bluetosman
What is passive preamp and how to connect them
A passive preamp controls the volume of the source just like an active preamp, except there’s no added gain, which means no added noise or coloration’s or distortions, they use all the gain that the source has to offer instead of throwing most of it away away. They replace an active preamp and go in the same position, between the source and the power amp.
Quote from Nelson Pass
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.
Its just a none powered, zero gain stage, usually for source selection and volume control. basically its a volume pot, switch and in-output connections in a box. Hook it up like a regular preamp source in - amp out.
Passives adds little to the signal ( minimaly a volume so that's the attraction. there is advantages and disadvantages with either passive or active preamps.
A passive preamp is one which has no amplification and provides an input selector and a volume control. In theory, the passive preamp has no distortion since there are no active devices (transistors, tubes, etc.) providing amplification. The output impedance can be quite high compared to an active preamp and, as such, is very sensitive to capacitive loading. Low-capacitance interconnects are mandatory to avoid HF rolloff and loss of dynamics.
I have been dablling with passive devices for years, but only until a few years ago, with the encouragement of georgehifi, above, I have taken it seriously, and purchased a nice passive device, which has, extraordinarily, convinced me, that active preamps, take " somethings " away from my recordings. Some people feel that going passive, robs the music of dynamics, punch, color, or makes the music lifeless. I have found, exactly the opposite. I can say, that details and information, on every recording I play, excels, in all of these sq parameters, and every parameter. The noise background is extremely quiet...... actually, non existent. With my dac, connected, on ( always on ), and no signal, my volume can be at max, and not a sound through the speakers, which are very efficient ( yes, power amplifiers are on ). Never had this with an active preamp, tube, or solid state. System matching becomes a major factor, in appreciating one less gain stage. Most sources today, should have a proper amount of voltage, impedance, and drive ( a robust power supply ), to pass the signal to the power amplifier.......In my system, for my ears and listening, I prefer passive. No right or wrong, imo......and the debates, as to which is better, are ridiculous, just like, analog vs digital, tubes vs ss, etc. Whatever " your " ears like, this is what matters........Enjoy ! MrD.
A few of the replies are saying no added gain, or no gain stage, but more precisely a passive preamp should use no active components in the audio signal path (e.g. it would be fine to use active components for a display or to support a remote control). Active components aren't only used to add gain, but can also be used as an input or output buffer, or implement feedback, etc. Roughly anything that includes a tube or a transistor is an active component.
The downside to a passive preamp are the downsides resulting from the lack of those active components. Impedance mismatches, voltage/current limitations, etc. can all suddenly start to play a role and affect the sound quality, accuracy, or precision.
You can see how this can make selling or buying a preamp much more of a hit-or-miss situation, where one person's experience does not at all translate into another person's experience.
The advantage of a passive preamp is that you minimize any potential non-linearity and noise introduced by those components that you've instead chosen to leave out.
You use and connect a passive preamp the same way you would an active one. However there may be some situations where it is inadvisable to connect more than one input or output at the same time, depending on the internal design.
MrD, and Neko both said it well. A major problem, which I learned the hard way is: Impedance Mismatches between passive pres and amp
I loved everything about the looks and function of a Hattor passive, alas, it was a mismatch for the amp I had at the time. I wish I could have kept it, but the cost to add a buffer was prohibitive, AND the sound of Buffers is a whole nother level of discussion.
Nord offers several Buffer options for their designs
@georgehifi How does one avoid impedance mismatches?
This is very important to me as I am putting together a used system from scratch starting with Dali Euphonia MS4 speakers. Thinking about the Classe CA-M600/CT-M600 monoblock amplifier. Would love 3 recommendations for passive tube preamps in the $1k, $2k, & $3k price ranges (used of course).
Using the accepted impedance matching ratio of 1:10 or higher. A 10khom series/shunt passive preamp is the best most versatile value to go for as it has: 10kohm input impedance 2.5kohm max output impedance.
The source (dac ect) should have an output impedance 10 x lower than the input of 10kohm passive pre (which most are) so sources with 1kohm or lower output impedance are a match.
The power amp/s should have an input impedance 10 x higher than the output impedance of the passive pre 2.5kohm (which most are) so amps that are 25kohm or higher are a match.
