Hi all, quick question. My crossovers have 2 pots each to adjust highs and mids. One of the mids pot is completely shot and the other one reads funky. Tweeter pots seem OK but they're 42 years old.
According to schematics, all pots are 5 ohm 5 watt:
But in real life, they're clearly different. Folks say the mids pots are 15 watt and the tweeters 5 watt, and that looks plausible:
My first thought was to just replace the old pots... but audio grade 5 ohm 15 watt pots only appear to exist in Australia
So now I'm considering replacing them with fixed resistors, since their utility is debatable to begin with.
I tested them (out of circuit):
Now for my questions:
a. That mid pot's 3.4 ohm halfway to 5 ohm read doesn't match a known taper. Is it fair to assume it was linear when new, and it just drifted over the decades?
b. I want a "flat" response, so I'm thinking 2.5 ohm fixed resistors (assuming those mids pots are in fact linear). As far as power rating, it's tough to find 5 and 15 watts in the same series but Dayton makes 2.4 watt, 1% wirewound rated 10 watt and 20 watt, so I'm leaning that way and it won't break the bank. Still, it would mean a significant increase in power rating over stock
c. I've done a bunch of reading about whether increasing resistors' power rating can affect sound quality, and the consensus seems to be that it won't make it worse and it might even make it a little better. Do you guys concur?
d. Now we're splitting hairs, but I gotta ask: my new fixed resistors will probably have much lower inductance than the pots they replace. Does that mean anything in terms of sound quality?
Thanks!
According to schematics, all pots are 5 ohm 5 watt:
But in real life, they're clearly different. Folks say the mids pots are 15 watt and the tweeters 5 watt, and that looks plausible:
My first thought was to just replace the old pots... but audio grade 5 ohm 15 watt pots only appear to exist in Australia
So now I'm considering replacing them with fixed resistors, since their utility is debatable to begin with.
I tested them (out of circuit):
- Tweeter pots measure 2.5 ohm at midpoint and 5 ohm all the way down, so that's all good per specs
- The one mid pot that sort of still works measures 3.4 ohm halfway, and 5.7 ohms all the way down. The other mid pot is too far gone to measure anything.
Now for my questions:
a. That mid pot's 3.4 ohm halfway to 5 ohm read doesn't match a known taper. Is it fair to assume it was linear when new, and it just drifted over the decades?
b. I want a "flat" response, so I'm thinking 2.5 ohm fixed resistors (assuming those mids pots are in fact linear). As far as power rating, it's tough to find 5 and 15 watts in the same series but Dayton makes 2.4 watt, 1% wirewound rated 10 watt and 20 watt, so I'm leaning that way and it won't break the bank. Still, it would mean a significant increase in power rating over stock
c. I've done a bunch of reading about whether increasing resistors' power rating can affect sound quality, and the consensus seems to be that it won't make it worse and it might even make it a little better. Do you guys concur?
d. Now we're splitting hairs, but I gotta ask: my new fixed resistors will probably have much lower inductance than the pots they replace. Does that mean anything in terms of sound quality?
Thanks!
Get those 20w they are cheap and good. You will not hear any affect on the sound quality with any of those.
Also, there is no way you can say what’s more linear without measurements. Actually, there is nothing linear about the response of the speakers, just the way they were making speakers those days. Buy 4 5 ohm resistors that way you can have 5 ohm and if you need to boost one of the levels you can parallel them to get that 2.5ohm
Also while you are in there change all the electrolytic to film caps. Any cheapest from PE will be better than what it is there now. I see those are big values, so you can get new electrolytic.
Also, there is no way you can say what’s more linear without measurements. Actually, there is nothing linear about the response of the speakers, just the way they were making speakers those days. Buy 4 5 ohm resistors that way you can have 5 ohm and if you need to boost one of the levels you can parallel them to get that 2.5ohm
Also while you are in there change all the electrolytic to film caps. Any cheapest from PE will be better than what it is there now. I see those are big values, so you can get new electrolytic.
I'm not sure your technical level, but personally I dislike using power pots for the same reason you are replacing them. Whenever possible sub a single value resistor.
Also, some infinity crossover designs suffered from less than optimal impedance curves brought on by last minute changes. I wouldn't do much to an Infinity crossover without first checking to see if there were upgrades which improve the impedance and or measuring the speakers electrically (using DATS or Room EQ Wizard) first. If you could find an online impedance curve that shows it to be a reasonable load then you'd be all set. If the curve is bad (i.e. has very low points) then consider a crossover rethink before replacing any parts. Not to mention that any electrolytic cap left in that could well be out of spec by now.
