SDA2 B crossover question

alandharper
alandharper Posts: 34
edited January 31 in Vintage Speakers
Hello all. I am new to these speaker, although I have done a bit or reading in this forum. Where to start. I got my pair a month or so ago. No Interconnect cable so I made one. I checked it for continuity and all was well. I also checked my amp for common ground It was. These are pin blade. When I used the blade, it was clearly not good. Something was grounded that shouldn't be. I was going to do a recap, so I started taking them apart. The blade of the interconnect is clearly wired to the ground of the speaker connects. I checked the interconnects from the inside and nothing was accidentally grounded. My confusion grew much worse when I checked continuity on the P3 section of the crossover board. There is continuity between + and -. I am lost. I should add that with the blade of the interconnect cable was not used, but the pin was, they sounded fine. I am lost and hoping for some clarity. Thanks in advance guys.
Post edited by [Deleted User] on
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Comments

  • F1nut
    F1nut Posts: 46,296
    When using the AI-1 or Dreadnought isolation transformer the blade connection is used. In your case all you need is the pin connection as long as you are 100% certain your amp is common ground.

    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • First of all thank you. I know you are correct simply because I have read many of your post and you are very knowledgeable on these speakers. Im just trying to decide why the blade, or negative would be there if I dont need it. I also dont have any Idea why the Positive and negative on the dimensional driver show continuity? That is to say, the contacts on the crossover board show that. That cant be right or good?? My effort is to learn. Thanks again for lending your expertise.
  • Sorry to be long winded. I thought these might help. These are untouched, by me at least. P3 is where I get continuity. I also question the bridge at L5? Like I say I am looking forward to an education. It is what I love about doing these type things. I learned to rebuild a fully automatic Dual turntable recently. Very satisfying. Thanks again to all for the lessons!e41ae4ybs7ua.jpg
    z24mlk8qab3x.jpg
  • Gardenstater
    Gardenstater Posts: 2,026
    edited February 1
    Hi, have you checked the schematic for your crossover? You say "continuity", but what DCR (resistance) do you measure? It looks like there should be continuity there but it would measure the resistances of the stereo driver plus three inductors. I'll bet that if you take one of the faston connectors (either the + or -) off of the stereo driver, you will no longer have continuity. If you are getting continuity there with all drivers disconnected from the board, then I think you must have one or more capacitors shorted out.

    I think F1 was saying to you that *if* you didn't have a common ground amplifier, you would need a Dreadnought and in that situation the blade would be used.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • OK. Just so yo know, I don't know what I'm doing with a multimeter. But I measured the board as it is out of the cabinet as you see it. I got a continuity reading from my multimeter by touching + to - on P3. I thought that was wrong or strange. I do get what F-1 was saying. My thinking is, if Polk says to use only a common ground amp, which I am, then why if I am following the direction of the manufacturer would I not use both pins of the interconnect cable. It just seems odd? I'm certainly not saying he is wrong, I just don't get it.
  • pitdogg2
    pitdogg2 Posts: 19,502
    well because polk designed them to be able to use non-common ground or monobloc amps. They (polk) also designed a cable with a small transformer called AI-1 (amplifier interface 1) the blade came into play because you need a ground to connect all the negatives at the end of the chain. In your case the blade just acts as a stabilizer to support the pin. think of it as dual function.
  • OK. I guess my concern was 2 fold. When I plug it in, bad things happen. It seems to ground the amp in a bad way. That's why I was looking for something wrong in the crossover. And secondly, I wanted to make sure I was getting all that these speakers had to offer when not using that ground wire. I see that talked about a lot. I have also seen where F-1 says using the AI-1 isn't really the best because it degrades sound quality. I just want to make sure and make the absolute best from these speakers. Finally I would like to say, I just like to understand how things work. Maybe some people don't care, but its part of the fun of it all to me.
  • Gardenstater
    Gardenstater Posts: 2,026
    Ha ha no problem. I too like to understand how things work. I think you should read up on how to use your multimeter first.

    Then, I would download and read the SDA Handbook, especially the parts about your speakers and the schematic for your 2B's.

    Then, I would check all the capacitors to see if any of them are shorted (zero or near zero resistance), especially the 20uF and 40uf
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • OK. So I have a personal question. If you were going to buy a new flavor of multimeter, and not break the bank, what would you buy. BTW, I have ordered all new caps and a new resistor. New tweeters as well. My multimeter I used in construction work for house electrical and I can barely read the settings anymore.
  • pitdogg2
    pitdogg2 Posts: 19,502
    You shouldn't have "bad" things happen when using the cable.

    Also you made a homemade cable. I'd have to think if it's giving you problems then something with the way the cable is made is not right.
    I've made many cables and only used the pin from an RCA jack after I ground off the ground petals.
  • Gardenstater
    Gardenstater Posts: 2,026
    Hard question to answer because I don't know what you want to be able to do. If you want it to be able to read capacitance then make sure you get one that does. The basic ones only read up to 20uF. If you want to be able to read milliohm resistances well basic multimeters only read to nearest 100 mOhm and you will need a more expensive meter that has more digits and has zeroing function preferably.

    Can you measure resistance with the one you have? That's all we're talking about right now. If you clip the two leads together does it show zero or near zero?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Well to be clear, the RCA part of it works like a champ. I cut off the pedals as well. Only when the blade side is connected do bad things happen. The cable is nicely made. I did check it to be sure. I guess I just feel like Im not using it right if I dont use the blade side. But like I say, when the blade to blade connection is made along with the pin pin something is grounding out.
  • Truthfully, I cant read mine anymore. The setting that is. I know by heart where volts are, and I can see where the "buzzer" setting is for continuity so thats what I was using. I need a new one anyway. Just looking for suggestion. Does HD or The Other L word have any decent ones. Amazon maybe? Brands? Just some direction would be appreciated.
  • Gardenstater
    Gardenstater Posts: 2,026
    edited February 1
    You didn't answer my questions ^^ :) I personally have 4 meters and I find them adequate for checking circuit resistances and continuity and so on. I wish I had a better one; one that has more than 4 digits and can measure capacitances that are much higher than 20 uF and milliohm resistances.

