Any Passive Pre Users?

soundfreak1

as far as remote control goes ALPS.akes a remote powered vol. Control.

Gadabout

Mark me down as another TVC user (same as Gaara). I tried a couple other pres in my main 2 ch system and the TVC has stayed there for a couple years now.

Scott

steveinaz

One thing to check when considering a passive linestage, is to make sure your amp has the input sensitivity to be driven to full output with all your sources (generally 2V or less for full output). The only occassional glitch I run into is a very few channels on DirecTV (Palladia is one of them) sometimes run very low output levels; I have to crank my passive pretty high on those channels, but I've never ran into a sitaution where I couldn't get enough output---and it never happens with any of my other sources. Keep in mind though, my Parasound HCA-1500 has a 1.2v input sensitivity---so it's a good candidate for a passive linestage.

Also keep cables as short as possible; my Placette has a .5mtr Kimber Hero going to the amp.

I-SIG

I love my Wyred 4 Sound pre-amp. Shoulda made the jump to this unit a couple of years before I did.

Wes

lanchile

C/P
Passive preamps have gained popularity in high-end audio circles. Provided that a high quality volume control is used, a passive preamp is often the easiest and cheapest way to reach high-end sound quality.
Actually, the term "passive preamp" is slightly misleading. The word preamp or preamplifier is not supposed to be a passive device, as a passive device may not provide amplification. So a better term than passive preamp would be passive volume control or passive control center.

DACT stepped attenuators are high quality volume controls and therefore also well suited as passive volume controls in audio systems.

A passive volume control is a passive device (no active electronics and therefore no power supply required) that replaces the traditional preamplifier.
Today, many signal sources such as CD players have sufficient output level to drive most power amplifiers directly. It means that no additional amplification is required, so for level purposes there is no need for a preamplifier. With a passive volume control in between, the signal from the source may be fed directly to the power amplifier. One other component you may wish is an input selector like for instance DACT's CT3-5-4.

There are some significant advantages using a passive volume control:
Cost savings. A very high quality passive volume control is cheaper than even low quality preamplifiers.
Improved sound quality. The non-linearities, noise and distortion from the preamplifier are avoided. Even the most expensive preamplifiers add coloration and distortion to the sound.

In many cases, a passive preamplifier sounds as good or better than the best active preamplifiers. In other cases, it is our experience that a good line stage following the volume control may sound more dynamic than a passive volume control. It seems to depend on many different circumstances, which solution is the better. For instance, the type and length of cable connected to the output of a passive volume control is critical. For those interested in comparing between a passive volume control and a buffered volume control, DACT offers the CT101 buffer/line stage for buffering DACT attenuators.

An active preamplifier usually has high input impedance and low output impedance. This fact makes the choice of interconnect cables relatively uncritical.
When the preamplifier is replaced by a passive volume control, the situation is different. The input impedance of a passive volume control is usually not as high as that of a power amplifier and the output impedance is usually high compared to a preamplifier's output impedance.
If care is taken in dealing with this issue it is not a problem in most Hi-Fi systems. The most important matter is to take care of the impedance of the interconnect cables. The output impedance of the source (for instance a CD player) is usually relatively low. Therefore, the interconnect cables between the source and the passive volume control are not as critical as the interconnect cables between the passive volume control and the power amplifier. The key factor to look out for is the loading capacitance on the volume control's output. In order to maintain a large bandwidth, the loading capacitance should be as small as possible. Otherwise, the load capacitance combined with the volume control output resistance makes a low pass filter that cuts away treble in the audible frequency range. At http://www.DACT.com, DACT offers a free tool for download. It is called the Attenuation Curve Calculator (ACC). With a few inputs, the ACC gives curves showing the volume control output frequency response.
The general recommendations when using a passive volume control are:
Use as short interconnect cables as possible from the source to the volume control and especially from the volume control to the power amplifier. The passive volume control should be placed near the power amplifier or even better built into it.
Use cables with low capacitance per meter. Many manufacturers of interconnect cables specify the capacitance.
Use low attenuator resistance values. Unless there are special concerns, we recommend using a DACT 10 kOhm attenuator for passive volume control applications. However, always make sure that the source (for instance the CD player) is able to "drive" the load. In the case of a passive volume control, the worst case loading of the source is with the volume control turned fully up. The load will then be the attenuator resistance in parallel with the input impedance of the following stage (often the power amplifier).

