jacob@psyche.mit.edu (Jacob Feldman) (03/19/90)
I am also very curious about the by-passing of the gain stage on high level sources. I have a PS Audio 4.6 which has the bypass option (only the volume control is in the circuit). Common sense (echoed by many salesmen as well as the PS Audio literature) seems to suggest that avoiding the gain stage can only be a good thing, as you avoid any colorations that it might introduce. However, my experience has been to the contrary: both the PS Audio bypass and an Adcom passive "preamp" I once heard have a flat, lifeless quality as well as a very peculiar, unnatural-sounding nasal timbre. This quality was distinctive enough and peculiar enough to suggest that it wasn't just a question of hearing the faults of the amp coming through-- at the very least, it wasn't just lack of some kind of euphonic coloration. I have no doubt that this phenomenon has some electronic origin that I just don't know but would be delighted if someone took a shot at explaining. -Jacob Feldman
dnwle@dcatla.UUCP (W. Lawrence English) (03/22/90)
In article <9003170016.AA25031@psyche.mit.edu> jacob@psyche.mit.edu (Jacob Feldman) writes: >both the PS Audio bypass and an Adcom passive "preamp" I once heard have >a flat, lifeless quality as well as a very peculiar, unnatural-sounding note: i have a ps audio 4.5, with this "straight line" mode. i have noticed that my cassette deck, in particular, seems to exhibit this. my guess is that specific devices, such as a given tape deck or tuner, are not designed to drive a power amplifier directly. power amps can have quite low input impedances ( as low as 10K ohm ), as opposed to the input impedance of a good preamplifier ( at least 100K ). <->---------------------------<+>------------------------------------------<-> <-> W. Lawrence English, Jr. <+> Society For The Incurably Pompous. By <-> <-> gatech!dcatla!dnwle <+> Invitation Only. "Send us your resume." <-> <-> ( your ad here ) <+> "We'll just see if you qualify." <-> <->-----------------------<+>----------------------------------------------<->
shankar@rnd.gba.nyu.edu (Shankar Bhattachary) (03/22/90)
In article <9003170016.AA25031@psyche.mit.edu> jacob@psyche.mit.edu (Jacob Feldman) writes: >I am also very curious about the by-passing of the gain stage on high >level sources. [............] (stuff on just having the pots in the path) >both the PS Audio bypass and an Adcom passive "preamp" I once heard have >a flat, lifeless quality as well as a very peculiar, unnatural-sounding >nasal timbre. Provided you don't need the gain of a high-level stage, I can see only one problem with bypassing the stage altogether. Driving a power amp directly off the pots presents the system with a high-impedance source in the preamp to power amp connection. It becomes important to ensure that cables are short, or have low overall capacitance, etc. I don't believe that cable interactions are important for solid state preamps, apart from obvious issues like avoiding noise pickup, and keeping connections clean and such. The output impedance of solid state preamps tends to be negligible. However, once you drive the power amp directly off the pots, that is no longer true. The high-level stage of the preamp may offer some buffering, which may be necessary for long runs of cable, or for higher capacitance cables. Other than that, any difference between the no-high-level-gain situation and the high-level-gain-in situation must be alteration of the signal by the high-level stage. Any other thoughts out there? There must be. -------------------------------------------------------------------------- Shankar Bhattacharyya, Information Systems, New York University shankar@rnd.gba.nyu.edu --------------------------------------------------------------------------
tarr-michael@YALE.EDU (michael tarr) (03/22/90)
One problem with bypassing the preamp is that you need a volume control and from my experience the variable output on most CD players sounds far worse than the fixed output (i.e the SONY 508ES). Any guesses as to why this may be true? Mike
caseyng@cie.uoregon.edu (Kong Ng) (03/22/90)
In article <9003170016.AA25031@psyche.mit.edu> jacob@psyche.mit.edu (Jacob Feldman) writes: >I am also very curious about the by-passing of the gain stage on high >level sources. I have a PS Audio 4.6 which has the bypass option (only >the volume control is in the circuit). Common sense (echoed by many >salesmen as well as the PS Audio literature) seems to suggest that avoiding >the gain stage can only be a good thing, as you avoid any colorations >that it might introduce. However, my experience has been to the contrary: hi, Using passive preamp means that you're giving up a buffer stage, say, between your CD player and power amp. The output impedance of an active preamp is in the vicinity of 100 ohm, while the input impedance of the power amp is >10k ohm. However, with passive preamp, the output impedance is rather high, due to the volume control (potential meter) that is usually 10k ohm. At this point, the \impedance matching between the passive preamp and the power amp becomes a problem. I am using a passive preamp for about 2 years. Careful attention to interconnects helps a little. I haven't compare my passive preamp to some great preamps, but it outperforms budget preamps <$500. The main advantage of the passive preamp is its transparency, natural timbre, and soundstage. However, it lacks dynamics and a pulpable bass. casey
chowkwan@aero.org (Raymond Chowkwanyun) (03/23/90)
I can confirm what Michael reported. The sound improved dramatically when I changed from the variable to fixed output on my Sony C7ESD (maybe this is a problem endemic to Sonys?). I experienced the so-called "lifting of the veil". The music came through smoother, more detail, more liveness. Is this what you found Michael? The obvious reason is that Sony implemented a cheap low-quality volume control. In general, I believe that the fewer components in the signal path the better. -- ray