Issue w/ Fender Blues Deluxe Reissue

[Don]

Not sure if this is the right place to post this but here I go,

So the issue has to do with Reverb. With my limited knowledge I think it might have to do with the reverb tank, or the tube which controls reverb (I'm not sure if this one is right at all). So if I turn the reverb on, and put the knob anywhere past four, the amp will start humming. The humming starts off quiet, and progressively gets louder and louder, probably within a span of ten seconds to a minute until it's just unbearable. So when this issue came about I decided not to even mess with anything, but I decided to troubleshoot around. So once it started humming, if I turned the reverb knob back down to zero, the hum will continue to go on. If during the humming, I use the provided pedal which turns reverb on/off completely, to turn reverb off, the hum will go away until I hit the button to turn reverb back on. The hum will happen regardless of what volume the amp is at, say it begins humming and I turn the volume/master/drive knobs to zero, it'll keep humming. If I put it in standby and unplug my guitar, then hit standby again, it'll start to hum and progressively get louder and louder. The only temporary solution I noticed, which would only last for a few days or until I move my amp or something is to shimmy the reverb tank away from the speaker, but don't hold me on that one. When I did this a few days ago the hum was completely gone and I was able throw the reverb knob all the way over to twelve without a hum. Also on some occasions if I shook the amp a little, enough to hear the reverb coils/strings or whatever make that weird swishing noise, the hum would go away, but if I were to start playing again the hum would come back and do its thing.

So with all that said, do you have any idea what the issue could be? I'd really prefer to fix it myself if it's simple enough, I just don't want to start poking at stuff I shouldn't be until I know what it is and I should be able to fix it.

[phatt]

So the issue has to do with Reverb. With my limited knowledge I think it might have to do with the reverb tank,

---------
The only temporary solution I noticed, which would only last for a few days or until I move my amp or something is to shimmy the reverb tank away from the speaker, but don't hold me on that one. When I did this a few days ago the hum was completely gone and I was able throw the reverb knob all the way over to twelve without a hum.

Judging by your observations,
Most likely culprit is Acoustic Feedback, obviously the tank is to close to the speaker with little or no acoustic isolation.

Does the tank have a bag it sits in?
Try remounting the bag with extra foam around it.
The idea is to completely decouple the tank from the body of the amp cab. Assuming it's factory issue, You would think by now Fender would have worked out the problem
Phil.

[Roly]

(hopefully the right) Cct attached.

Service manual;
http://elektrotanya.com/fender_blues_deluxe-deville_reissue_sch.pdf/download.html


First thing I'd do, looking at the circuit, is give the contacts on the Power Amp In socket a good clean, Deoxit or metho and a good scrubbing to make sure all the switch contacts are making good connection.

Second, what are the RCA connections on the tank like?  Corrosion can cause an open ground condition on the tank which can often have some very strange symptoms.  Wiring "wrenched" or frayed?

Is the tank in a padded bag, or not?

[g1]

As Phatt mentioned, if pulling the tank away from the speaker makes it quit, then it is a physical feedback issue, caused by the proximity of the tank to the speaker.  It is a fairly common issue.
Any chance you changed the speaker?  Otherwise, could the tank have moved in it's bag?  Sometimes it only takes 1/2 an inch.  Or it's possible the springs have stretched enough to cause the problem, in which case a new tank should solve it.

The part I don't get is that the footswitch will kill the feedback, but the reverb pot will not.  The only thing I can think is that the pot does not go completely to zero.
Does the level of the feedback change as you turn down the pot?

[Don]

Hey guys!

So after reading your comments I decided to go ahead and inspect the reverb tank, and I think I found the culprit.

g1, the pedal included with the amp literally cuts out reverb altogether as if you literally unplugged the tank while it's on, whereas the pedal is like incremental. I'm not 100% sure on that one but I think that's how it works. As for the level of feedback when I adjust the pot, it makes no difference. If the pot is above say, 4, it would trigger the hum. If I were to play with the pot on 1-3, just as an example, there would be no issue at all.

Roly, the connections all seemed fine in there and everything is nice and clean in there. After inspecting all the wires they seemed fine as well.

So to answer your question phatt, the tank sits in a nice bag, and sits on top of a piece of cardboard inside this bag which I believe is standard. However, if you take a look at the pictures below, I was given only three of these silicon grommets and little brass (?) metal pieces to put inside the four larger holes which I assume is to hold the tank in place on top of the cardboard to avoid any issues w/ the springs moving unnecessarily. Now if I'm not mistaken, there should be four.

http://i.imgur.com/SaRFnCk.jpg
http://i.imgur.com/tLdvrll.jpg

So I've lost hope in Fender since it seems like they're more like Ikea with all the missing parts and poor build quality. Even one of the feet was screwed on improperly. So my question is now; where the hell do I pick up a new set of these?

