Chario Reference 1000 Tweeter Replacement

Abstract

These Chario “Reference 1000” bookshelf speakers are from around 2002 and are a great “reference” for the kind of garbage I’ll never buy again. And there’s probably been 1000 examples of that! They were expensive and replacement with anything half decent would be too, but since I wouldn’t be seen dead in a hi-fi store nowadays, a repair was in order after one of the original tweeters went inevitably open-circuit. The tweeters were very cheaply made Scan-Speak model D2905/9000 and were replaced by more modern R2604-833000 units which hopefully are not as dodgy. Extremely shoddy assembly of the speakers also became evident once the drivers were removed, so the repair became an major overhaul and correction of their errors. A bit like owning an Alfa Romeo I guess. You get what’s coming. The current offerings from the company are more sleek-looking furniture pieces, but don’t be fooled. I’d simply recommend that you steer clear.

They look identical to speakers they called “Hiper 1000” (yes – spelt that way), and others called “Premium 1000” look similar. The word “Reference” appears only on a barcode sticker at the back.

Background

I purchased these new while working in Hong Kong when I had no free time to build things myself. Apparently they were manufactured in some kind of sheltered workshop specialising in spaghetti electrics. Unreliable, non-soldered crimp connectors barely hanging from the driver terminals, wires flapping about against the port tubes to explain the lovely added vibrato, and binding posts expected to maintain electrical continuity with the crossover PCB via plain nuts tightened down onto soft MDF without so much as star washers! Typical audio industry garbage? I suspect so! “Reference” indeed. Bah! And it got a whole lot worse when I had to dig deeper. The crossover PCB was mounted on a soft pad that covered just part of it. A wood screw tightens a floating end of the PCB down to the rear baffle flexing the board against the pad. This causes a resistor wire to detach from its solder joint! Also, the binding post contact pads on the PCB distorted badly as the nuts were tightened. The whole PCB distorted around the posts as there were no washers to prevent their solder joints from pushing hard against the rear baffle. And there was an inexcusable flaw in the circuit that required deletion! Just a load of incompetence IMO!

Original tweeters

I found a data sheet for the tweeters dated 1989 so they were quite ancient even by 2002. Perhaps they were snapped up as NOS. I have no idea. Anyway, they were designed such that any movement of a solder pad formed integrally with the terminals such as by pushing a crimp lug over them as intended breaks a glue joint. Resultant free movement of the pad guaranteed breakage of the hair-thin multi-strand wires to the voice coil! Also where these wires connect to the enamelled voice coil there is no solder and glue covering the joint corrodes the connection leaving an open circuit. They measured pretty badly when they worked, but complete failure was just a matter of time.

A soft black foam gasket ring sat on top of the white plastic ring to sandwich the solder pads, but being soft, that’s to me either grossly incompetent engineering, or deliberate planned obsolescence. “Conveniently”, they sold replacement domes/voice coils, but if you could still get them (which you can’t) they’d be more expensive than a new tweeter. The tweeters have been thrown on the junk pile.

Woofers

The woofers appear to be Audax and thankfully they’re intact.

One might assume that the enclosure, port and crossover were tuned specifically to the woofer, and the baffle recesses are specific to their peculiar shape¹. So it’s a good thing they still worked. The port opens through the floor and reaches almost to the top:

  1. The peculiar shape actually serves a purpose in allowing the tweeter to be mounted closer to the woofer, but in the case of these speakers, I doubt that the crossover was designed to any kind of precise driver alignment.

It was too difficult to photograph the crossovers in situ (but I was forced to remove them later – see below), but they seem to comprise at lease a second order filter on the tweeter going by the coil and capacitor count nearby the tweeter wires.

The binding posts on the back pass through 6mm holes in the MDF and the crossover PCB. Electrical connection was solely via standard nuts mentioned above threaded onto each post. Those bore down on square brass pads on the PCB – just visible in a photo below.

Yes they were from the “bi-wiring” era. Is that still a stupid thing? Complete nonsense of course with passive crossovers, so the shorting bars have always remained in place.

I added stainless toothed washers and replaced the nuts with M6 Stainless Nylocs for reliability. Also cable-ties now secure the speaker wires to the ports to stop the unwanted “vibrato”.

Amplitude response of speaker with the original tweeter

Fortunately I measured the acoustic output of the speakers a year or so before the tweeter failure:

You won’t get that kind of raw honesty in a measurement from any of the audiophile magazine “reviews” nor from the driver manufacturer’s data sheets or anywhere else where they’re trying to sell you something!

The quasi-anechoic gated near-field measurement is as unsmoothed as I can make it and shows a pretty ragged tweeter response (±4.5dB). The woofer seems quite reasonable at least as far as the measurement method allows. Reading through it suggests a crossover frequency of around 2 to 2.5kHz. I found references suggesting anywhere from 1450Hz to 2.5kHz on the ‘net for other Chario models with the same drivers, but the precise number is of no consequence. The measurement suggests that the tweeter output was 2 or 3 dB down and that there were obvious severe tweeter resonances. These had previously been addressed to some extent with a multitude of JRMC PEQ filters generated in REW, but the overall drop-off relative to the woofer SPL meant that was pretty much a lost cause as high Q “boost” filters are banned in my book.

