I have never experimented with a high end system that was not improved by active pre amplification. I am aware of the arguments for passives and the theory behind their less invasive circuitry, but find they are always inferior to the best active.
In reality, passive preamps must rely on the same contact switches, input and output jacks and wire to route signal. All of these introduce distortion and loss, without the benefit of the gain and impedance matching provided by an active unit.
An active preamp designer tweaks and voices the final product to maintain repeatable results. A passive unit must deal with unknown quantities and qualities of signal, each having an unpredictable effect because they are not corrected, damped, amplified or impedance matched.
Personality is certainly a factor in an active preamp as well. However, it's performance will be predictable in almost every situation. It is not uncommon for a wide variety of listeners to describe the sound of any given active preamp in the same way. Personal taste comes into play as to which brand name makes the listener happy with their existing components.
Driving directly from a low output source such as a CD player or D to A converter is just as bad. This set up does remove the additional passive parts but still provides no impedance or gain matching.
Worse, the output from these devices may supply adequate voltage for the desired sound pressure level without the control, contrast and huge dynamic swings necessary to make great sound. They appear to be doing a great job until a direct comparison is made against a high quality active unit. The problem comes in justifying the expense of the active that provides all positives for your system.
For reference, consider auditioning the Aesthetix Callisto. I think you will find this tube preamp has virtually no limitations. It's sonic signature may also be altered to your taste by experimenting with various tubes. If this unit is financially out of reach, there are many other fine active units for sale. I suggest you start by looking here at Audiogon for a BAT, Counterpoint, Audio Research, Atmasphere or perhaps even a transistor unit such as a Rowland, Gryphon or Presence Audio. |
You have one false statement in your subject paragraph: "Analogue phonos are able to produce the same kind of outputs." The output from a cartridge is very depandant upon the design, Moving Magnet, Moving Coil, etc.; the output ranges from ~0.2mV - ~1500mV. While the output as voltage may be suficcient to drive some amplifiers ( from the high end of the scale) you are forgetting the issue of Phono Equalization. The output from a phonograph/turntable MUST be equalized for the signal to be balanced music. There are many curves, but the RIAA is the only one used today for new recordings. There are primarily two means of effecting this EQ: the first is an Active EQ circuit, where the signal is amplified as it is EQ'd, the second is Passive. THe traditional problem with a passive design, is that the EQ will drift as the gain device (vacuum tube or transister) changes gain; thus the EQ can/will drift over time. Additionally the input "load" that most cartridges like to see is 47K Ohm, Not what most line level inputs like.
Using a passive pre-amp for line level ( CD, Tunner, Tape, etc.) can get you "closer" to the music, and there are many purists who have one source connected directly into their amp. This should not be done w/ a phono input!. But the down side is that most avtive pre-amps provide a level of protection for the downstream devices, which is lost in a passive unit. If you have considered balanced inputs, you will not be able to use a passive pre-amp.
The choice comes down to your listening preferences and system habits. if you feel that the reduced control allows you to hear more and that is OK, then get rid of the pre-amp. If the Phono is your primary source, you will need some type of Active Pre-amp.
Good luck |
I had an EAD DSP 7000 MK3 with balanced outputs. It worked great with my Audio Synthesis ProPassion Passive Preamp and Plinius SA-100 MK3. If you have the balanced version, you can adjust the output voltage from 2V all the way to 12V via dip switches located inside the DAC. The 8V setting sounded "wunderbar" in my system! Get rid of all those unnecessary circuitry, go passive!
Enjoy! |
marakanetz: while it may not be true with your transport/dac combo, some high-quality dcp's offer digital volume controls that may substitute for pots in analogue pre's. i'm personally acquainted with most of the accuphase line, having owned several of their components and listening at great length to most others. in my experience, the single-box acuphase dp-75v and the dp100/dc101 sacd/cd combo both sound significantly better when run directly to an amp of equal quality to the digital units than run through a pre, even one built by accuphase. soundstage widens and deepens and the sense of PRaT is quicker and more life-like. more importantly, the sound is cleaner, as though a veil were removed from the speakers.
