Query on Compensation Circuit

[ngccglp]

I did a search and noticed that the model 19 compensation circuit uses a 6 uF bypass cap. But many other forumers claimed to use a bypass cap of about 1 to 2 uF for an 8 ohm driver. Anybody know why there is such a big difference in cap values?

Thanks.

I'm using the 802-8D with the 511B.

[DNV47]

Check out the below link to a Lansing Heritage post. I found it to be extremely helpful in understanding the Model 19 xover.
http://audioheritage.org/vbulletin/s...826#post128826
But to answer your specific cap value question, isn't the value of the cap in parallel with the resistor "padding" network dependent on the cap value before the resistor padding network? Maybe I have this wrong but I thought if the series cap before the padded network is larger in value, then the parallel cap is smaller in value.

[ngccglp]

Thanks. Its a very interesting thread.

[ngccglp]

Hi,

I've managed to buy some 8 ohm L-Pads and built the equalization Model 19 circuit N1201-8A.

May I know whether R1 = High Freq LPad , R3 = Mid Freq Lpad

OR

R1 = Mid Freq Lpad , R3 = High Freq Lpad.

Thanks

[ngccglp]

Hi,

Could you explain 0-35 ohm for a 8 ohm Lpad? I thought an 8 ohm LPAD only gives 0 to 8 ohms of resistance? How to get 35 ohms of resistance?

Thanks.

[Tenorman]

An L-pad has two different resistive elements. One element, connected from lug 3 to lug 2, varies from 8 ohms in the full counterclockwise position to 0 in the full clockwise position. This would place it in series with the load (HF horn).

The other element, connected from lug 1 to lug 2, varies from 0 at full counterclockwise to 35 ohms and infinity at full clockwise in parallel to the rest of the load (HF horn plus 0-8 ohm pad) as to balance the load and result in a total of 8 ohms.

This explains it best:

http://colomar.com/Shavano/lpad.html

Also, on the schematic, note the "Min" and "Max" markings on R1 and R3.

When R1 is turned full clockwise, it is 0 ohms and L1 is shorted out of the circuit, and the HF horn is full on. When R1 is full counterclockwise, L1 is back in the circuit with the 8 ohms in parallel to it, adding some slope to the woofer and cutting down the horn.

When R3 is turned full clockwise, it is 35 ohms or infinity. When it is full counterclockwise, it is 0 ohms.

[Tenorman]

Sorry, could not edit my post... what I forgot to add was, these two L-pads, in this circuit are not being used as L-pads, but rather ingeniously used simply as variable resistors.

[Tenorman]

And to clarify my statement about "35 ohms and infinity", at full clockwise the L-pad's wiper should run off the end of the track of the 35 ohm element and read infinity on your meter, otherwise at full on, with an 8 ohm load, the total would be only (35 x 8)/(35 + 8) = 6.5 ohms.

The first little nudge off the full clockwise position will connect the 35 ohm portion.

[Tenorman]

For that crossover, R1 is the 0-8 ohm portion of an 8 ohm, 100 watt L-pad, connected to lugs 2 and 3 of that L-pad. This L-pad controls the overall level of the HF horn.

R3 is the 0-35 ohm segment of an 8 ohm 100 watt L-pad, connected to lugs 1 and 2. This L-pad controls the midrange.

[Tenorman]

The purpose of R6, the compensation capacitor in that crossover, is to lift the top end where the horn/driver combination tend to roll off. The exact value of the capacitor would depend on the particular horn/driver combination used.