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Smoke & Fire - Good Times and Blow Amplifiers

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  • prosigna
    started a topic Smoke & Fire - Good Times and Blow Amplifiers

    Smoke & Fire - Good Times and Blow Amplifiers

    I was adding my subs to an installed system in the local colleges theatre for a ballet. The installed system is composed of a pair of Peavey PV-112 mains with no subs, some Realistic speakers hanging in the lighting rig above the stage as monitors. All run by a pair of Peavey CS-800x4 4-Channel amps and a small Mackie mixer in the booth. Since the ballet has a very fine selection of music the lack of bottom end in this system has bothered me and I volunteered to add my subs.

    My subs are a pair old Peavey SP-118 driven by a PV-1500 amp in bridge mono using the internal crossover of the amp.

    I took the amp up to the alcove where the theatre's amps are and tried to figure out how to patch into the system. There are two patch panels in this alcove - one is a typical 1/4" TRS patchbay normalled passing the signal between different line sources and the 8 amp channels. The other is a 1/4" TS speaker patching panel attaching the amp outputs to the various 1/4" locations backstage and in the orchestra pit. I plugged a bannana-to-1/4" adapter into the amp in bridge mode, plugged a 12-ga 1/4" speaker cable from the adapter to the "A" speaker patch point going to the pit and began studying the signal patchbay. Pretty soon there was an oder, smoke, light inside my amp (where there are no LEDs), protect lights were bright red, then flames. A resistor on each channel's board burned up. I shut it off, metered the jack I had patched into, and it measured OPEN.

    Went home and grabbed a dinosaur CD-800, the really heavy ones from the early 80's. Patched it in and got the subs working but with a serious hum. Lacking adapters or more cables I put off tracking down the hum until the next day - it didn't seem to bother anyone in the production other than me.....

    Returned with many adapters, solder station, cables, the who tool kit for finding a ground loop and fixing the hum. Now when fired up channel B's LED would glow bright RED and channel 1 on one of the installed PV-800x4's began to glow bright green. This channel has no input signal and should NOT be flashing. I began to isolate the hum but then the output to the subs was much lower than earlier. These subs with this amp in this empty room should thump when AC/DC Thunderstruck is played.

    The Technical Director for the college is a great friend, a true artist, set designer, and lighting guru. He is not a sound man but he has wired up the whole system. I am beginning to help him understand where to lift pin 1 and also to NEVER CUT THE EARTH GROUND OFF THE POWER PLUG. I am very concerned that the speaker patch panel has fried two of my amps. This panel is a steel panel with standard panel mount 1/4" TS jacks. It dawned on my this was connecting the Neg. post of all the amp channels together - all 8 channels of the CS-800x4s and whatever amp I patched into the jacks leading to the pit. Also, in the pit the jacks are all panel mounted to the patch panel. Connecting the negative is in best case - it assumes no one flipped polarity between the speaker output and the patch point.

    Would y'all agree the speaker patch panel causing community between the negative posts is "bad" and possibly fried my amps?

  • Phil O'Keefe
    replied
    Originally posted by agedhorse View Post

    The bummer for you is that your amps are going to need fairly costly repairs.
    Yeah, it sounds like he let the magic smoke out - and everyone knows they won't work without the magic smoke. And magic smoke is expensive to replace...

    Leave a comment:


  • agedhorse
    replied
    In bridge mode, the sleeve MUST be isolated/floated through the patch bay and ALL associated wiring.

    What you have encountered is a common situation with installations not designed/installed by pros who understand the details underlying WHY things are done.

    The bummer for you is that your amps are going to need fairly costly repairs.

    Leave a comment:


  • Dookietwo
    replied
    There is a question I have. Is there the " Jumpers " installed in the crossover and PL-2 island sockets? The 1/4 inch jacks won't work if the jumpers are not installed. They sort of look like shinny Caps that plug into these sockets. Seen in picture. Click image for larger version

Name:	lg_For_Parts_or_Repair_Peavey_CS_800_Commerical_Series_Power_Amplifier_(6).jpg
Views:	1
Size:	70.4 KB
ID:	32438857
    Last edited by Dookietwo; 01-11-2019, 05:37 PM.