Also a few more side-notes, I recall reading a pretty interesting/funny thread somewhere else about the cardboard that they put these reverb tanks on top of, and how you get a better vibe with "vintage cardboard" and whatnot as a joke. But on a serious note, someone asked a question about possibly replacing that cardboard with a piece of metal or another material such as foam, would this be beneficial at all?

I also noticed that Fender seemed to do a really shitty job wiring this and they even hot-glued the reverb connections to the circuit board? Would I be better off removing that and re-soldering it on there? I've never worked on re-soldering connections on amplifiers but I do have experience with guitars so I'm not sure if this is standard... I do recall a story online of an amp-repair guy re-soldering connections and improving tone/sound from that. Would you guys recommend doing that in the future? Because seriously, hot glue seems like a cheap solution, correct me if I'm wrong.

http://i.imgur.com/UMZUuql.jpg

[g1]

  The hot glue is there in addition to solder, not instead of it.  It helps keep heavy parts or cables secure so they don't move around and degrade the solder connections.
So you want to keep it in place.
Are the four corner springs in place inside the tank?  They keep the inner pan centered  and help reduce the physical vibration.
Are there any screws going through those grommet inserts?  If not, you don't really need the brass insert and can use any kind of similar rubber grommet for the missing one.
As far as the cardboard, keep it but you could try some thin foam between the cardboard and the bag.

[Roly]

4/10 is very low for a springline to be feeding back, 'tho I did have an old Fender with a similar sensitivity that turned out to be a bit of broken dinner plate firmly jammed between the springline and the case (Greek wedding).


I'd get out my RCA extender leads (or a doona) and try it with the tank well isolated from the amp, and see if anything changes, cured/better/same/(worse).

Is this really acoustic feedback?  Yes or No mean quite different faultfinding pathways from here.

Wrapping the tank in foam might help high frequency feedback, but "humming" sounds like it's much lower in frequency and if so I don't think foam will help much.

I'm inclined to think that something is actually wrong, but that it won't be electronic, rather mechanical, such as something fouling the tank internal floating chassis (a mouse condo  ) or the like.


Yeah, the hot glue is very common for extra support, and a good idea too.

[Don]

Okay, that makes a lot more sense!

So just to clarify, I believe the issue is that the missing grommet offsets the reverb tank's balance causing the hum. This makes sense to me because whenever I moved it, I must have set it back up to a balanced position, then whenever the amp moved or whatever, the tank was off balanced again since there was only 3 grommets like a lopsided chair.

As for the setup itsslf,

There's a bag that covers the reverb tank with four rubber grommets on top of the price of cardboard. The bag is screwed down to the bottom of the amp, the screws going through the cardboard to keep it all in place.

[phatt]

Don said;
*it'll start to hum and progressively get louder and louder.*
Which suggests an acoustic problem not electronic.

As Roly hinted if the tank is moved away from amp/speaker/cab and working without Fback then the problem is almost certainly mechanical.
I'd look for that before I'd fiddle with PCB as those grey ribbon cables are very prone to breaking when moved around.

I'd flip that tank over and make sure the floating spring section has no rigid connection to the outer case. It should float freely on the 4 springs only, also check the transducer wires are not obstructing movement.
Those grommets look odd? I've never seen those before,, buuut,, Some tanks came with a lock down device for travel if this is not unlocked then it will certainly feedback.

If you replace the cardboard with metal or any other hard surface you will simply create a resonant cavity which will put you even closer to feedback.
Those of us that lived in the Vinyl era know all to well not to put a hard bottom panel on a turntable.
(showing my age )

Maybe take a pic of the inside might give us a better idea of what's going on.
Phil.

[Roly]

So just to clarify, I believe the issue is that the missing grommet offsets the reverb tank's balance causing the hum. This makes sense to me because whenever I moved it, I must have set it back up to a balanced position, then whenever the amp moved or whatever, the tank was off balanced again since there was only 3 grommets like a lopsided chair.

Nah, never; not with a tank in good working order, they ain't that sensitive, and they ain't sensitive in that way.


Have a very close look with a bright light, lens, and chopstick, at where the fine wires from the spring transducers get to the back of the RCA socket.  I've had these break off, make intermittent connection, and look for all the world like they were still connected until they got a poke.



