Amp sounds great at home but not at church

[guiltless]

An all too familiar problem. My amp (cathode biased, LTPI, el34, 5e3, Plexi, 18watt mutt with 390 at the plates and biased to 100%) sounds phenomenal when in the garage with 116-117v at the wall. When I get to the church, which is an old High School theater, the amp breaks up with a nasty fizz. I am sure the power is pretty dirty and a conditioner is needed. I haven't measured wall voltage there yet but I am wondering if getting a full 125v there would make my amp sound like this? I am wondering if a bump in voltage may alter my bias enough to possibly enduce crossover distortion?

I am tempted to bring a variac and a dmm everywhere I go so I can ensure 116v every time.

I am realizing that the amp was built in the garage with 116-117 at the wall and that has likely influenced my biasing resistor choices.

Any thoughts? Am I on the right track in thiking that I either need to carry a variac or bias the amp at an outlet with 120-125v?

Thanks in advance!

[Blue Strat]

We can either guess your can find out what's really happening. The voltage difference is a good theory. Then there's the difference acoustics of the rooms and untangibles like different days which confound us continually.

[guiltless]

It's definitely not a room acoustics issue. I compared the amp in the 2 locations with my head in front of the speaker. I definitely want to measure the voltages.

Oh, and the churches power amps flicker on occasion as well as random noises in the wireless systems.

[jay42]

I am tempted to bring a variac and a dmm everywhere I go so I can ensure 116v every time. More like an oscilloscope in this case.

[guiltless]

More like an oscilloscope in this case.

That would be my thought if the problem happened at home. But the issue seems to be the variation between locations. If it does turn out to be purely a voltage issue then I will likely try to get it on an oscilloscope and a variac and see why is going on at the different voltages.

I fear BlueStrat's comment about "different days" may be the case as it so often is :-/

We are moving locations soon so hopefully I will be leaving this issue behind. Though I really want to find out what it is.

[pdf64]

Another thing to consider is radio interference - if that gets on to grids it can screw up bias. Is the open side of the chassis shielded? Have suitable grid stoppers been used, especially at inputs?
Using a different longer guitar lead at church?
May be beneficial to check all tube cathode and plate voltages at both locations.

It's definitely not a room acoustics issue. I compared the amp in the 2 locations with my head in front of the speaker.
And you cranked the amp? Hope you used ear protection. Put more value on your hearing than to fritter it away.
Pete.

[Prairie Dawg]

G-d don't like electric guitars none. They's the spawn of the debbil. That's why you got them problems. Signed, Jeeter and Lester.

[guiltless]

G-d don't like electric guitars none. They's the spawn of the debbil. That's why you got them problems. Signed, Jeeter and Lester.

Ha ha ha. Got a good laugh from that one.

And don't worry Pete, my head wasn't literally in front of the cab. I was trying to make sure it was known that I was in front of the amp and not somewhere else listening.

Also, the head is actually all metal as it is a Bogen CH18 conversion. So it is shielded all around.

[Chrome Dinette]

You mentioned the place was formerly a HS theater. Make sure you aren't plugged into an outlet connected to a dimmer.

This could be dimmer related even if you are not plugged into one, but rule out the simple stuff first.

[guiltless]

Oh wow, I can't believe I never though of that. Thanks for the heads up!!

[guiltless]

Would something like this work well as a substitute for a Furman rack conditioner? I know it is not a regulator, but it says it is a conditioner and filters EMI/RFI.

http://www.overdriveelectronics.com/products/Panamax-PM8%252dEX-8%252dOutlet-Power-Conditioner%7B47%7DSurge-Suppressor.html

[HipKitty]

All rooms, regardless of their location, impart their own acoustics to an instrument...electric or acoustic, hence differing qualities of sound reinforcement products and services. Too many variable to detail here (or bore anyone with).

With that being said...a voltage test of the questionable power outlet would be the easiest rule-out.

[guiltless]

All rooms, regardless of their location, impart their own acoustics to an instrument...electric or acoustic, hence differing qualities of sound reinforcement products and services. Too many variable to detail here (or bore anyone with).

With that being said...a voltage test of the questionable power outlet would be the easiest rule-out.

Very excellent point. I would like to reinforce that this is definitely not a room acoustics issue. There is definitely an issue happening electrically or electromagnetically.

I will definitely be testing the outlet on Sunday.

