Out with the old, in with the new

My first amplifier I bought in 1979, a Technics SUV-6. I'd saved up for a set of B&W DM7s eventually decided to get a second hand pair of DM6s. So then I needed an amp. Mr Robinson, the Bowers & Wilkins salesman (the retail shop was I think already a separate business from the speaker division by then) suggested the SUV-6 and so that's how I ended up with it - along with a Technics SL150 turntable and an SME 3009 Series II tonearm. The only other change in my setup until this week was a Linn (ex demo from Grahams HiFi in Camden) with an Ittok which replaced the SL150+SME in 1987.  

That is until last week, when my trusty SUV-6 finally gave up the ghost. It's fixable I think but the input switch has been getting more and more temperamental for several years and last week it decided to stop working altogether.

Knowing I wasn't going to have time to fix it for a while, I decided to take the plunge and buy a new amp.  I did some estimates and figured for the GBP 200 I paid in 1979, with inflation and the exchange rate, I should be spending between $1,200 and $1,600.

So instead I looked for the cheapest reasonably well reviewed integrated solid state amp I could find.  And so plumped for this (bottom of the pile in the pic), the Yamaha A-S500, a B-stock factory reconditioned unit for $319. And I was in for a bit of a surprise.

I had always rather poo-poohed the notion that amps could really do much to alter the sound. After all it's simple a case of taking a signal and making it louder. The scope for 'error' was far lower than in the engineering of a turntable or a cartridge. And speakers, clearly have a huge impact.

And was I wrong!  The A-S500 is rated as 85W into 4 ohms, compared to SUV-6's 70W, but it's much wimpier. But that's only the beginning. It's completely lacking in bass compared to the SUV-6. On my Phase IV's there's almost nothing there below about 150Hz. The 31Hz open B notes in Becker's "11 Track of Whack"? The bass player appears to have taken the day off.

But suddenly the DM6s sound a bit more like a modern speaker - brighter and without the smiley face response curve. I haven't done any tests yet, but I suspect the new amp has flattened out the DM6 curve.

And that's is a bit of a problem since it suggest that the SUV-6 was as much a part of the smiley face as the speakers - and I used it do calibrate the Phase IVs and build the crossovers. Ugh!

On the plus side, I can always go back to individual driver testing and redesign the  crossovers; which I will undoubtedly have to do if I want to continue to use them with the A-S500. But if I repair the SUV-6 then I'll need the current crossovers. Not to mention that I am still thinking of getting a cheap tube amp at some point, and it's not clear how that will change the picture. And of course I've got the Phase Vs on the drawing board which I'll start building when...

I may have to build external crossovers that are matched to a speaker amplifier pairing.

Damn! Lots of work, lots of variables, not enough time (or money).

As low as it gets

The last day or two I've been thinking about the Phase Vs  at the same time as  I was listening to Donald Fagan's LP, "Morph the Cat", and I noticed that some of the base lines were fairly deep.

How deep?

Well, the plot on the left, generated in Audacity, shows that on track #4, "Bright Nightgown", the fundamental of the bass note is at about 34Hz. The open E on a bass guitar is 41Hz, and the open B on a 5 string comes in a 31Hz. For what it's worth, 34.65Hz is a C#. 

Since the Phase IV Mk2s don't really render much below about 60Hz, the reproduction of this note depends almost exclusively on the harmonics (of which fortunately there are several). This low note in "Bright Nightgown" is almost an octave (10 semitones) below what the Phase IV Mk2s can reproduce! 

And Walter Becker's "Down In The Bottom" from "11 Tracks of Whack" (right) does seem to have an open B - at 31Hz!

All of which has got me wondering how different would the sound be with drivers that could really generate those low frequencies.

I haven't tested the AC250F1s and really can't do a proper job until the enclosures are built. However, if the published specs are to be believed (and there have been some comments on the web to suggest they are not as reliable as one might hope) the 250F1's should cope fairly well down to 30Hz.

Which turns out to be just as well. We shall see...

Why Phase IV?

Just before going to college (1979) Graham, who worked at B&W, sold me a couple of 801 bass drivers. Phase I used these (they were really wonderful units) with Kef B110bs for the mid range and DM7 stand alone tweeters. The crossovers were stock 3-way units that crossed at 200 and 4k (at least as far as I can recall). I have no pictures of the Phase Is.

Phase II was a rebuild of the Phase I cabinet but used the same drivers and crossover. The result was fairly unsuccessful since I limited the bass response by making the air volume too small. Again, no pics.

Phase III was the intervening 30 years.

