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View Full Version : How to lift the "veil" from my L-300s???



Tweak48
10-03-2004, 02:09 PM
I recently purchased a nice pair of L-300s from an owner of the last 22 years; they are in nice shape. I promptly sent the 136 woofs off to Orange County Speaker Repair for new surrounds and a regauss.

Now that I have the system put back together, for some reason they just donít sound as good as I remember them sounding when I was a retail JBL sales person in the 70ís. The bass is every bit as good, but the mids and highs seem a bit veiled, and not open sounding. The HF extension seems okay, and you can tell they are capable of great dynamic range. As it stands now, they do not sound as good as my 4425ís, and I know they should/could sound even better. What to do? I can think of at least 3 solutions.

1. Replace the caps in the crossover. From the threads, it sounds like polystyrene is the way to go. I dropped some Solen polypropylene into my Altec n-800 crossovers and it really brightened things up on my Valencias, too bright actually. What voltage rating on the caps should I get? Theyíre not listed on the attached schematic. Any recommendations on brands?

2. Replace the diaphragms in the 077 and LE85 and regauss? Ouch! $225 each for JBL Ďphrams ($75 for Radians), plus $25 X 4 for re-gauss. Is all this really necessary? There is no aural indication of a ruptured diaphram.

3. Bi-amp? I did this with great success on my Altecs. Turned out much better than my recapped N-800 crossovers. I have a 2 way dbx unit laying around; I could cross at 800hz, drive the 136 directly and the 077 and LE85 via the crossover. From the looks of the 3133A schematic, the switch merely takes the woofer out of the circuit. Is that correct?

4. I could also take the crossover out entirely, biamp at 800 hz, and use a cap on the 077 at a strategic point. But where? Would the LE85 roll off gracefully?

So what is the best solution? Iíd really prefer to upgrade the crossovers and call it good if that will produce good results. I donít understand this "Bypass Caps" deal, but will read the thread one more time.

Comments would be greatly appreciated.

Bryan

L300 schematic below
http://audioheritage.org/vbulletin/attachment.php?s=&postid=4766

scott fitlin
10-03-2004, 02:32 PM
did you listen to them, and they sounded good? Open and airy?

Were the woofers in your speakers the original cones? I ask this because if they were the original cones, and you had them reconed, Im thinking maybe the cone paper is somewhat different from the original cone from 22 years ago!

To me, what your describing is a phenomenon known as smearing.

Figge
10-03-2004, 02:35 PM
get new JBL diaphragms for the le-85 and forget about the rest! i reacently changed dia:s in my 4430:s and i still look like this:jawdrop:when i hear them!

4313B
10-03-2004, 02:36 PM
"Now that I have the system put back together, for some reason they just donít sound as good as I remember them sounding when I was a retail JBL sales person in the 70ís."

Not surprised at all.

"I donít understand this "Bypass Caps" deal, but will read the thread one more time."

Photo showing where to solder bypass capacitors to a main capacitor. The main capacitor is a 6 uF Electro-Cap Mylar from the 80's. The top bypass capacitor is a 0.01 uF RelCap Polystyrene & Foil and the bottom bypass capacitor is a 0.01 uF AudioCap Polypropylene & Foil.

At the top of the picture is a 4435 network about to get the AudioCap bypass treatment.

scott fitlin
10-03-2004, 02:48 PM
Originally posted by Figge
get new JBL diaphragms for the le-85 and forget about the rest! i reacently changed dia:s in my 4430:s and i still look like this:jawdrop:when i hear them! Fresh reconed woofer, and recharged magnets, and the woofers are outdoing the tweeter and comp drivers! Possibly rediaphragm, and recharge the comp drivers, too.

Earl K
10-03-2004, 04:15 PM
Hi Bryan ( Tweak48 )

Here's my 3-cents


So what is the best solution? I'd really prefer to upgrade the crossovers and call it good if that will produce good results. I don't understand this "Bypass Caps" deal.

Recapping ( bypassing ) a la Giskards stock formula is the fastest & most direct approach to begin the process of revealing missing resolution .


