MP1 Transformer Hum?

[gindaddy]

Hey all... Noticed for the first time last night some minor hum in the transformer of my Version 1.38 MP1.  I've only had this unit for about 2 weeks, so new to me.  How much transformer hum is normal?  It does not really seem to be in the audio path.  I am looking at the MDRT, of course, but was wondering if this is normal for these stock transformers.  I did not notice it for the first week or so, but I could have missed it.  Was also wondering if anyone knows if the FX loop is before the EQ section in the MP1? Thanks...

[MarshallJMP]

Did you check the screws holding the transformer, they might be loose a bit?

[rnolan]

Hey gindaddy, the 2 screws that mount the transformer (well (pedantically) they are probably bolts) have their nuts inside the case, so pop the lid when you tighten them so you can ensure the bolts don't spin as you tighten.  If this doesn't fix it (a "little" hum is probably normal but in a rack you shouldn't notice it), then put in an MDRT, not only are the MDRTs quiet, they really open the unit up dynamically in a very nice way.

The loop is after the eq (as it should be (for a bunch of reasons)).  The loop send is always active and can be used as a mono out (useful if you are using a mixer of some sort (as some of us do) and you need another Fx/aux send that the mixer doesn't have (eg line mixer with only 1 stereo Fx send).  The loop return is toggled on and off (in/out) via the patch setting, it doesn't affect the send.  Remember the loop level control is a dual ganged opposing pot (turning send up turns return down and visa versa).

[gindaddy]

I did check out the bolts holding the transformer in the chassis, they were good and tight.  Definitely mechanical noise in the windings, as you can press on the windings, and the sound does mostly go away.  It does seem to be inducing some hum in nearby components, (TC G Major, in particular )... hmm... Looks like the MDRT is in my future, I assume it is a superior transformer in all ways...

[Iperfungus]

This is one of those strange issues a human being cannot get rid of.  :lol: :lol: :lol:

My MP-1's old transformer has always been dead silent...and the new MDRT is as well.
No hum. Never.

The JMP1 instead has some "hum" with the top lid screwed to the unit....if I remove the lid, no "hum"....when I put the lid in place, "hum".

A similar behavior I found on the B200S power amp.

At the end, I just decided that I can live with this...since the "hum" is very, very low.
Who cares.

[rnolan]

The MDRT is indeed a superior transformer in all ways  :thumb-up: (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm)

"The MDRT is a 24VA transformer which can deliver 12.6V to the heaters.The high voltage has gone up to 240Vdc / 8mA.
The original is only a 12VA transformer,only deliver between 8 and 9 V to the heaters and the high voltage is 190Vdc / 4mA.
So the MDRT will enhance the sound,better low end,less noise and the sound will sound less compressed."

[Iperfungus]

The MDRT is indeed a superior transformer in all ways  :thumb-up: (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm)

"The MDRT is a 24VA transformer which can deliver 12.6V to the heaters.The high voltage has gone up to 240Vdc / 8mA.
The original is only a 12VA transformer,only deliver between 8 and 9 V to the heaters and the high voltage is 190Vdc / 4mA.
So the MDRT will enhance the sound,better low end,less noise and the sound will sound less compressed."

Yes, it is!  :thumb-up: