Passive vs. Active Preamps

KeithR · « **Reply #20 on:** 30 Aug 2004, 07:39 pm »

Quote from: zybar

Hmmm...

Anybody notice the trend here?

Too bad John isn't making his preamp right now.

George

How about in comparison to VTL 7.5, Aesthetix, First Sound, BAT 51SE, Synergy ii, and the like.

I have no doubt it surpasses AI type stuff, but question is how does it stack up to the big boys.

I have thought about pairing a passive with my BAT tube amp...the Bent seems to be the only one with the functionality I require (XLRs etc).

I tend to see more active preamps in higher end systems....Mike Lavigne though is a proponent for the opposite, and he has had many hi-end actives grace his system.

JoshK · « **Reply #21 on:** 30 Aug 2004, 07:56 pm »

I heard the Bent in my system compared against my Cary SLP2002 and it made mince meat of the Cary.

shokunin · « **Reply #22 on:** 30 Aug 2004, 08:02 pm »

Anybody here try the Passive Transformer based preamp by Sonic Euphoria?

http://www.soniceuphoria.com/

When my system is back in order I was going to see if I can get a loaner from Jeff. Too bad the Bent Noh is Noh-Moh.

JoshK · « **Reply #23 on:** 30 Aug 2004, 08:15 pm »

I'm weary of autoformer based passives, IIRC, the Bent is not an autoformer but a true transformer.

zybar · « **Reply #24 on:** 30 Aug 2004, 08:33 pm »

If I was going to try an active at this point, it would be the Placette Active (especially the balanced version).

I thought about trying the Sonic Euphoria, but I ultimately just tried the Placette and Bent. The Bent was so good that I decided to hop off the premap audition train and concentrate elsewhere.

George

KeithR · « **Reply #25 on:** 30 Aug 2004, 11:44 pm »

Quote from: JoshK

I heard the Bent in my system compared against my Cary SLP2002 and it made mince meat of the Cary.

Yeah, I was never too happy with my 2002 as well. I should never have sold my SLP-98P, which I actually rebought after I moved.

I sold it due to the Wadia 861 which functioned well as a preamp (and I have considered going back to it)

avahifi · « **Reply #26 on:** 31 Aug 2004, 12:28 am »

In my book here is what a good preamplifier is supposed to do.

1. Provide an ideal resistive load for the sources connected to it. Many components (tuners, CD players, phono preamps, etc.) have audio output stages with very limited drive current capability and poor capacitive load drive capability and its hard for the preamp designer to know the details of all sources, so designing for the worst case source load is necessary.

2. Intercept and get rid of all RFI garbage. Your amplifier and tweeters become very unhappy when having to cope with harmonics of CD and Tuner switching frequencies, phono cartridge high frequency shatter, and just mundane stuff coming in on poorly shielded interconnect cables.

3. Have large reserves of drive current capacity and bandwidth to drive any load connected to the preamp outputs, including highly capacitive interconnect cables and strange amplifier input impedances.

4. Have active audio circuit gain stages that don't screw up the source material.

5. Have all the switching and control functions you need.

A properly designed passive preamplifier can do #1, and by default (no active audio circuits) #4. However, it can't do #2, #3, and likely #5 as you cannot turn the volume up, only down, so you are stuck with the maximum signal levels from your source. #1 is important, because with a passive unit, you are actually asking the source to drive the complete load between its outputs and the amplifier and that is usually asking too much.

Of course the downfall of an active preamp is that its rare to find one that does #4 properly, and that weakness often can outweigh doing all the rest really well. Thus I would suspect that a passive unit probably will "sound better" (if there is enough gain from the driving source) than many active preamps. But an active preamp that does everything really well will win hands down, unless you have really unusual source products that have superior audio stages built in. Note that the famous Sequera (or however you spell it - I am nearly the world's worst speller) FM tuner had (I have been told) one 25 cent LM301 IC per channel as audio output stages, a device whos slew rate you could measure with a sundial and about as much current drive as a firefly.

It would be nice to see this thread continue with some of the engineering objectives kept in mind.

Frank Van Alstine

Marbles · « **Reply #27 on:** 31 Aug 2004, 12:39 am »

Frank,

The Transformer based Bent pre that I have can do #'s 1, 2 and 5, no question for the equipment I have. With 2V input, it works well driving down to 10KOhm input impedence amps.

It does #3 very well too ...but my sources are at least 2V output.

Can't do #4 in my current set up, but it does have taps for a 6DB increase in output. Don't know how a passive can do it, but as mentioned it is transformer based.

I think that transformer (or even autoformer) based passive pre-amps have changed the equation a bit. It seems to be much better than the resistive passive pre's I've tried.

Wish I could discuss this with you engineer to engineer, but we are one engineer short, me

avahifi · « **Reply #28 on:** 31 Aug 2004, 12:46 am »

I am not so sure that transformer based passive preamp is going to do #2 well without representating either a capacitive or inductive passive load that the driving source will not be happy with.

With an active circuit you can make the audio gain stage its own RFI filter without introducing nasty side effects for the sources, except for the non-linearities built into the line stage itself of course.

A cynic might say which poison do you like least worst?

Frank Van Alstine

zybar · « **Reply #29 on:** 31 Aug 2004, 01:07 am »

Frank,

While I am no way qualified to discuss the technical aspects of all of my audio gear, I do think I am qualified to discuss what I hear.

In that regard, I prefer the Bent NOH passive preamp over ALL of my previous active preamps (including the AVA T7) that I used to own.

The Bent is more dynamic, passes more detail, and is frankly more enjoyable to listen to.

You are absolutely correct in that I can't add volume and I have to be careful about ic length/capacitance and the ability of my source to drive things. But I was willing to do this in order to get better sound.

BTW, out of the actives I owned or tried, I did think yours was up at the top of the list and have receommended it to people who can't use a passive preamp in their system.

George

Marbles · « **Reply #30 on:** 31 Aug 2004, 01:28 am »

Quote from: avahifi

I am not so sure that transformer based passive preamp is going to do #2 well without representating either a capacitive or inductive passive load that the driving source will not be happy with.

With an active circuit you can make the audio gain stage its own RFI filter without introducing nasty side effects for the sources, except for the non-linearities built into the line stage itself of course.

A cynic might say which poison do you like least worst?

Frank Van Alstine

You might be right, I've never really had a problem with that with any pre-amp I've tried.

tom1356 · « **Reply #31 on:** 31 Aug 2004, 04:28 am »

Quote from: avahifi

In my book here is what a good preamplifier is supposed to do.

Frank,
Few things make me less comfortable than
disagreeing with someone I respect, but
here goes.
1. I don't agree with the premise that it is
necessary to design for the worst case
source load. Can't we can do better by designing
a complete system and therefore not settling for a
one size fits all product?
2. O.K. but I don't see where this is a problem in any
well designed product. It certainly isn't a problem with the
passives I've tried or built. Most RFI problems are AC related.
Not using AC is an advantage to passives.
3. Considering that we are designing a system it should
be no problem to accomodate this with well thought out
choices in the other components.
4. Hmm...I've never heard of an active gain stage that
doesn't alter the source but you do basically admit to this
later in your post.
5. Agreed.

You said: "A properly designed passive preamplifier...can't
do... #5 as you cannot turn the volume up,
only down, so you are stuck with the maximum signal levels
from your source."
My passive plays as loudly as I could ever want because it is
part of a well designed system. There is no need to turn it up,
I only need to turn it down.
You said: "But an active preamp that does everything really
well will win hands down..."
Because of number 4 above I have
not found this to be true at all.
I know you are in the business of building and selling
active preamps but I am curious to know your experience with
TVC passives.
Thanks
Tom

tom1356 · « **Reply #32 on:** 2 Sep 2004, 03:38 am »

*tap-tap* is this thing on?

Bill Baker · « **Reply #33 on:** 2 Sep 2004, 04:22 am »

Quote

In my book here is what a good preamplifier is supposed to do...............#4 Have active audio circuit gain stages that don't screw up the source material.

