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All-tube SVT heads

A

Aharon

Jan 23, 2008
128
0
#1
Hi all.

Recently acquired an SVT 2 pro. Firstly would like to say I have been reading quite a bit about the different all -tube SVT heads out there regarding headroom, biasing, tube rolling, cab compatability/no. of speakers etc. I have furthered my knowledge immensly but am still wanting to know more.

The bottom line is clean headroom. At band volume the notes on the low E are causing a "farting" kind of break up. After reading extensively on the matter, I am unsure whether this is just what the amp is designed to do or if something is wrong.

The cab is a ported 610 (warwick) that has handled much higher volume and power load with my SVT 4 pro. I also briefly owned a Mesa Bass 400+ and the low end on that didnt fart out at louder volumes, leading me to believe the cab is not the culprit.

I like the subtle, harmonic saturation that occurs with a slight bit of drive, but I do not like any audible "distortion" particularly of the low end. I am not asking for the SVT 2 pro to be squeaky clean like my SVT 4, but surely this low end farting business is not part of the amps design? I opened it up and all the tubes seem to have a healthy glow and the bias lights are both green. I did a microphonics test with a chopstick on the preamp tubes and nothing came out of the speakers. I have tried different combinations of gain/drive/master and it all seems to bottom-out at around the same sort of volume.

Was it the extra 100w of headroom on the Mesa that allowed the low end to stay intact? Can I increase my headroom using KT88's without making the low end all flabby and retubing every 6 months? Do lower gain preamp tubes actually affect power tube break up / headroom or are they purely for tonal shaping? Does the SVT VR have more clean headroom?

Thanks in advance.


Gear used:

Svt 2 Pro (tubed with winged c 6550s)
Gibson Ripper bass (low output)
Warwick 611 pro (900w @ 4ohms, ported)
 
#3
Hi Jim.

The cabinet has never sounded like that before and it has been pushed harder using other amps (mesa 400 / svt 4 pro).

The distortion does creep in with the increase in volume, but predictably the low end is the first thing to go. If the low E is picked even medium/hard the sound wont come out clean.

Bit of a shame because I am happy with the general sound of the amp and consider it an improvement on the 4 pro aside from this problem.
 
#4
I'm not super familiar with the actual working of that amp, so not sure exactly what might be doing it. One experiment you may try, just to narrow down the source of the problem... Set up the cab with your 4pro, and go instrument into preamp of the 2pro, preamp out to the power amp in of the 4 pro. if that checks out the turn right around and do the same thing, using the pre of the 4pro and the power of the 2pro.
 
#5
JimWasHere said:
I'm not super familiar with the actual working of that amp, so not sure exactly what might be doing it. One experiment you may try, just to narrow down the source of the problem... Set up the cab with your 4pro, and go instrument into preamp of the 2pro, preamp out to the power amp in of the 4 pro. if that checks out the turn right around and do the same thing, using the pre of the 4pro and the power of the 2pro.
Click to expand...

The 2 pro requires a speaker load to operate safely, like any all tube amp do.
 
#7
Thanks for the replies so far.

I will certainly try using the svt 4 as a preamp into the svt 2 pro. The svt 4 has a notoriously clean pre that is extremely hard to clip so it might provide a clue. This will have to wait, but I will post my findings. Further suggestions in the mean time would be highly appreciated.

There is an authorized ampeg tech in my town but I really do not want to take it there because they will have it on their bench for months on end before I get an answer.

I have considered re-tubing it but to blindly dump £150-200 on a set seems innappropriate and I am still not 100% sure whether you are even supposed to put
KT88s in SVT heads or whether that is just an old wives tale / marketing. Not to mention the change in tone may be undesirable.

I run the EQ pretty much flat with ultra low and ultra high pushed in, bass knob at about 11 o' clock and mids at about 1 o'clock. Ive read about people advising against using the ultra-low but that doesnt really seem like a satisfactory solution to me (if indeed that is the problem).

This is tantilizing because the saturtaion and harmonics of the amp are very nice. Its just the low end response / distortion that is ruining it.
 
#8
Yeah... you're scooping out a lot of the good midrange content that will "cut" or "punch" through a band mix by using those switches. You're also using a lot (or all) of the SVT's power compensating for that.
 
