JBL D120 reproductions

[Harvey Gerst]

[quote=horseshead]

Yeah, OK.


Oh, and 16 ohm = 8 ohm. I've never seen a pair test higher than a 7.3 (Can anyone else substantiate that?)


The output transformer/tubes of a fender quad/dual showman/twin are all wired for 4 ohms load total. It doesn't care what speaker combination. If you put too much resistance (load) or too little it can kill the tubes too soon. I find it hard to believe that a company like JBL with such an unapproachable reputation for perfection of production and engineering design would just say, yeah, whatever, we'll just wing the impedance tolerances.

Rick

Sorry Rick, but he's right. While we did maintain pretty tight tolerances, our 16 ohm speakers were really about 8 ohms and our 32 ohm speakers were closer to 16 ohm. Why? To make them a little louder. Remember, these were tube amps we were feeding. If you have a big hunk of iron for a transformer, tube amps are a little less fussy about lower impedance loads. Later, JBL just added "8 - 16 Ohms" on the label.

We never said, "whatever". That expression didn't appear until many years later.

[toddalin]

If only I knew what the K120's sounded like I'd be able to say. I don't want to sound like the guitarist from the song in that home depot TV commercial that they also play on the phone when you're on hold, so...... no E120's for me I guess. No one yet seems to be able to describe the sound of a K series, only the D versus the E series.

Rick

OK, I let them go. Too bad too. At $90/pr, price was pretty good.

[Don McRitchie]

Back to the original question, Standel Musical Instrument Amplifiers was making copies of JBL's Alnico "D" series drivers for a time. I couldn't find reference to this on their current web site, but it may be worth a call to see in they are still in production.

http://www.standelamps.com/

[horseshead]

[quote=Harvey Gerst]

Sorry Rick, but he's right. While we did maintain pretty tight tolerances, our 16 ohm speakers were really about 8 ohms and our 32 ohm speakers were closer to 16 ohm. Why? To make them a little louder. Remember, these were tube amps we were feeding. If you have a big hunk of iron for a transformer, tube amps are a little less fussy about lower impedance loads. Later, JBL just added "8 - 16 Ohms" on the label.

We never said, "whatever". That expression didn't appear until many years later.

Should I keep all four speakers the same impedence rating, either all four rated at 16 ohms or all four rated at 8 ohms? When fender quad reverb customers wanted to special order JBL's what were put in there, 8 ohm or 16 ohm?

I've been wondering what were some home stereo models and brands that were created for the mass market and typically sold with JBL D120's,123's or 131's?

Rick

[horseshead]

Back to the original question, Standel Musical Instrument Amplifiers was making copies of JBL's Alnico "D" series drivers for a time. I couldn't find reference to this on their current web site, but it may be worth a call to see in they are still in production.

http://www.standelamps.com/

Thanks, I will call them.

Rick

[Harvey Gerst]

Should I keep all four speakers the same impedence rating, either all four rated at 16 ohms or all four rated at 8 ohms? When fender quad reverb customers wanted to special order JBL's what were put in there, 8 ohm or 16 ohm?

I've been wondering what were some home stereo models and brands that were created for the mass market and typically sold with JBL D120's,123's or 131's?

Rick

I'd keep them all the same. Most of the old fender transformers actually had multiple output taps that were set at the factory to accomodate different loads. If you look inside the Fender head, there should be some unused wires coming out of the output side of the transformer that offer other impedances.

There were never any home systems that used a D120; that was strictly a musical instrument speaker. D131's and D123's were often paired with 075's and even 175DLH's. The C39 cabinet could handle four D123's and an 075.

[horseshead]

OK, I let them go. Too bad too. At $90/pr, price was pretty good.

I am intested in the K120's. It just took me a week to realize this because it can get a little confusing reading different opinions from different people posting here, but I have decided that the best way for me or anyone to find the model JBL that I/they like the best is to try the different models.
Rick

[horseshead]

There were never any home systems that used a D120; that was strictly a musical instrument speaker. D131's and D123's were often paired with 075's and even 175DLH's. The C39 cabinet could handle four D123's and an 075.[/quote]

If not home systems, what were these, strictly JBL stereo systems, and strictly their professional line?

Rick

[horseshead]

DCR of C8RE120 is 6.3 ohms +/-10%
DCR of C16RE120 is 13 ohms +/-10%

I do believe that JBL tried to rate the impedance of the drivers' operating frequency range, especially on HF drivers...not just DCR.

