tamtamstudio

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« on: August 10, 2006, 05:19:14 PM »
Hi guys, I've just finished my 1st g9 (with shield and cut trace mod) and now sounds very good except for a noisy hum @100Hz -80dB.
S**T, I moved or turn toroid with no success..

Now my imagination is near to the end..what i have to try?
can you suggest me something else (except something like pray..) :cry:


rodabod

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #1 on: August 10, 2006, 05:48:56 PM »
How have you implemented your grounding generally? Star ground?

I've not made a G9, but there are some rules that people usually follow for grounding.

Maybe if you post a photo then people can help.

Roddy
Quote from: tv
punchy fat bastard chip

tamtamstudio


Greg

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #3 on: August 12, 2006, 12:13:05 PM »
It look likes you have your output XLRs very close to the power tranny... I usually try to keep my AC as far away as possible from any audio path. Also, you have some wires running the length of the chassis to the big PSU filtering caps... this is generally not good practice. Anything with AC you want to keep over to the right side of chassis... away from the PCB and input and output connections.

I don't know if this will solve your problem entirely... but it could be a contributing factor.
Greg Stein
New Orleans, LA

SSLtech

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #4 on: August 12, 2006, 12:22:34 PM »
100Hz... -I'd stop looking for induced hum and start looking at ripple.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

jensenmann

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #5 on: August 12, 2006, 12:30:04 PM »
Your output wires run unshielded from the PCB to the XLRs. If you take a look at the checkplot you´ll see that the middle output solderhole which is supposed to be ground has no connection to the PCB ground. For shielding the output wire you need to connect output-XLR pin1 to the starground (nowhere else).
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

mattmoogus

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #6 on: August 12, 2006, 01:15:08 PM »
You seem to have ground wires coming from the torroid bolt, this isnt a good idea as you can potentially make a shorted turn and burn out the transformer.


[email protected]
...btw I work for Joe :-)

CJ

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #7 on: August 14, 2006, 12:44:36 PM »
#1 culprit is heater noise
#2 would be xfmr location
#3 would be ground loop between source and amp and output listening device (headphone amp or stereo amp and speaks
#4 would be inadequate filtering-but if you followed the schemo, this is a non issue
#5 would be excessive lead length and location on input wiring.

Output wiring is now at 600 ohms, very difficult to induce hum into this enviro. I think. Anybody ever done it?
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

alk509

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #8 on: August 14, 2006, 01:03:00 PM »
Unplug that thing right now, before you kill your transformers!!! You have ground wires connected to the top of the toroids' mounting bolt! :shock:

Peace,
Al.

Lest laziness get the best of you!

SSLtech

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #9 on: August 14, 2006, 01:41:02 PM »
+1.

That you haven't burned something already is a miracle! You'll have so much current coarsing through your ground, I'm a little surprised!

-For sure your local ground will be MUCH cleaner, and as an added bonus, you're less likely to have it burst into flames!

Seriously. GROUND NOTHING[/u][/b] THROUGH THE TOROID BOLT.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.


Svart

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #10 on: August 14, 2006, 02:16:41 PM »
[email protected]?  I'd say that's respectable!

I get normal white noise at close to -75.  I use hot mics and NEVER hear the noise.
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

kiira

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #11 on: August 14, 2006, 02:29:44 PM »
Quote from: "SSLtech"
+1.

-For sure your local ground will be MUCH cleaner, and as an added bonus, you're less likely to have it burst into flames!

Seriously. GROUND NOTHING[/u][/b] THROUGH THE TOROID BOLT.

Keith


Why is that? You mean if the bolt touches a bare wire inside the totoid?

Kiira

alk509

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #12 on: August 14, 2006, 03:12:08 PM »
Quote from: "kiira"
Why is that?


Imagine what would happen if you short both ends of a power transformer's secondary to ground. Now notice that a metal mounting bolt is basicaly a single-turn secondary, with one of its sides connected to ground (the side that bolts to the case). Now picture what happens if you short the top of the bolt to ground as well.

BOOM! :shock:

Peace,
Al.

Lest laziness get the best of you!

SSLtech

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #13 on: August 14, 2006, 03:28:33 PM »
Yes, basically a bolt is a big, thick high-current conductor, passing through the center of the toriod.

If you think of a 1,000 turn 110V primary as being a conductor that passes through the center of the toroid 1,000 times, and a 100 turn 11V secondary as being a conductor that passes through the toroid 100 times, that's a reasonable analogy (numbers pulled out of the ether solely for the sake of example, but not totally out of scale with reality).

Now, no current flows in the secondary until you close the circuit between the two ends of the secondary conductor. -Open circuit secondary draws no current, and no power is drawn from the primary (other than essentially insignificant core losses).

