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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd October 2012, 04:34 PM   #8191
Pano is offline Pano  United States
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Thanks for the advice Lynn, I really appreciate it.

I have been looking seriously at Stanton because it seems a good fit for the old tonearm and the Stantons sound good. I was just afraid it might be too high compliance. I'll shop around for a new or vintage Stanton cart. The SPU is a great cart, as are some of the Denon MC, but I doubt I'll ever go that way.
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Old 3rd October 2012, 07:39 PM   #8192
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I used a Stanton 681A (spherical) in my college system, following the recommendation of the J. Gordon Holt "Stereophile" (back in 1971 when it was a real magazine). Fantastic sound on the Dual 1229 setup, way better than most crappy-sounding elliptical cartridges of the day. Tracks at 2~3 grams all day long, with far less record wear than all but the finest ellipticals. (Unless an elliptical has a near-perfect diamond and is exactly aligned in the groove - azimuth in particular - they have very high record wear. Pros used sphericals because they are much gentler on the records, since the contact area is much larger.)

The 500A is the ultra-tough radio station cartridge. Remember what FM sounded like in the early Seventies? That's what they used - not the delicate and finicky Shures, which would collapse the cantilever if you tried to back-cue them.

The radio-station Stantons have quite low compliance - again, it's because they are tough cartridges designed for back-cuing. The 681A is a more hifi cartridge, but I think it'll work in the Grado just fine. Whatever you do, avoid Shures, which are more delicate, have much longer cantilevers, and are quite sensitive to capacitive loading. Speaking of which, replace the badly corroded tonearm wires with modern Cardas or similar. You don't want the dominant capacitive term in the cart loading to be awful tonearm wires.

Last edited by Lynn Olson; 3rd October 2012 at 07:46 PM.
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Old 3rd October 2012, 07:52 PM   #8193
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Funny, the DJs also use conical tips to prevent record "burn". I've been shopping for a 680 or 681 but want to make sure it has the conical (spherical) stylus.

Pickering any good? They see very similar to Stanton.
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Old 3rd October 2012, 08:56 PM   #8194
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You could of course spend insane amounts and purchase an NOS Decca London Mk 5, not for export model, the grey shell, not the blue.

I always thought the Stanton 680 & 681 sounded better than any Pickering I managed to hear. You might also think on contacting Grado. John Grado is a very communicative fellow and they may have a suitable cartridge. Will certainly be more lush sounding than a Stanton, which might or might not suit your system.
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Old 3rd October 2012, 10:31 PM   #8195
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As I'm a lush myself, it ought to be a good match.
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Old 4th October 2012, 07:49 AM   #8196
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One thing to watch out for on these old-school moving-iron and moving-magnet cartridges is the requirement for a fair amount of load capacitance, sometimes as much as 200~300 pF.

As you might imagine, the heavy self-inductance and heavy external capacitance form an electrical 2nd-order lowpass filter. Why is this necessary for flat response? Because the mechanical system is peaked in the 18~22 kHz range ... the tip mass/vinyl compliance peak.

Moving-coil carts by contrast are mechanically flat, or have much smaller peaks. They are pretty much insensitive to cable capacitance because the self-inductance is orders of magnitude lower, as well as a much lower source impedance.

Moving-iron and moving-irons operate one way, and moving-coils another. Any of them can have low tip mass, which is essential for low record wear and freedom from end-of-side distortion. Low tip mass is completely independent of compliance; there are high-compliance carts with high tip mass, low-compliance carts with low tip mass, and vice versa. Unfortunately, tip mass is not usually specified accurately, and the few times it does appears in specs, it is merely the mass of the diamond, not the moving system.

Short fat cantilevers are desirable, skinny long ones are not. Cantilever flex is responsible for weird phase rotations at high frequencies, as well as aggravating the mechanical peak at HF. This HF peak is responsible for much of what we hear as mistracking. (Slewing in the preamp also stretches out mistracking events, making them much more audible. Fast preamps make the record sound quieter and sweeter in the HF region; I confirmed this for myself back in the Audionics days.)

So ... given that the cartridge may require a substantial amount of load capacitance for flat response, do it a favor and use proper caps in the preamp, like silver-mica's or air-trimmer types. Keep the cable capacitance as low as possible, since even exotic cables have pretty low-quality capacitance compared to a quality capacitor.

Since the load caps are an essential part of a 2nd-order lowpass filter that keeps the HF response flat, any variation in the cap detunes the filter and degrades the overall HF sonics. Thus, the suggestion to use a top-quality cap and solder it into the preamp at the RCA jacks, and use the lowest-capacitance and highest-quality tonearm wires possible. Any corrosion AT ALL in the tonearm wires will have a very destructive effect on the sonics, since this is a dry circuit and operates at very low current levels.

Last edited by Lynn Olson; 4th October 2012 at 08:00 AM.
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Old 4th October 2012, 08:21 AM   #8197
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For late arrivals bored by all this phonograph talk; the LTO Apollo (or Athena) has the following architecture:

The 15" bass driver is an Altec or current-production Great Plains Audio Alnico-magnet 416B, 16-ohm version, in a 4.5 to 5-cubic foot cabinet with a long thin vent along the floor, like a Fonken or Onken turned on its side. The vent is lined with wool felt to increase resistance and suppress internal organ-pipe modes. The best subjective tuning is a box frequency between 30 and 34 Hz.

The HF driver is a Radian 745Neo or Altec/GPA 288 with Alnico magnet and standard 288 aluminum diaphragm with 16-ohm voice coil. I have no preference so far; both are very very good, but the Radian might measure just a little flatter, while the Alnico-magnet 288 might have just slightly better tonality. Prices for both drivers are similar.