Also, some infinity crossover designs suffered from less than optimal impedance curves brought on by last minute changes. I wouldn't do much to an Infinity crossover without first checking to see if there were upgrades which improve the impedance and or measuring the speakers electrically (using DATS or Room EQ Wizard) first. If you could find an online impedance curve that shows it to be a reasonable load then you'd be all set. If the curve is bad (i.e. has very low points) then consider a crossover rethink before replacing any parts. Not to mention that any electrolytic cap left in that could well be out of spec by now.
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@PKI
I recapped my crossovers already, using the cheapest from PE indeed 🙂 I left the big 600uF and 1600uF caps alone though, they tested just fine (actually every single cap I replaced tested just fine).
On the other hand, the two power resistors on each side were in bad shape. Both 5.4 ohms showed signs of severe overheating yet still tested more or less OK, but one of the 9.4 ohms was open. I replaced them all with the aforementioned Daytons.
I recapped my crossovers already, using the cheapest from PE indeed 🙂 I left the big 600uF and 1600uF caps alone though, they tested just fine (actually every single cap I replaced tested just fine).
On the other hand, the two power resistors on each side were in bad shape. Both 5.4 ohms showed signs of severe overheating yet still tested more or less OK, but one of the 9.4 ohms was open. I replaced them all with the aforementioned Daytons.
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@eriksquires
Here is RS-II's impedance curve:
As you can see there's a 3 ohm dip above 100 Hz, while the EMITs are basically a 2 ohm load. Nothing terrible, though amplification needs to be planned accordingly if they are to sound their best.
I would not mess with crossover design honestly. These speakers would need so much to be up to modern standards, starting with a full rewire. It's a slippery slope I'd rather not get on. My goal is to put them back on the road at reasonable cost and effort while staying faithful to the original Arnie Nudell design. Properly driven RS-II are really fantastic sounding speakers.
Here is RS-II's impedance curve:
As you can see there's a 3 ohm dip above 100 Hz, while the EMITs are basically a 2 ohm load. Nothing terrible, though amplification needs to be planned accordingly if they are to sound their best.
I would not mess with crossover design honestly. These speakers would need so much to be up to modern standards, starting with a full rewire. It's a slippery slope I'd rather not get on. My goal is to put them back on the road at reasonable cost and effort while staying faithful to the original Arnie Nudell design. Properly driven RS-II are really fantastic sounding speakers.
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Just to be clear........ These are not "POTS"........
They´re called L-Pads.
Totally different technology. They consists of 2 windings, so that when lowering the impedace of one, you raise the imp. of
the other. This so the crossover sees a constant imp. no matter the setting, so the regulation "only" alters the volume and not
the crossover fequency.
They´re called L-Pads.
Totally different technology. They consists of 2 windings, so that when lowering the impedace of one, you raise the imp. of
the other. This so the crossover sees a constant imp. no matter the setting, so the regulation "only" alters the volume and not
the crossover fequency.
@Boydk
Thank you for your post. L-pads confuse me, honestly, so let me ask you this:
What i am trying to determine here is which replacement components I should get if I do keep tone controls as opposed to going the fixed-resistor route.
Thank you!
Thank you for your post. L-pads confuse me, honestly, so let me ask you this:
- Looking at the schematics and the pic I included in my original post, do you see evidence that the two physical controls (the "pots" themselves) are L-pads and not pots?
- If they were L-pads, wouldn't all 3 terminals be wired, instead of just 2?
- And if they were L-pads, shouldn't the schematics show a diagram of a wiper swiping two coils of resistance, instead of just one coil as shown?
- If I replace them with fixed resistors (there's a new wrinkle here, but more on that later), then the point is moot anyway, correct?
What i am trying to determine here is which replacement components I should get if I do keep tone controls as opposed to going the fixed-resistor route.
Thank you!
Not too bad, but a generally punishing load in the treble for the amps of the day.
Given the wiring they do look like simple pots. If one or the other speaker has one set correctly you can use it to gauge the resistance you need, or just buy a bunch of 2 ohm + 0.5 Ohm resistors. 🙂 Personally I like Mills for quality as well as size. They are remarkably small for the power rating, so long as they stay well ventilated.
Given the wiring they do look like simple pots. If one or the other speaker has one set correctly you can use it to gauge the resistance you need, or just buy a bunch of 2 ohm + 0.5 Ohm resistors. 🙂 Personally I like Mills for quality as well as size. They are remarkably small for the power rating, so long as they stay well ventilated.
I should have written a little more. You can make your own resistive ladder to determine exactly how much R you need. Wire together:
0.5R -- 0.5R -- 2R -- 2R
and use jumpers to pick any input output for almost any combination from 0.5R to 5R in 0.5 Ohm increments. 🙂 I guess in this arrangement 3.5R is not possible, but you get the idea.
