Why are some amplifiers so prone ito picking up RF

[Brian Gaff (Sofa)]

I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.
Brian

[Adrian Caspersz]

Post by Brian Gaff (Sofa)
I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.

To comply with 1990's CE susceptible interference directives, bandwidth
limiting filtering components were forcibly added to pre-amplification
stages - which annoyed some hi-fi journalists so as an aim to appease
them, these parts are probably made missing again...

I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

[Dave Plowman (News)]

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

My pre-amp - designed by Stewart Pinkerton, who used to frequent this
group - does use a balanced input. But with a Lo-Z MC cartridge. Although
I've built it into the deck itself, so only a few inches of wire between
cart and pre. So it sends to the power amp at normal line level.

[Phil Allison]

Adrian Caspersz wrote:
====================

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

** Cos it would make things worse - not better.

"Balancing" is completely useless for floating input sources.

FYI " floating" = no link to common or supply ground.


..... Phil

[Phil Allison]

Phil Allison wrote:
==================

Post by Phil Allison
====================

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

** Cos it would make things worse - not better.
"Balancing" is completely useless for floating input sources.
FYI " floating" = no link to common or supply ground.

** Update: I just remembered.

There is ONE exception - a special mode of connection to an RIAA pre called "feedback input".
In this mode, the signal from a MM cartridge is inserted in * series * with the inverting input of the pre-amp.
The usual input is grounded and the link between the NFB summing point and the minus input is used instead.

Why?
Both inputs then remain always at "virtual ground " with no noise penalty due to series resistance.
I have tried it and it seems to clean the signal up audibly - by just a tad.

Penalty?
You have to add grounded shielding over the RCA phono leads - some cooking foil does nicely.
Small price to pay - eh guys ?

FYI

At the time I tried this I was using a pair of Quad ESL57s, a Shure V15III pickup in a unipivot arm.
My lounge room was heavily damped with thick carpet and acoustics tiles.
The amplification was all SS, fully complementary PP with independent pre and main power amps.
Belt drive TT with heavy ( 1 inch thick perspex ) base perched on three soft coil springs.

Old school ....


..... Phil

[tony sayer]

Post by Phil Allison
====================

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

** Cos it would make things worse - not better.
"Balancing" is completely useless for floating input sources.
FYI " floating" = no link to common or supply ground.
..... Phil

Why should that matter if it is floating?, a Moving coil microphone can
be on a balanced input the whole input floating if it were a balanced
input via an input transformer?...

[Phil Allison]

tony sayer wrote:
==============

Post by tony sayer

Post by Phil Allison

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

** Cos it would make things worse - not better.
"Balancing" is completely useless for floating input sources.

Why should that matter if it is floating?

** Is that meant to be a question ? Or not.

Post by tony sayer
a Moving coil microphone can
be on a balanced input the whole input floating if it were a balanced
input via an input transformer?...

** A cork can float on water.



.... Phil

[tony sayer]

Post by Phil Allison
==============

Post by tony sayer

Post by Phil Allison

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

** Cos it would make things worse - not better.
"Balancing" is completely useless for floating input sources.

Why should that matter if it is floating?

** Is that meant to be a question ? Or not.

Yes it was a question!...

Post by Phil Allison

Post by tony sayer
a Moving coil microphone can
be on a balanced input the whole input floating if it were a balanced
input via an input transformer?...

** A cork can float on water.

I suppose it can as long as its not waterlogged;!..

Post by Phil Allison
.... Phil

[tony sayer]

Post by Adrian Caspersz

Post by Brian Gaff (Sofa)
I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.

To comply with 1990's CE susceptible interference directives, bandwidth
limiting filtering components were forcibly added to pre-amplification
stages - which annoyed some hi-fi journalists so as an aim to appease
them, these parts are probably made missing again...

Which shows what ignorant pratts some supposed audio journs are

Post by Adrian Caspersz
I've often wondered why turntable cartridges are mostly wired
unbalanced, when balanced is possible.

Indeed, often wondered what balanced operation isn't used more in hi-fi
audio?...

[Woody]

Post by Brian Gaff (Sofa)
I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.