[kevmin]

Does your church have a tube organ, such as a Hammond C3 with a tube Leslie? I noticed a problem being on the same circuit as the organ. I guess the power draw was too much. I plugged into an outlet on a different breaker, and my amp sounded normal again.

[guiltless]

Does your church have a tube organ, such as a Hammond C3 with a tube Leslie? I noticed a problem being on the same circuit as the organ. I guess the power draw was too much. I plugged into an outlet on a different breaker, and my amp sounded normal again.

We don't have an organ. But I fear that I am on the same circuit as the entire lighting system :jo

I am going to do some digging around on Sunday. This may all be moot soon as we may be moving.

[joeymazzola]

if you are using a wireless system at church, that could likely be the difference when it comes to your tone.

[guiltless]

Well, voltage out of the wall is 117v. Great for me, not for the amp racks. But that also means my issue is purely with the amp. Which was likely the case anyway.

I already pulled the 1000uf power cathode bypass cap and swapped it for a 100uf. That definitely helped a lot. I added a 47pf between the PI plates. Again, a subtle change. I then added a 100pf between the plate and cathode of V1... This change I didn't like. This will be removed.

Next, I am going to change out V1 from a 6sn7 to a 12ax7. I think with all of the boosting I do with pedals, the 6sn7 may not be taking kindly to them. And since I have too much trouble finding a good 6sl7, I am going to join the post 1955 world and go novial.

[Structo]

You are only getting 117v out of the wall there?

Man, if I owned a bunch of vintage Fender and Marshall amps, I would move to Orange County pronto.
Up here in the Northwest I'm at least at 120v, sometimes up to 124v.

But we have cheap hydro power so maybe they are more generous with the volts. Heehehe

[guiltless]

I am reviving this thread because I am finding this problem is popping up again. In my garage, wall voltage can be anywhere from 113-117. Our central church campus has wall voltage from 118-122 and is a purpose built sanctuary. Our southern church campus meets in a Jr High Multi-purpose room. In the garage and at the central campus, the amp sounds clear, punchy, articulate, bold... All of the things I built it to be. But when I plug in at the south campus, it sounds thinner and has that unmusical fizz in the overdrive. It sounds like blocking distortion. It also does it with the amp set clean, but using an overdrive pedal. Am I looking at nasty power here now as well? This is a different building than when I first posted, that is why I am rehashing. I have a nice power strip/"conditioner" with RF filtering, but it doesn't change things much.

I am not super concerned about maintaining line voltage but would a 1:1 transformer that I can put in a box help clean things up?

[Blue_n_Jazz]

1:1 would isolate you. A few volts +/- should not have that huge off an impact, unless your specs on your build would require that. Have you checked your source wiring/phase? If you haven't bought a circuit tester, DO! $7 at Lowe's or Home Depot could indicate if your PS is corrupt.
That said, I don't think it is electrical power source as the primary problem. Get another amp, a buddies if you have to, and repeat what you have been doing. I could be wrong, but I don't think you will find the same problem. If it does, there's your answer.
I am thinking it is in your amp. Go over the specs carefully and check and check. Re-solder your joints, check tubes, cables, the obvious.
Also, how are you supplying power to the amp from the wall? Exstention cord? If so, what gauge and how many feet?

[guiltless]

I'm not doubting that it could be my amp, but why would it sound great everywhere but that one location? We are pulling near capacity power wise at that building and are not running any sort of regulated power unfortunately. I have to plug into a 25' extension chord that, unfortunately, the other guy's amp (Orange Rockerverb 50) is plugged into. His amp doesn't sound as good there as it does at the Central location as well.

[Blue_n_Jazz]

What gauge is the wire? That is really important! IT sounds as if you have a slight decrease in power at that location. Combined with an extra 25' of cable, your amp which DEMANDS all the power it can, I think that is your answer. I am speculating that your extension chord is no more than 14 gauge wire, which should be OK. If it is 16 gauge, ditch it and save for you Christmas tree lights. I'd check to see the amperage you are pulling thru.
Do you need 25'? Go make an extension chord. Shorting it to 10' of no less than 14 gauge. I made mine out of 12 gauge. Remember that the longer the chord, the thicker the wire you need to compensate for loss.
Cumulative affects, thats my thoughts. If two amps are working inefficiently then power might be an issue. Find your power source amp rating, the length of it.