Julf wrote: > As one part of the monitoring chain, yes, but it is becoming less > common. For near-field monitoring, studios use active monitors that have > class D or A/B amps built in, and for listening room use class A amps > don't have enough power for modern, power-hungry speakers. > > IM distortion, just like HD, is caused by non-linearity. A badly > designed class A/B amp can have nonlinearity caused by the (gradual) > transfer from class A to B, and push-pull designs can have crossover > distortion. Neither are an issue with most class D architectures.
Hi Julf! Thought I'd reply to your second post of the day, although I found your potted history of Bell Labs interesting as well. My own gear consists of a Class A/B hybrid (but with the twin triode valves used in the pre-amp stage & MOSFET's used in the power amp)Pathos Logos amplifier driving my 2-way minimal crossover B&W 805S loudspeakers. Then I have 2 B&W PV1 subwoofers (which each contain a 500W Class D amp) connected in true stereo from the speaker posts of the Pathos amp which very handily has banana plug sockets built into its massive metal clamps. None of this gear represents the respective manufacturers' very latest takes on the subject, but I'm happy with the sound I get in my modest room. The Logos amplifier is biased to produce its first 30W in Class A, before a hopefully well-implemented transfer to Class B offering 110W into 8 ohms, or if you'd prefer 220W into 4 ohms. This simple doubling-up does suggest that they have made a decent fist of the power supply at least. It measures well (Pathos quoted specs: 2Hz-200kHz +/- 0.5dB; <0.05% THD (unspecified frequency/power); S/N >90dB; input 100KOhm) & doesn't sound particularly "tubey", so hopefully they've got the triodes operating in the linear range alluded to by Arny. Pathos's published design rationale is "valves are best for voltage amplification, solid-state devices are best for current amplification" which seems to an extent to chime with Arny's comments about the linear/non-linear range of valves, although I suspect it's something of an over-simplification for marketing acceptance. You can't really blame them for not wanting to give all their commercial secrets away. The Mk. 2 version apparently has some subtle improvements to the pre-amp stages, and the option of an inboard DAC giving it 9 inputs (2 digital, 2 balanced XLR analogue & 5 unbalanced phono analogue) whereas mine only has the latter 7. I wouldn't swap my Mk.1 since I don't need the DAC, but I might be tempted by their 50W pure Class A hybrid Inpol 2 amplifier at the right second-hand price: 50W per channel would be quite adequate given the size of my room, & I'd still have the 1000W of combined Class D amplification in the subwoofers to back it up where the main power of the frequency range for a music signal occurs. I bought my Logos second-hand from the dealer in Oxford who had supplied it new (I presume 4 years earlier) for 50% of the then going new price. I've used it extensively for nearly 8 years now & it's only popped 1 valve (heater element) in that time which also took out an internal board-mounted 1A fuse in the pre-amp stage obviously. I was able to sort this myself although I did have to buy a small set of hex drives since my screwdriver set didn't have one small enough to get the lid off. Blew a bit of dust out for good measure & fitted a matched pair of new Phillips tubes from Watford Valves who supply mainly musicians with a penchant for Marshall speakers with their valve amplification: again no silly prices, think I paid about £30 a pair. Got a spare set which may need to be used for the Digit, since the tubes are the same type. Have to confess now that I did have them cryogenically treated, not because I thought it would affect the sound but because it was a cheap option which I thought -*might*- improve longevity. Anyway they're doing well so far, & as far as I could tell (accepting Arny's point about forgetting after 20 seconds, which may yet consume the rest of my perception, who knows? I'm certainly not getting any younger) but could easily have simply been down to the original Sovteks being a bit tired if it was a genuine effect. I must confess that despite the size & weight of the beast, I had expected the box to be relatively empty, governed by the size of the large heat-sinks necessary to avoid the use of noisy cooling fans. Couldn't have been more wrong, it's full of stuff - there are pictures on Google images you can't miss if you're at all interested. It took me back to the practical difficulties in achieving Peter Walker's "straight piece of wire with gain" definition of the perfect amplifier... It nearly broke my heart that I couldn't find any of the B&W 805S's for sale second-hand anywhere back in 2009, so I had to visit their Portsmouth dealer Audio T to negotiate a new pair. Thankfully they didn't