2 in driver questions

[lfh]

Hi all,

like so many newbies before me, I've been silently following this forum for a couple of months. (I hold you guys responsible for the (JBL) blue rings under my eyes... ;) ) Since this is my 'Hello, world!' post, I better present myself:

I live in Stockholm, Sweden, and I got the "blue baffle blues" in my early teens, when my best friend's father introduced us to the world of pro audio. ("Boys, remember this: Studer make the finest tape recorders and JBL the best speakers money can buy.") Now, at 38, it's about time to do something about it! Thus, I'm gearing up for a couple of JBL-projects (got the Studers covered already :) ), the first of which will be an all-JBL multi-way rig for my bass guitar. More on that later.


My questions:

1. The other day I bought a pair of what the seller referred to as "grey 375:s with DE diaphragms". The foilcals are missing though, and the back covers look identical to that of my also newly purchased 2440 -- as opposed to the flat ones I've seen in pics of grey 375:s posted by Oldmics (see '375 and 2440 mid drivers'-thread) -- so I'm thinking the drivers are actually 2441:s (they do have the DE diaphragms). What's your take on this?

2. In the factory rediaphragm instructions it says "/.../ hook unit up to oscillator set at correct input voltage indicated on the appropriate technical manual and sweep according to technical manual. Listen for rubbing. Use small mallet /.../". Does anyone have access to the missing details on the sweep test? (Not that I think the actual figures are too crucial, but it would be nice to closely follow the shop instructions.)

3. All screws in the 2440 are missing. Are there special requirements on the screws holding the diaphragm (e.g. non-magnetic?) or will ordinary ones from the hardware store do?

Thanks in advance,

"lfh"

[lfh]

Ok, so I revise my first question:

1'. The unmarked "grey 375" back covers look exactly as that of the 2482 depicted here (http://www.lansingheritage.org/images/jbl/catalogs/1982-pro/page18.jpg), and the terminals are also of that type. Did JBL really sell that generation of drivers in grey color, badged as 37x? This seems unlikely to me, but the seller insisted they are 375:s, and he has been into audio since the 70:s (although he's more of an Altec guy than a JBL fan). Please enlighten me. (And no worries: I didn't shell out $$$ for "rare stuff". ;))

[Figge]

Halloj å välkommen ombord!

i guess someone will be able to help u if u get some pictures of the drivers up here...

as for Studer/Revox: i totaly agree!

as for !JBL: i totaly agree!



MVH Fredrik

[lfh]

Hej Fredrik! :wave:

Tackar, tackar! Trodde för ett ögonblick att man måste ha en avatar på en jättehögtalare för att bli upptagen i klubben. ;) (Sorry about the "encryption".)

I'll follow your advice and post a picture - a useful exercise per se. They look like vanilla 244x:s to me, but who am I to tell. Are those foilcals prone to falling off? If not, what could have been the reason to remove them? :hmm: Perhaps the drivers had some less desirable OEM badges...

Meanwhile I've searched the forum some more and found out that the screws indeed must be non-magnetic. Furthermore, it seems unwise to poke around in thes babies with a magnetic screwdriver - unless the name is Arnold Schwarzenegger, of course.

As to the the sweep test, I've found a post by boputnam where he states "On drivers, hook unit up to oscillator set to 3-4 volts at proper frequency (550Hz on 1-inch drivers, 350 Hz on 2-inch drivers)".

So far,
Fredrik (också)

[Figge]

hej Fredrik! du kan ju alltid ha en av dina studer som avatar...skulle nog funka bättre :)

nice name!:yes:

now im no expert on the subject:no:but those look like 2440/41:s to me...the 375:s ive seen all were flat-back...

the "gray 375" isnt that the one in the pic below?

i guess the drivers are the same, just difrent back covers, correct me if im wrong.


however i pulled the horns in my 4430:s and found there were 2421A:s 1 with flat back cover and one had a back just like yours!

so just hookem up and :rockon1:

btw what studer u have?

peace/F

[boputnam]

Originally posted by lfh
Did JBL really sell that generation of drivers in grey color, badged as 37x? :yes: And, according to this thread, Oldmics considers it to be amongst the rarest...

http://audioheritage.csdco.com/vbulletin/showthread.php?s=&threadid=1308&highlight=375+2482 - see Oldmics 12-12-2003

And yes, those oval foilcals do commonly come loose... :(

[lfh]

Originally posted by Figge
the "gray 375" isnt that the one in the pic below?

Oh, that should be the predecessor - the "humpback".

After reading Bo's post, I carefully re-read Oldmic's overview of the various 375:s:

"Up at 12:00 "O" clock is the version that I consider the rarest.That would be the grey colored 375.This was introduced after the humpback and has the rounded end cap as do the 2440 series."

So "rounded" refers to the shallow ramp and plateau clearly visible in my pic? Looking closer I just barely see that feature in Oldmic's pic. However, I see no traces of the round countersink, so the castings are for sure not identical, even though they both may be described as rounded.


Originally posted by Figge
however i pulled the horns in my 4430:s and found there were 2421A:s 1 with flat back cover and one had a back just like yours!

Most interesting! I figure this subject is worth a thread of its own. We need the full scope on all permutations! :) It's a pity the broshures with few exceptions show the drivers laying on their backs. :(

But you're right - hooking them up is more important than the number magic! I have to wait some five weeks for my horns to cross the pond, though...

I have two mono C-37:s. I'll make one stereo machine out of them any year now... (Got new "Schmetterling" heads on the shelf :yes: )