19 Jul
2010
19 Jul
'10
7:58 a.m.
Chuck Guzis wrote:
On 18 Jul 2010 at 22:12, Ben wrote:
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 $$$ for that. Now I know why consumer products vs commercial
products have a 10x difference in price.
Certainly
for testing. RRun the heaters off a battery. If the hum
goes away, at least you know where it's coming from.
I found my hum ... Poor
magnetic shielding between the power supply
and the pre-amp output transformers. Not much I can do unless I can
order custom shielded chokes and power transformers as well as
shielded 10K to 600 ohm output transformers. I don't have the $$$ 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. --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.
Ben.