4344 BUILD, and some questions for the pros :)

[jlwitherell]

Hey guys,

Trying to get finished up on my new build and am stuck on a few items (being a bit of a newbie):

1) Anyone know where to source some L-Pad knobs like original JBLs? And/or, does anyone have the diameter/depth of them (so I can at least make the recesses and help move forward)?
2) Is it OK to mount terminals directly attached to MDF, or, is getting something like high voltage insulation board necessary? The L-pads don't need insulating washers do they?
3) I'm going to build Giskard's charged coupled network (and have very limited electrical knowledge). It calls for a 3 Mohm resistors for the charging. I'm wondering of I'd be safer using two 2.2Moh's in series in case one fails? Or does this never happen?

Thanks for any help in advance, been having lot's of fun! Special thanks (so far): I stole JBLP's router jig design (worked awesome) as well as got a lot of ideas from his amazing build. He also provided me with his baffle layout plans (thanks so much), and Odd gave me the box plans which for me were modified a bit. Some pics of the build:

[JBLP]

You're going fast; you will overtake me!!!
Good work Josh.

[audiomagnate]

[QUOTE=jlwitherell;367153]...calls for a 3 Mohm resistors for the charging. I'm wondering of I'd be safer using two 2.2Moh's in series in case one fails? .../QUOTE]
I would just use what the design calls for and not try to second guess it by changing any component values. Nice work.

[jlwitherell]

JBLP: Thanks man! your project has been much more than just helpful. I've found a fair bit of extra time lately, it's been fun Getting excited to hearing these! I'm hoping to have them running before it gets too cold, but most likely will have to do the final exterior finish come spring time.

audiomagnate: Thank you. I've read (somewhere, and in a few places) that anywhere from 2 to 6 Mohms is fine for the charging, my thought is that if I only use one resistor, and it fails, perhaps the battery could send too much DC to the speakers and fry them, but I'm not sure. This is why I was wondering if two in series (which are still within the total range; (2) 2.2 Mohms in series would be 4.4, and still in range) could possibly be a safeguard, as if one fails I'm still within the acceptable range of resistance... My guess is you're correct and I'm over thinking it..

[Odd]

Very nice woodwork!

1. Parts Express and many others.

If you use the 4355 crossover, l-pad for mids. are 16 ohm
I have only found 16 ohm with short Shafts 3/8"

2. Cut out one large hole in the back panel and mount a plastic plate or other material on the inside and mount terminals on this.

There is no reason for two resistors, it passes no current here

[jlwitherell]

Thank you Odd!

I couldn't find Knob replicas searching around the internet, all I was able to find were the knobs that don't recess like old JBLs do. But, I found a guy on EBAY who makes them out of either delrin or alumimum and I ordered the delrin (hope they work!). The L-Pads I ordered from parts express and apparently when arrived are made by Dayton, which is cool as these are the same capacitors I'm using. They are all 8 Ohms.

Thanks for the tip on mounting, heading to a Plastic shop today to see what I can find.

Still a little confused on the resistor. 3MOhms is a huge resistance value so it is limiting the current from the 9v battery greatly. My wondering is do resistors ever go bad and as such the 9 V battery could sent too much DC to the speakers. If so wouldn't using two of slightly less resistors safe guard this. I apologize if I'm not understanding correctly, or just plain being dumb!

[fpitas]

Still a little confused on the resistor. 3MOhms is a huge resistance value so it is limiting the current from the 9v battery greatly. My wondering is do resistors ever go bad and as such the 9 V battery could sent too much DC to the speakers. If so wouldn't using two of slightly less resistors safe guard this. I apologize if I'm not understanding correctly, or just plain being dumb!

As Odd said, it passes insignificant current, it's just to bias the capacitors. A single 3M resistor is fine.

[grumpy]

seems like ebay seller "sign-shop" (Timmerman) sold foilcals, grill pegs, and other bits... I don't recall if he
also was the person who at one time made replacement L-pad knobs... might be worth contacting
if no one else remembers who it was that had been making these. I might be remembering incorrectly.
Maybe try the sketchy search feature here...

Also, if a 3Meg resistor to fail, the most likely scenario would be an open or intermittent, not a short...
so I wouldn't lose sleep over it.

[hjames]

That's him but it was sign--shop with 2 dashes in the username!

http://www.ebay.com/sch/sign--shop/m...p2047675.l2562

Write him directly see if he has the knobs ...

I've gotten speaker grill pegs and various JBL "foilcals" from him in the past and he's easy to deal with!

seems like ebay seller "sign-shop" (Timmerman) sold foilcals, grill pegs, and other bits... I don't recall if he
also was the person who at one time made replacement L-pad knobs... might be worth contacting
if no one else remembers who it was that had been making these. I might be remembering incorrectly.
Maybe try the sketchy search feature here...

Also, if a 3Meg resistor to fail, the most likely scenario would be an open or intermittent, not a short...
so I wouldn't lose sleep over it.

[jlwitherell]

seems like ebay seller "sign-shop" (Timmerman) sold foilcals, grill pegs, and other bits... I don't recall if he
also was the person who at one time made replacement L-pad knobs... might be worth contacting
if no one else remembers who it was that had been making these. I might be remembering incorrectly.
Maybe try the sketchy search feature here...

Also, if a 3Meg resistor to fail, the most likely scenario would be an open or intermittent, not a short...
so I wouldn't lose sleep over it.

LOL, nice, that's who I ended up getting the knobs from! Thanks Grumpy & hjames. Also, Grumpy - thank you very much for the single resistor failure scenario, that is exactly what I was looking for...

[jlwitherell]

Progress is still being made, I'll get some pics up shortly but coming up on a couple more questions:

1) As far as tuning; it appears original 4344's were tuned somewhere around 30hz or so (Anyone know the actual tuning Hz?). When I run WinISD 50hz tuning gives almost a completely flat response and steeper slope at around 50. Tuned to 30 gives a much more gradual slope, more on the low end, but losing some higher. What is the consensus on which method is better (what sounds better)? Flat with steep slope, or let her go lower like what appears was original? (I'm guessing that somewhere around 30hz will be what is recommended)

2) Back to the crossovers. For the charge coupled design do I put 3Mohm resisters at each charging spot, or one for the entire crossover and branch off of it?

Thanks for any help guys!
Josh

[Odd]

Try tuning to 32Hz

3 Mohm resistors at each charging spot.

[martin2395]

Try tuning to 32Hz

3 Mohm resistors at each charging spot.

That's a good question actually, why do you need a separate 3mOhm resistor for each pair when they still go to the same point on the battery?

[Odd]

That's a good question actually, why do you need a separate 3mOhm resistor for each pair when they still go to the same point on the battery?

You challenge my old school skills.
Ok, there is a voltage drop across each resistor.

[jlwitherell]

But what about the resistance change being in a parallel circuit (admittedly, within a crossover network I don't know how this actually would measure out). But, in true parallel the total resistance is the reciprocal of the added reciprocals of the various resistors: For four 8 ohm resistors in parallel, the circuit would read 2 ohms. 1/8 + 1/8 + 1/8 + 1/8 = 4/8 (reciprocal) = 8/4 = 2.