#9
christw said:
You're also using a lot (or all) of the SVT's power compensating for that.
Click to expand...

You're also using a lot of the cab's available excursion with that ultra low switch, while your perchieved volume is lower. I would say that it's possible that you're pushing the cab harder than it seems. Try running without those switches too, eq set totally flat, and see what happens?

GL either way :D
 
#10
The tube amp has a much bigger low end, also it will sound better with a sealed cab and any overdrive will probably sound better and more controlled. Run a compressor before the svt it you want the most clean headroom out of the amp while using the current ported cab. Roll off some of the low end or better yet, use one of Fdeck's high pass filters. I've done that with my svt and ported cabs. Makes the OD sound better too. More grit and less fart.
 
#11
Thanks again for the replies.

The SVT 4 has an ultra-low and the cab has never had any problems handling that, even at gigging volume and with OD pedals in front of it. Perhaps the cab is working harder / in a different way with the tube head compared with being powered by a mosfet power section?

I did try turning the ultra low off and while made the distortion less noticable, it was most certainly still there. But I will say that if the head cant handle its own EQ options then that seems a little dissapointing and suprising.

I will have to try and do some more conclusive experiments using the two heads and possibly a different cab if I can find one to borrow, but I am still very eager to hear further suggestions and factual information regarding these amps.
 
#12
The description you give sounds fairly close to my SVT-II (non-pro). Low end definition will be the first thing to go as you increase the gain. My preamp will typically start clipping as any of the my EQ is set much above unity --especially the lower frequencies.

The Pro has a separate volume and gain knob, correct? How high do you have those set? I typically get my best "clean" voicing below 2 on my master volume (no separate gain). After three or four my head doesn't get much additional gain, just additional breakup.
 
#13
The pre on the 2 pro seems very sensetive to clipping. I play a gibson ripper which is very low output compared to a lot of other basses and its still setting off the red light anywhere beyond 10-11 o' clock.

Ive tried setting the input gain just below the point where it starts flashing constantly and working up the master volume to the required volume. Ive also tried doing the opposite and maxing out the master and using the gain as a volume control. The latter seems to yield the best results, but the low E notes are still very uneven sounding and prone to "farting".

Any other SVT users care to shed some light on the matter?
 
#17
Aharon said:
Thanks again for the replies.

The SVT 4 has an ultra-low and the cab has never had any problems handling that, even at gigging volume and with OD pedals in front of it. Perhaps the cab is working harder / in a different way with the tube head compared with being powered by a mosfet power section?
Click to expand...

If you were using it in bridge mode, that would be no surprise at all. If you weren't using bridge mode, are you using the same tone that you are on the SVT4? Is your bass's pickup closer to the string on the E side? The SVT4's rated 4 ohm output off of one side is only 100w higher than that of an SVT.

But I will say that if the head cant handle its own EQ options then that seems a little dissapointing and suprising.
Click to expand...

Knowing your equipment and it's capabilities is important with regard to both buying and using it. An SVT was not loud enough for me on several occasions. I would never ask an SVT to do an extremely loud scooped tone. I'd want an SS amp with significantly higher RMS output. A GK 1001RB-II would probably be a lot more in line with what you want, speaking from personal experience.

Aharon said:
The pre on the 2 pro seems very sensetive to clipping. I play a gibson ripper which is very low output compared to a lot of other basses and its still setting off the red light anywhere beyond 10-11 o' clock.

Ive tried setting the input gain just below the point where it starts flashing constantly and working up the master volume to the required volume. Ive also tried doing the opposite and maxing out the master and using the gain as a volume control. The latter seems to yield the best results, but the low E notes are still very uneven sounding and prone to "farting".

Any other SVT users care to shed some light on the matter?
Click to expand...

Clip lights traditionally come on around the -6db mark from actual preamp clipping IIRC. Crank away, especially if you want more dirt to your sound. It'll help compress those hard hits on the low E, give you a little more preamp grit when you dig in, and make it a little less prone to power amp clipping.
 
#18
just turn down the pre gain till the e stops farting regardless of the light is doing. I have owned a 2 pro for about 13 years and have never had that problem. is the bass active? if so dont boost the bass knob on the bass itself. run the bass flat.
 

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