Separate names with a comma.
Discussion in 'Epic Threads' started by Sidney Vicious, Feb 23, 2008.
What are the details? Mic'ed? Small house? Type of tunes?
In a nice size bar/burger joint in downtown baton rouge. Not mic'ed, daisy chained with a lil dawg champ.
Rosie Ledet. It's zydeco music.
Right on! Lil' Dawg and a GA-5, nice. I'm gigging mine tonight too...medium sized, mic'ed through the PA. It's been working like a charm. Just enough stage volume.
Voodoo BBQ...we're zydeco/funk from the Northwest
Sorry i have to make correction...i'm a lil burnt
After a few songs, they sound guy mic'ed my lil dawg champ but not the GA5.
I had no monitor for guitar, but the two amps on stage we plenty!
All the tone enhancing mods posted here are very interesting (and nicely documented) and I look forward to trying them (so I can finally put my EE degree to some use). I want to take some time playing the stock circuit with the 8F150 i've got on order before doing much tinkering. That said, I am interested in doing a few things to make the amp as noiseless and free of hums & buzzes as possible. Here's a list of what I've found on this thread so far:
1. Add tube shield to the 12AX7 preamp tube.
2. The thing that made the most difference in noise was shielding the top and edges of the cabinet with heavy duty aluminum foil. Amps spray a lot of noise, that tends to wreak havoc with single coils. Shielding the cab completely seals the electronics electrically, which reduces that crap quit a bit. I use Reynolds heavy duty aluminum foil, spray on some 3M spray adhesive cement, fit to the cab top - in the case of the GA-5, the foil should run down the sides and into the chassis slot to complete the ground. Alum foil makes for a good noise shield.
3. Shield the signal lead off the vol pot to pin 7 of the preamp tube socket.
4. Break the ground buss between the preamp and power sections.
Does anyone have any other suggestions to minimize hum, buzz, and background noise?
Make sure if you break the ground buss, that the new "preamp buss" is grounded to the chassis in some way. I recommend installing common Switchcraft 1/4" jacks, and this will take care of it. However you arrange it, as long as the buss is connected to the ground on the 1/4" jacks, that makes the connection to the chassis.
Single ended amps are bad about hum. Another thing that one can do that will have a big impact, is to convert the filament supply to DC. Gee posted his Baby Vox Mod schematic for the VJ on this thread a ways back, that shows this. I don't believe filtering as high as 4700uF is necessary. I would think that 200uF would be more than enough, but I'm not experienced with DC filament supplies...
Thanks for the reply "Specialty Guitars".
FYI, I was poking around for a more "industrial strengh" shielding foil and found 3M makes several.
The one I found particularly interesting due to the "form factor" can be seen here:
I think a few pieces of this would do the trick!
Tape Type: EMI Shielding
Adhesive: Acrylic, Conductive
Backing, Carrier: Aluminum Foil
Size: 6.00" W x 1.0' L (152.4mm x 304.8mm)
Thickness: 0.007" (7.0 mils, 0.178mm)
Usage: Shielding, Grounding
Alternatively, I'm wondering how the smooth, relatively thick base of a disposable aluminum baking pan would do as compared to thinner "reynolds wrap" product.
Note MOUSER has some good options for 3M Self Adhesive EMI/RFI Shielding Sheets in convenient sizes:
Hey Sevan, you're really on it! Excellent.
I'm not sure that thicker shielding is really better, but I just don't know. I believe that whatever is easiest to work with (some amps use screen instead of solid foil) is the way to go.
If you've ever seen guys who work on sensitive RF equipment, they work in "cages" or "screen rooms" to block any RF and other crap from getting to the equipment they're working on. As long as the metal mesh or screen enclosing the equipment is tight enough to block the wave lengths of the frequencies desired, that's good enough. In an amp, 60 and 120 hz are the big issues, and these are large wave lengths, so even window screen mesh should work as well as any foil.
So I don't believe that thicker foil would be better, but I'm not 100% certain.
I have used self adhesive foil tape for heating duct work that does the trick nicely. You can find rolls of it at Home Depot for a good price. Easy to work with.
I've got a ton of that stuff in my basement - great idea!
I find the HD Reynolds does the trick with a few smears of contact or even rubber cement. Effective. Easy. Cheap.
Has anyone had problems with a cabinet or speaker buzz? It's especially noticeable on the E and A strings and neck pickup, even at low volumes. Haven't been able to find it so far which makes me think it could be the speaker. Thanks for any suggestions!
I have, big time - and it turned out to be parasitics from some instability in the circuit. The remedy is a 1.5k resistor between the preamp socket pin 7 and the signal lead that comes off the volume pot.
On older Fenders, I've seen alum screen mesh stapled to the underside of cab tops, sandwiched between the open chassis bottom and the cab top.
Yep, parasitic oscillations can manifest themselves in all sorts of ways. The ones that sound like a blown speaker, or blown output transformer can send you down an expensive and frustrating long and winding wrong road...
No no no - thanx to Paul!
Some good info about parasitics and how to diagnose & cure them can be found here (from pg 61 onward):