Choice of new tweeters

I didn’t care about a perfect match for the originals as they were clearly nothing to write home about. There is something that looks identical called a D2905/930000 (and other variants of the same driver) that would drop straight in, but nothing I could find had comparable T/S parameters and they all probably have the same terrible internal construction as my originals given that they look identical. And they’re unjustifiably expensive.

The nominal impedance needed to match, and the quoted efficiency needed to be 2 or 3dB higher. Also since I had no schematic for the crossover network to confirm a crossover point (nor the motivation to measure it electrically), I needed a tweeter with a low resonant frequency and good LF extension for an adequate safety margin given I had no intention of changing the crossovers. At first impression, getting them out looked like risking cracking the PCBs anyway, since they seemed to have some kind of double-sided adhesive tape or other adhesive behind them.  This turned out to be a false assumption on my part (see below). And of course the faceplate had to be the same diameter to fit the recess. Anyway it all lead to the Danish made R2604-833000 ring radiator tweeter. It’s 2dB more efficient (92 vs. 90) which is ideal and if its output is too high a shelving filter could be keyed into JRMC easily enough. They’re probably built just as crap-like as the originals, but these are hardly high fidelity speakers warranting an OCD spending frenzy. And indeed upon arrival there was immediate confirmation in a faceplates made of plastic. Euch!

  • Aside: There are Vifa and Peerless versions of this tweeter with different model numbers. They look identical from the front, but are made in China and don’t have the double magnet. I’ve placed a personal ban on Chinese products where alternatives are available – even if more expensive. China is an all too powerful international bully run by low-witted descendants of Mao’s generals. They need to be pulled inline with international values and smarten themselves up before I buy anything Chinese with a clear conscience.

Installing the new tweeters

Of course nothing is meant to be easy, so a “simple” tweeter replacement soon becomes a major overhaul!

5 screw holes instead of 4, and connection terminals that protrude beyond the baffle cut-out aperture requiring filing of recesses in the MDF.

Another pet peeve of mine is the tight arse or bone lazy use of wood screws to mount speaker drivers into MDF. It’s pathetic! Wood screws are for wood! Tee-nuts should always be installed in the back of an MDF baffle before assembling the enclosure and machine screws must be used. The way I usually do it is shown on the right.

Woofer screw holes drilled out to 6mm ∅ for M5 bolts and tee-nuts. New 5mm ∅ holes for the tweeter’s M4 bolts and tee-nuts. The old holes were filled with PVA and cosmic dust then sanded smooth:

The crappy white foam padding was removed in favour of grey foam egg crate cut to the same shape plus a small amount of wool.

Speaker wires got new crimp connectors both crimped and soldered, then covered in heat shrink tubing:

A borrowed clamp to press in the tee-nuts:

Plywood block with cardboard padding to protect the veneer.

Beeswax applied to veneer.

Almost forgot the gasket, but tweeter installed:

Faceplate about 1mm thicker than the old one, but that’s just too bad. Why do these driver manufacturers insist on inconsistency? 4 holes, 6 holes and even 5 holes and plates of different thicknesses! What a PITA! At least they kept the diameter the same. There’s the only praise they get.

All together again:

With MACHINE SCREWS and TEE-NUTS like an engineer would do it!

Back where they belong

Attached to a Pioneer A-30 integrated amp set in Direct mode (as a power amp) with an old Sony Vaio laptop and a Focusrite Solo USB audio interface (that equals ANY highfalutin audiophile DAC‘s sound and cost only AUD150):

All the old tweeter resonance-correction filters in JRiver’s DSP Studio were deleted – just leaving a 17Hz high pass and a 50kHz low pass filter in place (that’s because years ago I foolishly converted a bunch of SACDs to 176.4kHz FLAC not realising they contain a mess of noise over 50kHz).

Do they work?

Of course they do! As a super-precaution I did check the amplifier just in case it did something to the original tweeter which it didn’t. DC offset a mere 5mV and a clean (non-oscillating) signal into a dummy load seen on my oscilloscope. And they sound fine.

Measurement

This is on-axis and gated at about 600mm. Can’t be bothered doing polar measurements.

  • A note about the slight upward rise from 10kHz to 20kHz is under Crossover Topology below.

SPL numbers are uncalibrated, but the scale is the same as for the old measurement. Looks better at ±2dB and the additional 2dB efficiency certainly came in handy, but to be fair, the original measurement (scroll up) had the grille cloth in place and this one didn’t. Same Earthworks calibrated mic used both times.

Simple PEQ applied in JRMC flattens it to:

Addendum

The goodness was short-lived, so the story isn’t over yet!

The new tweeter in one speaker started to make intermittent crackling sounds while music was playing. WTF! Swapping the speakers left to right relinquished the power amp, PC and DAC from blame. The crackle followed the speaker. Swapping the tweeters from the left to right enclosures showed it wasn’t a tweeter either.  The crackle stayed with the right enclosure. Must be something between the binding posts and the driver. The crossover has to come out after all.