The horn is an Azurahorn AH425, which is a custom-designed (bespoke) LeCleac'h with a T ratio of 0.707 and matched for a compression driver with an exit angle of 8 degrees. The AH425 diameter is 16.5" and works best in free-air mounting with about 2 inches of separation from the top of the bass cabinet.

The preferred lowpass crossover for the bass unit is 3rd-order Bessel at 700 Hz, with a Zobel compensator for the woofer inductor. I use a nominal value of 12 ohms as the design-center for the 700 Hz lowpass filter.

The preferred highpass crossover for the HF driver is a 700 Hz 4th-order that is transitional between Bessel and Linkwitz-Riley 4th-order. This is based on subjective auditioning with the Radian 745Neo and might be a little different for the Altec/GPA 288. The attenuation is best accomplished with an autoformer or transformer with selectable taps at -15, -14, -13, and -12 dB, and a 16-ohm shunt resistor between the highpass filter and the autoformer/transformer. The design center for the 700 Hz highpass filter is 15 to 16 ohms (the shunt resistor in parallel with the input Z of the transformer sets this value).

The direct-arrival response of the HF system is very flat and does not require in-band equalization; the same applies for the 416B woofer, which is also quite flat in the working range. The free-air mounting of the AH425 allows precise time-alignment; in practice and by measurement, the lip of the AH425 is about 1/2" in front of the bass cabinet.

The overall system efficiency is around 99 dB/meter/2.83Vrms, and is set by the woofer. The GPA 416B Alnico 16-ohm driver appears to be 1 to 2 dB more efficient than the official Altec specs for the traditional 416, which I see as a plus for the overall design.

This system exists in prototype form and I've already done some subjective optimizing as well as measuring the frequency and time responses. Subjectively, it sounds like a big Ariel, with a lot of Altec tonal vividness to the overall sound.

A future variant of this system will have two 15" woofers, probably an Alnico 416B and possibly an Alnico 515 as a companion, with slightly different crossovers for each. That would raise efficiency by 3 dB or more, and increase headroom by 6 dB. Cabinet volume would increase to 8 to 10 cubic feet.

Last edited by Lynn Olson; 4th October 2012 at 08:39 AM.
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Old 4th October 2012, 09:11 AM   #8198
DeonC is offline DeonC  South Africa
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Hi Lynn

The LTO Apollo sounds yummy. It's just a pity it won't fit in my room.

Just a quick digression back to vinyl- what is your opinion on the London Decca Gold and, Super Gold, and the rest of London family of cartridges? They have a very direct input (the cantilever is long, but the coils sit above the tip. The following description comes from the Divine Audio page:

Other cartridges (both moving coil and moving magnet) have styli mounted on the long end of a thin tube (cantilever) which works like a lopsided "see-saw." The short end of the cantilever attaches to either a coil of wire or a magnet. At the fulcrum point, a flexible "rubbery" sleeve functions as a pivot, allowing the stylus/cantilever assembly to respond to the "wiggles" in the LP groove. Because the front section of the cantilever, which holds the stylus, is much longer than the rear section that is attached to the coil or magnet, a large movement of the stylus is transformed to a smaller movement at the coil or magnet, possibly causing cantilever-design cartridges to sound dynamically compressed and lacking in transient attack. London Decca's engineers advise that this problem with dynamics and transients is compounded by the cantilever's "rubbery" fulcrum point which tends to absorb a significant amount of the stylus-generated motion before it can reach the coil/magnet electrical generator assembly. Also, a smearing of the sound is said to occur, which many folks refer to as "cantilever haze."

The Super Gold has no long cantilever and no "rubbery" fulcrum point to absorb, dissipate and smear the vital musical energy. Instead, the stylus is attached directly to a magnetically active metal support just a few microns thick (armature) which passes through the center of the main generating coil positioned only about 1 millimeter above the stylus! The stylus motion is not inverted or "transformed" to a smaller value, as in long cantilever designs. Flowing from this immediate positive-direct scanning of the groove is a breathtaking, lifelike quality. The listener tends to feel that the performing artists are actually in the same room, with a startling, palpable presence.


Your opinion will be greatly valued.

Thanks,
Deon
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Old 4th October 2012, 09:23 AM   #8199
DeonC is offline DeonC  South Africa
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Hi Lynn

Quote:
Originally Posted by Lynn Olson View Post
The vent is lined with wool felt to increase resistance and suppress internal organ-pipe modes.
Would a large passive radiator on the back of the box not possibly be an option? I'm thinking an 18'' PR should be ok, or maybe two 15'' units? The only problem is that most PRs I know about are very low Fs, meant to tune a small box low, not a large one like the LTO Apollo. Therefore a DIY or custom-made solution might be needed (or a mod to an existing unit). Will this work?

Deon
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Old 4th October 2012, 02:55 PM   #8200
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In recent cartridge news, I got a used Stanton 681 with a NIB conical stylus. I'll let you know how it goes once I have it up and running.

Tone arm wire is a bit of a problem, as there just isn't much room. Originally the arm had very small magnet wire in a braided shield. With age it had become brittle, corroded and the varnish was flaking off. At the moment I'm running two tiny shielded Mogami cables made for lavalier mics. It will be replaced with an even smaller Mogami 4 conductor shielded cable. That will allow me to run the cart balanced, if I choose to - maybe via a pair of BudP's microphone transformers. The arm cable will hit a 4 pin XLR that can break out to 2 RCA or go balanced to a balanced phono preamp. I will try to figure out the capacitance of the cabling.

Sorry for the off topic, this really should be in another thread.
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