morley wah-volume hum

[lonewolf]

I have a morley wvo pedal that is quiet when first turned on...after a while it develops a hum..the transformer also gets pretty hot as well...anyone have any ideas why this is happening?..all the electrolytics have been replaced

[deadastronaut]

..all the electrolytics have been replaced

i'd check that first...correct way round?...+  -

http://www.morleypedals.com/downloads.html

[Paul Marossy]

Transformer getting hot I wouldn't worry about too much, that probably isn't abnormal. I would probably start with checking the orientation on the electrolytic caps and going from there.

On anything with a transformer and diode rectifier in it, I always suspect the power supply filtering if it's making noise like that and I've ruled out other potential sources for the noise.

[lonewolf]

..1) I have checked all of the caps for correct polarity.....2).the voltages stay the same as the level of gain increases.(+25vdc/+55vdc).it is not like a 60 cycle hum or dc leaking past a decoupling cap....could it have something to do with the darlington transistors(MPS-A12/MPS-A06)...??something is causing the gain to increase with the device sitting on(no guitar signal).causing the noise...as the gain increases so does the heat from the transformer....3)..the resistors are all within tolerance...

[Paul Marossy]

Hmm... I suppose it could be those darlingtons to blame. I don't suppose the LDR could have anything to do with it? I don't know, I have zero experience with those things. 

[lonewolf]

this is a tricky one for sure...I dont think the ldr's are the problem since they are similar to a pot...If I stick my finger in front of them they act as they should....I am going to socket the transistors and replace them with MSP-A42 ones...they match the nte numbers...mammoth electronics have a MPS-A12 # I dont  know about the A06 part...probably a voltage rating difference..one transistor is for the boost the other is for the wah circuit...0.99 cents for 30 of them from china via ebay...I should probably have just gutted it...but already in $$$$ replacing all the electro radials...

[Paul Marossy]

It seems like something is drifting with a change in temperature. But what? Curious problem you have there...

[lonewolf]

I agree...Found this in my closet ..I didnt know I still had it...stopped using it around 1985 because of the humming.....I thought the electrolytics were the cause...but It made no difference...I dont think the resistors are causing this...there are 3 green little poly caps and the darlington transistors......I dont think replacing the input or other film caps will solve this...so I will roll the dice and swap the trans....

[runmikeyrun]

had a similar issue with a Boss pedal a few years ago.  Turned out it was a bad filter cap on the PS, the one that goes from positive to negative.  Check that if your pedal has one.  I knew mine was bad because it was getting hot to the touch.