potentiometers in quantum line

[meridian]

Hello, for restoration of my QLS-1 I wonder how the 5 ohm potentiometers work. I do not have the originals and use 8ohm Yamahapotentiometers instead. On the internet I found that potentiometers have 3 contacts, the middleone being the whiper. It is mentioned that the resistance between the outer 2 should be a constant value (5 or in this case 8 ohms) and that the resistance between whiper and contact varies between 0 and 5 or in this case 8. However resistance between the outside contacts varies from 8 to infinite ohms...
Anybody can help me out?? Is this the same for the 5 ohm potentiometers used in the quantum-series?
Many thanks,
Meridian

 

[banffskiing]

Usually the pots will have an adjustable range of 270 deg but sometimes when you get to the limits, it will lose continuity completely hence you will read infinity. As for the difference between the 5 ohm and the 8 ohm pots
You will get a little more attenuation with the 8 ohm. Most likely you will have the pot adjusted somewhere on the middle so it shouldn’t make any difference. As for which of the three terminals you connect, find the one (measured from the wiper) that causes the resistance to decrease as you turn the pot clockwise.

banff

 

[Kencat]

Meridian,

Here are a few pics that may help out. The pot is just a coiled wire imbedded in the ceramic. The wiper center terminal is connected to the two outer terminals via the wire coil. As you said, the resistance between the outer terminals will be the total restance of the coil. 5 Ohms for the Infinity pots. At the center position, the resistance from center terminal to either outer terminal will be 2.5 Ohms. As the wiper is rotated, the resistance to a particular outer terminal varies with the distance of the contact to that terminal, the greater the distance the greater the resistance. Note that the resistances from the center to outer #1 + the resistance from center to outer terminal #2 adds up to 5 Ohms at all times.

The next picture is of the wiring in my Q2's. Note that the Midrange pot uses all three terminals, whereas the others only use 2. You should find that this matches the QLS-1's as well.

I have to disagree with banff's assesment though, that using the 8 Ohm pots makes no difference. The center position of the 8 ohm pot will give 4 Ohms vs the 2.5 Ohms of the 5 Ohm pot. Also, at the ends of the shaft rotation, there will be an extra 5 to 8 ohms that did not exist in original design. The center position now is attenuating more that design. This means that the shaft position will be off center for flat reponse of the tweeter and MBC, but, the midbass circuit is messed up with the series/parallel design (which I don't really understand, but I think the overall impedance seen by the amp to these drivers is now different from original design).

To know that those QLS's are at factory spec, I think you need those 5 ohm pots. Any issues with the midranges will be suspect untill you've got the correct pots in there.

Without being an electrical engineer, to me, (IMHO), any deviations from factory design can lead to unpredictable results.

Hope the pics help.

 

[banffskiing]

Ken
Guess I was only looking at the tweeter and the midbass circuits. On the schematics it shows only two connections to the pot while the midrange pot uses all three. I don't believe I would use the 8-ohm pots for the midrange since that would change the overall output to the mids regardless of the pot position. Also you are correct about the center adjustment position being 2.5 ohms VS 4 ohms. If Infinity's idea was to have the pots adjustable from -2.0db to +2.0db,(with center being flat) and you were using the 8 ohm pot, then the max attenuation would greater than -2.0db but as far as the max output, don't believe there is no diff. since you are only using two legs. And yes if it is adjusted to the center position it will not be flat at that point.

Now let me throw the wrench into everything.
The original pots that I removed from mine are all 8ohms and not 5, but the one's I just got from Infinity are all 5ohms. The originals are made in Japan and have 8 ohms stamped onto the back plate. Not sure if maybe there were replace at some time or not. Not sure but I think I will connect them as they are according to the drawings using the 5ohm pots. Also look at the picture of the original, it looks different from the one Ken has.

Meridian
What were the original values that you removed?

 

[banffskiing]

After a closer examination here is a schematic of the pots that were used in my qls-1. They were not using the 35 ohm side only the 8 ohm. so I guess this was a substitute or maybe it was all they had at the time. Also the end section of the 35 ohm resistor is coated with a material that does non conduct. So that once you turn the pot past 35ohms, it touches this coated material and the resistance goes to infinity.

Ken
looks like the pot you have is just a single resistor inside.
The replacements I ordered are like that as well 5ohms from end to end
and .2 to 5 from the wiper to either end pending which way you turn it.

