Low Volume on Marshall Valvestate VS265

[sjg1047]

Hi everyone,

I'm new to repairing amps (this is my first project) and am working on a Marshall Valvestate VS265. I recently purchased this amp second hand. The seller noted that there is a mild hum, even when there isn't a guitar plugged in. After purchasing, I noticed that the amp sounds kind of nasally. However, when I turn on the chorus, the amp really opens up and sounds great. For some reason, it seems that something in the chorus circuit brings out fullness and bass depth that is missing when it's turned off. It's as if the volume is turned down when chorus is off.

If anyone has any advice, suggestions, or thoughts, these would be much appreciated!

Here's a couple of things I've already tried:

• Inspected large resistors and capacitors for damage.
• Inspected board for burn marks from high temperatures.
• Removed and cleaned ground connections.

Overall, I haven't yet found the "smoking gun". Thanks for reading and any help is greatly appreciated! I'm new to this, so tips for items to check are greatly appreciated!

[g1]

Try switching the wires on just one of the speakers, does this make the nasally problem better or worse?

[sjg1047]

Try switching the wires on just one of the speakers, does this make the nasally problem better or worse?

I haven't tried this exactly, but did try using the external output jacks to run the amp head to an external cabinet. The problem still persisted. I will try switching the wires just to confirm though. Thanks for the suggestion.

[sjg1047]

I should have posted this earlier... Please see below for a link to the schematic:

http://www.amparchives.com/Amp%20Arc...265r_2x65w.pdf

vs265r_2x65w.pdf

[sjg1047]

Try switching the wires on just one of the speakers, does this make the nasally problem better or worse?

Thanks g1 for the suggestion! This worked perfectly!

In hindsight, this makes total sense. Turning up the speed on the chorus didn't have much effect, which was another indication that the polarity was reversed. One of the previous owners installed a different speaker but accidentally swapped the connections. Really excited about this amp! It sounds great!

[g1]

You still have the hum issue?

[sjg1047]

Yeah, the hum is still there. It's not very loud, but it's still there.

Are there some common culprits to look for?

[g1]

First plug a cable into the input and short the tip to the sleeve. This will tell you if the jack switch is not closing when nothing is plugged in.
If it makes a difference, you need to clean or replace the input jack.
Beyond that, check the level of AC voltage on the main filter caps and the filter caps for the lower voltage supply (+/- 15V).

[sjg1047]

Yes, opened up the chassis and found that the back jack switch is not fully making contact with the cable removed. Once the cable is inserted, it makes full contact with the cable jack. Will see if I can bend this back into place.