[johj]

Hi,
 
I've got an Emmeline "The Hornet" by Ray Samuels Audio amplifier. It has the option to run off a battery or with a 12VDC regulated power source. So far I've only used it with my battery-powered MP3 player, running on a 12V power supply.
 
Now I recently acquired an ODAC to play music from my PC. However, when I connect it to the amp there's a loud siren sound from the amp output! If I disconnect the 12V power supply and run the amp off battery, the siren noise goes away. Any idea what might be causing this?
 
Thanks,
 
- Johannes

 

[johj]

I disconnected the DAC and instead touched the amp chassis with the ground part of a USB cable. This reproduced the loud siren noise. I also tried a different 12VDC power supply for the DAC but the noise was still there.
 
So to me it appears that USB ground is noisy which is somehow picked up by the amp. What's to blame here?

 

[ClieOS]

I think it is not a 'noisy' USB ground, but a poor implementation that lead to ground loop issue. That is, voltage from the DC adapter is leaking to the PC via the USB ground channel.

 

[johj]

Quote:

I think it is not a 'noisy' USB ground, but a poor implementation that lead to ground loop issue. That is, voltage from the DC adapter is leaking to the PC via the USB ground channel.

 
Ah, so you think the problem is with the DC adapter plugged into the amp? In which component, exactly, do you think there's a poor implementation? Any suggestions on what to do to resolve it?

 

[ClieOS]

Quote:

 
Ah, so you think the problem is with the DC adapter plugged into the amp? In which component, exactly, do you think there's a poor implementation? Any suggestions on what to do to resolve it?

 
Well, if a portable amp is designed to also allow DC adapter powered, then I will expect it to have some implementation that addresses any possible ground loop issue. If it doesn't, then it is a poor design. Then again, Hornet is such an old model that perhaps Ray simply didn't have PC audio in his mind when designing.
 
If ground loop is the case with Hornet, I don't think there is much you can do to the Hornet itself besides not using the DC adapter. Other wise, you can try using an USB isolator which will break up the ground loop between the PC and the Hornet (*more precisely, between PC and ODAC). I can't be 100% sure if this will work but it is the only thing I can think of.

 

[duncan1]

I looked up the company seems high audio spec BUT it went to GREAT length   to state ONLY their PS works CORRECTLY into its amp.-Do NOT use any other or input filter could blow .
    Question= Are you using the ORIGINAL PS? Because if you say its a loud siren noise that is not NORMAL component  noise that you would hear from hi-fi equipment
          What you are hearing is HF OSCILLATION due probably to OVER VOLTAGE!.  

 

[ClieOS]

The OP has mentioned he is using a 12VDC regulated, so it is up to spec even if it is not the stock adapter. Plus, if it is an voltage issue, it would have happened regardless of what he is connected the Hornet into. Since it only happens when he connect it to ODAC, it points to a ground loop issue.

 

[johj]

Quote:

I looked up the company seems high audio spec BUT it went to GREAT length   to state ONLY their PS works CORRECTLY into its amp.-Do NOT use any other or input filter could blow .
    Question= Are you using the ORIGINAL PS? Because if you say its a loud siren noise that is not NORMAL component  noise that you would hear from hi-fi equipment
          What you are hearing is HF OSCILLATION due probably to OVER VOLTAGE!.  

 
I don't have the original power supply so I have been using another 12VDC supply. I've tried two different power supplies which both resulted in the loud noise. I'm wondering what are the DC Voltage tolerances for the Hornet though - perhaps it's really picky?
 
Quote:

The OP has mentioned he is using a 12VDC regulated, so it is up to spec even if it is not the stock adapter. Plus, if it is an voltage issue, it would have happened regardless of what he is connected the Hornet into. Since it only happens when he connect it to ODAC, it points to a ground loop issue.

 
I contacted RS Audio (the manufacturer) who suggested I might have a problem with the USB power supply. I'll try the setup on another computer to see... I'll order a USB isolator regardless to see if it solves the problem...

 

[ClieOS]

A problem with USB power supply? ODAC is powered by the USB port. As I said, it looks like a ground loop issue and from the Hornet, not the ODAC. Anyway, hopefully the USB Isolator will help.

 

[johj]

So I tried the set up on my home computer and with two different power supplies (yes I know I'm changing a lot of variables here, but bear with me )
 
With the first (cheap) 12V power supply, the DAC would repeatedly get disconnected from the PC whenever I plugged it to the amplifier(!)
Linux system logs show loads of lines like:
 
 

[603717.954052] hub 7-0:1.0: port 1 disabled by hub (EMI?), re-enabling...
[603717.954060] usb 7-1: USB disconnect, device number 7
[603717.958795] cannot submit urb (err = -19)

 
With the second (expensive laptop grade) 12V power supply, there was no problem at all. I could disconnect / re-connect the devices without any USB issues.
 
I did not experience the siren noise from either power supplies though, but it should be noted that both are ungrounded. Does that mean a ground loop is less likely to occur?
I might try the working power supply at work tomorrow (where I initially had the ground loop issues). Either way I've got a USB isolator on the way as well...

 

[ClieOS]

That's a bit scary actually. I can't be sure but it would take something major to disconnect the DAC. Possibly the amp is sucking up power from the USB power line via the DAC, causing the current to drop under the minimum requirement for the DAC and thus disconnecting it. That's is not supposed to happened at all. I really won't recommend you to use any DC adapter for now until you can be sure of what is causing all the issue.

 

[johj]

Quote:

That's a bit scary actually. I can't be sure but it would take something major to disconnect the DAC. Possibly the amp is sucking up power from the USB power line via the DAC, causing the current to drop under the minimum requirement for the DAC and thus disconnecting it. That's is not supposed to happened at all. I really won't recommend you to use any DC adapter for now until you can be sure of what is causing all the issue.

 
So a ground loop can't somehow cause USB disconnects? What tests can I perform to pinpoint the exact issue?

 

[ClieOS]

Quote:

 
So a ground loop can't somehow cause USB disconnects? What tests can I perform to pinpoint the exact issue?

 
That I don't know.

 

[duncan1]

Does it work okay with JUST the battery?-If so then as stated in their ad-using another PS than their own could have damaged the charging components and the 15000mf filter-cap- if so that fault wont go away  as the battery BYPASSES the charging components.-UNLESS the charger is plugged in[switch in socket.]  Do you have a link to the circuit diagram?

 

[johj]

Quote:

Does it work okay with JUST the battery?-If so then as stated in their ad-using another PS than their own could have damaged the charging components and the 15000mf filter-cap- if so that fault wont go away  as the battery BYPASSES the charging components.-UNLESS the charger is plugged in[switch in socket.]  Do you have a link to the circuit diagram?

 
Yeah it does work fine with just the battery in the hornet and the DAC.
Also, it works fine with the power supply connected to the hornet as long as I'm using a battery-powered source (like my MP3 player).
 
Unfortunately I couldn't find any circuit diagram for the amp.