CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 1 minute ago, babadono said: Did you ever hear it(or any) unmodified one? Yes but not on my gear so a comparison wouldn't be valid. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 Yes our sense of hearing is very....how do you say non deterministic. And subjective even from one minute to the next. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 Also I forgot to mention on these D75s I am fixing the ridiculous grounding scheme of the XLR input pin 1. The as built by Crown connects pin 1(the shield ) directly to the signal ground. Classic and classically wrong. I wonder if the newer versions of this amp are sill the same? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 2 hours ago, babadono said: Yes our sense of hearing is very....how do you say non deterministic. And subjective even from one minute to the next. Then you asked if I had heard a non modded one because????????????? Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 Yea sorry about that. I posted before I thought about it. I guess perhaps I thought maybe you heard them side by side. At least that might be different than say the Duke one day and then an unmodified one two months later. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 On 12/19/2016 at 7:03 PM, Marvel said: I think Mark sent me all the info on this but I'll have to dig through file on a hard drive to find t... Bruce @Marvel do you have something that shows all the mods he did? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 31 minutes ago, babadono said: @Marvel do you have something that shows all the mods he did? I do. When are you going to get a cell phone? All of Marks posts are gone from the forum as far as I know. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 @babadono did you get my e-mail? Quote Link to comment Share on other sites More sharing options...
jwc Posted February 7, 2018 Share Posted February 7, 2018 3 hours ago, babadono said: What do you want done? Not sure. Wanted to see what John recommends. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 30 minutes ago, CECAA850 said: @babadono did you get my e-mail? Yes, replied to it directly. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 8, 2018 Share Posted February 8, 2018 2 hours ago, jwc said: Not sure. Wanted to see what John recommends. How many do you use at one time? Quote Link to comment Share on other sites More sharing options...
John Warren Posted February 8, 2018 Author Share Posted February 8, 2018 On 2/6/2018 at 12:47 PM, babadono said: I have increased the slew rate to approx. 10 volts per microsecond from the as reported by JohnWarren anemic 3 volts per microsecond. I'm interested in changes, not absolute magnitudes. My anemic 3V/us is not a slew-rate, it's a compensated slew-rate, measured at 15kHz. I spooled-up the potentiometer to output a healthy voltage, in this case ~23Vp-p and then simply measure the time required to settle after responding to a 15kHz pulse. By comparing the time required to reach steady-state, an "apples to apples" comparison between op-amps, changes in compensation, output transistors and so on can be readily determined by storing the image before the change and then comparing after. An alternate approach would be to set the goal posts at 10 and 90% the vertical response and measure the time between. Plot below is example using the TLE2079 op-amp with compensated slew-rate of a bit over 3V/us loaded with 8 Ohm power resistor. Thought this thread had died, fancy that. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 8, 2018 Share Posted February 8, 2018 Thanks John, I will try to duplicate your tests. The way I was/am currently doing it is just feeding a pulse generator set to 1Khz but with 100 nanosecond rise and fall times. This gets changed to a differential signal by an "OUTSMARTS" demo board from That Corp. I then feed this into the balanced inputs. I make the measurement at 20Vpp and do the math. I then increase to 40Vpp and making sure it tracks. Of course with an 8 ohm load on the outputs. @John Warren Edit: I test with the differential to single ended converter included because it adds 1 more op amp to the input circuit and because that is how I am going to use the amps. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 8, 2018 Share Posted February 8, 2018 1 hour ago, John Warren said: Thought this thread had died, fancy that. Yea winter time is when I have time to do this kind of stuff. Quote Link to comment Share on other sites More sharing options...
John Warren Posted February 8, 2018 Author Share Posted February 8, 2018 15 hours ago, babadono said: Also I forgot to mention on these D75s I am fixing the ridiculous grounding scheme of the XLR input pin 1. The as built by Crown connects pin 1(the shield ) directly to the signal ground. Classic and classically wrong. I wonder if the newer versions of this amp are sill the same? On the ones I've seen, Pin 1 on both XLR input sockets are on dedicated trace to chassis ground which ties to Earth plug on 3-prong. P16 is circuit ground last time I looked. Curious to see what your seeing, can you post photo? Quote Link to comment Share on other sites More sharing options...
Marvel Posted February 8, 2018 Share Posted February 8, 2018 17 hours ago, babadono said: @Marvel do you have something that shows all the mods he did? Somewhere, but I haven't been able to find it yet. Bruce Quote Link to comment Share on other sites More sharing options...
babadono Posted February 8, 2018 Share Posted February 8, 2018 5 hours ago, John Warren said: On the ones I've seen, Pin 1 on both XLR input sockets are on dedicated trace to chassis ground which ties to Earth plug on 3-prong. P16 is circuit ground last time I looked. Curious to see what your seeing, can you post photo? The boards(amps) I'm working on are circa 1990, they are D75s, yours is perhaps a D75/45 A ? Looks like they have fixed the pin 1 grounding scheme (maybe). A picture will take a least until tomorrow IF I can remember to bring my camera. BTW I still see something labeled "1" going all over the place including to another point labeled "S" and then to a main trace that I'm guessing is signal ground. Here is the schematic I am working from. These older units have hardwired (by hand) connectors not soldered to the board directly. D75_J0116-4_original.pdf Quote Link to comment Share on other sites More sharing options...
babadono Posted February 8, 2018 Share Posted February 8, 2018 I found this in the "Duke" thread linked to in this thread and found it semi amusing: "Dean--- The level controls as configured need 8" of shielded cable, and they use socket connectors to plug into the board. Shielded cable + series resistance is always to be avoided." As a statement of fact as if every one knows level controls and shielded cables are bad. What utter non sense. Oh my gosh 8" of wire might add 0.001 ohms to the 47k input impedance, whatever will we do. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 9, 2018 Share Posted February 9, 2018 Some pictures of my work. Like I said on these older units there is a lot of hand wiring. On the close up of the XLR connectors you can see pin 1 now goes directly to a grounding lug on the chassis(added by me). It used to daisy chain over to the sleeve connection of the unbalanced 1/4" input jack which then directly connected to signal ground. See schematic in previous post. And yes I know C218 is missing on PCB. It was reworked by someone previous to my obtaining this unit and they used the wrong value capacitor. I am going to procure the proper part. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 12, 2018 Share Posted February 12, 2018 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. Quote Link to comment Share on other sites More sharing options...
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