djk,
I must admit I had not checked as where in the amp the ua739 is.... I have just tried to but it seems that Crowns web site is off line.
I must admit I had not checked as where in the amp the ua739 is.... I have just tried to but it seems that Crowns web site is off line.
Having now seen the schematic....djk is quite correct.
The ua739 is an integral part of the design and it's own gain/phase is manipulated by external compensation around the op amp itself in order to promote stability of the whole amp when closed loop.....in other words don't touch those op amps! Virtually no other part would work OK in it's place. That'll teach me to open my big typeing finger before seeing the facts
maybe...
The ua739 is an integral part of the design and it's own gain/phase is manipulated by external compensation around the op amp itself in order to promote stability of the whole amp when closed loop.....in other words don't touch those op amps! Virtually no other part would work OK in it's place. That'll teach me to open my big typeing finger before seeing the facts
maybe...hello,
Glad the ic arrived, that was fairly quick, and what a super job you have done with the boards etc etc.....
Im paranoid about the old ics failing and i have started replacing them as i sell my amps now!
I have had one go s/c and what a mess it made of a perfectly good amplifier. (never had one go s/c ever before) still have 20 or so ic's available..... why change what works fine anyway, sure the crown designers know a damn sight more than i do!.
good job all round shawn
Glad the ic arrived, that was fairly quick, and what a super job you have done with the boards etc etc.....
Im paranoid about the old ics failing and i have started replacing them as i sell my amps now!
I have had one go s/c and what a mess it made of a perfectly good amplifier. (never had one go s/c ever before) still have 20 or so ic's available..... why change what works fine anyway, sure the crown designers know a damn sight more than i do!.
good job all round shawn
krmaudio said:
Thanks! It did get here quick! A few more little things before I get back to the DC300A. I still have not found a great metal shop here in Toronto that can anodise 1's and 2's zzz.
Working on it,
Shawn.
Shawn,
I have been following your progress and am very impressed with your staying ability and attention to detail on this project. I as well as everyone else watching is looking forward to see the finished product and your report on the sound of this old sweet classic. Great job with the reporting.
Gibbi
I have been following your progress and am very impressed with your staying ability and attention to detail on this project. I as well as everyone else watching is looking forward to see the finished product and your report on the sound of this old sweet classic. Great job with the reporting.
Gibbi
Gibbi said:
I'm listening to the DC300A but I ain't saying nothing until it has all the components in it that I want. I'll tell you right now, there is nothing wrong, just a couple simple glitches. I can't really eliminate these glitches until all the final components are in place, then I will resolve them here @ DIY.
Thanks Gibbi! ... and all those that support this type of project. I have profound respect for the folks that designed this piece of gear and managed to run it through production for ~20 years+! That says a lot. I know it will never sound like a good modern transistor design, many of which are here for free @ the DIY site for any person to try their hand at but the DC300A from Crown will always remain in the foundation of semiconductor amplifier history. To me the DC300A is a 69 Cougar and I don't think such a vehicle was ever intended to stack up against a 2006 BMW sports car, they are completely different and their only common may be that they are cars and have four wheels? My job here is to restore this muscle car and share it with everyone who cares. I hope at some point others may take inspiration and do the same to their own DC300A.
Thanks everyone for the good words.
I'm working on it,
Shawn.
Edit: Edit requested by Shawn - anatech 😉
Finish
I have looked around and still I'm trying to find a small (local) outfit to finish off the metal work.
Flames...Hmmn...Perhaps a decent auto body shop could do it wonders? But I guess I'm trying to find an outfit to stencil the original scheme onto the face. Perhaps I should give up and go radical for fun?
Cheers!
rdf said:
I have looked around and still I'm trying to find a small (local) outfit to finish off the metal work.
Flames...Hmmn...Perhaps a decent auto body shop could do it wonders? But I guess I'm trying to find an outfit to stencil the original scheme onto the face. Perhaps I should give up and go radical for fun?
Cheers!
Hi Shawn,
Man, I'd call that a success! That's one heck of a nice job. Time for body work I guess.
-Chris
Man, I'd call that a success! That's one heck of a nice job. Time for body work I guess.
-Chris
Shawn,
Far better than the original was. One of the downfalls of the original Crown was the cheap PC boards with the super thin copper.
Great job!!!
Far better than the original was. One of the downfalls of the original Crown was the cheap PC boards with the super thin copper.
Great job!!!
Fixes
Thanks again to Joe. I followed the documentation you provided and installed the anti-pop and anti-squeal mods and the start up and shut down noises are barely audible.
Also there was the compensation circuit changes to handle faster output devices. I made those mods to the amp as well.
The power supply caps from Apex Jr. were a shoe-in replacement to the old ones. 2 X 17,000uF has been upgraded to 2 X 47,000uF!
I modified the driver board to allow the use of 100K volume pots and I purchased some decent Alps pots on line.
After I completed the final modifications I made adjustments to the bias circuitry and some cool stuff occurred. R109 and 209 turned out to measure within 1 ohm of each other. Also the input and output offset pots are in the exact same location for the left and right channels. This really means nothing but to me it shows the precision of using tight tolerance devices.
Perhaps tonight I will crank it up a little.😀
Cheers,
Shawn.
Thanks again to Joe. I followed the documentation you provided and installed the anti-pop and anti-squeal mods and the start up and shut down noises are barely audible.
Also there was the compensation circuit changes to handle faster output devices. I made those mods to the amp as well.
The power supply caps from Apex Jr. were a shoe-in replacement to the old ones. 2 X 17,000uF has been upgraded to 2 X 47,000uF!
I modified the driver board to allow the use of 100K volume pots and I purchased some decent Alps pots on line.
After I completed the final modifications I made adjustments to the bias circuitry and some cool stuff occurred. R109 and 209 turned out to measure within 1 ohm of each other. Also the input and output offset pots are in the exact same location for the left and right channels. This really means nothing but to me it shows the precision of using tight tolerance devices.
Perhaps tonight I will crank it up a little.😀
Cheers,
Shawn.
Pictures on the Net
Research is going well Chris! 🙂 I feel I'm listening to the amp the original designers "wanted" to hear. 😉 It sounds great. The bass sounds well matched to the mid and high. Before the rebuild it was too tight in the low end and the highs seemed to be almost shrill. Now it seems well balanced and the bass is super deep and full.
I put a few minutes into the web location and put up a temporary gallery. When I find time I'll make a great little website that will better reflect this project and in it I'll include all of the documentation that I have. So go check out the DC300A web site.
Cheers,
Shawn.
anatech said:
Research is going well Chris! 🙂 I feel I'm listening to the amp the original designers "wanted" to hear. 😉 It sounds great. The bass sounds well matched to the mid and high. Before the rebuild it was too tight in the low end and the highs seemed to be almost shrill. Now it seems well balanced and the bass is super deep and full.
I put a few minutes into the web location and put up a temporary gallery. When I find time I'll make a great little website that will better reflect this project and in it I'll include all of the documentation that I have. So go check out the DC300A web site.
Cheers,
Shawn.