I know Art has has his reasons but 600 Ohms is still quite a bit. |
I happen to come across some literature on the Audible Illusions L-1/3A preamps with output impedance of 1.2 kohms. Art Ferris designed them with tubes in parallel (thus halving their impedance),utilizing low-capacitance potentiometers,and increasing the preamplifiers current drive. Which prevents/minimizes high frequency rolloffs even with long cable runs. |
I posted this some time ago, but, I can't find it in the archives. It was originaly pubished in "the absolute sound" and written by David A. Wilson. I am of the understanding that "TAS" suffered a fire some time ago and this article is no longer available. With that in mind I don't think "TAS" will object to me posting it:" Guidelines For the Consumer...
IMPEDANCE.....PREAMP OUTPUT...........POWER AMP INPUT........
"HIGH"1.......OVER 600 OHMS...........OVER 100 K OHMS.......
"MEDIUM"1.....200-600OHMS.............20 K OHMS TO 100 K OHMS
"LOW"1........LESS THAN 200 OHMS......LESS THAN 20 K OHMS....
------------------------------------------------------------------------------------------
1In DAW's opinion, no official standards exist." |
Gunbei,
Thanks very much for the advice/info re: Luminous Audio AXIOM. I will check it out and maybe give Tim a call.
I did indeed decide to go for the Shallco on the BC21.1. Everything I've read/been told recommends it. Gilbert and BC have been excellent to deal with and his pumps and purse are a hoot. I think they'd be great for a second system in the bedroom, with great WAF I would think. ;-)
Max |
Gunbei, I'm not a Rowland owner and I'm basing this on a recollection of an old review, so please take this accordingly. I believe that Rowland believes(d) in matching output to input impedance as a form of power transfer. Maybe some Krell fans can report if this is the same thing that Krell does with their CAST system. |
Max,
Congrats on getting the BC21.1. Gilbert and Blue Circle are the kind of people that make this hobby fun. I'm thinking of ordering a pair of his high heel pump monoblocks! Did you get your BC21.1 with the Shallco stepped attenuator?
A passive pre that I like very much is the Luminous Audio AXIOM which in its basic form is only $125. With the AXIOM in the path it's obvious what the BC21 adds to the sound because no one region of the sonic spectrum is accentuated. What I noticed as the main differences are its balanced sound and excellent, detailed bass. However, with the AXIOM the midrange magic is missing and the depth of soundstage and liquid flow is gone as well. Ahh, those 6SN7 tubes!
http://cgi.audiogon.com/cgi-bin/cl.pl?preatran&1068325570
I still think the AXIOM is an excellent unit and Tim with Luminous Audio will make sure you get a unit that matches the output voltage and impedance of your source and input impedance of your amp. He'll also take in to consideration the sensitivity of your speakers and configure a unit that has the right amount of degrees of attenuation for your application.
It only has one input and one output, so it's basically just an attenuator, and it's about the size of a portable Smartdisk Firewire drive. Even if I rarely use it I won't sell it because I like it and who knows, I may be in your situation one day.
Good luck! |
Hi Gunbei,
Thanks for your response. I got the BC22 spec from Gilbert and the BC21.1 spec from the review on Soundstage. I had been thinking about a different pre that requires an amp with 50kOhms to operate ideally. I've decided to go with the BC21.1. :-) Can't wait to get it, but it won't arrive until later this year. :-( The midrange is where the magic resides.
Question: what should I do for a pre while waiting for the 21.1? I'm thinking maybe my old Denon receiver or the Channel Islands Audio passive VPC-1 (only US$250) to tide me over for now.
Max |
Max,
I've owned the BC21 and BC22 for almost two years now and had no idea what the specs were!!! Obviously they match very well, and have a nice sound. If your specs are correct it creates an interesting conundrum for me because the preamp that didn't match with the Aleph 3 was in fact the BC21! Oh well.
