This topic has been discussed at length in the forums more times than I can count. You might want to take a look at what is already been said. At a high level, you will note that people have some passion around this topic. There are different types of passives. Resistor based, transformer based, autoformer based, and others perhaps. These tend to be zero gain designs, so that all they can do is attenuate the volume from the source. They do not amplifiy. Resistor designs burn the extra volume off as heat, whereas transformers work by decreasing voltage by increasing current. You need to do some work to ensure that your source has high enough voltage to match the input sensitivity of your amp. Otherwise, you may not be able to achieve the desired volume. Also, especially with resistor passives, you need to make sure you have a match in input and output impedences, and you will need to keep the length of your IC's short. Otherwise, you may experience aberations at certain frequencies. They do not require AC power. They tend to be reletively inexpensive compared to active preamps at a given level of performance.
Personally, I like the transformer based designs (also known as TVC's) but I am not so hot on the resistor based designs. Most of the passive advocates will tell you they like the transparency and low noise of passives. Advocates of actives will claim passives result in a weak sound with no body, and will gladly sacrifice noise and transparency to get that body.
I haven't seen Sam's latest love affair? What piece is he hot on this time? |
I will answer part of your question. The main circuit of a passive preamp typically does not require a power supply. So no AC power required. In some cases, such as those using Light Dependent Resistors a power supply and AC power is required. You may also require power if your passive features remote control volume like the Placette RVC and no longer available Bent Tap (although I think you can still get the DIY remote kit). The idea and one of the main attractions of a passive is simplicity and to act just as an attenuators and possibly input switcher. Now for the rest of your question spend the next several days reading this thread and I think all your questions will be answered: Lightspeed Attenuator - Best preamp ever? |
Yes a lot has been written about the passive/active debate.
In a nutshell, the math (on which all electronics is based) goes against you when you run a passive system. The Lightspeed is no exception. You can improve the situation slightly by using setups that operate at lower impedances, but then your source has to support that operation, which is not something universal to say the least.
OTOH active line sections with marginal design will be easily beaten by a passive setup. So if you want to boil it down, on the cheap use passive, if you want the best you will have to go active. |
How could a passive preamp improve the sound of the amplifier?
Anyone..... |
Thanks to all have been responded. I have now begun my reschooling in basic electronics.
BTW, Brownsfan: Sam's current wunderlich (I know, bad pun) is the Music First Passive pre-amps. He wants to (again) do away with all active pre-amp because of all the "nasties" they ad to the music. Yes, but at what price and convenience?? |
If set up correctly, a passive preamp can sound as good or better than the some of the best active preamps out there. In my system, I have a high quality stepped attenuator built into the input section of my amp. Keep the interconnect 6 feet or less from digital source to amp and make sure the input impedance of the amp is at least 10x higher than the output impedance of the source. All digital source these days have enough output voltage to drive most amps to clipping. If you listen to vinyl, it gets more complicated. This is by far the best "Preamp" I've had in my system in 25+ years. |
It's funny, I was very very happy until I got a really nice active preamp. My Luminous Axiom blew everything under $1000 out of the water by far, but now that I have a nice active I can actually hear what I was missing---- primarily dynamics. Playing songs at the same volume in the beginning began to piss off my neighbors with the active when they weren't much louder with the passive. I was very happy with my passive and would use it again if I didn't have a job and means to buy something nicer. By the way, I did not like the Axiom at all with my turntable, it never sounded right. |
The best preamp I've had in my system is transformer-based and available sometimes for peanuts on ebay.fr:
Search for the Redson RC-1080 |
Lets list what a preamp does:
1. source selection
2. voltage gain
3. attenuation
4. buffering (impedance matching)
5. tone control (older preamps,typically)
Now, it is up to user to define his needs,since "the simple is the better" (or Okahm's razor) principle works in audio as well!
I ended removing the 2.,4.,and 5. |
Sounds real audio, it can't and to those in the passive camp that is a good thing? |
I think Atmasphere presented a balanced (and correct) view. And thanks for sparing us the partial differential equations and first principles analysis of why passives are inherently at a disadvantage.
I have benefited from use of passives while building my system. Along the way I've used passive or passive mode pre's from Adcom, McCormack, Endler, and two from Promethius. I now use the superb Promethius Signature TVC which runs about $2800 new. This was an easy choice for me, because I use a single source and don't need phono. Before you jump out of your skins, I do love vinyl and may go vinyl at some point. My current fixation on digital is primarily driven by the enormous advantage on availability of music, and the fact that my ModWright Sony is so good.
I have been careful to assemble a system around using a passive for volume attenuation and I could care less about remote control. At this point, my system is pretty good. I'm willing to begin to consider using an active. I expect at some point to A/B the Coincident line stage (5-6K) against my Promethius. No remote, 2 balanced inputs, all the money goes toward capability that I will use. By all accounts, it is a terrific piece. I'll be happy to keep it if it beats out the Promethius, even by a narrow margin.