have any in stock. The salesman enquired slightly desperately whether I wouldn't like to hear a pair first, but was totally wrong-footed when I told him that my hearing was shot at my age (bare-faced lie, I'm afraid!) & that the reason I wanted them was that my partner who was in charge of all interior design matters liked the look of them (that was closer to the truth, they are quite pretty for loudspeakers). I then demanded a 15% discount for cash, & said if they wouldn't do it I'd call all the other B&W dealers in the UK until I found one who would. That sealed the deal, which wasn't so bad for them since all they had to do was order them in & take my money. Perhaps I should have asked for 20% off! I couldn't resist the matching stands which were clearly over-priced but matched the speaker shape perfectly. I did decline the £100 "magic" stand weighting filler they offered me, & did that job myself with a £3 bag of kiln-dried sand from B&Q the DIY chain. I had a lot to throw away as well, it's a shame that didn't sell the stuff in smaller bags! It all turned out quite well because shortly afterwards B&W discontinued the 805S (which had sold well at £2000 RRP, including stands) and replaced it with the 805D more or less identical from the outside but with an "improved" crossover and the diamond tweeter they already fitted to the floor-standing siblings. The only problem was that the price with stands shot up to about £4500. The 805D is now on its 3rd iteration, with many people not liking the D1 sound: the price has stayed high. Audio products seem to be becoming what an economist would term "Giffen goods". I've bi-wired the 805S's in accordance with B&W's recommendations although I remain unconvinced that this can really make a difference. The decent OFC & directional (how can that work with an alternating signal??) cable from my local electrical supplier was about £2 a metre & I only needed 12 rather than 6 metres to bi-wire them (equal lengths for each channel, of course, i.e. 4 x 3m lengths) I went for it, foolish or not... B&W published specs for 805S: Free-mounted 25mm aluminium dome tweeter; Kevlar fibre 165mm bass/midrange; Matrix cabinet with Flowport reflex loading; 2-way split crossover; -6dB at 42Hz & 50kHz; 49Hz - 22kHz +/- 3dB on reference axis; Within 2dB of reference response - over 60 degree arc horizontal, over 10 degree arc vertical; 88dBspl (2.83V, 1m); 2nd & 3rd harmonics (90dB, 1m) - <1% 100Hz - 22kHz - <0.5% 150Hz - 20kHz; Nominal impedance 8 Ohm (min 3.7 Ohm); Crossover frequency 4kHz; Recommended amplifier power 50W - 120W into 8 Oh on unclipped programme; Max recommended cable impedance 0.1 Ohm. I got my first PV1 in 2009 off eBay when it was the current model & very much in vogue; got the second this year off-eBay (whatever that means!) for not much more than half the price I paid 8 years ago, although it's a much later production model from its S/N since there's now a new "digital" PV1D with a remote control. No thank you, I want to set it up right & leave it alone! B&W published specs for PV1: Active closed-box sub-woofer; 2 x 200mm mica/aluminium cone long-throw drivers; -6dB at 18Hz &40/140Hz adjustable; +/- 3dB 21Hz -31/110Hz adjustable; 500w continuous; Input impedance 100kOhm (presumably speaker level input?); S/N >90dB; Active 2nd-order LPF, variable cut-off frequency; 20.5kg (heavy enough not to hop about!). I have some idea what most of the foregoing means, but what I like about my system are these characteristics: 1. It performs well on all the kinds of music I have, which is most 2. It works in my smallish & squarish concrete box of a room 3. It only requires to me get up to switch the amplifier on & off 4. It only has 2 knobs, one of which is bypassed completely (DAC) & the other one doesn't go round in the way you would expect 5. You can turn off all the displays, leaving only a small number of LED's to mask temporarily with insulating tape if I choose to listen to it in the dark - it then becomes very hard to identify where the speakers are, so that you can concentrate on the soundstage 6. It all fits into the corner of my room, making it visually unobtrusive 7. There are no visible wires 8. The triodes are in the "dead zone" a couple of feet behind & more or less midway between the speakers, eliminating any audible "microphony" at least until my ears begin to bleed at which point it's the least of my concerns 9. It is quite aesthetic & therefore partner-friendly 10. Now that I don't have a partner, it leaves me lots of room to spread car bits all over the floor Now how do you measure that? Dave :) ------------------------------------------------------------------------ Golden Earring's Profile: http://forums.slimdevices.com/member.php?userid=66646 View this thread: http://forums.slimdevices.com/showthread.php?t=106914
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