Why do you use a passive preamp over an active one in your system?
- Thread starter joeinid
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audio.bill
Active member
I have used several different passive linestages over the years and find they do have some strengths over most active preamps in the right system. System matching is critical to determine whether a passive preamp will work in a given system and it's really best to try any specific setup to determine suitability. The general rule is that they work best with high input impedance amps and low output impedance sources, and that you will have enough gain without an active linestage. The benefits in a well matched system are absolute silent backgrounds and a very transparent sound. In the right system their sound can be captivating. If you have shortcomings in the source or amp they will be clearly revealed with a passive linestage. Another potential limitation with a passive linestage can be limited dynamics, but if it's a good match this shouldn't be the case. I've found that to achieve comparable or better sound quality with an active linestage is generally very expensive. For those like myself using analog front ends an active linestage is usually required for the additional gain that they provide. Hope this helps!
kevinkwann
New member
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- Oct 2, 2014
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- 106
Not necessarily. Input impedance is only part of the equation. The input sensitivity of the original MX-R, for example, was 25.53 dB according to measurements done by Stereophile. This is lower than optimal--much lower--for a passive solution. While there are no hard and fast rules, I wouldn't even consider passive preamplification unless the amplifier being utilized had gain of >28 dB.
audio.bill
Active member
Kevin makes a very valid point in that the total gain of the amplification chain is a further consideration. With a passive linestage the only gain will be provided by the power amp alone, so depending upon your source output voltage and the sensitivity of your speakers lower gain amplifiers can cause further compatibility issues.
Jack
Active member
Joe
If your primary source is going to be the Lumin and you use the balanced outputs into the Hattor the 4 volts provided should help alleviate part of the problem. I used the STP-SE with your Nords for a brief time and they are speced at 26 db. I didn't find it to be a problem and I think I was running the DAC out of the SE outputs at that time. I think Marty has used his Hattor with multiple amps.
If your primary source is going to be the Lumin and you use the balanced outputs into the Hattor the 4 volts provided should help alleviate part of the problem. I used the STP-SE with your Nords for a brief time and they are speced at 26 db. I didn't find it to be a problem and I think I was running the DAC out of the SE outputs at that time. I think Marty has used his Hattor with multiple amps.
The MX-R20 have a 25.1dB gain according to Stereophile measurements; this means they need 2.7V from the source for 300W output. With the Lumin's 4V balanced outputs there won't be an issue at all with a passive pre.
Even if a source max output would be only 2V that would limit the MX-Rs max output at 160W, retaining about 3dB of headroom, which is a good thing.
Even if a source max output would be only 2V that would limit the MX-Rs max output at 160W, retaining about 3dB of headroom, which is a good thing.
Randy Myers
Well-known member
I am very satisfied with the STP-SE. I doubt I have ever pushed it beyond the passive mode into active, but it is nice to know that if needed it is there.
I līke the way the pre-amp just gets out of the way. Extremely open sounding, and dead quite.
I līke the way the pre-amp just gets out of the way. Extremely open sounding, and dead quite.
- Thread Author
- #11
I believe this article is a good summary presenting the pros and cons of the passives.
http://www.tortugaaudio.com/what-is-a-passive-preamplifier/
I've noticed that people who chose active over passive usually cited poor dynamics as a reason.
Lumin players have 4V XLR output and 2V RCA output. So low source voltage is not a problem for Lumin users. Some people have too much gain in their systems, so Lumin offers an optional setting of "low analog output level" to help slightly.
My personal system has Lumin XLR output to STP-SE.
http://www.tortugaaudio.com/what-is-a-passive-preamplifier/
I've noticed that people who chose active over passive usually cited poor dynamics as a reason.
Lumin players have 4V XLR output and 2V RCA output. So low source voltage is not a problem for Lumin users. Some people have too much gain in their systems, so Lumin offers an optional setting of "low analog output level" to help slightly.
My personal system has Lumin XLR output to STP-SE.
Yes, with only 0.55dB max gain the KX-R is just a buffer that helps matching the source to any amp. Makes sense to get one if you have a low input impedance amp; but it's not the case with Ayre's 2 megaOhm input MX-Rs.
I think you should try the balanced Tortuga and Placette passives with your Ayre amps before deciding to get the KX-R.
From the Tortuga article:
Regardless of the level of gain (or absence of gain, i.e. unity gain), all active preamps buffer the input from the output. A buffer acts as an electronic firewall between the source and the amp. A good buffer has very high input impedance making the job of the source very easy. Easy means the source puts out very little current while sending out the audio signal (i.e. voltage). Conversely, a good buffer has very low output impedance and high current delivery capacity making it compatible with virtually every amplifier in the world regardless of the amp’s input impedance. This broad compatibility is arguably the only benefit of active preamplifiers. A good buffer can enhance the dynamics (pluck, punch, slam etc.) of the music if the source isn’t quite up to the job.
