Irritating buzz... where is it comming from???

[carlosfm]

For me the problem is just one: the two noisy channels are exactly those that are more far away from the star ground.
I'm always insisting on this: the ground wires must be as thick and short as possible. And ideally at same distances.
I made some edit on Devius' layout.
From the star ground point to the PSU, it must then go one thick wire.
When I say thick, it's 2.5mm multi-strand, 1.5mm minimum (not recommended here).
I would also change the position of the trafo, rotate 90º.

PS: I would disconnect mains earth, definitely not good for audio. I was once sent to Texas for saying this, but it's my experience, and it will always be my oppinion.

 

[Devius]

Nordic:

I would say the metal you are using is too thin to make much of a difirence.

I also think that way, but it's all I got. It's about 1mm thick, and I guess it should have been at least 2mm thick. I'll try to get some more scrap metal.

Greg Erskine:

Amp is reasonable quite with no input cable plugged in. Plug input cable in (just cable) buzz increases dramatically

That's also what I get. Did you try to connect the input directly to the amp board? You have to use the input signal wire and the input ground wire directly connected to the board. If you get silence you probably have the same problem as me. My guess is that the input wire from the input plug to the amp board is the responsible, and is picking up the noise radiated by the transformer and probably also some RF interference due to a large current loop area between the amp and the input. When you connect the input wires directly to the board, the input current loop area is reduce to almost nothing and if there is some noise present it is probably being picked up by the PSU wires.
I didn't try with a pot as you. I just route the signal from the cd player through a pre-amp. The pre-amp is quiet and is not responsible for any noise since it's headphones output is dead silent. I also tried direct connection from the cd player output and the noise is the same as when using the pre. My cd player is a standalone unit and not a cd-rom inside a pc. Those tend to produce lots of noise!! Try to use another signal source.

...to try re-routing them so that they don't pass so close to the transformer. the problem may be that the transformer is inducing noise into the PS wires.

That would be ideal, but those wires in reallity are even closer to the transformer than the drawing ones and it is absolutely impossible to route them any far from the tranny. The only way would be to route them through the outside of the box lol

You are correct as to the distance to the transformer. Both pairs are at the same distance, but since I can't route the wires, I'll attack the other difference between them: PSU wire resistance hoping that it'll reduce the noise intensity just enough to make it acceptable.
This 6 channel amp is to be used with a PC, so absolute noise free background is not necessary as the PC's fans are way noisier.

 

[wintermute]

For me the problem is just one: the two noisy channels are exactly those that are more far away from the star ground.

But when he moved the transformer away the noise went away, the ps wiring would have remained the same....... I think it is more a proximity issue. even if those wires were the shortest, but passed that close to the transformer, my bet is that those would be the channels with the problem.... I could be wrong though just my gut feeling.

Tony.

 

[wintermute]

Nordic:


That's also what I get. Did you try to connect the input directly to the amp board? You have to use the input signal wire and the input ground wire directly connected to the board. If you get silence you probably have the same problem as me.

I forgot about that aspect have you tried swapping around the input wiring from the input sockets to different amp boards?? maybe use the input furthest from the transformer to connect to amp's one and two and see if that changes your noise level in those amps??

Tony.

 

[carlosfm]

But when he moved the transformer away the noise went away, the ps wiring would have remained the same.......

Yes, there are two problems there, I adviced that at least the trafo should be rotated by 90º.
The gound problem will become more clear when he connects the signal to all the 6 channels.

 

[Devius]

maybe use the input furthest from the transformer to connect to amp's one and two and see if that changes your noise level in those amps??

Impossible! lol As I said earlier I'm using a 7 pin + shield input plug, so theay are all there. There is no farther away. This amp's case is so badly designed (what the hell was I thinking????!!! ) that the only place to position the input plug is in front of the transformer Dumb... All the other spaces at the rear panel are ocupied by the heatsinks. Addendum to the previous advices to anyone building a multi-channel amp:

- If you don't know much about proper layout and wiring techniques, or if you want to build a case as compact as possible, don't try to do a multi-channel amp

In response to Carlos post, I'll try rotating the tranny. Actually I was convinced that the rounded sides of a transformer were the ones that radiated the most. I already tried rotating it 90º but it was the other way. The connection pins were facing the input plug.
And I'm already in the process of making one very thick ground cable. It is about 4mm in diameter.

