ADA Depot - A Forum To Support Users of ADA Amplification Gear

Let's Get Technical => Troubleshooting Problems => Topic started by: MR THUD on September 14, 2021, 01:27:38 AM

Title: MP1 - Developed very loud hum on tube settings
Post by: MR THUD on September 14, 2021, 01:27:38 AM

Hi Guys,

Im really enjoying my MP1, but it has developed a problem.
On all the tube settings there now is a new loud hum (solid not pulsing and sounds 'transformer'y' ), you can play over the top of it and that seems to cancel it out to some extent. But it is way louder than the usual noise I have been used to with my MP1.

I tried relocating the racks and using a different power point and decent multi plug, but the noise continued.
I tried other input and output leads, but no change.
If you unplug the guitar the noise continues.
If you unplug the amp and other rack effects and only power up the MP1 and just use the headphone out, the noise continues.
I have some (possibly buggered) 12AX7 valves here, so I tried swapping out the two valves in the MP1 but the noise continued.

So, the status is that it appears to be fully functional, but now with loud '60Hz cycle hum'.. or something, but only on the Tube settings. On the solid state patches it operates as before with an acceptable level of 'different sounding noise' (i.e. normal).

Any ideas? or do I need to take to the ADA hospital (Assuming I can find a suitable service/repair guy in the Brisbane area).

Thanks in advance for any help!

Cheers,
Gerard.

PS... I just read through some old posts, it sounds possible that my issue could be due to caps on the tube board..
Will have a close look to see if I can spot any that look ruptured (I recall my old Marshall Plexi that had huge blue caps that were always exploding and leaving yellow crap everywhere. Not easy to miss!).

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: Micky on September 14, 2021, 12:35:58 PM

Hi MR THUD,

I had the same problem.

MarshallJMP suggested me to change the three big capacitors on the tube board with high temperature version: problem solved.

Micky

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: Harley Hexxe on September 14, 2021, 02:41:30 PM

More than likely, it sounds like bad caps to me too.

      There are a few competent techs around Australia, I'm sure you'll find someone who can help set you straight.

Harley 8)

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: MR THUD on September 14, 2021, 07:37:03 PM

Thanks Guys!
Will take that advice as first thing to try, new high temp caps it is then.
Anyone know the model number for the better/ high temp caps?

In parallel I will try contact Mr JMP, as he has helped me source parts before and may have some for sale.

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: MarshallJMP on September 15, 2021, 11:38:31 AM

Mail me and I'll tell you what to order with your local electronics shop

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: MR THUD on September 16, 2021, 08:44:39 AM

Cheers, Philippe.
I have sent you an email and also attached some photos.
Hopefully they get to you ok.

Thanks!
G.

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: Moff40 on August 28, 2022, 03:19:19 PM

I know this is an older thread, but I just noticed the same thing with an MP-1 that was recently resurrected from the dead.  Coincidentally, I had ordered the tube board electrolytics a week or two ago, in case I needed them on my other MP-1.  Time to warm up the soldering gun again.  :)

***EDIT*** Changed the caps, and all is well.  :)

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: rnolan on August 29, 2022, 06:31:33 AM

 :whoohoo!: good news.

Title: Re: MP1 - Developed very loud hum on tube settings
Post by: MarshallJMP on August 29, 2022, 11:38:14 AM

Great!! :thumb-up: