A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

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billshurv
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by billshurv » Fri Apr 26, 2019 3:19 am

I think it is very safe to say that this is a torture test and most MC users will not have anything like that level of mains fields anywhere near their turntables. I'll take two!

KMN
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by KMN » Fri Apr 26, 2019 9:40 am

Wow. That is impressive, especially after learning about the the details of the hum torture chamber you are running it in. That's a lot of gain and a lot of cable with all that stray field around. I think I might need one too.

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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by emrr » Fri Apr 26, 2019 10:08 am

Very nice!
Best,

Doug Williams
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Gold
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by Gold » Fri Apr 26, 2019 12:48 pm

Looks good Wayne. I think my DL103 into your MM preamp with a Lundahl 1:8 stepup is about the same. I don't have FFT setup yet so I can't quite do an apples to apples comparison.

I've been quite happy with this setup. I think I have a resonance around 10K. I underdamped the cartridge because to it sounded constrained fully damped. It's probably due to that.

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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by Audio1Man » Fri Apr 26, 2019 6:01 pm

Hi Wayne
Is the “HUM” Electrostatic or Magnetic? What is the difference in FFT by wrapping the pickup in Alum foil vs putting it in a steel paint can and closing the lid? What is your area lighting type? Incandesce, fluorescent tube or switching fluorescent / LED type?
Duke

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mediatechnology
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by mediatechnology » Fri Apr 26, 2019 8:30 pm

Thanks everyone!

It's magnetic. Aluminum does nothing.
Lighting is all LED and it occurs with them off.
The hum hot spot are the huge transformers, running with a fair degree of core saturation, in the APC UPS units.

My magnetic hum sniffer (a telephone pickup coil and battery-powered R-S amp) also nulls to the exact same angle in the field.
It hums like a b*tch near the APCs.
Guitar pickups are also a problem in this room as well as the spring reverb.

Quite a bit comes from ingress into the DL-103 itself.

I'm not worried about it: In this particular case you wouldn't want to monitor at a level where you could actually hear it.
If the needle were to drop or the platter start spinning the monitors would be destroyed.

I actually ran gain up in a deep fade to listen to the noise floor, couldn't hear it beneath the surface noise, and quit afraid I would run into the intro of the next cut.

I'm not going to spend any time on it right now because as a practical matter its so deep in the mud as not to matter.
I do want to get some mu-metal to quieten the spring reverb and I'll try lining the metal Hammond box with it.
Not sure I can do much to shield the DL-103.
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terkio
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by terkio » Sat Apr 27, 2019 8:06 am

First off, thanks to show all this nice work.
I do want to get some mu-metal....and I'll try lining the metal Hammond box with it.
I am very interested about this.

Audio1Man
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by Audio1Man » Sat Apr 27, 2019 4:19 pm

Wayne

What about placing the BIG TX into a 5 Gal steel paint can? This may give you another 10-20dB reduction.

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mediatechnology
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by mediatechnology » Sun Apr 28, 2019 7:22 pm

I need to pickup a clean paint can.
It will fit in a 1 gallon.
I usually keep those but used the last ones for some stain.
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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Post by brianroth » Sun Apr 28, 2019 8:26 pm

How about using a Hoffman "screw cover pull box" without the knock-outs as an outer shell? Widely available from electrical supply distributors. Heavy gauge steel.

I'm thinking about getting a decently sized one...maybe 8x8 or larger....and poking Neutrik XLR and TRS jacks into the side along with some binding posts for DC power. Then I can sit my solderless protoboards, perfboards, new PC boards inside and have some magnetic shielding.

Bri
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