 

[meridian]

Hello! I just finished my two speakers, throwing out all pots...
and using fixed resistors... I reinstalled the 13.6 MF in the midrange path and have no distortion anymore, so Kencats theory was correct.
Problem is that my speakers sound dull as midbass, mids and highs are connected through a 5 Ohm resistor... so the maximum decrease on the 5 ohms pots...
I hope to solve this by using a separate amp for bass and the others, allowing me to attenuate to my liking. Of course level of midbass, mids and highs cannot be changed between them. (except for a treble control on the amp...)
Banff, there were no original potentiometers to be replaced, they were simply not there. I measured my 8ohm potentiometers but value between the two ends seems to be way up in the 30ohms... Value between one end and the wiper is 0 to 8 and the other side 0 to more than 30 ohms or infinity...
As the impedance of the mids varies with frequency, the resistance of the parallel potentiometercircuitry is important: in a parallel circuit the lowest resistance gets the most energy. This could be why I had distortion and maybe damaged my mids with my 8 or 30+ ohms potentiometers...
Thank you very much for the pictures and schemes, I will wait for the original potentiometers to avoid more damage...
Looks like infinity was not so crazy after all, cheers!

 

[Kencat]

Hello! I just finished my two speakers, throwing out all pots...

:lmao: :lmao: Makes me think of the scene in the old movie Cannonball Run where the Italian guy rips off his rearview mirror and throws it away. Glad it all worked out Meridian. :thmbsp:

I will wait for the original potentiometers to avoid more damage...

Have you purchased some 5 Ohm pots , or did you win those Q2 xovers on Ebay (they went for over a 100$ this last time)?

Oh, aside from sounding dull, any other first impressions of the sound ? Bass response?

 

[Kencat]

After a closer examination here is a schematic of the pots that were used in my qls-1. They were not using the 35 ohm side only the 8 ohm. so I guess this was a substitute or maybe it was all they had at the time. Also the end section of the 35 ohm resistor is coated with a material that does non conduct. So that once you turn the pot past 35ohms, it touches this coated material and the resistance goes to infinity.

Ken
looks like the pot you have is just a single resistor inside.
The replacements I ordered are like that as well 5ohms from end to end
and .2 to 5 from the wiper to either end pending which way you turn it.

Banff,

Looks like someone put in some replacements that were more of an L-pad. Per the schematics, the simple 5 Ohm variable resistance pots should work as intended :yes: .

 

[meridian]

I finished both speakers! placement was a bit difficult but now I am getting good sound...
later more listening impressions folks!
I connected the woofers with the 4 ohms to the 1400MF as this gives the best sound...allthough banff and kencat advise otherwise?
I found calculator on the web and only this combination makes sense, giving a -6db dip at the resonance frequency 29-32Hz and impedance peak...
anyone tried calculating the filters before? they are first order and bandpass. Please try and let me know if you find the same results as me.

 

[Kencat]

Meridian,

Congrats on getting those finished :thmbsp:

Sounds like you are not quite happy with the sound though. ?

With the woofers, what is it about the sound that is better with VC1 on the 1400 mF cap??? What was deficient when it was the other way?

I am wondering if there was (is) a different problem still, that is being masked when you connect the woofers not to print. Are the midbass couplers and front tweeters wired out of phase with the woofers and mids?? If the midbass coupler is wired IN phase with the woofers, the resulting sound is horrible (I tryed it on my Q2's...took two songs and I could not stand it..put them back out of phase quickly).

As far as using the calculators....I'm not sure (pretty much doubt it actually)if they apply to the Watkins dual voice design. The two VC's act as a system to negate the impedance spike at resonance that would be on VC1 alone. There must be interaction between those 2 VC's wound on top of each other, and the choice of caps and inductors on each VC is probably subject to different mathematics and even developed through experimentation.

Did you swap only the caps, or did you swap the entire circuit with the inductors as well. I would guess the inductors are more critical here, as they dictate the higher frequencies that can get to the woofer.

I guess I could be totally wrong figuring VC1 is the 4 ohm and VC2 is the 2 Ohm. The schematic for the RS 2.5 shows this spelled out though (http://www.infinity-classics.de/infinity/technik/manuals/RS_2.5_technical_sheet.pdf)

The 20 mH inductor is on the VC2 for the RS4.5, RS2.5, and the Q1, Q2, and Q3 schematics. All this makes me pretty sure VC2 is the 2 Ohm coil.

Hey, how about that listening review btw???

 

[meridian]

watkinswoofer vc 1 or 2? listening impressions

First listening impressions:

Speakers are in a 9.5 m by 5 m wide room with an L cut out at the opposite end of 3*3meters. As I have installed 5 ohm resistors instead of potentiometers I have 2 use two amps to get the bass,mids and tweeters to play the same loudness as the bass.

Preamp is an acurus act3 or magnum mp 330 se ,amp in bass is magnum mf330 (english high end 2* 170 W on 4ohms ) amp on the rest is just a maranzt integrated pm-64 mkII... Turntable is rega planar 3.


Speakers are about 1 m from the rear and the side walls and about 6 meters from listening position.

good sides:
The high frequency selector is a bliss: ribbon highs are very delicate and sweet, even in my room wich is underdampened.
Voices and piano are clean. All the domes and tweeters make for a good record listening, they never seem to be "shouting " at you...
Room is filled at lower volumes too.
On movies they dig really deep

bad sides:
Something is missing, the real "feeling of being there" is clouded...
Imaging seems blurry? could this be due to the amps, or the midbass that is bipolar, too close to the wall and too loud (no potmeter remember?)...

