So, this MT-15 hum. What is normal?

[TRGuy]

I picked up an MT-15 today. my second PRS amplifier after the J-MOD100.

Firstly - It sounds phenomenal. Pretty much as good as my JP-2C. Seriously.

But it is all in vain due to the already infamous humming. I wanted to check if the hum on mine was normal compared to other models, and then decide from there whether to keep it or not (I probably won't, as it's pretty unbearable.)

Firstly - the hum is evident whether the standby is on or not. It takes a few seconds from power on to start humming, but once it starts it's there. It doesn't get any louder as the volume or channel changes.

Secondly, the hum volume. With my iphone to the speaker, using a decibel meter, the meter reads 37.7db without the amp on, and 69.9db with the amp on but the standby off (purely the hum.) . Thats a lot of humming.

I know that everyone says that it's because it's so small, but it's the same size as the JP-2C, which fits in reverb, three channels, MIDI, 2 EQ's, a boost circuit etc with zero noise, so I don't really buy that.

Is this normal, or is this amp specially affected? I've emailed the PRS guys as well!

Cheers all.

 

[bodia]

This was not the experience I had with my MT-15. I pre-ordered when it was announced, and got an early one in May, or early June. I played it quite a bit from then until I went Modeler in February. Never had any hum with mine. Well, I did, but it turned out to be a patch cable on my pedal board. Brand new one, too. I know three others that have the MT-15 and have not experienced this hum.

 

[bodia]

Not sure if this thread is talking about the same thing.

https://forums.prsguitars.com/threads/so-the-mt-15-still-had-problems.37825/

 

[TRGuy]

Played around with tubes. The V5 tube definitely makes a difference, brings the hum down from 69.9db to 57.4db (when I replace the 12ax7 for a 5751...). However, still there and still annoying.

Weirdly, with the lead volume about half, I can actually hear my guitar signal when standby is turned off.

 

[TRGuy]

And fwiw, tapping the V5 tube rings loudly and amplified through the speaker even when the volume is at zero.

The fact that two out of three PRS amps I’ve owned have had major issues doesn’t fill me with brand loyalty.

 

[elvis]

Some people have swapped V1 with satisfactory results.

Seems like the MT is especially susceptible to hum.

I very much don't understand why everyone hears noise and guitar signal with the amp in standby. Typically standby kills the plate supply to the power tubes. I wonder if the MT biases the output tubes but shunts the signal in standby. That would explain this.

 

[László]

As a studio guy familiar with acoustics, I’ll mention that 35 db of background noise roughly the noise floor in a typical “quiet” room in a home without a guitar amplifier on.

I have two PRS single channel amps, the HXDA and DG30. They’re 100% dead quiet. I wouldn’t judge PRS amps by a model outsourced to China.

No doubt you’ve already thought of this question, but I’ll ask more or less as a reminder: have you measured the noise with your guitar/pedalboard/switching system, etc., unplugged?

I know you’re experienced, and a TR owner (as was I for a dozen years). But sometimes we forget to think of the obvious.

 

[TRGuy]

As a studio guy familiar with acoustics, I’ll mention that 35 db of background noise roughly the noise floor in a typical “quiet” room in a home without a guitar amplifier on.

I have two PRS single channel amps, the HXDA and DG30. They’re 100% dead quiet. I wouldn’t judge PRS amps by a model outsourced to China.

No doubt you’ve already thought of this question, but I’ll ask more or less as a reminder: have you measured the noise with your guitar/pedalboard/switching system, etc., unplugged?

I know you’re experienced, and a TR owner (as was I for a dozen years). But sometimes we forget to think of the obvious.

Hey buddy. Yeah, this is all with just the MT15 in the signal chain. In fact, this noise is the same whether there’s a cable into the input or not. It seems like something is inherently wrong with the V5 slot to me, not properly grounded etc.

Yeah, 35db was the idle room noise without the hum. C70db with the hum, which puts it somewhere between conversation and a lawnmower.

 

[TRGuy]

Some people have swapped V1 with satisfactory results.

Seems like the MT is especially susceptible to hum.

I very much don't understand why everyone hears noise and guitar signal with the amp in standby. Typically standby kills the plate supply to the power tubes. I wonder if the MT biases the output tubes but shunts the signal in standby. That would explain this.

I appreciate that it’s a small amp, but the JP2C is the same size, so I suspect it’s more an issue with production, especially as some people seem to have more issues than others. It is especially strange that it hums loudly, and guitar signal bleeds through, with the standby off.

 

[dmatthews]

Have you tried putting a short, high quality cable in the effects loop?

 

[TRGuy]

Have you tried putting a short, high quality cable in the effects loop?

Not yet, I’ll try that tonight.

 

[László]

Hey buddy. Yeah, this is all with just the MT15 in the signal chain. In fact, this noise is the same whether there’s a cable into the input or not. It seems like something is inherently wrong with the V5 slot to me, not properly grounded etc.

Yeah, 35db was the idle room noise without the hum. C70db with the hum, which puts it somewhere between conversation and a lawnmower.

Gosh, I’d take it back, or contact PRS.

 

[vchizzle]

Firstly - the hum is evident whether the standby is on or not. It takes a few seconds from power on to start humming, but once it starts it's there. It doesn't get any louder as the volume or channel changes.



Cheers all.

Not normal, either needs to be repaired or replaced by dealer if you bought it new.

 

[andy474x]

Yeah, 35db was the idle room noise without the hum. C70db with the hum, which puts it somewhere between conversation and a lawnmower.

That does sound excessive. I think it’s normal for them to have some hum that’s independent of the MV settings, mine does, but it’s bearable especially in a band context. Since it doesn’t change with the MV, it’s a substantial hum relative to “bedroom” volume, but in relation to full band volume, much more normal for the amount of hum many high gain amps have.

I would pursue a repair or exchange. Don’t expect dead silence, but it should be tolerable.

 

[TRGuy]

Have you tried putting a short, high quality cable in the effects loop?

Tried this today, makes no difference.

After playing for a while, the hum actually gets louder. I'm sending this back, I'll buy one again when PRS can confirm they've fixed the issue. I'm not going to roll the dice on a replacement.

 

[jvin248]

.

Without hearing the actual hum noise, since you are hearing it while on standby and if regardless of where you set the volume knob level .. it could most likely be a 'leaky'/failing filter (power supply) capacitor. When you return it, tell them that's what it sounds like and they should see about repairing (rather than just putting it back out on the floor for someone else to get caught up in).

.

 

[BrianC]

I had this amp, sold it based on the tone, but the hum WAS concerning to me as well.

I never had this issue with my other PRS amps or other brands in my home.

 

[László]

I’d let either the dealer or PRS sort it out. You’ve tried. Let them do their part.

 

[TRGuy]

Yup, exchanged it with the store for a new one. New one has no real hum, which is nice!

Definitely good ones and bad ones out there, it seems.