Avoiding feedback from turntables

Once a year me and some friends organize a party for creative computer enthusiasts (aka demosceners).
Since me and one of the other organizers also like to dj with vinyl, we use the opportunity to play a set on Fridays.

However, we've had problems with feedback from the turntables two years in a row, and haven't found a way to avoid it yet. We've taken some countermeasures to reduce vibrations from the table/floor, but it seems like the problem actually is air vibration and not feedback coming from the table (we tested holding one of the turntables up in the air, but that didn't do anything).

Apart from having a heavy and dampened table (we use a couple of sleeping mats, which resembles acoustic foam), what can be done about feedback? Are some cartridges/styli better than others , does slipmat thickness have any effect, and so on..?

Are you sure they are grounded properly?

Whenever I've used those hench Shure carts I haven't had any problems. Not even a skip. But I dunno about feedback

Shatner's Bosom said:

Are you sure they are grounded properly?

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Yes, they were grounded to the DJ mixer (NI Traktor Z2), turntables and mixer on the same power (grounded) power circuit.

Just to be clear, it was feedback - not ground noise/humming. As long as we stayed below the tipping point for gain/PA volume there was no noise at all. When we went above it (and we tried various combinations of input gain on the DJ mixer, volume levels on the DJ mixer channels, master level on the DJ mixer, input gain on the PA mixer, channel levels on the PA mixer and master level on the PA mixer).

This could be dodgy phono cables on the turntables. I've had this numerous times with old 1210s, including my own.

lug00ber said:

Yes, they were grounded to the DJ mixer (NI Traktor Z2), turntables and mixer on the same power (grounded) power circuit.

Just to be clear, it was feedback - not ground noise/humming. As long as we stayed below the tipping point for gain/PA volume there was no noise at all. When we went above it (and we tried various combinations of input gain on the DJ mixer, volume levels on the DJ mixer channels, master level on the DJ mixer, input gain on the PA mixer, channel levels on the PA mixer and master level on the PA mixer).

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sounds like a problem with the ground cable, I get this sometimes when I have my turntables grounded to my A6 dodgy but then connect it properly and it works fine

Gloxxy said:

This could be dodgy phono cables on the turntables. I've had this numerous times with old 1210s, including my own.

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Feedback problems because of dodgy phono cables? How does that work?

Cables should be good btw, grounding as well. They are used regularly at home, never had any problems. Could also avoid the problem by cutting the bass on the dj mixer (removing the frequencies that seemed to cause the feedback).

lug00ber said:

Feedback problems because of dodgy phono cables? How does that work?

Cables should be good btw, grounding as well. They are used regularly at home, never had any problems. Could also avoid the problem by cutting the bass on the dj mixer (removing the frequencies that seemed to cause the feedback).

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My phono cables on my 1210s aren't the best as my turntables are nearly 20 years old. I get low frequency hum from the speakers until I play around with the phono cables when they are plugged into the mixer. I've had this playing in clubs a lot though. When a tune is playing and there is no bass part playing then there'll be massive low frequency bleed coming out of the speaker system. It will only happen when the stylus is on the vinyl, there is no bass part playing on the tune and the low frequency EQ is at 12 o'clock.

This could happen because of a number of things. The surface that the turntable is on, the stylus, the phono cables.

Aside from all that has been mentioned regarding earthing and cables etc, the only time I once had an intrusive buzzing sound (that wasn't grounding feedback) was due to a headshell not being properly connected to the arm. This just required taking it out and re-fitting it again. Is this a problem that is occuring between both decks? as you haven't singled out any particular one.

The demoscene thing sounds cool. I used to have an Atari ST with tons of cracked stuff in the early 90's and quite a few of those demos. In fact my uncle ran a group where people would come together to work on this sort of thing and share stuff. Many many moons ago this was. Ironically we still have one of the 4-way plug adapters where my studio is now which says ST-Users group on it. Must be 25 years old or so that.

Optimal Prime said:

Aside from all that has been mentioned regarding earthing and cables etc, the only time I once had an intrusive buzzing sound (that wasn't grounding feedback) was due to a headshell not being properly connected to the arm. This just required taking it out and re-fitting it again. Is this a problem that is occuring between both decks? as you haven't singled out any particular one.

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The issue was the same for both decks, although microscopically less for the deck farthest away from the PA.
Also, these issues are not present at home, it was at that venue only (with a PA, not just home monitors).

The demoscene thing sounds cool. I used to have an Atari ST with tons of cracked stuff in the early 90's and quite a few of those demos. In fact my uncle ran a group where people would come together to work on this sort of thing and share stuff. Many many moons ago this was. Ironically we still have one of the 4-way plug adapters where my studio is now which says ST-Users group on it. Must be 25 years old or so that.

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The ST was my first computer, back in 1990 Several of the leading cracking crews on the ST was brits, actually. There's still a demoscene (and even new cracks appearing from time to time) for the ST, with parties and new stuff being released all the time. Hardcore will never die

It sounds like something to do with the electrics of the building you are in. I don't know a great deal about it, but where I live, it's pretty old and I've had occasional sounds entering my setup (inteference noises) when I put the stuff in this boiler room to turn it into a little home studio not long ago. Sometimes it would only be on for a limited time which made me think it might have had something to do with a device such as the actual boiler itself switching on.

The ST was my first computer too which I must have gotten around the same time as you. My uncle had his a few years before I got one, but I was young at the time and never ended up going to one of these groups he ran. I think one of the cracking groups went under the name pompey pirates, and one of the members there was involved in that group. I've not really gotten into the ST though for years, although there's a podcast I sometimes listen to called Retro Asylum which is dedicated to a lot of ancient stuff. I've been on there too talking about the ST.

Every feedback issue I have had has been the original phono's on technics. costs 60 quid to replace.