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Thread: Crown PSA-2X Indicator Lights Mono Mode?

  1. #1
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    Crown PSA-2X Indicator Lights Mono Mode?

    Last night I put the Crown PSA-2XH in the system. This is used in mono mode to push my W15GTI sub at 12 ohms or the W15GTI in parallel with a 2235 at 5 ohms total.

    On initial installation, using the unbalanced input, I had a ground hum. I removed the jumper strap and this partially helped the problem. I then undid the ground lug on the power plug and the unit now operates with dead silence.

    The bass is far cleaner and more powerful than my old amp could ever do (150 Watt dBX sub amp). In fact, using a dBX subharmonic synthesizer, I can turn both the bass boost and the subharmonic levels up to full with no distress from the amp or speaker..., something I could never do with the dBX amp.

    I put it in mono mode and used unbalanced input for Channel No. 1, as noted in the used manual. The volume control for input Channel No. 2 is set at minimum, also as noted in the manual.

    My question is related to the green indicator lights that denote 1.2 volts present at the output. It would seem to me that either the indicator light for No. 2 should come on and go off exactly the same as at Channel No.1, or should not light at all (most probably the former as the Channel is putting out power in mono mode). However, I note that this is not the case and while the lights do track each other to some extent, they are certainly not the same as expected. I can find no mention of this in the manual.

    Do other people with PSAs note this same thing or do your green lights come on and go off in unison in mono mode?

    When I had the unit open I replaced a diode (D113) for the indicator system, and while it is related to the green light, it is only used to keep the "error" light from false triggering.

    If other peoples unit lights run in unison, I'll reopen the unit and replace this same diode in the other channel (D213). If not, I'll call it done and button things up.

    Thanks,

    Todd



    Thanks. I need to know before I button up the cabinet again (a two person operation).

  2. #2
    RIP 2010 scott fitlin's Avatar
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    With no signal present, both green signal presence indicators should be off. They both light in unison when the amp is used in the bridge mono mode.

    The reason your able to push the amp harder than whatever you were using previously, is the PSA-2,s lower input sensitivity. It takes 2.1v to drive that thing to full output. But, it allows you to open up your crossover, and other signal processing, and this sounds great, as you already found out.

    The sound that amp has on the bottom is terrific. Tight, impactive, deep, and CLEAN!
    scottyj

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    Quote Originally Posted by scott fitlin
    With no signal present, both green signal presence indicators should be off. They both light in unison when the amp is used in the bridge mono mode.

    The reason your able to push the amp harder than whatever you were using previously, is the PSA-2,s lower input sensitivity. It takes 2.1v to drive that thing to full output. But, it allows you to open up your crossover, and other signal processing, and this sounds great, as you already found out.

    The sound that amp has on the bottom is terrific. Tight, impactive, deep, and CLEAN!
    EXACT unison, or just close to unison? My Channel No. 2 light seems to lag No.1 slightly (i.e., No.1 comes on first at a slightly lower volume setting).

    Actually in bridge mono mode, it takes 2.2 volts for full output. My old amp also had low input sensitivity and I was hoping the Crown would be a little higher. Not a big deal, I just run everything else a little quieter. (I'm using the unbalanced input and my balanced inputs have a fixed gain that may or may not be higher than the unbalanced input.)

  4. #4
    RIP 2010 scott fitlin's Avatar
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    Quote Originally Posted by toddalin
    EXACT unison, or just close to unison? My Channel No. 2 light seems to lag No.1 slightly (i.e., No.1 comes on first at a slightly lower volume setting).

    Actually in bridge mono mode, it takes 2.2 volts for full output. My old amp also had low input sensitivity and I was hoping the Crown would be a little higher. Not a big deal, I just run everything else a little quieter. (I'm using the unbalanced input and my balanced inputs have a fixed gain that may or may not be higher than the unbalanced input.)
    Ok, they run pretty much in unison, maybe not 100% but close enough.

    What you may be able to do, is take the amp to a Crown authorized service tech, and maybe they can change the fixed resistor back to a pot that you can then adjust to suit your needs! Its a small pot, Im sure they can find something, this is what I would do. The adjustable input sensitivity on the balanced input card was from 0v to 10v, this would come in handy.
    scottyj

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    Quote Originally Posted by scott fitlin
    Ok, they run pretty much in unison, maybe not 100% but close enough.

    What you may be able to do, is take the amp to a Crown authorized service tech, and maybe they can change the fixed resistor back to a pot that you can then adjust to suit your needs! Its a small pot, Im sure they can find something, this is what I would do. The adjustable input sensitivity on the balanced input card was from 0v to 10v, this would come in handy.
    Actually, no need to go to Crown. I just wanted to know if they were the identical or close. As I noted previously, when I opened it up to clean it, the wrench touched diode D113 (a glass diode) breaking its case. I replaced the diode with a 50 volt, 1 amp diode (circuit carries 15 volts) and was wondering if this could have caused the difference. While diode D113 is in the circuit for the green indicator light (hence my suspicion), the schematic notes both D113 and D223 (the same diode for the other channel) were a later addition that could be retrofitted to earlier units and their purpose is to prevent false triggering of the IOC light. I think it is doubtful that this is causing the signal lights to vary slightly, if yours also vary somewhat. If I really thought this to be the case, I would go back in and change D223 to a similar diode as D113 so that, hopefully, they would be identical again. The idea is to find out and do it before I put the entertainment center back together, a 2-person operation.

    If the sensitivity were that much of an issue, I could follow the schematic and change the fixed resistor back to a pot, or use a different value resistor. Nice of Crown to put the schematics on-line.

