Phono RFI problems

In a bid to simplify, I've replaced my outboard phono stage with the optional phono board for my ATC pre. So far so good, it's only been running for a couple of days but seems pretty decent. Cart is an Ortofon Rohmann (low-output MC, about .25mv), phono board is set for maximum gain (adjustable through jumper settings, but there's only 2 settings, normal and high).

I've noticed periodic RFI problems today, which I've never had a problem with before, on occasion pretty severe.

Anyone have any experience of good ways to reduce or eliminate the problem?

-- Ian

 

Use your CD player

 

Ian - does that make you officially ''without valve''?

Are your interconnects shielded BTW?

Chris.

 

hi Chris

Not totally valveless - still have a WAD kit to build...

Yes, ICs are shielded, but I might try some others and see if there's any improvement. I've had a suggestion on PFM to try ferrite rings, so I'll have a go with that.

Here's an amusing thing: I thought this would be an opportunity to test a snake-oil product or two, so I've ordered a kettle lead from Russ Andrews. It's a £30 job, it claims it has "Kimber's unique cable weave to remove RFI". We'll see.

Any other suggestions?

-- Ian

 

Hi Ian,

I would try a different interconnect cable if you have one to hand. The electrical properties may be have enough difference to stop you picking the taxis.

It seems that the combination of the phono board, pre amp & cable are acting as a tuned circuit for these radio frequncies.

Ferrite rings is a common way of dealing with it.

What's it like when you try the pre amp on normal setting?


SCIDB

 

Cheers Dean. Luckily I have a wide variety of ICs to try (for a cable sceptic, I have quite a few cables). I'll probably fiddle with rack positions to get the pre further away from the TT as well, although options are limited there. Worth a try though.

It's only a problem on the phono input, everything else is fine. First step, ferrite rings and different ICs.

-- Ian

 

The RA power cable will do NOTHING for the phono stage- it's airborn RFI and thus ferrite rings/ICs are the only way to solve it...

Now if anyone can tell me why I get hum on my Rega P2 (low level) but not on my Planar 3, I'd love to know - really annoying!

 

Dom,

have you checked the wiring in the tonearm? - I find that if certain wires touch eachother it hums.

It could be that anyway.

 

In that case, you might want to try a sheet of ERS (the dish cloth stuff ). Might help to refresh the parts that ferrite rings might not, although the ferrite rings definitely sound like they should be the first port of call.

 

I'm with Chris on that. Check your tonearm wiring, whenever I've had hum that's been the cause.

Old Russ doesn't distinguish airborne RFI from the variety that travels by car or bike, so his claims should be tested I reckon.

Henry - OK, I'll bite. Anyone got a spare dishcloth they want to lend me, or, alternatively, can I buy some on a money back guarantee? If so, where from?

-- Ian

 

Right, this is really pissing me off now. I'm using ferrite clips, which seems to reduce the problem, but it's still there, and far too intrusive.

Anybody got any other suggestions? I've just emailed ATC and the dealer for advice, but all opinions welcome. Looks like I may have to revert to using an external phono stage.

-- Ian

 

I know you're not really into all this snake oil and fairy dust but perhaps Stillpoints ERS could help you out?

http://www.stillpoints.us/1Pages/ers_products.html

http://www.enjoythemusic.com/magazine/equipment/1103/stillpointsers.htm

People who have used it here (WM and António & maybe a couple of others) swear by it.

Michael.

 

Cheers Michael, I did ask above if anyone knew where I could get it from SOR, don't want to buy it if/when it turns out to be useless...

So, anyone got a sheet spare they could lend me or know where I can buy it on a money-back basis? This will be a good test, if nothing else.

-- Ian

 

Just a thought, but if youve isolated external sources of RFI - perhaps its picking it up inside the unit?

Perhaps some sort of internal damping/RFI shielded internal cable changing etc?

 

I'm thinking of ordering some ERS myself. If I do I should be able to lend you a sheet. Won't be until sometime next week though.

Michael.

 

Cheers Michael, if I don't find some other way round it I may take you up on that if you find you have a spare sheet.

Time to start experimenting with some case dampeners/shielding I suppose.

-- Ian

 

Ian, is the phono amp a high input impedance - such as 47000 ohms - like you would use for a MM cartridge?

If so, why not try a 1k ohm resistor [or even lower - down to about 100 ohms min] across the L and R phono amp inputs [ie between hot and screen left and hot and screen right].

 

Graham, according to the manual the impedence is switchable between 100 and 47k ohms, currently set to 47k ohm but I'll try changing it (needs 2 jumpers that I don't have, so time to raid some of the old SCSI hard drives in the office for the necessary).

-- Ian

 

Definitely drop the impedance, before the dance of the 7 dishclothes..

Note 100 vs 47k could reduce interference voltage by [up to] 470 ie 53.4dB!! and white noise by sqrt470 [up to - depends on the amp] 26.7dB [I think...?]

 

As to contacting ATC, I wouldn't hold my breath waiting for them to reply to that email... I've emailed them on several occasions, never to receive a reply. Not a mark of poor customer service, simply a sign of old-school leaning, methinks. Give them a ring and you'll find them very helpful.

Dunc