Building the 4345/4344

[B&KMan]

The layout....I just followed the schematic

Ian

Hello again Mr Mackenzie...

I continue my quest of information for buiding a DC charge blend caps for replace my 3143 networks (4343)

Do you have a better pict and any complementary info for modificstion of schematic ???

Thanks for all

Jean

[geowal3]

Hope I can interject a related question here about the 3145 "equivalent circuits" provided by Giskard for Ian’s 4345 project, without twisting this thread too badly.

I don’t understand much at all about these circuits but am confident I can assemble them. I am working up a variant of a 4345 (triamped, 2245H, 2123H and 2441/2405, crossed over at 250 and 1100Hz). Many thanks to Ian for all his detailed posting on "how to", and all the others that contributed so freely of their time along the way, especially Giskard!

Will the equivalent circuit for the 2421 work for the 2441? I am assuming that since they are both 16 ohms nominal that they will. Secondly, in both the 2405 and 2421 equivalent circuits, there are resistors shown in series with the inductors; are these actual resistors or are they just the resistance values of the inductors?

Many thanks!

[Ian Mackenzie]

I am away at the moment, I will try and respond by the weekend.

Ian

[4313B]

My original equivalent circuit:

[4313B]

New simplified proposal - someone with custom 4344's would have to give it a try. It should be perfect.

DCR values are extremely important and this model is based on Jantzen 18 and 20 AWG coils.

Use gangs of resistors to achieve proper power handling.

[4313B]

Hope I can interject a related question here about the 3145 "equivalent circuits" provided by Giskard for Ian’s 4345 project, without twisting this thread too badly.

Will the equivalent circuit for the 2421 work for the 2441? I am assuming that since they are both 16 ohms nominal that they will. Secondly, in both the 2405 and 2421 equivalent circuits, there are resistors shown in series with the inductors; are these actual resistors or are they just the resistance values of the inductors?

I edited the schematics to show the DCR.

You can try it with the 2441 and let us know what happens.

[Ian Mackenzie]

I am curious, what are the differences in the voltages drives b/n the equivalent circuit with the simplified schematic?

Ian

[4313B]

Orange is "old equivalent", green is "new equivalent", white is actual "tapped autotransformer" model.

Orange was done from 1981 Engineering Design Specification voltage drive using datapoints - all L-Pads open - all 8 ohm dummy loads.

There is enough slop in the L-Pads that both are viable - the new model should be cheaper to build with less parts.

[geowal3]

Many thanks Giskard! I certainly will provide feedback on "what happens" using a 2441 at the end of this project - but it will be a while.

I see another possible pitfall, but don't know enough to evaluate the problem. The graph below shows output of the electronic crossover I am working with. ("Stuck with" would be more apt - it's fixed at 1100 Hz 24db/Oct and built into a BGW triamp, and there no changing it now).

Is there a problem in with the way that the high pass "new equivalent circuit" for the 2441/2421 will "see" the input from the electonic crossover, and/or a problem between the MF output to the 2123 and the new equivalent circuit?

[Robh3606]

"Is there a problem in with the way that the high pass "new equivalent circuit" for the 2441/2421 will "see" the input from the electonic crossover, and/or a problem between the MF output to the 2123 and the new equivalent circuit?"

You have me confused The electronic crossover will be driving the amp. The speaker crossover will see a bandwidth limited input from the amp and filter it the same way as a fullrange signal. Is that rise in HF response real on the graph??? If it is it will change the response independent of the crossover. You may be able to use the 2405 trim pot to get most of it. It will change the slope a bit on the 2421/2441 roll off to the 2405. Can you tailor it for flat response by changing out part values in the crossover?? OK You have a 3 way active crossover at 300Hz and 1100Hz. The HF driver is a 2421 or 2441 and the UHF is a 2405?? Why are you concerned with the High crossover point?? You only have to build the low pass half of the 2421/2441 filter and the 2405 High pass. Once you match the attenuation between the 2421/2405 the active will set the average level for both drivers and you will have the pots to adjust. The 2123 is bracketed by the filters in the active crossover and should not be affected at all. I also run an active 4 way with points at 50Hz 300Hz 1200Hz same slopes 24dB L/R. Use the same midrange driver 2123. It should work fine using the passive between the 2421/2441 and the 2405.

