Resurrecting a Crown DC300A

Jump to Latest
#443
ACD said:
Mine got the LF357 😉

In the last 5 years I have only seen one (1) DC300 II for sale in Denmark at a price app. $400.- ......
Click to expand...

$400 for an older used power amp is a hefty price. Perhaps it says something about the longevity of the product. 😉 I went looking all over and I can't seem to find more of them. Perhaps they are becoming rare.
 
#447
djk said:
The last page of the DC300AII manual shows the schematic for the version with the LF357.
Click to expand...

Hi guys, as far as i know, The much later dc300a mkII had the best main board, has anyone got any............

I know there are a few pics in the crown manual, but they dont tell that much, most black front dc300amkII appear to have early pcbs, maybe there werent so many genuine mk2 versions, just a lot of mk 1.5's!

has anyone got a later version????? (3 ic mainboard)

all the best


:hot:
 
#451
DC300A Update

I learned a lot on this project but it seems there is much more to learn.

anatech aka Chris B. let me bring the boat anchor over to his place where he cracked it open and set it up for a distortion test and an overall look-see. I was suffering from the abuse :xeye: of New Years Eve so I will leave it to Chris to list the details of the test.

The left channel immediately gave him grief as he tried to adjust the DC offset to zero and in the end adjusting the bias gave a best reading near 1.8% THD! That was a serious blow to my amplifier building ego but the right channel came through much better giving a final reading of less than 0.05%THD.

I think we both concurred that a huge limiting factor could be the uA739 Op Amp and its circuitry. The only way to prove the design better would be a different build with a better Op Amp circuit.

Way back, when I stuffed the driver board I made a pin placement error on Q105. The unit was powered up and I immediately found the error. I replaced the transistor with a new one just in case but I now realize I should have replaced Q104 and Q107. I am working on the left channel tonight and hope to have it sorted. Oddly enough the damn thing sounded good so I am a little stoked that it may sound even better. 🙂 I do worry the five TO3 outputs on that portion of the rail may be affected.

Rebuilding an amplifier like this or building one from the ground up is a lot of planning and work when hand crafted by one person. I now regret that I did not purchase additional transistors and match the devices. Why go through all of the work and leave out something that may improve over all performance and stability. In fact, I don't think I will ever build an amplifier again without matching the devices.

Chris was a gracious host and his home would be a play ground for any audio enthusiast! OMG the test equipment, the audio equipment both old and new! :bigeyes: A great person and a great experience.

Cheers,

Shawn.
 
#452
Hi Shawn,
It's great to see you found the problem with minimal loss. You are welcome back and we'll set your bias and do some final testing and listening.

Yes, the amplifier didn't sound too bad when you first brought it over. So much for designing by ear! The residual from the THD meter looked pretty terrible. Certainly much worse than I expected to see. The other channel settled in as intended by the original designers of this amp.

I'll say that you workmanship looks very good up close and personal. A very clean job!

-Chris 😉
 
#453
The show must go on...there is a new member in the family! I picked it up yesterday from a failed eBay seller. Got for $75. It is older than the previous model I worked on but not by much. Almost identical except it is in better cosmetic condition but perhaps it doesn't show yet. I can see most of its life was in a rack as the aluminum extrusion/chassis has very few scratches on the rear.

So what d'ya say? Toss it in the lake or rebuild it? 😉

Shawn.
 

Attachments

  • dc300a partii.jpg
    dc300a partii.jpg
    80.4 KB · Views: 1,074
#458
VINTAGE 60'S CROWN AMP DC-300A parts or repair
$77.08 Jan-25 03:20

VINTAGE CROWN DC300A DC-300A SERIES II POWER AMP
$199.99 Jan-23 16:30
(BIN, no bids)

Crown DC-300A Parts Repair Unit
$99.00 Jan-15 17:21
(BIN, no bids)

Crown DC-300A Series II Power Amp
$167.50 Jan-14 20:03

Crown DC300A Power Amplifier
$141.28 Jan-22 18:30

VINTAGE CROWN DC300A POWER AMP
INCLUDES RACK CASE
$200.00 Jan-22 06:29
(no bids)
 
#459
whew.....three days later and I finally finished this thread.

very nice work fo sho!

I have a Crown ps-400 that's not too happy. I was considering going down the same road and rebuilding it. Anyone know how similar is it to the dc300a, or other 300's? I also have a few of the 150's that need help.....Attack of the Killer Clowns I guess......heh🙂
 
#460
camusmuse said:
whew.....three days later and I finally finished this thread.

very nice work fo sho!
Click to expand...
I wonder if I could do a second restoration in three days? 😉

I have a Crown ps-400 that's not too happy. I was considering going down the same road and rebuilding it. Anyone know how similar is it to the dc300a, or other 300's? I also have a few of the 150's that need help.....Attack of the Killer Clowns I guess......heh🙂
Click to expand...

The 400 has a quasi output stage and a "signature" opamp on the front end but other than that I would guess they are similar yet very different. Get out your soldering iron and your camera. 🙂

Cheers,

Shawn.
 
You must log in or register to reply here.
Top Bottom