I had any number of amps - including a Quad 33 - which had such
problems, and in most cases a few very cheap components would overcome
the problems.

Small clicks and some RF pickup can be easily blocked by a small cap -
maybe 10nF - across each diode of the bridge rectifier.
Many amps had big smoothing caps which had relatively high inductance. A
smaller non-polarised capacitor - say 0.1uF in parallel, and an even
smaller disc ceramic such as an additional 1nF often did wonders.
Having said that, if the amp had a fully regulated power supply (which
few did) most of the above would not apply.

RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

[Phil Allison]

Woody wrote:
===========

Post by Woody
I had any number of amps - including a Quad 33 - which had such
problems, and in most cases a few very cheap components would overcome
the problems.

** ????

Post by Woody
Small clicks and some RF pickup can be easily blocked by a small cap -
maybe 10nF - across each diode of the bridge rectifier.

** Drivel. Such caps stop switching noise being generated from the power diodes.

Post by Woody
Many amps had big smoothing caps which had relatively high inductance.

** Absolute drivel. Biggest myth out about electros and you just revived it.

Post by Woody
smaller non-polarised capacitor - say 0.1uF in parallel, and an even
smaller disc ceramic such as an additional 1nF often did wonders.

** Blatant nonsense.

Post by Woody
Having said that, if the amp had a fully regulated power supply (which
few did) most of the above would not apply.

** Stop it - you're making me laugh.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

** That mod can be effective against strong local RF.

But the best cure is to RF ground all cable shields ( and speaker wires) as they enter the metal cases of equipment
RF travels on the OUTSIDE of cables and so is rendered harmless if you stop it entering the insides of electronics.

FYI " RF ground" means either a direct link or a 0.1uF cap link.

...... Phil

[Trevor Wilson]

Post by Woody

I have noticed this over the years, and  assume its all down to
filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.

I had any number of amps - including a Quad 33 - which had such
problems, and in most cases a few very cheap components would overcome
the problems.
Small clicks and some RF pickup can be easily blocked by a small cap -
maybe 10nF - across each diode of the bridge rectifier.
Many amps had big smoothing caps which had relatively high inductance. A
smaller non-polarised capacitor - say 0.1uF in parallel, and an even
smaller disc ceramic such as an additional 1nF often did wonders.
Having said that, if the amp had a fully regulated power supply (which
few did) most of the above would not apply.

**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors. Noise enters via other means.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

**Not needed when the product has been properly designed.

[Phil Allison]

Trevor Wilson wrote:
=================

Post by Trevor Wilson
**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors. Noise enters via other means.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

**Not needed when the product has been properly designed.

** The only common form of annoying RF noise injection into home hi-fi gear is down to the domestic fridge switching on and off.
( Less common ones include strong local sources of RF energy like airport Radar, TV transmitters and taxi radios. )

The fridge issue is due to arcing of the contactor that starts and stops the motor every 20 mins or so.
Arcs are strong RF sources and radiate via power cabling between the fridge and the fuse panel.
Makes normally fit a suppression cap inside to quench the arc and this does a good job until it fails.

IME fitting a mains filter in line with the fridge does little to help.


....... Phil

[Trevor Wilson]

Post by Phil Allison
=================

Post by Trevor Wilson
**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors. Noise enters via other means.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

**Not needed when the product has been properly designed.

** The only common form of annoying RF noise injection into home hi-fi gear is down to the domestic fridge switching on and off.
( Less common ones include strong local sources of RF energy like airport Radar, TV transmitters and taxi radios. )
The fridge issue is due to arcing of the contactor that starts and stops the motor every 20 mins or so.
Arcs are strong RF sources and radiate via power cabling between the fridge and the fuse panel.
Makes normally fit a suppression cap inside to quench the arc and this does a good job until it fails.
IME fitting a mains filter in line with the fridge does little to help.

**Yep. Allowing the RF any kind of antennae is a bad thing. Even sillier
is to fit a mains filter to the hi fi system. Nonethless, a lot of money
can be extracted from the terminally stupid this way. Here is one
charlatan (rather well-known, as I understand it):

https://www.russandrews.com/which-mains-filter/

Please Phil, do not eat your lunch before reading this shit. You'll puke
it up.

