How important is the pre-amp?


Hello all,

Genuine request here for other's experiences.

I get how power amps can make really significant changes to the sound of a system. And of course speakers have an even bigger effect. And then there is the complicated relationship between the speaker and power amp. But I wonder about pre-amps.

In theory a well designed preamp should just act as a source switch and volume control. But does it add (or ruin) magic? Can a pre-amp color the sound? Alter pace and timing? Could you take a great sounding system and spoil it with the wrong preamp? Stereophile once gushed (while reviewing a preamp that cost as much as a car) that the preamp was the heart of the system, setting the tone of everything. Really? Some people don't even bother with a preamp, feeding their DACs straight into the power amp. Others favor passive devices, things without power. If one can get a perfectly good $2K preamp, why bother with 20K?

What your experiences been?
128x128rols
smandlej- I have the Townshend Allegri Reference (upgraded from the "standard" Allegri). This was well reviewed by Martin Colloms of Hi-Fi Critic and Raphael Todes of Allegri String Quartet fame, the latter uses the Bartok and found the Reference worked far better for volume control/sound quality. I believe both reviewers now own and use the Refernce in their own systems.
 This unit requires no expensive mains lead or support as it incorporates Max's podium style feet, but you could use one of Max's platforms as well.
From my perspective, this is the most important element of my system, and using it is like upgrading all my source components in one go !! It does require a substantial run-in period and benefits from balanced interconnects between pre and power. Martin uses solid state (Naim) whilst Rapheal uses valves - it works well with either - see millercarbon's post above. 

Good to know. It has been quite a few years since I really dug into this subject. Was really interested in improving my integrated amp which at the time one was using trim pots the other a stepped attenuator, neither one a true preamp just a volume control. The more I learned the more clear it became that transformers are the way to go.   

That was a long time ago so I forget all the technical electrical reasons. But the real reason they've been forgotten is my memory tends to low prioritize the moot point. Because ultimately there will always be someone willing to throw enough time and effort and money at it to solve that part of the problem.  

The one they can't solve is the seemingly simple volume control. For that they always fall back on a resistor of some sort. Trim pot, variable resistor, stepped attenuator- whatever you want to call it is just a resistor used to control volume. These things are inherently lossy and noisy and problematic.  

Transformers on the other hand, where resistors have problems transformers have benefits. There is a reason after all why we use them all over the place for isolation and power conditioning.  

But I gave up on transformers because a) hard (read, expensive) to find good ones and b) even harder to find one with all the taps needed to make a good volume control, and then c) you still need a lot of really high quality switches.  

But yeah, like you say, eliminates an expensive power cord, can be incredibly transparent, and passive, so slight gain in not adding any field noise to the system.  

I read the Colloms and Todes reviews, thanks. In the nearly 30 years since I looked into it there must have been a hundred thousand preamp questions and discussions. Yet I could count on my fingers the times transformers have been discussed. This kind of thing deserves a lot more mention and attention. Transformers, I mean.
Transformers on the other hand, where resistors have problems transformers have benefits. There is a reason after all why we use them all over the place for isolation and power conditioning.  
You solve one problem; you introduce others. Then it gets tricky.


The issue with transformers is loading and inter-winding capacitance. All transformers have inter-winding capacitance. If the transformer is not loaded correctly (usually too lightly) the capacitance may play a role causing the frequency response to be less than flat. This coloration can be easily heard.

Transformers are called that because they transform impedance. It goes both ways; you're not insulated on the input from the output. So if the output load is reduced, so is the impedance on the input side.

What happens when you have a transformer with multiple taps used as a volume control? Since you are working with a variable turns ratio, to keep the transformer linear you need to have the correct load at both the input and output. You can't, as a designer, expect to always see the same source impedance and you certainly don't see the same load impedance since all power amps are different in that regard. On top of that you have the moving target of variable turns ratio.


So you'll need a lot of switch contacts, not just the ones to change taps but another set with resistor to correct for the changing load impedance as the turns ratio is varied. 

This has to be done right, else the unit can introduce coloration.
I agree that a high performance preamp is important with respect to the performance of a hi-fi system as a whole, but I disagree that the preamp’s sonic performance is always tightly correlated with the price. Sometimes you pay a lot of money for heavy cases, thick, engraved faceplates, name brand recognition, other cosmetics, etc. I prefer to spend the money on advanced circuitry, the best vintage vacuum tubes, high quality stepped resistor motorized volume attenuators, point to point wiring, dual mono power supplies, outboard power supplies, etc.
I disagree that the preamp’s sonic performance is always tightly correlated with the price.
Funny- I was just commenting about this on another forum. I agree the price doesn't have much to do with performance. Those that price to a formula will be less expensive generally speaking. My philosophy runs very similar to yours.