2 Crown DC-300A's

[SteveL]

I have 2 dc-300a's in the shop and would appreciate any help offered.

#1 This one takes 3.5 minutes to for the positive side to stabilize and after that it will work OK. See pics of the output below.

#2 This one has 62VDC on the output of one channel and all the output and driver devices test good in the circuit. I suspect a bad zener, but haven't found any that read bad (yet).

The big drawback to being able to repair these is that the schematic I have isn't the circuit in these amps. The schemo I have show 20v Zeners and no IC, while these amps have 10v Zeners and an IC. Very odd.

 

[JohnRoberts]

The DC300 amps are DC coupled so even modest DC voltage errors at the input get amplified by the amplifier's full gain.

JR

 

[moamps]

The big drawback to being able to repair these is that the schematic I have isn't the circuit in these amps. The schemo I have show 20v Zeners and no IC, while these amps have 10v Zeners and an IC. Very odd.

 

[Gus]

https://www.crownaudio.com/en-US/products/d-series

 

[SteveL]

Awesome! thanks much MOAMPS. This will definitely be helpful.

 

[SteveL]

Thanks Gus! More good info.

 

[JohnRoberts]

I've heard that story repeated multiple times over the years. I never heard somebody claim actual credit for it.
===
Indeed it is plausible to use a DC300 as an emergency console power supply.

JR

 

[SteveL]

[The DC300 amps are DC coupled] --

With me now in a "Total-Panic" mode,

Anyone need a +62VDC power supply? You pay shipping...

 

[JohnRoberts]

[I've heard that story repeated multiple times over the years] -- You have??? From where??? By whom???

[I never heard somebody claim actual credit for it] -- Well.....it was actually me!!! In fact, at that point in time, I had owned and used a CROWN SX-722 reel-to-reel tape deck which I had taken along with me that evening so I could record the show directly from the console on a couple of 10-1/2" reels of AMPEX tape.

The warm-up band was a local Indianapolis band called "The Faith Band" (later, just called "Faith") and the headlining act was "Black Oak Arkansas" who had a hit song called "Hot And Nasty". Over the past four decades whenever I just might pull that tape out and play it for some reason, within my mind I am mentally transported back to that backstage area where all of the broadcast gear was set-up (I even used my own pair of JBL 4311's for the broadcast mixing) and of my frantic scrambling around trying to find whatever I could to "jerry-rig" something together in order to try and save the broadcast part of the concert!!!

From the way I take your comment of "I never heard somebody claim actual credit for it", I can't tell if that is a good or bad thing. Sounds a bit "ominous" to me.

/

That time frame is correct for when I first heard the stories repeated and DC300s were popular back then.

I won't name names but the story I heard was generally shared by an engineer on a live sound reinforcement forum (like PROSOUNDWEB.com), since that is not an obvious application for an audio power amp. IIRC a 9V battery was also used as the input voltage reference in that story I heard.

I have probably repeated hearing about the story myself once or twice because it's interesting in a geeky way. Losing a console power supply can happen in live sound. That's why live sound professionals sometimes carry a spare console power supply. Modern consoles are probably more reliable now than back then.

JR

PS: I just did a search over at Prosoundweb and found a couple sound engineers claiming that they used DC300s for emergency console power supplies, and one example of me sharing the unusual DC300 application anecdote. At least one of the guys who said he did it, credited hearing about the idea elsewhere and did not take credit for coming up with it himself. If you want names search "DC300 and console" .

 

[Gavin Pursinger]

Fortunately I have 2 power supplies for my console...I also have 2 dc300a Crowns...I would never thought of this...backups are a good thing to have...what could possibly go wrong !!!

 

[JohnRoberts]

Fortunately I have 2 power supplies for my console...I also have 2 dc300a Crowns...I would never thought of this...backups are a good thing to have...what could possibly go wrong !!!

The scary thought is trying to rewire up a console power supply umbilical while the curtains are waiting.

I had one related experience at a trade show last century where the large console I was trying to demo in our booth lost it's power supply. I was able to rewire a different but similar console PS that was not being used, to git er dun... As I recall that was more than a little stressful. In that case my time pressure was hours not minutes.

As I said that's why serious professionals used to carry backup power supplies. Hopefully the modern consoles are more reliable often with switching PS built right inside, and DC300s are unlikely to be found anywhere nearby.