Wiggle the RCA connector.  These are often just crimped together and these crimps can lose electrical continuity.  If this is happening on the earth side to the tank body (and it is most likely only earthed at the receive end), then you will get very sensitive and intermittent hum pickup.


{yeah, sticking the turntable on a bunch of jumpers at a party  :lmao: }

[phatt]

Bouncy floors? I once helped out a mate, hanging a whole DJ console from the roof of a venue via chains and dog clips as the floor was so bouncy. As a bit of extra entertainment we would set it gently swinging side to side, had a few people looking on in disbelief.
Phil.

[g1]

The only temporary solution I noticed, which would only last for a few days or until I move my amp or something is to shimmy the reverb tank away from the speaker, but don't hold me on that one. When I did this a few days ago the hum was completely gone and I was able throw the reverb knob all the way over to twelve without a hum.

If this is the case then it's definitely a physical problem caused by the proximity of the speaker.  And I doubt you were able to shimmy it very far so it is operating right on the border of oscillation.  If it's such a critical location, then it could be that the grommet is making a difference, put a temporary support there, even cardboard, to raise that corner as much as the grommet would and see if it helps.

[Don]

Okay, back again,

So I isolated the reverb tank from the amp and played for about ten minutes, more than enough time to provoke the hum, and I had no troubles. After that, I put the reverb tank back into the amp as close to the front as possible, past the initial place where it was screwed down, hopefully to pick up whatever was causing the issue. I only encounter a small hum, which was constant and low, not as annoying as the hum I've been talking about this entire time. I may go back and put it on top of the mounting holes to see if I still pick the small hum there, or if I get the increasing in volume hum again.

I forgot to mention that only two of the grommets were actually in place when I took the radiator out of the bag, so one was flying around in there which may have added to the lack of balance and the increasing volume of the hum, this time around I had all three in which may have fixed the issue but I don't want to stop there, just in case.

So I took a few pictures for you guys of the inside of the radiator, as I do have a question in regards to it. As I said, all the cables seem fine and are all making proper contact.

So if you take a look at this guy, you can see those two grommets on the inside aren't the same... I'm not sure if that was done on purpose and whether I should leave them alone or just put the one on the right into place. This also makes the entire innards off-centered - http://i.imgur.com/cnzgCql.jpg

Here's a picture of it longwise - http://i.imgur.com/1zbsyTm.jpg

And two pictures of the circuit boards, excuse the quality - http://i.imgur.com/jONoYB5.jpg http://i.imgur.com/6jFunaP.jpg

[g1]

  That inner grommet could well be the problem.  The pin should be in the center of the grommet.  That will allow the inner pan to "float" whereas right now it is hung up on the pin and can't move.
Fix it and see if it helps the issue.

[Roly]

radiator

eh?   

Oh yeah, I can see that now, however it would be helpful if we stuck to conventional terminology to avoid confusion; the whole thing is a (reverb) "tank" or (reverb) "springline".



Woah, there's ya problem, right there.  g1's on it.

Look at the internal floating chassis.  Towards each end it has a grommet with a locating pin.  The idea is to limit the travel of the internal floating chassis under extreme shock.



Now look at the grommet and pin on the left hand end and compare to the grommet and pin on the right hand end.

The left hand one is as they both should be, the pin within the grommet hole with some spare space around it.

Now look at the right hand one where the pin has somehow become trapped between the grommet and the floating chassis.  This will mechanically connect the floating chassis to the main chassis and is undoubtedly the cause of the greatly increased sensitivity to external vibration.  Your "floating" sub-chassis isn't.

Add some extra foam padding where the outside grommet is missing by all means, but the basic cause of your excessive sensitivity is the miss-location of the over-travel limiting pin.    {It may not be a bit of broken plate, but it is having exactly the same effect of rigidly mechanically coupling what should be a free-floating assembly to the outside world.}

Make it like the other one, allowing the internal sub-chassis some freedom to float, and your problems should be over.


{It's hard to imagine how it got displaced like that, it would require a very heavy shock just to displace the floating chassis that much, then even more force to drive the pin back between the grommet and the sub-chassis.  Since this is exactly what these pins are supposed to prevent I suspect that some heavy-handed "busy fingers" have been at this assembly at some point.

I've seen a Fender Twin go cartwheeling down a dirt road and Marshall stacks topple over, and I find it hard to imagine an impact strong enough to do that, yet leave the rest of the amp case intact.}

HTH