Carr Rambler oscillations on certain notes

[SFMUSICMAN]

Not sure what happened to the sound file (thought it was ok to post small attachments here)

Here's a link to the same file so you all can hear what I'm hearing.

Does it sound like a tube issue?

http://www.sendspace.com/file/l13xgu

[Firestorm]

It sounds frequency-dependent. Have you tried connecting a different speaker?

[pdf64]

Sounds like tube rattle to me, probably a power tube with slightly loose screen grid wire. Try a pair of Winged Cs from a good vendor that burns them in. Better than 90% of the NOS dross dregs floating around now. Pete.

[SFMUSICMAN]

Well, I sure didn't expect this response but here it is from the man himself, Steve Carr:

"What you are hearing is fairly normal - there is some intermodulation distortion in the Rambler and it has a lot of 2nd order distortion that can add some synth sounding notes - this is why it is so rich and thick sounding -- all that harmonic distortion. You also get some of this with vintage style power supplies which we use.

Try not to focus on it it is sort of what give the rambler its character!"

Is that what y'all are hearing too - "second order distortion"?

[Firestorm]

It's not a flaw ... it's a FEATURE!!!

[David Root]

Well, let me try to flesh that out a bit.

"Second order distortion" I think refers to harmonic distortion, which can be second order even harmonic distortion (2nd, 4th etc.) or second odd order distortion, 3rd, 5th etc harmonics. Or both of course. Harmonic distortion even order is like a Fender, odd order more like a Marshall. Nothing wrong with either, within reason.

I was under the impression that the Rambler is a derivative of a Blackface Fender Pro or Super. Sounds like it may be more on the tweedy side.

IM (intermodulation) distortion however is very unmusical and non-harmonious and is caused by one frequency modulating other frequencies in a non-octave sum-and-difference mode relationship. For example, 600Hz fundamental modulates a 2K fundamental. You get 2k-600Hz, 2K + 600Hz, 2K minus 2x600Hz, 2K + 2x 600Hz, that kind of thing, a total cacophany. Fortunately the IM overtones are low amplitude and get lower as they multiply, like harmonic distortion overtones only not nice sounding. It murders clarity, sort of smears the sound.

It is unavoidable to some extent and can be difficult to minimize and I would hazard that "vintage type" power supplies with less than adequate filter caps might not help in that regard.

Other than that I would defer to someone with more knowledge of and experience with distortion artifacts than myself.

[pamaz67]

i tend to think it's a mechanical issue linked to the speaker or to the tubes.
i've owned a carr rambler and have built some amps based on that design. never ever heard of such problems
A decent technician with a scope and a signal generator will tell you in 5 minutes if that's an electronic issue or something else.
BTW I would have expected form Carr company a different answer, due the very high quality of their products. What he said is not enough.

FWIW : the rambler supply is good enough for not having such problems. the supply is using poliprop solen caps for filtering the Supply . which is definetely one of the "secrets"of the sound quality in the rambler

[SFMUSICMAN]

good news...Backline (from tdpri.com) totally fixed this "second harmonic oscillation" issue. He can explain it better than me but we found out (I believe) a screen resistor for one of the 6L6's had gone bad. He replaced that and the wierdness went away while leaving the thick and rich 2nd order distortion intact.

There is some minor tube rattle in the 6L6's (also with replaced ones) so he is suggesting some dampers of some sort to quiet that minor issue, but the main issue is resolved thank God!

Not sure if Steve Carr could really hear what I (and Backline) heard but it definately wasn't musical until the resistor was replaced.

Amazing work Backline thank you. This has been eluding several techs for over 3 years.

Many thanks for everyone helping out

[pdf64]

Does it sound like a tube issue?

http://www.sendspace.com/file/l13xgu

That link sure did download some insideous add-ons that take over explorer. I just spent half an hour clearing it out - beware!
Tip - look for iLivid in the 'add / remove programs' control panel.
Pete.

[SFMUSICMAN]

sorry I was using the link at the bottom which was only the download to the file.
Don't click on any of the large "download buttons" Instead, "Click here to start download from sendspace" is the link you want directly to the file.

Didn't know how to attach the file to the post here.

[pdf64]

The link in the post previous to that one worked fine. I thought there must be a prob with the 1st so went to the second, but when I tried it the 1st one was fine.
Pete.