0.5R -- 0.5R -- 2R -- 2R
and use jumpers to pick any input output for almost any combination from 0.5R to 5R in 0.5 Ohm increments. 🙂 I guess in this arrangement 3.5R is not possible, but you get the idea.
Anyone that looks at the posted schematic or the picture will see that there are only two connections made to each of those those potentiometers. So even if they were L-Pads, without three connections they would behave exactly like a single potentiometer. I'm not sure why Boydic was so confident with this wording. He's absolutely right in that most well designed crossover typically use L-pads so the crossover point would not change with attenuation. If these were my speakers I would put a 4 ohm L-pad in place of those pots and connect all three terminals of the L-Pad.
Was that a new, condesending way to write my name?? If so, you left out a K 🤣
Did it ever occur to you, that maybe the schematic was drawn wrongly?? Wouldn´t be the first time, someone confused
the "open end" way of drwing the symbol for L-Pads
Only way to check is physically look at the actual crossover in person, to see how it´s connected.
I won´t believe for a second, that a speaker brand like Infinity would put a "POT" in series with a speaker-voice-coil,
thus f-ing up the frequency response/crossover freq. by adjusting the level of mid´s and high´s.
EDIT: See the picture now..... only saw the schematic yesterday.
What a terrible way of doing things....... I´m baffeled by the poor standard.
If it was me, I would by 2 L-Pads and do it the "right" way, when already planning to change parts.
It would be nothing other, than a great improvement.
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I didn´t see the picture yesterday. Hopefully I´ve explained myself in the post above (#11) 😉
Should note that as drawn, the L-Pads have a very wide range. If we imagine the wiper reaching the bottom of the drawing, the two terminals of the driver are then connected to the same conductor, which by definition has 0 volts across it and the driver is then effectively shut off. 😉
Again I'm not too cozy with L-pads, so two quick comments:
- They only seem to come in 8 and 16 ohm, which is quite a ways from the original 5 ohm?
- They would involve changing the original wiring in which only 2 pot terminals are wired to one in which all 3 terminals are. What would go where? I kind of feel like redesigning crossovers is a bit of a stretch for me honestly
Boydk: Sorry for the error. I was sitting 12 feet from the screen in the recliner and the k sort of looked like ic from back there as I typed quickly to get off to dinner.
Here's a guy selling 4 Ohm L-pads. It could be wired as the original simple variable resistor, using IN & OUT, or you could attach the ground to have it work as an L-pad with constant source resistance. If you have a measurement microphone you could see what effect it had on the crossover.
https://www.ebay.com/itm/305931078452
The other option is to just spin the knobs ten times to clean the contacts or spray some contact cleaner in there.
Here's a guy selling 4 Ohm L-pads. It could be wired as the original simple variable resistor, using IN & OUT, or you could attach the ground to have it work as an L-pad with constant source resistance. If you have a measurement microphone you could see what effect it had on the crossover.
https://www.ebay.com/itm/305931078452
The other option is to just spin the knobs ten times to clean the contacts or spray some contact cleaner in there.
I heard back from the Australian supply house that carries the 5 ohm 15 watt potentiometers I linked in my first post. Cost for two would be US$41 including air shipping, which is actually pretty reasonable.
So we have 3 options here:
1. L-pads
2. Fixed resistors
3. Australian pots on mids + keep original twitter pots which test and operate fine
If I'm understanding the theory correctly, L-pads used in conjunction with the original wiring (2 terminals wired) are simple variable resistors? If so, it misses the point of using them. I'm also not comfortable modifying the original wiring, I figure that if Arnie Nudell had wanted L-pads he would have used them and designed for them.
So... Option 2 or option 3? What say you?
PS - @olsond3 I've tried deoxit on the mid pots and they're too far gone
So we have 3 options here:
1. L-pads
2. Fixed resistors
3. Australian pots on mids + keep original twitter pots which test and operate fine
If I'm understanding the theory correctly, L-pads used in conjunction with the original wiring (2 terminals wired) are simple variable resistors? If so, it misses the point of using them. I'm also not comfortable modifying the original wiring, I figure that if Arnie Nudell had wanted L-pads he would have used them and designed for them.
So... Option 2 or option 3? What say you?
PS - @olsond3 I've tried deoxit on the mid pots and they're too far gone
It looks like you need a majority vote, so make a poll option and see what comes on a top. It all comes to you to decide in the end. People have their preferences and opinions. I posted mine above, so did other people 🙂
An 8 ohm 15W L-Pad attenuator should work, just connect it as a rheostat, it won't change the crossover design and give you more adjustment range. My 2¢.
It may come down to what part best fits in the space. L-Pad or rheostat, either will work. I would set what ever you get to 3.4 ohms and note the position and install it.