    Thanks




  6. #6
    Senior Member Rudy Kleimann's Avatar
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    My guess is the replacement diode. Is it in the display circuit?

    As an electronics hobbyist, I seem to recall that "glass" diodes are made with the semiconducter germanium as opposed to silicon. Germanium diodes are used in low-level signal applications, as they incur only about 0.3 volts across them to go into forward conductance mode, where silicon diodes require about 0.7 volts to conduct. perhaps the 0.4 volts greater voltage drop is throwing the display out of calibration on that channel.

    You are apparently handy with a soldering iron, so why don't you try to order the exact replacement, or if NLA, matching replacements for both channels? While you're at it, you could probably put in the input level pot too?

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    Quote Originally Posted by Rudy Kleimann
    My guess is the replacement diode. Is it in the display circuit?

    As an electronics hobbyist, I seem to recall that "glass" diodes are made with the semiconducter germanium as opposed to silicon. Germanium diodes are used in low-level signal applications, as they incur only about 0.3 volts across them to go into forward conductance mode, where silicon diodes require about 0.7 volts to conduct. perhaps the 0.4 volts greater voltage drop is throwing the display out of calibration on that channel.

    You are apparently handy with a soldering iron, so why don't you try to order the exact replacement, or if NLA, matching replacements for both channels? While you're at it, you could probably put in the input level pot too?
    I am aware of the voltage drop and exploit this feature of diodes on my garden railroad to slow trains in certain areas using multiple, cascaded 6-amp diodes for a constant voltage drop. This actually works better than resistors where the resultant voltage on the tracks is dependant on the load on the power packs (and engine).

    OK, being anal, as I assume most of us are, I re-opened the unit and pulled out the unmolested diode of the other channel. I read the forward and reverse resistances which were actually very low (under 800 ohms in one direction). I then went through my parts and came up with 30 diodes that I tested in a similar manner.

    The variance was actually quite extreme ranging from 21K to 4.5 megs in the same direction that produced about 800 ohms on the factory piece. I selected the two lowest values that were most similar to each other (about 0.4 megs in the same direction that read 800 ohms on the factory piece). I replaced the factory diode as well as the other that I had previously installed (that read about 0.8 megs in the same direction) and called it "good."

    I buttoned up the unit and perhaps the indicators track each other a little better. As before, Channel 2 typically lags Channel 1, but not always.

    Still, I had to know before I reassemble the cabinet; a two person job.

  8. #8
    RIP 2011 Zilch's Avatar
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    Resistance? You want to match the forward voltage drops, I would think, at the circuit operating current.

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    Quote Originally Posted by Zilch
    Resistance? You want to match the forward voltage drops, I would think, at the circuit operating current.
    Yeah right.

    I'm just trying to get two values that are near similar and based on the apparent change, or lack there of, I don't think that this component plays a part in the actual level that drives the display, even though it is in a portion of the display circuit.

    I'm satisfied that if going from a germanium to silicon diode with totally different, easily measurable, parameters didn't produce a really noticable change in the display between the two channels, the differences between two diodes from the same manufacturer and lot number with similar easily measureable parameters certainly wouldn't be expected to produce a difference.

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    Quote Originally Posted by Zilch
    Resistance? You want to match the forward voltage drops, I would think, at the circuit operating current.
    OK, I ran voltage drive on the good diode. The Crown schematic shows these as simple 1N4004 units, but this is definitely not the case!

    Using a 1.5 volt battery and a 10,000 ohm resistor, the voltage drop across the stock unit I took out of the Crown is more than 0.3 volts less than any of the various diodes I tested in a similar manner. And I tested all kinds of diodes that I pulled from my junk pile that includes a TV, VCR, power supply, and thermostat.

    Interesting that the diode has color bands red/brown/black that would indicate to me a 1N21, (though not all diode makers use the same code system) an extremely sensitive, discontinued part. Only thing is every 1N21 that I could find a picture of was metal encapsultated and looked nothing like a simple glass diode.

  11. #11
    RIP 2011 Zilch's Avatar
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    Use 100 Ohms to pass more current through the diode, around 10 ma using 1.5 V battery.

    Silicon diode should drop about 0.7 V, Shottkey or germanium, 0.3 V.

    I could easily see them using a forward-biased diode to establish a reference threshold for the indicator stack, but I'm don't have the schematic to know what they're doing in fact.

  12. #12
    Senior Member Rudy Kleimann's Avatar
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    Exclamation Resistance test?

    A resistance test on a diode really gives you nothing useful. Many volt meters manufactured in the last 15 years has a "diode test" function that is usually one of the settings in the "ohms" scale. This is specifically designed to indicate the threshold voltage at which the diode has sufficient voltage across it in order to achieve forward conductance.

    Because of the varying nature you have discovered among different brands of the same "1Nxxxx" type, the diodes in both channels should match each other in brand and type. I would change them both.

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    Quote Originally Posted by Zilch
    I could easily see them using a forward-biased diode to establish a reference threshold for the indicator stack, but I'm don't have the schematic to know what they're doing in fact.
    No problem. Pages 6-25 and 6-26.

    Thanks,

    Todd

    http://www.crownaudio.com/pdf/legacy...manual3of7.pdf

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    RIP 2011 Zilch's Avatar
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    They don't set a threshold. All I can see is that they prevent the output of u100d and u200d from dropping below -15.7 V. How that would false trigger the IOC lights, I don't get, either.

    What's "IOC" mean?

  15. #15
    Senior Member Rudy Kleimann's Avatar
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    IOC= "Input Output Comparator". Crown's Acronym for their clipping/distortion detection circuit.

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