JR

 

[RoadrunnerOZ]

There’s always the 24V batteries from the show-hire trucks - they can last for a show and you can still start the truck (as long as you don’t use the second battery). Set of jumper leads and some heavy cable with the battery removed and you’re away. Heard of that being done at an outdoor festival in the ‘80s.

 

[RoadrunnerOZ]

1 This one takes 3.5 minutes to for the positive side to stabilize and after that it will work OK. See pics of the output below.

#2 This one has 62VDC on the output of one channel and all the output and driver devices test good in the circuit. I suspect a bad zener, but haven't found any that read bad (yet)

I’d be checking the IC’s at the input and their rail voltages

 

[Gavin Pursinger]

Jim Dandy to the rescue!!!
Everything is scary right before the curtain goes up.
My 300a Crowns are 70 lbs of worth the trouble each

 

[JohnRoberts]

Jim Dandy to the rescue!!!
Everything is scary right before the curtain goes up.
My 300a Crowns are 70 lbs of worth the trouble each

maybe my search engine is lying it says only 45# each.
===
The CS1200 amps that I had to hump around at too many trade shows back last century were an actual 70# each.

There were some heavier amplifiers but not many...

JR

 

[Gavin Pursinger]

45# or 70#...my memory is as bad as my right hip !!!
Crowns are doing studio duty these daze. I still enjoy them
I stand heavily corrected -

 

[JohnRoberts]

[There were some heavier amplifiers but not many] -- I was one of the first "BOSE Professional Products" dealers back in the mid-1970's and the BOSE 1800 Power Amplifier weighed-in at 80-pounds!!!

Somehow.....my little 2-man audio company ended up selling -- MORE -- BOSE 1800 amplifiers than any other dealer back then and the BOSE Corporation called up one day asking, "Just what are you doing to sell so many of these amplifiers"? The funny part was.....what they didn't know is that my little audio company was also buying up BOSE amplifiers from other dealers so we could supply what we were selling to our customers!!! The BOSE Corporation sent us a certificate announcing that my little audio company was "The Largest BOSE Professional Products Dealer in the United States". That was fun!!! We sold 4 BOSE 1800's just to one band alone because I had designed for them a "stereo tri-amplified" PA-system that used CROWN VFX crossovers for the low/mids/highs and CROWN D-75's for the high-end. It was a really cool system!!!

/

I don't know if i still have it, I might have thrown it away already, but I recall buying a surplus 1801 transformer several decades ago... I don't recall that old transformer being very heavy. My home brew power amp (4x250W) I built back in the 70s used a transformer that weighed 65#.

As I get older I am trying to clear out the detritus from all my sundry projects that will never happen. I just went out to my laundry room and that old transformer is long gone. I suspect it went out during one of my purges.

IIRC that Bose amp went pretty heavy on aluminum for heat sinks something like a dozen TO-3 power output transistors per amp channel, all passively cooled (no fan).

probably some decent aluminum scrap value too.

JR

 

[RoadrunnerOZ]

I’m seeing something different here - in a flight case 80 pounds
https://www.vintagetoysforboys.be/e...-series-1-professional-stereo-power-amplifier
I remember doing a regular Sunday gig in Melbourne in a long skinny restaurant-bar, plus another by the river on Thursdays in a similar venue - we used 4 x 1800’s with 4 pairs of Bose 802’s on stands with stereo delays feeding 3 of the amps to get the PA sound in sync with the stage. The only gigs I did that were such a heavy lug with amp racks heavier than the speakers. 2 amps per rack plus delays. Then there was the stage foldbacks…..

 

[JohnRoberts]

I’m seeing something different here - in a flight case 80 pounds
https://www.vintagetoysforboys.be/e...-series-1-professional-stereo-power-amplifier
I remember doing a regular Sunday gig in Melbourne in a long skinny restaurant-bar, plus another by the river on Thursdays in a similar venue - we used 4 x 1800’s with 4 pairs of Bose 802’s on stands with stereo delays feeding 3 of the amps to get the PA sound in sync with the stage. The only gigs I did that were such a heavy lug with amp racks heavier than the speakers. 2 amps per rack plus delays. Then there was the stage foldbacks…..

fans in the flight case.... probably smart for professional applications.

JR

PS; I don't want to start a heaviest amp contest but I recall some heavy iron from Crest back in the day.

 

[RoadrunnerOZ]

fans in the flight case.... probably smart for professional applications.

JR

PS; I don't want to start a heaviest amp contest but I recall some heavy iron from Crest back in the day.

I’m sure there’s a few boats with rectangular anchors