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guytou 18th November 2005 12:24 AM

amcron dc300a shemetics
hello everybody !I am looking for it . I know there was a useful link on this forum , but i can't find now:confused:
if would anyone would recall to me ...

Thanks in advance !

djk 18th November 2005 07:32 AM

guytou 18th November 2005 12:03 PM

Thanks a lot djk !:smash:

I have the DC 300A "tout court" , I am not aware about the differences with the series II , I hope that's quite the same .

djk 19th November 2005 01:30 AM

The manual linked to has all but the DC300 data.

DC300A has uA739, DC300A II has two LF357, very similar otherwise.

Most common problems:

10uF 160V bootstrap cap

Transistors forming CCS off bootstrap supply, always replace in pairs.

10V zeners for IC front end.

amplifierguru 19th November 2005 03:01 AM

The LF357 has a substantial 'sonic signature'. I am very familiar with this chip as I used it in my commercial GB1b amplifier and line stage of the GB1a preamp in 1988. I quickly replaced these with the quantum leap cleaner OPA627/637. Chalk and cheese.

It helps to bias the output stage as well of you will have a substantial forward path discontinuity ( big gain drop) at zero crossing (resistive load).


djk 19th November 2005 03:34 AM

The DC300A is biased AB+B for a reason.

If you want to re-engineer the thermal compensation, be my guest.

The Carver M1.5T also uses the LF357, but sounds much better than a DC300A. The DC300A is an old work horse, fine sounding hi-fi it never was.

IMO: Fix and use for bass, or let it go down the road.

amplifierguru 19th November 2005 03:46 AM

Hi djk,

Have to agree. But I'm sure that, if used in a low duty full range 8 ohm hi fi application the heatsink could easily handle 25-50 mA of output transistor bias. After all, it has done a fair job of road PA use under worst conditions. I'll have a look at the thermal comp.


"fine sounding hi-fi it never was." I think this could be easily corrected.


djk 19th November 2005 06:41 AM

I don't care enough for the way they sound to fix them. It would be great if you could engineer a fix for these, I have a couple of dead ones laying around.

I was wondering if I could shoe-horn your new amp into a D150 chassis (52V), got a couple of those corpses too.

amplifierguru 19th November 2005 06:53 AM

Hey djk,

You approach these things differently from me! I see a problem as a challenge - particularly with Crown as I see a lot of competent and inspired (for the time) design there, with few surmountable weaknesses.

Perhaps it's my outlook - low footprint, recycle, clean air to breathe, something left for future generations that I search for the good features and try to solve the weaknesses to 'save' the
value in the product.

It's just my way. It works for me. A GAIAN philosophy.

Yes my GB150D is fine with 52V supplies and would probably do about 120-140W depending on supply strength.


djk 19th November 2005 07:11 AM

Recycle is what I am hoping to do with these, nice power supply on the DC300A.

Mine have the A739, that seems like a lost cause.

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