MP1 Classic | Hum in Dist. Tube Voicing

[MarshallJMP]

Schematic;MP-1 Classic Power Supply & Peak Meters section B4

On the PCB,on the right side of C186 (3300µF16V).It's one of those 4 big caps near the transformer,the one closest to the front.

[Griphook]

Thnaks for that info.
I just measured both the R382 and also the AC coming from the stepdown Transformator.

R382 has got 503kOhms which is the maximum tolerance of that Resistore right? I first have to find a local dealer who has Resistors with this tolerance.

And just for Interest, I got abot 113V AC coming from the Power Supply. Is this too high or just right?


Are the Voicing Curcuits seperated from each other or is this R382 an "over all" Resistor? And is there anything else I can check, before I start soldering, so I can just do it all in once?

[MarshallJMP]

Did you desolder one side of the resistor?You have to do this to get an acurate reading.Else you measure through other circuits.

I think the standard US voltage is 117V??But 113 should be fine.

[Griphook]

No, didnt de/soldered anything. Okay, so my measurement is not helpful at all ^^

Wikipedia says 120V O.o
But the Stepdown Trafo only provides 110V.

EDIT: To get that higher volume of TP9 I believe the R382 has to be lower than 499k?
Although I dont thnik so, can too less Power (110V instead of 120) damage my curcuit?

[MarshallJMP]

Not helpfull well not correct, I think it's even a bit higher.

The higher the resistance the higher the voltage.

Nah a lower voltage won't hurt.

[Griphook]

Since there is another topic with my MP1-Classic, I thought, I just replace this one too.
Do you think, a 499k 5% would be ok, instead of using 1%?

[MarshallJMP]

Well try to get as close as 499k

[Adafan]

Hi Everybody,

I come on this post because I trhinking to have the same problem...
I have a whistling only on the tube distortion.
And this doesn't disapear when I roll off OD 1 and OD 2... But

I measure the 200V test point And I am 209 V. This seems to be High apparently.

Problem is that I a m a newby in electronic  :dunno:

Impossible to find the R382. How do you do to finding the "right" resistor?

If somebody have pics for me, that will be great...

Sorry for this request, but I don't understand how find the right resistor without pics or putt-off all the resistor...  :dunno: :dunno: :dunno:

Sebastien



PS : Sorry for my English

[rnolan]

Hey gibson2612, it's a bit blurry (see attached) but I'm pretty sure R382 is vertical mounted and next to (to the right) of C186 which is the  last big power capacitor in the group of 4 in the top right hand corner of the schematic (C193, C183, C182, C186).  So these are part of the power supply and near the power transformer. As MJMP said earlier  :thumb-up:

Schematic;MP-1 Classic Power Supply & Peak Meters section B4

On the PCB,on the right side of C186 (3300µF16V).It's one of those 4 big caps near the transformer,the one closest to the front.

[Adafan]

Yes, thanks my friend. Your document is absolutly what i need. I check this tomorow and coming to you ; ) ; ) ; )

Thanks again.

Seb

[rnolan]

No worries, I hope it sorts the issue for you.  Haven't heard if it worked for Griphook yet.
So you need a 499k ohm resistor with a tolerance of 1% (may be harder to get as allot of resistor tolerances are 5%)Tolerance = how much a resister can be up + or down - from it's stated value.  And ADA wouldn't have used a 1% if the didn't think it needed it.

[Adafan]

I check it today. And she give me 510/511 k... I going search one with 1% tolerance. But that seems to be hardly...
You think i will checking somewhat else???

Sebastien

[rnolan]

Did you desolder one side of the resistor?You have to do this to get an accurate reading. Else you measure through other circuits.

I think the standard US voltage is 117V??But 113 should be fine.

Hey gibson2612, that's a similar reading to the "incorrect" reading Griphook got.  As MJMP says, you have to desolder (and pull out of the PCB) one side of the resistor to get an accurate measurement (or desolder both ends and remove it, then measure).