Crown DC-300 Schematic / Service Manual

[Biasrocks]

I've got one of these beasts in here for repair.

Looking for a service manual or schematic for the original DC-300 (not the A version). 

Can't seem to find one from the usual online sources.

Mark

 

[gridcurrent]

1

 

[JohnRoberts]

I think they're around ..

quasi-complemenatry output stage

check the output devices...

JR

 

[Ethan]

page 2 [posted for gridcurrent]

 

[JohnRoberts]

page 2 [posted for gridcurrent]

Yup page two reveals the quasi-comp output stage... all the power devices are NPN with complementary drivers Q111 and Q114 upstream..

Check the big NPNs for CE shorts... Shorted outputs could damage drivers too.

JR 

 

[Biasrocks]

Will do, thanks guys.

Mark

Check the big NPNs for CE shorts... Shorted outputs could damage drivers too.
JR

 

[gridcurrent]

The service manual is available here:
http://www.crownaudio.com/en-US/products/d-series

The DC 300 is quite famous, not so much for blowing up,
but for igniting  connected loudspeakers.

Two  suggestions:
a.  install a blocking capacitor, 10 uF would be appropriate, in series with the input control.
b.  install a 10 ohm 5 watt resistor in series with the output capacitor (C5), and move that network to the amplifier side of the output inductor (L1).

 

[PRR]

http://www.crownaudio.com/en-US/products/d-series
DC-300 Service Manual
http://adn.harmanpro.com/site_elements/resources/969_1425479684/DC-300-Service-Manual-dc300-sm_original.pdf

"300 WATTS AND A CLOUD OF SMOKE
Basic Service Suggestions for the
CROWN DC-300 Amplifier"
"PART IV: BLOOD SWEAT AND THE SMELL OF BURNT PARTS"

113 pithy pages about DC-300 service, written soon after #2000 was built. You don't find such honesty in ANY other service manual.

 

[Biasrocks]

Thanks for this.

I'll see if the owner will go for it.

Two  suggestions:
a.  install a blocking capacitor, 10 uF would be appropriate, in series with the input control.
b.  install a 10 ohm 5 watt resistor in series with the output capacitor (C5), and move that network to the amplifier side of the output inductor (L1).

 

[Biasrocks]

Pithy is an understatement.

113 pithy pages about DC-300 service, written soon after #2000 was built. You don't find such honesty in ANY other service manual.

 

[JohnRoberts]

I've heard of DC300 power amps McGuyverd to serve as console power supplies in bind... send a 9V dc from a battery into one input, reverse to polarity to the other input and adjust gain for desired DC output voltage.

Speakers really don't like DC... I recall a spate of speaker failures while I was working at Peavey from a competitor's budget power amp that had the bad habit of clipping asymmetrically injecting enough DC into the speaker to cause it to release smoke prematurely. Painful to pay warranty claims because of another company's flaky design, while the market perception was that the speakers just couldn't handle the amp's power... they actually couldn't handle the amp's DC output when clipped..

There is absolutely no DC music, so no justification for DC response in any*** audio path. For power amps, the last line of defense before hitting the speakers, HPF are very useful IMO.

DC 300 is a relic and belongs in a museum or used as a boat anchor. They had a reputation for being rugged, not for sounding good.  YMMV

JR
 
**** of course when adding HPF to too many stages in series, the response sums and corner frequency can creep up toward the passband, so poles should be set arbitrarily low.

 

[PRR]

The early (no chip) DC300 was and still is a fine sounding amp. I gave-away a Phase Linear 400 because it was harsh; the DC300 never offended me, and I never suspected it was unfaithful to the music. It still has fans.

I can't see fixing a 40 year old DC300 just for bulk power, new bulk-amps are so cheap; but if someone has lived with it and loved it all these years, it may be worth some work.

 

[JohnRoberts]

The early (no chip) DC300 was and still is a fine sounding amp. I gave-away a Phase Linear 400 because it was harsh; the DC300 never offended me, and I never suspected it was unfaithful to the music. It still has fans.

I can't see fixing a 40 year old DC300 just for bulk power, new bulk-amps are so cheap; but if someone has lived with it and loved it all these years, it may be worth some work.

Both are quasi-complementary NPN output stage so neither has a technology edge.  Bob Carver eventually earned a decent rep for sound quality but the early Phase Linear were more known for cheap power that would fail if you looked at them cross-eyed.