Phase IV was my attempt to build speakers using much cheaper drivers (my father, bless him, threw out the 801 drivers when he was cleaning out his attic in 1990). "Phase IV" (1974) was also a fairly memorable science fiction film for which "Silent Running" (1972), a slightly more memorable (also science fiction) film, was the supporting B-feature when I saw it (probably in 1976).

That there is a Mk1 and a Mk2 was an accident. I hadn't planned to build a Mk2, but as I noted earlier in the blog, it was a spur of the moment thing.

Aren't you sorry you asked?

Sparsness revealed

Listening to Pat Metheny "Bright Size Life" I realize for the first time how sparsely 'populated' it is. Having never looked closely at the sleeve (I listened to it mostly - but not exclusively - in the car for some reason) I see now that it's a trio! Of course having Jaco Pastorius on bass helps give the illusion of many more people, but even so...   

So why does this matter? Well, that I noticed I think suggests that the MkIIs are reveling much more detail than the DM6s. When you're listening for differences it's not hard to imagine ones that sometimes aren't really there. But this time I wasn't; I just put on the disk for something to listen to and the instrument separation leapt off the page. They may not be perfect but they're good enough to keep.

One month on..

A month of living with the Mk IIs and I'm not disappointed. They're not as clear as perhaps they could be, and spatial separation doesn't leap of the page, but they do reveal more detail than the DM6s. This may be a function of reflection in a small room. Of course, you might rightly suggest that a pair of 40 year old loudspeakers is hardly the best benchmark. Not only is physical deterioration potentially a problem, but technology and design have moved on since the 1970s.

That being said, it's all I've got (other than a pair of Kef bookshelf speakers I bought in 1990 - which I don't know I can find anyway). So I'm going to use the staircase approach. The Mk IIs are better than the B&W. The Phase V should, if I get things right, be better than the Mk IIs.

Of course, I'm not entirely sure what happens when the next design is worse than it's predecessor. However, using better drivers (I have already bought the AC 250F1s for the woofers) in the Phase V should reduce the likelihood of that happening.    

Phase IV complete

Sunday evening. The painting is finished, the cabinets polished. All that remains is mounting the drivers: Which was going fine until the last unit, which was taken from the original Mk 1 prototype (left rear, white cab). These drivers were 6 months or so older than the ones in the Mk 2s (red) and turns out weren't exactly the same size. They were significantly (about 1 mm) larger in diameter, which meant the openings in the baffle had to be re-routed. Without anything in the middle to locate the router this is a bit of a problem. Silver Flute has a long way to go in terms of manufacturing consistency.

However, 6am Monday morning, before it got too hot, I cut a plug to go into the baffle opening and re-routed the hole. By 8:30 they were finally finished.

Both were tested. The graph below shows the two Phase IV units (one black, one red) and one of my old DM6s (blue). I was (am) concerned about one of the Phase IVs having a 9dB drop around 162 Hz but then THe DM6 has a drop of 14dB @ 248 so the problem isn't quite as horrible as I first thought. Still it's not great; and worse yet I don't know what's causing it. I thought for a moment it was a polarity problem between the woofers and the mid-range but reversing the woofers polarity made things worse so that wasn't it. Most likely it's a feature of the cabinet which is a bit of a shame since at this stage I don't really know what I can do.

However they sound very different in the mid and upper mids from the B&Ws. I think they resolve a lot more detail but I'm so accustomed to the B&W sound - rather warm and soft like an old pillow - that the Phase IVs will take a little getting used to.

Finally, I'd like to thank Mark Zachmann for creating Speaker Workshop which has been an invaluable tool.

This will be the last post for a while. I have a three more projects lined up (replacing the B&W crossovers, building a smaller version of the Phase IV with only one 4ohm woofer, the then the Phase Vs for which the design work is done). But for the moment I'm going to spend some time getting used to the Phase IV Mk2s. 

Progress update

The (new) second cabinet is now built and waiting the final coat of paint. The first crossover is built and mounted in the first cabinet, which is now in use. The second should be up and running in two weeks.  One mildly interesting anecdote: while I had the speaker on it's back (the crossover is mounted inside the base), one of our cats decided to sit on the tweeter. Light for a cat she may be, but 8lbs crushes a soft dome tweeter. Somewhat mortified, I removed the driver, and then the dome and voice coil from the magnet. From the back I gently pushed the dome back into shape and smoothed out the wrinkles (!) with my thumbnail. (High tech stuff, speaker building). Without much in the way of expectation I remounted the driver and ran some tests. I then ran the same test with an undamaged tweeter of the same make and model. Result? There is really no noticeable difference in the frequency response. So it turns out that you can crush a tweeter's dome and as long as it's dome shaped it seems not to matter.