Have a POT ( potentiometer, rheostat) in your Crossovers ?

[LowOhms]

Do you have POT ( Potentiometer) in your Speaker-Level crossover ??……..


or, ........ helping out many ALTEC OWNERS


The “ideal” Altec speaker – level crossover would NEVER EVER use a potentiometer or a rheostat to pad down the tweeter level, to match our less-efficient woofer. If you currently use a crossover with a potentiometer, you are seriously degrading your ALTEC’s potential fidelity and in-the-room performance.

The finest solution to this degrade is to change out the POT for a fixed value wirewound power resistor, that is properly soldered in place, using good solder. I realize, many want to keep a POT, for the ease of adjustability, so here goes :

The problem with any potentiometer ( rheostat ) is the wiper arm to resistive element interface. First, the contact area between the wiper arm’s conductive material, and the pot’s resistive area is a small one,. Second, it employs a mechanical connection, not a soldered one, and this connection is MOST inadequate electronically.

Due to this small ( inadequate) contact area, music’s instantaneous peak currents, during playback, are truncated, emasculated, and distorted. Dynamic range, and fidelity suffer. High frequency noise, distortion, and audible irritants occur due to the wiper-element interface, what is called the diode effect, from the mechanical connection, NOT equaling a soldered-in power resistor..

The best solution with speaker-level crossovers is to place just one speaker in the middle of the listening room, and select a compromise Ohmic value resistance, to pad down the tweeter. Both speakers should then have installed in them a high quality, higher power ( 10 Watts or more) resistor, equal values for each speaker, soldered in place, to pad the tweeter .

Such ALTEC speakers then need to be placed in the room, with symmetrical corners and side walls. The end-user should methodically, over time, position the two ALTECS by listening to music, so to find the best sounding speaker location, and overall balance, in the end-user’s listening room.. Only a few of you on this Forum may be willing to do this. I intend to do this in Q1/2017.

OK, I would like to show you all a FAR better way to employ a POT in your speaker level crossover. For a large number of discriminating listeners, this is an easy, reversible DIY implementation.

My most trusted audio friends like the sound of Ohmite resistors. For decades, Ohmite has made a 25 Watt “H” Series 25 Watt potentiometer, a good sounding and nicely engineered part. “ H “ stands for “ heavenly “ .

In January 2017, I found I can achieve easy and substantial sonic benefits, by using TWO such pots, where one previously existed. The two are mounted in what is termed “ dual ganged” or “ in tandem “ or “ concentrically ”.

These two Pots are then electronically connected in parallel, at each of their three terminals. The pots' Ohmic value needs to be doubled, due to paralleling, and the Ohmic values should be EQUAL to each other. For example, if your circuit calls for a 20 Ohm pot, parallel two 40 Ohm “ H” 25 Watt pots, which becomes a 20 Ohm 50 Watt rated pot.

The HUGE advantage is that you now have two wipers, to pass the audio signal to the driver. Law of Squares, you can now pass two squared, or four times the instantaneous peak currents, inherent in music playback. Audible distortion goes down, you have less inherent diode effect.

So, what did “I” hear, going to two paralleled pots the first time, on January 4, 2017???

- a far more natural sounding presentation

- better harmonics and colors of the instruments

- far better inner - detail

- audibly better dynamic delineation

- far less distortion in the entire tweeter range


Can I ever go back to a single potentiometer in a speaker level crossover?? You have to be kidding me, NO WAY ! I will eventually go a fixed, soldered-in resistor. Maybe a 10 Watt Ohmite , they have an “ Audio Gold ” series, and I use Wonder Solder ( Mike Percy ) for solder connections.

In my next post, I can perhaps put forth some ideas of how to most economically execute this.. Ohmite makes a “ rheostat tandem coupling kit ”, part number 6532 which it sells for about $65 a throw, and I will show you how to DIY duplicate it functionally, at ACE hardware, for less than two dollars in carefully selected hardware store parts. Stay tuned., that’s another post, with photos, if there seems to be sufficient sincere interest.



Low Ohms, …………Jeff Medwin

[LowOhms]

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Got a POT in your Speaker-Level Crossover?... Improve it . - drlowmu - High Efficiency Speaker Asylum

Have FUN, I am !!

