Active Vs Passive Preamp

Hello all Buddies,
Preamp as I have mostly gathered has been one of the least discussed equipment (almost on all forums)....Even cables are discussed more .

I recently moved from Integrated to Pre-Power combination and as usual started off paying least priority to preamplification. However I was lucky to meet some knowledgeable people, one of them being our very own Siva ji, who gave me some guidance towards the contribution of preamp in a audio chain. In the process I also got to try out a couple of them and compare them with each other.

Yes, they made significant contribution in deciding how music sounds and to decide what and how much finally comes out of your speaker.

So now I have a nice pre-power combo which matches almost all the criteria I had set initially when I upgraded from Integrated to pre-power. The preamp is an "Active" tube Preamp which is very transparent yet warm. This thing is as good as it gets for anything in under $3000 range. I knew this is a gem.

Now, the other day another audiophile visited my place to listen to the setup and he brought along a very good passive preamp. This passive preamp has a TVC inside and is made from premium components. This passive device costs close to $3000 .

I didnt know what to expect from a passive preamp. Moreover since my Source and Power amp are all solid state gears I always thought a tube preamp is required to keep the warmth around the sound and a passive is eliminating that .

But as once we connected it, it was magic from the first moment onwards. The details were unimaginable. The transparency was almost walk through. The warmth was gone but it was replaced with reality. The instruments now had so much more attack and decay that it suddenly made no sense to add any warmth to it. When we connected back the active preamp, it was again nice and warm but a bit cloudy. Needless to say the micro details were hidden within the cloud and you could only get a faint sound of it (that too if you concentrate). All this thing with an active preamp which is superb and was almost flawless previously.

For whatever great things the passive did there was one thing that was disturbing. The "Bass". Bass was not as tight in the passive as the active preamp. This was clear. Not that the passive was very bad...but relatively the bass was tad rounded and a bit loose. In some tracks the looseness was very evident and in some it manged to pull off without attracting any anomalies in bass. Just to emphasize once more, the bass in the passive was a little loose "relative" to the active. It was still pretty listenable and nice. But as I understand, since the passive brought out so much more resolution in the mids and highs, why is it that the same level of resolution is not available at low frequencies ?

My source and power amp both give out very taut bass lines, I know that well. My power amp has an input impedance of 10 kohm and an input sensitivity of 1 Volt. The source has a RCA output impedance of 146 ohm and output voltage of 2.45 Volts. I did speak to the designers of the passive preamp and we calculated that the preamp output impedance in the worst case would be 166 ohms that is when I drive it to the full volume. For most of the real world listening volumes it would be well under 100 ohms (taking my source into consideration). This data definitely shows that theoretically there is no impedance mismatch problem between the pre and power. But practically our listening test does show that there is a problem in pre-power matching which resulted in loose bass.

It would be nice to hear what other members of the forum think about this scenario and also it would be great if you guys can share your experience/views about active vs passive preamps.

One thing that I learnt from this exercise is that there is a lot of information on the CD which the CDP retrieves, the speaker can resolve and in most cases a good power amp can deliver which are choked at the preamp level. Which also justifies why preamps can get very expensive. A good active preamp which can "preserve" the info coming in from the source (like a good passive does) and still drive the power amp well is not an easy thing to make or buy. It can definitely be the most expensive component in the chain...justifiably so!!

abhi.pani schrieb:

Hey Guys, I could not check the forum on the weekend but WOW I am pretty overwhelmed with the response (both quality and quantity). I can see various line of thoughts out here starting from Impedance mismatch to Transformer Winding Characteristics. Hello Amp_Nut, Your observation of the transformer characteristics is pretty interesting. If a transformer is really designed to give better HF (which I was getting) and compromise on LF then I am blocked. I am just banking upon the factor that these guys at MFA are one of the masters in the world transformers and are supposedly one of the best passive preamp makers. Yes they do have higher end preamps than the one I tried and they say that their better preamps have a "bigger core". Something you have pointed out. I did have a detailed discussion with them on phone and surprisingly they did not admit that there could be a transformer related issue which could have caused the problem. They definitely said that there higher end preamps do better bass but they also simultaneously said that this preamp should have worked with my power amp specs. Whatever be the case trying out a different passive TVC definitely seems to be the next logical step for me. That would clarify the issue better. Hi Bombaywalla and Arj, My room definitely is far from ideal. I do have some bass related problems. While I have treated my room upto an extent, I have not yet done anything significant for bass. All I am doing is finding the best feasible listening position where bass is cleaner. I have tried some bass traps at the corner recent which didnt work . Someone very knowledgeable had visited my place a year back and had immediately pointed out that my room has a good amount of standing waves. Now I am not talented enough to find out the sonic difference between a bass boom caused by standing waves versus bass boom caused by corner reinforcement. However, this knowledgeable gentleman also told me very clearly that corner traps wouldnt solve my problems and I would need a "Helmholtz Resonator" . Now I really see that corner trap is not working . While I do feel that there should be some treatment for the corners of my room but looks like that is not enough. I have to talk to Helmholtz Bhai for some respite . As for the preamp giving out lumpy bass.....yes it did add a little looseness and rounded structure to the bass which made the sound a little lumpy. May be in a very well treated room it would have sounded more acceptable.

Abhi,

From my impedance calculations, I seem to agree with the MFA folks that the bass issues do not appear to be related to the pre-power impedance mismatch.


seeking an audience with Helmholtz-bhai is a good idea but I am also wondering if you can make use of the info in this weblink?

http://www.ethanwiner.com/acoustics.html

it might be more amenable to implementing given where you are physically located. I personally do not think that your tube traps are a loss - you need to fine tune them & also add more aesthetically pleasing treatments. I say this 'cuz you already have time & money & understanding invested in your current room treatments.
(alternatively, you can junk what you have & start fresh with Helmholtz resonators).