[MarinRider]

The general consensus seems to be that passive preamps lose a bit of drive and control at the frequency extremes compared to active preamps. The reason usually cited is the inability of the relatively high output impedance to drive the interconnect cables properly.

So why not get rid of the cables that are causing the rolloff by locating the volume control right at the input to the power amps, you may also need to ensure a low capacitance input to the power amp by removing the vhf filter cap and using transistors with low miller capacitance or by using cascodes etc.

In other words - go back to the lowly integrated amp - and save a load of money and a load of stuff in the signal path.

I have got very good results doing exactly this, soundwise you get the best of both worlds, drive and control like an active pre and detail and tonality like a passive.

Do you agree or have I lost the plot?

[Brad V]

It's funny you mention that, as Hantra and I ran an experiment a little over a week ago.

He brought over his Audience AU24 Interconnects. We hooked them up between my DAC and Preamp and it sounded so good. Then we decided to try to connect the IC between the DAC and amp. I'm running a SET amp, so I don't have to worry about ear damage, without a preamp/volume control in the mix. Without the preamp in the middle, the sound didn't come close in quality. Now I can see why an extremely good preamp makes more of a difference than I had thought.  

I have to say YMMV, as there are very two systems that are alike. Where someone might need a preamp, another person might prefer it unaltered, etc...

[tkp]

There is no free meal in this world.  The performance of passive preamp depend greatly on the source that is driving it.  Degrade in performance with long IC is only a side effect of the true problem which is low power transfer ratio or in another word the ratio of the amp. input impedance divided by the output impedance of the source.  A good active preamp would have an output impedance under 100 ohms versus 1 kohms or more on a typical source.

[nathanm]

Don't worry folks, the RIAA is hard at work making your CDs louder and louder and it won't be long before you will be able to hook your speakers right up to the output of your CD player!  Hooray!

[Hantra]

Heh. . . Funny Brad, I was just going to mention that. . .

It was quite a revelation for me that life without a pre-amp was NOT better than life with a GOOD pre.  It all depends on the pre-amp.  I am quite sure that the market is overstocked with pre-amps that we would all be better off without in our systems, but for the ones that are great, they can take it to another level. . .

[cyounkman]

Brad, in your experience, it sounds like the (likely) very high input impedance of your SET amp was a disastrous load for your DAC, which, like most was (probably) just designed to drive the (hopefully) benign load of a preamp.

The scenario above, or something like it, is the generally-accepted explanation for lackluster performance in systems with a passive preamp, despite the theoretical advantages.

In my case, my integrated amplifier has a passive preamp (just a volume control, basically) built in, mated to a very sensitive amp (I think it goes to full power on 300-600 millivolts? Don't quote me.). As such, I can't drive the amp with a real preamp to see what the difference would be. [The amp, in general, is fast, dynamic and detailed, but I wouldn't describe it as warm.]

My current GamuT CD-1 puts out 4 volts, so it obviously shouldn't have a problem driving the amp directly. My previous Audio Aero Prima, with its higher-output-impedance tube stage, was less stellar. Anyway, I'm hoping the steroidal output of my cdp gives me a free ticket to play with passive in the future and not get burned.

Marinrider: re: your last point, someone unfortunately beat you to it. [let me check my email...]

http://www.tweakaudio.com/Ultimate%20Attenuators.html

The company is EVS, which does various mods and sells tweaky little bits like these. It's a shunt-based attenuator that you mount directly on your amp's rca input. There's a big knob, and another rca input for your source cable. Dual mono, obviously.

This is the height of tweaky inconvenience, (imagine bending over to reach the back your amp every time you need to adjust the volume--it makes those hairshirt dual-mono no-remote pre-amps look like the lap of luxury.) but it makes a lot of sense theoretically. For me, though, it's the answer to a question that no one's asked.

(I'm sure some enterprising person could market a sonically transparent remote control for them -- some Rube Goldberg contraption made out of a small gearbox, those wands from a set of venetian blinds, and a bunch of tinkertoys.)

I guess the sane person's compromise is to buy a remote-controlled passive box and use the shortest possible length of extremely low impedance cables to connect to the amp. But I think the amp's input impedance is the gating factor in most systems.

[MarinRider]

My initial impression of my passive with short cables approach was very good but after a while I realised something was missing - just like every time I've tried a passive in the past. How many times have I been round this particular Audio Circle? (Answer: more than 5).

Fortunately I did not resort to extreme methods or major surgery to try this experiment.

Logic still tells me that passive pre's with correct interfacing must be better than any active pre because there is less in the signal path. Anyway normal service has been resumed and one of my collection of pre's (Linn Kairn, Grounded Grid, homebrew AD817 pre) is back in the system.

Chris - Thanks for the EVS info, it's reassuring to know I don't need the padded cell just yet!

[Tonto Yoder]

EVS discontinued those a little while ago.  To point out the obvious, there are two attenuators pictured (plugged into each other)--in actual use, each one's RCA gets plugged into the amp inputs.

Like you say, they seem inconvenient.

[Psychicanimal]

I recently switched to the Channel Islands passive pre-amp.  I plan to use it with a Marchand X9 electronic crossover, which I have not received yet from modding at Modwright.  So far the Channel Islands turned out to be much better than my Melos in most respects.  I guess it has more to do with the volume pot than anything else.