Blues Junior Noise

CasinoBoogie · June 26th, 2008, 11:21 AM

Hi folks, seems there are alot of Blues jr. users around here so I thought someone may be able to help me out

Picked up a Blues Jr. this morning, tried it out in the store a bit and but not for extensively as I've borrowed one a couple times before for gigs/recording

In the store everything was cool but getting it home I realised when you turn it up full whack there is a horrible kind of moan. I expect a little hum but it doesn't sound healthy, anyone else get this??

The box i took home was the last one in the store and the demo amp and they did say I could bring it back when they have new ones in and swap it for a boxed one. might be worth doing

teleamp · June 26th, 2008, 11:29 AM

Return it, unfortunately, its cheaper for Fender to pass the QC responsibilities on to the consumer.

CasinoBoogie · June 26th, 2008, 11:32 AM

you know I have never bought a single piece of guitar gear or even guitar that I haven't had to return or get fixed, its such a pain since the store wont get the amps in for a couple of weeks so i can't gig with it next week

Billm · June 26th, 2008, 11:52 AM

"horrible kind of moan?"

Sounds like it's haunted.

Is it a continuous sound or is it on the trailing edges of notes?

If the former, it could be a microphonic tube that you hear when you crank it. If the latter, it could be phase inverter oscillation. There's a simple cure for PI oscillation:

http://home.comcast.net/~machrone/bjr/oscillate.htm

CasinoBoogie · June 26th, 2008, 12:22 PM

No its continuous, underlying hum, like the sound of one of those mini fans or something or hair clippers

I tried it with humbuckers and its not as bad, still present though

Billm · June 27th, 2008, 06:25 AM

If the amp only does this with a guitar plugged in, it's most likely amplifying electrical interference via the pickups, as from a fluorescent light or other noise source. The BJr is a high-gain amp and will greatly magnify any noise that gets into the system. But...

Tubes, especially V1, are the largest source of hum. Try swapping V1, V2, and V3 (the 12AX7s) around to see if there's a quieter configuration.

The amp is biased hot, and an EL84 idling at full spec (or beyond) is a noisy beast and you may have a particularly hot-running pair of EL84s. They're probably Groove Tubes and they're color-coded. If they're blue, put in white. If they're white, try red. Or go right to the reds. They run a little cooler. (Go figure why Groove Tubes did the color codes backwards.)

A third possibility is direct coupling from the power transformer to the output transformer, but this is typically not a problem on the export model because the PT is higher quality than the US power transformer. An angled metal shield cures the problem. It looks weird, but it works. More info on my site.

CasinoBoogie · June 27th, 2008, 10:01 AM

gee there certainly are some knowledgable folks around here, I do appreciate you taking the time to try and help me out too

I spoke to the store this morning and they said they're getting new amps in monday and I can just swap it for a new one (mine was the ex demo and they had said anyway i could do this if i wanted) so i think thats the safest option

shame to have to wait and its a hassle taking it back but I do love these amps alot, will be worth the wait in the end

June 26th, 2008, 11:21 AM	#1 (permalink)
CasinoBoogie Tele-Meister Join Date: Jan 2007 Location: London Posts: 161	Blues Junior Noise Hi folks, seems there are alot of Blues jr. users around here so I thought someone may be able to help me out Picked up a Blues Jr. this morning, tried it out in the store a bit and but not for extensively as I've borrowed one a couple times before for gigs/recording In the store everything was cool but getting it home I realised when you turn it up full whack there is a horrible kind of moan. I expect a little hum but it doesn't sound healthy, anyone else get this?? The box i took home was the last one in the store and the demo amp and they did say I could bring it back when they have new ones in and swap it for a boxed one. might be worth doing

June 26th, 2008, 11:29 AM	#2 (permalink)
teleamp Tele-Holic Join Date: Oct 2006 Location: Central TX Age: 49 Posts: 590	Return it, unfortunately, its cheaper for Fender to pass the QC responsibilities on to the consumer.

June 26th, 2008, 11:32 AM	#3 (permalink)
CasinoBoogie Tele-Meister Join Date: Jan 2007 Location: London Posts: 161	you know I have never bought a single piece of guitar gear or even guitar that I haven't had to return or get fixed, its such a pain since the store wont get the amps in for a couple of weeks so i can't gig with it next week

June 26th, 2008, 11:52 AM	#4 (permalink)
Billm Tele-Meister Join Date: Mar 2008 Location: New Jersey Age: 61 Posts: 390 1 Photos	"horrible kind of moan?" Sounds like it's haunted. Is it a continuous sound or is it on the trailing edges of notes? If the former, it could be a microphonic tube that you hear when you crank it. If the latter, it could be phase inverter oscillation. There's a simple cure for PI oscillation: http://home.comcast.net/~machrone/bjr/oscillate.htm

June 26th, 2008, 12:22 PM	#5 (permalink)
CasinoBoogie Tele-Meister Join Date: Jan 2007 Location: London Posts: 161	No its continuous, underlying hum, like the sound of one of those mini fans or something or hair clippers I tried it with humbuckers and its not as bad, still present though

June 27th, 2008, 06:25 AM	#6 (permalink)
Billm Tele-Meister Join Date: Mar 2008 Location: New Jersey Age: 61 Posts: 390 1 Photos	If the amp only does this with a guitar plugged in, it's most likely amplifying electrical interference via the pickups, as from a fluorescent light or other noise source. The BJr is a high-gain amp and will greatly magnify any noise that gets into the system. But... Tubes, especially V1, are the largest source of hum. Try swapping V1, V2, and V3 (the 12AX7s) around to see if there's a quieter configuration. The amp is biased hot, and an EL84 idling at full spec (or beyond) is a noisy beast and you may have a particularly hot-running pair of EL84s. They're probably Groove Tubes and they're color-coded. If they're blue, put in white. If they're white, try red. Or go right to the reds. They run a little cooler. (Go figure why Groove Tubes did the color codes backwards.) A third possibility is direct coupling from the power transformer to the output transformer, but this is typically not a problem on the export model because the PT is higher quality than the US power transformer. An angled metal shield cures the problem. It looks weird, but it works. More info on my site.

June 27th, 2008, 10:01 AM	#7 (permalink)
CasinoBoogie Tele-Meister Join Date: Jan 2007 Location: London Posts: 161	gee there certainly are some knowledgable folks around here, I do appreciate you taking the time to try and help me out too I spoke to the store this morning and they said they're getting new amps in monday and I can just swap it for a new one (mine was the ex demo and they had said anyway i could do this if i wanted) so i think thats the safest option shame to have to wait and its a hassle taking it back but I do love these amps alot, will be worth the wait in the end