I think most stereo/5/7/9 channel "receivers" are transformer power
supplies and AB designs. At least the couple dozen I've owned. Maybe
the latest $100 ones at Best Buy are now SMPS. If the power label says
100 to 240v or the box is too light, or the distortion isn't sub 0.1%
then it might be SMPS or class D etc. The higher end amps usually have
toroidal transformers.
I think the most common audio RFI problem is pickup by the speaker leads
and rectification in the output transistors. CM chokes at the amp output
make a big difference. Then CM chokes on power and low level RCA signal
leads (good cables help a lot). Balanced shielded low level XLR
connections usually make small signal RFI not a concern on high end
equipment.
There have been a few class A power amps, one was the Perreaux PMF 3150
from ZL, I could fry an egg on mine @ 150w/ch. Awesome sound tho. Now
on ebay for more than I paid in 1994. I see they are back in business
with A/AB MOSFET amps. Other rare bird class A amps on ebay as well.
I haven't seen an "SMPS" in mid/high end other than in the rare Bob
Carver designs (Carver & Sunfire) which have a signal following power
rail. Awesome 800w/ch.
The only in production transformer coupled semiconductor amps I know of
are from fabled McIntosh, the ultimate wizards of transformer design. $$$$$
Most all of the car amps > 20w are switched mode power and class D.
Awful sound.
Ebay and the local thrift stores are good places to look for older
receivers w/o the 4k and HDMI bells and whistles and almost always AB
plus linear power supplies. At lower power levels (<50w) a complete AB
amplifier on a single chip. (TI, ST)
Grant KZ1W
On 10/13/2020 09:02, Rob Atkinson wrote:
The problem with solid state is that if the RF field is strong enough,
a cheap analog solid state amp will pick up enough RF on the internal
leads and the transistors will rectify it. This is especially a
problem with cheap plastic enclosures. Tubes are less vulnerable to
this even if run unshielded. As someone else pointed out, tube amps
have output transformers that isolate the speaker leads. The problem
is solved whether the problem is the amp generating RFI or being
vulnerable to it. You might not get it all, but bypass caps on the
audio inputs will usually be the death blow.
73
Rob
K5UJ
On Tue, Oct 13, 2020 at 8:25 AM Hare, Ed W1RFI <w1rfi@arrl.org> wrote:
Many of the old solid-state amplifiers also have analog supplies. The key is
-- weight. If it's got iron, it's analog.
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|