Bas-x A-100 feature request - Passive Preamp Mode

[Chris]

Hi,

I'm really loving this little amp! I am using it in a small designated music room for testing small speakers. I'm currently listening with Focal 905 speakers I picked up from Music Direct. Fantastic speakers! My input is the crazy small Raspberry Pi Zero W with various DAC "Hats" streaming music from my LMS audio server. Amazing sound!

I also have some powered speakers I want to test. I know I can hook these up to the "Loop" rca outputs on the Bas-X.

I was thinking it would be cool if there was a mode where when the Bas-X was in standby mode it could still pass the audio through the volume control and out the loop output rca's to the powered speakers. It would be a kind of passive preamp mode?

I think this would be a very cool upgrade to the Bas-X that would make it even more flexible.

I bet the Emotiva Wizards could figure out how to do this?

-CB

[petew]

The preamp needs to be booted up to talk to and manage the volume control chip. There are other powered chips handling analog audio into and out of the volume control chip. No way that's all happening with the unit in standby.

[leonski]

The preamp you want is the W4S STP SE. It is basically 'passive' to some level before adding gain.

www.stereotimes.com/amp082912.shtml

And it overall gets good reviews.

I could probably build you a good passive using a resistor stepper, for 400$ or so. Maybe more, depending on casework, connectors and switching.

[Boomzilla]

Hi Chris -

Passive preamp mode is a terrible idea, even without the limitation that petew mentioned. Why? Because there's no way to know what output-impedance the source device has or what input-impedance the downstream amplifier has. This is generally considered important because both were designed with expectation that the output-impedance of the source would be significantly lower than the input-impedance of the amplifier. To make this happen, the preamp normally has a fixed input-impedance (traditionally, up to 47K-ohms) and an output buffer amp that has a low impedance.

If this isn't the case, or if the impedances are wildly mismatched, all sorts of frequency response artifacts occur. For example, I've found that driving a high-input-impedance, 300K-ohm tube power amps works fine with a tube preamp. But if I try to use that same tube preamp with a solid-state power amp, sometimes it gets ugly.

Such issues are easily avoided with a preamp that has active buffer outputs to keep its output-impedance reasonably low.

Cheers, Boomzilla

[Chris]

I have much experience with Passive mode and am aware of system matching but it is not a "terrible idea".

I built a PS Audio passive preamp kit way back in 1980's and had a good time with it. I also have Channel Island's great passive preamps as well.

Back to the BasX A-100, without knowing the details of the circuitry I was just throwing out an interesting usage scenario to consider. For example, I'm pretty sure my XMC-1 will pass TV video even in standby mode so these types of things are possible.

Right now to use my BasX A-100 with my powered speakers I will have to disconnect the speaker connections from my other passive speakers. Allowing a pass through volume control (passive or buffered) while in a "special standby" mode would be an interesting feature. Whether it tickles the Emotiva engineers itch is another question.

The BasX A-100 is an interesting creation as it stands considering its ability to also drive high impedance headphones by moving a jumper. Clearly the Emotiva engineers were having a good time and thinking outside the box when they designed it. This is how great products become "Classic" products.

-CB

[garbulky]

Oct 15, 2017 11:25:11 GMT -5 Chris said:

I have much experience with Passive mode and am aware of system matching but it is not a "terrible idea".

I built a PS Audio passive preamp kit way back in 1980's and had a good time with it. I also have Channel Island's great passive preamps as well.

Back to the BasX A-100, without knowing the details of the circuitry I was just throwing out an interesting usage scenario to consider. For example, I'm pretty sure my XMC-1 will pass TV video even in standby mode so these types of things are possible.

Right now to use my BasX A-100 with my powered speakers I will have to disconnect the speaker connections from my other passive speakers. Allowing a pass through volume control (passive or buffered) while in a "special standby" mode would be an interesting feature. Whether it tickles the Emotiva engineers itch is another question.

The BasX A-100 is an interesting creation as it stands considering its ability to also drive high impedance headphones by moving a jumper. Clearly the Emotiva engineers were having a good time and thinking outside the box when they designed it. This is how great products become "Classic" products.

-CB

Chris you are 100% right about the basx status. As it stands the basx a-100 is going to go down as a real hot classic. When you have headphones that need its kind of power there is NOTHING like it on the market anywhere near its price. And I'm talking about 1 grand headphone amps!

I LOVE this product and think they need to use this exact circuitry and repurpose it for a dedicated ultra high end monoblock class A headphone amp setup selling for $600-1000. It'll beat out everything out there.