[Dave Plowman (News)]

Post by Trevor Wilson
**Yep. Allowing the RF any kind of antennae is a bad thing. Even sillier
is to fit a mains filter to the hi fi system. Nonethless, a lot of money
can be extracted from the terminally stupid this way.

When I rewired this house, I included a dedicated radial circuit for the
AV stuff. With its own earth too direct to the house ground point rather
than to the earth bus in the CU. Of course can't swear it helps, but I get
no fridge etc splats.

[tony sayer]

Post by Phil Allison
=================

Post by Trevor Wilson
**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors. Noise enters via other means.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

**Not needed when the product has been properly designed.

** The only common form of annoying RF noise injection into home hi-fi gear is
down to the domestic fridge switching on and off.
( Less common ones include strong local sources of RF energy like airport
Radar, TV transmitters and taxi radios. )
The fridge issue is due to arcing of the contactor that starts and stops the
motor every 20 mins or so.
Arcs are strong RF sources and radiate via power cabling between the fridge and
the fuse panel.
Makes normally fit a suppression cap inside to quench the arc and this does a
good job until it fails.
IME fitting a mains filter in line with the fridge does little to help.
....... Phil

Haven't heard Fridge thermostat noise for ages now Phil..

And no noise being picked up on the QUAD 33 originally made in 1967 on
the desk here! Mind you the DISC input isn't used but i might get around
to plugging up the Technics PL12 unit if i can find a gramophone record
anywhere;!...

[Jim Lesurf]

Post by Trevor Wilson

Post by Woody
Small clicks and some RF pickup can be easily blocked by a small cap -
maybe 10nF - across each diode of the bridge rectifier. Many amps had
big smoothing caps which had relatively high inductance. A smaller
non-polarised capacitor - say 0.1uF in parallel, and an even smaller
disc ceramic such as an additional 1nF often did wonders. Having said
that, if the amp had a fully regulated power supply (which few did)
most of the above would not apply.

**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors.

Alas, my experimental evidence clashes with your beliefs. :-)

...depending, of course, of your definition of "almost no"...

But the measured reality I found was that some noise can, indeed, enter
that way.

Post by Trevor Wilson
Noise enters via other means.

Yes, it can also do that.

Jim

[Phil Allison]

Jim Lesurf wrote:
=============

Post by Jim Lesurf

Post by Trevor Wilson
**Nope. A common fallacy, preyed upon unsuspecting buyers by purveyors
of all sorts of silliness connected via the mains supply. The facts are
more simple: Almost no noise can make it through the power transformer,
rectifiers and filter capacitors.

Alas, my experimental evidence clashes with your beliefs. :-)

** No it doesn't.

Post by Jim Lesurf
...depending, of course, of your definition of "almost no"...

** Drivel.

Post by Jim Lesurf
But the measured reality I found was that some noise can, indeed, enter
that way.

** Only RF - and then SFA as far as *audio* gear is concerned.

Tuners are another ball game.
You deceptive, smartarse Pommy turd.



...... Phil

[Dave Plowman (News)]

Post by Woody

Post by Brian Gaff (Sofa)
I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.

I had any number of amps - including a Quad 33 - which had such
problems, and in most cases a few very cheap components would overcome
the problems.

Very unlikely the problem came from within the 33. It is very well
filtered.

[Jim Lesurf]

Post by Woody
I had any number of amps - including a Quad 33 - which had such
problems, and in most cases a few very cheap components would overcome
the problems.

The 34 is similar in my experience.

Post by Woody
Small clicks and some RF pickup can be easily blocked by a small cap -
maybe 10nF - across each diode of the bridge rectifier. Many amps had
big smoothing caps which had relatively high inductance. A smaller
non-polarised capacitor - say 0.1uF in parallel, and an even smaller
disc ceramic such as an additional 1nF often did wonders. Having said
that, if the amp had a fully regulated power supply (which few did)
most of the above would not apply.