The above is good for "nearly" 100% of systems out there
Good practice also is to use low capacitance interconnects (100pf per ft or lower), which most good quality ones are.
Tube sources should be questioned as they have output coupling caps that "may" not be large enough value, and easy fix though.
I have a passive that I ran in my system for a long time and really enjoy it. However right now I am enjoying the distortion that a tube pre has to offer. If you have the gain,a passive is the next best thing to straight wire.
If you have the gain,a passive is the next best thing to straight wire.
Hit the nail on the head, it’s the most transparent/dynamic/uncolored way of getting the sources signal to the poweramp/s
Quote from Nelson Pass
Nelson Pass,
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.
@georgehifi I have sent you an email asking for pricing info for the Lightspeed Attenuator. A friend and I will test it seeing as though the reviews have been rave. Excellent work, George. Incredibly excellent work. However, when I am having a party (I have them quite often) and would like to change among sources, it would be great to have a passive tube preamp that can accomplish this. I have read about the Schiit Freya among others. Would you make any recommendations? Thanks so much for your time.
I own the original version of the Schiit Freya and it can switch immediately (the newer Freya + "improved" version shuts off the tubes when one of the other outputs, passive or FET, are utilized...so you have to wait for the tubes to warm up if switched) between the 3 modes...passive sounds fine but the tube mode sounds better for my tastes. Just more "there" there. Switching among modes keeps the tubes honest since if you notice a degradation of some sort with the tube mode you simply replace the tubes.
@georgehifi I have sent you an email asking for pricing info for the Lightspeed Attenuator. A friend and I will test it seeing as though the reviews have been rave. Excellent work, George. Incredibly excellent work. However, when I am having a party (I have them quite often) and would like to change among sources, it would be great to have a passive tube preamp that can accomplish this.
Sent with mandatory propaganda attachments. And yes as Wolf points out the Freya is a great universal unit, I have recommended it many a time here on Audiogon. As for a passive though the transparency/dynamics of the Lightspeed has no equal, as there are no contacts in the signal path in the circuit. https://ibb.co/XbCsn2B
Passive preamps are more difficult to get properly integrated because of the potential impedance mismatch. A mismatch that can also vary by volume setting.
Also, without active input/output buffers, the individual components' circuit electrical characteristics will travel through the entire chain, e.g. the downstream amplifier's input circuit is "seen" by the DAC's output circuit. This in itself can make the volume settings inaccurate, in addition to having an impact on other aspects of the sound character.
Lastly, although this is probably less of an issue in my opinion, people do want gain on occasion.
smodtactical How come passives are not more popular? Everyone seems to use active and seems more commonly made as well.
They are, and now going direct because so many sources now have volume controls are taking over from them now. But if you don’t have source volume control passives are the next most transparent/dynamic/uncoloured way of having a volume contrpol.
A Quote from Nelson Pass
“We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more. Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.”
I stumbled upon an integrated unit that has both active and passive preamplification. Creek Destiny2. Although may be frowned upon in high-end circles, I find the ability to chose between passive and active (Destiny2 offers gain of 3, 6 or 9 dB) to be advantageous when choosing between source and music genre. Jazz, classical and acoustic vocals shine when passive sourcing CDs or LPs, allowing the output stage of the CD or phono stage to drive the amplifier. Laid back yes, pleasing immensely so. Active, well think Baba O'Reilly, or any other guitar based rock LP.
When considering using a passive line stage one should also consider the output voltage of the source components and the input sensitivity of the amplifiers. While the CD standard output via RCA is 2 Volts and the HDCD standard output via RCA is 2.2 Volts, many don't play be the rules. Some are over and some are under. Other perhaps considered legacy components such as tuners, tape decks, etc., are often well below (and less likely above) and might not be able to drive amplifiers to the full power output that the consumer paid for.
CD standard output via RCA is 2 Volts and the HDCD standard output via RCA is 2.2 Volts, many don’t play be the rules. Some are over and some are under.
Yes that was the Redbook standard way back in early 80’s when it was first stated by Philips.
For the last 10-20 years I’ve found "the majority" are way over, more like 2.5v even to up to 6v on some dacs I've seen is the output these days. Only few tube output and "boutique" ones I’ve seen are under 2v And as far as the amps input sensitivity the majority only need 0.5 to 1.5v input for to be driven to full output
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