JBL C40 first impressions

Lucky Pierre

Lucky Pierre

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It sounds like crap. A little muffled, congested, very little high end to speak of, no sparkle. I have no idea how long its been since this speaker was played for any length of time, but it does seem to sound a little better in the couple of hours it has been playing.

I believe it has the 030 load; D130 15" woofer, 075 "Bullet" tweeter, and N2400 crossover. The potentiometer seems to do very little, if anything, to change the sound. I imagine the crossover needs to be rebuilt.

I am currently using my Realist mid-50s mono amp, streaming radio to an Arcam miniBlink Bluetooth DAC. The amp is a rebranded Grommes LJ-2; tubes are 6SC7, 6SL7GT, 6V6GT x 2, 5Y3GT. Amp was gone through by a local tech about 6 years ago. It might not be the best sounding amp, but I don't have another mono amp to compare it to yet. I have another of the same amp but from a year or so later, but I do not know the condition. I do have an amp arriving on Saturday, which may have EL84 x 2. I won't really know until it is here, though.

This speaker will be a dedicated mono system. I don't expect it to by a stellar performer, but I have other systems for that.

​

 
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Peter_L said:
It sounds like crap. A little muffled, congested, very little high end to speak of, no sparkle. I have no idea how long its been since this speaker was played for any length of time, but it does seem to sound a little better in the couple of hours it has been playing.

I believe it has the 030 load; D130 15" woofer, 075 "Bullet" tweeter, and N2400 crossover. The potentiometer seems to do very little, if anything, to change the sound. I imagine the crossover needs to be rebuilt.

I am currently using my Realist mid-50s mono amp, streaming radio to an Arcam miniBlink Bluetooth DAC. The amp is a rebranded Grommes LJ-2; tubes are 6SC7, 6SL7GT, 6V6GT x 2, 5Y3GT. Amp was gone through by a local tech about 6 years ago. It might not be the best sounding amp, but I don't have another mono amp to compare it to yet. I have another of the same amp but from a year or so later, but I do not know the condition. I do have an amp arriving on Saturday, which may have EL84 x 2. I won't really know until it is here, though.

This speaker will be a dedicated mono system. I don't expect it to by a stellar performer, but I have other systems for that.

​

Click to expand...
You can try just a single cap in line to the tweet, maybe between 4 and 8 microfarad and give it a listen. Impredances are usually in question with golden age JBL but ballpark will tell you if something is toasted, gunked, open, or dried out, right?
 
That's unfortunate! dedicated mono systems can be stellar performers. that's the only way I listen to music now.

Can you DIY tube circuits? I would recommend buying a pre-war radio with a simple SE circuit and modifying it to add a line input for your bluetooth source, control volume digitally. you can get awesome old radios for <$100 all day long.

 
I wouldn't say it is unfortunate yet. This is the first time I listened, and the amp is a bit of an unknown. Things will be sorted out at some point.

I do not know much about the N2400 crossover. Do they often need new caps? I have or had a couple of later JBLs, L19 and 4311B, that definitely needed to be recapped.

We'll see how things sound when I get my new mono amp that is inbound. I figure a week or two of work and that will be ready to try. Single mono amps are pretty easy to find and generally not too expensive. I'm not talking about Macs or anything. Rather the amps that truly came from the mono age.
 
I think that Grommes is basically the same as the Bell 2122. I went through great trouble to source a matching pair of those and was disappointed with the final sound.

as a 'control' amplifier, you may want to try the PJ Miaolai A7. it's 50 bucks, sounds decent, bluetooth built in. will let you hone in on how you like the speaker by hooking up one channel.
 
I have one of those little chip amps,or whatever you call them. It's no problem connecting only one speaker?

I have another of the same amp. I have to check it out to see if it is usable. If it is, I'll try it. If it's not, it can be a tube donor. I just today received a DeWald N-5000B. It will get recapped, and whatever else it needs. PP EL84--it should sound really good. I may also be picking up a carillon amplifier from the late '40s. I believe is has 6L6 x 4. Who know how this one will sound, but it should have plenty of power.

