Active Pre-amps V/s Passive Pre-amps

what's your definition of a passive amp? without poower supply? then i haven't heard any yet.

yep....just a volume control and a source inputs....the box could be powered for a remote but the singnal path is thru the volume control only so it remains unchanged.
Heard a lot of good stuff about passives....but not all passives are good....I believe making passive pre-amps is a sort of a black art :-)

Hi

1. Are the dates on the forum correct? This message can't be three years old, or is it?

2. Active preamps use active devices (tube/s, transistor/s or op-amp/s) in the signal path. Passive preamps use only passive devices (devices that do not need external current to operate) in the signal path. It really is that simple.

3. The main reason to go passive is if you're sure of the level and impedance matching between source and amplifier. With modern sources sometimes it's not a problem and sometimes it is. Passive is not so much black art as it is hit-and-miss. As with anything related to audio there's a lot of snake oil and chinese black bamboo extract floating around and as the adage goes, caveat emptor. Normally it consists of a source switch and a passive attenuator or pot in series with the signals. Each of these comes at various price points, with a point of diminishing returns.

4. An active preamp is a difficult piece of equipment to engineer, as the signal paths tend to be complex and have a lot of active devices with sonic signatures and distortion mechanisms. In addition most solid state designs have some form of local or global feedback, which according to purists degrades the sound. Then there are voltages present on the inputs and outputs of the devices, which need to be removed by coupling through a capacitor or a transformer, which again affects the sound. Preamps costing thousands of dollars don't promise audio nirvana either, and there is as much black art here as in passive pres...

Overall if your source and amplifier are not too fussy, then a passive pre is generally sufficient and due to the absence of colouring components, and may sound better - an unfair and incorrect generalisation, but one I find true.

I only use a single volume control in line with the signal, so you could say I have no preamp at all, not even a signal switcher. I actually unplug and replug connections each time I need to change the source (once in 3/4 days).

Use Passive for the last 11 yrs - and its a point of NO return to an active pre (be it SS or tube). My Passive model is the ProPassion, made by Audio Synthesis of UK. Design is Dual Mono, Single input, single output. Uses Shallco mil spec switches, Vishay Bulk Foil resistors, WBT connectors, Pure silver with Teflon insulation internal wiring.

Hey Audio_Engr..
Will most defintely try out a passive Preamp using Dale resitors in the future.
but as of now i am using an ALPS Rk-27 Blue Velvet dual gang 10k log pot(2000 rupees) in my new DIY amp.
I must say it sounds absolutely fantastic!
some small gremlins to be taken care of(on the input wiring of the amp) and the amp should be done by the end of the week.

Manek schrieb:

yep....just a volume control and a source inputs....the box could be powered for a remote but the singnal path is thru the volume control only so it remains unchanged. Heard a lot of good stuff about passives....but not all passives are good....I believe making passive pre-amps is a sort of a black art :-)

very true Manek.
a passive pre supposedly give the most distortion free output. but choosing on also depends a lot on your source output. and apparently getting one right is not as simple as putting a volume pot in the path !

If your source has a good output power where it can continue to act as a current source, then a passive pre amp is a good optipn as it provides the cleanest sound and almost not addition of distortion.

but if your source is on the weaker side, then it acts as a voltage source which is not very good and suffers degradation asit is sees the Power amp impedances directly .


I was give this explanation once from a regarded audiophile. hence i don know the actual technical reasoning on the current source/voltage source, but was able to understand that as a current source it will give out the required output current in a stable manner hence be accurate, but a voltage source would try to keep the voltage stable but the actual signal may not always be accurate enough as it depends on the input impedance of the amp.

Arj's explaination of current & voltage source is absolutely spot on! While I have been successful in implementing my Audio Synthesis ProPassion passive controller, I could do it only because of the following:
1. My DAC gives out an output of 6.55V @ 18 ohms output imp.
2. My Power amp sens. is 0.5V for full output @ 20 kohms input imp.

Hence, the passive perfectly fitted in whereby I never need to cross ever more than 2 o'clock position. Also use a very low cap interconnect @ (37pF per metre) short length of 0.5 metre between passive & pwr amp (a very important section) for the passive to truly work well & not either roll-off HF on higher vol settings or roll-off LF at very low vol settings.

Bottom line, its quite a task to make the passive fit well but if you can, will only be rewarded with utter bliss! With the noise floor now so low, the 3D aspect takes a totally new dimension as well as transparency. My passive not only replaced a $5000 vacuum tube pre coming from a stalwart manufacturer in 1995 but also took the pants off it.

