12-10-13: Unsound
Perhaps I've been misled, but I thought the redbook standard output was 2 volts? I haven't ever had occasion to look at the redbook specification document, but the de facto norm seems to be "full scale" (i.e., maximum) amplitudes of 2 volts unbalanced and 4 volts balanced. That would be based on the usual convention of defining balanced amplitudes as corresponding to the instantaneous difference between the voltages of the two signals in a balanced signal pair, the 4 volt number therefore reflecting each of the two signals being 2 volts. Ralph's designs are balanced, of course, although they often provide both balanced and unbalanced inputs. I suspect that is why he mentioned 4 volts. Best regards, -- Al |
Audiolab, what Atmasphere said about voltage levels is essentially correct (given my subsequent clarification), although his comment is most probably not applicable to the proprietary CAST interface that is provided on your amplifier.
For conventional (non-CAST) preamp outputs, the max output spec that for most high-end preamps is much greater than 4 volts represents the maximum output voltage they are CAPABLE of providing. That number SHOULD be much greater than the maximum output voltage they will ever be called upon to provide under reasonable input voltage conditions, in order to provide margin and assure good distortion performance.
For the non-CAST balanced input of your amp, the 3.58 volt sensitivity spec represents the approximate amount of input voltage that would cause the amp to put out its maximum rated output power (700/1400/2800 watts in this case(!), into 8/4/2 ohms respectively), assuming that spec is defined in the same manner that nearly all other amp manufacturers define it.
Most amps will be driven to their maximum rated power by inputs in the range of about 0.5 to 2.5 volts for unbalanced inputs, or around twice those numbers for balanced inputs. If you research the specs for amps from various manufacturers you will see that.
I have no knowledge of the voltage levels that the current-mode CAST interface operates at; perhaps the 18 volt figure you mentioned relates to that.
Regards,
-- Al |
Ralph (Atmasphere), thanks for the link and the comment about CAST. I see what you mean, and I agree. So I have no idea what the 18 volt figure mentioned by Audiolabyrinth would pertain to. That figure does not appear anywhere in the manual, btw, which includes a fairly comprehensive set of specs. Perhaps it was a miscommunication he had. I would expect that 18 volts into that amp would stand an excellent chance of destroying the speakers, the amp, and the eardrums of anyone nearby, if a fuse didn't blow first :-) Regards, -- Al |
The specs indicated in the manual for the Krell 700cx are 3.58 volt sensitivity (for its balanced input), 26.4 db gain, 700/1400/2800 watts into 8/4/2 ohms respectively.
26.4 db is a voltage gain of 20.89, based on db = 20log(Vout/Vin).
20.89 x 3.58 = 74.79 volts.
(74.79 squared)/8 = 699 watts into 8 ohms, corresponding almost exactly to the 700 watt rating.
Double that into 4 ohms (= 1398 watts), and double it again into 2 ohms (= 2796 watts). The results again correspond almost exactly to the rated power capabilities.
Ralph, I think you were right in the first place!
Concerning Keith's reference to "3.58 volts min," that is probably the result of a miscommunication. Sensitivity specs are usually neither min nor max, they are simply the (approximate) input voltage required to drive an amp to its rated maximum output power. And based on these calculations, that certainly appears to be the case here.
Regards,
-- Al |
An additional point: The 700cx is spec'd as being capable of putting out a maximum output voltage of 84 volts RMS.
Based on the amp's voltage gain of 20.89x (see my previous post), that output voltage would be produced by an input voltage of:
84/20.89 = 4.02 volts.
Therefore if someone indicated to Keith that the amp can handle an input of 18 volts without clipping either what that person said was misunderstood, or that person misunderstood the question, or that person didn't know what he was talking about.
Regards,
-- Al |
Michael (Swampwalker) & Charles, thanks very much for the nice words. 12-14-13: Audiolabyrinth
Almarg, Can you look into this for me, the spec of 18 volts input to clip, this is the max input told to me over the phone by krell, you can do more of the math and engineering calcalating for me to find a explanation for me?, LOL!, I will never use over 10 volts to input anyway!, just currious to know my amp,, when I said that the 3.58 is the min that krell told me, they said that because all of their pre-amps put out around 6 to 8 volts for balanced operation, and this will not do nothing harmful to the krell 700cx, its the normal that I am told by krell if useing a krell pre-amp Keith, the comments and calculations I already provided are based on a thorough look at the manual and the specs, so anything further I might add regarding the 18 volt number would be highly speculative. A speculative guess that comes to mind, though, is that perhaps it represents how much voltage the input circuitry of the amp can tolerate without the possibility of damage when the amp is in standby mode, or is turned completely off, or both. Regarding "their pre-amps put out around 6 to 8 volts for balanced operation," keep in mind that what any preamp puts out is dependent on the setting of the volume control, and on how much voltage is sent into the preamp by the source component, as well as on the gain of the particular preamp (preamp "gain" being the relation between its output and input voltages when the volume control is turned all the way up). So it's a bit misleading to speak of a preamp as putting out 6 to 8 volts, or any other particular number. Also, as Ralph and I both indicated earlier, the MAXIMUM output voltage spec that is often provided for preamps should be (and usually is) much higher than the highest output voltage that the preamp would ever be called upon to put out under reasonable usage conditions. Regards, -- Al |
12-19-13: Georgelofi
Nuforce dac 9 has RCA Output impedance: 0.01 Ohm. I see that in the specs at their website, and in the manual. Surely it is a typo, though? Regards, -- Al |
