Deang Posted July 31, 2003 Share Posted July 31, 2003 Before you pull the vanishing act on us -- what should I be looking for in a preamp if I use an amp with the following: Input Impedance: 412K ohm Input Sensitivity: 1.3V for full output Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 31, 2003 Share Posted July 31, 2003 Hey, Dean: I'm not pulling a vanishing act, per se' Really just taking the time to get myself ready for school. Once that starts, things get really crazy. I want to take some time to enjoy the amps I just finished. They are are so freaking quiet and clear sounding! But this isn't a plug for those -- sorry bout that. I'm just excited to be able to spend some time with them this weekend. You have a sensitive amplifier! Let me give it some thought, with the provision that it is only my opinion, Ok? I need to know some other specifics though -- kind of cables you use (do you know the per/ft capacitance of your interconnect?) length of cables from preamp to amplifiers, etc. I'm not sure what speakers you are using, either....all that info. would help. Are you looking for tube, solid state, combination....vintage, what? One is coming immediately to mind, which is one I have considered myself -- I'll tell you why after I come back from taking my dawg to the vet. Erik Quote Link to comment Share on other sites More sharing options...
Deang Posted July 31, 2003 Author Share Posted July 31, 2003 I use the Cardas 300B Microtwin. The capacitance is 42.9 pf/ft, and I use a 1 meter pair. I do have a 6SN7 SRPP Line-stage coming from Hong Kong, and I guess I'm hoping I get a good match. If not, I'll have to sell and try again. The only specs useful in the context of what we are talking about is: Output Voltage: 2V (Max25V) 23 steps volume control with 1/4W(1%) resistors I use the RF-7's, 100-102db/watt. I'm certainly still interested in your suggestion. Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted July 31, 2003 Share Posted July 31, 2003 Erik, the question I posed to you in the other thread was answered above. No need to reply Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 31, 2003 Share Posted July 31, 2003 Oh, you've already got one on the way! Well, that makes the choice lots easier -- use that one for awhile and see what you think. SRPPs are good, and it probably has a reasonably low output impedance. In your case, because of the very high input impedance and sensitivity of your amps, really low output impedance is not such an important factor. The Moondogs and Horus both have an input impedance of 100K, and are set up for max output at 2 Volts in. at 1.3 Volts, your amplifiers are effectively capable of 100% output with about half of the output of a CD or DVD player. If the preamp you are getting has min. 2 volt (pretty common line level voltage)and max 25 volt output, you certainly won't have problems driving the amplifiers. Cardas cables are really well made cables with outstanding termination, however 43pfd.ft is rather high -- these would not be good candidates for a passive preamplifer; and if the cables are long, that of course makes things worse. Just as a contrast, Dean, my interconnects are around 15pfd/ft, but terminated with BNCs (for the amplifier connection)and RCAs on the other. In short, whatever I would suggest to you would be for as low gain a linestage that you can get away with. The RF-7s (I remember now...sorry!)probably won't be as picky as my crossoverless Lowthers (those things pick up the smallest of noises!), so you might be fine! One thing I might do, since your amplifiers are new, is to listen to them on their own for a little while before inserting a preamp. This might give you a better feeling for whatever changes a preamplifier (whatever the make or kind)makes in the sound of the overall system. It will also give you a baseline for comparisons of different linestages -- if that should become necessary. So, if you have a means of controlling the output of your CD player, I would go straight into the amplifiers for a little while. This is really what I want to do with the Horus, so maybe I can get permission from Marie to let me keep things how they are for awhile. I want to get to know the sound of the Horus as intimately as possible, and without the possibly light alteration that may take place from inserting a complicating factor into the mix -- that being an active preamplifier. But this one you are getting sounds good, and I'd take a stepped attenuator with fixed resistors over a continuously variable pot anyday. Ron Welborne has actually spent some time addressing the potential noise issue with preamps, and has come out with a product with which I'm sure you're familiar -- the BP linestage. Battery power most certainly must be quieter than rectified AC from the wall socket, and it is a low gain preamp that uses tubes originally designed for automobile use. It is a version of Jack Eliano's linestage that uses transformers on the output. It's a nice looking preamp, and comes with an attractive outboard battery PSU. It might be a bit of a tweaky thing to work with, though, since one has to switch back and forth between charging mode, etc. A solid state preamp (especially if you have sucky hearing like me!)can actually sound very, very good with tubed amplification. In my case, I noticed more pronounced high frequency response, and I don't at all mind a treble and bass control to boost or reduce those areas. I have a Dynaco PAT4 that I got for next to nothing on ebay, that sounded surprisingly good! The balance control has completely gone out on it, so it's not being used at the moment. But lets see how this preamp you have already ordered sound! Quote Link to comment Share on other sites More sharing options...
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