John Warren Posted February 13, 2018 Author Share Posted February 13, 2018 I have a somewhat earlier D75 that I'll teardown here: http://www.northreadingeng.com/Audio/group/ Might give you some clues? Quote Link to comment Share on other sites More sharing options...
babadono Posted February 13, 2018 Share Posted February 13, 2018 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. Quote Link to comment Share on other sites More sharing options...
Speed Posted February 14, 2018 Share Posted February 14, 2018 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 ! Quote Link to comment Share on other sites More sharing options...
babadono Posted February 14, 2018 Share Posted February 14, 2018 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. Quote Link to comment Share on other sites More sharing options...
jwc Posted February 14, 2018 Share Posted February 14, 2018 I sent two D-75A to John Quote Link to comment Share on other sites More sharing options...
Speed Posted February 14, 2018 Share Posted February 14, 2018 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... Quote Link to comment Share on other sites More sharing options...
babadono Posted February 15, 2018 Share Posted February 15, 2018 On 2/7/2018 at 8:32 AM, CECAA850 said: Have you seen where new D75's are going for $199? @CECAA850 where? For @Speed Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 15, 2018 Share Posted February 15, 2018 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. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 15, 2018 Share Posted February 15, 2018 Here's one. https://www.ebay.com/itm/Crown-Audio-D-75A-Two-Channel-55W-Power-Amplifier-/372159622023?_trksid=p2385738.m4383.l4275.c10 I can't find the other ads. May have been a sale. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 16, 2018 Share Posted February 16, 2018 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 . 1 Quote Link to comment Share on other sites More sharing options...
babadono Posted February 17, 2018 Share Posted February 17, 2018 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. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 17, 2018 Share Posted February 17, 2018 @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....... Quote Link to comment Share on other sites More sharing options...
babadono Posted February 17, 2018 Share Posted February 17, 2018 On 2/15/2018 at 7:43 AM, CECAA850 said: Here's one. https://www.ebay.com/itm/Crown-Audio-D-75A-Two-Channel-55W-Power-Amplifier-/372159622023?_trksid=p2385738.m4383.l4275.c10 I can't find the other ads. May have been a sale. Thanks @CECAA850 I did see that one after you suggested trying Google shopping. Where is this guy getting new D75a s ? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 17, 2018 Share Posted February 17, 2018 No idea. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 19, 2018 Share Posted February 19, 2018 Link to D75a schematic earlier in this thread is broken. Can someone re post it? For @Cantilope @John Warren? @The Dude? Quote Link to comment Share on other sites More sharing options...
The Dude Posted February 19, 2018 Share Posted February 19, 2018 D45-75A J0650-2 Rev B.pdf Quote Link to comment Share on other sites More sharing options...
babadono Posted February 19, 2018 Share Posted February 19, 2018 Thanks dude the @The Dude Is there a power supply page also? So is the 2.7 ohm between DC rtn and chassis (R6) always in circuit? Or is there a jumper terminal on the back of the D75a just like the D75? Looks like pin 1 of XLR and sleeve of TRS at input jack is tied to DC rtn(signal ground, P16). Kind of hard to jibe this schematic with photos John Warren posted earlier. Well I'm rambling, just thinking out loud, don't know if any body is following this. But I will continue with the mods to my non A units. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 23, 2018 Share Posted February 23, 2018 So I got two of the five D75s up and running with all mods. And then while doing a load test on one it went poof. Got a hold of a respected tech down here in San Diego area and he basically told me I'm an idiot for thinking a 50 watt into 4 ohm per channel amp should be able to put out 50 watts per channel for more than a couple of minutes. It actually melted the insulation between the windings of the power transformer. So now I will replace the transformer with the one from the fifth unit. Quote Link to comment Share on other sites More sharing options...
Shiva Posted February 23, 2018 Share Posted February 23, 2018 31 minutes ago, babadono said: So I got two of the five D75s up and running with all mods. And then while doing a load test on one it went poof. Got a hold of a respected tech down here in San Diego area and he basically told me I'm an idiot for thinking a 50 watt into 4 ohm per channel amp should be able to put out 50 watts per channel for more than a couple of minutes. It actually melted the insulation between the windings of the power transformer. So now I will replace the transformer with the one from the fifth unit. If you want a Crown amp that you will have a very hard time pushing beyonds its limits, I would recommend looking into the Crown K2 amp. Putting out 500 watts a side at 8ohms. I use one at home as a stereo amp and am quite happy with it. https://sandiego.craigslist.org/csd/msg/d/crown-k2-amplifier/6475181113.html Quote Link to comment Share on other sites More sharing options...
babadono Posted February 23, 2018 Share Posted February 23, 2018 Thanks @shiva but I only need a few watts as these are going to be used to run the mid/tweeter driver on a pair of Jubes. Its just I am old school. If an amp is spec'd at 50 watts it should do it all day in my book. And on these old Crown units I thought Crown was truthful in their specs. I know on their current offerings the wattage specs are . Quote Link to comment Share on other sites More sharing options...
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