Hi Frank,
I do agree with most everything thing on your list and would have to say #4 is the most critical with active units. I have heard high dollar active preamps that that screwed up the source material worse than an inexpensive (but well thought out) passive unit. In my opinion, the choice in the attenuator is the most critical. Passive units with cheap volume pots are not worth the time it takes to put them together and find them to produce a dark, veiled presentation. A high precission pot or even better, a stepped unit is a must. IMHO.
As can be seen in my original post, I do not mention a preference as I have heard good results from both worlds. All of the products I deal with are tube amps with 100K input impedance and have found a good passive device [can] mate very well with most of them.

Another problem with many active tube preamps mated to tube amplifiers is that you are blasted out of your listening chair with the slightest touch of the control. It seems to many tube pres are designed to work with solid state amps and have to be pre-attenuated to be used with tube amps. A properly devised voltage devider works nicely in this application but many DIY'er do not do this "properly" and end up screwing up the impedance. This is easily overcome but is usually an inconvienence to most consumers. Therfore, it is crucial to know how well the synergy will be between the products you own prior to making any buying decissions. When putting together a modified tube system for my customers that includes an active pre and tube amp, I make the synergy happen before it leaves.

Tuckers · « **Reply #34 on:** 3 Sep 2004, 06:14 pm »

I have heard the Bent Audio NOH MKI and it is special. It beat the pant off the Spectral DMC 30 I had at the time.

I think the attenuation control is one of the things that messes with the sound the most. Commercial passives usually put much more of the budget into the attenuator than an active that has so many more parts to budget for.

Except for the transformer-based passives, I have preferred actives over any passives I have heard.

Paul L · « **Reply #35 on:** 3 Sep 2004, 06:54 pm »

Tuckers, could you care to list what resistive base passive you have heard?

If a poweramp is properly designed, its first stage can do everything a linestage can do and there is no need for active line stage. Transformer base is different concept but you are hearing the sonic signature of the transformer just like tube power amp that has output transformer. If you hear a well designed OTL tube amp that you will know what a real tube amp sounds.

Marbles · « **Reply #36 on:** 3 Sep 2004, 07:00 pm »

Quote from: Paul L

Tuckers, could you care to list what resistive base passive you have heard?

If a poweramp is properly designed, its first stage can do everything a linestage can do and there is no need for active line stage. Transformer base is different concept but you are hearing the sonic signature of the transformer just like tube power amp that has output transformer. If you hear a well designed OTL tube amp that you will know what a real tube amp sounds.

Paul, with the Bent (S&B TX102 silver transformers) I have, I cannot hear any sonic signature....maybe it's the absence of a signature that makes it so appealing?
That goes for the Seiden switch as well.

Paul L · « **Reply #37 on:** 3 Sep 2004, 09:17 pm »

Marbles,
I won't be that confident about the absent of sonic signature of any component. My experience is that ANY component that is on the signal path has its sonic signature even as simple as a resistor having the same spec. If you consider how long is the wire required to wind a transformer, there has to be some sonic signature.

There is a thread in Audioasylum that Ozzy and Hyperion exchanged the discussion of the Bents and our Little Wonder. Ozzy said the older version of the Bent sounds better the newer version (or least with his ears). I think that is the indication of the sonic difference between the two version of the Bent's transformer. I will leave the comparison of our unit out from this discussion.

Marbles · « **Reply #38 on:** 3 Sep 2004, 09:48 pm »

Paul, while I'm sure it has a signature, it has less of one than any other component I have heard, regardless of what that compnent is. Every time I A/B it against other pre/pro's, it sounds like they have the signature.

I honestly cannot hear a signature of this pre as I can with cables, other pre's, speakers, amps etc...

Now to do a search on AA to see what those guys say.

Marbles · « **Reply #39 on:** 3 Sep 2004, 10:07 pm »

Paul,

I just looked at the thread in question. Most of the Bent pre's (before the NOH) were kits. They have MANY solder points from the Seiden switch to the transformer taps. I suspect that not all were done as well as mine was.

I had an Electrical Engineer with a more than $1000 solder station build mine.
He is totally anal about the smallest details.

I won't presume anything about the way Hyperions Bent was made or the corresponding equipment paired with it.