Passive preamp w/Rogue Medusa and Rega DAC


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.
You have great system parameters for a passive.

Your cdp at 2v has double what it takes to clip your amp at 1v.
It's output impedance will be fine into a 10k or 20 k logarithmic passive, if going the way of a potentiometer I would use something like the Dact [url][/url]
The input impedance of your amp at 200k is very passive friendly and your speakers are fine with mid range efficiency.

All in all you couldn't ask for much better, and you will hear your source in the cleanest, most dynamic and uncoloured possible way.

Cheers George
Good Point George and I think that would make the Lightspeed Attenuation a very good aprox. 450.00 option. That is the one I would chose if I had his equipment.
Thank you for saying so Marqmike, I refrained from saying so, otherwise I would have had the wrath of the anti passive preamp brigade coming down on me, yet again!

Cheers George
I am a happy Lightspeed owner and user :)
Thanks to all for the replies. I have been reading the massive LS Attenuator thread with great interest. (I will probably get to the end of it by 4th of July). I would love to try it but the only catch for me is that I need a remote control.

I think a reasonable path would be to try the cheapest passive I can find in my system. If it works and I like the nature of what I am hearing, I could then upgrade to a better passive and keep the cheaper one as a back-up. (while selling my current pre-amp).

Even if I don't like it, trying one is definitely something I should experiment with.
Definitely worth a try Sam for the money, compared to the cost of a good active preamp.
The sound you'll get with a passive pre in your setup will be honest to the source, the frequency and dynamic range of it will not be limited, and it will be uncoloured, with zero distortions, you may love it.
If not then the search begins to find what all the different actives preamps will bring to the sound, as they all sound different.

With a passive friendly system such as yours, and probably more than 75% of other owners, here is a quote from Nelson Pass who calls it like it is. (one of the true gods of audio).
Cheers George

Nelson Pass,
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

To get the same transparency and gorgeous sound you could spend thousands on an expensive pre-amp or spend a few hundred for the Lightspeed. It all depends on how much you like to throw away your money. I personally like money and LOVE my Lightspeed.
If you need a remote, a Tortuga LDR passive is the way to go. I had one in my system for a couple weeks and I was very impressed.
Thanks for the great responses on this thread. I definitely want to try a passive. I have arranged to borrow a simple volume pot to put in my system to see if the gain is sufficient. If it is, then I will pursue a better one to try out.

I would love to try the Lightspeed but my listening room is in the family room so a remote is essential.

The concept of the passive makes so much sense. In my case, the preamp is not in the same class as the rest of the gear so the benefits could be substantial.
Sruffle, where are you located? You might get someone close by to hook up a lightspeed to your set up to see if you like it or not... Just a thought.

The remote control issue bothers me and can be a pain sometimes. At times, I set the volume and leave it. Other times I get volume ADD, and thank George for introducing some sort of physical activity into this hobby besides moving speakers an inch, daily.

I'm working on some sort of remote control device... Rubber band around the volume knob connected to a servo? There's got to be a way to make something remote controlled to move the volume knob.
I've had a few customers who have taken it on themselves to add their own remote volume controls to their Lightspeed Attenuators, like these aftermarket ones.



They can be coarse in their action. And the remote buttons don't last.
I cannot afford to use them as for me they're just not reliable enough especially the hand sets.
With the Lightspeed being very reliable as it is, and at the low shipped price it is, I don't need or can afford to have returns coming back because of these after market remotes, from companies that look like their here today gone tomorrow, then spare parts become a problem as well.

The only companies that make good quality ones are the big boys Sony, Yamaha, Panasonic, ect and you cannot get these quality ones for the small manufaturers like me.

Cheers George
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

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."

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!

05-30-14: Sruffle
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!

Definitely worth a try with your system, to hear it at it's most transparent, dynamic and extended from top to bottom.
Just make sure the one you try has a 10kohm or 20kohm logarithmic (A taper) pot inside it.
And that your interconnects are <100pf (picofarad) per foot capacitance, which quality ones usually are.

Cheers George
How are people liking the Tortuga's these days?

I like the concept and approach and have seen some good reviews but have not heard these.
Well, I made the leap. I replace my modded Acurus RL-11 with DIY passive that uses the Tortuga LDR3V2 board. I received it this weekend and gave it a trial run Saturday and Sunday. My first reactions were mixed. Because I was juggling taking care of the kids and getting used to the remote I didn’t really get a good feel for the sound but I will say that I wasn’t bowled over right out of the gate.
The second night I was able to sit down and really dig in. I am not a reviewer but my impressions were:

1) Lower noise floor – I listen to a lot of live Grateful Dead and this was particularly noticeable on several live recordings.

2) Increased detail

3) Better tone and timber - on jazz recordings, horns and saxes seemed more pure and free flowing. Additionally some glare was removed from my system.

This was exactly what I was hoping for. One thing that I did realize is that the Acurus has a great remote. I am going to order an Apple remote to see how I like it.

I was looking for some of the typical characteristics that critics of passives highlight. Other than not liking the remote as much, I didn’t sense any deficiencies. Maybe I will in the future but for now I am very happy with the decision to go this route. This is a great component to build a system around. The money saved from upgrading the preamp can now be put into a DAC upgrade somewhere down the line.

Again, thanks to all the responses on this thread. This has been a significant upgrade for relatively minor dollars that will give me much listening pleasure going forward. I may post some more impressions after further listening