JBL L40, Carver Magnetic Field Amplieir PM-15

[ff1d1l]

Brought a haul of quality spacejunk back to the lair today.

A rather world-weary pair of JBL L40s and a Carver Magnetic Amplifier (Low Feedback High Headroom) PM-15.

The JBLs, after a little laying on of hands and averting of eyes from foam surrounds about to go feral, sound very good. Definitely worth re foaming.

The Carver apart from some very low level just up from the noisefloor ticking, which seems to be an electrical artifact of the same mechanical noise produced by the fan, drives the JBLs with aplomb, and together they make for a very listenable sound. Looking on the net it appears that despite only being the size and weight of a normal rackmounted amp, this has a huge output of 450w into 8ohms, 600w into 4ohms and was a quality item designed for studio/high end PA use. I'd characterise its sound as B......I.....G, dynamic, detailed and smooth.

Anyone with experience of these, particularly the Carver? I'm quite smitten...

Between these and the Urei 809s I picked up on friday it's turned into a bit of a week.

[walpurgis]

The JBL L40 is a superb speaker. You wouldn't expect a 10" woofer and a 1" dome tweeter to work that well together, but they do! They are well worth sorting and using. You'll find them outstanding. :)

[ff1d1l]

The JBL L40 is a superb speaker. You wouldn't expect a 10" woofer and a 1" dome tweeter to work that well together, but they do! They are well worth sorting and using. You'll find them outstanding. :)

Yes, looking on the net the tweeter is run from very low down, much lower than most designs. As acquired, one tweeter was pushed in, but the tweeters are quite dismantle-able so I was able to wholly successfully gently push and re-form the dome back out from behind. I also took the bass units, 127As out and thought them the least impressive JBL woofers I'd seen! Small magnet and comparatively lightweight - nice basket though. Nevertheless they do, in conjunction with the tweeters as you say, produce an excellent sound. I tried them up against the Urei 811s and they didn't disgrace themselves, far from it.

A fair amount of cabinet talk when playing bassy material. Even so, and with the lousy surrounds, bass definition and detail are well above average. A pair of 4410s I have seriously benefited from internal reinforcement of baffle and cabinet walls and hard soldering internal connections - I might do the same to these, post re foam.

No one is admitting to having one of these Carver Magnetic Field Amplifiers then?!!!
Looking on the bay they don't come up often, but don't make huge money when they do either. Something of a sleeper, then, as the sound is pretty impressive...

[walpurgis]

I do remember the Carver amp, just not tried one. I believe they were a respected design.

[struth]

Good amps the carvers. used to suffer from fan problems etc but well made. typical us build but possibly a bit ott for a home stereo

[ff1d1l]

a bit ott for a home stereo
???!!!:eyebrows:

[Audioflyer]

If my memory serves me right.
The JBL 127A woofer uses an Alnico magnet and the tweeter was made by Audax to JBL specification with a low cross-over point.

[Spectral Morn]

I vaguely remember the Carver pm15 but not well enough to say much more than that. Bob Carver was better known for his valve amplifier designs and panel speakers - recently gone back in to doing valve amps after he moved on from Sunfire - and if I recall right the solidstate gear was just away of having bread and butter kit in the range rather than just the Silver Sevens and Amazing speakers.

http://img811.imageshack.us/img811/8775/97665291.jpg

http://img.canuckaudiomart.com/uploads/large/10231-carver_amazing_loudspeakers_silver_edition.jpg



Regards Neil

[ff1d1l]

I vaguely remember the Carver pm15 but not well enough to say much more than that. Bob Carver was better known for his valve amplifier designs and panel speakers - recently gone back in to doing valve amps after he moved on from Sunfire - and if I recall right the solidstate gear was just away of having bread and butter kit in the range rather than just the Silver Sevens and Amazing speakers.

http://img811.imageshack.us/img811/8775/97665291.jpg



http://img.canuckaudiomart.com/uploads/large/10231-carver_amazing_loudspeakers_silver_edition.jpg



Regards Neil

From Wikipedia

Carver caused a stir in the industry in the mid-1980s when he challenged two high-end audio magazines to give him any audio amplifier at any price, and he’d duplicate its sound in one of his lower cost (and usually much more powerful) designs. Two magazines accepted the challenge.

First, The Audio Critic chose a Mark Levinson ML-2 which Bob acoustically copied (transfer function duplication) and sold as his M1.5t amplifier (the “t” stood for transfer function modified).

In 1985, Stereophile magazine challenged Bob to copy a Conrad-Johnson Premier Five (the make and model was not named then, but revealed later) amplifier at their offices in New Mexico within 48 hours. The Conrad Johnson amplifier was one of the most highly regarded amplifiers of its day, costing in excess of $12,000.

