Ampeg SVT-CL Bias Lights and slight buzz

[Eskimo Spy]

Okay, I just got my SVT-CL, and I have a question about the bias lights...

There are two lights, a red and a green for each set of three tubes. When I am playing, the red lights light up with the signal. This is normal behavior. But should the green bias lights remain lit under normal conditions?

Also, how much noise should I expect from the head? Running through a 4ohm cab, even after switching the polarity switch to all three positions, there was noticeable, but not terrible buzz.

 

[JimmyM]

Okay, I just got my SVT-CL, and I have a question about the bias lights...

There are two lights, a red and a green for each set of three tubes. When I am playing, the red lights light up with the signal. This is normal behavior. But should the green bias lights remain lit under normal conditions?

Also, how much noise should I expect from the head? Running through a 4ohm cab, even after switching the polarity switch to all three positions, there was noticeable, but not terrible buzz.

bias lights: every cl i've used has bias lights that stay green unless i'm playing.

noise: nothing beyond normal operating noise that you'd hear out of any other amp. it's possible you could be picking up interference from something in your house, though. dimmers, flourescent lights, tv's or monitors nearby...etc. also, being too close to the amp with the bass can cause noise. so rule interference out before you go tearing apart your amp.

 

[Eskimo Spy]

The bottom lights stay green, the top lights flash red with the signal.

I hear buzzing, and when I put it in standby, the buzzing goes away. It is plugged straight into the wall, no strip between it and the wall, but it's a 4 year old house, not a 40 year old house. And it's a brand new head, so I'm not tearing anything apart! If it's broke, they can fix it.

That said, I'll see if the buzzing still exists when I plug it into my new Aggie DB 410 cab when it arrives tomorrow. I ran it into my Ashdown ABM 410T cab tonight just to see what it sounded like tonight.

 

[JimmyM]

my house is only 2 years old and i can't get a clean signal in most of my house.

 

[Eskimo Spy]

Hmph. My Ashdown runs without much noise, but like I said, it's not horrible, just noticeable. It still sounds fantastic though.

 

[johnk_10]

it sounds like you're describing a normal amount of noise to me, but some preamp tubes can be noisier than others.
you bias lights are operating perfectly as described in the manual on page 7.

 

[Alexander]

The bias lights should stay lit green when not being played. You can adjust the bias screws until this is the case. Even when they are both green, you have some play and IME can adjust until they are both green AND the buzz goes away. If you cannot do this, or the bias adjustment does not hold over time, then you might need to get the amp serviced.

If both lights show (and stay) green and you cannot dial out the buzz with the bias controls, I agree with others that you might have a noisy tube somewhere or dirty signal.

 

[Eskimo Spy]

Well, my new cab won't be in until tomorrow. I'll connect it and see if the buzz is still there with a surge protector, if it is, I'll try adjusting the bias, then try swapping out the preamp tubes.

 

[ajunea3]

I've noticed that if I bias my CL too far in either direction I get buzz; and the more I over- or under-bias the amp the stronger the buzz gets. Try fooling more with the bias lights to see how they affect the noise.

 

[babyjo]

It sounds like you may be using an instrument cable instead if a shielded speaker cable. Using an instrument cable instead of a speaker cable will destroy the head and cabinet.

 

[babyjo]

Verify that the cable is a speaker cable. It is often difficult to tell the difference. Also, with an SVT it is good to use a thick speaker cable. The thicker the cable, the less noisy it is.

 

[akane3]

hello,

I have an svt-cl, and it sounds great and seems to be working just fine. There is no buzz and it is loud and punchy, however... the bias lights are basically the opposite of what is described in the manual. They are red when not playing and the signal makes the green light turn on. When I re-bias I can not get the red light to turn off without the green turning off first. Does anyone know what is wrong? and if this is a problem why does it seem to be working fine for so long?

 

[B-string]

Could just be a fault in the user bias indicator (LED) circuit. Doesn't effect amp operation but makes user setting of bias unreliable.

 

[InsanityAmps]

The cl is supposed to be biased between the range of both green to green plus red almost coming on. The last time I had one of these in I checked the bias manually and found that proper bias(60% which is still cold to some) was actually achieved with both red lights on. The way ampeg has you bias those amps in the green is pretty cold. Good for tube longevity but maybe not as warm as some like. I think the best setting, sticking with Ampeg's 'both green lights on only' would be to turn the bias knobs until you see the red leds come on then back them up just enough to turn the red leds off and no more. If they are not biased close to each other there will be a hum in the output that does not change with volume and gain knobs and the more they are off, the more hum you will have. If the hum goes up and down with the volume knob then it is something in the preamp.

 

[akane3]

So changing the tubes wont fix this problem? Or is it even a problem?