Source of this Distortion (Fizz)

[russ6100]

Hi All,

I recently bought a used DRRI that's been modded pretty nicely (Mercury Magnetics OT, PT and choke, Brimar power tubes, Weber Blue-Dog).

Although the amp is immaculate, there is a top-end fizz present when the amp is pushed *at all*, which I highly suspect to be due to a speaker that needs to be broken in....

This is a clip of the amp, a semi-hollow's neck PU (57 Classic), tone rolled back to 6, volume on 9, into the Normal channel of the DRRI, Volume on 11 O'Clock, Treble at 10.5 O'Clock, Bass at 10.5 O'Clock, with a SM57 1 ft in front of the speaker, slightly off-axis.

http://www.russletson.com/sounds/DRRI_TEST_11_OCLOCK.mp3

I know there is some amp distortion present, but I'm thinking that fizz on top is from that Blue-Dog that needs a good breaking in...

What say you?

 

[russ6100]

bump

 

[cram]

Do you have another speaker to swap or extension to test the amp with?

 

[russ6100]

I don't - yet.

Since I'm wanting to use this amp primarily for jazz, ,my plan has been to replace the Blue-Dog but I haven't got around to it yet.

 

[cram]

No doubt! When I've had concerns of how an amp was sounding through a speaker - swapping the speaker to isolate the amp or be able to say it happens with this vs not happenning with that is a big help to a lamen like me.

Even when I didn't have a spare amp/cab, I could visit a friend who did and there's also the amp tech I use in boston who has two cabs to test with for that exact reason.

The buzz is noticable in your clip.

 

[steveb]

I don't know.... that doesn't sound right at all. Does the reverb channel have the same fuzzy sound, too?

If it's the speaker, something is wrong with it. No amount of break in time will make it better.

 

[russ6100]

I don't know.... that doesn't sound right at all. Does the reverb channel have the same fuzzy sound, too?

If it's the speaker, something is wrong with it. No amount of break in time will make it better.

Reverb channel has it even worse, or at least it's even more accentuated by the presence of the bright cap on that channel (which all DRRIs come stock with).

I dunno - I've heard that some speakers, before being broken in properly, have an annoying fizz on the top end. I haven't bought any truly "new" amps or speakers in years....

Well, I'll know something when I swap the speaker....

 

[Jay Strange]

preamp tubes???

 

[djw]

Tubes. Preamp or could be a power tube. I had a similar problem with one of my amps recently, and the problem went away when I swapped out a pair of power tubes.

 

[steveb]

Since it's happening on both channels, the problem could be at the end of the preamp section, or in the power section. Try swapping V3 & V6. V6 is the last preamp tube before going to the power tubes. V3 is the reverb driver, which you're not using anyway. |If the noise is still present after the tube swap, it could be the power tubes or the speaker.

I have a friend who had a brand new Vibroverb reissue, & it sounded weak & somewhat distorted. In fact, it may have been a similar fizz to yours. Changing the phase inverter tube (V6) fixed it right up.

Hopefully, that's all that's up with yours.