2. amps-preamps
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Passive Stage preamp vs Active Stage Preamp

As you all probably know lots of integrated amp designs (solid state) exersise the passive preamp part design which are basicly either transformer or a high quality potentiometer and simple input circuitry.
Many of us know that most of the CD players have a sufficient enough output voltage to feed the power amp (from 1V upto 3V) Same thing with DACs. Analogue phonos are able to produce the same kind of outputs.
The input sensitivity of power amp <=500mV
For somehow I've been experimenting with loaned WADIA No 15 DAC with variable output that has just a passive potentiometer and connected a variable output directly to my Bryston 3b-st. The result was deeper soundstage and details vs. setup through Bryston 11b preamp. The only drawback was that the volume range is much smaller than with preamp.
Can anyone summarize all advantages and disadvantages in using passive preamps vs. active?
Does it make a sence to try a passive stage preamp in my current solid state setup which is Theta Data II -> EAD DSP700 ->...
and analogue J.A. Michell GyroDec -> Delphini phono ->...
and ending with Bryston 3b-st?
Also if such exists, describe an importance of using active stage in tube setup.(Impedance matching?)
128x128marakanetz
tom_nice
387 posts
 
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.
herman
2,261 posts
 
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.
sean
6,231 posts
 
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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sqjudge
96 posts
 
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.
arupg
42 posts
 
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.
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