Passive Pre-amps

I can't see any way for a pre-amp to be more true to the source than a simple passive resistive design. Simply putting a couple of resistors in line to reduce volume level will do practically nothing to damage the quality of the signal. At any rate, an active design will have many more resistors in the signal chain.

This is only the case if your source and load equipment is suitable or such a set-up though. A resistive passive pre-amp basically shows a high-ish source impedance to the load equipment. The long cables going from source to pre-amp to power-amps can also load more capacitance on the source. To those who don't know much about electronics this could sound confusing, so it basically means your load equipment (the power amps) should have a high input impedance usually 50K Ohm or higher, and you should use sensible interconnects with low capacitance like pro mic cable.


So that said, what passive pre-amp models are available these days? I can't actually think of many, especially if one would like remote control.

 

Types or manufacturers?

I've had 3 of them; a pot in a box (Axiom by Luminous Audio), an attenuator in a box (diy) and a TVC (Promitheus).

Read about LDR's but not heard one.

There must be lots of manufacturers making them though.

 

I mean models of such pre-amps.

 

Are you including TVCs (some of the MFs offer remote control) or just resistive types?

 

Creek spring to mind.

 

and Audio Synthesis

 

Nva P50/P90

 

So am I the only one with an Audiosmile passive then?

It was followed by a Promitheus TVC then Eva Mk I and II LDRs from diy paradise (remote only) and now finally back to an active.

 

Nope I've got one too! No remote though

 

I have the Lightspeed LDR passive preamp (no remote though).

I previously owned the Promitheus TVC albeit in a different system and room so I can't compare apples to apples but nevertheless I feel the Lightspeed is a much better passive preamp.

 

The Creek does look nice. I thought it wasn't made anymore but don't know where I got that idea. Affordable too at £240.

 

My passive isn't avaialble anymore. It is the tapped transformer type making it a better match for a wider range of kit. However stuff like MC outputs lost some immediacy, especially when a step up was used. I presume there are only so many windings a signal can be subjected to before the benefits are outweighed by the limitations of using transformers.

 

As you say, transformer volume controls can match a wider range of kit since they present a higher input impedance and lower output impedance than a resistive passive. I used one based on the Music First transformers for a long time and it was superb. They do still vary the impedance with the level setting though, so it can change the sound 'as you go' on a source that has a highish output impedance of perhaps some aggressive output filters.

The main problem I think is that while some transformers have really really low distortion, other have terrible distortion! There is no telling what is what for the end user. When I was developing the transformer output mods for the Behringer Mods I tested about 6 different brands and some of the well respected ones were very poor.

 

I had an S&B based TVC, I sold it recently. I still have a DACT attenuator based pre that I use with Gainclone. During a bake-off (I'm not sure you attended this one), The TVC came on top, followed by DACT and then resistive ladder. Apart from the TVC all can be made for reasonable money. T even told us how we can add a remote.

 

There's a similar passive pre made by Icon Audio for a little more than the Creek, I was tempted to get one a while back but have stuck with an active pre for the time being.

Going back even further, the QED Vector and Vector Reference were both switchable passive/active pre-amps with good reviews, mid/late 90s models I think.

 

I've got an old Audio Synthesis PAS-02 stepped attenuator, it dates from about 1993 IIRC:



I like it; it's simple, does the job, as green as it can be as it uses no power, and has nothing in it that will wear out / need servicing. Just the thing for the TV/office system that's on all day.

There are some incredibly cheap passive pres available on eBay these days too, e.g. this for under 55 quid landed.

Tony.

 

Using a 28-step AVC (autoformer volume control) that's been expertly housed in a nice box with inputs and preamp out. Very nice indeed!

http://www.intactaudio.com/atten.html

 

The best preamp is no preamp. Just put a stepped attenuator before the buffered output of every source device then use a switch to choose between them. The benefits of a single additional component like a passive but with none of the drawbacks (such as they are).