Autotransformer Taps Questions?

[DizRotus]

Taps on the Fourth of July seems appropriate. Is the common ground (tap 0)[1] on the autotransformer always connected to ground?

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

After a diligent search of the forum, Ive located several charts that indicate combinations of squawker connections to the taps on the autotransformer to adjust the attenuation of the squawker, but I cant find the answer to the question above.

Currently, the autotransformer in the Type AA network has the following connections: 0 to common ground, 4 to Squawker (+) and 5 to 13 uF. Apparently that attenuates the squawker 3.8 dB. I want to go to 4.6 dB attenuation, which calls for connecting squawker (+) to tap 5 and squawker (-) to tap 2. Does tap 0 stay connected to common ground? Does tap 5 remain connected to 13 uF?

I am in the process of completing the bass reflex mod to the La Scalas that I restored for the high school band. I decided to do the version through the top vented out the back. In the unlikely event that the band director doesnt like the change, plugging the new hole in the bass bin would not be too difficult. Pictures and an evaluation of the results will follow. I expect to need to adjust the attenuation of the squawkers, i.e., the questions regarding the autotransformers.

---

[1] ALK Squawker level and the transformer instructions, page 1.

[Guest " "]

Taps on the Fourth of July seems appropriate.  Is the common ground (tap 0)[1] on the autotransformer always connected to ground?

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

After a diligent search of the forum, Ive located several charts that indicate combinations of squawker connections to the taps on the autotransformer to adjust the attenuation of the squawker, but I cant find the answer to the question above.

 

Currently, the autotransformer in the Type AA network has the following connections: 0 to common ground, 4 to Squawker (+) and 5 to 13 uF.  Apparently that attenuates the squawker 3.8 dB.  I want to go to 4.6 dB attenuation, which calls for connecting squawker (+) to tap 5 and squawker (-) to tap 2.  Does tap 0 stay connected to common ground?  Does tap 5 remain connected to 13 uF?

 

I am in the process of completing the bass reflex mod to the La Scalas that I restored for the high school band.  I decided to do the version through the top vented out the back.  In the unlikely event that the band director doesnt like the change, plugging the new hole in the bass bin would not be too difficult.  Pictures and an evaluation of the results will follow.  I expect to need to adjust the attenuation of the squawkers, i.e., the questions regarding the autotransformers.

---

[1] ALK Squawker level and the transformer instructions, page 1.

Very good question.

The closest I can get you to 4.6 using the t2a is a value of 4.5.

I attached the only schematic from klipsch that i have seen that shows the tap, atten, imped for the t2a.

For your question, the key goal is finding a tap setting that will yield approx a 3x imped value.

To get a value of 4.5, my estimates suggest that leaving tap 5 connected to in-line + and leaving tap 0 connected to in-line gound WHILE connecting the squawker + to tap 4 and the squawker - to tap 1 will accomplish a 3X imped step up value and provide the -4.5 closest value atten possible with the t2A.

please note the phasing arrangement on your version of the klipsch network. Some implementations reverse + and - on the squawker, is so, just follow thru at taps 4 and 1 using the same phase reversal arrangement.

There are other autoformers avaliable that have as much as 12 possible tap settings, but using the approach I just presented can provide a significant amount of flexibility in determining the step up or step down imped:atten.

If you want more combinations, let me know.

[DizRotus]

Thanks for the prompt response. It's not -4.6 dB per se that I'm trying to achieve, but rather one step down from the present squawker setting of (+) to tap 0 and (-) to 4 (See attached Type AA schematic). <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

One of the original proponents, if not the original author, of the LS bass reflex mod, djk, suggests (+) to tap 2 and (-) to tap 5. Dean G[1] also suggests that the stock setting produces -3.8 dB and that the setting suggested by djk results in -4.6 dB, but neither indicates if tap 4 should remain grounded and neither speaks to the existing connection between tap 5 and 13uF.

---

[1] See Dean Gs Autotransformers for Dummies (or the Mentally Deranged) attached to the next post.

[DizRotus]

Dean's handy autotransformer chart.

[Deang]

I should never have posted that chart. It was a cheat sheet for me and others who often work with the 3636 and 3619, but doesn't really offer much help for most. The charts assume you already have a basic understanding of how to use the units, and how to scale the parts values based on the various impedances that are presented in the different parts of the network.

