Switched to Star ground, picking up FM?

Folsom · « **on:** 22 Dec 2008, 02:17 am »

In my Audiosector 3875 I decided to reduce some noise or something by switching to star grounding.

I soldered PG+, PG-, CG-Right, CG-Left, and with a 100ohm resistor in the path wire that connects to the chassis.

When I turn my amp on I have a tiny bit of noise which I am afraid is just from my transformer being so close to the rectifier board. Which reminds me anyone know anything to isolate this thing from that? I tried copper foil grounded to neutral but that just made the FM worse, did nothing for killing noise.

I have Hawthorne Silver Iris speakers. I would like for them to be dead silent with no source on but with amplifier on.

Lastly I have some subwoofer amps getting their information from high level in. I tried turning them all the way off to see if it helped but it did nothing but kill their transformers noise.

Folsom · « **Reply #1 on:** 22 Dec 2008, 05:43 am »

Well I redid some stuff, eliminated a lot of wires, reduced it all, but still got well heh... noise. It has to be the damn toroid. When I power it on the frequency which is really loud from the toroidal sounds like what is in the speakers.

markC · « **Reply #2 on:** 23 Dec 2008, 02:18 am »

Try a small value cap in series with your ground resistor to chassis.

JoshK · « **Reply #3 on:** 23 Dec 2008, 06:43 pm »

Quote from: markC on 23 Dec 2008, 02:18 am

Try a small value cap in series with your ground resistor to chassis.

Sounds like you made an antenna somewhere. Don't jump to conclusions that what you did was wrong. You may very well just not implemented it well enough. Mark's advice to try lifting the ground is good. I would try his solution for a short term test, but if it works them parrallel the cap with a small valued high watt resistor and a pair of 10a diodes (in opposite directions).

Folsom · « **Reply #4 on:** 23 Dec 2008, 09:12 pm »

I found out that 5% of 3875 chips pick up FM. I am going to put 330pf capacitors on the V+ and V- in. The hum though, that I want to kick. I wonder if an earth ground to the chassis would help. It is so the hum of the transformer

.

Folsom · « **Reply #5 on:** 23 Dec 2008, 10:14 pm »

Well that is a big no. I made sure every piece of the chassis is grounded well by doing some sanding on paint... I just got more FM. My case seems to be a bit of an antenna. I hope the capacitor thing will fix it.

*Scotty* · « **Reply #6 on:** 23 Dec 2008, 10:40 pm »

DOS,Have you verified that the hum is coming only from amp by putting shorting plugs in the inputs. My chip amp has barely perceptible noise when I put my ear next to the speaker. The speakers are 96dB. This is the system noise level from the CD through the preamp with over 20 feet of unshielded IC between the preamp and the power amp. I think if you can get the amp grounded correctly it should be dead quiet. My 500 watt toroid is about 1 inch from the rectifier and power supply capacitor bank and I have not had any hum resulting from the proximity of the transformer next to the power supply caps and rectifier. The wiring from the Jensen capacitor bank to the chip board is about 2 inches. My input jacks are isolated from the chassis and hot and signal ground go to the board.
Good luck with the noise problem.
Scotty

Folsom · « **Reply #7 on:** 24 Dec 2008, 08:57 am »

I try it with the CD player off every time. I could unplug it from the amplifier.

I have tried with the subwoofers unplugged which use the high level in from the amplifier, but they hum a lot so maybe it is them and I fixed all the other stuff but the FM which I either need a better grounded socket for (no earth) or the capacitors on 7 and 8 pins.

f2a · « **Reply #8 on:** 24 Dec 2008, 02:31 pm »

every body like the silent speaker without signal on amp ,
can you remove the input connection from pcb ?and listen to speaker .

*Scotty* · « **Reply #9 on:** 24 Dec 2008, 10:14 pm »

I would suggest that you do not under any circumstances turn on your amp without the inputs terminated by a source or shorting plugs. If your CD player has a tube output stage or a less than stellar SS output stage it could have an output impedance that is substantially above zero which is what shorting plugs have. This won't matter as much if your ICs are a shielded design. Is the hum and noise substantially louder when the CD player is on compared to when it is off.
Scotty

f2a · « **Reply #10 on:** 25 Dec 2008, 05:50 am »

Different between unplug the source like cd player and input terminal removing complete ,we try to finding hum noise and maybe we should to insulate the mine grand from the rca input terminal and changing to another place .. so its better to remove complete connection of rca and listen result in speaker .