Now, 1Amp drawn through our 110V primary will equate to a 10Amp current in the secondary. (W=IV, power is unchanged, so of volts go down, current goes up and vice-versa.)

So consider our 1-turn conductor. (The bolt.) -As long as nothing which passes outside of the toroid's core connects the two ends of the bolt to each other electrically, no current flows. As soon as you short them together, you have a turns ratio of 1000:1 (1,000 turn primary, 1 turn secondary). Since the secondary is shorted, it tries to pass as much  current as it can and things get pretty nasty. Don't be calmed by the fact that a 1000:1 turns ratio gives you 0.11Volts from a 110Volt input... 1 amp flowing in the primary will give you 1,000 Amps flowing through the secondary bolt!

A thousand amps. Think about that... it's enough to weld with. And welding  is exactly what can happen.

In reality, if you short a secondary, the instantaneous current flow is WAY larger than what the transformer was designed for, and the core saturates, wire burns and all sorts of nastiness breaks loose... basically be VERY careful with toroids. If possible, use a plastic cap on the top of the bolt: -if the conductive tip of the bolt touches the top of a conductive metal case, the same thing happens. -I like to use those plastic "rod-caps" on my toroid bolts for exactly this reason.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

CJ

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #14 on: August 14, 2006, 06:07:12 PM »
Well, the amp is functioning, could this be possible with the torroid shorted?
If your fuse dosen't blow withg a shorted turn, something is amiss.

Two more things, make sure your soldering iron is off, they can induce incredible hum from 4 feet away, and sometimes hum will go down with the lid bolted on.
Everybody tests with the lid off, for obvious tweaking and measuring purposes.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

kiira

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #15 on: August 14, 2006, 09:39:26 PM »
Thanks Al and Keith. So the bolt is electrically part of the transformer and shorts if both ends get grounded and causes trouble because of the high current induced by the toroid in the bolt. I hope I have that right.

I've never used a toroid yet.. though I have a couple here. Thanks for the info I think I'd feel better using a plastic bolt or something else non-conductive. Ha... I've been working on tube stuff for um, seven years or so and I've never had an accident and I don't want to break that trend.

Kiira

tamtamstudio

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #16 on: August 20, 2006, 01:05:02 PM »
:green:  I'm back from holiday.. sorry guys!
I'd tried many combinations, at first i'd removed the ground from the toroid bolt. no big differences.
Ground star, now is:
1. AC inlet to chassis bolt
2. INPUT Left to chassis bolt
3. INPUT Right to chassis bolt

(sorry, no photos now)

Now, some specs, on BOTH channels NO differences:

with gain & output closed: -82.5 dB @100Hz
with gain & output open (with an SM58 connected in quite room): - 65.5 dB @100Hz
with gain & output open +low cut filter (high pos) (with a SM58 connected in quite room): - 70 dB @100Hz

Here some voltage (with all tubes inserted):
capacitor pinout [229V - 0 - 239V]
capacitor C14 239V
capacitor C15 (heater) 229V

IC 78012 out: 11.8V
IC TL783 out: 236V (after R37: 229V)

trafo HT pinout AC 210V output
trafo HT pinout AC 15,4V input

What do you think guys, all is correct?
 :?

SSLtech

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #17 on: August 20, 2006, 01:12:03 PM »
I'm still saying this:

If it really IS 100Hz, it's from AFTER THE BRIDGE RECTIFIER!

Think about it: anything before is 50Hz, anything after is 100.

There are three probable causes: Ripple, ripple and ripple.

Of course, there is also the occasional possibility of hum induction from the lines coming from the rectifier to the reservoir caps, but the first thing to measure is ripple.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

tamtamstudio

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #18 on: August 20, 2006, 01:17:12 PM »
I'm thinking, you are totally rights!
.. but ..  :oops: what can I do.. I'm not really an expert.. have you a suggest? :cry:

jensenmann

G9 hum @100Hz -80dB problem..not solved.. Now SOLVED!
« Reply #19 on: August 20, 2006, 04:41:42 PM »
Measure the PSU B+ with your DMM in AC mode. This will give you the ripple voltage. Let us know how much it is.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort


 

Related Topics

  Subject / Started by Replies Last post
0 Replies
935 Views
Last post August 29, 2006, 09:01:54 PM
by pucho812
30 Replies
6819 Views
Last post March 02, 2010, 03:15:58 PM
by SaMpLeGoD
17 Replies
5841 Views
Last post April 13, 2007, 08:43:58 PM
by Stagefright13
18 Replies
3394 Views
Last post December 25, 2014, 12:29:53 PM
by aclac