Eros & "Passive Pre?"

[milosz]

I see the output impedance of the Eros is 4k, I assume then that I will not run into noticeable trouble driving my power amp through my 50k-pot-equipped "passive preamp"-
provided Eros has sufficient gain to drive the amp- which I won't really know till I try it.

I will be using really short interconnects- less than 12 inches.

So, assuming there will be enough gain, it should work fine-  unless there is something I am not considering???

If anyone can think of something I missed in this idea, please let me know.

[Doc B.]

The Eros into 50K should be fine.  The 50K passive into your amps might be more of an issue. You typically want a ratio of somewhere around 1:3 to 1:10 between the output impedance and the source impedance. So the amps should have an input impedance of 150K at minimum (250K would be better) to work their best with the passive control. Not saying it won't work, just that the higher the ratio the more theoretically optimal the setup.

[milosz]

Lowest input impedance of any power amp that I have is 500k. Some exceed 1 meg....

The first stage of any of my power amps with which I'd use the EROS into a 50k pot volume control  are JFETS, the specs say 500k or 620 k or just "over 500k" depending on the amp. One amp has a pentode as the input stage, this is over 1 megohm and very low Miller capacitance...

So I'm guessing it will all be fine.

[Doc B.]

Load match should be OK. Even so keep those cables between the 50K pot and the 500K amp input as short as possible and well shielded.

[tttubes]

I've been using a passive with silk tvc's with great results into my welborne labs Apollo amps.

[levlhed]

I started looking into a way to switch between the Eros and my DAC/computer into Crack/Speedball.  I liked the idea of a passive pre but after reading about the impedance issues I stumbled upon Transformer Volume Controls or TVC as mentioned above.  Though I don't really need volume control..all I really need is a hi-fi switch box, ideally with a pair of outputs so I can send audio to another pc for recording/etc.

Should a TVC based pre work well?  I'm specifically looking at the Promitheus Audio TVC unless I stumble upon something else!

[Paul Joppa]

If you just need a switch box, they are available for very little money. Radio Shack used to have several models, for instance. Many of them are labelled for video use and may have three channels, but you don't need to use the video one. They are not of course the best quality switches, but it will get you running while you search for better options. I used one for a few years, until I wound up with the FP-III prototype.

[levlhed]

Yeah I guess I *could* just use an A/V "clunk box", but that seems dirty and wrong...$1,000's of audio equipment run through a $30 piece of plastic and tin?