Once I settle on an amp, I will be digging into the speaker. I assume the crossover needs some attention.
 
Peter_L said:
It sounds like crap.
Click to expand...
Seems like a reasonable assessment to me. But then I guess it depends on a person's expectations and frame of reference.

I love the look of the Harkness, the sound... it is not my flavor.

Here is the schematic. I really doubt there will be any issues with these old 6uF caps and the autoformers rarely fail... that said, I am no fan of vintage JBL crossovers. If I was going to make changes to the crossovers I would replace them entirely after analyzing the performance of the speakers and individual components.
JBL N2400.webp
 
A few additional thoughts on these speakers.

The 075 tweeter has a very narrow dispersion pattern. If you are off axis it may not be covering your listening position.
Also, these tweeters' performance can degrade over time due to abuse. This abuse can be environmental causing excessive oxidation, or it can be electrical. It is rarely from over powering them, but abusing them due to amplifier clipping is not uncommon. The symptoms of either form of abuse would be elevated distortion and possibly loss of the highest frequencies.

The D130 is pretty durable and that is one of the reasons they were adapted for use as guitar speakers, but if you have an early version with a paper surround, these do tend to fail and can cause excessive distortion and additional loss of low frequency response.
 
Can you share pics of the innards? Would like to see what the front/back of those drivers look like. Maybe the crossovers are tired?
 
Thank you for the schematic!

There will be much listening and analyzing before I do anything to this speaker. I may have detected a bit of crunch in the tweeter when I listened briefly when I brought it home, but I am not sure. If the tweeter is damaged, I will attempt to repair it. I seem to recall reading somewhere that the diaphragms are no longer available, but I might be wrong, so a replacement may be in order. The other option is to replace with a potato masher, and the N2400 crossover with an N1200. Will this combo work with the D130?

I got this speaker because it is a BIG, beautiful, not too common JBL cabinet with a pretty good set of components. Plus, I have mono amps sitting around doing nothing. I will keep it as a mono system in our kitchen for background music or music when I cook. Hi-ish fidelity in this setup is perfectly acceptable to me. Plus, there is a serious WOW factor with a speaker this large.
 
Audionut said:
Can you share pics of the innards? Would like to see what the front/back of those drivers look like. Maybe the crossovers are tired?
Click to expand...

This is what I have so far. I opened it briefly the other day just for a look. I will get deeper into it in the future, and document with pictures. One question I have is how does one access the drivers? It looks like the front baffle unscrews from the front. Is this correct? Otherwise it looks like I would have to remove part of the horn assembly.

IMG_E4990.webp

IMG_4975.webp

CR40_2.webpIMG_4976.webpIMG_4977.webpIMG_4978.webpIMG_4979.webp

IMG_4980.webp
IMG_4981.webp
 
The drivers look to be in beautiful condition. I am not suggesting your tweeter is bad, but if the tweeter is no longer up to spec, short of finding a NOS JBL diaphragm, you will be out of luck. I am aware of multiple people measuring the current crop of aftermarket diaphragms and they are no good.

The good news is that JBL produced several tons of these tweeters over the years so finding one that measures and sounds good is possible. Do not be concerned about 8 ohm or 16 ohm versions. They are all identical. The actual impedance is in-between the two and JBL originally labeled them as 16 ohm and then changed them to 8 ohm... only the labels are different.

Looking at the visual condition of the woofer, I imagine it is fine.
 
Appear to be in great shape.
but old and because so will have these types of issues to iron out. Polish up those priceless legs.
 
Time to update this project. I spent an hour the other day with Esperanza Spalding on this system. I now think that this speaker can sound really, really good with the right internals and amp. Amp is now an Altec 339D, and a potato masher is on the bench. As soon as I have the right crossover, I will swap the tweeters and see what happens. The 075 and N2400 will then go into a C38 I got recently that has a single D123.

IMG_1274.webpIMG_1277.webp
 
I have a customer with a pair of these from is dad. Custom black cabinets. I set him up with period correct electronics including an Altec 353A integrated tube amp (6L6) that we restored and they sounds really good.
 
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