The left side of the page shows the various attenuation settings if you do the following: 1) swamp the autoformer with a 10 ohm resistor, 2) float the ground for the squawker, and 3) scale the parts on the input side of the autoformer to account for the lower reflected impedance. I recently saw an example of a person doing this who didn't do #2 and #3 -- and then stated they didn't care for the sound using the swamping resistor -- not surprising.

The right side of the page reflects the attenuation settings if the autoformer is not swamped with the resistor, and the taps are fixed. However, with each step down in attenuation, the reflected impedance goes up -- and this lowers the capacitor value at the primary position. The chart also assumes one knows that tap X on the 3619 is an output tap, but an input tap on the 3636, and of course -- the T2A has neither of these taps, and the 3619 has no 'Y' tap. At any rate, the intent of the sheet wasn't meant to act as a primer for network design -- just a cheat sheet I made up for myself to help me keep things straight in my head -- since at the time I was working with both units in different ways.

If you want the finer increments in attenuation for the squawker that the autoformer provides -- you have to build another network. IOWs, you have to swamp the autoformer with the resistor, float the ground for the squawker, and change 13uF to 40uF. You should change the tweeter filter too -- if you want to do it right.

[Guest " "]

DizRotus

There are approx 30 possible combinations for using the taps on the t2a autoformer as an imped multiplier, at least 10 of them are inverses of each other.

So, sure, I could probally come up with at least 4 taps setting combos that achieve any specific goal.

[DizRotus]

I realize that many combinations to achieve many levels of squawker attenuation are possible and that finer adjustments could require reworking the network. That is not my present concern.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

At present I only need to know what to do with the existing common ground at tap 0 and the existing connection of tap 5 to 13 uF. If, as djk suggests, I move (+) from tap 0 to tap 2 and move (-) from tap 4 to tap 5, are the existing connections of tap 0 to common ground and tap 5 to 13uF maintained?

[Guest " "]

I realize that many combinations to achieve many levels of squawker attenuation are possible and that finer adjustments could require reworking the network.  That is not my present concern.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

At present I only need to know what to do with the existing common ground at tap 0 and the existing connection of tap 5 to 13 uF.  If, as djk suggests, I move (+) from tap 0 to tap 2 and move (-) from tap 4 to tap 5, are the existing connections of tap 0 to common ground and tap 5 to 13uF maintained?

>

you are getting three different answer to your question from three different folks, all of which, if veiwed independently, are correct.

If you want to implement djk's solution, disreguard my accounting of the associated taps settings for the solution I provided. My solution requires 5 and 0 as well as 4 and 1 to be used. So my solution is not compatible with either Dean"s or djk's.

In terms of Dean's solution, I'll defer to him, if his solution is compatible with djk's implementation.

I think if you seperate the 3 different senerios, you will have 3 options on how to accomplish the change you intially asked about.

[Deang]

Tap 0 always connects to common.

If you don't swamp the autoformer with the 10 ohm resistor, float common for the squawker, and change 13uF to 40uF -- you're not going to get 5 and 2 to give you 4.6dB of attenuation.

With 13uF and fixed taps, you get -3db, -6dB, -9dB, and -12dB. With your current configuration, all you can do is drop to tap 3 to get another 3db of attenuation -- but then you have to add a 15 ohm swamping resistor in parallel with the squawker (across pos and neg on the barrier strip) to keep the crossover point from shifting. If you don't want to use a resistor, then you have to change 13uF to 6.5uF.

[DizRotus]

After studying the AA schematic, I was certain that tap 0 had to stay grounded and that the lead into the autotransformer from 13uF should stay in place at tap 5 (sounds like a Brubeck song).

Alas,I confess ignorance. How would I "float common" and "swamp the autoformer" as you suggest ? Please recall that these are used in a band room, not in a home 2 channel system. What is the simplest and least expensive way to attenuate the squawker, if necessary?

Thanks Dean.

[Deang]

What is the simplest and least expensive way to attenuate the squawker, if necessary?

I provided the solution in my last post, "...With your current configuration, all you can do is drop to tap 3 to get another 3db of attenuation -- but then you have to add a 15 ohm swamping resistor in parallel with the squawker (across pos and neg on the barrier strip) to keep the crossover point from shifting. If you don't want to use a resistor, then you have to change 13uF to 6.5uF."

[DizRotus]

Dean,

I have ordered the caps necessary to make the change from 13 uF. I'll also try the 15 ohm resistors becuase they're inexpensive and I want to compare them with the cap change. I expect to use the caps as the permanent mod.

Thanks again for a prompt and informative reply.

I still would like to understand how and when to "float the ground."