Does the sound of an output transformer change with hours on the amp?

[leadfootdriver]

How about the whole amp in general? I remember when I built an amp and turned it on for the 1st time, it seemed real harsh and noisy. Was I imagining things, or did I just get used to how it sounds?

[Gingertube]

The Output Transformer - NO
Other Amp components - YES, in particular capacitors and possibly tubes as well.
I used to "poo poo" discussions of "running in" components but experience has taught me it is real.
Cheers,
Ian

[R.G.]

There are certainly part that age, and can cause changes in the sound of an amp. If I had to rank them by most to least changes in sound with age, the OT would be really far down the list as long as it was well made to start with. In particular, electro caps change capacitance and dry out; resistors drift; contacts get dirty and covered with metallic oxides; tube sockets, more so; tubes age and drift.

Nothing lasts forever, but OTs are pretty simple and pretty robust.

[leadfootdriver]

Thanks fellas.

So, would you say then in general that an amp will mellow out with age; as in it gets less harsh where the highs round over slighty?

[Justin Thomas]

Speakers definitely age, and suck up moisture from the air... I think that's the biggest one I can think of, and maybe part of the "bjggest difference made by any single component is changing the speaker" mystique. I think there's truth to that, and usually I'll try to "dehumidify" a speaker before I replace it for sounding mushy or soft. I think I read it in a Dr. Z i terview, and it's free, so worth a shot to me.

On another note, I think my amps sound better as they run longer, and a quick way to accelerate the warmup is to leave it in my hot truck for a few hours... (insert tape-over-mouth smiley here...) Hey, I'mnot gonna show up at a gig 3 houts early just so I can leave my amp on...

Justin

[Chuck H]

Thanks fellas.

So, would you say then in general that an amp will mellow out with age; as in it gets less harsh where the highs round over slighty?

Like Justin said. Speakers almost always mellow with age. And as R.G. said, transformers are simple and robust and there's not much to drift in the nature of their operation.

Component drift on the circuits is a crap shoot. An e-cap drifting can make an amp more harsh or more mellow depending on the circuit it's in. Usually more mellow because ecaps are used as decouplers in the power supply and guitar amp power supply nodes are often, but not always arranged in out of phase pairs so any additional coupling results in gain reduction. The nature of the impedance of ecaps makes this effect most prevalent in the HF. Burn in is another matter. Many times I've experienced (by ear, never actually tested) ecap burn in for new builds where the caps don't perform at optimum efficiency for days or a week and an amp will actually get more punchy and tight as their performance improves.

There are many cases where a drifted resistor can make an amp brighter. CC's usually drift high. A higher than spec resistor in a preamp cathode can cool the bias and raise plate voltage a tad making an amp a little brighter, a higher than spec resistor in the tone stack slope position shift the balance toward the treble and a higher than spec NFB resistor in the series or shunt position can make an amp either more "harsh" or more "cold" sounding.

Overall I would say that burn in is just burn in. an amp will change a little. Usually a tad mellower mostly due to speakers. Same with age due to, again, speakers and also due to how most guitar amp power supplies are arranged and ecap age. Grossly bad resistor drift isn't rare, but less common a phenomenon.

All these affects can line up to give an amp a very characteristic sound. Brighter in some ways and having mellowed in others. It's not unusual for someone to refurbish an amp, as in new filter caps, check and replace drifted resistors, replace the old crappy Oxford with a new Jensen, etc. only to find that the amp lost all it's mojo Most "guru's" attribute this to vintage parts, which is just stupid. In the case of an amp with a "special sound" these sorts of operations would go much better if parts being replaced were tested and close performers were chosen. As in "this plate load resistor is drifted to 122k!" Well... Use a 120k 1% part to replace it! Filter caps are tougher but some can be done to avoid parts that have insanely good electronic specs compared to the old, worn out caps. And we have a good many speaker offerings today so finding a close replacement is only limited by budget and effort.

Ok, I didn't mean to get all SGM about it, but this is my 2C on the matter.

[R.G.]

You bring up a very good point. Guitar speakers are not speakers in the sense of transparent reproduction of signals like hifi speakers are.

Guitar speakers are MUSICAL INSTRUMENTS and they are not perfectly interchangeable. It's worth considering a guitar speaker to be like a violin. It's an assembly of parts, of which a critical one is a panel of wood fiber which is coupled to a mechanical frame that holds the panel. The composition and materials of the panel, it's resonances, how tightly or loosely it's held, the resonances of the panel, the frame, the damping of the adhesives, even the humidity contained in the resonating panel makes a difference.

We are willing to think all this automatically about acoustic guitars, but think speakers are interchangeable.

Sigh.