Crown DC-300A II Restore with Measurements

[grayxxx]

Langston :300A Series II journey

I saw your MOD parts list.......It seems you went with the OEM bias specs after
some review of 50v and the factory bias specs 0.31-.35V were the best.

Has anything changed concerning your MOD parts of the 300A Series II and the finale
factory bias.31-.35V .....setting. No displacement in the "space time continuum" or anything we should no about that you would like to add......or confess to.....their has to
be more to the story......and the update of the 300A Series II journey....look forward
to your response.

thank you for post and picture and all concerning the 300A Series II journey and your
input and work.
gray


300A Series II journey
OEM bias specs are 0.31V to 0.35V across the pair of 5.6Ω 1W resistors on the output boards:

Now... The reason I decided to skip the Variac for trying to diagnose the maximum output variations I've seen as I've restored this amp is because when I re-biased to the top end of the OEM spec, I got close to the OEM power back. Thus I'm convinced that biasing was the primary independent variable responsible for the dependent variable of power. The amp also got very cool to the touch again and as a result will probably stay in spec longer than I will. A definite keeper.

 

[jackinnj]

The amp also got very cool to the touch again and as a result will probably stay in spec longer than I will. A definite keeper.

Are you sure it wasn't oscillating previously.

 

[grayxxx]

Thread (Crown DC-300A II Restore with Measurements)

Are you sure it wasn't oscillating previously.

jackinnj .....The quote was from Langston....on his redo of his Crown 300A Series II and his summation that the original OEM specs bias .32-.34V were the best after his review and multiple adjustments made on the Crown 300A Series II bias setting . I was reading the Langston (thread) on the Crown 300 Series II and was wondering if Langston had upon review of his redo of the crown 300 series II amp.....did he have any additional thoughts.....I have 2 of the 300A II up for redo....

Langston thoughts and facts on measurements of the 300A II amp. and how
in the end the factory settings bias setting were correct and how he views measurements of the amp in the process important during his redo and thread. Langston thread on the Crown 300A II was well written as well as his
execution of his redo and measurements. He did a pdf of factory parts list to
be replace and MOD updates in a pdf as Factory parts / MOD parts list, very nice redo thread on Langston's part.

thanks for your reply, jackinnj ....gray

Langston Holland wrote: Thread (Crown DC-300A II Restore with Measurements)

Now... The reason I decided to skip the Variac for trying to diagnose the maximum output variations I've seen as I've restored this amp is because when I re-biased to the top end of the OEM spec, I got close to the OEM power back. Thus I'm convinced that biasing was the primary independent variable responsible for the dependent variable of power. The amp also got very cool to the touch again and as a result will probably stay in spec longer than I will. A definite keeper.

Here are the new max output measurements:

Max Output vs Bias 2.pdf

 

[grayxxx]

Iholland ....Just a question on your redo of the crown 300A II, how has
it faired and have you done anything else and or still using.... 300A II.
thanks gray

Hello Everyone!

This is the first of several posts I’m going to make in this thread. This is the first time in a few years that I’ve posted on an online forum and will try not to make a mess of it.

Background

This is yet another DC-300A II refurbish experience that in my case was world’s easier than the Amazing Effort by Shawn 10 years ago. This is because I cheated and bought one that was already in good condition. It was sold initially to a home owner in Canada that made its way to the US, then finally to me a few weeks ago via FleaBay™. I spent (2) days on it and a couple of weeks deciding on and waiting for parts orders. The one thing that will be different about this post is that I’m a measurement nut. Audio, to a large extent, is a means to an end of empirical learning for me and if you’re foolish enough to follow along, I bet you too will see some stuff you haven’t come across before. 🙂

Though I’ve finished the refurbish, I haven’t listened to the amp yet. I was afraid to connect it to my loudspeakers prior to measurement and afterwards figured the "before" listening experience wouldn’t be indicative of a new OEM unit anyway. I’ll add a post to this thread in a week or so after doing some serious listening and see if this amp really earns its broken glass with good bass reputation.

Per Shawn’s and a few others comments both here and on the Crown Forum, and the good initial condition of the amp, I chose just to upgrade the electrolytic and ceramic disc capacitors and leave it at that. The 1N270 germanium diodes used in the limiting circuitry work properly, so I left them in place though I did buy spares for the future in case they become unobtainum.

OEM Parts to Upgrade

View attachment 574700

Replacement Parts

View attachment 574701

And for completeness, here’s a link to the Service Manual and the Owner's Manual.

Finally, as will be seen in following posts, what’s inside now matches the pretty outside:

View attachment 574702

View attachment 574703