Grounding Problem/落地問題

這幾天忙裹偷閒, 切了部McIntosh C22. 一開機, 不得了, deeee deeee 聲不絕於耳. 研究之下, 應是落地做得不好之過.

聽了恩師"秋官"意見, 水線落機箱做地. Volume 制即落地. 底板個GND我自己決定唔用.

請問各位大哥, 我這個做法可是正確?

D "deee deee" 聲沒有了. 但我想知/學的是為什麼呢? 這個改動為何可將 D "dee dee"聲消滅? 這些 dee dee 聲是否由"回路而來? 請各位大哥指教.

Assembled a McIntosh C22 from DIYZONE lately. During the test run, the "noise" (deee deee like) from improper grounding is unbearable.

After taking some advices from my colleague, I decided to modify the ground part. First, ground the "GND" wire from the 13A plug directly to the chasis. Second, ground the "GND" from the volume control directly to the chasis. Third, removed the GND wire from the PCB totally.

Dear brothers, am I doing the right thing? I do realise that the noise is gone. BUT why would my modification above elminated the "deeee deee" noise? Is this noise a kind of "feedback"?

Please advise. Many thanks!

CAT

你個底板的地已經有輸出處和機箱連在一起，輸入的地亦落了地，因和輸出連在一起。請問原來有 dee dee 聲是如何接的。

White CAT,

You need to sure there are single GND connection for all, it cannot be a loop created.

Also, pls pay attnetion on Small signal area and large signal GND

e.g.

Signal output GND -- Power supply GND -- Singal input GND -- Vol GND -- tube PCB GND
If the mounting point is by Signal o/p GND, you will see a longer path happen.

Hope you can understand what I mean la.

CAT HO

Dear Accphoto,

Original Design:

1. Signal In using silver plated copper wire, NOT coaxial. Signal (L+R) into Volume Switch L,R in. Volume Switch GND goes to PCB GND.

2. Volume GND just goes to PCB GND. No extra wire going to chasis.

3. 13A plug GND goes to Signal in / out common GND (the thick copper wire), not to the chasis.

CAT

KK Sir,

有d明, 有d唔明. 我明白最好是一點落地 (星型). 但基於我絕無緊有的電子常識, 有時唔知點先做得到這種arrangement.

請問我現在這個做法可是okay? 有無再可以改善的地方?

CAT

[quote:9155613bc1="alfcat"]Dear Accphoto,

Original Design:

1. Signal In using silver plated copper wire, NOT coaxial. Signal (L+R) into Volume Switch L,R in. Volume Switch GND goes to PCB GND.

2. Volume GND just goes to PCB GND. No extra wire going to chasis.

3. 13A plug GND goes to Signal in / out common GND (the thick copper wire), not to the chasis.

CAT[/quote]

咁你係地連水線，無落機箱地，90% dee dee 聲......
另外輸入，和輸出線最好用 co-ax, co-ax 線在輸入端接地，另一處空接，這樣不會有 gound loop.
你的 dee dee 聲是因為你機箱無落地，所以 dee dee 聲。
做前級,我通常在輸入端連水線跟機箱接,然後連 volume 地和 pcb 地。 Output 地連 pcb 地但不會接機箱。
做後級則真接在 power  -Ve 處落地。

Dear Accphoto,

There is one thing I don't quite understand. Is it necessary to connect the "GND" wire? I mean for US, Japan and alike, they only have Live and Neutral; they don't use GND. Yet, their Hi Fi are the best among the world .....

Another point for inquiry. I am using Coaxial for the signal in. There is NO ground at the RCA plug side. Am I doing it right?

What is the difference between GND (水) wire and the Neutral (地) wire?

Please advise. Many thanks.

CAT

GND is something that normal connect to the metal part of the building .
Neutral  is 火線的回路，completely different.

USA power supply  has GND, look at the "real" USA plug. There is a ground.

I do not Japan power supply had gound or not.

Some equipment will normal gound to Chasis only, this should be ok but gound to "GND" wire will normally has a slient background.

For CO-ax socket, normally , I will solder the  -Ve to gound on  socket side and the -Ve  is not connected on other end.

Dear Accphoto,

Oh, I see now. As I don't really know the Chinese terms for these wires. I thought that GND = 水 and Neutral = 地. That is why I have all these confustions.

So my connection here is okay? I have the signal in / out / volume switch all ground to the chasis.

And I put the chasis GND to the GND wire of the 13A plug is a correct move.

Still got some confusion about the coaxial signal path. I put the -ve to the Volume Switch GND but left the RCA socket side unconnected. Should I reverse the cable instead? OR since I have both sides GNDed already, it doesn't really matter.

CAT

其實師父以前教落，Co-ax cable 只 ground 一面因為 ground 兩面會有 Ground Loop, ，那一面就看每個人喜好，我兩面都試過，發覺 ground RCA socket 那面噪音小點，你可自已試試。

Dear Accphoto,

I will for sure try it out later. Dealing with my CD player these days ...  :cry:

CAT

Attach an example of star grounding hope it may helps.

