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Bottlehead Forum Welcome! Need support, you got it. Or share you ideas and experiences. |
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Bottlehead Forum Welcome! Need support, you got it. Or share you ideas and experiences. |
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In Reply to: foreplay posted by fonz on October 4, 2000 at 07:47:39:
Now fonz, before we proceed further towards answering your questions/concerns, we need to sit down and clairfy the notions of "gain".(1) In broad generalized terms, amplifier "amplifys" sound. In other words it has to have "gain" in order to amplify signal to a certain level.
(2) pre-amplifier(aka preamp, line amp, etc.) as the name said, pre-amplify the signal before sending it to the power amp. The purpose of a preamp is to provide sufficient gain to drive the power amp. Relatively speaking, power amp may not have that much gain compared to a preamp stage but the sole purpose of the power amp section is to deliver as much "drive" to drive the speakers as possible. Anothe main benefits of preamp stage is that it "lowers" the impedance.
(3) Buffer amp in rather "generalized" terms, meaning it acts as a "buffer" between the 2 stage. In electrical terms, it's considered to be mostly an impedance converter converting high input impedance into lower impedance for ease of driving long interconnect cables to minimize signal loss and alteration due to resistance/inductance/capacitance. Buffer stage usually has no gain (gain no more than 1) esp. tube buffer stage which consists of a Cathode Follower.
The only exception is perhaps a Mu-follower or SRPP stage which offers gain yet lowers the impedance in a considerable manner.How much gain do you need?
Ans: Unless you have some ancilleries that can provide 4 volts rms with fairly low output impedance from the RCA jacks (no more than 10kohms, IMHO), you can then eliminate the need for extra "gain" to be able to propel your power amp to a sufficient SPL level (maybe using a passive attenuator to adjust the level). Unfortunately many sources such as RIAA phono preamp stage, cassette tape deck, CeeDee player, etc. it's output side doesn't possess both properties at the same time (low impedance and high output). In this case 1 of the 2 possibilities can happen: (1) if you have high source impedance and yet fairly high output then you can go with a "buffer" stage to lower your impedance to a satisfactory level before feeding it into the power amp. (2) IF you have high source impedance and low output then you'll need a preamp to effectively lowers the impedance and give it a bit more "kick" before feeding it into the power amp.
Foreplay: IT comes with a gain of somewhere around 18. Is that too much? My answer is:"It depends."
Why? In case of driving 2-stage SET power amp which , due to the lack of gain stage, often requires a considerably higher input swing in order to get the full output. In this case, Foreplay can swing out more than 8Volt to get virtually anything singing.
Question: What if I have a fairly sensitive power amp (like Bryston SState power amp) which doesn't need extra gain before I get a full blast?
Ans: Ok! In this case, a "Buffer" stage is probably what you'll need. While I do not stop people from trying a preamp with gain in this case, too much gain can be a bad thing. Most likely you'll experience some background noise as a result (more like hissing...).
Bottomline: If a little bit of gain is what you're looking for then yes, Foreplay can be configured with a "deeper" attenuator to give the best of both worlds to you. How much gain is "too much"? No, IMHO there's no definite answer to that. You'll have to look into your existing power amp before you can make judgements on that part.
Good luck!
Quest ;^>
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Follow Ups
- ah...the notion of "gain"... - Quest 16:17:47 10/04/00 (0)
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