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  • Dookietwo
    replied
    Originally posted by prosigna View Post
    LIke you said - pin 1 is lifted and 2 and 3 are swapped. But since the amp is grounding 2 to1 - then you are running what was 3 - now phase reversed - into ground. This does not seem like you have actually isolated the ground but have grounded pin 3 of the crossover to pin 1 of the amp. If you are going to connect Crossover pin 3 to amp pin 1 why lift pin 1 to start with?
    No , pin 1 is grounded , not lifted in the Cs800 so its like any other XLR input to a power amp. The problem is Pin 2 is combined to Pin 1 through a circuit Peavey called Quasi Ground which was fine back when the amp was manufactured as all Peavey Mixers, eq's etc used Pin 3 as positive and pin 2 as neg. Today the standard is pin 2 for Positive. The CS800 amp you have doesn't have a Normal Balancing input. In a normal Balanced input Pin 1 is ground , Pin 2 is Positive, and Pin 3 is reverse polarity of pin 2. A balancing circuit Reverses the Polarity of Pin 3 and Combines it with pin 2 for a 6 db increase in output and any noise that was picked up in effect canceled out. The quasi ground system takes pin 2 and through a circuit shunts it to ground. If you reverse pin 2 and 3 going into the amp it now takes pin 3 and shunts it to ground (not a problem for your crossover) and the pin 2 positive that comes from upstream (mixer / crossover ) goes to pin 3 of the amp as Positive. So it doesn't effect equipment up stream from the amp. This also maintains proper polarity if your using this amp and a modern one to drive subs that are close together. If you want true balanced input you'll need a Peavey PL-2 balanced input can. Then you'll have a true balanced input. I have the quasi ground PC schematic somewhere. I'll see if I can find it.

    https://www.bing.com/images/search?q...ns&FORM=HDRSC2

    Edit for clarity. Right now coming out of your crossover Pin 1 is ground, Pin 2 is Positive , Pin 3 is reverse Polarity of Pin 2. By putting Pin 2 INTO Pin 3 of the amp you are keeping your crossovers Positive Pin 2 from reaching ground. Pin 3 from your crossover shunted to ground is not a problem in sound quality or other issues. Pin 2 positive into Pin 3 on the old Peavey amp is the same as going to a modern amps pin 2. Peavey tried to set their own standard back then. With out the Pl-2 balancing transformer its not a true balanced input.
    Last edited by Dookietwo; 01-11-2019, 05:21 PM.

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  • prosigna
    replied
    LIke you said - pin 1 is lifted and 2 and 3 are swapped. But since the amp is grounding 2 to1 - then you are running what was 3 - now phase reversed - into ground. This does not seem like you have actually isolated the ground but have grounded pin 3 of the crossover to pin 1 of the amp. If you are going to connect Crossover pin 3 to amp pin 1 why lift pin 1 to start with?

    Leave a comment:


  • Dookietwo
    replied
    [QUOTE=prosigna;n32437603 Also since 1&2 are bonded a phase reverse is ineffective.[/QUOTE]

    This I don't understand. The CS 800 bonds Pins 1 and "2" to the quasi ground circuit. Input Pin 3 is hot. Plug a normal Pin 1 ground Pin 2 hot , Pin 3 out of phase cable into the amp and 1 and Postive 2 are connected and this is shorting the normal hot. A Phase reversal XLR can or cable will put Pin 2 into pin 3 and Pin 3 into pin 2. So now pin 1 and 3 are connect together and this isn't seen as a problem other than the loss of 6 db's of gain in a "True" balanced input. I had a few patch pin reversal cables I used all the time and it always worked as it should.

    Leave a comment:


  • prosigna
    replied
    I have run into a number of amp manuals that say something similar to "in bridged mode all speaker wires must "float" above ground". That is a phrase that never sunk in until this week. lol. I checked that patch point on the panel before plugging in to be sure it was empty - metered as open - so I proceeded. Expensive lesson learned.....

