SVT Input Level

[CptnOblivious]

I'm running active pickups, a boost, and a preamp pedal, so pretty hot but not crazy. On the SVT Classic there's 2 inputs. Is it just preference which input to use? I've always heard if you're passive use the 0db and if you're active use the -15bd. Using the signal I described above it just seems to sound and work better in the 0db input. Is using the different inputs just the same as turning the pre knob or is there something else going on there?

 

[Wasnex]

Use the input that sounds best IMHO.

It varies from amp to amp what actually occurs. Often the input impedance changes, but not always.

The input will have both series resistance and shunt resistance to ground.

Here is a couple of signal flow workups for the SVT CL:

This is the 0dB input (J1). The signal passes up through a switching contact in J2. This puts R1 (22K) and R3 (100K) in parallel. I believe this puts the effective series resistance at about 18K. R4 shunts some of the signal to ground. I believe this shunt resistance is the input impedance (3.3Meg).

Equivalent circuit:

Now let's look at the -15dB input:

Here the signal only passes from J2 through R3, so the series resistance is 100K. Since the series resistance is higher, less of the signal will pass through. Ground is provided through J1 to R1. This puts R1 (22K) and R4 (1Meg) in parallel. Effective impedance to ground is about 21K. Since the input resistance is significantly lower, more of the signal is shunted to ground.

Equivalent circuit:

 

[CptnOblivious]

Use the input that sounds best IMHO.

It varies from amp to amp what actually occurs. Often the input impedance changes, but not always.

The input will have both series resistance and shunt resistance to ground.

Here is a couple of signal flow workups for the SVT CL:
View attachment 4880269

This is the 0dB input (J1). The signal passes up through a switching contact in J2. This puts R1 (22K) and R3 (100K) in parallel. I believe this puts the effective series resistance at about 18K. R4 shunts some of the signal to ground. I believe this shunt resistance is the input impedance (3.3Meg).

Equivalent circuit:
View attachment 4880282

Now let's look at the -15dB input:
View attachment 4880272

Here the signal only passes from J2 through R3, so the series resistance is 100K. Since the series resistance is higher, less of the signal will pass through. Ground is provided through J1 to R1. This puts R1 (22K) and R4 (1Meg) in parallel. Effective impedance to ground is about 21K. Since the input resistance is significantly lower, more of the signal is shunted to ground.

Equivalent circuit:
View attachment 4880285

Wow this is interesting man. It's gonna take me a long dang time to understand this but I'm gonna try my best.

 

[JimmyM]

Number of times I use the active setting with an active bass: 0. And that goes for any amp.

 

[Old Fart]

My experience is the same as Jimmy's. If I ever got a better sound from the -15db jack, then I would use it. This has never happened.

 

[Dave W]

Same here. I almost exclusively run active basses and I've never used the active input on any amp.

 

[Wasnex]

I have had situations where I used the padded input, but it is rare. It depends on how hot the output of the bass is, how much headroom the front end of the amp has, and what sort of tone I want.

My #1 is a Yamaha TRB6P. It's an active bass, but the output is not super hot. The one amp in my collection where I may use the padded input is my Ashdown CTM300. If I want a pushed sound, I use the regular input. If I want a cleaner and more dynamic sound, I use the padded input.

Another example. I have seen quite a few complaints that the Orange AD200B is hard to adjust because the preamp has a lot of gain. Some people roll lower gain tubes such as 12AT7 or 12AU7 into the preamp, so they can turn up the preamp more before the onset of distortion. Before going through the hassle of putting in lower gain tubes, I would use the Active input. I normally use the Passive input on this amp with no problems (I think it has stock tubes, but I bought it used, so who knows).

 

[JeezyMcNuggles]

I'm running active pickups, a boost, and a preamp pedal, so pretty hot but not crazy. On the SVT Classic there's 2 inputs. Is it just preference which input to use? I've always heard if you're passive use the 0db and if you're active use the -15bd. Using the signal I described above it just seems to sound and work better in the 0db input. Is using the different inputs just the same as turning the pre knob or is there something else going on there?

If you wanna drive it, plug into the 0db regardless