    If that is all you want to do, then get a brand new one (you will be able to read it!) from Harbor Freight for $7.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • I didn't answer because I was avoiding the question. B) . I dont think that its doing much when in the buzzer setting other than saying yes or no to a connection. If Im going to get one and learn to read it properly, I dont mind spending more than 7 bucks on it.
  • Gardenstater
    Gardenstater Posts: 2,026
    As long as your problem isn't visual impairment then take a picture of your meter and I'll tell you how to set it to read resistances. It would be the lowest setting on the dial past the continuity setting. Most meters still give you a resistance reading in addition to the buzzer on the continuity setting.

    If visual impairment is part of the problem, then you'd better make sure you get one from a brick and mortar store so you can hold it in your hand and determine for yourself whether or not you can read the settings.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Ummm. The settings have been worn off from traveling around in a tool box for several years. Are Tenmas any good? I have a Microcenter near me and they are reasonable if they arent junk. Model 72-10395
  • Gardenstater
    Gardenstater Posts: 2,026
    edited February 1
    Tenma. That's a 3999 count auto-ranging meter. Auto ranging is usually better because the meter picks the appropriate range to get the best resolution. It has a high input impedance of 10MOhms which is very good. It takes a 3V coin cell CR2032 which are $3 for two online. I don't know if most brick and mortar stores carry them but at least they aren't expensive.

    I like that it can read capacitance up to 100uF with a resolution of 0.1uF. Good for checking capacitors in audio crossovers.

    I don't like that it apparently has a resolution of 0.1 Ohms so the smallest it can show is 100mOhms. That might not matter to you. It also does not zero out so you will have to subtract the resistance of the test leads.

    It won't be able to check inductance value of the inductors in your crossovers which is a pretty cool feature that probably not very many meters have. I would like to have that also. Don't know how expensive such meters are.

    It seems to only come with basic needle probes. It would be good to have alligator clips also but I'm sure you can get those as a separate purchase somewhere.

    http://www.farnell.com/datasheets/2371078.pdf

    http://www.farnell.com/datasheets/2609252.pdf

    PS: No reviews on amazon and I don't have any personal experience with the brand.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • [Deleted User]
    [Deleted User] Posts: 7,659
    I've used Tenma instruments for a very long time.
  • F1nut
    F1nut Posts: 46,296
    I have also seen where F-1 says using the AI-1 isn't really the best because it degrades sound quality.

    I believe you have taken something out of context.
    Well to be clear, the RCA part of it works like a champ. I cut off the pedals as well. Only when the blade side is connected do bad things happen.

    Your amp is not common ground. You can't test this stuff simply using the continuity setting.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • pitdogg2
    pitdogg2 Posts: 19,502
    What amp is it ?
  • Gardenstater
    Gardenstater Posts: 2,026
    I went back to look at schematic again. I had previously thought P3 was the stereo driver output, but I now think it is the Tweeter ouputs. Nothing is labeled P1, P2, P3 on schematic.

    If that's the case then there should be conductivity between those two points through what looks to be a 0.4mH inductor. This is one of the schematics with the nightmare from hell midget font (Autocad?), and a low resolution scan. So whatever your meter reads will be the DC resistance of that inductor and would definitely cause continuity buzzer to go off.

    Get the SDA Handbook and look at your schematic

    https://us.v-cdn.net/5021930/uploads/editor/qx/d5a14j8apinc.pdf
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Ok. Thanks to all who chimed in first. So generous. F-1, yes I have realized I need to learn to test this better. working on a new multimeter that would work better. Mine was for house wiring. I don't know why I remember you saying the AI-1 degrades the sound. Sorry about that. The amp I was using is a Rotel RX 1052. I am switching to my NAD 7175PE because it has an outstanding phono preamp. I have a Adcom GFa 555II in the works.
  • F1nut
    F1nut Posts: 46,296
    Ok, that Rotel is a stereo receiver not an amplifier. I'd be surprised if it is not common ground.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • I do think that it is. The NAD can for sure be used as a preamp, and The Adcom has been said to be a good match. It was recently gone through and is fresh. I would like to Test these for myself. Partly for confirmation and partly to know how to do it properly. I just can't read the setting on my old meter.
  • Gardenstater
    Gardenstater Posts: 2,026
    What make and model# meter? Look up the owners manual where there will be pictures of the dial and instructions on how to use. Problem solved hopefully.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Capital Electric MAS830B
  • Gardenstater
    Gardenstater Posts: 2,026
    Is this it? Looks like the 200 Ohm range setting is the lowest it has and that is 1 click CW from the continuity. That will give you a resolution of 0.1 Ohm

    https://www.mgl-euman.com/downloads/OEM-Catalogue-EM_05_2020_EN.pdf

    ewq375tvwhjp.jpg

    yesc9xyet6t3.jpg
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • To add to my question, in this photo, in positions C4 and S1. I believe S1 is the poly switch that is best to be removed and a jumper in its place. What about C4. should it stay? Also the black switch (not pictured) on the tweets wire. Does she stay or should she go. Anyone who has listened to these in both or all combinations please give your insight. Thanks again guys. I have all my parts, I really want to educate myself and test my new plus my old caps to see where they were in error.
  • And.... forgot the photom33381li2akq.jpg