Phono3 new build hum

[Steebo123]

Hi

Just completed a PSU3/Phono3 build. First time with a WD kit since the new regime, very impressed with quality of packaging, manual and casework. Great job, Matthew!

However, I have a major hum issue. I have checked all voltages, and took care to route signal cables inside away from HT and heater lines as much as is possible. I am trying it with my "spare" TT, a Thorens TD 160, RB250, Shure M97. I have run a separate wire from the grounding pin on the phono to the casework of the TT, but to no avail. Whilst stil testing, I am plugging the phono3 into my portable Olympus digital recorder, and listening on headphones out.

Any ideas or suggestions welcome.

Steve Vaughan

[pre65]

How close is the PSU to the Phono 3 ?

[Steebo123]

As long as the lead that was supplied, about 75 cm

[pre65]

That's nearly 30" in old money, should not cause any problems.

[Steebo123]

Any other ideas anyone?

[FreddieT]

Steve,

Without wishing to teach anyone to suck eggs it is wise to make sure that there are no mains transformers (not just the PSU3) or wall wart PSUs in the proximity of the Phono3 (including above & below in your rack) as it pretty sensitive to stray magnetic fields I find.

The other possibility is a ground loop. However, I'm assuming that the Olympus is battery powered or has an isolated DC supply (i.e. there is no mains earth connection), so this probably isn't the cause. Worth checking the HT rail in the PSU & Phono3 for ripple (if you have a scope, but bear in mind the HT voltage before DC coupling!) and then check the capacitors on that rail are soldered correctly.

If none of that works then the more experienced folk on this forum (you know who you are) are very good at sorting this sort of thing.

F.

[Richard]

Hi Steve,

Two possible issues;

1) Rega arm is earthed via one phono braid (can't remember which) and needs disconnecting at arm end and a new separate earth lead fitting. This usually causes just a little hum in one channel.

2) Phono case "earth" post is actually signal ground which means it is lifted from mains earth by 100R. PSU case earth post is actually mains earth. You can check these out with a meter from the case post to mains plug earth pin (to find 100R for Phono case and 0R for PSU case) to make sure your wiring is all correct.

From there, you can connect the TT/arm earth wire to either if it is "floating" (not grounded elsewhere) but if it is also earthed to mains earth by any mains earth on the TT, and you then connect it to Phono case post, you will lose the 100R lift. Hope this is making sense. For a similar reason be sure Phono case metalwork doesn't ground out by touching or connecting its post to any other unit in the system. (It is there for connecting the TT/arm earth wire to and then only if it is floating.)

[Steebo123]

Hi Freddie

Thanks; all units were in a separate room to my manin system, my workshop area, just for testing, no other transformers around. Yes the Olympus (using this as headphone amp just for testing)was on battery.

I would welcome any other suggestions.

[Steebo123]

Hi Richard sorry just seen your post. I will try these things.

Cheers

[John Caswell]

I know this is going to be a silly question, but have you got the cover fitted and is it definitely earthed to the chassis, by scraping the paint off around one of the fixing holes and using a lock washer between the cover and chassis?

John