Below clipping I expect both to sound similar while i never did a blind test between them.  I looked at the PL schematic among others when designing my DIY amp in the early '70s and as I recall the PL VI protection circuits didn't protect squat, and the experience of most reflected that.

Amps like Crown and BGW were nominally more reliable for professional sound use. The PLs were loved in Hifi markets for their bang for the buck power.

JR

 

[Gene Pink]

Both are quasi-complementary NPN output stage so neither has a technology edge.  Bob Carver eventually earned a decent rep for sound quality but the early Phase Linear were more known for cheap power that would fail if you looked at them cross-eyed.

Below clipping I expect both to sound similar while i never did a blind test between them.  I looked at the PL schematic among others when designing my DIY amp in the early '70s and as I recall the PL VI protection circuits didn't protect squat, and the experience of most reflected that.

Amps like Crown and BGW were nominally more reliable for professional sound use. The PLs were loved in Hifi markets for their bang for the buck power.

I had a"Flame Linear" 400-II for many hears, put it through hell in PA use, never had a problem with it.  Never even blew the rail fuses, the thing actually had fuses on the +/- PS rails. Maybe that was an answer to the lousy current limiting.  Lent it to an EE friend trying to make a puppy dog sale, it came back with the bias set to "room heater" mode. Guess he was trying to clean up the crossover distortion. Rumor was, the PL-909 output transistors were meant for TV horizontal output use, but I dunno. Something absurd like 700V C-E rating.

Speaking of current limiting, this post is the first time I have seen the original 300 schem., never owned one. That's some wacky current-limiting, although I like they way they sum the emitter resistor voltages on the (+) side. What is that switch for? I heard rumors of them having a current-drive feature, maybe that is it? More study is needed.

Also had 8 DC-300a's at some point, not a one of them ever failed, either. But knowing their reputation, I made up twenty crowbars into  the web of dual binding posts. Yes, JR, I stole the circuit from the CS-800, but I don't feel guilty, bought the triacs, SBS, and the NP caps from Peavey. And at li$t price, I feel they were adequately compensated.

Gene

 

[JohnRoberts]

I never personally blew up any, but my housemate blew up his flame linear 700 (back in the '70s) by just probing around inside.

JR

 

[Biasrocks]

Pulled four of the six output transistors so far, the 2N3773's.

The two Driver transistors (Q1, Q4) test ok and appear to be the original part (Solitron). The two Output transistors that I've pulled so far (4 in total) show shorts between the Collector and Base. They are all branded Motorola and the other working side has RCA's and  Solitron's.

There's no mica  insulator separating the Collector from the heat sink that it's mounted on, grounding the Collector (case).

Is this how it's supposed to be?

Check the big NPNs for CE shorts... Shorted outputs could damage drivers too.
JR

 

[JohnRoberts]

Pulled four of the six output transistors so far, the 2N3773's.

The two Driver transistors (Q1, Q4) test ok, but the two Output transistors that I've pulled so far show shorts between the Collector and Base.

There's no mica  insulator separating the Collector from the heat sink that it's mounted on, grounding the Collector (case).

Is this how it's supposed to be?

Only if the heat sink is floating and isolated from chassis.. The collectors for the top devices connect to +V supply

The collectors for the bottom devices connect through a .1 ohm resistor to output. 

The schematic is in this thread,.

JR

Check the big NPNs for CE shorts... Shorted outputs could damage drivers too.
JR

 

[Biasrocks]

The heat sink is not isolated from chassis ground.

The working side is directly connected to the heat sink as well. I'll take another look at the schematic, but colour me confused.

 

[JohnRoberts]

The heat sink is not isolated from chassis ground.

The metal to-3 case is connected to the internal device collector... there are usually transistor sockets where screws that hold the transistor down to the heat sink complete the electrical contact to the rest of the circuit.  If the heat sink is grounded to the chassis, there will be mica insulators between the transistors and the heat sink.  If there is heat sink grease, look for a washer hidden in the grease.

That schematic will not operate with all the collectors shorted together and to ground.

JR

The working side is directly connected to the heat sink as well. I'll take another look at the schematic, but colour me confused.

 

[Biasrocks]

Thanks John.

Yes, there is a tab inside that connects the collector to the circuit through the screws that secure the transistor.

I'm not finding any mica insulators, I'll order them up an install them. 

Someone has been here before me, that always makes me nervous.