What does the acronym DCR stand for? And thanks edgewood, I did find description of the sound of K's a few posts back.

Rick

[horseshead]

I have a line on a possible pair of K120's reported to be in good condition (someone is in line infront of me though). Are those of interest to you and if so, how much are you looking to spend?

Are those the ones you already let go for $90? If not, then I would need to know if they are original cones before offering a price.

Rick

[Harvey Gerst]

There were never any home systems that used a D120; that was strictly a musical instrument speaker. D131's and D123's were often paired with 075's and even 175DLH's. The C39 cabinet could handle four D123's and an 075.

If not home systems, what were these, strictly JBL stereo systems, and strictly their professional line?

Rick

Sorry if it was a confusing answer. Lemme see if I can clear it up. The 15" D130 and the 12" D131 were designed as hi-fi speakers, period. At one point, Bob Crooks of Standel and Leo Fender started selling them as options in their guitar amps. The D123 was also a hi-fi speaker and was never used as a guitar amp speaker by any of the manufacturers.

From the large number of repairs we/I/JBL was getting back from these amp manufacturers, two things became apparent to me:

1. These guys were selling the shit out of these speakers, so there was a big market out there.
2. The standard D130 and D131 wouldn't hold up long-term as an OEM product for musical instument applications.

I approached Bill Thomas to let me design some speakers for this market that would:

1. work better without blowing up (due to mismounting, and surrounds
drying out and cracking),
2. increase sales by expanding the line to include a 10" speaker and a 15"
bass speaker.,
3. use existing JBL parts to reduce development and manufacturing costs.

Bill agreed, and I came up with the D110F, D120F, D130F, and the D140F.

While I would have liked to include the lower powered D123 in the MI line (for use in multiple 12" speaker systems), I decided that the popularity and power handling of the already well known D131 would probably give the D123 limited appeal. The D123's sound great in a Twin, for example, as long as you don't push them really hard. I had a D123 in an Ampeg Portaflex, and it was a wonderful sound.

The D110F in fact uses the D123 motor (magnet assembly and 3" voice coil).

So, the C39 with four D123's and an 075 was strictly a home hi-fi speaker, while the D130's and D131's did see early MI use, until the introduction of the "F" series.

That clear things up?

[horseshead]

The D131 is almost identical to the D120F, maybe 1dB more efficient. The surround on the D131 will dry out and crack sooner than the D120F.

I remember something you wrote here a long time ago about one of your contributions in the development of the D120/130 and how adding some goop to the surround of a D131 prevented the surround from drying out and cracking too soon and it also may have helped something else.

Which speaker is more efficient - the D120 or the D131? I guess Do you think mixing 120's and 131's that you would hear the loss of volume in - I don't know - which speaker is less efficient? see question above

Rick

[Harvey Gerst]

I remember something you wrote here a long time ago about one of your contributions in the development of the D120/130 and how adding some goop to the surround of a D131 prevented the surround from drying out and cracking too soon and it also may have helped something else.

Which speaker is more efficient - the D120 or the D131? I guess Do you think mixing 120's and 131's that you would hear the loss of volume in - I don't know - which speaker is less efficient? see question above

Rick

The D131 is slightly more efficient than the D120F - because I opened the gap slightly on the D120F to prevent the voice coil from rubbing and burning out. The difference in efficiency between the two models is negligable. The D120F will keep working for a lot longer than the D131, under harsher conditions.

[johnaec]

What does the acronym DCR stand for?

As far as I know, it stands for Direct Coil Resistance or Direct Current Resistance. It's the measured value in ohms you'll get when measuring across the loudspeaker leads when nothing, (crossover, other wires, amp, etc.), is conected to it. Manufacturers typically publish "nominal" impedance, which is more of an average value over a range of frequencies, since it can vary greatly by frequency. DCR values are good for verifying normal continuity, and for comparing speakers when trying to closely match pairs. Someone else can probably give a more definitive definition - mine's the "Cliff Note's" version...

John

[Harvey Gerst]

What does the acronym DCR stand for?

Rick

DCR means DC resistance; the measurement of the voice coil resistance at rest.

When the voice coil starts moving to an AC music signal, the measurement varies with frequency (and a lot of other factors), and that's called "impedance". Speaker impedance is usually measured at around 400 Hz, but impedance can vary wildly at other frequencies. DCR is usually about 70% of the specified impedance.