Savyasaachi: My diy passive was an Elna switch with Holco resistors in 1993-4. Finally, a personal dialog with Martin Colloms who raved the Audio Synthesis Passion passive in HFN those days convinced me; I got rid of the diy stuff to settle for a custom made one using the most premium parts. Settled for a Dual Mono one after discussion with David Heaton (Oh! a lovely fella) of Audio Synthesis which was custom made.

audio_engr schrieb:

Arj's explaination of current & voltage source is absolutely spot on! While I have been successful in implementing my Audio Synthesis ProPassion passive controller, I could do it only because of the following: 1. My DAC gives out an output of 6.55V @ 18 ohms output imp. 2. My Power amp sens. is 0.5V for full output @ 20 kohms input imp. Hence, the passive perfectly fitted in whereby I never need to cross ever more than 2 o'clock position. Also use a very low cap interconnect @ (37pF per metre) short length of 0.5 metre between passive & pwr amp (a very important section) for the passive to truly work well & not either roll-off HF on higher vol settings or roll-off LF at very low vol settings. Bottom line, its quite a task to make the passive fit well but if you can, will only be rewarded with utter bliss! With the noise floor now so low, the 3D aspect takes a totally new dimension as well as transparency. My passive not only replaced a $5000 vacuum tube pre coming from a stalwart manufacturer in 1995 but also took the pants off it. Savyasaachi: My diy passive was an Elna switch with Holco resistors in 1993-4. Finally, a personal dialog with Martin Colloms who raved the Audio Synthesis Passion passive in HFN those days convinced me; I got rid of the diy stuff to settle for a custom made one using the most premium parts. Settled for a Dual Mono one after discussion with David Heaton (Oh! a lovely fella) of Audio Synthesis which was custom made.

Hey audio_Engr,

Well let me jsut state that super high end attenuators work only when the entire system, incuding the room is on par.

Besides, ultimately, the reason for going for a precision Attenuator/Pot is to see to that the signal is ture and not being manipulated by unwanted elecronics.

Finally, it boils down to whether the POt is properly matched so that the imageing is perfect.
You donot gain anything more from adding a POt or attenuator.

The ALPS works just fine for me.
By putting my passive Pre, active crossover and amp modules in one single case, i have toatally eliminated interconnects . The output from my POT is fed directly into the active crossover which is just 4 inches from the POT. the outputs from the xover is inturn fed into the amp modules which are not more than 10 inches away. Ineffect, i have tried to keep the signal length as short as possible to keep the influence of the cables to a minimum.

Will soon take some measurements and post the results.

Savyasaachi

P.S Which is the DAC that you are using?

actually I have tried the Rothwell attenutators and find them OK. My DAC givees a +5V output and I have an active preamp..hence need to use attenuators.

Am thinking of going passive but unable to find a good Pre amp with a remote

Arj schrieb:

actually I have tried the Rothwell attenutators and find them OK. My DAC givees a +5V output and I have an active preamp..hence need to use attenuators. Am thinking of going passive but unable to find a good Pre amp with a remote :(

Check the ALPS website..

I think the RK-56/58(don't know the exact model number..but is supposed to be one of the very best) should cost you about 850$.

Silicon chip have a straight forward and esay to build remote conrol for stereo amps.
i think u can tr y to integrate and modify it to your needs.

Excellent Thread. Thanks for initiating it, Maneck...

[quote]
Aliases-Benkenobi
Benkenobi_redux said:

ALPS Rk-27 Blue Velvet dual gang 10k log pot(2000 rupees) in my new DIY amp.
I must say it sounds absolutely fantastic!




1. Is the Blue Velvet Pot available against Rupee Payment in India ? Anything similar as a motorised pot with remote ? ( locally available )

2. A tip... while you are at it... Try reconfiguring the pot, so that it is fed thru a 10K metal film series resistor. The Junction of the pot (fixed point) and series resistor is your Pot output.

Connect the Pot slider so that it shorts the pot to ground. That way, the pot is not in the signal path ( a debatable description). To my ears, this always sounds better... Would be great to have your feedback on this forum.

3. My 2 cents on the Passivce vs active pre amp...

The Passive Pre is VERY demanding on the Source and load impedence, and the interconnects add to the loading. The sound is certainly a Hit and miss. All this has ofcourse been very well stated above by others, and I fully agree.

The tonal characteristics of the active and passive alternates will almost certainly depend on the Drive and load impedences, but to my ears, the True Test of an active vs Passive pre is Not the Tonal balance but Spatial Imaging, specially holographic Image Depth.

Remember, we double our system costs, for stereo, spending on 2 amps, 2 speakers etc. A single channel can deliver the same tonal Fidelity as a 2 channel setup, but Not Spatial Imaging. THAT is the TRUE purpose of stereo ( another debatable statement by me ).

To my ears, a GOOD active pre amp has Always delivered better spatial imaging than a passive ( I suspect its to do with maintaining subtle ambience related signals ).

Contra views welcome.

Cheers

Amp_Nut schrieb:

1. Is the Blue Velvet Pot available against Rupee Payment in India ? Anything similar as a motorised pot with remote ? ( locally available )

The RK-27 pot is available through RS components.
www.rsindia.com

ALSP do have a motorised pot but don't think RS stocks it.

Amp_Nut had raised an issue of Spatial Imaging (esp. Holographic Imaging) which he says is done better by an Active pre.

All I can tell you folks is that in this dept, my passive blew apart a $5000 Audio Research Tube active pre by miles and because of this Holographic Imaging I simply cannot go back to an Active pre again. Tried several very expensive ones off friends as a trial but none could touch the passive. Its way ahead of active pre.... (if done right!) i.e. source drive, impedances, cable considerations, amp input considerations all matter very much.

Hi audio_engr

Great to know that you have a winner.

Cheers !