new user with a possible ground loop problem

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frederico
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new user with a possible ground loop problem

Postby frederico » Tue Jan 01, 2019 6:49 pm

Hi guys and gals.

First post here so a little introduction to begin with. I'm new to Cyrus, having picked up a Streamline 2 and an 8 power earlier this year. I use the streamline as a pre-amp and DAC, audio source is Plex streaming through a chromecast audio, optically feeding the streamline. The 8 power drives a pair of Kef R300s and generally I'm extremely happy with the result.

Last month I decided to upgrade my interconnects from budget ones to a pair of Chord Chorus 2s. Now I have problems with a low level 50-60hz hum through the speakers.

I've checked:
- that the interconnects are seated properly in the terminals
- there is nothing else connected on the power strip
- swapping out the power strip for one without surge protection, on/off switches and neon lights
- disconnecting all other appliances in the room
- replacing and also reseating the power cords to the pre-amp and amp

I guess the budget interconnects were not shielded because the problem only occurs with the Chord interconnects, so I assume they are creating a ground loop where there was not one before. The hum is not present without the pre-amp on, and switching back to budget interconnects also solves the problem. However it is also possible that there is a problem with the Chord interconnects and this is not a ground loop problem.

Can anyone suggest a cheap fix other than going back to the budget interconnects? I've see ground loop isolators, are they any good? Can anyone recommend one?
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Cyrus Streamline V2
Cyrus 8 Power
Kef R300
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mickbald
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Re: new user with a possible ground loop problem

Postby mickbald » Tue Jan 01, 2019 11:17 pm

Try using 1 original and 1 new cable. If that works ok swap out the new cable for the other half of the pair. If one fails it will show you have a faulty new cable - probably the ground not connected tightly. Tighten up the plugs on both ends and see how it goes. The plug has two halves that need to be screwed tightly together.

frederico
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Re: new user with a possible ground loop problem

Postby frederico » Thu Jan 03, 2019 9:55 am

Many thanks Mick. I ran the test as you suggested, good idea. Both halves of the new cable are fine as they perform identically, with no ground loop hum when used on the left channel. Similarly, both create a ground loop on the right channel, which (to me) means I probably have a dirty or dry solder to earth for that channel at either the pre or power amp. I should add that the hum is really quiet, unnoticeable to most people, but now I know it's there it's distracting.

Is there any other testing I can do to isolate the issue to one unit? The power amp has balanced XLR inputs so presumably I could buy a single RCA to XLR adapter to test only the pre-amp in isolation. Would that yield useful results?

What might my options be? It's probably not worth paying £300 to have Cyrus service the offending unit especially if it's the power amp as I'll likely upgrade it in a few years and many people are using balanced interconnects so the issue wouldn't bother them edit: but I could have it independently serviced.

I could get an inline ground loop isolator - there's even one that has both balanced and unbalanced terminals: https://www.amazon.co.uk/dp/B0009GUOQA/ref=cm_sw_em_r_mt_dp_U_4MDlCbKE96PZ0

Image

But the cost of that plus another (decent) set of interconnects would probably be getting on for a few pounds. I've also read that I could break the loop by cutting the connection to the shield at one end of the interconnects. Good idea or not?

thanks!
Last edited by frederico on Sat Jan 12, 2019 10:37 am, edited 2 times in total.
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Cyrus Streamline V2
Cyrus 8 Power
Kef R300
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Re: new user with a possible ground loop problem

Postby hifinutt » Thu Jan 03, 2019 12:48 pm

you need to fix the underlying problem rathter than add more components

can you try another pre or a power amp to see which component needs repair ? then there maybe other cheaper repairers if its the amps

are there any cu`ers near you ? what part of uk are you ? i can`t stand hum in any shape or form
1]bc pre 3 vbs
msb s200 power amp
/vbs1 FM1 tuner
onkyo sacd , tannoy eaton legacy 2] schiit freya , firebottle hybrid monos , bc 3.5vbs, marantz sa8005 , reference fidelity impulse ta`us horns3] rotel , harbeth p3esr

frederico
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Re: new user with a possible ground loop problem

Postby frederico » Thu Jan 03, 2019 1:16 pm

that's good advice.

I'm in East Sussex (UK). Would you think I could isolate the cause with an RCA-XLR adapter? For a couple of pounds it would be worth a punt. Then I can take the offending unit to a local repair shop. edit: doh! The 8 power doesn’t have XLR inputs
Last edited by frederico on Sat Jan 12, 2019 10:38 am, edited 1 time in total.
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Cyrus Streamline V2
Cyrus 8 Power
Kef R300
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Re: new user with a possible ground loop problem

Postby mickbald » Thu Jan 03, 2019 3:48 pm

OK, so now you know all cables are good.

Leave the RH channel with no cable plugged in.

If you plug one cable into the left (good) pre amp output and the other into the left (good) power you should get no hum. Now plug the cable into the RH power. If you get the hum the power is the problem.

If not reverse the process and check the same with the RH Pre output. If you get hum you have a faulty Pre.

It could be that there is a broken wire / dry joint on the input or output socket.

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Re: new user with a possible ground loop problem

Postby frederico » Sun Jan 13, 2019 1:29 pm

Thanks for the patience everyone. The problem is not solved but I have some clarity around the conditions under which I have hum.

I went back to basics and checked the cable connectors, cleaned all contact points and moved any wiring away from mains cables. Then I decided it was time to get structured with my testing. Here are the scenarios I tested together with the results (click for bigger image).

