So I have been on the fence, do I or don’t I get an external preamp. Well, I remembered that my Class A Oppo HA-1 headphone amp / preamplifier had a high quality preamp built in and decided to use my ACTIVE speakers via that HA-1. Well lo and behold when I set the Gustard R26 dac (bypassing it’s built-in preamp) to fixed volume output and controlled the volume via the HA-1 (which has an analog control knob) with connected active speakers via xlr my sound jumped a level in the best way possible. I have attached a description of the HA-1 circuitry and the preamp specifications.
I welcome your input on why the improvement??? Kinda dumbfounded once again. How can this be and thank you in advance for educating a newbie.
Hifi Rose 150b streamer feeding Gustard U18 DDC via USB, Gustard U18 Feeding the Gustard R26 DAC via i2s, R26 feeding the Oppo HA-1 Class A discrete headphone amp / preamplifier via xlr analog in, HA-1 feeding Active speakers via XLR out.
FYI ( I do use the xlr output / preamp of the Gustard R26 DAC to feed my Ferrum OOR amp at Fixed volume for headphone use). I am doing my best to avoid the volume adjustment on the R26 DAC since the volume control is digital.
I don’t know the detals of your specific equipment but the general rule is you want to run the dac at full volume and adjust volume down the line, typically on the amp.
The reason is that you loose some information by controlling the volume digitally.
So I suspect this is not a pre-amp issue but rather the result of running the dac at full volume.
Also, the pre-amp has always been in the signal path so nothing changed there.
Short answer, yes.
The volume % on the preamp is the amount of the preamp’s sound signature being injected into your system.
A tube edit: pre-amp [/edit] at a ‘theoretical’ 50% volume is adding half of its total potential tube flavour to the sound that goes through your headphones / speakers.
@orrman Thank you for the reply. The reason for my question, and I do appreciate your response, is it is my understanding that a preamp doesn’t typically change the quality of the sound. To use an overused word, it is typically transparent. So I was trying to better understand with my chain why did I experience a change in perceived quality of sound. I believe @NickZ 's insight was helpful and the change is due to where I am adjusting the volume in my setup. The external preamp vs the internal preamp of the DAC.
Yep the volume adjustment definitely plays a part but I’d say that generally any component added would introduce changes. I personally don’t believe there are transparent components.
The volume control on most pre-amplifiers (or headphone amplifiers) simply attenuates the signal feeding the amplifier/gain/buffer stage.
Properly implemented the volume setting’s sole contribution to the ultimate output are a) any mismatch in channel balance (assuming a potentiometer based volume control) and b) Johnson-Nyquist noise (quantum noise).
Johnson-Nyquist noise will go DOWN as you turn the volume dial UP. This is because you’re reducing the resistance in the circuit as you increase the volume (decrease the attenuation).
Otherwise, most amplifiers/gain stages/buffers will be FULLY in effect regardless of the volume setting.
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ALL amplifiers, pre or power, have an effect on the signal. No one has managed to design an amplifier that doesn’t add both noise and distortion. Within our understanding of physics, you can’t build an amplifier that doesn’t. But … good pre-amplifiers will do this at well-below-audible levels.
It is probably seems like we say this all the time, but the answer is, “It depends.” In this case, the main question would be the ability of the source component to “drive” the input stage of the power amp.
Lots of possibilities, which is why Schiit, for example, provides both passive and active (buffered) operation of their Saga and Freya preamps.
In my experience the volume pots of passive preamps tend to flatten dynamics and slightly change the tone. I hear no impact from passive switch boxes without pots. On top of this, passive preamps are much more common on the low end and thereby often focus on value over absolute quality. There may be exceptions, but I usually prefer active preamps.
I look at volume control as being in 3 categories: (1) potentiometers, (2) resistor ladders, and (3) magnetic.
“Pots” are usually conductive plastic and even the nice ones, like an ALPS Blue Velvet, are cheap ($2 to $20 to the consumer, probably half that or less to manufacturers buying in reasonable quantity). The amount of attenuation is simply the amount of plastic that the signal passes through. Lots of potential to degrade the sound here, which is why some people replace them in vintage gear with…
Resistor ladders, i.e. stepped attenuators, which are usually thin-film resistors tightly matched (0.1% or better). Channel balance is maintained at all levels, and these have very little potential to degrade the sound. For me, these are the value leaders, as they’re not much more expensive than better pots (this one is $30), but perform quite a bit better.
Magnetic means transformers (so “transformer volume control” or “TVC”), and those are expensive, though some are in the same range as modestly-priced active preamps. This approach avoids the impedance matching question completely, along with worrying about cable lengths. Music First Audio makes some nice ones, but I think there are other players (Townsend?, probably some Japanese companies) at these levels.
My desktop use case will always keep the volume control with the amp (does anyone even make a headphone power amp?), but for a 2-channel speaker-based endgame setup, I would definitely be thinking TVC.
Hope I’m not “talking down” to folks here. I sometimes forget who the techies are, and I’m just trying to help the OP and others understand that there’s a lot of different approaches to what seems like an easy question (why/how a preamp impacts sound quality).
