Phono Stage in Erhard PH-10 picking up radio stations.

[Agohman]

Strange thing happening today. My phono stage in my Pas 3 with the PH-10 and Aikido line stage w/ no tone controls just started picking up the local FM radio station that is a mile from my house. First when I turned on my turntable today I noticed a low frequency hum. I thought it might be the outer ground clips on the RCAs of my turntable were a little loose and picking up some ground hum. I first unplugged only the left channel and when I went to squeeze it a little tighter, my finger touched the ground and center positive pin at the same time and the FM station started playing through my right speaker. The only other thing plugged into my preamp is a DAC which is off but it doesn’t do it through that when I turn it on. For troubleshooting purposes I plugged my turntable into a Schiitt Mani 2 and then into another input on my pas and no radio signal. So I think that pretty much traces the problem to the PH-10 phono preamp circuit board picking up the FM signal. Any advice on how to shield it from the FM radio frequencies?

[Agohman]

Also it’s not necessary FM frequencies because I found out the station also broadcasts over AM.

[Holger]

this is a new one. I have never heard something like this in all the years I have been selling the Z-PH10.
Somehow I find it strange though that it only suddenly started today. Have you made any changes with RCA cabling, position of the turntable, position of the PAS, or anything at all.
Double check the input wiring for the Z-PH10 from the RCA sockets, also double check soldering, making sure there are no dry joints anywhere around the Z-PH10 wiring or the Z-PH10 pcb.
Would it be possible for you to take some photos of the wiring etc to the Z-PH10.

[Agohman]

I upgraded the RCA’s on my Technics SL-1200 MK2 to some nicer Mogami cables about a month ago. It’s been fine up until today. It’s extremely overcast today, I wonder if that in conjunction with the station being so close is the culprit. I wired the connections from the RCA jacks on the pas to the input on the PH-10 with nice 14 gauge speaker cable. Could that possibly be causing it because it isn’t shielded? I’ll post some pics of the wiring Saturday. That’s the first time I’ll get a chance to open it up.

[Holger]

if I understand you correctly, the hookup wires you used to the Z-PH10 inputs are not shielded?
They must be shielded, either using Mogami style shielded audio cable or a twisted pair hookup wire. The signal level from the turntable is extremely low and very prone to noise pickup if not properly shielded. I would change that first, then try again.

[Agohman]

Okay thanks Holger. I’ll swap that out Saturday or Sunday and update you.

[Agohman]

So I replaced the wiring from the z-ph10 to the inputs with monoprice shielded cable yesterday. It’s all I had lying around. Tested this morning. It still picks up the radio stations. However I think this is “normal” because I replicated it with the Schiit Mani as well. It only happens when I unplug one of the RCAs from the turntable with the other channel still plugged into the preamp. Then I have to physically with my fingers touch both the negative (outer metal) and positive (inner pin) on the unplugged rca jack to get it to start picking up the radio station. I suspect it’s using my body as an antenna. If I use the same hand to touch both connections it comes in staticky and if I touch the ground with my left hand and the positive with my right it comes in clearer. The radio station is only audible if the preamp is turned up above 3/4 of the way on the volume. Now I don’t know why I wasn’t able to do it with my Schitt Mani plugged into another channel of the preamp the other day but I was able to replicate the same thing this morning.

Now as far as the “hum” I was hearing the other day I think it would be better described as a “hiss” or “air sound” which I think is just the physical sound of the cartridge that gets louder when you turn up the volume of the preamp. Which doesn’t really become audible on my preamp until about 3/4 of the way up on the volume. It isn’t audible at all when playing a record. So for scientific purposes I measured the decibels of both the z-ph10 and schiit mani at full volume without a record playing. The measured hiss of the cartridge at full volume on the z-ph10 was 51db and the Schiit Mani was 56 db. Probably the difference in gain between the preamps. Not sure what the gain of z-ph10 is but the Schiit Mani is set to 48db.

So I think that solves that problem that wasn’t really a problem in the first place. Lol

[Agohman]

Here’s some photos of the preamp.

[Holger]

glad you got it all sorted. The gain of the Z-PH10 is around 40dB.