FWIW I fitted diode bypass caps to the bridge of the Armstrong 700 range
amps, and also designed the amp itself to strongly reject garbage on the
power rails. This made them fairly good at ignoring clicks and RFI from the
mains.

The diode caps don't only suppress snap noise. They also clamp everything
on the bridge together in voltage at RF.

Post by Woody
RF pickup was usually associated with high gain input stage. Easily
cured by insertion of 1K resistor in series with base connection of
first transistor close to transistor and a 4n7F ceramic capacitor
between base and emitter of the same transistor.

I just used passive signal conditioning at the input before any gain
stages. i.e. series R, shunt cap. This rolls off the ultrasound
sufficiently to avoid any nonlinear effects that let RF generate audible
effects. Again, with an amp design that has decent rail crap rejection.

None of the above is more than sensible design so far as I'm concerned, and
costs pennies. But some designs seem to have no awarness of RFI.

Jim

[Trevor Wilson]

Post by Brian Gaff (Sofa)
I have noticed this over the years, and assume its all down to filtering,
but that does not seem to be the whole story. No mater how much filtering to
try to put in with some designs you get clicks bangs and sometimes weak
radio transmissions from short waves or analogue land mobiles. You do not
seem to get the data noises from digital though unless you bring a mobile
near a very sensitive input like a microphone or pick up.
Brian

**It's complicated. I was service manager for Marantz, back in the late
1970s. Most Marantz amps, back then, were pretty decent products and few
issues WRT RF pickup were reported. Except for one model - The 4070. A
POS, 12 Watt/ch, 4 channel amplifier. So bad was this unreliable
monstrosity, that Superscope (the Marantz parent company) issued a
modification sheet for that model. It was a bugger of a job, involving
the fitting of various ceramic caps and isolating some of the earthing
within the amp.

I also had experience with a couple of instances of analogue TV 'frame
buzz' inserting itself into a couple of systems. One, belonged to a mate
and we finally solved the problem, by lining the inside of his speakers
with aluminium foil and using coax cable for speaker leads. In the
second instance, I supplied the customer with a zero global NFB
amplifier, which effectively dealt with RF pickup via speaker wires.

[Jim Lesurf]

Post by Trevor Wilson
I also had experience with a couple of instances of analogue TV 'frame
buzz' inserting itself into a couple of systems. One, belonged to a mate
and we finally solved the problem, by lining the inside of his speakers
with aluminium foil and using coax cable for speaker leads. In the
second instance, I supplied the customer with a zero global NFB
amplifier, which effectively dealt with RF pickup via speaker wires.

Did the amp not have a sensible Thiel/Zobel network? If it didn't I'd have
been wary of leads with a high shunt capacitance.

Jim

[Trevor Wilson]

Post by Jim Lesurf

Post by Trevor Wilson
I also had experience with a couple of instances of analogue TV 'frame
buzz' inserting itself into a couple of systems. One, belonged to a mate
and we finally solved the problem, by lining the inside of his speakers
with aluminium foil and using coax cable for speaker leads. In the
second instance, I supplied the customer with a zero global NFB
amplifier, which effectively dealt with RF pickup via speaker wires.

Did the amp not have a sensible Thiel/Zobel network? If it didn't I'd have
been wary of leads with a high shunt capacitance.

**My mate's amp was a Sinclair 80(?) or something like that. It was as
reliable as anything else that Mr Sinclair designed. Which is to say:
Not very. The other system was extremely problematic. The guy lived
around 100 Metres from a TV transmission tower. He had tried 10 or so
different amplifiers. None could deal with the frame buzz (yes, he tried
a Quad 405/44 combo). I supplied him a locally built, zero global NFB
model, which solved the problem.

[Phil Allison]

Trevor Wilson wrote:
=================

Post by Trevor Wilson

Post by Jim Lesurf
Did the amp not have a sensible Thiel/Zobel network? If it didn't I'd have
been wary of leads with a high shunt capacitance.

**My mate's amp was a Sinclair 80(?) or something like that. It was as
Not very.

** Note; Masterful Understatement.

Sinclair amps were not products but kit items for home enthusiasts .
TW has no shame .....................

