Ben bfranchuk at jetnet.ab.ca
Mon Jul 19 09:58:50 CDT 2010

Chuck Guzis wrote:
> On 18 Jul 2010 at 22:12, Ben wrote:
>>> Certainly for testing. RRun the heaters off a battery. If the hum
>>> goes away, at least you know where it's coming from.
>> I found my hum ... Poor magnetic shielding between the power supply
>> and the pre-amp output transformers. Not much I can do unless I can
>> order custom shielded chokes  and power transformers as well as
>> shielded 10K to 600 ohm output transformers. I don't have the $$$ for
>> that, but it does prove you can get rid of hum if you don't use cheap
>> off the shelf parts, but parts made for low hum and noise.
> Any chance you could simply change the orientation of one or the
> other?

I tried that, but not much change in the hum.
The main problem is the power supply, I got all crappy open core
inductors, that hum like mad. This will require a rebuild, but I
don't have $$$ for that. Now I know why consumer products vs commercial
products have a 10x difference in price.

> --Chuck

Now that I know where my hum is from, I can get back to
computer design.  No not a Z80, but 9/18 bit CPLD
cpu design I plan to build. 6850 ACIA, Simple IDE interface
32KB ( 9 bits of ram ), 512 byte EEPROM for boot straps (
bits #3 is duplicated as bit #4 to give 9 bits),A cpu CPLD
and a GLUE CPLD and a bit 74HCT for misc parts.


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