Attenuator location in a preamp

[swinginguitar]

what is the theory/best practice surroung where to place an attenuator in a preamp design?

assuming 2 gain stages, would it be before, after, or in between the stages?

in my minds eye i'm seeing impedance changes if at the input/output....

[cjd]

With two gain stages, between.

A project I'm working on at the moment is getting an input buffer for the reason you noted, and the attenuator will be at the input side of the output gainstage.

[swinginguitar]

that aligns with what i was thinking.

what do you think of balance controls? un/necessary..nice to have?

[swinginguitar]

also, would it be redundant to use something like a PGA2311 volume chip as the attenuator in a discrete preamp design (meaning, the chip can function as it's own preamp/buffer in reality)

[JonMarsh]

Depends on your target for the overall performance, including input noise performance in a first stage buffer, and total output drive capability.

[cjd]

When I have balance controls, I'm forever tweaking - recordings are all over the place in my main setup, but the best stuff ends up being at 0. I don't bother with it now and just listen.

I've never worked with the PGA2311 or similar so no idea. But then, I barely know enough to not blow things up when it comes to this type of stuff, so really am not the best person to be answering.

[swinginguitar]

Depends on your target for the overall performance, including input noise performance in a first stage buffer, and total output drive capability.

Go on.....

[BobEllis]

For a nice (likely better sounding) alternative to the PGA2311 take a look over in DIYAudio.com for "Lightspeed" and "Poor Serbian Man Optical Volume Control" in the line level section. There are people selling boards/kits/parts so you can build from whatever level you are comfortable with. One thing I like about the concept is you can create multiple matched attenuators quite easily.

What are your sources? How is your system laid out? Are the preamp and amplifiers in close proximity? Input impedance of amplifiers? Are you in a n electrically noisy environment?

Most modern (digital) sources are capable of driving a 10-20K attenuator directly without a buffer. Often the digital source will output a high enough signal to drive an amplifier directly without any further gain stage. Depending on your amplifiers' input impedance, sensitivity to source impedance variations, the length of cable and environmental noise, you may not need a buffer on the output stage, either. Sometimes a buffer/gain stage with significant current drive capability after the attenuator comes in handy though.

As a minimalist whenever possible, I'd first try just an attenuator without any buffers/gain stages. If that works, you have had the least possible impact on the signal. If needed, I would add an output buffer/low output impedance gain stage. I'd only add an input buffer/gain stage if your sources are low level or high output impedance (like tube gear tends to be). There's my two cents, if it's worth that much.