XtremePlace Forum

Faq Galaxy => Faq On Audio => Topic started by: terfyo on October 08, 2019, 07:55

Title: Please advice! Hum issues!
Post by: terfyo on October 08, 2019, 07:55
Would like to seek advice from all the gurus out there!

Introduction of equipment;
Krell KSA200s [Krell]
Audio Research LS8 [ARC]
Vienna Acoustics Baby Beethoven Grand [VA]

So there is the hum problem.
when i have the Krell, without any inputs, only connected to the VAs, turn it on, a little buzzing here and there, probably some transistor rush, etc. not really audible from a distance.

so now, i connect the ARC outputs (unbalanced) to the Krell (unbalanced), dang, the hum starts. The ARC does not have any inputs connected to it at all. this is basically a preamp to power amp test. of course, when i am using unbalanced inputs on the krell, i will need to put in the shorting pins to the XLR inputs as stated in the owner's manual.

Both ARC and Krell are connected to the same power strip, so i think that kills the ground loop issues.
I've checked continuity between the ARC chassis and the Krell chassis, there is no issue.

Any thoughts?
Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 08, 2019, 10:41
The KSA is already an oldie but regardless you should not hear buzz or what so ever when power on.
Suggest that you open up to check for loose joints first.
Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 08, 2019, 10:46
Btw have you tried powering the KSA directly from the wall socket ?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 08, 2019, 12:16
Yes. Have tried direct UK to IEC from wall socket.
The amp by itself without any inputs doesn't have any hums.

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 08, 2019, 13:13
Wait let's start all over again. Has the preamp & amp been with you for a long time or ?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 08, 2019, 13:18
Wait let's start all over again. Has the preamp & amp been with you for a long time or ?
Has always been with me. For many years already.
Until recently when I moved place to Hougang...

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 08, 2019, 13:38
OK let's start with the simplest first. Open up the inter connect to check on soldering also confirm that ground is not touching signal pin of rca. At times nuts happens where the ground wire comes detached. If all ok then open up your ARC preamp to check the same at the rca socket & ground wire to the pcb.

Cheers
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 08, 2019, 13:51
I've checked the RCA interconnects last night. Switched out the Interconnects as well. The ICs are fine.

I'll probably head on to check the preamp.
I do have an Easter electric MINIMAX dac with preamp function as well. So I connected it directly to the power amp and the result was the same humming. Just louder than the ARC.

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 08, 2019, 14:19
Just to be sure use another IC & if the same then problem is in the amp.
Capacitors drying up can also cause hum but you can only check condition via ESR meter.
Whose it might just be a loose wire or solder in the amp.
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 08, 2019, 15:16
Hi, if your equipments need repair, can pm me.
I know a few good technicians.
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 08:47
Hello to all,
I have solved the hum issue but i need some explanation as to why this solution works.
Perhaps somebody can explain to me the logic behind it.

I was recommended by a technician to lift the ground for the preamp, which should solve the problem.
by lifting the ground, i would tape ground pin at the iec inlet of the preamp so that when the power cord is plugged in, the ground is not connected.
Well, this does not solve the issue and as soon as the amp is powered on, even when the preamp is not powered on, the hum sets in.

However, when i "lifted the ground" for the power amp, (of course with the preamp grounded), the hum is totally gone!
I made sure to check that the power amp chassis is grounded to the preamp chassis, also made sure that the power amp chassis is grounded to earth using a multi-meter, before turning the power amp on.

Any possible explanation as to why this can work?

Cheers. ??? ???
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 09, 2019, 09:23
Hi Terfyo, you mean the earth ground from the poweramp is lifted and the hum issue gone?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 09:26
Hi Terfyo, you mean the earth ground from the poweramp is lifted and the hum issue gone?
Yup. That's exactly what I did.
Only at the IEC power cord there. of course, the picture shows the preamp, but i did it for the power amp, couldn't take a photo because it was a hell lot of weight.
(https://uploads.tapatalk-cdn.com/20191009/455bdcb191df7ef4465698bf0010b751.jpg)

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: aero88 on October 09, 2019, 09:33
Terfyo, so you lifted the ground for both preamp and poweramp right?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 09:35
Terfyo, so you lifted the ground for both preamp and poweramp right?
Nope, at the end of the day, the preamp is grounded, but the power amp is lifted.
Title: Re: Please advice! Hum issues!
Post by: wizardofoz on October 09, 2019, 10:47
Please DON'T use TAPE to lift a ground permanently as you are asking for trouble. Get your power cable modified or do it internally in the equipment but only if it is safe to do so based on manufacturer confirmation.


WARNING lifting grounds of equipment designed to have them should really only be used for problem determination by competent technicians. The ground is there for SAFETY RESONS...dont risk your life.
Title: Re: Please advice! Hum issues!
Post by: Boxerfan88 on October 09, 2019, 13:25
WARNING lifting grounds of equipment designed to have them should really only be used for problem determination by competent technicians. The ground is there for SAFETY RESONS...dont risk your life.

Agree 100%, be careful !

Very interesting scenario, interested to know root cause...watching this thread...
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 09, 2019, 14:28
Terfyo, i have pm you his contact.
Please let him check.
Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 09, 2019, 15:53
Lifting ground is a no no especially for power amps. If you've been using the same set up without issues before why is it happening now ?
It is clear now that you've got a ground loop issue somewhere along the chain.
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 16:19
Lifting ground is a no no especially for power amps. If you've been using the same set up without issues before why is it happening now ?
It is clear now that you've got a ground loop issue somewhere along the chain.