1. Replace the caps in the crossover. Yes, I'd recommend this. As Giskard just showed, the first step would be to tryout the stated bypass formula - while retaining the original mylar caps. If you want to replace some of the main caps , I defer to Ian MacKenzie who has had good luck using 2425 ti diaphragms with the signal filtered through Hovlands on the way to the driver . He does , of course, have a lot of class A electronics so that must be considered. If you decide to replace with 2421 aluminum diaphragms then I'll let others suggest the most suitable polyproyplene cap makes. The SonicCap sounds interesting but then again so does "MultiCap" with it's builtin bypassing scheme, as well as North Creeks' Crescendo caps. All of these are Film & Foil Polypropylene types.
2.
Replace the diaphragms in the 077 and LE85 and regauss?
I'd also recommend new diaphragms for the le85 ( I have no opinon about the 077 ). You can go with either type of metal diaphragm - but you should adjust your cap type ( manufacturer ) to complement whatever metal grabs yor fancy ( or pocket book ) . One of my 288-8K diaphragms ( aluminum ) must need replacing - its' missing some low mid information that it's mate quite easily reproduces. This makes sense since Aluminum is known to "work-harden" over time with usage. This hardening effects the Fs of the compliance - effectively raising it into an audiable area . ( Think stiff surrounds on le14a woofers - less bass ) The rest of the midband response starts to suffer, sounding more "forced" and "strained". HF repsonse starts to droop a bit - but I don't know why this happens with a ferrite magnet type driver . I own a few of those Radian replacements for 2426s and the Altec version. Both Radian models lack the original transient response of the 2425/6 or Altec 902 type diaphragm. Now, they do sound similar to the Altec 908 diaphragm. I figure it's the plastic suspension damping the transients - it's just not as nimble as other types of suspension schemes - such as the embossed "diamond" type or the tangential swirl of the Altec 902 or 288 drivers .

3.
Bi-amp? I did this with great success on my Altecs. This is what I do. I use some polystyrenes into a Bryston 2BLP-Pro to create the first pole of a typical 2 pole setup . The other pole comes from passive components in line with the speaker. You could implement something like this with your setup - if you bought a HF amp and $ 10 to $20 worth of polystyrene coupling caps ( values dependant on the input impedance of your High Frequency amplifier .

4.
I could also take the crossover out entirely, biamp at 800 hz, and use a cap on the 077 at a strategic point. This approach would unnecessarily waste some builtin EQ that your existing passive crossover provides from the passive components.


ABOUT POLYSTYRENE Film & Foils : IME, One can overuse them and dramamtically effect the sonic results. I believe that when used as a bypass cap they are best twinned with a polypropylene foil ( in speaker level crossovers ) not as a replacement for the polyproyplene .


Here's a story to illuminate why it's best to stick with Giskards' mentioned ratios.

Right now I'm listening to day #2 of a new balance between Film & Foil Polypropylene & Polystyrene . The base caps are 400 volt , 6.8uf Solens ( per DC leg ). The circuit is for the HF "boost" on my Altec 288-8K drivers . It's an all DC biased setup so the cap values are twice as large with twice as many present. Values are .18uf (Polyprop) & .02 (Polystyr) bypassing 6.8uf of Solen MPP types. The sound ?? Anything but what would be expected by anyone reading the labels on the electronic componentry. Right Now; it's quite "milky-soft" while being full of "air" . PLUS: The leading edge of notes are somewhat "feathered" . It's really quite the opposite of the "Too Bright & Over-Articulated" sound that one would expect from Solens filtering sound originating from a Bryston amplifier . There is also an apparent soft compression happening up to about 10K. So now I'm curious as to whether or not this "milk" will clarify in a weeks time leaving the "air" & "soft-compression". Now, It's possible my Film & Foil Polypropylenes are actually Mylar Foils - that would somewhat jive would predicted results. I guess that's the price I pay for using surplus caps - Though the results are a very pleasant, listenable sound :D

<> Earl K

Mr. Widget
10-03-2004, 05:32 PM
I agree Earl's recommendations.

I would add the likelihood of any of the compression drivers needing a magnet recharge is quite remote. Furthermore if these were in a sane person's home their entire life the LE85 and 077 diaphragms are most likely fine. I would try the crossover caps first. Those old electrolytic and mylar caps do age.

Widget

Audiobeer
10-03-2004, 06:23 PM
:banghead:

Tweak48
10-30-2004, 10:34 AM
.....................at least it surely sounds a lot better.

Thanks to everyone that responded. I decided to go with Earl K's suggestion; the fix that would take the least effort, and for which I had all the items at hand; biamping. Also, Mr. Widget's rationale made sense that it is unlikely that a pristine set of L-300s like mine would have overdriven 077 and LE85 units needing diaphragms and magnet recharging.

