FS/Trade: Two ACMP-73 with issues

E

erniebb

New member
I have couple of the group buy ACMP-73 I'm selling or trading. I have not done extensive investigation but both has some hum issues that I have no time to deal with. The specific issue for each one:

ACMP-73 #1: It has hum when EQ is engaged
ACMP-73 #2: It has hum when gain is dialed above 7 o'clock

So in a sense they are still usable with no EQ on #1 but application for #2 is somewhat limited. I really don't want to wait, or investigate myself as I don't have the ability. I'm open to offers but the catch is I'm selling as a pair and as-is. If offers are too low then I'll wait until fixes emerges. I can do ebay/paypal if needed. FYI I'm also cross-posting at GS, PP and PSW.
 
I have 4 of the ACMP 73s I got in the buy, and would consider a few more.

What would you be interested to trade for?
i have rack mount mixers, a couple of Delta 1010s etc....
 
tmix said:
I have 4 of the ACMP 73s I got in the buy, and would consider a few more.

What would you be interested to trade for?
i have rack mount mixers, a couple of Delta 1010s etc....
Click to expand...

Delta1010 sounds interesting - I'm using 1010LT right now but I'm thinking to get something like a Audiofire12 down the road...

I don't think I need a mixer. Do you have any other things you may be willing to part with? You can PM me if you want.
 
The fixes are pretty much known. The problem is that there are about eight or ten different flaws in the design, any one of which can cause the hum problem, several of which make other aspects of the hum problem worse, etc.

The core problem is that they used really lousy power transformers that produce way more EMI than they should.

Another problem is that they routed the power bus right beside it.

Another problem is that certain boards can oscillate due apparently to a poor choice of transistors.

Another problem is that the power supply has a distinct 60 Hz ripple.

Another problem is that the inductors are not shielded.

I could probably keep going for a while. My point is that the fixes tend to be specific to the individual unit unless you can afford to replace the power transformer. Otherwise, you pretty much just have to try all the different fixes until one or several of them work well enough in combination to get the noise floor low enough.
 
I've been utterly unable to find a replacement transformer with the same specs. It has way, way too many secondaries, all at nonstandard voltages. To replace the transformer, you'd pretty much need to redesign the power supply circuit, too. :)
 
You must log in or register to reply here.
Back
Top