Humidity?

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 8 Jul 2015 4:39 pm

As I mentioned in a recent post, I picked up a 1977 LTD400 a couple of weeks ago. I've gigged with it twice and love it. Something weird going on, though.

On Monday evening, the first real swampy weather of the year rolled into New Hampshire. By Tuesday a.m. (yesterday) we had very high humidity, thunder storms, heavy rain, etc. It was a sudden and radical shift in humidity. I noticed that the LTD suddenly had lost its highs; I had to completely reset the eq on the amp to get anything like the sound I had been hearing for the past two weeks. Today it was going the opposite way (although it could have been partly a result to me confronting the new eq I had dialed in): all thin and brittle.

Here's where things get very interesting. By late afternoon, the amp was starting to give a noticeable harmonic distortion; not a pleasing sound on a Peavey. I did a quick check to make sure it was the amp; went straight into the amp, tried my NV400, etc. Yup: it was the amp.

But(!) around the same time, the weather broke (actually an hour or two earlier). There was a precipitous drop in the relative humidity; down from @90% to @50%. By the time I tried the amp again after dinner, the sound had returned to normal.

Even though I keep my study controlled for humidity, the dehumidifier was struggling to keep it below 55 all through yesterday and today, then it plunged to about 48 in my study in less than an hour late this afternoon.

I know that humidity can affect tone pretty strongly, but can it affect an amp that way, making it swing back and forth tonally and even distort? I would guess this amp has the original filter caps and could use an overhaul, but it seems weird that it would go back and forth tonally so quickly--all in line with the stark changes in the humidity from Monday through this evening.

Thoughts?

Craig Baker · Post by **Craig Baker** » 8 Jul 2015 8:35 pm

Hi Dan, Interesting post.
With Li'l Izzy operating at very high input impedance, I have found humidity to definitely cause problems. This is why the circuits are sealed. Believe it or not, humidity and contamination really make a difference. Also, it is important to clean all flux from around and between any high impedance points on the circuit board.

As crazy as it sounds, even keeping the insulators clean on the 1/4" male plugs is important to preserve the high frequencies. This has been my experience, and when you mentioned high humidity and loss of highs, you got my attention and I just wanted to share.

Hope this is helpful.

Craig

Darrel Roberts · Post by **Darrel Roberts** » 9 Jul 2015 7:37 pm

Probably a bit odd but I've never had a problem with it. I live on the coast of Alabama/ Florida and have played most of my adult life usually 100 yards from the Gulf of Mexico. There's bar/ resteraunts all up and down the beach as you could imagine. Never had a problem. Played the same bass amp (David Eden) that I bought in the 80s. Still sounds like gold. Ok I had to replace the fan. The place I play most will run six bands a day. Now they do leave all electronics powered up 24/7. They've got three stages. As far as amps, guitar, bass, and steel, no problem. I lived on a boat for ten years. All gear aboard. All sill in use with no problems. May be an exeption but can't think of any other players complaining. Just my experience.

Craig Baker · Post by **Craig Baker** » 9 Jul 2015 8:34 pm

Darrel,
My case is probably the exception. Over the years, I never had a problem either. Then a few years ago I was testing a Li'l Izzy, getting it ready to be shipped and it just sounded like a bare wire. I fooled with it for an hour or two, took the board out and it measured OK. Re-assembled it and it failed to operate properly. Finally, I noticed some contamination around the tip insulator on the 1/4" plug. Cleaned it thoroughly and "bingo" it worked like a charm.

Later, I got in touch with the IC manufacturer and learned that contamination and humidity can play havoc with high impedance circuits. I tested the circuit using a quick spray of water and sure enough, it immediately ceased to perform properly until I dried it thoroughly, overnight. If it were purified water as in a laboratory it might not have the same effect, but humidity in the air is far from pure.

So the problem is indeed rare, but I am now a believer.

Sincerely,
Craig

David Higginbotham · Post by **David Higginbotham** » 9 Jul 2015 8:40 pm

I live in Southwest Louisiana surrounded by water with atrocious humidity and I've never encountered an amp issue like you've experienced. I'm fairly certain you may have other electrical problems that may be exacerbated by high humidity or lack thereof. No question as to whether humidity affects wood, we all know it does. But sealed electrical components in amps and other electrical equipment I think would have been addressed during the engineering phase.

Also, amps heat up fairly quickly and would act as a drier inside the amp which would certainly reduce or eliminate the amount of moisture in the air.

I have experienced those amp issues when pots were bad, capacitors that were old, and dirty input jacks.
Dave

Rich Upright · Post by **Rich Upright** » 10 Jul 2015 12:12 am

I think it's all psychological. I live on Florida's western Gulf Coast, which is Humidity City, & I ain't never had a problem with an amp, guitar, steel, whatever. Only problem was speakers disintegrating from the humidity. Happened to my BW & to my Cerwin-Vegas in my stereo.

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 10 Jul 2015 6:00 am

I'm thinking that it is as David hinted: an electrical problem in the amp being exacerbated by changing humidity. Or maybe just an electrical problem; the more I think about it, even if my dehumidifier was having trouble keeping up those two days, the level never did go above 57 or below 45 in the room, so it shouldn't have hit the amp hard.

One factor I failed to mention (but was reminded of by Craig's post) is that I just started using the buffer feature in my Goodrich LVW pedal (a 120 with a "built-in" matchbox). But that shouldn't have an effect either.

I think it's all just a reminder that this is roughly a 40 year old amp and is way over due for some basic maintenance, some new caps, etc. Now to decide where to get that done. Anyone know whether the Peavey factory would be amenable to installing some of Brad Sarno's recommended replacements? I'm guessing not. I'll probably seek out someone local to do the work.