My test configuration was to use an active dbx 223 2-way crossover crossed just slightly over 800 hz. I used a 125-watt s/s amp directly wired to the 136 woofs, and a tube 65-watt amp wired to the existing stock JBL crossover.

With a 24 db LR slope on the active network, and not knowing how quickly the JBL crossover rolls off the woofer, I thought it would be better to error on the side of both drivers covering a bit of this area, rather than having a frequency drop out from being too low. Any comments on this approach would be appreciated

QUESTION: The woofers were simply disconnected from the crossover and the leads taped. Does removing the LF load from the crossover change the crossover points on the MF and HF? Do I need to insert a resistor simulating a 136 load??

Anyway, the presence, clarity, and imaging have greatly improved. The increase in dynamics is staggering; clearly the biggest improvement, just as I was when I first biamped my Altec Valencias.

I think I can live with this setup for a long time. At least until next year.

Thanks for all the technical help. I'll attach some photos as soon as my kidís digital camera.

:)

Alex Lancaster
10-30-2004, 10:38 AM
Glad You liked it better, it gas been discussed, and I would put an 8 ohm 10 watt generic resistor to "simulate" the 136, also, I would use a 300W/ch amp for the 136īs, to have headroom.

Earl K
10-30-2004, 01:31 PM
Glad it's working out . :)

Regarding some other "biamping" approaches .


Here's a Hybrid approach;

As mentioned above, I'd try running full-range signal through some Passive Line Level HiPass Capacitors into your HF amp. "Polystyrene" caps are a good choice. This approach avoids the DBX for the horns. Values of @ .022 uf for this cap ( into a 50K input impedance ) will give you a nice gentle HiPass, starting somewhere below 400 Hz . Do you know the input impedance of your HF amp ? This "HiPassed" signal, after going through the L300s' internal crossover, will end up offering an acoustic slope that it pretty close to the original system design. Coupled with the steeper LowPass for the woofer ( from the DBX/AMP ) - plus - the fact that you've taken the woofer inductor out of its' circuit, will maintain the cleaner sound you've just acquired. There should be the added bonus of better resolution "uptop" because of the avoidance of unnecessarily putting the HF signal through the DBX. Additionally, this approach may offer a better transition between the woofer & horn .

regards <> Earl K

Mr. Widget
10-30-2004, 01:38 PM
I like your thinking Earl.

Bryan, I would strongly suggest that you follow Earl's suggestion. You can use his cap value if your tube amp's input impedance is 50K ohms, if not it is simple to calculate the correct value.

Widget

Ian Mackenzie
10-30-2004, 08:57 PM
What is the existing Tube amp?

Regards Earls comments about film/fpil and class A.

They go hand in hand, and pending if your amp is Triode you should get nice performance with the better film foil caps.

Class A gives resolving power , dynamics and clarity. Nice caps deliver transparency with more silence b/n the notes.

If you search there ws a good thread rcently about cap comparions. You tend to get what you pay for.

I myself, a self confessed JBL fruit cake, find the better and newer crop of film foils more liquid and transparent and less brite than bypassing mylars bypased with other blends and I figure better to get it right first time tha spend endless hours farting around. Besides the 077's need only 1.0uf and 1.5uf, not too expensive with even the best of the best.


Ian

Tweak48
10-31-2004, 09:16 AM
Earl K, Mr. Widget and Ian;

I certainly would be easy to run some caps in-line prior to entering the HF amplifier. It couldn't possibly hurt avoiding those op-amps in the dbx unit either (although it sounds pretty darn good for a cheap active network).

If one of you can calculate the correct value of caps, I'll sure give it a try. Polystyrene, right?? BTW, the input inpedence on the tube amp is 100kOhms. It's a p/p amp running EL-34s in tetrode mode (VTL).

So is it necessary for me in install a 8 ohm 10 watt generic resistor to "simulate" the woofers on the JBL crossover, now that they're directly wired to the s/s amp?? I was not sure if removing the woofer load from the crossover changes the crossover points.

Thanks for the tips.

Bryan

4313B
10-31-2004, 10:37 AM
Just be aware that the only thing that saved you from blowing your amplifier running the L300 without the LF transducer connected was that little conjugate (Zobel) that was still in the circuit. Even so, that's only about a 2 ohm load at certain frequencies.

I believe the 2.2 mH inductor and 20 uF capacitor without a load, and conjugate, dead short somewhere in the 700 to 800 Hz range.