And there it is:

It wasn’t double sided tape after all. Just a round foam pad that’d been there for 20 years:

What struck me immediately was the terribly tarnished and bent nature of the brass pads where the binding posts bolts bear down. More hopeless engineering is evident where there are two solder joints per pad. When the bolts are tightened down, the solder joints press hard against the rear baffle. Here’s the evidence:

Two dimples in the internal veneer alongside each binding post. Distortion of the PCB and the brass pads is the inevitable result! IDIOTS! Sorry Chario, but this just shoddy garbage IMO.

  • Aside: This reminds me of some “typical” audiophile bull dust marketing by a speaker manufactures called “Magico” or something. It went on about the “sonic glory” (or whatever) of their enclosures because they went to the extra trouble of veneering both sides of each panel. Well guess what? That’s how it comes from the suppliers! If not veneered on both sides the MDF stock would all warp!

And the further I looked, the worse it got! Who does this kind of thing?

The nameplate need not be metallic! Why place a potential shorting bar right across the customer’s amplifier? The mm clearance might be OK elsewhere, but they’re only anchored into soft MDF!  I think the answer is to add a little PVA when screwing the posts back in – just to firm up the MDF a bit.

OK

Brass pads given the Scotchbrite treatment and a coating of solder:

Washers slightly thicker than the solder joints to stop the PCB bending:

Was going to epoxy them down, but a better idea was to place them over the binding posts before reinstalling the board.

Many solder joints re-flowed and some hot melt glue added to stop things rattling:

I’m not on the recapping bandwagon and they all looked fine, so none needed replacing, but see that wirewound resistor above with red lettering. Well a wood screw goes through that hole in front of it to secure that end of the board to the rear panel. As the screw is tightened, the board bends because the rubber pad under the board falls short and the solder joint to the resistor lead breaks! The resistor was hanging loose in a dry joint. Absolute ignorance or a couldn’t care less attitude on the part of the manufacturer IMO.

The answer was a proper sized neoprene pad and the screw now goes through it!

All fixed!

Crossover topology

I traced out the crossover network and the tweeter section is a simple second order high pass with one exception. There’s a leading series resistor to attenuate output, but it has a 1μF MKP capacitor across it. As this looked odd, I modelled it in 5Spice.

I guessed a value for the inductor and simply used a 4Ω resistor for the tweeter to get an idea. And it simulates like this:

The 1μF capacitor causes the response to rise gently above around 10kHz. It’s up 1.5dB by 20kHz (and the full 8dB by 300kHz). Deleting the capacitor leaves the response flat across 20kHz at roughly -8dB. The capacitor would have been to counteract the falling response of the original tweeter per the Scan-Speak data sheet:

My own measurement actually confirms this with a slight rise for the new tweeter which has a flatter natural response, so that capacitor was later lifted.

The bass section is a 2nd order low pass with two strange sections. Firstly, a parallel RLC network provides around a 3dB boost across about 400Hz which doesn’t seem to show up in my microphone measurements so is probably warranted, but secondly a very strange set of components is placed across the input terminals:

Again I’ve used a simple resistor (R3) for the woofer and the inductor values are guessed, so the actual shape of the curve below is likely inaccurate, but C3 (actually two caps of 220μF and 100μF respectively) and L4 are stupid and don’t do anything useful! R6 represents the measured resistance of the coil L4. If say 3Ω input impedance is added (as though using a valve amp) bass attenuation of 3 to 4dB is the result.

With a low impedance input per a modern transistor amplifier, the circuit simulates as follows:

Amplitude in red. Phase in blue.

Remove C3, L4 and R6 from the simulator and the output is identical, but with the benefit of much lower demands on the power amplifier.

Attach the speakers to a valve amp and you get something like this:

As noted above, the value for L4 is a guess. It could be a lot lower, but the series resistance overrides and a lower inductance value leaves the simulation basically unchanged.

A woofer in a ported enclosure has two impedance peaks. Maybe Chario’s “engineers” were attempting to counter those in one hit so that the speakers didn’t sound boomy when used with valve amplifiers. But it’s a band-aid on a hernia because the series resistance of the coil (7.8Ω) dampens the Q and merely provides an overall bass reduction as shown. For example, had the series resistance of the coil been just say 2Ω, the resonant dip would appear like this:

But it isn’t, and although it might disguise (but not target) one failing of any valve amplifier, it is obviously a completely pointless circuit for a solid state amp and is lame as it presents a low impedance load for nothing, so this section was disabled by lifting a couple more capacitors.

  • Incidentally for benefit of OCD “re-cappers”, all 6 capacitors removed from these speakers measured on-spec for both capacitance and ESR!

Regular readers of my blog (if there are any) would know of my contempt for valve amplifiers and those who claim they’re hi-fi. They are not! This just backs up my stance. If you think your precious valve amps sound different to solid state amps, it’s most likely that you have incompetent passively crossed speakers behaving badly with them and you just happen to enjoy the sound of herniated audio! 😛

More to come if I can be bothered (which I probably can’t) …

 

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