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Ampeg SVT-II appreciation thread
- Thread starter i_got_a_mohawk
- Start date
Since you asked, it suggests you are not at tech. So if you want it fixed, take the amp to a good tech.
It's a pretty simple circuit.
R42 and C6 bypass a small amount of highs around the Volume control. R42 limits how much highs pass through the capacitor. The Bright switch bypasses R42, so more highs pass through the capacitor.
Could be bad switch, a broken connection, bad capacitor.
Thanks for your help and the circuit. I will leave the repair to a technician.
I've never noticed much effect from using the Ultra High switch on my SVT-II either, but maybe it's not defective... The Manual seems to indicate It's boosting the 8kHz frequency range, and says it more noticeable at lower volume levels... So It's kinda understandable that we wouldn't notice much deference if we play in loud rock bands; and if our cab didn't have a tweeter and was limited to a 5kHz frequency, and if you happen to play with old dead flatwound strings like I do. Not to mention further issues if we've played in loud rock bands for years and have somewhat damaged our higher frequency hearing ability.
Here's a link to the manual: https://ampeg.com/pdf/SVT-II300.pdf
haha (laughing) ... it's probably true that our ears have had to endure a lot. But I can remember very well that when I pressed the UH switch on my SVT II, the treble was noticeably increased. Sometimes so bad that there was a whistle. Or was that already the beginning of the end? Thank you very much for the link to the instructions!
I've been trying to find out when my amp was made. I looked at a ampeg pdf for the serial #, this doesn't seems to match at all. Appreciate any help
Hi, according to my information the explanation is as follows:
TNB = Part Number
D = North America
B = 1989
9 = September
0008 = Device # 0008
Regards Jurgen
TNB = Part Number
D = North America
B = 1989
9 = September
0008 = Device # 0008
Regards Jurgen
- Apr 3, 2003
- 35,515
- 19,939
- Disclosures
- Editor-in-Chief, Bass Gear Magazine
Nice! Those Baer cabs do love some tube power. I will have to try my ML-112's with my SVT-II. Good call!
Just had a weird problem with my SVTII.
was recording using the balanced out on the amp. I noticed a hum from my amp through my cabinet and thought it was maybe from someone elses amp plugged into the same power strip… ha.
Then I mentioned the hum so we checked the recording, the signal to the board was really distorted.
We tried some stuff and it cleared up for a bit, probably because I turned the amp off.
It came back ten minutes in.
It did emit really bad hum to my cabinet when I turned the graphic EQ on.
Turned off the power once and it cleared up, wonder if this is a bad preamp tube.
Thoughts anyone? Is there a tube that drives the graphic eq and balanced out but not the power amp?
was recording using the balanced out on the amp. I noticed a hum from my amp through my cabinet and thought it was maybe from someone elses amp plugged into the same power strip… ha.
Then I mentioned the hum so we checked the recording, the signal to the board was really distorted.
We tried some stuff and it cleared up for a bit, probably because I turned the amp off.
It came back ten minutes in.
It did emit really bad hum to my cabinet when I turned the graphic EQ on.
Turned off the power once and it cleared up, wonder if this is a bad preamp tube.
Thoughts anyone? Is there a tube that drives the graphic eq and balanced out but not the power amp?
I wonder if the DI is phantom safe. Turn phantom off. You can try lifting the ground, but the schematic does not show a switch for that. Disconnect the DI and see if the problem with amp clears. If no, the amp probably needs repair.
We tried a few different things so actually i guess it wasn’t specifically with the balanced out on the amp.
Sounded like a bad preamp tube (like a really bad sounding dirty distortion pedal) through the board but was only a moderately loud hum through my cabinet. Weird.
We tried pulling signal from the preamp out too now that i think about it. I turned the amp off and back on and it cleared up but it came back 10 mins into the track.
Got the amp plugged in and hot now and it’s dead quiet. Guess I will leave it for a few hours and see if it acts up.
Wouldn’t be surprised if it has a failing preamp tube. They’re pretty old.
Does Pre/Post have any impact on the distortion? When set to Pre, the DI takes the signal off at the front end of the preamp; after V1a and V1b. This is before all of the controls.
In Post the signal is taken after the Graphic switch...right before the Preamp Out. The entire preamp is in the signal path and the DI circuit is solid state. So if the output of the amp is clean, I don't see anyway it can be a tube. However since you said the output of the amp was distorted, it could be a tube. If the problem comes and goes when you switch the graphic in and out, it's related to the graphic.
Post/Pre had no effect, either way I got the moderate hum through my cab but no distortion through it. The distortion was only on the recording.
Switching graphic on had no effect, only weird thing with that was at one point switching the eq on caused a crazy loud hum through my cab which the volume control had no effect on, that happened only once.
At one point I switched the polarity switch on the amp it killed the hum through the cabinet but it came back.
Wonder if it was a problem with the board and not my amp…I can’t recall for sure if the hum through my cab went away when we unhooked the cable from the board..
Could be DI circuit damaged, gain too high on the mixer, or the mixer is damaged.
The SVT II manual has this block diagram.
AFAIK the manual does not document the output level of the XLR out. If it's line-level, it may need to be padded down 20-30dB to avoid distortion inn the mixer. If the mixer has a pad, try engaging it and resetting the input gain.
Well decided to do some preamp tube swapping on this.
Got to the point it was an audible hum through the cab, maybe 150hz or so, louder through the graphic eq and during rehearsal playing nonstop for 30-40 mins it would intermittently get louder. Power off and back on would bring it back to the quieter hum.
Took a spare 12ax7 to swap around. Started at v1 and made my way down. Swapping out v3 ended up making the amp dead silent again through reg eq and through graphic eq. Then went and played a chill gig. No acting up. But didn’t use the line out on the amp.
Feel good about this. Probably have a loud rehearsal this week and have a loud show later this week. Should be able to check the line out on the amp then.