Post by Trevor Wilson
The other system was extremely problematic. The guy lived
around 100 Metres from a TV transmission tower.

** WHHAAAAAAAATTTTT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Lucky if his brain was not fried like a hamburger.

Post by Trevor Wilson
He had tried 10 or so
different amplifiers. None could deal with the frame buzz (yes, he tried
a Quad 405/44 combo). I supplied him a locally built, zero global NFB
model, which solved the problem.

** So would a few ferrite rings in the right places.

No way would a Professional Vampire like TW spoil a sale by suggesting that idea....


....... . Phil

[Jim Lesurf]

Post by Phil Allison

Post by Trevor Wilson
**My mate's amp was a Sinclair 80(?) or something like that. It was as
Not very.

** Note; Masterful Understatement.
Sinclair amps were not products but kit items for home enthusiasts .
TW has no shame .....................

To clarify: Sinclair did indeed produce and sell a variety of non-kit audio
items. You can find examples represented here

http://ukhhsoc.torrens.org/makers/Sinclair/Leaflets/index.html

The first 'hifi' (sic) amp I could afford was a Sinclair 2000 amp. Wasn't a
kit I had to assemble but a finished (sic) product.

Yes, it was crap.

Jim

[Phil Allison]

Jim Lesurf Is a Mental Retard wrote:

================================

Post by Jim Lesurf

Post by Trevor Wilson
**My mate's amp was a Sinclair 80(?) or something like that. It was as
Not very.

** Note; Masterful Understatement.
Sinclair amps were not products but kit items for home enthusiasts .
TW has no shame .....................

To clarify: Sinclair did indeed produce and sell a variety of non-kit audio
items.

** But NOT the project 80

https://worldradiohistory.com/hd2/IDX-Consumer/Archive-Everyday-Electronics-IDX/IDX/70s/Everyday-Electronics-1974-08.CV01-OCR-Page-0053.pdf

** Which consisted of " modules " you put together like Mechano.

If you were gullible enough to buy the POS.
Massive scam.



..... Phil

[Don Pearce]

On Thu, 26 Aug 2021 03:28:32 -0700 (PDT), Phil Allison

Post by Phil Allison
================================

Post by Jim Lesurf

Post by Trevor Wilson
**My mate's amp was a Sinclair 80(?) or something like that. It was as
Not very.

** Note; Masterful Understatement.
Sinclair amps were not products but kit items for home enthusiasts .
TW has no shame .....................

To clarify: Sinclair did indeed produce and sell a variety of non-kit audio
items.

** But NOT the project 80
https://worldradiohistory.com/hd2/IDX-Consumer/Archive-Everyday-Electronics-IDX/IDX/70s/Everyday-Electronics-1974-08.CV01-OCR-Page-0053.pdf
** Which consisted of " modules " you put together like Mechano.
If you were gullible enough to buy the POS.
Massive scam.
..... Phil

He started his life in electronics selling reject Plessey Micro Alloy
transistors he had rescued from being dumped under a road as hardcore.
He spent days sorting out the ones that still had some measurable gain
and sold them.

d

[tony sayer]

Post by Trevor Wilson

Post by Jim Lesurf

Post by Trevor Wilson
I also had experience with a couple of instances of analogue TV 'frame
buzz' inserting itself into a couple of systems. One, belonged to a mate
and we finally solved the problem, by lining the inside of his speakers
with aluminium foil and using coax cable for speaker leads. In the
second instance, I supplied the customer with a zero global NFB
amplifier, which effectively dealt with RF pickup via speaker wires.

Did the amp not have a sensible Thiel/Zobel network? If it didn't I'd have
been wary of leads with a high shunt capacitance.

**My mate's amp was a Sinclair 80(?) or something like that. It was as
Not very.

Too bloody right!...

Post by Trevor Wilson
The other system was extremely problematic. The guy lived
around 100 Metres from a TV transmission tower. He had tried 10 or so
different amplifiers. None could deal with the frame buzz (yes, he tried
a Quad 405/44 combo). I supplied him a locally built, zero global NFB
model, which solved the problem.

Ever tried threading the connecting cables through ferrite rings at
all?...