to much hum jcm800

[giordydiver]

hi , today I have played my new amp, wow amazing sound , very impressive. the only problem is the hum, it start at 1.5 master and is a lot. what can I do to reduce it?

[d95err]

Impossible to help unless you give more info. Pictures? Any mods?

General hum-reduction methods include improving the grounding and elevating the heaters.

[neikeel]

Impossible to help unless you give more info. Pictures? Any mods?

General hum-reduction methods include improving the grounding and elevating the heaters.

[giordydiver]

so, my amp is a 2203 with 6550, zero loss fx and sir 34 mod.

http://i64.tinypic.com/2qw3gut.png
http://i65.tinypic.com/2lnx1ye.png

[neikeel]

Probably a grounding issue.

However I would tidy up the heater wiring on V1 (tighter neater twists and moved away from the socket hard into the corner of the chassis).

I cannot see where your pot rail, V1 cathode and jacks are grounded - best to a dedicated ground (tight serrated washers cutting into metal not paint/plastic coating) near the input jacks. Make sure that the preamp can has ground to the pot bus tail.

Cut off the pot bus to exclude the bass pot and presence pot. Take dedicated ground wire from the presence pot back to the PI can cap ground in the corner.

That should help. There are other ways (full Larry grounding scheme) but in a relatively high gain amp any extraneous noise (hum/hiss will be amplified as the volume goes up.

[giordydiver]

Probably a grounding issue.

However I would tidy up the heater wiring on V1 (tighter neater twists and moved away from the socket hard into the corner of the chassis).

I cannot see where your pot rail, V1 cathode and jacks are grounded - best to a dedicated ground (tight serrated washers cutting into metal not paint/plastic coating) near the input jacks. Make sure that the preamp can has ground to the pot bus tail.

Cut off the pot bus to exclude the bass pot and presence pot. Take dedicated ground wire from the presence pot back to the PI can cap ground in the corner.

That should help. There are other ways (full Larry grounding scheme) but in a relatively high gain amp any extraneous noise (hum/hiss will be amplified as the volume goes up.

ok thank i do a new heater wiring between v1 and v2...v1 v2 and jack are grounded togheter on the pot chassis. i dont understand you last advice for bass and presence pot

other thing my heater voltage is 3.5v for filament and the bias is 48/52ma two valve, 30/35ma other two.

[neikeel]

ok thank i do a new heater wiring between v1 and v2...v1 v2 and jack are grounded togheter on the pot chassis. i dont understand you last advice for bass and presence pot

The inputs need to be grounded to chassis - not just pots.

The second bit means the bus rail is to be shortened and the presence pot (PI tail) has a dedicated groundto the PI filter can.

The idea of the Larry scheme is to break the amp grounding into nodes (inputs, preamp, PI and power section etc). The aim is secure grounding at each node to avoid ground loops and avoid cross talk betwen sections.

Look at the SDM scheme with alternative grounding. 2203 alt grounding!

[giordydiver]

ok so, new wires to v1 an v2, presence wired to pi filter cap, input wired to chassis, tap the rail bus to chassis.. correct?

where can i found SDM schemati?

[neikeel]

https://drive.google.com/folderview?id= ... jdaSFNBOGM

[giordydiver]

So i re wire heather v1 and v2. For the ground I listen your advice. I isolated imput, preamp, presence and PI filter, final ecc...each of this node ground separately on chassis. check my layout i have ground together PI filter , 0 of heater from PT, and bias wire from PT , so now I have isolated each of this..tomorrow I try, I hope this reduce the hum

[giordydiver]

So i re wire heather v1 and v2. For the ground I listen your advice. I isolated imput, preamp, presence and PI filter, final ecc...each of this node ground separately on chassis. check my layout i have ground together PI filter , 0 of heater from PT, and bias wire from PT , so now I have isolated each of this..tomorrow I try, I hope this reduce the hum

So I tried the amp, I can notice a better sound ,more definited and also with 10 on gain I have no hiss. But the hum situation is the same, maybe a bit less, but it start at 1 master volume and at 4 of master il too too much what can I do?

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http://s14.postimg.org/72k29fqgx/image.jpg
http://s2.postimg.org/74vhrrqrt/image.jpg

[danman]

Have you tried replacing preamp tubes in v1 and v2 yet? If the MV affects the volume of the hum then it may be one of the tubes before the PI.

[giordydiver]

talking to an engineer friend who works in this camp would say that certainly the cause is the induced magnetic field caused by the transformers too close and rings that are created in the holes in the frame under PT. other can be a potentisl different to hight between heater circuit and anodic circuit

[herbvis]

Get an fx loop. Put an isp decimator in it. No more hum or hiss.

[Doug H]

beautiful amp.

The v1 heater wire is still less than perfect. I don't know how easily hum can be induced into the plate wire, but one of the plate wires spends some time parallel to a single heater wire, that's the kind of thing you want to avoid. For the moment you could bend the blue wire such that it wasn't running alongside the red heater wire to rule it out.

Where are the speaker jacks grounded? I think I see the common, but where is the ground reference for the speakers?

A great article on grounding. I'm not suggesting changing everything as suggested in this article, but it might give you some ideas as to the source of your hum.

http://www.aikenamps.com/index.php/grounding