Fender Bassman Cab Insulation

[admin]

No, not at all Don. I can only conclude at this point that the 50 watt amplifier does not have enough juice to drive the speakers adequately at increased volume.

[fatcat]

No, not at all Don.

Then that probably rules out microphonics as a cause.

I can only conclude at this point that the 50 watt amplifier does not have enough juice to drive the speakers adequately at increased volume.

That's a good possibility. Yesterday I was testing the Janglebox with my 360, and after that on a whim I cranked the volume way up on the '64 Bassman and got some sorta thump/buzz for a very short time when hard hitting barre chords mid neck.
I don't think it was the speakers as they're Vintage 30s rated 60 wt. each.The amp probably ran out of headroom.It's not something that I'd ever have noticed as I never play that Bassman that loud.
But: It's still SWAG.

[admin]

Don: That's eaxactly the sound that I am talking about with the 50 watt Bassman head. It is most noticeable midneck. It disappears using the 100 watt head. I am grateful for this validation. It is not the speakers or the cabinet as it is reproducible using the Marshall cabinet as well.

[soundmasterg]

Any chance you could record the noise it makes and post a link up here so I could hear it? I could tell you if it is a sound the amp could be making or not.

greg

[admin]

Greg: I will try to get a recording. In the meantime, by way of description, the antithesis of sound springs to mind. This sound certainly cancels an otherwise great tone. Lower the volume or double the wattage of the amplifier and the problem goes away.

To add a bit, this bassman head is heard when the volume reaches 2 or 2.5 and not before. What is with that, anyway?

[fatcat]

The volume problem is probably due to a dirty pot,and more so if it's crackly thru it's range.A worse possibility is one which it has permanently gone open for a short part of it's travel.
Neither cleaning nor replacing is a very hard task, just be careful inside any tube amp as they can bite.

[admin]

I have continued to listen and make changes to the positioning of the insulation inside the cabinet. This along with backing off a tiny bit from the treble setting has all but eliminated the problem. I still do not have an explanation either than a breakup up of the sound at higher volumes when treble is pushed hard producing a harshness that is not otherwise heard in this amplifier and cabinet combination.

[jnbass]

Ah h_ll, I always thought that the insulation increased the damping factor of the cab.

[admin]

Perhaps I should go for R-75, Jared.

[VRICKY63]

Yes....R-75 would make for a " Warm " tone

[admin]

A great post, Rick. Batten down the hatches, we may see more on this theme.

For Greg: Do you suppose that I am simply describing clipping? I do not know what a "square wave" sounds like but intuitively it must be something like what I have described.

[johnallg]

Peter, FWIW I think you are hearing the amp clip. Since the 100w head does not do it with that speaker, I think you have your answer.

[admin]

Thanks, John. I am beginning to think that this is the best explanation. Whatever I do hear is certainly the antithesis of music.

[soundmasterg]

An actual audio sample of the problem would be very helpful, but it could be some motorboating in your 50 watt bassman, which is a sort of oscillation at low frequencies. It can be caused by poor grounding, defective filter caps, incorrect filter cap values, not enough decoupling between tstages, poor routing of wires inside the amp, etc. But I'm just guessing that this is the sound your amp is making. Does it sound at all like the putt-putt sound that a outboard engine makes? (Hence the term "motorboating)

Greg

[admin]

Greg: I will try to get an audio sample. Your motorboating description does not fit, at least to my ears and again. It only occurs at what I would descibe as the peak with high volume, otherwise the amplifier and speakers sound fantastic. It is not the breakup I am accustomed to, but like exceeding the limits. I am not sure if it is a mechanical limitation of the speakers of a limitation of the amplifier.