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John Warren

Crown D-45 schematic

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Cool, Thanks @John Warren. I could put a output relay that does not connect the speakers until the amp has come up. So many modern day amps have this. But I would really like to understand with the minor mods I have made why it is unstable.

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I bought 3 of the D-75A amps off eBay, to go with Jubilee's I ordered. The amp I use for the LF, has been great. The first amp I used for the HF was fine for a while. Then the Red IOC light started coming on periodically, on the right channel. Followed by a static sound on the right channel like the singer has a bad lisp, you could even hear it on cymbals. I replaced that amp, with my third. It played great until the other night, when the left channel red IOC light started coming on. I'm getting a bad feeling it's going to start acting up, as well. I never play louder than 100bd, usually closer to 80-85db. Any ideas on what I should do ?

I have xlr to rca cables, and I am tempted to use my Yamaha consumer amps, and hope I don't have noise issues. I wish active Xovers had rca connections !

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I plan on using a couple of these D75s I am working on for the mid/high on my Jubes. I intend to use one in bridged mode for each the left and right channels. I am discouraged to hear you are experiencing trouble @Speed Are yours brand new? Or used? If used you have no idea what they have been through. But a competent tech should be able to fix it for you if you're not up to it. The schematic is readily available as posted right in this thread in fact.

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4 hours ago, babadono said:

Are yours brand new?

eBay buys. I do see new ones on occasion.  Do amps develop problems more with age, or usage ? That would help determine if a new one is worth buying. Not sure when Crown stopped making them... 

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1 hour ago, babadono said:

@CECAA850 where? For @Speed

I can't find dada on my phone.  I'll look tomorrow.   There were several places if I recall correctly.   You might try Google and click the shopping tab.

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On 2/12/2018 at 12:19 PM, babadono said:

Well this sucks. Units will not power up into 4 ohm loads in two channel mode. But will power up into 8 ohms bridged. Also will run 4 ohm loads if I plug the load in after power up. Outputs are latching to the positive rail.

Well i have backed out all the mods except the bigger filter caps and better op amps and it still won't come up into 4 ohm loads. The +10 volts gets sucked down to almost 0. Building up a +10 and -10 volt little regulator board to see if I can keep the voltages up through power up .

  • Sad 1

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Yes SIr, that was it! Amp powers up now into 4 ohms. This is a GREAT way to end a Friday. The zener regulators that are in the amp don't have enough poop to keep my op amps of choice working when the amp is loaded with 4 ohms.

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@John Warren Did you see my above couple of posts? I figured out why I was having trouble with 4 ohm loads. Now what I want to know/try to do is make a beefier +/- 10 zener source so I don't have to build 4 more regulator boards. The existing zeners are 10V 1/2 watt with 910 ohms series resistance to B+ and B-(approx 30V). To get the extra current needed I calculated 300 ohms and just barely 1 watt zener. But to be safe I'll just go with a 5 watt zener. I am surprised at how small a package those come in now a days and how inexpensive. Now the waiting for the parts to arrive.......

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On 2/15/2018 at 7:43 AM, CECAA850 said:

Thanks @CECAA850 I did see that one after you suggested trying Google shopping. Where is this guy getting new D75a s ?

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