Input Voltage level

[triode17]

To fellow tube amp designers, what input voltage do you use as a standard? 0.316v (-10) or 1.22 v (+4) or what? i am redesigning my SE amp and adding an input stage. I think all my builds use a different level depending on the topology.

 

[triode17]

What is the highest level of source signal that you want it to accept? Give it some headroom above that.

The CD player which is 2v RMS max but all the signals are going through the preamp so i can set any level i want.

 

[BinaryMike]

I generally try to design power amps for 707mV rms input sensitivity. That's 1Vp or 2Vpp, which simplifies internal gain calculations a bit. I'll give the amp a little more overall gain if it turns out to be easy with the major components I settle on, and I'll accept numbers up to 1V rms or slightly greater if I'm struggling to hit the target. So the acceptable sensitivity range for me is roughly 500mV to 1V rms.

 

[triode17]

Thanks Mike and Retro. Let's see what others have to say as well.

 

[triode17]

The gain of each stage and the power output you want is going to have a direct bearing on the input sensitivity the front end needs. Any FB in the mix?

I understand that, I know how to stage the gains but just want a feel for what levels are out there. Say using my PAS3x.
And there's no feedback.

 

[dcgillespie]

I don't design around a set sensitivity level per say because that doesn't take into account the power output capability of the design. Let's face it, all else being equal, an 80 watt amplifier is going to send twice the quiescent noise to the speakers than a 20 watt amplifier is, but for all practical purposes, in my listening room with Cornwall speakers, 20 watts per channel is more than enough. As a result, I take into account the total gain of the amplifier, and more typically strive for a sensitivity based on a gain of about 11 in all of my own units. That way, the 20 watt amplifier will be driven to full power with an input signal of about 1.15 vac rms, while the 80 watt amplifier will require about 2.3 vac. Both of these input level requirements are well within the capability of any good preamp, but by adjusting the sensitivity level to the power output capability, it makes for a much more practical installation in the listening room. An 80 watt amplifier with a 1.15 vac input sensitivity connected to a PAS amplifier and Cornwalls is going to be pretty noisy in my listening room, while a 20 watt amplifier with that sensitivity rating will not be -- but both can still be easily driven to full power so that the capability of both can be realized, while importantly, the volume control when using the 80 watt beast won't be operating in the weeds.

Dave

 

[BinaryMike]

I respect Dave's point of view, but considering that folks often choose speakers with sensitivity appropriate for the amp they'll be used with, then it makes more sense to standardize amplifier input sensitivity.

 

[gadget73]

Also worth considering the max output of your preamp. If it tops out at 2v, you don't want something that needs more than that for full boogie. If this isn't paired with an active preamp I'd probably aim for a lower input voltage just to make it friendlier for more sources. If going with a gain stage that has a lot of possible drive, don't make it so sensitive the volume control is barely cracked either.

 

[triode17]

I respect Dave's point of view, but considering that folks often choose speakers with sensitivity appropriate for the amp they'll be used with, then it makes more sense to standardize amplifier input sensitivity.

Dave, I have to agree with Mike. The Cornwalls are 101 dB/w SPL so any amp. would show its noise here. I want the same level settings for each amp to reach full power. This way, I can interchange the five amps. I have without concern.