Shadowfax
Well-known member
So I guess my VAC is somewhere in the middle? I have Normal and High Gain and a Buffered Passive Mode. I'm not the most electrical savvy so still not sure.
The article mentions Buffered, but under the Active section. So that's what confuses me. I don't really have one or the other.
From the noted article
"Conversely, a good buffer has very low output impedance and high current delivery capacity making it compatible with virtually every amplifier in the world regardless of the amp’s input impedance. This broad compatibility is arguably the only benefit of active preamplifiers. A good buffer can enhance the dynamics (pluck, punch, slam etc.) of the music if the source isn’t quite up to the job."
So I gather it helps make this pre more compatible with a wider range of amps?
I usually run in Normal Gain, but find when I play it at the same volume in the BP Mode, I can still have a conversation in the room because the slam in missing. So again I assume that is what is meant by "lacking dynamics"?
I don't spend enough time just listening to the BP Mode but it does provide a nice clear sound that can be turned up without your head being pounded.
This is the description from the VAC manuals-
In the Passive-Buffered mode the amplifying triode (V4) is bypassed, and the controls are fed
directly to a Class A impedance translating Class A triode tube (V5). Since the output is buffered,
there are no gross cable interaction problems of the type encountered with passive control centers;
since there is no gain stage, this mode has ‘unity gain’. The VAC Passive-Buffered mode is
capable of driving long cable runs and the preamplifier may be located some distance from the
power amplifiers.
Since the Passive-Buffered mode has zero gain, you may need to turn the volume controls well
clockwise...the exact position depends on the output level from your source, and the sensitivity of
your power amplifiers and loudspeakers. Many audiophiles have the belief that it is never good to
run volume controls wide open. With a circuit of this type, however, it is actually preferable to do
so. Don't worry about where the control is set, just be concerned with how it sounds. The Passive-
Buffered mode does not invert absolute phase with respect to the line inputs.
So how does my VAC differ from one or the other, if there is a simple explanation?
The article mentions Buffered, but under the Active section. So that's what confuses me. I don't really have one or the other.
From the noted article
"Conversely, a good buffer has very low output impedance and high current delivery capacity making it compatible with virtually every amplifier in the world regardless of the amp’s input impedance. This broad compatibility is arguably the only benefit of active preamplifiers. A good buffer can enhance the dynamics (pluck, punch, slam etc.) of the music if the source isn’t quite up to the job."
So I gather it helps make this pre more compatible with a wider range of amps?
I usually run in Normal Gain, but find when I play it at the same volume in the BP Mode, I can still have a conversation in the room because the slam in missing. So again I assume that is what is meant by "lacking dynamics"?
I don't spend enough time just listening to the BP Mode but it does provide a nice clear sound that can be turned up without your head being pounded.
This is the description from the VAC manuals-
In the Passive-Buffered mode the amplifying triode (V4) is bypassed, and the controls are fed
directly to a Class A impedance translating Class A triode tube (V5). Since the output is buffered,
there are no gross cable interaction problems of the type encountered with passive control centers;
since there is no gain stage, this mode has ‘unity gain’. The VAC Passive-Buffered mode is
capable of driving long cable runs and the preamplifier may be located some distance from the
power amplifiers.
Since the Passive-Buffered mode has zero gain, you may need to turn the volume controls well
clockwise...the exact position depends on the output level from your source, and the sensitivity of
your power amplifiers and loudspeakers. Many audiophiles have the belief that it is never good to
run volume controls wide open. With a circuit of this type, however, it is actually preferable to do
so. Don't worry about where the control is set, just be concerned with how it sounds. The Passive-
Buffered mode does not invert absolute phase with respect to the line inputs.
So how does my VAC differ from one or the other, if there is a simple explanation?
- Thread Author
- #15
Last edited:
audio.bill
Active member
While VAC calls their BP Mode 'passive', it's actually an active buffer (they describe it as an "impedance translating Class A triode tube (V5)".) They're using the term 'passive' since it's a zero gain stage but it's clearly active as they describe it.
- Thread Author
- #18
Hi Jack,
The Lumin is my primary source right now but I will need to hook up a TT and may eventually add another dac, a la Lampizator. I miss mine terribly.
The Lumin is my primary source right now but I will need to hook up a TT and may eventually add another dac, a la Lampizator. I miss mine terribly.
Shadowfax
Well-known member
It basically just bypasses the gain tubes, but still uses the other set. It does have the sound characteristics explained about Passive, but really a hybrid between the two types.
Are there any other Pres that have similar features?
CPP
Active member
Same here " Lumin XLR output to STP-SE."