SWR Bass 350 Distortion on low E string at all volumes ?

[CobaltSixty]

Getting distortion at all volumes. Does not get worse or change duration w increasing volume. Low level distortion "underneath" the string sound.

All controls flat or otherwise. Does not distort w other strings. all screws tight, etc. Running a Peavey Scorpion 150W 15" in a TNT Cab.

Please help.

[CobaltSixty]

Oh, Hello, Please, and THANK YOU everyone.

[MarkusBass]

Have you tried changing valve in the preamp? Isolate the problem. Check whether it's the problem with the preamp, or with the power amp. Plug in the preamp to another power amp. Plug another preamp to the power amp. If it's the power amp, it may be caused by incorrectly set bias of output transistors.

Mark

[CobaltSixty]

Thank you MarkusBass.

I have a new tube in the preamp.

I checked 4 preamp tubes, various types with low gain, high gain, etc. no change to the problem, but I DID find a tube I liked better than the original !

Preamp / Power amp - how do I separate them ? I am technical w science background but I have never worked w amps in this depth. I know all the safety stuff but I cannot read schemos good enough to tell which module is which.

Must it be done by de-soldering the preamp and re-out to another power amp ?

A schemo is on this site, shall I post it here.

Thanks again for your time sir !

[Steve L]

A signal generator and scope are what you really need here, however have you tried another speaker first?

What you are describing is a very common symptom of a bad speaker.

Steve

[MarkusBass]

You don't have to desolder the preamp. There should be EFFECT SEND/RETURN and PREAMP OUT/POWER AMP IN jacks. Use them. Connect the preamp to another power amp and some other preamp to this power amp.

Mark

[CobaltSixty]

THAT's what I was going to ask next !

I could not decide if the speaker should be distorting on ALL notes or just the Low E. I decided it should be distorting on all notes and moved suspicions to the Amp.

Sounds as if I may have been wrong (surprise, surprise) XD.

I will replace the speaker, the old scorpion was on the list of retirees anyway.

[CobaltSixty]

Yes, yes.

So obvious NOW.

Thanks again.

What a great forum !

[CobaltSixty]

Well now I suppose I should ask the Forum Folks before I buy a speaker.

Anyone have overwhelming opinions on a replacement 15" or a Peavey TNT 150 Cabinet ?

I have only experience w the scorpions but scientific curiosity makes me want to put an eminence in there.

I need to be able to produce a lot of LOW end, the Eminence Basslite C2515 will NOT do that in that cab.

Thanks guys.

[CobaltSixty]

FOR a Peavey TNT 150 Cab.

Sorry...

[fredy2]

You reaally need to sweep the frequencies with a variable audio signal generator. I found that noise/distortion on a Peavey cabinet was due to the logo on the grille rattling. Also you can replace the basket on a Scorpion speaker for a lot less than a whole new speaker. The new basket costs about $70.

[J M Fahey]

And the cabinet is kind of small.
Not bad, just small, the problem with 99% of combos, so no speaker will work miracles there.
In my experience, a much better, improved, strong magnet speaker will sound louder and cleaner than the original one, but for some reason will (psychologically?) appear to have slightly *less* bass.
Truth is, it will heve more damping, and bass will be tighter, "dryer", *because* it's a better speaker.
To get the big bass you crave, build a new box, at least 2X the original volume, and turn your chassis into a head, by mounting it in an approppriate enclosure.
jm2c

[J M Fahey]

NOW that I re-read it, I notice (slow mind of mine) that you were using a 350 head with a 150 Speaker.
Of course you cooked that poor voice coil.
One early symptom is the adhesive bubbling, which scratches and buzzes, most noticeable with low frequencies and independent of volume.
Doom is close by.
Buy *at least* a 250W RMS or higher speaker.
EVM´s and some PA type Eminences come to mind.