Low Ohms .... Jeff Medwin

- - - Updated - - -

[horndawg]

Thank you for sharing your findings. As a suggestion, you could also try the 50W or 75W rated pots made by Ohmite in place of the paralleled 25W rheostats. They are the JS and GS series rheostats. From the spec sheet, one 25 Ohm 75W rated pot, has a higher max current rating than two 50 Ohm 25W units run in parallel.

In addition, using a single pot simplifies the install process and saves both time and money. The money part is not insignificant as there are 4 pots and 2 coupling kits required. Following some research online, I was able to find the 25W pots at around $36 ea. and the kits at around $50 ea. That's $244 before shipping and taxes for a stereo parallel pair. Compare this to the cost of two 75W rated rheostats at around $104/pair.

[Todd W. White]

I have a pair of ALTEC MODEL 6's in my office. Each has 2 rheostats. All 4 are dirty and have rendered the Model 6's unlistenable. I would like to disconnect the 4 rheostats and replace them in the circuit with fixed resistors.

Not sure how to select the right values without taking up a lot of time and going a bit nuts in the process.

[BillWojo]

Hi Todd, really the only thing you can do is clean them good with deoxit, assemble and adjust to where you like them. After that either live with them or carefully pull them and measure where they are and replace with heavy duty wire wound non inductive resistors.
If they are 30 years old and have never been cleaned, a good cleaning might get you quite a few more years out of them. They make both a cleaner and a lube. I would give it several good cleanings and than lube them.

BillWojo

[LowOhms]

Hi Todd, really the only thing you can do is clean them good with deoxit, assemble and adjust to where you like them. After that either live with them or carefully pull them and measure where they are and replace with heavy duty wire wound non inductive resistors.
If they are 30 years old and have never been cleaned, a good cleaning might get you quite a few more years out of them. They make both a cleaner and a lube. I would give it several good cleanings and than lube them.

BillWojo

Thats good solid advice. My suggestion to consider: How about carefully positioning ONE speaker in the middle of the room, after cleaning the stock pot, and determine an OHMIC VALUE. Then, replace the pots in both speakers with a GOOD high power FIXED resistor, soldered in place, which will easily sound better than ANY pot can. Position the speakers individually, in the room, for best balance, with fixed resistor crossovers. That is the best way to do it, assuming flexibility of speaker positioning in your work place.

Low Ohms.....Jeff

[Elitopus1]

What if one speaker is in a corner and the other is along a straight wall? I think its better to use HF padding that makes the speakers sound equal rather than putting equal padding in each speaker.

I suppose you could put acoustic panels on each side of a corner speaker instead of padding it more. If WAF allows

[LowOhms]

What if one speaker is in a corner and the other is along a straight wall? I think its better to use HF padding that makes the speakers sound equal rather than putting equal padding in each speaker.

I suppose you could put acoustic panels on each side of a corner speaker instead of padding it more. If WAF allows

Good question.


Do NOT confuse equal or unequal Ohmic padding of two tweeters, with the use of any Pot versus a FIXED and SOLDERED-IN resistor !!!

Move both the speakers to another set of walls, maybe 90 degrees in the room, so that both speakers have corners. That is EXACTLY what I have to do, in my living room, in the coming weeks. I will then listen near-field, with some acoustic paneling behind my seat on the wall in back of me.

Presently, one pot, for the VOTT in the open hallway, is 3.14 Ohms, and the other VOTT, in the corner, at about 0.78 ohms. ( I use the equivalent of 9 AWG to each terminal of my 515B driver, so I don't need to pad the tweeter as much , and enjoy better overall transfer efficiency, two 57 1/8th inch runs of m22759/11 12 to each woofer polarity, 14 AWG to the 802, single runs.)

Find an average " compromise Ohmic value ", ( maybe listen to one speaker in the middle of the to-be-used wall, loaded against it ) and DUPLICATE exact same resistor value for each speaker. A pot, even my much improved double 25 Watt Ohmite F pots, can not compete with the improved sonics I get with a fixed highest-quality SOLDERED-IN resistor.

Your wife will LOVE the resultant sound, especially if she has already LET YOU put VOTTs in 'de living room. I am single.

Jeff .......... Low Ohms