Passive preamp w/Rogue Medusa and Rega DAC


All,

I have become intrigued with the concept of a passive pre. At the moment, I think my preamp is the weak link in my chain. Key system components are MacMini-Rega DAC-Acurus RL11 pre-Rogue Audio Medusa-Fritz REv 7 speakers. At this point I am not ready to shell out the cash for a good active but thought about experimenting with a passive. I have concerns whether a passive will work in my system. Here are the basic specs on the DAC and Amp:

- Rega DAC: 2v output, 600 ohm output impedance
- Rogue: 200K ohm input impedance, Input sensitivity: 1.0V RM
- Fritz speakers 89db, 4 ohm
- Cables are all 1 meter or less

My concerns are the output impedance of the DAC is high (but the input impedance of the Rogue is very high and I can' figure out if the gain on the Medusa will be sufficient to run a passive.

Given the high input impedance of the Rogue, I think it will work with the DAC but am not sure. Based on the above, does it look like there are any limiting factors that would prevent a passive from working?

Any comments are appreciated. Thanks.
sruffle
Why wouldn't you just upgrade your dac to something like the Benchmark DAC 2 which can be run direct into your amp.

Personally, I think your DAC is the weakest link by far...especially if you consider how much more the DAC impacts the sound.

I'm not saying that a pre amp isn't important, but just because a pre amp is old, doesn't mean it's a weak link.

With a DAC, it's a completely different story. Newer dacs are making great strides and I wouldn't count Rega as a trend setter in that realm. (I've owned their digital products in the past and found them acceptable, but not state-of-the-art.)
His Rega dac get some good raps, even over the Benchmark, in some of the a/b's done.

But you are right Labtec going direct with a dac or cdp that has a digital domain VC is the only way to better the transparency of good a passive pre.

You just have to watch that digital domain VC's are used in the top 75% of their full output, otherwise you can run the risk of "bit stripping". EG: 16bit resolution down to 14bit then 12bit and so on the lower you go with them, if he has very efficient speakers he may not even be able to get to 75% let alone over it, before it becomes too loud for him.

This is when a good passive attenuator is the next best in transparency, as the remote controled digital domain VC of the dac/cdp can be full up then with no risk of "bit stripping", and the volume then set by passive pre attenuation.
And then you can still use the remote volume of cdp/dac within it's top 25% so you can adjust it from your listening chair.

Cheers George
http://www.rogueaudio.com/Contact_Information.htm

Ask your question at the source.
I've always thought that that only way of going one better than using a passive pre from dac/cdp to the poweramps is by going direct if the dac/cdp has a digital domain VC, and so long as it's used no less than 75% of full as I've stated in above posts.

Here is a statement fronm the designer of the TotalDac one of the best digital front ends you can get.
"Volume control:
I have made many different volume controls, including high end pots, relays, Shallco + stepper motor, LDR... The best sound was with the digital volume control made inside the FPGA of the DAC d1, made with a 69bit resolution. It was the only way not to "listen" to the volume control components. This digital volume control allows not to have cables and connectors in the signal path."

http://www.totaldac.com/principles.htm

http://parttimeaudiophile.com/2014/05/30/high-end-2014-totaldac/

Cheers George
Very interesting points about going straight from the DAC to the amp. One thing that I need is a really good remote control. I haven't done the research but I think that may be hard to find. This is something I should look into further.

The idea of a passive never occurred to me until recently when I upgraded the connections between my MacMini to the Rega. I got more detail but I also started hearing more glare. My initial thought is that the preamp was probably more to blame than the Rega. Going with a passive would be affordable and take the Acurus preamp out of the equation. As a bonus it would let me put more of my budget to upgrading the DAC in 2015.

Like most people, budget is a major issue for me. My original plan was to save up and spend 1.5K sometime next year on a good tube preamp. The year after that, I planned to upgrade the Rega DAC - by then I will have a good feel for how to address DSD (do I want it or not).

I may still go down that path but it seems that investigating a good passive (or finding a DAC to go direct to the amp) are worthwhile things to look at.

In the meantime, I will be borrowing a passive to determine if using one is even feasible in my system. Thanks for all the comments. This has been a great thread!