Studio Pre hiss problem

[sepsis]

ok, I recently got a Mesa Boogie Studio Pre and I'm running it into a Tech 21 Power Engine.

I have a hiss problem though. Basically, I can't really say that the hiss is always 'on'.
Thing is: when I palm mute a chord (open E for example) and let it ring, there is a hiss sound (more like an 'ocean wave') that rises in about a second from when I play the note. Weird huh? And this hiss seems to affect the tone. When I turn Treble to 0 the hiss is not that noticeable but it IS there.

So, I've changed cables, I've changed the wall socket but the hiss is still there. I tried plugging the Studio Pre into a small Marshall amp that a friend brought by (in the input of the amp) but I really can't say if the hiss is there because the sound is just awfull either way
I've thought it may be the Tech 21 but when I play with my sansamp (or another preamp) there is no hiss whatsoever.

So, I thought there maybe an issue with a tube. A opened it up and tried the thing 'touch the tubes with a pencil' but there were no microphonics. But I'm no tube expert, so, is there a chance it's still a tube problem? Any ideas?
I'm almost definetaly gonna change the tubes....what do you suggest? Maybe some JJ's? Or should I keep the Mesa Boogie tube? I could use some more gain

 

[sepsis]

I changed the V1 tube but the hiss is still there! Is it worth changing the other tubes?
Any ideas of what might be the problem? :?

 

[riddler]

Maybe its just the settings you've dialed in. With Gain and Treble High (7 to 8 ) the hiss seems a normal thing to me.

 

[goodwill559]

Also, there's more hiss when the fat and/or bright switches are engaged.

 

[sepsis]

I've tried the Treble to zero but the hiss was still there. Same for the fat/bright switches. No difference in the hiss I described
I'm not talking,however, about a normal hiss like you describe which occurs from very high settings. I know what that sounds and what i'm experiencing here is a very unusual hiss that seems to be ''rising'' (=volume wise) when I palm mute a chord.

Anyway, today I found this picture of the studio
http://i33.tinypic.com/xfrgvt.jpg
And I was surprised because mine is like this: http://img166.imageshack.us/img166/2188/111yy4.jpg
Yes, I'm stupid. I hadn't noticed that one spring was out :lol: However, the Reverb control works just fine. Could that broken spring cause the hiss I describe?

I'll give it a shot again as far as the treble and gain knobs are concerned :?

 

[goodwill559]

it also looks like your rear guitar input has been disabled and your front guitar input wiring doesn't look right but it is partially cut out of the picture,

is the hiss present in all five of outputs, loop, direct R & L, recording R & L, or limited to certain outputs?

also, try double checking that the at7 is in the reverb socket (the socket nearest the reverb pan) and not in the remaining 4 sockets, mine did not like having at7's anywhere else and behaved very badly when not tubed with ax7's, YMMV

 

[sepsis]

here are some pics of the front input with cable plugged in. Hope it helps
http://img205.imageshack.us/img205/4330/154lk1.jpg
http://img205.imageshack.us/img205/7448/153tu5.jpg
http://img87.imageshack.us/img87/3136/155qc1.jpg

the reverb tube is ok.

I'll try and take some better res pics and upload

 

[goodwill559]

so it definitely looks like the front input jack has been switched out with a replacement and i no longer own a studio pre so i can't provide details of the wiring for comparison,

and it may have nothing to do with the input jack wiring anyway, but anytime someone attempts mods or alterations, there's always the potential to worsen rather than improve performance

have you verified hissing on all outputs yet?

edit: in answer to the question about the broken reverb spring creating the noise. i would pull the reverb tube to eliminate the reverb circuit from the signal path and if that works to eliminate the problem, then you've narrowed it down, if not, then it is elsewhere,

 

[sepsis]

yeap, all outputs have the same hiss problem

 

[goodwill559]

ok, have you played with eq in and out to verify that circuit is not causing the noise?

also, do both lead and rhythm channels have the noise?

 

[sepsis]

eq doesn't make a difference

when i'm in rhythm mode, I can't really say there's that annoying hiss. At the same output volume, rhythm channel is super clean compared to lead mode. Even if i play all volume up, there's a hiss in the clean mode but it's not disturbing like the lead channel, it's normal and barely hearable. Whereas in lead mode the hiss is noticeable even at lower volumes. So, yes rhythm seems to be fine

 

[goodwill559]

are you using a known good tube for your substitutions? you mentioned replacing v1, that didn't solve the problem,

put the original tube back in v1, then swap v2 with a good one, and if that doesn't eliminate the noise, restore v2 to the original tube then pull v3 and replace with a good tube

v4 is for the main outs, v5 for reverb, since the noise appears on all outputs, you can probably eliminate v4 as the cause, and since reverb has no affect, you can probably eliminate that as the cause as well,

if it's not a tube, it's a component or connection in the signal path which is the cause, and if so it'll be more difficult to pinpoint,

i'm out of ideas so it might be time to find a good tech

 

[francm]

I would look at the power amp. Does the problem happen with other preamps or is it just the Studio Pre?

 

[sepsis]

i forgot to inform that I found the source of the problem

It was the crappy zoom gfx8 i used for the effects.

You see, I tried running the zoom after the studio pre to use it for effects but the tone suckage was just TOO much.
But the zoom has this option which you can use an external drive effects unit to bypass the zoom's drives. So, i connected the preamp in the loop of the zoom. Turns out it caused all this hum. I don't know why I hadn't noticed it before, although I tried it many times to see if it was zoom's fault. Anyway, I threw out the zoom and ordered a TC Electronic delay pedal (arriving Monday).

Problem solved