In this test:
IC1 are my old interconnects, IC2 are the Chord Chorus interconnects.
My original setup is Test 2a. The new ICs in place are Test 1a.

I have found a local independent who will service both the pre and the power amp, but I would really appreciate your thoughts as to what might be going on here as I don't feel qualified enough to make sense of the results.

Thanks!

Image
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Cyrus Streamline V2
Cyrus 8 Power
Kef R300
--------

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Re: new user with a possible ground loop problem

Postby frederico » Sun Jan 13, 2019 3:51 pm

Have done some more reading up on the topic, there's a good thread on the art of sound forum https://theartofsound.net/forum/showthread.php?42613-Ground-loop-between-pre-amp-and-power-amp.

Is anyone able to confirm or refute my thinking below please?

1. Despite the lack of CE markings on either the Streamline or the 8 Power, both units are double insulated (as there are only two pins on the mains cable socket) and therefore a ground lift circuit will not improve matters.

2. Because PreTest 3 shows hum on the right speaker I can assume that the R channel on the Power amp is faulty and it is somehow picking up a current on the R channel from somewhere inside the power amp.

I seem to be able to also create hum on the L channel of the Power amp using either of the L or R preamp channels as sources, but only using IC2, not IC1. I don't have a decent explanation for this. Is it possible that the small amount of resistance in IC1s would isolate the signal sufficiently? Or that interconnects have a sound profile such that they might allow a given frequency to flow or be impeded? That would blow my mind.

Perplexingly I seem to be able to kill the Power amp R channel hum with IC1s but not IC2s from either L or R pre-amp source. What might explain this?

Sorry for all the newb questions, I'm hoping that this might be helpful for others searching for solutions to similar topics in the future.
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Cyrus Streamline V2
Cyrus 8 Power
Kef R300
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Ianmac
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Re: new user with a possible ground loop problem

Postby Ianmac » Sun Jan 13, 2019 9:07 pm

It is extremely difficult to diagnose your problem without having hands on with the equipment.
Looking at the table you have produced I would guess that the issue is with the input of the amplifier.
Perhaps the best clue is that it works with one set of cables and not the other. Both cable sets measure OK electronically so the only other variable will be the mechanical tolerance associated with the different types of phono connector, pin diameter and outer inside diameter.
The input connectors to the Cyrus amps Ive owned are made up of two pairs of phono female connectors mounted onto a thin laminate/plastic plate held in position with one screw and connected by long fixed metal connecting strips onto to the main amplifier PCB. . If the holding screw is not 100% tight , over time, with plug insertion and removal , the connecting strips to the main PCB get flexed and the solder joints to the main PCB suffer, the solder cracks and connection is intermittent and often varies with the force needed to insert the phono plug. Usually the ground connection for both vertical phono sockets is one piece of brass with one connection to the PCB. This means for L and R inputs you have two ground connections onto the main PCB. When one of these solder connections gives trouble it is possible that inserting the adjacent Phono socket can cause an issue!
Its a pig to fix by resoldering the joints as,if I remember correctly, the whole PCB needs to be removed.
It is possible to link the ground connection of the Phono sockets inside the amp but you need to know what you are doing.
I assume you have a meter since you have measured the resistance of your cable..
Connect your cables into the amp and measure pin to ground resistance for the different cables that may help give you a clue.Should be high around 47Kohm, if there is a ground problem the measurement will go very high to open circuit.
You can also make up a shorting phono plug to help fault find.
An oscilloscope would readily show you where the problem lies but I presume you dont have one.
Sorry I cant be more helpful but I dont have any Cyrus amps around to open up and take some photos for you.

Id make contact with your local service guy and see if he can help.
Sytem 1.
Engineered SA-NMR Renderer (Ianmac PSU) :BelCanto CD-2: Technics 1200 (Ianmac Bearing + Ianmac PSU+Ianmac arm): DACT-Ianmac phono pre >Benchmark DAC2 HGC>2*Ianmac-Hypex NCore monos> ATCSCM40 : Ianmac filters
System 2
Engineered SA-NMR Renderer (Ianmac PSU) :Benchmark DAC1.Sony CDP D11 pro: 2*-Hypex Ncore monos: Kef ref1-2.
IMF's

frederico
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Re: new user with a possible ground loop problem

Postby frederico » Wed Jan 16, 2019 5:35 pm

Ian, thank you so much for the detailed reply. What a great community this is.

I followed your advice and started to test for resistance between centre pin (and outer connection whilst I was there) and chassis ground. I spent a while testing and recording the results before the penny dropped. Outer connection (return) to chassis ground gave me around 10kΩ resistance with the old ICs but 0Ω with the new ones. So why would that be?

It's because I am an idiot!

The new ICs have a slightly shorter centre pin and so the RCA plug seats more deeply than the originals. The return connection of the outer RCA plug on the new IC was making a connection between the two cases. Because both pre and power amps have double insulated cases (ie. they are ungrounded) and each contains a toroidal transformer, the cases were getting mildly excited by the electromagnets. Pushing the RCA plug on too far was introducing this to the return path of the interconnect signal.

Solution: don’t push the IC plugs on quite so far. Hum is now completely gone.

Hopefully someone else will benefit from this :)

Thanks again all, I've made a donation to the forum running costs to express my gratitude for the help!
--------
Cyrus Streamline V2
Cyrus 8 Power
Kef R300
--------

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Re: new user with a possible ground loop problem

Postby mickbald » Wed Jan 16, 2019 5:46 pm

Good news about te fix. And thanks for the donation.