Rob

[geowal3]

Rob, appreciate the carefully crafted response. Sorry I have you confused - I thought I was the one confused. Your bottom line is very reassuring! Here's what I think I know:

1. Yes, the rise in HF response is real. As I understand it, it is designed in to the beast as purpose built for a JBL 2441 and a CD horn - but don't hold me accountable on that! However, I don't believe that is a problem for me. First, I am 61. Second, in my former life I spent 27 years in the army, about half of it around tanks. So my ears are probably "down" something like 150dB @2500Hz or whatever. (It's not that bad, I know I can here above 7K for sure!!)

2. IF there is a problem in the HF or UHF range, as you say, the pads in the passive crossover may handle it, but I cannot make any changes in the electronic crossover (WAY over my head!). I would not tackle it myself, and having BGW (or, actually the company that bought them out in 2003) do it would probably be comparable to the cost of, say, a space shuttle launch.

3. In my very limited understanding, it seems there may be a "gap" between the 2123 and the 2441, (how do I say this?), because the 2123 (MF) is "down more" on the triamp graph relative to the output to the 2441 on Giskard's graph. Even more amateurishly put I suppose, in Giskard's graph, the 2441 lower end is related to a particular slope for the MF (in my case a 2123 but I don't think that is relevant). On the triamp graph, the MF output appears to match the HF output at a lower point (maybe 1020Hz?) than on Giskard's graph (maybe 1080Hz?). Am I reading the graphs correctly, and if I am, is this a problem? Or will adjusting the output levels of the triamp handle this "discrepancy"?

Thanks for your patience!

[Robh3606]

Hello geowal


Giskards graphs also show the network attenuation that is needed to match the drivers outputs. Both the 2421 and 2405 need a good bit of attenuation because of their higher sensitivities. With the active crossover as long as you can adjust the individual drivers you should be fine.

Rob

[geowal3]

Thanks for the insights Rob. I have been trying to get down to the brass tacks of ordering components for these networks. Two concerns arise.

First, Giskard says to use "gangs of resistors" for proper power handling. How do I determine the handling capacity to shoot for ? The 2441 is rated at 150 Watts @ 1KHz, but I would never come close to cranking it that high, so what's a reasonable level? I realize this is a flaky question, but can someone provide a rough guideline?

Then, once that answer is in hand, how do you determine the number and value of resistors to satisfy a given requirement? Let's say the desired power handling capacity is 60 watts, and, as an example, let's take the 15 ohm resistor in Giskard's HF network in post 170. Using 10 watt resistors, I would need six 90 ohm resistors in parallel, correct?

Secondly, I have been researching numerous threads on the forum to learn more about what capacitors to get. What a blackhole topic that is !!! Along the way I have read quite a bit about charge coupled networks being very worth the extra expense. Presuming that would be true in this case, how would these circuits be modified?

[4313B]

First, Giskard says to use "gangs of resistors" for proper power handling. How do I determine the handling capacity to shoot for ?

Well you could use a calculator program as found here.

[woodstocksound]

Under Construction

This thread will be dedicated to those members wishing to construct the vintage JBL 4345/4344 Professional Series Studio Monitors.

Over the next few weeks I will document blue prints (in JBL Blue..LOL) and provide a Step by Step Guide to Enclosure and Crossover Network Design & Construction.

Some of you will have already been this route with the 4343 so please your collective wisdom and knowledge is most welcome

Ian Mackenzie.

Rob ,do you know of anyone who would have the drawings for the JBL 4550 BKA cabinet ? Any help would be much appreciated. Thanks... Darryl /Woodstock Sound