If you get the BC21.1, it should have a sonic signature a bit closer to neutral [whatever that is] because they use 6922 tubes as opposed to the 6SN7s in the BC21. The BC21 has a very nice full bodied midrange and upper bass for those folks that like that. I do. ;-]
Unsound, what approach does Rowland take to power matching? Thanks. |
While the guidelines above are generaly true, some manufacturers such as Rowland have different philosphies about impedance and "power matching". |
This is exactly what I have been trying to figure out, impedance matching. I am probably going to go with a pre and an amp from the same manufacturer, Blue Circle. The BC22 amp has an input sensitivity of 22kOhms, whereas the BC21.1 preamp is said to have an output impedance of 180 ohms, which translates into a 122:1 amp:preamp ratio.
Does this make sense to you? I'm not very technically knowledgeable, so please forgive my ignorance.
Thanks.
Max |
Hi Kool. Yeah, It may be that the AI has a lot of gain. But its 1.2Kohm output impedance mated to the Aragon with 22Kohm input impedance actually works out to 18 times, so it's well within the 10 times guideline. I've heard people say the range is 10-100 times. |
Kool39,
in cases with tube preamps you have enormous gain and output voltage to bring to the imput of amp. In this case you realy don't want the input impedance of the amplifier being too high since you will have much less volume controll capabilities from your preamp.
In case with passive preamp the philosophy stays near-same if you have high output voltage source. In my case I have passive/active pre with simple bipolar output stage that I switch sometimes when I play vinyl and turn off when I play CDs. I have approximately 0.5V out of my phono preamp with 0.5mV output cartridge and my VTL amplifiers have 0.55V input sencitivity(after recent mods). ON some records I feel lack of bass and have to switch the gain back-on and on some records it's plenty enough especially on 45rpms. |
Wonder if that is how the Audible Illusions L-1 and the Aragon 4004 MKII seem to mate so well? It surely cant be impedance because the Aragon is 22kohms where as the Audible Illusions is 1.2kohms which is in the lower limits of what is recommended. But the Audible Illusions has enormous gain. |
Clyde, what we've done is to give you a heads up on possible problems, because in most cases you shouldn't have a problem.
My experience of impedance mismatching with the excellent Aleph 3 is a pretty well known issue and was corrected to a great extent with the release of the Aleph 30. The input imedance of this amp was bumped from 23Kohms to 47Kohms which is pretty much in the standard. The BAT VK200 I use has an input impedance of 100Kohms.
I checked up on the Cinenova Grande 5 and it actually has a pretty low 27Kohm rating, so as Marakanetz advised make sure the preamp you pick has enough gain to drive it. I'm confident you won't run into problems though because this is a popular amp for home theater and most processors should be able to mate with it.
Good luck! |
Thanks form the info Marakanetz and Gunbei! Being new at this I didn't know it was that complicated. I'll do a lot more investigating before I decide on a pre amp. |
Marakanetz has it right.
Usually the easiest way is to use the same brand, but that may not necessarily be what you'll musically like the best. Did that make sense? Heheh.
Components within a certain brand shouldn't have impedance matching problems, but when mixing different brands careful selection is necessary. Case in point. I auditioned a friend's Pass Aleph 3 for a month and loved its sound. Fabulous on guitars and great layering front to back! But its low 23Kohm input impedance wasn't a good match for my system, which resulted in big loss of dynamics even with the volume cranked way up. In the end, even with the great sound I couldn't consider owning it with my current system.
What Marakantz has detailed is a good guideline for matching any preamp to an amp, but it becomes even trickier when throwing a passive preamp into the mix. Then you have to consider the output impedance and output voltage of your source components along with the amp's input impedance. |
The simpliest way is to take preamp of the same brand as amp.
Other cases you should match the input sencitivity of amplifier to the gain of preamp:
If input sencitivity of amplifier is low than preamp should have a high gain or the other way arround...
Not all cases are trivial and you should also know the other variable such as input impedance. In trivial case the input impedance of amplifier should be 10x of output impedance of preamp but this ratio is valid if the output of preamp is relatively high since transfer of voltage has substantial losses and the losses are certainly not linear since you're dealing with complexed signal i.e. music.
The ideal case is when input amp's impedance is too high and the output impedance is too low but if the output voltage capabilities are substantially higher than input sencitivity of amplifier than even 10x-rule has its own tolerances in that case... |
