So I had a triad 14684 choke clone lying around...200mA, 125ohms, 5 henries. I had the crazy idea to try a choke input filter with a 2-5881, 3 12ax7 build. Sounds great but there is definitely power supply hum...the first filter after the choke is a 40uF with the OT CT and screens attached.
So i'm guessing the choke doesnt have enough inductance for this application? Could beefing up the filtering after the choke help this? It's not terribly loud, but its there.
choke input filter hum
Moderators: pompeiisneaks, Colossal
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: choke input filter hum
Filament lead dress? Or did you say DC filaments?
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
Hey skybolt-
I have ac filaments in this one. Amp was dead quiet before with the standard clc network..HOWEVER..I just rushed this choke in to try it this way- so I left the choke leads uncut. The extra long leads are right up against the 6.3v leads up at the pilot light...hmm
I'll chopstick it around tonight and see what happens. Hope I can get it to work because I love how it sounds, lots of sustain and smooooth...
I have ac filaments in this one. Amp was dead quiet before with the standard clc network..HOWEVER..I just rushed this choke in to try it this way- so I left the choke leads uncut. The extra long leads are right up against the 6.3v leads up at the pilot light...hmm
I'll chopstick it around tonight and see what happens. Hope I can get it to work because I love how it sounds, lots of sustain and smooooth...
Re: choke input filter hum
What is the orientation of the laminations to the other iron? How far apart?
You may have some coupling creating the hum. No amount of chopsticking will fix it if that's the problem. Got a picture? It just needs to show us all the iron.
You may have some coupling creating the hum. No amount of chopsticking will fix it if that's the problem. Got a picture? It just needs to show us all the iron.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
Phil, I dont have a picture right now...but i'll try to explain. With the chassis on a table, facing the control panel trannies up, the transformers from right to left are: PT(laydown) mounted like you would see in a fender tweed, 2 inches from that is the open frame choke(2 bolt mount), than another 2 inches the OT mounted pependicular to the choke.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
...oh, and BTW, would this thing need to be air-gapped with all the current flowing through it? It's about the size of a 25 watt fender OT.
EDIT..contacted manufacturer and it is air gapped.
EDIT..contacted manufacturer and it is air gapped.
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Re: choke input filter hum
Did you trim the choke leads yet? Any change?
You had a PT and an OT 4 inches apart, PT laydown, that's OK. Now you have an open frame choke between them and only 2 inches between each piece. I'd say you're pushing your luck, especially as the choke is open frame.
You should also run the minimum inductance calculation I think, your instinct is good there, but I don't know the voltage and current. If you're running a fairly tweedy 350V and 100mA draw, Min. inductance is (350/0.1)/1100=3.2H, so you're OK with a 5H choke.
You had a PT and an OT 4 inches apart, PT laydown, that's OK. Now you have an open frame choke between them and only 2 inches between each piece. I'd say you're pushing your luck, especially as the choke is open frame.
You should also run the minimum inductance calculation I think, your instinct is good there, but I don't know the voltage and current. If you're running a fairly tweedy 350V and 100mA draw, Min. inductance is (350/0.1)/1100=3.2H, so you're OK with a 5H choke.
Re: choke input filter hum
Just 'cause the orientation of the lams seems to follow the "rule" it's not a sure thing. I'd look first at the lead dress of the choke and then I might look to see if there another location for the choke. As someone else observed, it might just be too crowded.
You might see if you can jerry rig a case over the choke to give it a bit of shielding. As a test, you might make a cardboard box and cover it with kitchen foil. Tape it down and see if it helps. This is cheap and will take you 10 minutes.
You might see if you can jerry rig a case over the choke to give it a bit of shielding. As a test, you might make a cardboard box and cover it with kitchen foil. Tape it down and see if it helps. This is cheap and will take you 10 minutes.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
Thanks for the tips guys...i'll try some things.
I just noticed the choke leads arent twisted together either.
I just noticed the choke leads arent twisted together either.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
David-
The supply voltage directly after the choke is about 270v. Total current at full tilt is around 170mA.
I have a 5k OT I want to try...I think im going to mount the ot in the center, and put the choke on the other side of the chassis, away from the PT. I'm also going to beef up that filtering on the CT and screens.
The supply voltage directly after the choke is about 270v. Total current at full tilt is around 170mA.
I have a 5k OT I want to try...I think im going to mount the ot in the center, and put the choke on the other side of the chassis, away from the PT. I'm also going to beef up that filtering on the CT and screens.
-
redtoploader
- Posts: 27
- Joined: Fri Dec 14, 2007 2:27 am
Re: choke input filter hum
Well, I did these changes and the hum reduced signifigantly. I'm guessing the filtering on the first node did most of the trick, I bumped it to 100. Now i'm going to move the screens to it's own node and put some of its own filtering on that.
I have almost 260 on the plates, running darn near or at class A operation...top-boosty type preamp. Sounds really nice.
I have almost 260 on the plates, running darn near or at class A operation...top-boosty type preamp. Sounds really nice.
choke calculation
David I would like to know more about the calculation you made :
I would like to be able to calculate it myself.
Thanks, Alf
The numer 1100 in the equation , where does this come from ?You should also run the minimum inductance calculation I think, your instinct is good there, but I don't know the voltage and current. If you're running a fairly tweedy 350V and 100mA draw, Min. inductance is (350/0.1)/1100=3.2H, so you're OK with a 5H choke.
I would like to be able to calculate it myself.
Thanks, Alf