The Dude Posted December 13, 2016 Share Posted December 13, 2016 The stock transistors may be just fine. Is there any thought on upgrading them as well? This cool, I like these sort of things. Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 18, 2016 Author Share Posted December 18, 2016 More on the Duke mods here: http://www.northreadingeng.com/Forums/viewtopic.php?f=8&t=11 Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 20, 2016 Share Posted December 20, 2016 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 Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted December 20, 2016 Share Posted December 20, 2016 So the MC33079 is an upgrade per John's THD test. Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 20, 2016 Share Posted December 20, 2016 The MC33079 is the original part, but has a lower slew rate than Mark's replacement. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted December 20, 2016 Share Posted December 20, 2016 Yeah, upgrade not the right word. Lower THD compared to those other two chips it seems so at least better than the other two with regards to noise. So even with ICs there are compromises? Quote Link to comment Share on other sites More sharing options...
djk Posted December 21, 2016 Share Posted December 21, 2016 "but has a lower slew rate than Mark's replacement. " The SR doesn't need to be over 1V/µSec for the design. Q100, Q102 provide the voltage gain. C101, C103 affect the audio quality way more than anything else in the circuit. The stone-slow and anemic (gain wise) MJ15015 (a selected 2N3055) will be a problem driving low impedances. Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 31, 2016 Author Share Posted December 31, 2016 (edited) On 12/20/2016 at 7:35 AM, Marvel said: The MC33079 is the original part, but has a lower slew rate than Mark's replacement. If SR mattered, you'd see it in bandwidth, HF distortion, etc. and you don't. SMPTE and 20kHz %THD of four op-amps swapped in the D-45. Signal source impedance 660 Ohms, amp at full power into a resistive, 8 Ohm load. The AD713 and TLE2074 devices have +SR of 20V/us. The MC33079 at 7V/us and the TL084 is about 10V/us. These are chips that have been around for a while and available in 14 pin DIPs. If you wish to attribute the differences in sound between different op amps then SR, as djk has eluded too, is not a factor (unless it's too low). Edited December 31, 2016 by John Warren goofed up units Quote Link to comment Share on other sites More sharing options...
babadono Posted February 6, 2018 Share Posted February 6, 2018 Just buttoned up the first of 5 Crown D75s that I am mod'ing. I replaced the P.S. caps, all coupling caps, put machined sockets in for the I.C.s, up graded the opamps to LME4920s and LME 49710s and then started adjusting the compensation capacitors. I have increased the slew rate to approx. 10 volts per microsecond from the as reported by JohnWarren anemic 3 volts per microsecond. Also adjusted the IOC circuit to turn on the red LED at clipping not 10 or 20 dB below. I am getting 40 watts per channel out into 8 ohms and over 100 watts bridged into 8 ohms. I have not yet tried 2 channel into 4 ohms . Second unit is mod'ed and will be on the test bench this evening. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 6, 2018 Share Posted February 6, 2018 5 minutes ago, babadono said: Just buttoned up the first of 5 Crown D75s that I am mod'ing. I replaced the P.S. caps, all coupling caps, put machined sockets in for the I.C.s, up graded the opamps to LME4920s and LME 49710s and then started adjusting the compensation capacitors. I have increased the slew rate to approx. 10 volts per microsecond from the as reported by JohnWarren anemic 3 volts per microsecond. Also adjusted the IOC circuit to turn on the red LED at clipping not 10 or 20 dB below. I am getting 40 watts per channel out into 8 ohms and over 100 watts bridged into 8 ohms. I have not yet tried 2 channel into 4 ohms . Second unit is mod'ed and will be on the test bench this evening. But how does it sound? Quote Link to comment Share on other sites More sharing options...
babadono Posted February 6, 2018 Share Posted February 6, 2018 Like an amp. Actually as of yet I have no idea. This is all on my bench here at work after hours that I work on them. But seriously are you thinking or saying I should leave one un mod'ed and then compare? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 22 hours ago, babadono said: Like an amp. Actually as of yet I have no idea. This is all on my bench here at work after hours that I work on them. But seriously are you thinking or saying I should leave one un mod'ed and then compare? If you want to see if it was worth it, yes. Have you seen where new D75's are going for $199? Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 On 12/10/2016 at 3:23 PM, CECAA850 said: Try this D-45_Update_The_Duke_Klipsch-1.pdf I am quite late to this as I was not even a member of the forum when this was done. But I read through that whole linked thread and still don't completely understand all that was done. I see the P.S. capacitance was increased and some coupling caps were changed. Some slower but quieter opamps were changed. Speeding up the slew rate was alluded to but I did not see what was done to accomplish this explained. And changing the input impedance? On the D75s I am modifying all one would have to do to increase the input impedance (unbalanced input) is to change the gain pots from their standard 25K to the desired 47K(practically would be 50K as this is a standard value). Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 14 minutes ago, CECAA850 said: If you want to see if it was worth it, yes. Have you seen where new D75's are going for $199? No I did not see the $199 deal. I got these 5 units for $130 total. Someone on this forum posted an alert last year that a guy in San Diego had like 30 of these he wanted to get rid of. He wanted $50 a piece originally. By the time I got down there like 2 months later he was practically giving them away. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 3 minutes ago, babadono said: I was not even a member of the forum when this was done I owned the Duke for many years. It was a sweet sounding amp. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 7, 2018 Share Posted February 7, 2018 Just now, babadono said: I got these 5 units for $130 total. Nice! Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 I wanted to mention also that I am very fortunate in the fact that I got a schematic of the D75 off of Crown's website. So far the amps I'm working on are built exactly like the schematic shows. This is a huge plus. Quote Link to comment Share on other sites More sharing options...
jwc Posted February 7, 2018 Share Posted February 7, 2018 I shot an email off to John Warren. I'm interested in having my D-75s updated. Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 18 minutes ago, CECAA850 said: I owned the Duke for many years. It was a sweet sounding amp. Did you ever hear it(or any) unmodified one? Quote Link to comment Share on other sites More sharing options...
babadono Posted February 7, 2018 Share Posted February 7, 2018 7 minutes ago, jwc said: I shot an email off to John Warren. I'm interested in having my D-75s updated. What do you want done? Quote Link to comment Share on other sites More sharing options...
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