Thank you WINDWSS,

I will study it when I have time. If I don't understand, I will ask my Physics Panel.

CAT

Cat,

Let take a look for my PCB layout. I think you can get some idea from me because you still not fully understand what I mean for high power GND and small signal GND.

Left hand side top is 6.3V regulator for tube, it is direct connect two wire to tube and the main GND is connect to very beginning at the top layer with HV.

Left hand side bottom is tube regulator, it output the HV to tube(right hand side), please note, you will see a THICK GND connect to the right hand side. It is called high power GND. A perfect DC source should be a DC, not AC components inside.

For the right hand side, you will see a tube preamp, I set the GND point whcih is under the tube are (a large circle) it is a GND point connect to metal chassics. It is a small signal GND, (also is for Input and output)

If I using the PSU GND to connect a chassics. It will cause
1) A small signal GND like a antenna to pick up many noise.
2) Larger protential difference from 2 GND.
3) The 50Hz (100Hz) will be pick up from main PSU if have bumping effect.

TEXT, Diagram are COPY RIGHT to www.hififever.com and KK.HO

Hope you can help you la, cat cat.

KK.

[quote:e7fa424183="kk_ho"]Cat,

Let take a look for my PCB layout. I think you can get some idea from me because you still not fully understand what I mean for high power GND and small signal GND.

Left hand side top is 6.3V regulator for tube, it is direct connect two wire to tube and the main GND is connect to very beginning at the top layer with HV.

Left hand side bottom is tube regulator, it output the HV to tube(right hand side), please note, you will see a THICK GND connect to the right hand side. It is called high power GND. A perfect DC source should be a DC, not AC components inside.

For the right hand side, you will see a tube preamp, I set the GND point whcih is under the tube are (a large circle) it is a GND point connect to metal chassics. It is a small signal GND, (also is for Input and output)

If I using the PSU GND to connect a chassics. It will cause
1) A small signal GND like a antenna to pick up many noise.
2) Larger protential difference from 2 GND.
3) The 50Hz (100Hz) will be pick up from main PSU if have bumping effect.

TEXT, Diagram are COPY RIGHT to www.hififever.com and KK.HO

This board is available now, please contact admin if you need this.

Hope you can help you la, cat cat.

KK.[/quote]

多謝KK Sir的指教. 小貓現在病了. 好了之後會細心 investigate. 到時再請教.

CAT

Dear KK Sir,

看了你的回覆大半天 ... 還是不太肯定明唔明.

是否 HV (e.g. PSU) 的地不好同 Signal 的地連在一起?

是否 HV GND 跟水線走而 Small signal GND 就落金屬機身?

CAT

CAT,

I lend the PCB (real board) for you.

Please come to take at SAT. (phone to me again to confirm)

You will understand more.

PS : you need to return the board to me after your study.



KK.

KK Sir,

你真好人, 我一定會還 asap. 但係我沒有你的電話 ....

CAT

Cat,

但係我沒有你的電話 ....
// please found in the old post, as you said, you are the highest post message man in HF web //

For the PCB, please come to take after 10-Mar.

Or, you come at SAT, I open the PCB layout SW and tell you the secret step by step about the design skill.

For the PCB placement and layout, it is a highest pressure, because if you get a wrong, you will loss alot.

KK.Ho

Dear KK Ho sir,

Nice to meet you in today’s UCD Class D power amplifier demo. The machine is good!

In this topic of “grounding”, I would like to express my opinion and refresh the purposes of grounding as below:

The primary purpose of electrical grounding is for "safety to human being". Nothing is more important than safety and classified as mission critical importance. Regarding the noise problem caused by improper grounding in audio system, it is classified as functional critical to the system.

In America, it is called “ground”. In British, it is called “earth”. In general, the purposes of electrical grounding are: (Ref: http://www.epanorama.net/documents/groundloop/why_grounding.html)

1) Protection to human being in case of equipment damage (safety critical issue).
2) Protection to the electrical system (overvoltage protection to property)
3) Voltage stabilization (same reference point in whole electrical system)

In audio system, improper grounding will cause noise problem. It usually refers to “ground loop” problem (ref: http://www.epanorama.net/documents/groundloop/). It can be divided into two parts:

1) interconnect cable
2) electronic device unit

In part I, digital signal is not sensitive to ground loop while analog signal is sensitive to ground loop. (ref: http://www.epanorama.net/documents/groundloop/digital_audio.html
) Both unbalanced and balanced analog signal cable exist ground loop problem. The basic requirement of cabling is:
1) Unbalanced analog signal cable: 1 conductor plus shield
=> (+) signal connect to center of conductor and (-) signal connect to ground and shield
2) Balanced analog signal cable: 2 conductors plus shield
=> (+) signal (hot) connects to Pin 2, (-) signal (cold) connects to Pin 3 and ground connects to Pin 1 and shield.

The simple solution to solve ground loop problem is to connect one end of cable with shield connect to ground and lift up another of cable with shield not connect to ground. Which end of cable should not connect to ground? Normal practice is the end “input” to next electronic device. Hence, the grounding depends on previous level of equipment and any problem in grounding will not transfer to next layer of device. If you argue about to lift up at “input”, but not “output”, it is a normal practice, there is not research support that you cannot do at “output” end.