 

[steenoe]

I just finished building a pre and a power amp. The problem is that upon connecting the two there is a buzz. I've done all the usual procedures to eliminate any earth loop. The strange thing is that the buzz only shows when the signal cable from the pre-amp is connected to the power amp. There is a phones output on the pre and it's completely silent. Also, when the two are not connected, the power amp is also extremely quiet. One last detail is that the buzz is only present when there is soemthing connected to the input, so if one channel is connected but the other one is not, the connected one produces buzz but the other doesn't. If this was an earth loop the buzz should be always present right? Any ideas??

Hmmm, that kind of sounds like a problem we had before If I could just dig up the thread If you have a crazy input, put in some new rectifier diodes! Said it before, and Again I will do a search for you!! Its the bridge spilling over some nasty Sh#t.

Steen

 

[wintermute]

hi Devius,

I was assuming that it was a row of RCA plugs!!! it is a din plug is it?? the round type with 8 pins?? This is getting weirder and weirder

Tony.

 

[Greg Erskine]

That's also what I get. Did you try to connect the input directly to the amp board? You have to use the input signal wire and the input ground wire directly connected to the board. If you get silence you probably have the same problem as me. My guess is that the input wire from the input plug to the amp board is the responsible, and is picking up the noise radiated by the transformer and probably also some RF interference due to a large current loop area between the amp and the input. When you connect the input wires directly to the board, the input current loop area is reduce to almost nothing and if there is some noise present it is probably being picked up by the PSU wires.
I didn't try with a pot as you. I just route the signal from the cd player through a pre-amp. The pre-amp is quiet and is not responsible for any noise since it's headphones output is dead silent. I also tried direct connection from the cd player output and the noise is the same as when using the pre. My cd player is a standalone unit and not a cd-rom inside a pc. Those tend to produce lots of noise!! Try to use another signal source.

Thanks Devius,

I have attached a picture that shows signal input wires (blue and green cat5) from rca plugs to amp PCB are very sort. The cat5 signal earth going from rca plug to PSU star earth may be a problem but I didn't think so.

I've used these toriods in lots of amps and haven't had this issue with them, so I don't believe my toriods generate significant interference.

Generally speaking, in recent times, I have noticed issues with generic rca input cables and my DVD players (and this test CDROM player). When I was using one of my DVD players I could generate more noise by placing the pot on top of the unit. My gut feeling is the rca input cable is acting as an aerial. The particular amp in the picture doesn't have any input filtering or zobel on the output.

On my main system, using a CD player, I don't have these problems at all. Most of my amps are 100% dead quiet.

Replacing the CD player with one of my DVD players and I have issues similar to my test system.

regards

EDIT: I just went to check my test system and the issues I described have disappeared. All I have done in the last few days is take a picture. I can't seem to introduce to problem again. Very bizare, all I can think of is some external source of interference has gone.

 

[Devius]

Yep, it's a 7-pin DIN. Why did I use a 7-pin DIN for a 6-channel amp I hear you asking? Well, remember I started this project a few years ago and I didn't know much about electronics back then (not that I know much now). Somehow I believed there was a need to provide a ground wire from the pre-amp to the amp apart from the shield. They were both built at the same time to be used exclusively together, so a plug containing all the wires from one to the other seemed like a wise decision I won't even tell you what kind of cable I'm using in between them so don't ask!

I hope that at least this long thread can be of some help to a novice like me wanting to do a similar project.

Steenoe: I'm using a 35A 600V bridge. The KBPC type.

Greg Erskine: That is quite a mess!! :O Try twisting psu wires together (+V/-V and GND) and all other wires that are complementary and see if it helps.

