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Old 4th January 2013, 11:10 PM   #31
Enzo is offline Enzo  United States
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Q102,103 are lmiters, but they are not there to limit idle current necessarily. They work by shunting the signal at the bases of Q100, 104, the predrivers. If the output is slammed over to a rail, they can't do much about it.

If an output xstr shorts, it often takes out the emitter ballasts, those pairs of 1 ohm 5w. When those open, that leaves the p[oor litle 2200 ohm resistors as the remaining current path, and they burn up.

75v on the output, with 10 ohms across? Your speaker was capacitor isolated, so while it may show its impedance to the signal, it wonl; show any resistance to the idle current. In any case, I figure that 75v is the peak of about 53vRMS if it were a signal, and into 10 ohms I get about 280 watts. I don't expect this amp to be limiting anything at 280 watts.

You want to get 0.6v on the base of Q102? Then you need to get that much voltage dropped across those pairs of 1 ohm. But wait, there's more. Those 2200 ohms act along with the diode and 100 ohm across the BE of Q102. They form a voltage divider. SO get enough current flowing through those 1 ohms to make enough voltage drop to make it through that voltage divider to turn on Q102. Takes a lot.

Put your MOV across the transformer primary. That will protect the circuitry, but still be on the amp side of the breaker. NO new fuses required.

I have attached a crude hand drawn AC wiring for this amplifier. MAybe it will be useful to you.
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File Type: pdf PV PV1.3K AC wiring.PDF (27.6 KB, 53 views)
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Old 5th January 2013, 02:39 AM   #32
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Thanks for the AC schematic. I wasn't sure I could avoid dropping screws or standoffs to take the AC board off and trace it out.
Thanks for explaining what a "VI" limiter does. Takes significant current to make this one (Q102,103) restrict base drive current to the predriver transistor, I suppose. Yes, I replaced a bunch of 1 ohm 5 W emitter resistors, too, when i replaced the Output Transistors.
The hand drill is too long to fit in there and drill the hole for the enclosed screw terminal strip on the transformer bulkhead, without taking the transformer out again. To screw the MOV and CL101 turn on surge NTCResistor into. On the back wall they go with the fuseholder, thanks anyway. No more dimming lights at turn on, I hope.
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Last edited by indianajo; 5th January 2013 at 02:43 AM.
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Old 31st March 2013, 03:51 PM   #33
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hello there, this might be qiute off topic but i've recently bought an old pv 2000 that is in reletively good nick but i've heard bad things about running them into 2 ohm. Is this true or are they unreliable at that level?

cheers
mikkel
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Old 31st March 2013, 07:25 PM   #34
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Enzo will be along eventually, but I would be suspicious of 2 ohms per side at 1000 watts per side. That would be sqrt(500) or about 22.6? something amps, out of three power transistor pairs. That sort of violates the safe operating area chart of the MJ15024-25, don't you think? You could do that level for a little while which meets the FederalTradeCommission specifications for watt rating years ago, but the heat sink would heat up eventually in a band or bar setting. At 2000 watts would be happier with a PV-1.3k with 5 output transistor pairs per side even though it doesn't carry the rating on the nameplate. The guy that sold me the CS800s was running the SP2-XT speaker in parallel with a 15" woofer horn monitor speaker for 4 ohms on that amp for his band setup. That amp has 4 output transistor pairs.
If you bridged the two sides of a 2K and ran mono, 2 ohms on 6 transistor pair would be more of a sure thing. I don't have any speakers that will take this level and I run my SP2-XT at about 60 W peak 1/8 watt average in my living room, so you really need to hear from band sound men or bar owners.
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Last edited by indianajo; 31st March 2013 at 07:34 PM.
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Old 31st March 2013, 09:04 PM   #35
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Im sorry but 50% of that answer is beyond me. The plan was to run 4 kick bins into 2 ohms per channel (350 - 400w each) and it is supposed to be used in an outdoor setting. Do you think its better off run them in bridged mode to achieve this or are you saying that i would have been better off buying a pv 1.3k for running into 2 ohm?


I'm sorry i don't understand the detailed technical side of your answer but it is appreciated regardless.

Many thanks
Mik
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Old 31st March 2013, 09:32 PM   #36
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I suspect the rumors you have heard are right. I think the 2k watts name of the PV-2k is probably a short term rating rather than full time rating. It may have the power supply to deliver the rating, but not enough output transistors. You might get away with 450 w/ch but I wouldn't go much above this full time. This is odd for Peavey; usually the watt ratings in the amp name are very conservative. I'm saying PV-1.3k has 5 transistor pairs, CS800 has 4, PV-2K has three.
If you can get an old CS800x or even a no-suffix model, or a PV-1.3k, it would be tougher in continuous duty PA use at this watt level with one more output transistor pair. All these old amps needs new electrolytic capacitors (if not replaced already), heat sink cleaning and probably new fans to be reliable at this late date. However, they are extremely repairable, well documented on the internet, and parts are available from Peavey and generic electronic distributors, since the part number conversion of Peavey numbers to industry part numbers are not a secret like some other manufacturers. They are easy to get apart and back together, too. The only disadvantage, the transformer models are heavy compared to fancy tech switcher supply competitors or the CS800s which is also a switcher. The CS800s I bought used in 2010 is tripping the breaker, probably needs new power supply electrolytic capacitors like I said. I only paid about $100 for it, though, maybe less. It came as a package deal with 2 SP2-XT speakers (about $350 each on craigslist) a 12 input Peavey mixer, a stereo 16 band equalizer, a Digitech Quad 4 effect unit, 2 speaker stands (poles) a road case, and a 100' 24 channel snake, $1000. All but the speakers, snake, and stands had little cheap problems.
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Last edited by indianajo; 31st March 2013 at 09:41 PM.
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Old 31st March 2013, 10:51 PM   #37
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Right i get you know, the more transistor pairs the better (in laymans terms). Its a shame becuase i had the opportunity to buy a 1.3k instead of the 2k but thought against it because of the markings on the front. Alas the uninformed have made yet another mistake.