Thanks for all the feedback, folks![/b]

Craig Baker · Post by **Craig Baker** » 10 Jul 2015 9:31 am

Dan,
Are you certain it's the amp that's at fault? Try the guitar direct to the amp. . . then add in the volume pedal. Could it possibly be happening in the high impedance buffer circuit? I don't think Goodrich sealed them.

After WWII, there was a pile of surplus radio equipment available, some new, some used, but the circuits were all coated with a clear varnish to keep out moisture and fungus. It wouldn't surprise me if Georg remembers this.

Craig

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 10 Jul 2015 9:37 am

Craig,

when the problem was occurring, I went straight from the guitar to the amp, and had the same sound. Also tried swapping cables. Also tried going into my NV 400 where there was no problem. It was the amp.

Craig Baker · Post by **Craig Baker** » 10 Jul 2015 10:07 am

Dan,
If that's the case, you either need a tech who's good at troubleshooting, or one who's good at guessing.

It will be interesting and educational to learn what the cause is. Please let us know.

Craig

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 10 Jul 2015 10:11 am

I should add, though, that the problem has not returned.

For a 1977, this amp is extremely clean, so I'm guessing it hasn't been "rode hard and put away wet." My hunch (hope?) is that replacing some of the components that tend drift over the decades, and checking all the solder connections should take care of any lurking ailments.

Craig Baker · Post by **Craig Baker** » 10 Jul 2015 11:48 am

Georg,
I remember modifying WWII Command sets in the early '60s. The varnish was a pain to remove before soldering was possible, but they worked in B-17s and their dots and dashes earned some QSL cards for me.

If I recall, the varnish was supposed to fight-off the high humidity of the jungles.

Craig

Jack Stoner · Post by **Jack Stoner** » 10 Jul 2015 1:30 pm

I've been in Florida 19 years and the only "humidity" problem I've run across was flakey jacks in the house amps at Catfish Johnny's Restaurant (where we have the Florida Steel Guitar Club jams).

I was in the staff band there for 13 years and also maintained all the equipment. Two amps, both Peavey, had to have the input jacks cleaned every November when we started the Winter season shows/jams. One amp was a TNT115S bass amp and the other was an older hybrid guitar amp (solid state preamp and tube power amp section). There was also a Peavey XR600F PA amp but it never had a jack problem in either the XLR or 1/4" jacks.

I'm sure there are others, but those are the only two I've encountered. I've never had a problem with any of my own equipment.

Richard Sinkler · Post by **Richard Sinkler** » 10 Jul 2015 3:35 pm

I don't suffer from humidity problems. I suffer from HUMILITY problems.

Sorry Dan... I having a tough time right now, and humor (not that this was funny) is the only thing keeping me going.

Now back to our regularly scheduled program.

Dave Grafe · Post by **Dave Grafe** » 13 Jul 2015 12:52 pm

Sounds like Molex

John Billings · Post by **John Billings** » 13 Jul 2015 3:17 pm

For a reason having nothing to do with amps, I am starting to be suspicious about transformers and humidity. I have something, not an amp, that works perfectly when the humidity is low, and does not work when it's high. It's a florescent ceiling fixture. Nothing in it but a transformer.

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 13 Jul 2015 3:48 pm

Well, I think I may have uncovered a sad truth behind the shifting tone of my amp: the hearing in my left ear seems to be a lot clearer than that in my right. Can I send my head to Peavey to get it fixed???

John Billings · Post by **John Billings** » 13 Jul 2015 3:49 pm

See an ENT, right away!
JB

Donny Hinson · Post by **Donny Hinson** » 13 Jul 2015 5:10 pm

Humidity may affect a speaker or cabinet, but the heat generated when an amp operates should preclude any affect on the amp, itself. Amp placement and room acoustics can wreak havoc on sound, too. An amp will have different sounds, depending on how close it is to a wall, and how high the ceiling is.

Don't sweat it. Get the best sound you can, under the circumstances, and then just go on playing. Inconsistencies can never be eliminated, because there are just too many variables in the equation. $:\$

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 15 Jul 2015 3:50 am

**UPDATE**

So, today another round of pea-soup-like humidity rolled into town and, sure enough, the thin and (very slightly) distorted tone returned to me LTD 400. The humidity on my study had not gone up much, and the dehumidifier wasn't even running when I came in this morning, so it couldn't be fighting too hard to keep up.

I went through the usual sequence of eliminating culprits. But(!) this time I heard the same distortion in my NV 400 (did I just miss it before??). When I swapped out my volume pedal everything cleared up on both the NV and LTD 400.

So, it is something going on in my Goodrich LSW, an old version of the 120 with a battery-powered buffer built in. I had never used the buffer feature until shortly before all of this started occurring, so there must be some connection. Even if I switched off the buffer, the altered tone and distortion persisted. This would suggest it was something other than the buffer circuit causing the trouble. But when I put in a new battery, this pedal sounded fine. That shouldn't have made a difference with the circuit switched off, but it did, so there you go.

The main news for me is that the LTD is fine (which is really welcome news because I love this amp!). I usually bring an extra vp to gigs. I guess now I'll just keep really handy for a while, and I'll plan on making sure my spare 9v is fresh.

Craig Baker · Post by **Craig Baker** » 15 Jul 2015 6:57 am

Dan,
If you still have the old battery, it would be interesting to measure the voltage under its normal load while operating the buffer. We've had units operate as low as 2 volts, but there is a point where the wing stalls and you crash. Circuits are designed to operate at their proper voltage. When the power supply is out of parameters the results can be anybody's guess.

Craig

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 15 Jul 2015 8:09 am

Craig:

well, this is very weird. The old battery reads 8v. What the heck? So it wasn't the battery. I'm stumped.

Dan

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Humidity?

Humidity?

Not the amp!!