 

[steenoe]

Steenoe: I'm using a 35A 600V bridge. The KBPC type.

At least someone pays attention Try a new bridge!
If you dont have any, I will send you some. Just let me know
I had this problem some time ago, and didnt really think it was the bridge causing the trouble! But it was. A crazy input spells defective rectifier!! Some of you guys should listen

Steen

 

[Greg Erskine]

Greg Erskine: That is quite a mess!! :O Try twisting psu wires together (+V/-V and GND) and all other wires that are complementary and see if it helps.

Hi Devius, please note I just editted my previous post stating that the problem I had on Tuesday night has disappeared on Sunday morning with no explanation.

It may look a little messy, but I have found that the only result is a very small amount of hum that is only noticeable when you place your ear against the speaker. I have used a common star earth on this test rig, its just the wires are all over the place.

It looks like I have been chasing my tail and I need to start from the beginning again if the problem comes back.

regards

 

[carlosfm]

Greg, off-topic, but I noticed you have both negative output binding posts on the left side to the positive.
You should standardize that. The negative (ground) binging posts should both be on the inner side.
Swap the binding posts on the left channel (on the pic).
If you use 'standard' layouts you will never make mistakes when connecting the wires, and you don't even have to look.

 

[Greg Erskine]

Thanks Carlos,

On my "real" amps I do the right thing, but on my test rigs I try to minimise wire length and wire crossovers, but I don't why?

regards

 

[Greg Erskine]

All fixed.

 

[Devius]

Greg, you may have a bad solder joint somewhere and by moving the wires, or something like that, fixed the problem, but it may comeback later on. Check all connections very carefully. Besides an external source of noise that's the only explanation I can find to tour (now extint) problem. I only wish my buzzing went away that easily lol

 

[Greg Erskine]

Hi Devius,

Bad solder joint, not bloody likely. Without sounding too pompus, I achieved expert soldering status 20 years ago. Now, could the alligator clips make a bad connection, likely. Could I have two wires touching that weren't supposed to, yes.

I have tried everything to re-introduce the problem, wrapped input wires around and across the toriod, moved the 240 wires in parallel with the speakers wires, input wires directly over the CD switchmode PSU etc. Nothing of course.

Very strange, it must have been a bad earth connection somewhere.

regards

 

[Devius]

Greg, you were really lucky

Today I managed to achieve a satisfying situation regarding buzz. I replaced the wires in amps 1,2 with thicker ones, installed the transformer as recommend by Carlosfm and also installed a shield in the transformer. The buzz is gone although there is a hissing sound audible at close distance to the speakers. Amps 5,6 have additional low level hum besides the hiss, but I suspect it's because I haven't replaced PSU wires yet.

Steenoe, what bridge would you recommend? I also have a GBU6K that's rated at 6A 800V, a Fagor FB3502 rated at 35A 200V and some 1N5406, 5408 diodes.

 

[carlosfm]

Now, could the alligator clips make a bad connection, likely.

Likely?
No, very likely.
I've had problems with aligator clips many years ago, and I tell you what you must do when you buy a bunch of those cheap things: open them all and solder the wires, if you don't wanna have problems!
Some of them are so badly crimped that they only work by pure luck, at a certain angle.

You'll only have a little work once, then you'll have peace of mind.

 

[wintermute]

glad to hear you finally got it solved Devius I guess the thicker wires are harder to induce a current in with a given level of magnetic field.... seems to make sense, I suspect the transformer rotation and sheilding all helped too. (I might have to go back and look at my 100W amp which has a buzz in one channel... though I have tried heavier wiring on it (up to 8gauge ) with no luck... I think it is mostly the position of the torroid... but it's given me hope that it can be solved

Carlos, I had the exact opposite with mains earth. When I had the chassis earthed and did not have the amp connected to chassis I had buzz, when I connected the amp to chassis it completely went away.... admittedly I didn't try with amp connected to chassis and mains earth not connected (for saftey reasons), though I did install an earth loop breaker for when I use with my PC which is also connected to mains earth.

Tony.