Using DACT stepped attenuators as passive volume controls is straightforward. Please also see Fig. 1.
If you use a 2-deck DACT attenuator as volume control you will have a volume control that regulates the sound level in both channels at the same time. Due to the accuracy of DACT attenuators (tracking between the two channels is within ? 0.05dB), there will be no need for a balance control to compensate for potentiometer inaccuracies. However, to compensate for channel balance errors in the other equipment or in the recording, a balance control may be needed. A good choice is DACT's CT4 stepped balance control.
If you prefer to have independent volume control for the two stereo channels, you may use one 1-deck DACT attenuator as passive volume control for each channel.
If your other equipment is balanced (XLR sockets) you may build a balanced passive volume control by using either a 4-deck attenuator or two 2-deck attenuators.
Finally, a passive 6-channel volume control may be built from a 6-channel DACT CT2 attenuator.

organ

Wow! Just finished reading the posts. Thanks for sharing your pics, experience and technical knowledge on passives. I had no idea quite a few people are into passives.

txcoastal1

Correct me if I am wrong, the Wyred 4 sound dac 2 has its own volumn control

So with PC>>>to DAC>>>to amp>>>speakers....would that make it a passive pre and work? And would I have to worry about impedance matching?

FTGV

txcoastal1 wrote: »

Correct me if I am wrong, the Wyred 4 sound dac 2 has its own volumn control

So with PC>>>to DAC>>>to amp>>>speakers....would that make it a passive pre and work? And would I have to worry about impedance matching?

I suspect since they are using the ESS 9018 dac chip they are usng it's optional digital attenuation feature.The stated output impedance from it's analog stage is stated as 100 ohm's so no impedance mismatch issues.

maximillian

soundfreak1 wrote: »

as far as remote control goes ALPS.akes a remote powered vol. Control.

From what I found, Alps makes motorized potentiometers. To make them remote controlled you need to add a micro to interpret the IR remote and control the potentiometer accordingly.

http://www.analogmetric.com/goods.php?id=1132

I've read some reviews on these types of products. Most are bad with complaints about crosstalk. There might be good ones out there but I haven't found any yet. Anyone know of one?

heiney9

My Dared and Adcom both use motorized ALPS pots, no a single complaint about noise, cross talk, etc. It comes down to implementation and design of the circuit used to control it. As with anything you can run the gammit from poor to excellent, it just depends on implementation, quality of parts and $$$. I'd rather have a motorized ALPS pot than cheap digital volume control circuits. Good digital volume control circuits are expensive compartively.

H9

maximillian

^1 of course. But I was looking at more of a DIY solution that stayed clear of the "poor" category. Perhaps by the time I spend the $$$ in an acceptable DIY solution it would be easier to just buy a quality off-the-shelf unit such as you mentioned. Just checking out the options for now.

mhardy6647

DIY can be quite inexpensive if you want to go with resistive attenuators rather than transformers or autoformers.

zingo

Stereo Knight makes a few passive preamps, one of them does have volume control. It's a well designed until as it's electronic circuits control the volume and input switching, but the signal path is a completely passive TVC design. Their TVC designs have good system synergy as the transformer can provide a better mate to active electronics, and they are very transparent sounding. They also have a version of that preamp that active and tube based; mmm... tasty....

maximillian wrote: »

Anyone ever done any passive pre that has a remote control to it? I would think an easy project would be to use something like a digital potentiometer tied to a microcontroller for control. The micro would also read from a universal remote for the user interface.

http://www.intersil.com/data/fn/fn8178.pdf

I actually worked with this chip in a previous job for doing basic audio control, so could make one if I had time. Yet I would think there are good DIY kits out there already.

zingo

I current have a Luminous Audio Axiom II passive pre and it's the best bang for the buck in my mind. Sound quality is great and the design is very simple, but it still has a nice look and great components and finish. If you're looking DIY, check out the Axiom II first and compare the cost of parts to build your project.

steveinaz

That's a cool looking piece!

