So how did they used to get turntables to work in radio studios?

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dudeboy9
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So how did they used to get turntables to work in radio studios?

Post by dudeboy9 » Thu Feb 12, 2015 9:21 pm

I am GM of an LPFM station here in Northern Nevada - KGLJ. We are almost there on all our testing but one new issue has come up. We would like to do some retro turntable work but we are getting so much RF interference from our own signal the TT won't even run let alone play decently over the noise. I am fairly certain this is the problem as I tested it by putting the TT in my car with an inverter. Once about a block away it runs just fine. Any closer and it won't turn - just kind of jiggles back and forth. We have plenty of clearance to the antenna FCC-wise - at least 30'. We only are allowed an ERP of 100 watts and run around 260 watts on the transmitter to get that. So ... how the heck do we get this thing to run? Clearly there was a time when ALL music was produced by turntables and they somehow managed to do it with power ratings far above ours. Any suggestions?

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Deep Thought
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Re: So how did they used to get turntables to work in radio studios?

Post by Deep Thought » Thu Feb 12, 2015 9:30 pm

What kind of turntable is it? You can't just use any old thing you find in a high RF field. If you're only 30 feet from your antenna, you are literally being basted in RF.
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dudeboy9
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Re: So how did they used to get turntables to work in radio studios?

Post by dudeboy9 » Thu Feb 12, 2015 9:48 pm

It's a Marantz 6350Q.

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Re: So how did they used to get turntables to work in radio studios?

Post by Deep Thought » Thu Feb 12, 2015 10:16 pm

In that case you need to address the grounding and possible RF shielding of where you're trying to use it. Radio stations used quartz-locked turntables like that for years but the studios were constructed to control the high RF levels that are present in co-located (at the transmitter site) studios. I'd start by making sure the studio equipment is properly grounded to the same point as the transmitter, tower and antenna, and make sure that the AC power feed to the studio is also properly grounded.

I don't have any direct experience with that turntable, but it may just not have enough RF filtering and shielding.
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Re: So how did they used to get turntables to work in radio studios?

Post by dudeboy9 » Thu Feb 12, 2015 10:34 pm

Thanks for the Deep Thoughts on this. I believe we have our grounding under control. We were downright obsessive about it as I know from CNC machines in my business you can't ground too much. We drove two separate ground rods, one connects to the antenna and the other to the studio racks and all equipment. It then is all interconnected too the utility ground. The AC power is also hooked up to these ground rods. We did this because it is a hundred+ year old church building that has no original grounding system. The TT itself has a ground on the RCA cable that grounds to a lug on a small mic to line amp. I even tried building a faraday cage out of a box and aluminum foil around the TT. Still no luck. Shielding the entire studio is not an option. Looks like maybe we are out of luck?

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Re: So how did they used to get turntables to work in radio studios?

Post by ChuckG » Thu Feb 12, 2015 10:48 pm

dudeboy9 wrote:It's a Marantz 6350Q.

That's a fairly old TT, IIRC. 1970's vintage, quartz locked direct drive. I'd start by making sure it's control electronics are not marginal due to age- perhaps replacing the caps and beefing up filtering and bypassing. Wrap the power and signal cables through ferrite chokes. (Faraday cage won't work if the interference is riding in on the cables)
You may have to do the same to whatever you are using for a cartridge preamp once you get the table spinning correctly.
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Deep Thought
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Re: So how did they used to get turntables to work in radio studios?

Post by Deep Thought » Thu Feb 12, 2015 10:49 pm

Most of the original radio station turntables used synchronous AC motors and a rubber puck to drive the table, which was a heavy flywheel. They laughed at RF. The pro-grade direct-drive tables were designed for the environment. It may just be that the Marantz, which is a decent consumer-grade table that is popular with collectors, just can't handle it.
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Re: So how did they used to get turntables to work in radio studios?

Post by dudeboy9 » Thu Feb 12, 2015 10:59 pm

You may be on to something with the cables bringing in RF Chuck. I can halfway get it to run if I use an extension cord out of the studio. Still a ton of noise though coming from the cartridge. I'll try the wraps next. The cap replacement had occurred to me too. But before I get too into this old girl perhaps a different TT would be an easier course. Any suggestions Deep Thoughts - keeping in mind we are your typical broke Non-profit LPFM station?

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Re: So how did they used to get turntables to work in radio studios?

Post by Deep Thought » Thu Feb 12, 2015 11:13 pm

If using the extension cord works better then it's coming in though the power cord. A simple RFI filtered power strip might do the trick. Be sure you plug the turntable and the preamp into it. You might also want to see if you can find some of the snap-on ferrite RFI choke filters to use on the turntable leads. If you still have a Radio Shack open in the area, they have one which works pretty well. #273-0105
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Re: So how did they used to get turntables to work in radio studios?

Post by dudeboy9 » Thu Feb 12, 2015 11:34 pm

Thanks guys. Time for lights out. I'll try all the above and get back to you here.

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Re: So how did they used to get turntables to work in radio studios?

Post by Kent T » Wed Sep 23, 2015 9:04 pm

You need a proper turntable for broadcasting work built and designed for this job. Technics SL-1200 Mk II at minimum. Technics SP series like the SP-25, the SP-15, and SP 10 MK II are superb as are Russco, Harris/Gates, QRK and similar.

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Re: So how did they used to get turntables to work in radio studios?

Post by RodeoJack » Thu Sep 24, 2015 11:47 am

Kent T wrote:You need a proper turntable for broadcasting work built and designed for this job. Technics SL-1200 Mk II at minimum. Technics SP series like the SP-25, the SP-15, and SP 10 MK II are superb as are Russco, Harris/Gates, QRK and similar.
In their day, all of that was true. I don't think I'd use a rim-drive table today though... and maybe not even a belt drive. With a Technics table, the rumble factor you'd be looking at with the other brands isn't a consideration. Get enough compression running with a quiet track, and motor isolation was also a problem with some of the old guys.

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Re: So how did they used to get turntables to work in radio studios?

Post by Deep Thought » Thu Sep 24, 2015 11:55 am

RodeoJack wrote:Get enough compression running with a quiet track, and motor isolation was also a problem with some of the old guys.
With some of the ridiculous amounts of processing in use today, isolation of the turntable itself from what it is sitting on is also a bigger problem than it was back in the Optimod 8000 days.
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Re: So how did they used to get turntables to work in radio studios?

Post by Kent T » Thu Sep 24, 2015 9:25 pm

It is broadcast standard or it is not. Marantz is home use only. Can it meet or exceed NAB requirements? If not, it does not belong in a control room. Belt drives at their best are classical format only. Which means DD or idler only to meet the requirements for start up time on the platter and cueing accuracy.

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