i do agree with albert porter that you will not likely prefer a digital source run directly to an amp (tube or ss) if you are a diehard valve fan. a great tubed pre, like the aesthetix callisto or its sister phono stage, the io, will sooth the soul of many who'd rather be playing vinyl records than listening to a laser detect the binary reflections off a piece of metal-coated plastic. i additionally confess that i've not heard ANY source, no matter how cheap or dear, that didn't sound better played through a boulder 2010 preamp. 'course one might expect such after plunkin' down $36k. -kelly |
It has been said many times that simpler is better. I believe that to be true in a lot of situations but is not always true in passive preamp. Albert talks about impedance matching being a problem in passives. It is a misnomer to talk about matching impedances because in a standard pre / power combination the output impedance of the preamp is many times smaller than the input impedance of the amp. It is the desirable low (~100 ohms) output impedance of the active preamp designs that allows the pre to drive the capacitance of interconnects without frequency degradation.
If one was to match the output impedance of the preamp to the input impedance of the poweramp you would only get half of the open circuit voltage output of the preamp into the amp. Tube amps typically have a higher input impedance that solid state but the designer is free to set the value to practically any value within reason. With the higher input impedance of a tube design it MAY be more sucessful with a passive pre. The biggest problem with a passive preamp is the higher output impedance (1000 ohms or greater) can react with the capacitance of long cables and dull the top end. I use a buffered passive design most of the time. It has a gain of one but an extremly low output impedance. I find that it can drive most power amps to full output and has the ability to drive a capacitive load with ease.
Several of the variable output CD players have a low output impedance. If they have enough voltage output to drive your amplifier to full output, I would believe you could do no better. I feel that the best sounding preamp is no preamp at all! If the system does not require the added gain or a lower output impedance, I do not feel the added switches and circuitry can improve the sound.
Chris |
I recommend a "Search" in the Audiogon Forum archives, for this topic has had a lot of discussion. I don't know that there is any "importance of using active stage in tube setup": I've been happily using passive preamps with three tube power amps. You don't want an impedance MATCH between passive and power amp, but rather a power amp input impedance 5 or ten times as high as the passive's output impedance, namely, the "size" of the passive, typically 10K ohms. But I've also used a 10K ohm passive with Pass Aleph 3's, whose input impedance is only 23K ohms. I think the more crucial factor is whether your source output stages are up to driving a passive, or whether they need active preamp help. In general, don't believe what lots of people will tell you: that dynamics MUST be hurt by using a passive. They CAN be excellent, with good source output stages. |
I agree with most of the above with a few exceptions. I agree that a passive pre-amp is difficult to implement, but not "always" bettered by an active. I have tried several different combinations and have found at least one that works. It requires the following 1) a front end designed to drive an amp directly 2) a very high quality passive stage 3) an amplifier with sufficient gain to make up for the lack of gain in the passive preamp. The recommendation of the Aesthetix units is right on the money. I am using the IO phono unit through a Placette passive preamp and it is very nice. However, the IO is specifically designed to have enough output to drive an amp so in that sense it could be considered a phono stage and active preamp in one. The statement about lack of balanced options is also incorrect, Placette offers a balanced version of their passive preamp. |
I'm pretty much with Albert on this one. While i haven't played with a LOT of passives ( a few ), i have always had better results with an active unit. Don't know the specifics as to why, as i've tried TONS of various cables, source / amplifier combos, etc...
As to the rated sensitivity of an amp, don't take that spec as being written in stone. A single tone can generate a higher output level than a broadband dynamic signal. Since music is a broadband dynamic signal, you might need more than the specified amount of input voltage to reach full output even though the amp meets spec under test conditions on the bench with individual narrow bandwidth tones. Sean
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It has been shown that any realtime electrical signal (music)can be broken down into a series of sine waves of varying amplitude, frequency, and phase using the Fourier transform. Fourier analysis shows that music is composed of a linear sum of many sine waves. If an amplifier is linear and has sufficient bandwidth to pass all audio harmonics, then it will clip with a sine wave at the same peak to peak value as it does with music. The confusion can result when comparing the RMS value of a sine wave to the RMS value of music. This is usually not a problem in a CDP because the voltage output is usually specified as an RMS value at 1 KHz and at 0 db recording level. I agree that the 0 db output level must be greater than the input sensitivity of the amp because music is not recorded at 0 db on a disc. |
I agree with Aisip. I use an Audio Synthesis "ProPassion" which is dual mono, single input, single output. This is a killer device. You need a strong drive, i.e. above 6V to get the max and when this happen, god bless you. |