"QUESTION: The woofers were simply disconnected from the crossover and the leads taped. Does removing the LF load from the crossover change the crossover points on the MF and HF? Do I need to insert a resistor simulating a 136 load??"

Remove the 2.2 mH inductor from the circuit and forget about it.

Earl K
10-31-2004, 10:56 AM
Hi

EDIT : Giskard beat me to a ( succinct answer ) but ;

Capacitance :
(A) Does the amplifier have a transformer isolated input with no DC blocking capacitor ?
- If yes, then placing a simple inline .01uf cap will give an @ Fc point of 159 hz . I do say approximate because the 100K is likely not deadon the mark. Anyways, this point Fc point is now @ 2 octaves away from your internal passive point. I'd keep it in that general area. That way the phase-shifts are predictable.

(B)If your amplifier has another type of input topology that includes a DC blocking cap - then that cap ( now electrically end to end with your new cap ) has an effective value that totals the sum of the reciprocals .

An example; Say the existing DC blocking cap is 5 uf . That means adding the recirpocals of 5uf & .01uf. The math is .2 + 100 = 100.2 . Flip that reciprocal total ( 100.2 ) back to a real number and you have a new effective capacitance of .00998004 uf . So, effectively no net change from scenario "A". Certainly not worth spending more money on a bigger capacitor.


Re; attaching an 8 ohm load to the LF side of the crossover .

No resistor;
There is still a highly loaded, series inductor , a parallel capaitor and paralleled zobel (RC ) across the outputs of your amp. That equals a funky series LCR (resonance filter of sorts) with the shunt capacitor "bypassing" the R in the Zobel . This should give an asymetrical notch to the existing crossover slope - somewhere within in the stopband. Whether or not the impedance of this notch ever approaches a low enough Z point to upset the stability of your tube amp is anyones guess.

To calculate the effect of this LCR filter, one would need to know the motional impedance (Z) range down in the stop-band, below the Fc and the HP portion of the crossover. This is very likely a fruitless and fatiguing excercise in math. An advanced Passive Crossover modelling progam ( "Spice ) would be really useful here.

With the 8 ohm load LF ;

- With that 8 ohm load there, the amp will be "encouraged" to deliver a frequency range of (@ 200 hz to 800 hz ) into the load resistor for heat dissipation. That utilizes ( uses up ) some capacity ( current draw ) within the powersupply of the tube amp that otherwise could be reserved for higher frequencies.


iWhat would I do ?

I'd unsolder one end of the series inductor in LF area of the crossover . This makes a clean and utter break in that one area of the crossover. No LCR filter reflected back to the amp - therefore no "Low Z notching" effects.

iWhat should you do ?

Consider the above solution , if you're not comfy with that then add the resistors; And, for the sake of creating a heat-related safety/margin, make it (2) 16ohm resistors paralleled together to derive your 8 ohm load or better yet (4) 32 ohm resistors paralleled .

As I now see in the reply preview, "Like He Said" ( Giskard & Alex ) :D

<> Earl K

Tweak48
11-01-2004, 04:55 PM
Actually I just lifted one leg off, and pulled the loose insulator over the lead for easy reinstallation in the future. All without removing the crossover; just popping the top off.

It's a darn good thing that someone (Giskard?) had previously posted a schematic for the N333 crossover. All the inductors and big caps were partially submerged in a pool of wax, and there was no way I could read the values, so THANKS!!

I couldn't be happier with the improvement in sound quality. I actually think it improved even more with the removal of the inductor from the circuit. Could that be possible or am I psychoacoustically BS'ing myself?? It seems like distortion lowered and response smoothed a bit.

Anyway, you guys made a BIG improvement in my system. I may even like them more than my 4425s.

Earl K
11-01-2004, 05:09 PM
Hi Tweak


Could that be possible or am I psychoacoustically BS'ing myself?? It seems like distortion lowered and response smoothed a bit.

No B.S. : the technical benefits of "circuit refief" make sense . You've essentially taken a lot of current strain off the Power Supply of your tube amp. Most people should be able to hear the difference between an amp struggling to maintain it's composure versus an amp confidently cruising along. That LCR circuit would have been reflecting a frequency dependant low impedance dump that might have been approaching the "Three Mile Island" area.

Also, don't discount what "relief" and a "good glass of red" will do for improving the overall listening experience. :D

<. Earl K :)