Download Noise Reduction Tips..

Untitled Document
From:
Date:
Subject:
Page 1 of 6
Ed (ed.kozek@spotfire.com)
9/22/2001 9:25 AM
BEST noise reduction tips
I thought I'd start a thread here for homebrewers who want to thwart unwanted noise in
the design stage. What are your top noise reduction tips?
I've got a couple:
1. Shield the wire going from the input jack to the first preamp tube (remember, only
ground one end).
2. If the PT and OT and near each other, make sure they are positioned perpendicular
to each other.
Any one else?
From:
Date:
Subject:
Ray Ivers (RAGEray@aol.com)
9/22/2001 1:08 PM
Re: BEST noise reduction tips
Ed,
Good thread! All below are IME:
1) If you're going to use AC heater power, use CT heater windings if possible, tightly
twist heater wiring, and tuck it into chassis corners if possible, away from signal wiring.
2) Think of 'signal ground' as 'signal negative', which is really what it is, and treat it with
all the respect you would give to 'signal positive'.
3) Keep 'power supply negative' separate from 'signal negative', except at one point
(see #7).
4) Connect the main filter cap negative terminal to the PT CT (full-wave) or diode-bridge
negative (full-wave bridge), and then to 'power supply negative'.
5) High voltage capacitors at the HT to individual gain stages/blocks are not mainly filter
caps, but rather signal bypasses - see #6 below.
6) Connect each gain stage's cathode resistor/capacitor negative, grid resistor and/or
gain pot negative, and signal bypass capacitor negative together, and then connect that
to 'signal negative'.
7) 'Signal negative' should be connected to chassis near the input jack (sometimes thru
a 10 ohm resistor to minimize ground looping); 'power supply negative' should be
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001
Untitled Document
Page 2 of 6
bonded (permanently & intimately connected) to chassis near the power cord, to the 3prong power cord's ground wire.
8) If you're going to clone an amp and don't think you have the theoretical chops to
redesign it for lower noise from the outset, clone it exactly , layout and everything; it's a
lot easier to make a properly -functioning amp quieter than to troubleshoot a noisy
design, so take advantage of the original designer's hard work in getting a functional
design/layout.
9) Ask questions at Ampage. :)
A lot of these are deliberately kind of vague, to allow them to apply in a general way to
more amp designs. And of course there are about a million other noise reduction tips
and tricks out there; I'd love to know about a book that treated this subject with the
depth it deserves, rather than just as one chapter.
Ray Ivers
From:
Date:
Subject:
Carl Z (carl@zwengelamps.com)
9/22/2001 3:37 PM
Re: BEST noise reduction tips
Ray;
Definetly what works for one amp may not work for another when it comes to noise
reduction. Just follow some solid rules and the amp should be nice and quiet. Getting it
stupid quiet is another story.
I'm gonna bust on you a little here. You said...
'power supply negative' should be bonded(permanently & intimately
connected) to chassis near the power cord, to the 3 -prong power cord's
ground wire.
I've got a big niggle with this one. The rule, well actually I believe it's a requirement for
commercial equipment, is to NEVER EVER share the safety ground with any other
ground connection in the amplifier.
The ground connection from the power cord should also be somewhat longer than the
hot and neutral so that it's the very last wire to break should disaster strike.
Carl Z
From:
Date:
Subject:
Ray Ivers (RAGEray@aol.com)
9/22/2001 6:16 PM
Re: BEST noise reduction tips
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001
Untitled Document
Page 3 of 6
Carl,
Hey, if you've only got one issue with all those potentially controversial items, I must be
doing OK. :)
Thanks for that info about the safety ground. It certainly shouldn't cause any extra noise
to ground the power supply negative to a point nearby the safety ground, instead of
directly to it.
I purposely left out any items related to ground lifting, too, because of the safety angle.
Maybe on another thread related to noise reduction with interconnected components...
Ray
From:
Date:
Subject:
Carl Z (carl@zwengelamps.com)
9/23/2001 3:30 PM
Re: BEST noise reduction tips
I purposely left out any items related to ground lifting, too, because of the
safety angle.
I've always kinda wondered about raising the audio ground a little above "real" ground
by connecting it to a single star point throug a big ole 10ohm resistor or something. It's
done frequently in low power ss gear but these ain't no 20w boom boxes running on
25vdc!
From:
Date:
Subject:
aron (aronnelson@bigfoot.com)
9/23/2001 8:26 PM
Re: BEST noise reduction tips
Ray,
Thanks for the tips!
I have a questions about #7.
I currently have a star ground setup, should I try and connect the preamp (well, circuit
board ground) to somewhere near the input jack rather than at the star point?
Does it make a difference?
From:
Date:
Ray Ivers (RAGEray@aol.com)
9/24/2001 1:56 AM
Subject:
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001
Untitled Document
Page 4 of 6
Re: BEST noise reduction tips
Aron,
If your amp doesn't hum now, I guess you can leave it as is... but I don't think I would
ever recommend sharing high-ripple-current power-supply grounds with low-level signal
grounds. I think at the very least I would ground the first gain stage's common ground
point to the input jack ground, and then ground that to the chassis near the input jack. If
it hums more, connect it back the way you had it.
