The future of preamps

12-10-13: Unsound
Perhaps I've been misled, but I thought the redbook standard output was 2 volts?

I haven't ever had occasion to look at the redbook specification document, but the de facto norm seems to be "full scale" (i.e., maximum) amplitudes of 2 volts unbalanced and 4 volts balanced. That would be based on the usual convention of defining balanced amplitudes as corresponding to the instantaneous difference between the voltages of the two signals in a balanced signal pair, the 4 volt number therefore reflecting each of the two signals being 2 volts.

Ralph's designs are balanced, of course, although they often provide both balanced and unbalanced inputs. I suspect that is why he mentioned 4 volts.

Best regards,
-- Al

Perhaps I've been misled, but I thought the redbook standard output was 2 volts?

For digital sources, preamps may also provide DAC and DSP, in addition to the functions that Ralph notes. I can foresee more HT style functionality creeping into the traditional preamps as digital sources continue to dominate, but I don't see the preamp going away.

A preamp has four functions:

1) control gain
2) provide any needed gain
3) provide input switching
4) control the interconnect cable

Of these functions, most digital sources provide one, which is to control gain. Unfortunately, Redbook specs call for the digital device to put out 4 volts, which is far too much for any power amplifier, so right away the signal has to get knocked down (and on the way, degraded) in order to be useful.

The problem is that many volume controls degrade the sound, and if they are not buffered (as in passive controls) the math often works against you, causing loss of bass if the control is anything less than full on, and often a lack of dynamic punch. This is caused by the resulting output impedance of the control in series with the source being so high that the interconnect becomes of sort of tone control that is interjected.

Now you could throw a lot of money at that problem by looking for just the right cable and many audiophiles do. But the simple fact is that the passive control is a big compromise, not based on the quality of the control so much as the approach: the control and interconnect effectively interact with the source impedance to behave as a filter.

One way around this is to have a PVC with a lower resistance value overall, but this can be hard for some sources to drive.

A buffered volume control does not have this problem. You will find that most preamps are far less susceptible to the cable than passive controls are as a result.

FWIW, the industry would be better off if the output of digital devices was limited to about 2 volts. One really does have to wonder what the authors of the Redbook were thinking!

Due to the variability of competence in line sections of preamps, you will find that the issue of passive (and TVC) volume controls VS active line stages will be an on-going debate. There are line stages that can so completely control the interconnect cable that you can no longer hear the differences between them. IMO/IME this is when you really start getting to transparency, as the filter I mentioned earlier is removed.

Since I ventured into computer-based (source-)audio I've passed on hardware preamps. I guess luck, or perhaps even taste has seen to it that none of the poweramp/source-direct constellations that have gone through my setups have turned out less than favorable - i.e. where impedance/gain matching have tilted the sonics towards the anemic or body-less, something that is quite often reported to occur when named matching goes wrong. My current, and by all accounts future volume control option is 24-bit (preferably 32-bit in the near future) dithered digital attenuation via JRiver MC19; it works and sounds excellent. From what I'm able to assess it's not digital volume controls like the one I'm using right now that inflicts any character on the sound of the sort an analog volume ditto and associated component of the hardware preamp with cables as a whole would create, so whatever character arises with the use of a software-based digital volume control, insofar the poweramp/DAC-direct combo is an electrically suitable match, is more likely to be an "effect" created, and to be corrected elsewhere. This, at least, is my stance as is.

The future use of hardware preamps may maintain a certain level due to the continuing bloom of turntable/LP use. I'm likely never to return to analog, so the hardware preamp won't either.

Personally, I don't see preamps disappearing from this hobby anymore than I see tubes and vinyl disappearing.

IMHO, the preamp is the heart and soul of the system. In my experiences, finding the *right* preamp has always been the most difficult task in assembling a system that draws me into the music.

Most digital based components have enough gain output to drive an amplifier, but what about turntable users and those who run more than one source?

Great future as they do make a difference, more so then the power amps. This is especially true if you are into vinyl, as they contribute much more then any combined unit. I have a knock off of the HK Citation 1 (VAS) and it is a joy for vinyl listening. The design of this unit is almost fifty years old, so when you marry it with current SOTA parts, like VAS did, it comes close to blowing away many Audio Research units. I think, aside from the DAC technology, pre amps will around along as there is vinyl.