and elsewhere and see where it lives.

[daz]

Thanks Enzo. I will have to follow your suggestions later, as i won't have the amp here for a few days. I believe i did ground the grid but i forget what happened. So i'll do that again and report. As for the hiss, i didn't say it's coming from both before and after. The hum seems to come from after, the hiss from before, determined by grounding the wiper of the treble pot and witnessing the hiss gone but hum still there between about 4 and 8. anyways, i'll re-read your post and check whatever you suggested within a few days. Thanks.

Forget the hum, if it is a problem after the hiss is fixed, we can look at it then, otherwise, let's look at one problem at a time.

SO you aren't really telling us the volume control is making hiss, you are really telling us there is hiss, and the volume controls the level of it, yes?

The normal channel and the bright channel are identical except for the littl brightness cap on the volume control of the bright channel. SO are you reporting that the bright channel does NOT hiss like the normal? Oh wait, I see later you tell us this.



Pick one, the hiss is coming from before the pot or after it, I'd agree, but not both. If the pot turns the level of it up and down, then the pot is after the source. If the treble pot can kill the hiss it is before that too. A little hiss is normal from gain, but I'd expect more of that from the bright channel. SO regardless, we have somewhere between the input jack and the treble control so far. Grounding the inputs doesn;t stop it, but does grounding the tube grid? I'd short pin 2 to pin 3 with a screwdriver to see.

DC voltages like on the plate can get in the way of grounding certain points in the circuit, but you can still do it using a cap. The value is not important, I reach of a 0.047uf because I have a ton of them handy. Ground one end of the cap, and a clip wire to the other end. Use that cap to "ground" points in the signal path. You can thus ground the plate with the cap and see if the noise is killed. DOn't freak out when it makes a pop as the cap charges.. And don't forget to discharge teh cap to chassis before touching a grid, as that will make a loud pop also. The cap will shunt a lot of signal to ground. If it has no efect, the hiss is coming in later. If it kills or seriously dulls the sound of it, then the hiss is coming through the point you shunted.


And warm up your scope. You know the hiss is at certain points like the volume and treble controls, so go ther and see what it looks like. Now go back to like the plate of the first tube and elsewhere and see where it lives.

[Enzo]

Ah, well that is part of why I suggest we tackle one problem at a time, so two different sets of symptoms do not get confused, at least in my mind.

[daz]

Ok, i grounded both grids and pin 2 shuts it down to a large degree but it still does it, just maybe 10% as loud. Pin 7 shuts it down 100%. Zero noise, sound of any kind, just dead quiet. So I assume that shows that it's w/o a doubt before the volume and after the input grid. Any suggestions besides shotgunning it? I have no scope by the way.

[daz]

Well, i figured as few parts as there are between the input grid and volume i may as well shotgun the caps. haven't tried the cathode cap yet, and now that i think about it wouldn't that seem likely? anyways, i will. But i swapped the 3 tone stack caps and they're all good. I'd try the cathode next.

EDIT: cathode cap fine, resistors 4 5 6 and 8 are fine. C5 i believe is good. As I said earlier, tried different tubes and tightened sockets. Not much left

Replaced C35 filter and checked r60,61....no change

[daz]

F me, i'm done with this freakin' thing. Now the other channel is doing it and the normal channel is much better. I DID just change some tube again just now but the sockets are tight and i then replaced the tubes after noting the change and it just stayed like this, IE: bright chan doing it. Unless anyone has a suggestion i'm just going to zip it up and be done. This is just too wacky.

[52 Bill]

Ok, i grounded both grids and pin 2 shuts it down to a large degree but it still does it, just maybe 10% as loud.

No stage will be completely silent. At 10% how does it compare to the other channel?

Try changing R1, R2, or at least try plugging into jack #2 and turning the guitar volume down. That will remove R2 from the input circuit.

[daz]

No stage will be completely silent. At 10% how does it compare to the other channel?

Try changing R1, R2, or at least try plugging into jack #2 and turning the guitar volume down. That will remove R2 from the input circuit.

Thing is, like i said above the channels are now opposite, IE: the bright channel is now doing it and the normal isn't. I do realize there is going to be some noise and at the moment i thing the normal channel is within normal limits as the bright channel WAS and now isn't. I think the fact they switched should be a major hint as to where to look but it would then seem to have to be after the grid at pin 7, but if so then it shouldn't have gone 100% silent when grounding pin 7 as it did.

There is something else going on too, and i'm sure it must be related but it's seriously intermittent as in only showing up on rare occasion. that would be staticy sounds and even motorboating that lasts a short time and most often happens as the amp warms up. I checked the filters and they all seem good and voltages are right.

[oc disorder]

Although your problem sounds specific to the pre-amp the custom shop Vibrolux is known to be noisy.

See these for example :-

Removing all hiss from Custom Vibrolux Rev. - Fender Stratocaster Guitar Forum

FenderŪ Forums ? View topic - Hiss in Custom Vibrolux Reverb

Fender Vibrolux Custom

http://music-electronics-forum.com/t27902/

It appears to me the designer applied the er um mods that a lot of amp fanatics do to their own amps.
Like removing neg feed back changing the caps etc.
It also appears as the circuit board has components missing , that the board can be/ is?
used for the vibroverb as well populating it with some different components.
Its certainly not one for the hi-fi guitarist ....if one exists !
The tone stack is different too with an extra tap/lug on the treble pot.
But some blues/rock guitarists seem to like it as it is!

[daz]

Great, thank you ! That will save me a lot of trouble. I wondered if it was normal for this amp, looks like it is. Although i can't figure why the channels are different as noise goes and one is usually quieter and how that reversed at one point ! There however IS a issue with it but now i know they are not related. Thanks a lot for that info !

Although your problem sounds specific to the pre-amp the custom shop Vibrolux is known to be noisy.

See these for example :-

Removing all hiss from Custom Vibrolux Rev. - Fender Stratocaster Guitar Forum

FenderŪ Forums ? View topic - Hiss in Custom Vibrolux Reverb

Fender Vibrolux Custom

http://music-electronics-forum.com/t27902/

It appears to me the designer applied the er um mods that a lot of amp fanatics do to their own amps.
Like removing neg feed back changing the caps etc.
It also appears as the circuit board has components missing , that the board can be/ is?
used for the vibroverb as well populating it with some different components.
Its certainly not one for the hi-fi guitarist ....if one exists !
The tone stack is different too with an extra tap/lug on the treble pot.
But some blues/rock guitarists seem to like it as it is!