Ray
From:
Date:
Subject:
Nigel Brewer (nigelbrew@webtv.net)
9/30/2001 2:19 PM
Re: BEST noise reduction tips
Now I am really confused. I have read too many conflicting ideas concerning the whole
grunding issue.First off, if you grond near the input jack, is it a star ground or a buss
ground. Would a buss ground cause ground currents from later stages to flow into more
sensitve pre amp stages?As far as using capacitor ground lugs as star ground points,
this at least makes sense in the way it is explained on Randall Aikens site, and how
much ripple is left once you get to the pre-amp stages anyway.could someone please
explain?thanks in advanceNigelhttp://www.mp3.com/nigelbrewer
From:
Date:
Subject:
Ray Ivers (RAGEray@aol.com)
9/30/2001 4:12 PM
Re: BEST noise reduction tips
Nigel,
As you know, a star ground is multiple grounds connected to a single point, and a buss
ground is multiple grounds connected to multiple points on a grounding buss. It is quite
common to combine these two topologies.
First off, if you grond near the input jack, is it a star ground or a buss ground.
It depends. If all grounds are connected to this point (bad idea IMO), it's the star ground.
If just the first gain stage's grounds are connected to this point, it's a local star ground. If
this is simply the chassis ground point of a buss ground, then it's simply that - the
chassis ground point of a buss signal ground.
Would a buss ground cause ground currents from later stages to flow into
more sensitive pre amp stages?
Not if it's done correctly. Any grounding scheme can be done incorrectly, it's just a lot
harder in theory to do the star grounding scheme incorrectly since the principal is so
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001
Untitled Document
Page 5 of 6
simple. That does not mean that I recommend star grounding for each and every
possible grounding application, as I have seen more noisy star-grounded amps than
buss-grounded amps; it's extremely difficult to get the necessary zero ohms resistance
between all points of a star ground to make it work perfectly.
Sorry if I was unable to condense 18 years of chasing down, studying, and finally pretty
much getting a handle on grounding techniques into a single reply. :) My advice would
be to trace electron flow (both AC and DC) from the main power supply filter cap's
negative terminal to its positive terminal, through each gain stage, and see if any current
flows through an early stage before it flows through a later stage. If it does, you have
the potential for hum and who -knows-what else. This also really helped me get a feel for
the whole negative-signal-path aspect of grounding, and took me away from the simple
chassis-ground aspect which is only one fairly small part of it IMO.
Ray
From:
Date:
Subject:
Nigel Brewer (nigelbrew@webtv.net)
9/30/2001 5:05 PM
Re: BEST noise reduction tips
I think Carl Zwengel made a good point by saying that what works for one amp may not
work for another, I mean, the way the stages are arranged must influence this to some
degree, an also whether the preamp power supply is a paralell branch configuration, or
if all the filters and Isolation/voltage dropping resisters are in series.I most definetly have
the first pair of power filters (2 60uf 500v Cornell Dublier)) connected to the h.t centertap
then to the first starground pont on the chassis. the speaker jack is conected the
cathode of the power tube receiving its signal from the inverting side of the phase
inverter, then to the first star point on the chassis. the bias ground also goes to this
point. To reduce the amount of connections going to the same terminal The Screen
Filters (30uf times 2)are grounded to the chasis "downstream"but close to the main star.
The remaining driver stage filter (30uf)and preamp filter caps go to another point close
to that one.I also like the idea of connecting togeather the local grounds of stages that
are out of phase with each other to create some sort of humbucking effect, and reduce
the amount of wires for a cleaner layout. Thats what I am working on at the moment,
any other ideas?Gotta go, Its kickoff time forRedskins Vs. ChiefsI predct the skins will
loose by at least 2 2 touchdowns that is!thanks,Nigel
From:
Date:
Subject:
Daver (bluefire@voyager.net)
9/30/2001 6:34 PM
Re: BEST noise reduction tips
Would multiple star grounds be a good idea? Like each stages grounds and filter cap
grounded, say, near that preamp tube. Maybe using the tube socket mounting screw to
mount a ground tab/terminal. Does the chassis material matter in choosing a ground
scheme? Thanks!
Daver
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001
Untitled Document
From:
Date:
Subject:
Page 6 of 6
Ray Ivers (RAGEray@aol.com)
9/30/2001 8:10 PM
Re: BEST noise reduction tips
Daver,
If chassis material matters in a given grounding scheme, IMO that grounding scheme is
absolutely incorrect no matter how well it works.
Imagine a 5F6A tweed Bassman circuit in a Lucite chassis, with a two -prong power
cord. It is possible to design such a unit to be absolutely power-supply-hum-free, but to
do it IMO you will have to be able to think of the signal ground buss as 'signal negative'
and the PS ground buss as 'PS negative'. Chassis ground will not exist, since
electrically you do not have a chassis.
This is a visualization I do when thinking out grounding schemes. It is not UL -approved
or a recommended construction, just a mental aid I find helpful. :)
Ray
http://www.firebottle.com/fireforum/fireBB.cgi?forum=ganoise&thread=141123
... 10/1/2001