Of note that in both cases, the challenging amplifier could only be treated as a “black box” and could not even have its lid removed. Nevertheless, Carver, using null difference testing, (null difference testing consists of driving two different amplifiers with identical signal sources and exact levels, but out of phase by exactly 180 degrees. If the amplifiers were 100% identical, no sound would be heard. If sound was heard, the audio amps had different properties). Bob Carver used "distortion pots" to introduce amplifier characteristics, fine-tuned to null-out any sound differences. His "motel-room" modified amplifier sound was so similar, Stereophile Magazine editors could not tell the difference between his amplifier and one costing more than $10,000. This amplifier was marketed as the M1.0t for about $400.00. Bob Carver may have single-handedly debunked any number of theories about sound quality by using physics, blind and double-blind testing and unbiased measurements, such as "Gold-plated" speaker wires sound better than copper wires, etc.) Carver successfully copied the sound of the target amplifier and won the challenge. The Stereophile employees failed to pass a single blind test with their own equipment in their own listening room. He marketed “t” versions of his amplifiers incorporating the sound of the Mark Levinson and Conrad Johnson designs which caused him some criticism by those who failed to understand the true nature of the challenge — that it was possible to duplicate an audio amplifier's sound in two completely dissimilar designs. In light of this criticism, Carver went on to design the Silver Seven, the most expensive and esoteric conventional amplifier up to that time and duplicated its sound in his M 4.0t and later models which sold for some 1/40th the price (around $600–$1500).

[Macca]

I read somewhere (might have been here years ago) that although the Carver amps could not be distiguished from the originals that didn't last forever since part of the way he did it meant that they were not stable. So the ones that were marketed to the public were not exactly the same as those he made for the test. But I don't know if that is true or not.

[Audio Advent]

There's a similar amp on ebay (http://www.ebay.co.uk/itm/CARVER-PM-1200-POWER-AMPLIFIER-PROFESSIONAL-MAGNETIC-FIELD-450WPC-8Ohms-GWO-/121621231965) which gives links to some info, HERE (http://www.hifiengine.com/manual_library/carver/pm-15.shtml) and HERE (http://www.pauladamy.com/PDFs/pm-1200_manual.pdf) The latter is the manual for the PM-1200 like the one for sale but they look similar. The first link of those last two also has a link to the manual of the PM-15 but I think you have to register with the forum first.

[ff1d1l]

There's a similar amp on ebay (http://www.ebay.co.uk/itm/CARVER-PM-1200-POWER-AMPLIFIER-PROFESSIONAL-MAGNETIC-FIELD-450WPC-8Ohms-GWO-/121621231965) which gives links to some info, HERE (http://www.hifiengine.com/manual_library/carver/pm-15.shtml) and HERE (http://www.pauladamy.com/PDFs/pm-1200_manual.pdf) The latter is the manual for the PM-1200 like the one for sale but they look similar. The first link of those last two also has a link to the manual of the PM-15 but I think you have to register with the forum first.
Thanks....very useful info. Wondered what some of those wierd link things on the back were. And now know it should have a dust filter over the fan intake...

[User211]

I didn't like The Amazing speaker much. Whilst I do like his reaction to the Apogee Scintilla, declaring it the finest speaker he had heard, I thought The Amazing to be ripping of Apogee aesthetics without the benefit of the planar magnetic driver that made/makes their sound so unique.

Some nice KT88 amps from Bob with stupidly high power ratings, claimed to be Scintilla worthy. Would love to hear a pair one day, driving said speaker. It will never happen I suspect.

[ff1d1l]

Well, some months down the line my Carver returns from my friend who seems to have failed to fix it. The issues are a low level ticking sound through the output, and fans which try to turn, and sometimes even manage a revolution or two (perhaps they're French?). I hoovered the whole thing out, and gave compressed air blasts to the fans, then servisol and deoxit, but with no real progress.
Any suggestions/recommendations for someone who'd be able to fix it reasonably cheaply? I don't want to seem a cheapskate, but these don't seem to be worth that much.
I wouldn't bother, but ticking aside, the sound is extremely impressive (and I'm not easily impressed!). I think repaired, this would be a keeper.

On the JBL front, I replaced the shockingly bad surrounds, then even landed on USA ebay a pair of nice grilles with JBL badges and all. They're very nice sounding and would show a clean pair of heels to some of the faves on AOS, like MS Pageants, Ditton 15's, JR149s* etc, and will probably end up as monitors for my lad who's doing a music tech course and wants to get himself a little studio together.
Now, if only the Carver could be fixed, he'd have an amp for them....

*all of which I either own or have owned...just in case other AOS'ers think I don't know what I'm talking about!

[hifi_dave]

We sold many pairs of the JBL L40, back in the day. A lovely, exciting, lively speaker for not much money.

You could try Jez at Arkless for the repair of your Carver amps.

[ff1d1l]

We sold many pairs of the JBL L40, back in the day. A lovely, exciting, lively speaker for not much money.

You could try Jez at Arkless for the repair of your Carver amps.
Thanks...been in touch and am going to drop it off next time I'm in the N.E.