In part II, it refers to the circuit design of grounding in PCB or something else in electronic device unit.

=> Circuit design for grounding:
1) i.e. grounding in digital vs analog circuit
2) i.e. grounding in high voltage (HV) vs Low voltage (LV) circuit
http://www.epanorama.net/documents/groundloop/in_circuit.html
http://www.epanorama.net/documents/groundloop/audiocircuit_grounding.html

=> Star grounding (commonly used technique)
http://www.aikenamps.com/StarGround.html
http://www.geofex.com/Article_Folders/stargnd/stargnd.htm
  
Finally, noise problem is not solely caused by improper grounding, but also due to other reasons such as RFI and EMI issues. (ref: http://www.epanorama.net/documents/groundloop/othernoise.html)


B. regards,
alant

Alant,

Nice to meet you today too.

For my expression:

1. All of the signal is consist of GND, otherwise, it cannot be work.
2. User need to classify the power source, input signal buffer, amplififer stage, feedback stage.
3. The most "critical" problem is "how to connect those GND together?"
4. Which is the first, which one is the final?

Even you use a STAR GND, you should know their problem.

A small signal GND wire may be look like a ANTENNA to pick up something.

Sure, user should prevent to create "GND LOOP"

Let discuss later....need to sleep la.

KK.HO

Sorry KK Sir, I didn't call again Sat as not feeling too well ....

Call you again when I get back from China after Mar 23 ...

CAT

Cat,

Please call me at non-lecture class period.

And 1 PCB is prepare for you already

KK

I just finished my SP-10 last Sunday. For grounding, here is some tricks :
1. Use input gound to connect to the chasis and earth wire.
2. For the input wire, it is better to connect only one side, I use the volume gound as the connecting point for the gound.
3. All power supply negative connect to the gound wire,

No more "dee dee" sound in my case.

accphoto, cat,

your suggestion is close to my PCB layout.

accphoto, you can come to see our PCB.

I cannot say it is the super best, but no hum hum noise la.

KK.HO

Many thanks for all this information.

Will come back for more after I return from the China Trip (Mar 23).

See you guys then!

CAT

Cat sir,

Any chance to visit your home to see your CAT?

KK

Dear KK Sir,

I will be leaving on Sat morning. Now busy packing things and giving homework to my other boys.

You, Modi Sir and William are always welcome at my home.

Just don't laugh at my CHEAP Hi Fi ... ha..ha...

CAT

Still got one or two days of holiday and I made up my mind to modify my McIntosh C-22. The C-22 was no good sounding in the first place, which is a bit surprise to me as this should be a classic.

重有兩日假, 幫架 McIntosh C-22 大搬家. 從 Entry 100 case 搬去個舊 case.
架 C-22原先是唔好聲的, 我都唔知點解 ....

First, I moved it from the Entry 100 case to an OLD case, saving much space and shortened the wires.

Second, using a aluminium plate and a 8-pin socket, make the 6BM8 horizontal instead of original Vertical.

將枝 6BM8 用個搭掤架 + socket = 變打橫.

Third, following Accphoto's advice, ground the wires at the RCA signal in side instead of grounding it at the volume switch.

跟 Accphoto 兄教路, signal ground 放在 RCA 頭入口那面, 唔放 Volume 制那邊.

Result: Believe it or not .... almost NO noise. The C-22 now indeed sounds like a C-22 (tho' I still think the Marantz 7 is better .. perhaps because of the music I listen to).

結果: 出人意表! 架機靜了好多好多. 終於似番架 C-22 啦.

Dilemma: The C-22 sounds almost as good as the Matisse. The Matisse wins over in details and clarity. The C-22 wins over in female vocals; its warm and sweet sounding. What do I keep TWO pre-amps for??  :shock:  :?:  :shock:

問題來了: 原先想把這架 C-22 賤賣. 現在同架 Matisse 咁上下好聲... 點算? 我要兩架 Pre-Amp 做什麼 ... 但兩部機各有所長 ... 真頭痛 ...

CAT

Enjoy your DIY work.....  

ACCPHOTO,

I had some doubt need your advice.

For the choke say 15H, 150mA, does it mean that we should use minimum 150mA? if the mA <150 will create problem?

my power trnsformer is 100mA, before add in the choke, voltage afetr tube rectifier is 350V  but when add in the choke it become ~700v and above....i read a book by jone morgan say if mA too small for choke may create problem like this..any method to slove it?

i remove the choke and use CRC after the tube rectifier, still same problem , voltage will got very high... >500V

but if connect the choke without cap to the rectifier tube then the voltage is ok ~350v

maybe i should fully connect to the load then only test it right?

SHow your circuit before I can comment on it. 150ma should be good enough for a lot of application. Most per-amp will only take 10ma and some take up to 20 ma. Even a 300B poweramp will take about 80ma per channel.  It should not be any problem for you to use 150ma choke on 100ma transformer but not  the reverse.