Bassline I am unsure: vc2 is 2 ohms or 4????
With vc as the 2 ohms I seemed to get less bass...
to kencat: on the link you referred vc2 is indeed 2 ohms; but the 4ohms i connected to the largest capacitor!


Could anyone from the us maybe call mr watkins and simply ask (I am way over in Belgium...)

Seems to be the only way to know for sure...
Midbass and tweeters are out of phase, as on the scheme, only the rear tweeter is in phase with domes and bass.

 

[meridian]

watkinswoofer vc 1 or 2? listening impressions

First listening impressions:

Speakers are in a 9.5 m by 5 m wide room with an L cut out at the opposite end of 3*3meters. As I have installed 5 ohm resistors instead of potentiometers I have 2 use two amps to get the bass,mids and tweeters to play the same loudness as the bass.

Preamp is an acurus act3 or magnum mp 330 se ,amp in bass is magnum mf330 (english high end 2* 170 W on 4ohms ) amp on the rest is just a maranzt integrated pm-64 mkII... Turntable is rega planar 3.


Speakers are about 1 m from the rear and the side walls and about 6 meters from listening position.

good sides:
The high frequency selector is a bliss: ribbon highs are very delicate and sweet, even in my room wich is underdampened.
Voices and piano are clean. All the domes and tweeters make for a good record listening, they never seem to be "shouting " at you...
Room is filled at lower volumes too.
On movies they dig really deep

bad sides:
Something is missing, the real "feeling of being there" is clouded...
Imaging seems blurry? could this be due to the amps, or the midbass that is bipolar, too close to the wall and too loud (no potmeter remember?)...

Bassline I am unsure: vc2 is 2 ohms or 4????
With vc as the 2 ohms I seemed to get less bass...
to kencat: on the link you referred vc2 is indeed 2 ohms; but the 4ohms i connected to the largest capacitor!


Could anyone from the us maybe call mr watkins and simply ask (I am way over in Belgium...)

Seems to be the only way to know for sure...
Midbass and tweeters are out of phase, as on the scheme, only the rear tweeter is in phase with domes and bass.

 

[banffskiing]

Meridian

Just looked thru my notes for when I talked to MR. Watkins about 6 months ago. He said the low impedance was the solid black wire. That means VC2 the low and VC1 is the higher impedance. I played the woofers while they were not in the cabinet and the lower impedance coil only kicked in on the lowest frequency material. That kind of makes since otherwise, the overall speaker impedance might be even lower than it already is.

 

[meridian]

thanks to motivation and help from you guys I relooked at my speakers and reconnected them, with vc2 as the 2.2 ohms.
this time it seems to work out fine, strange but good

I also found away to use my potmeters too!
now I can finetune my mids and midsbass. first experiments helped already to clean up the bluriness.
I am curious for more now
thx folks!
Tuning will take time, I ve got the 2 amps to fiddle with and the two potmeters... Adjusting possibilities are great but offer an enormous amount of possibilities and finding the right 'on the spot ' one, takes time.
I'll let you know how the listening improves

 

[Kencat]

Meridian,

sounds like you are getting things slowly moving toward the better. That's great :thmbsp:

Man, you have a wonderful large listening room. I noticed though that you had the speakers at about 3 M apart, but your listening position was 6 meters. Have you tryed moving your listening position closer to the speakers ? This might help on the imaging...sounds like you may be too far back???

Experiment with the proximity of the speakers to the walls. Perhaps closer to the walls will help enhance the bass. It's hard to second quess room acoustics, but if you play around enough you can find that magic spot

How is it sounding now BTW ? (After the holidays are now over :beer: :drunk: )

 

[meridian]

After tweeking for a while I found the right sound!
allthough two domes are broken and one emit, sound is... superb.
Bassline is great on everything, on house music they pound really great making you want to turn it op, on guitar and piano they give weight and realness to the instruments. On movies you can hear how incredibly low they go... I only don't dare to turn them up to loud on movies as I don't want to break them...
Since I restored all the emits (except one) I now hear a complete speaker instead of parts of highs and bass mixed together.
Voices are wonderfull.
This is the best passive speaker I have owned (better then B&W 801 and nautilus 804). I am currently restoring my altec 512's active towers and my altec bias 550 monsters! these are still better in some aspects.
However due to the mediocre amplification on the mids and highs (integrated marantz) I think these speakers are not playing up to their full potential yet!
If I put them on ebay I will give a sign! there are currenly some watkins woofers on ebay in france (not mine)! get them folks!!!

 

[Tronhead]

Like you QII's. Mine were stolen in Colorado. Never got them back. It took at least two people to steal them and that was about all I could tell the police.
Great pair.