Understand that it is very dangerous to do that.
So the puzzling thing is that when i lift the ground of the preamp, the hum still persists.
When i lift the ground of the power amp with the preamp grounded, the hum disappears.

This is especially weird when only the pre and the power amp is connected together.
If i just power on the power amp without any inputs, there is no hum (just some slight hissing).
Just when i plug in the interconnects, starts to hum, even when the preamp is not turned on.

Oh btw, did i mention? if i just connect the interconnects, and the interconnects are not connected to the preamp, there is no hum.
I tried another preamp, there's hum as well.
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 09, 2019, 17:15
Terfyo, there is nothing wrong with your preamp.
Is your power amp problem.
Maybe transistors shorted.
Don't let it power on for too long, or else more damages may happen.
Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 09, 2019, 18:38
You brought up a good point aero 88. My initial thoughts wasto check loose solder joins etc then the caps first there after transistors.
Being a class A amp the next culprit could be the vas transistors. In any case thing it's better to get it service if you not diy competant.

Cheers
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 19:26
You brought up a good point aero 88. My initial thoughts wasto check loose solder joins etc then the caps first there after transistors.
Being a class A amp the next culprit could be the vas transistors. In any case thing it's better to get it service if you not diy competant.

Cheers
I've actually had it checked by a tech who gave it a clean bill of health.
Zero hum when tested at his place.
But the hums came back when I brought the amp back home and plugged it into my setup.

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 09, 2019, 22:14
Are you able to check your wall socket if the earth is properly grounded ?
The other option is to get the tech to drop by your house to assist in checking.
Yep chasing down hum can be a real pain. On my system There's only 2 sockets
& the wires are individually runned from the breaker just to this sockets.









Title: Re: Please advice! Hum issues!
Post by: terfyo on October 09, 2019, 22:29
Are you able to check your wall socket if the earth is properly grounded ?
The other option is to get the tech to drop by your house to assist in checking.
Yep chasing down hum can be a real pain. On my system There's only 2 sockets
& the wires are individually runned from the breaker just to this sockets.
Yes. The sockets are grounded properly.
I've checked this.
I'm now checking with Krell US for then to confirm that cheating the earth at the amp is safe.
If they confirm it's safe, then I'll leave it that way. Since all the hum is gone.

Sent from my SM-N975F using Tapatalk

Title: Re: Please advice! Hum issues!
Post by: jaffrie on October 09, 2019, 23:59
If that's the case to be safe never touch the chassis of the amp when powered up.

Cheers
Title: Re: Please advice! Hum issues!
Post by: wizardofoz on October 10, 2019, 00:24
I assume you have changed the IC's between the amp and pre and ruled out any issue there. Are you using balanced XLR or RCA?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 10, 2019, 07:21
Yes, have switched out the ICs between pre and amp.
Tried both SE and XLR.
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 18, 2019, 13:27
So what is their reply from US?
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 18, 2019, 23:00
favorable.
as long as there is an IC connected to another equipment that is ground, it is safe to lift the ground from the power amp.

oh btw, i have recently bought the EMI Power Line Tester from an MO and realized that when my airconditioner is not turned on, the reading shows 450mV there about. However, when my AC is turned on, with the compressor cut in, the reading is 1,500mV.
That is some real noise there. I have tested almost every other socket in the house and am getting about the same reading.
I'm using the Starmex Inverter system.

Anybody got any ideas on how to reduce the noise injection into the power line when the AC is running?

Title: Re: Please advice! Hum issues!
Post by: Boxerfan88 on October 18, 2019, 23:05
use a 240v-240v isolation transformer?


Sent from my iPhone using Tapatalk
Title: Re: Please advice! Hum issues!
Post by: terfyo on October 18, 2019, 23:08
i do have a balanced transformer which i have custom made by Koba in Chinatown.
the transformer helps with approximately -200mV from the reading purely from the socket.
Any ways to kinda like, remove this problem of the AC?
Title: Re: Please advice! Hum issues!
Post by: AndrewC on October 19, 2019, 06:54
...
oh btw, i have recently bought the EMI Power Line Tester from an MO and realized that when my airconditioner is not turned on, the reading shows 450mV there about. However, when my AC is turned on, with the compressor cut in, the reading is 1,500mV.
...
Anybody got any ideas on how to reduce the noise injection into the power line when the AC is running?

You've got a classic case of ground loop caused by leakage current into your home's ground by a high-powered appliance.
(https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ground_loop_-_leakage_currents.svg/2880px-Ground_loop_-_leakage_currents.svg.png)
(A=Your Air-conditioning system. C1=Your Pre-Amp. C2=Your Amp)

If you look at the picture, it also explains why lifting your Pre-Amp's ground won't solve the problem, but lifting the Amp's ground does (breaks "I" current flow). Instead if lifting the power-Amp's ground, a safer option would be a signal isolation transformer for your 2 channels. Something like ;

(https://www.canford.co.uk/Images/ItemImages/large/57-451_01.jpg)
 
An AC isolation transformer for your entire sound system would be a good (albeit bandaid) solution. Addressing the root-cause would mean getting an electrician to re-wire your Air-conditioning power cables so that it doesn't leak/induce stray currents into the ground.   

Good luck!  :)
Title: Re: Please advice! Hum issues!
Post by: aero88 on October 21, 2019, 09:08
Hi Andrew,

Well said. But just curious will the hum isolation module affect the sound quality?