maximillian

That does looks sweat. However, I've decided against passive pre since I don't want to have to worry about impedance issues. I'm looking through past posts for recommendation on an active tube or SS pre. Lots of choices. Still also toying with a DIY project too.

steveinaz

What amp are you running? As long as the amp has an input sensitivity to be driven to full output, you should be fine. Most sources output 2.0v, so if your amps input sensitivity is at or below that--you can drive it to full output.

heiney9

Even if there isn't an impedance mis-match not all passives sound the same and not all passives sound better than actives. IMO, and in my experience you need to aquire a taste for passive pre-amps. I do run my Adcom in passive mode but I feel it's missing a little of the dynamics and the soundstage is smaller on most material compared side by side. Which presentation is correct???? No one knows for sure.

It's about flavors and preference's, but running passive isn't some saviour that's going to save you from the evil active circuit.

Try it out and see if you like it, but don't automatically assume it's going to be "better"

H9

heiney9

AR: What's your position on passive versus active preamps?

NP: You'd think that a minimalist switch and variable resistor in a box would be as good or better than active stages, but often it is not.

Some of the issues are well understood; for instance if the resistance value of the potentiometer is low, the source can have bass issues due to the output coupling capacitance and higher distortion due to greater load current. At the other extreme, if the resistance is too high it can create distortion and high frequency issues by presenting a high source impedance to the power amp.

Then there are things that don't show up in the usual measurements and we simply observe that the active circuit sounds better than the passive.

I file these under "How About That".

heiney9

Is impedance matching an issue? Passive volume controls do have to
make a trade-off between input impedance and output impedance. If the
input impedance is high, making the input to the volume control easy for
the source to drive, then the output impedance is also high, possibly
creating difficulty with the input impedance of the power amplifier. And vice
versa: If your amplifier prefers low source impedance, then your signal
source might have to look at low impedance in the volume control.

tonyb

heiney9 wrote: »

It's about flavors and preference's, but running passive isn't some saviour that's going to save you from the evil active circuit.

Try it out and see if you like it, but don't automatically assume it's going to be "better"

H9

Very good Brock, well said.

The passives I've listened to have had a different sound, some better, some not so much. Regardless, this hobby is full of flavors to suit anyones ear but don't assume a passive is the ultimate. Doesn't hurt to try one out though and see if it blows your skirt up.

heiney9

That's one of the reasons I LOVE my current set-up. I have the choice of running passive, active or tubes all at the flip of a switch. Let's face it in this hobby we are about 95% dependent on the source material. It's the one thing we can't change other than buying a different "version" if one is available. Certain source material sounds better played back in one of the 3 situations.

We are slaves to the source material.

H9

audiocr381ve

Can anyone explain how something like the Pass B1 BUFFER fits into all of this?

heiney9

audiocr381ve wrote: »

Can anyone explain how something like the Pass B1 BUFFER fits into all of this?

Read about it from the horse's mouth. Probably the best, most indepth explanation you will get.

http://www.passdiy.com/pdf/B1%20Buffer%20Preamp.pdf

heiney9

Here's another. This one is much better explaining. The Pass article is more about DIY build

http://www.enjoythemusic.com/magazine/equipment/0708/first_watt_b1_preamplifier.htm

heiney9

The so-called "passive preamp," an attempt to achieve the ideal line stage without a buffer stage, has in my experience been a sonic failure. Lifeless and comatose are two descriptors that immediately come to mind. Simply inserting a volume control between the source component and power amp ignores two important interface issues. First, there's the issue of impedance matching. Ideally, input impedance should be high and output impedance should be low. That's difficult to achieve without the use of an active buffer or at least a transformer.

The second interface issue has to do with the ability of a stage to drive long and/or reactive interconnects

heiney9

More insightful reading for those interested.

http://www.enjoythemusic.com/magazine/equipment/0102/preamplifiers.htm

zingo

I've built the B1 before and it's a great no-gain preamp.

audiocr381ve

heiney9 wrote: »

Read about it from the horse's mouth. Probably the best, most indepth explanation you will get.

http://www.passdiy.com/pdf/B1%20Buffer%20Preamp.pdf

Somehow missed this. Thanks Brock.

steveinaz

Going passive was one of those "ah-ha" moments for me, It would take a mighty good active pre to unseat my Placette.