I Think I now want to Tackle quieting Down my Pig

[Platefire]

It's a Pignose G40V. Stock except I modded the cab/Baffle to take a 12" Speaker instead of a 10". Also I run a 12AY7 in V1 for a cleaner more Fender like sound.

I'm happy with the performance of the amp except it's got a pretty loud hum that gets louder as you turn up the Master Volume. You turn the MV all the way down, hum completely goes away. So I'm thinking that means the issue is in the preamp??!!

I've tried different known good tubes and has seemingly no effect on the hum. I haven't replaced the filter caps, but on the other hand, I don't think it is the filter caps or wouldn't it hum even when the MV is all the way down?

I avoid this amp because of this hum but otherwise it's a pretty good sounding amp----so I need to get this solved. It's small, plenty loud and easy portable----so I would appreciate suggestions of how to trouble shoot this. pdf Schematic attached. Thanks, Platefire
 

 

[sluckey]

That pig is a copy of the high gain Marshall Jcm-800 2204. They are known to be noisy. I've never heard any sound clips from you that would indicate you are interested in this type amp.

Wanna try a simple experiment? Temporarily turn it into a Plexi. Simple. Temporarily remove R14 and R15 (disconnecting only one end of each resistor is good enough for this test). Use a gator clip lead to connect the VOL pot directly to V2A grid. Of course you can just solder a wire jumper. This removes the V1B cold clipper stage and makes the amp sound like a Plexi. Play it some to see if the sound appeals to you. If it does, there are a couple more tweaks that may improve the sound.

See pic...

[Platefire]

Hi sluckey
I've had this amp for 15 years or more. Wouldn't have bought this amp ordinarily but at $50, I couldn't resist.I have used it some when I was playing with a traveling group. With other noise makers around you, the hum is not that noticeable until everyone quits playing:>) I knew it was a modified Bassman F56A circuit but had no idea is was a JMC-800 2204 circuit.

I've avoided working on it because of the PCB. I do love a quiet amp though and clean is my main sound. I use dirt boxes for the OD and Dist. So I've come to the conclusion it would be worth chancing hopelessly butchering this amp rather than it withering away in the closet.

So yes! I would be willing to experiment and try some stuff. You have to realize though after being retired for 10 years, I am now a Wal Mart employee who's main station is in Hardware. So I'm more limited on time now.They say a journey of a thousand miles begins with a single step. So I will pull the chassis and see what kind of mayhem I must encounter to get at these parts to be disconnected. I'm petty sure the PCB will have to be pulled to de-solder at the bottom of the board. Thank you very much Platefire

[Platefire]

Well I did the jumper thing. Except I didn't disconnect R14 and R15. I just disconnected the V1B grid wire where it connected V2a pin #2 and suspended in the air out of the way. I tried running a jumper wire with alligator clips to C21 junction with Vol pot output, but it was just to small and tight to grab hold. So I got some hookup wire and made a pretty decent mechanical connection for the jumper to each connection point. Well the thing sounded great and dead quiet. Since your suggested experiment is a success I would propose this--------why not make it switchable between a Plexi and a 2204???
Seems like it would just require a SPDT switch. Connect the V2A grid pin to center pole of switch, connect the jumper from C21 to one side and the grid wire output from V1B out R15(that I previously disconnected) to the other side. Since the 2204 part of the circuit is still alive, it may as well be made usefull if you was to get a hankering for noisy high gain:>) What you think sluckey? Platefire 

[DummyLoad]

Well I did the jumper thing. Except I didn't disconnect R14 and R15. I just disconnected the V1B grid wire where it connected V2a pin #2 and suspended in the air out of the way. I tried running a jumper wire with alligator clips to C21 junction with Vol pot output, but it was just to small and tight to grab hold. So I got some hookup wire and made a pretty decent mechanical connection for the jumper to each connection point. Well the thing sounded great and dead quiet. Since your suggested experiment is a success I would propose this--------why not make it switchable between a Plexi and a 2204???
Seems like it would just require a SPDT switch. Connect the V2A grid pin to center pole of switch, connect the jumper from C21 to one side and the grid wire output from V1B out R15 to the other side. Since the 2204 part of the circuit is still alive, it may as well be made usefull if you get a hankering for noisy high gain:>) What you think sluckey? Platefire

because the switch would most likely add more noise than what you had going with the original 2204 configuration. i'd strap V1a + V2b in parallel, but then again it's a PCB, so that may be more of a headache. if you like it now, leave it, use a decent pedal for more gain.


--pete

[sluckey]

What you think sluckey? Platefire

Oink! Oink!

[Platefire]

What you think sluckey? Platefire

Oink! Oink!

Has the tone of affirmation!

[Platefire]

Now if you had said a loud shrill "WEEEEEEEE" I would figured that in the negative. 

[sluckey]

wee wee weeeeeee!

[Platefire]

Hoay ymay! Emay antedway tiay witchablesay


Labay Labay Labay

[sluckey]

Maybe something like this. Probably gonna pop when switched. May help to put a 1M resistor between V2A grid and chassis.

[Platefire]

Hay sluckey, I've already run the jumper, soldered it in and it works great. I thought about the switch a little bit but truthfully I don't think I would ever use it. It's even quiet now with my single coil guitars, so that's pretty neat. I was off today so I went ahead and put it back in the cab. I'm  just thankful the pig is now usable for my purposes, if I want to play it out somewhere. It's so small, portable and loud it qualifies as good grab and go amp. Believe me, in my Senior way, that counts for a lot. Also i appreciate Dummy Load chiming in. It may not seem that I'm listening but I am. Always appreciate and respect your opinions and certainly glad I have access to your guys help through this forum. Don't think I'll be building any more, just improving my old builds. Thanks, Platefire

[Platefire]

Hello Ya'll!!! 
Wanted to come back and on hind sight comment on this jumper mod on the pig. I have really enjoyed this amp since doing this mod. As I understand it, this mod basically or pretty close, made it into a Plexi circuit by jumping the extra gain stage. Anyway I have always been a fan of Allman Bro's Les Paul tone and using my Les Paul through this amp is closest I've ever got to it. Another wonderful thing is the amp noise after this mod is almost dead silent. I love a quiet amp and this one is. So I just wanted the say if you get  your hands on a stock G40V, this is a worthy mod. Platefire

[Willabe]

Hi Plate, glad your loving that amp and glad you stopped in to say hey! 

[Platefire]

Hello Willabe

Good to touch base with you again. Always been a pleasure amping with you guys. Take care, Platefire