In his post dated 3-22-13 in this thread Ralph provided what I consider to be both a uniquely excellent explanation and an extremely persuasive proof of his contention that a balanced interface MEETING CERTAIN DESIGN CRITERIA (which unfortunately are not met by most audiophile-oriented components) can completely eliminate interconnect cable artifacts. See also his post dated 3-28-13 in that thread, which responded to some questions I had on the issue. Which is not to say, however, that I take an ideological position against passive preamps, or against having no preamp. As I see it, in audio there are usually multiple ways to do you know what to a feline and achieve good results, to express in a different way a point that Charles, for one, has made many times. In my own case, fwiw, the question is moot, as I require a full function preamp. Some of the reasons for that being: I want it to be able to drive multiple outputs (both volume controlled and not volume controlled), as well as select among multiple inputs; I want to be able to mute the speakers while listening to headphones, without having to turn off the power amp; my power amp is located too far from the preamp for a passive preamp, or direct drive from many source components, to be suitable; and the output levels of some of my source components would probably be marginal without some added gain. I'd expect those kinds of practical requirements, that a goodly number of people undoubtedly still have, to be among the reasons that preamps are unlikely to go away anytime soon. Regards, -- Al |
12-24-13: Audiolabyrinth
I have a problem with 32 volts out-put, although Ralph has gain controls outside of the signal, I want to know if that is a control to the output volts, My amp is fully driven at 3.58 volts!, clipping is 18 volts, an explosion! The 32 volt number could be 1000 volts and you still wouldn't have a problem. That is the highest voltage the preamp is CAPABLE of putting out, which as Ralph and I both indicated several times earlier in the thread should be (and usually is, for most high quality preamps) MUCH greater than the highest voltage it would ever be required to put out in normal use. The M-1 is spec'd as providing 14 db of gain, for line-level (non-phono) inputs. Which means that with the volume control turned all the way up the output voltage will be 5.01 times greater than whatever voltage is provided to it by a line-level source, at any given moment. Turning down the volume control would reduce that level as necessary. Also, once again, clipping is not 18 volts. Perhaps that number just applies to the input circuit of the amp, or perhaps the person who provided that number is confused. But since the output of the amp is spec'd as being able to provide a maximum of 84 volts rms, and the gain of the amp is spec'd at 26.4 db, per a calculation I provided earlier in the thread (on 12-13-13) the output of the amp will clip when the input voltage exceeds approximately 4.02 volts. Regards, -- Al |
Audiolab, I'll try this one more time, and then I'll cease and desist. The 32 volt spec is NOT A PROBLEM FOR YOUR AMP OR FOR ANY OTHER AMP IN THE KNOWN UNIVERSE.
Everything else being equal, the higher that number is the better. That number has NOTHING whatsoever to do with where you will set your volume control, and it has NOTHING whatsoever to do with how much voltage the preamp would be putting out in actual use.
How much voltage the preamp puts out depends on three things: The voltage that is sent into it by the source; its gain (which is a moderate 14 db in this case, for non-phono sources); and where the volume control is set. Again, where the volume control is set has NOTHING to do with the 32 volt number. Again, how much voltage the preamp puts out in actual use has NOTHING to do with the 32 volt number.
Please re-read the numerous posts Ralph and I have both made in this thread about specs on preamp output voltage capability.
Peace. Regards,
-- Al |
I took a look at the statements in the manual for the Krell 700cx that pertain to DC. As someone having no dog in this fight, I would offer the following comments: 1)The relevant section on page 14 (pdf page 18) begins with the statement that: The high DC output of tube preamplifiers may exceed the DC protection circuitry of Full Power Balanced amplifiers. Excessive DC level in a signal can damage amplifiers, speakers, or both. The coupling capacitors in Full Power Balanced amplifiers must be engaged when using a tube preamplifier. Note that the statement does not refer just to tube preamplifiers having DC coupled outputs, it also encompasses the great majority of tube preamps that have coupling capacitors at their outputs. How are those preamps supposed to output "high DC"? Also, note that when it refers to "the high DC output of tube preamplifiers," it does not make any reference to fault conditions. As if to say that all tube preamps routinely output high levels of DC, when operating normally. Which is nonsense, of course. 2)On page 19 (pdf page 23): Q. My speakers are rated for 150 Watts. Are the Full Power Balanced 400cx or 700cx models too powerful for them?
A. No. A speaker seldom is damaged from overdriving. More often, damage occurs when an amplifier that lacks sufficient power is asked to handle heavy demand situations such as high playback levels. These amplifiers may have very high 8 Ohm power ratings, but in heavy demand situations they can be driven into clipping (in which DC current goes to speakers due to loss of amplifier power). Clipping can damage speakers. This reflects a complete misunderstanding of how overdriving an underpowered amplifier can sometimes damage speakers. It has nothing to do with DC. The reason is that a clipped waveform has increased high frequency content relative to the original signal, which can damage tweeters. All of the above doesn't speak well, to say the least, for the credibility of whoever wrote the statements in the manual cautioning against the use of tube preamps without the amp's coupling capacitors being in place. 3)I have participated extensively in these forums for more than five years, and I cannot recall a single instance in which an amp or speakers were reported as having been damaged by DC emitted by a tube preamp. 4)I second all of the comments by Charles about the credibility Ralph has established via his lengthy track record as a respected designer and manufacturer of very high quality equipment, and that he has further established as a result of his extensive contributions to these forums. Regards, -- Al |