    The issues I was having with the CS-800 was due to worn out 1/4" jacks on the back of the amp. I think they are all shot so I soldered up an XLR patch special for this amp - avoiding any 1/4" inputs I was using to patch the single input from the crossover to both channels. A phase-reverse/ground lifted Y-cable built special for the cs-800. Since pin 1 and 2 are bonded in the amp a pin-1 lift adapter was ineffective. Also since 1&2 are bonded a phase reverse is ineffective. I am now the proud owner of a phase-reversing, ground-lifing, Y-cable. Basically pin-2 of the female is soldered to pin 3 of (2) males. Nothing else is connected. Ground has now been isolated AND pin three is hot. Everything works quietly and with power to spare.

    The technical director and I are going to replace the steel panel in the speaker patch bay with a piece of Plexiglas to prevent any future issues. Also we will replace the (4) 1/4" jacks in on the patch panel in the pit with isolating panel mounts.

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  • Dookietwo
    replied
    Originally posted by prosigna View Post
    Thanks. I am aware of the pin 3 hot issue and the strange pin-out for the XLR. What is it you think I did that could have damaged circuits in their system? The XLR of the amp never touched their system - it ran up to the sub out of my crossover. The crossover was being fed by the system.

    I got the CS-800 back up and running correctly. We moved it down to the sub location - avoiding any of the installed speaker patching. The PV-1500 is on its way to the shop for repair - hope it can be revived for a reasonable price.
    As I'm sure you know by the sound of your post that all equipment is tied together by the ground. At the very least you shorted Pin 1 and 2 together at the crossover Sub output. I didn't know it was your crossover. I also don't remember the value of the CS-800 quasi-ground circuit and the load it gave to the crossover. I started out with the CS400 and 800's before they even had the DDT protection's in the output. Like you I don't like the fact that all the amp grounds may have been tied together at the patch panel. A look at all the amps that were used circuits should show you more. The first amp you tried was digital I believe. I had a PV 2600 for some time but can't remember for sure if it was digital or not. I do remember it being rock solid. Some of those amps are a bridged output design even in stereo mode and may have not liked that patch panel shared ground at all. The old CS800 boat anchor may have humed/buzzed and soldiered on. Hate to say it but you missed it. Hard to say what the cause of the first amp failure was but it wasn't the patch panels fault it was the operators. Trust but verify! Like you I know how tough it is to walk into someone else's problem. No good deed go's unpunished!

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  • prosigna
    replied
    Thanks. I am aware of the pin 3 hot issue and the strange pin-out for the XLR. What is it you think I did that could have damaged circuits in their system? The XLR of the amp never touched their system - it ran up to the sub out of my crossover. The crossover was being fed by the system.

    I got the CS-800 back up and running correctly. We moved it down to the sub location - avoiding any of the installed speaker patching. The PV-1500 is on its way to the shop for repair - hope it can be revived for a reasonable price.

    Leave a comment:


  • Dookietwo
    replied
    Page 4 , patch panel 1. https://assets.peavey.com/literature...s/80300068.pdf

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  • Dookietwo
    replied
    Remember the older CS- series amps XLR inputs are not the same as standard amps today. They wired PIN 1 to ground, Pin 2 NEG (out of phase), and Pin 3 HOT. Also it has a Quasi Ground system in them shunts pins 1 and 2 through a circuit if your not using PL-2 balancing transformer cans in the socket for them. This is taking your current systems Hot, pin 2 , and shorting it to ground through the quasi ground circuit. VERY not good!
    Today's standard is Pin 1 for ground, Pin 2 for Hot and Pin 3 for Neg (out of phase)
    At the very least make a cable that reverses Pin 2 and 3 before it plugs into the CS800 amp you have or purchase a pin reverser to try. Something like this.

    https://www.parts-express.com/in-lin...SABEgL6WPD_BwE

    By doing what you did you may have damaged some circuits in their system. Google your cs800 amp and learn about it.

    Leave a comment:

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