Folsom · « **Reply #11 on:** 26 Dec 2008, 10:00 pm »

I unplugged the CD player (RCA connections) and the FM went away. I wonder what is picking up the FM now... The cables? Perhaps I will earth ground the chassis on the CD player (did not have it stock, from like 1988 or something, but it has a 1541a chip, sounds great (like a very expensive unit great, old Adcom), upgraded it a lot).

I then unplugged the connections to the subwoofer and got a reduction in the 60hz hum but it is not gone. I still assume that the toroidal being within an inch of rectifiers etc might be the one doing it. However the FM is confusing.

JoshK · « **Reply #12 on:** 27 Dec 2008, 03:44 am »

Sounds to me like maybe your cables are antennas. Do you have a floating shield? Floating on one end that is? If that is the case, you might try adding a small cap (couple nf's) to the amp end between the shield and return (neutral). This way it blocks EMI (low freq) while not allowing for the shield to be an RF antenna.

The above solution is thanks to Wayne of Bolder Cables who taught me that trick.

Folsom · « **Reply #13 on:** 27 Dec 2008, 04:39 am »

I have MIC cables. I am using one inside conductor for signal and outside for ground.

I have been told that it is not smart to use both inside ones or impedance will be too low.

f2a · « **Reply #14 on:** 27 Dec 2008, 06:25 am »

Quote from: Destroyer of Smiles. on 26 Dec 2008, 10:00 pm

but it has a 1541a chip, sounds great (like a very expensive unit great, old Adcom), upgraded it a lot).

You know that this chip is 2 power supply amp or dc connection

.and in this kind of topology sound is too enough good for listening music . but how abut musicality ?i start 2 power amp since I was 14 years old with sansui famous integrated amp(during that times) diy ,so I build and check so many new audio chip .result = good sounds in bandwidth - good in distortion- good in price -easy to build and repair –small spice –good in rejection noise (not in your kit)- but no more lovely sound and you will tired in listening music over 60 minuet

In fact they are good in 2 back speaker amp for cinema 5.1 . never forget in your kit the company use the best design in box and its useful in out put sound ,if you can remove your 60 hz noise from your amp and you love the transistor sound for ever .

JoshK · « **Reply #15 on:** 27 Dec 2008, 07:58 am »

Quote from: Destroyer of Smiles. on 27 Dec 2008, 04:39 am

I have MIC cables. I am using one inside conductor for signal and outside for ground.

I have been told that it is not smart to use both inside ones or impedance will be too low.

For digital maybe. For analog line level signal this isn't true. The outside one is a shield? Measure the DCR from end to end for both inside and outside to see what you get. Then look inside each chassis to see how the connectors are terminated. Are either or both sides of the connectors (cd player or amp) isolated from the chassis?

Folsom · « **Reply #16 on:** 27 Dec 2008, 05:46 pm »

My amplifier's input is isolated from the chassis for sure. The cd player is hard to tell, but I would guess yes.

JoshK · « **Reply #17 on:** 27 Dec 2008, 06:39 pm »

I don't know. I'd just start process of elimination. Something is acting like an antenna. Try to isolate it so you can determine what it is.

Folsom · « **Reply #18 on:** 31 Dec 2008, 09:20 pm »

It is the RCA cables FOR SURE. I unplugged them from the CD player side and got like twice to ten times the amount of FM radio.

The RCA jacks on the CD player are isolated.

I will try re-doing them with a drain CD player side and using the internal two wires instead.

Folsom · « **Reply #19 on:** 31 Dec 2008, 10:22 pm »

Same results with shield as drain.

Same results without shield as drain.

Is it the connectors

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=091-056

Or the wire?

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=100-220

Or is it a combination of no real earth ground and having anything long connected to the chassis which is earth grounded? My RCA jacks are isolated.... (should be anyways, the got plastic spacers on each side)