Is no preamp really better that a good preamp?


Hi All, I have PS Audio gear, and both my DAC and my phono section have enough gain to run directly to the amp. Is this really the optimal arrangement, or might I actually get better sound by adding a good preamp, say a Cary or a Modwright tube unit, to the mix. Thanks in advance.
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Showing 3 responses by atmasphere

A preamp line section has 4 functions:

1) control volume
2) select an input
3) add any needed gain
4) control the interconnect cable

The two latter functions are not done by passive controls of any sort. That 4th function is also poorly understood, not only by audiophiles but designers too. Often if you have a digital source, you may not need the gain and so a passive might seem attractive. But the interconnect cable will be far more critical with a passive control.

Quite often if a passive is involved, people report a loss of bass impact and overall dynamics as the volume control is reduced in level from full on. This is likely due to the source having some sort of coupling capacitor at its output, which is then in series with the control. Unfortunately, the Red Book specification for CD demands that the output of the CDP or DAC be high, in fact so high that it can clip all known amplifiers if the signal is not somehow reduced. So a volume control is essential.

Now if you don't need the gain, the obvious solution is a buffered volume control. This is essentially a volume control with some sort of follower circuit (either tube or solid state) that has no gain but does isolate the control from the interconnect cable. This allows for vastly reduced coloration due to the interaction of the volume control and the cable.

Since I listen mostly to LPs, a buffered control in my system is insufficient as the extra gain is handy! But if you plan to play only digital the buffered volume control is your best bet if you don't go with an active line section.
George makes a good point- if a preamp robs you of transparency and detail, its not helping!

The same can be said of an improperly applied passive control.

In both cases, audition is necessary.

It is not correct to say that all active preamps take away from detail and transparency or add colorations. Some give you *less* coloration with greater detail and transparency.

But it is also not correct to say that all passive controls take away from detail and transparency or add colorations. Some give you less coloration with greater detail and transparency; **in either case its all in the setup.**

The issue is you have to pay attention to variables and interconnect are one of the bigger sets of variables. For example, I like to have my preamp and turntable near the listening chair, and my amps as close to the speakers as I can get them. So my interconnects are 30 feet long. A passive does not work in this situation. To get around cable problems, I run equipment that supports the balanced line standard (defined in the AES file 48) and thus the cable does not contribute or detract from the sound.

A further variable in input and output impedances of the equipment in use. This can work badly with either active or passive systems- again- its all in the setup!

When the cable ceases to be part of the system sound (regardless of how you go about it), that's a good thing. If you are running a passive system, the obvious lesson here is keep your cables short!

How in g**s name can a active preamp give you more REAL detail (not perceived detail because of distortions) from the source than the same well match direct source to poweramp.??

Please produce some laws of electronics in your answer and not voodoo speak.

The answer to this was in my prior post. However I like to use engineering principles since you asked; we can start there... normally in any situation where we are driving a load, as a general rule of thumb the source will have about 1/10th the impedance of the load. This is a good practice to insure proper bandwidth and low distortion of the source.

When you put a resistance in series with the source, the source will begin to have troubles driving the load. Now when the series element is a volume control, one might argue that the control itself becomes the source but this is not entirely accurate. The source becomes that of the volume control and the original source together, along with whatever effects are imposed by the interconnect cable between the source and the volume control. Many sources use a coupling capacitor at their output; such sources can suffer frequency response aberrations when a series resistance is imposed between the source and the load it has to drive (which in most cases will be an interconnect cable and the input of an amplifier).

Generally speaking, these errors can be reduces if the source is of low output impedance and the volume control is a fairly low value, for example 10K ohms or less. The issue here is the ability of the source to drive such a load, but if that is the case the effects of the cable between the PVC and the input of the amp will be better controlled and the series resistance between the source's output coupling cap and the amplifier's input will not likely impose much of a frequency response error.

When you get into higher source impedance and higher volume control values the cables play a larger role. This is partially due to capacitance. You can calculate the minus upper 3db point by the formula f=1,000,000/2xPi x C x R, where R is the source resistance in ohms, C is the capacitance to ground (that of the interconnect cable) in microfarads and f is the -3db point in cycles per second.

The cable between the source and the volume control should not be ignored.

While the ear cannot detect phase shift of individual frequencies, it can detect phase shift in a band of frequencies (generally as a tonality but high frequency phase shift can also affect imaging), generally phase shift effects can be heard to 1/10th the cutoff frequency, so if your -3db point is at 50KHz, there will be effects down to about 5KHz.

When you put a PVC after a source, as far as the amp is concerned the output impedance of the source is increased, conversely from the perspective of the source the load impedance is decreased. This can lead to the low frequency cutoff being increased in frequency. To avoid phase shift in the audio passband, the cutoff should be about 2Hz as phase shift components (which to the ear sound like a loss of impact) can be heard to 10x the cutoff frequency. So of this moves from 2Hz to 5Hz phase shift components can have an effect at 50Hz rather than 20Hz.

Thus it can be seen that while a PVC is a very simple device, if incorrectly used it can act as a simple passband filter. Keeping the phase shift components out of the audio passband is the key to success and is why they can work so well in some systems but not in others.


we are discussing about what the OP's question is, stop rambling about passives, GET A GRIP MATE.

"Is no preamp really better that a good preamp"

And I also addressed this in my prior post, which (in a nutshell) says that in some cases a passive will be better and in others an active will be better, thus both must be auditioned. I thought you would be happy that I was agreeing with you that passives can work...