I've heard far more actives that I dislike than actives I like. I auditioned a 20K BAT preamp that was very good. I've heard some other less expensive BAT stuff I also thought was pretty good, but I'm just not sure any of it could displace my Promethius. Most of the rest I've heard left me with an authentic "no thanks" reaction. What some hear as "body," I hear as unnatural dynamics compared to live music--the absolute reference.
I respect Atmasphere's advocacy of properly executed actives. His position is based on math, yet he stipulates there is a pragmatic consideration also. What each person has to do in assembling a system is define their needs and priorities. For people who need a full function preamp, it probably makes sense to put a good bit of money into the preamp and build out.
I started out a Maggie guy on a limited budget, so utilizing a passive "on the cheap' made some sense. |
When it comes to active preamps Ralph is the only designer I know that adds one more item to the list of what an active preamp should do and that is control the interconnect. As someone who is very passive friendly I can respect this point of view. If an active preamp is "acting" as a tone control then it is a flawed design or designed to perform that way, which in my opinion is wrong headed thinking, or it cannot control the interconnect and its artifacts. Transparency should be the key attribute of any preamp.
BTW I currently use a passive with my analog set up (tape and vinyl) with no issues. That is soon to change though. |
While I'll agree with Sam's article about passive pre's I did have a chance to listen to that particular passive unit for several weeks and it was extremely good but I still preferred Steve McCormack's VRE-1b pre-amp and by a wide margin, which by the way only puts out 6dB of gain. There's an axcellent review that just came out here:
http://www.ultraaudio.com/index.php/equipment-menu/284-smc-audio-vre-1c-reference-preamplifier
(Dealer disclaimer) |
Marebg, you forgot one of the most important things a great active is needed for.
- great sounding music from a stereo system
At least this has been my experience even when all the stars were aligned perfectly for a passive to shine. |
Do you suppose that Sunnyjim is really a troll, recognizing that we haven't all gotten our fists bloodied over the passive vs active debate for at least a month? |
Lets list what a preamp does:
1. source selection
2. voltage gain
3. attenuation
4. buffering (impedance matching)
5. tone control (older preamps,typically) Let's get rid of #5 for now- passives don't have them, most good line stages don't either. To that list we can add 'control (and limit) the effects of the interconnect. So: 1. source selection 2. voltage gain 3. attenuation 4. buffering (impedance matching) 5. control the effect of the interconnect cable. The the latter 2 aspects are not served by any passive or transformer device. If you have ever heard the difference a cable can make, then you might appreciate that if the preamp is doing its job, the difference between a $100 cable and a $10,000 cable could be rendered inaudible. Now some people want to pay for the cable so that they can say that they did that, but if you are not one of those people you might consider that you can get the same or better performance without that $10,000 cable if your line stage is built with that ability in mind. I find the colouration of uncontrolled cables to be unacceptable in any system. Sure it sounds transparent, but where is the body and impact? Not making it to the amplifier is the answer. To get around this problem people with passives will spend of lot of time and money sorting out the cable issues as best they can. So if you are thinking passive or TVC, keep in mind that the interconnect is the hidden and mandatory cost. |
I am not sure if a good TVC needs a particular cable or not. For me, I kept using the existing cable. But the most important aspect of a TVC (passive), I learned was the "gain" aspect.
You have to be absolutely careful in selecting the amp (and speakers - which I consider secondary) that you will be using with the passive. I was looking for a very good amp which was highly sensitive. the lower the sensitivity number, the highly sensitive it would be. The Parasound that I have has a sensitivity of 1V for full power (250 Watts). There are other amps that are more sensitive than this amp - but they are all tubes, and I did not want to go that route. When I got the combo in place, it sounded better than the integrated I had in place. But when I moved to the new room and wanted to place the speakers 4 feet in front of the wall, I missed the bass and body.
It was only when I moved up to XLR, that I actually got the "body" of the music that I was missing. I have my speakers 4 feet from the front wall and 30" from side walls and find that I have a great bass. Honestly, it is a night-and-day difference in my system. I believe this is the body and impact that Atmasphere is talking about. But again, it was a "gain" issue. Most people whom I have interacted with before, use TVC with tube amps. So, gain is not an issue for them, even when they use RCA.
I would be more than eager to compare my TVC with the Parasound JC2 preamp to see what more an active preamp can do in the system. If at all I upgrade the TVC to a active preamp in future, it will be either this preamp or the newer version of JC2. But my next upgrade will surely be CDP/Transport with a balanced output, that will ensure much more gain in my system. |
Atmasphere, Anyone who spends $10,000 on an IC has a problem no pre-amp can cure. :) |
Atmasphere, I am not sure I understand the "5. = control the effect of the ic" if it isn't already included in the 4. ie the low output impedance sees the ic's impedance+amps input imp. |
Here's my recipe for building a system around a TVC: Start with a source capable of 4V output (XLR) with output impedance below 100 ohms. Amps (Plinius) have 38dB gain in balanced mode. Genesis 350 speakers are anything but shy for bass and slam. Easily capable of concert level SPL's. I have cheap cables. |
Brownsfan, I think I agree with you; I have seen this, but really I used that example to make the point but it was also something I had experienced (BTW the person that had those cables was ecstatic that he was able to sell them and actually have better sound at the same time). |
