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Preamplifiers - do you need one in a Linn streamer hifi system?

There has been much discussion since Linn announced in the spring of 2015 that it was no longer going to manufacture stand-alone preamplifiers.  Linn also stated adamantly that the internal volume control which is present in all their streamers' digital circuitry was superior in every way to the analogue volume controls found in preamplifiers. 

 

This statement confounded much of the hifi community - Linn arguably make some of the best preamplifiers in the wortld.  Moreover many Linn enthusiasts who already owned preamplifiers, and used only a streamer as their hifi source, began to wonder if they had been unnecessarily conned into buying preamplifiers in the first place by their Linn dealer, understandably keen to sell an extra box.  The polemic has been driven to higher levels by the fact that many system owners much prefer the sound of their music if it has been through a preamplifier.

 

Linn remain adamant that a preamplifier cannot possibly add anything worthwhile to the signal, and that the best preamplifier is a piece of wire.  The reasons for this are various - previous ideas that the volume control internal to Streamer might pick up noise at lower levels have been discounted and graphs have been published showing that streamer-induced noise is less than the best preamplifier background noise.

 

 

I must admit that I really have an open mind about this debate.  I can follow Linn's argument, and it sounds convincing.  But I am also aware that things happen in hifi that cannot be explained.  There is no convincing argument why some mains cables sound better than others - at least I have never been convinced.  But to my ears, some do.

 

I decided to explore the situation as far as I could with the equipment available to me.  I have an Akurate DS streamer, and a Tundra power amplifier.  I have tried this system in three ways - without a preamplifier, with a Lejonklou preamplifier, and with a Linn preamplifier.  The Lejonklou made the sound sweeter and better defined, the Linn made it harsher and less perferable.  At least to my ears.

 

When the streamer is configured for external volume control, i.e. a preamplifier is employed as the volume control, the streamer is simply set to 80.  Linn maintain there is no extra circuitry;  the volume is simply  always set at 80, which is described as zero gain, and emerges from the streamer at the suitable line level to feed into the preamplifier.

 

streamer with preamplifier

 

What happens to the sound inside of the Linn streamer when the internal volume control is used?  According to Linn the output can be adjusted between 0 and 100 in the digital domain.  The signal then feeds directly into the power amplifer which obviously amplifies whatever signal arrives on its input by a fixed amount.  All volume changes are made within the streamer.

 

streamer without a preamplifier

 

It has been suggested by the pro-preamplifier lobby that the signal which emerges at signal level 80 sounds better than when it is attenuated by the streamer digital circuitry to say, 60, a good everyday listening level.

 

It will be noted that I have scribbled in the approximate input and output impedances typical of Linn and Lejonklou equipment.  It is important that output impedences are much lower than the units that they feed.  This ensures that the following amplifier (or preamplifier) does not effectively overload the signal source - doing so could compromise the desired level frequency response and ultimately cause distortion.  Good design practice requires the following input impedance to be at least 10 times the source impedance. In this case the specification is about 33, which is excellent.  For more on this design consideration see, for example this Audiogon discussion.  Some sources say even a 5:1 ratio is fine.

 

 

What I found myself wanting to do is to hear what the music sounds like when it emerges at "80", the golden level advocated by the pro-preamplifier lobby.  How do you do this without driving your speakers so loud that, among other things, your ears are rendered incapable of discerning good from bad?

 

I needed to build an attenuator which approximately fooled my power amplifier into believing that it was receiving a signal at level 60 when it was in fact emerging from the streamer at level 80.  I constructed this attenuator.

 

attenuator details, in circuit

 

 

You will note the following:  the 3,900Ω and 1,000Ω & resistances form a potential divider, resulting in approximately 20% of the output level of the streamer presenting itself to the power amplifier.  I have found that by using these values, when I set the signal level to 80 on the streamer internal volume control, it sounds, to my ears, about the same as level 60 without the attenuator.

 

You will also note that I have endeavoured to maintain good practice as far as impedance matching.

 

In this configuration the streamer sees  3,900Ω + (1,000 // 10,000)Ω ≈ 4,800Ω.  Which is more than 14:1 which is fine.

Similarly, the power amplifier sees  (3900 + 300)Ω // 1,000Ω ≈ 808Ω.  Which is better than 12:1.  Also fine.

 

The attenuator was very easy to make - I simply soldered a male and female phono connector back to back (by the earthing terminals) and the two resistances were easily mounted.  No, it did not look pretty, and no it was not screened (quite unnecessary to do this).

 

I have been listening to this over a couple of days in the following modes:

 

With the streamer's internal volume control active feeding directly into my power amplifier.

With the streamer's internal volume control active with the signal going through the attenuator into the power amplifier.

With the streamer's internal volume control switched off, listening via the attenuator to a signal at the magic level of 80.  Obviously one is unable to vary the volume in this mode - but as I explained, via the attenuator 80 is a comfortable level.

 

And my findings?

 

Well, so far I have reached no conclusions.  My wife could not hear any differences.  I could encourage myself to believe that at 80 the signal seems a bit more dynamic, seems to breath a little more easily, and maybe have very slight treble attenuation. But nothing I would care to demonstrate to others.

 

The attenuator is now out of the circuit and normal service has been resumed.  On the face of it, with my equipment, Linn are right.  Unless you need to switch sources, there are no clear advantages to owning a preamplifier.

 

Which leads me to wonder what is happening in the cases where good friends much prefer a preamplifier in the circuit.  What are they listening to?  Wonderful subtle tonal colourations, clever circuitry that increases or decreases a signal's dynamic presentation?  Or what? I have to be convinced - as I have heard argued - that a preamplifier is required for the best impedance matching.

 

 

Do please try this yourself - take great care with volume levels when taking the attenuator in and out of the circuit.  Don't run you hifi at high levels without an attenuator.  Always turn the volume right down before making any adjustments.   Please contact me with your findings.


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