Im glad to hear that the amp is serviceable though, i will try to find a good electronics shop to have a look at it and hopefully with a bit of TLC it will run (fairly) well @ 400w per channel. Thank you for taking time to formulate a reply that i can understand, you have been very helpful. Next time i will go for a 1.3k if i have the chance!

Regards Mik
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Old 1st April 2013, 06:11 PM   #38
Enzo is offline Enzo  United States
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Just my opinion.

I don't think it is fair to an amp to just count the transistors. I learned a valuable lesson many years ago working on a Carver PM1.5. Nice amp, I like them, though I hate working on them. I found out the hard way that that amp will not drive a sine wave into a load at full power for any period of time. I caalled Carver and discussed it, and they told me that was normal, the ampo wasn't designed to amplify sine waves, it was designed to play music. And in fact, the amp would amplify music all day long at full power. Just not sine waves.

Music is not sine waves, music is a periodic sort of signal. Those thousand watt kick drum peaks are just that, peaks. And at a half second apart, they give the amp plenty of time to rest. So your 22A is about 8A per device if there are three of them. Those are MJ15024, which are 16A devices. Does 5 transistors have potentially better current potential? I suppose it might, but the question is not that, the question is whether the 3 transistors are up to the job.

In the decades I have been involved with servicing Peavey gear, I have never had a reason to doubt their specs on anything. There are plenty of people who just object to 2 ohms no matter what. 40 years ago, I heard the same things about 4 ohms. If Peavey says an amp will run reliable at 2 ohms, I am inclined to believe them. They do have other products with 2 ohm rating where the 2 ohm output is reduced considerably. IN other words it is OK to run 2 ohms on those as long as you don;t expect full output. They do that because a lot of people don't understand that simply connecting 2 ohms to something doesn;t stress the amp. It is only when you try to put a lot of power into the 2 ohms that stress might occur.

And that brings me to another point. The amp is rated to put out 1000 watts into 2 ohms per channel, but are you going to be asking it to do so? If your speakers are rated to 500 watts, that does not mean they will be taking 500 watts, it only means that is the maximum they can withstand. You may not ever drive them that hard.
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Old 8th January 2014, 07:11 PM   #39
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Okay, I'm ready to document my proposed fix for the PV1.3k melting the triac off the PWB when an output transistor shorts, instead of blowing the breaker. I repaired the trace with a 16 ga wire, then watched it melt that wire. No more relying on the triac crowbar for me, I paid 6x for each SP2-XT speaker what I paid for the amp ($600 for 2 speakers, $55 for a blown amp).
See the circuit diagram below. With the flying power supply rails, most disconnect circuits won't work unless you do the digital work with the flying +-16v op amp supply. I was taught to not put analog and digital on the same circuit, so to keep from stuffing two wall transformers for DC in there, I used a lot of $.37 optoisolators.
This circuit draws from the Michael Bean two NMOS fet design, but instead of putting the fets source to source in the speaker hot, I put them in the power supply rails. This takes two photovoltaic optocouplers (fet drivers) instead of one per channel, but might save some $5 output transistors someday if I trip over a speaker cable on the stage. I'm relying on the automotive fuse to detect overcurrent in the speaker line. Further work could use current transformers to measure the current out, and an op amp, But that would require another wall transformer to make op amp supplies, or sucking power off the existing driver or PS boards without adding a connector in a butcher job with drilled holes etc. A heat sink temp sense would be a lot simpler with only one supply and one FET. The existing thermo cutout snap action thermostat is silly but I'll leave it in to avoid buying a $23 roll of blue 10 ga wire. Any thoughts?
Among the things I find questionable, I've never seen anybody put the fets in the rails instead of the speaker line. 74HC74 IC's will source or sink 3 ma, but I don't know if a gain of 3 is enough to drive PN2222 into saturation where they only drop 0.7 v at 10 ma LED current. I don't have LM340-6 or 7806, and the LM340-5 seems to be working fine with a 1n4148 under the common to make 5.6 v, but I don't know if anybody else has ever done that. 6.2 v would be even better on that triple LED in the green/fet driver line on Qbar. I'm getting close to trying it, but it is 10 deg out in the garage where I have to build the fet heatsink/mount bracket, so playing with my new Windows 7 and TINA-TI is more fun today. Pity it doesn't have optoisolators or 74hc74's on the sim. Those current sources as optoisolators are klugy, my apologies, but it beats drawing it out on notebook paper (which I have been using for 43 years) and trying to photograph it where you could read it. My first foray into sim software. I designed stuff for Ford-Aerospace using graph paper for timing diagrams, and a pencil, back before horned toads were exterminated around Houston.
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Last edited by indianajo; 8th January 2014 at 07:26 PM.
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Old 20th March 2014, 03:45 AM   #40
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Hello I am new to this site and looking for help with a peabey pv1.3k .Problem one and not a problem but on output board the ceramic resistor are not the same that peavey has in the parts diagram .There is .68 ohm instead of 1 ohm and 1/4 watt are 1.5 k and on the drive boards where there is to be .033mf there is 1.5 ohm e 192 standard series resistor any help would be nice
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