Promitheus TVC and interference/ground buzz

I recently bought the Promitheus TVC preamp from Larkrise and have been very pleased with the results particularly when using it with the xlr Promitheus silver cable, and think it is excellent value for money. However I have found that when I have used it with EAR 519 and Melody SP3 power amps that there has been a noticeable buzz/noise from the speakers (Tannoy 15DMT's)when my Panasonic plasma screen is switched on (I should mention that I also use my hifi setup for my Pace freeview box for watching TV programmes). This noise does not occur with my other amps such as the First Watt F3 or Gamut power amps or when I use my Adcom active preamp in the system. Anyone any ideas as to why and if any suitable measures that can be taken. I note that the S&B transformers used by other TVC manufacturers are shielded, also some manufacturers have a switch for different ground configurations.

 

thats the pace digi box .....I've had similar ....there are no easy answers I ended up making a shielded mains lead for the pace ...but you can't now get the fig 8 mains plugs [I can't find any]

 

Yes, the MFA has such a switch and like you I only get it from a TV source. The switch cures it. If you look on the MFA website I think you'll find an explanation there and maybe some ideas on how you could add a switch yourself.

Edit: specifically, here http://www.mfaudio.co.uk/datasheet1.htm under the heading of connection considerations.

 

In reply to Zanash its not the Pace, as when this is turned off but the plasma is still left on the buzz remains, the buzz only goes when the plasma is turned off. I have heard that plasmas do emit alot of radio interference, although the plasma and TVC are around 2-3 feet apart. I do note that the interconnects that I use are unshielded Kimber and Promitheus. I am usin the xlr input and the rca output don't know if this has a bearing.

 

Would a ferrite on the earth cable of a shielded power cable help?

 

I have one at each end of the plasma power cable already. I'm wondering if the input impedance of the power amps and and the output impedance of the TVC is part of the problem, particularly as the EAR's being primarily for studio work have a relatively low input impedance I belive of around 20k, not sure what the Melody is however. As I previously mentioned I dont get any trouble with the active Adcom preamp, which points the problem more towards the TVC.

 

I'm no expert but I don't think you'd get hum as such from an impedance mismatch, just roll-off or something.

Because of the output level of my TV/sat box relative to CD source, I get a sort of humming/buzzing if I select the TV source without volume adjustment. Instead, I turn up the sat box and turn down the TVC vol by 10 dB or so. This reduces buzz from the TV by increasing the attenuation of the input sugnal (along with th buzz) that the TVC does.

 

no, this has nothing to do with the impedance mismatch. actually, this issue is overblown with TVCs. the impedance mismatch results in a slow, sluggish sound, bass roll-off, lack of drive, speed and energy in lower registers...

i think that your problem is down to the nature of xformers promitheus uses. they are very sensitive to the RFI and you obviously get it from other devices close to the TVC in your rack. if they would be shielded or grounded you wouldn't (ok, 95%) have this issue.

as you can't shield the trannies now (maybe you can, but.......), you can try if grounding your xformers would make a difference. for this you will need some soldering.

the best for you is to go to www.audiocircle.com forum, to general audio subforum and to find a mamooth-like promitheus thread, around 140 pages. in the last 2-3 pages someone post instructions how to ground the trannies. this was initiated with a sonic benefit, but i would try this first in case of a high-RFI situation like yours.

if this doesn't work, and there is nothing to guarantee it will, you have to experiment with a position of the TVC or a device that causes the RFI.

there's many promitheus users there at audiocircle forum and someone will know what to do if this is not correct.

 

I think you may find its still the pace box ...an earth loop between that and the tv ....maybe

 

just read where the ferrites are try 1/3 distance from each end ...

 

On the whole of the cable or just the earth?

(I have a humming device so have a vested interest )

 

The ferrites at present are placed close to the plug and socket at either end of the power cable, I'll try reposisting just to see if any improvement. I think the problem most likely is connected with earthing arrangments with the various bits of equipment, but why it should buzz with some equipment and not others not really sure.

 

I have a similar problem when I connect my M-audio Delta 1010 to my pre amp. Its more of a buzz than a hum. The solution is to isolate the offender from the preamp using a transformer on each lead.