A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
billshurv
Posts: 436
Joined: Thu Feb 01, 2018 6:07 am

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

Post by billshurv »

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
Posts: 53
Joined: Sat Jan 20, 2018 2:49 pm

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

Post by KMN »

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.
emrr
Posts: 570
Joined: Sun Mar 02, 2008 10:27 pm
Location: NC, USA
Contact:

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

Post by emrr »

Very nice!
Best,

Doug Williams
Electromagnetic Radiation Recorders
Gold
Posts: 677
Joined: Sat Dec 01, 2007 5:20 pm

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

Post by Gold »

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.
Audio1Man
Posts: 18
Joined: Mon Feb 04, 2019 2:09 pm
Location: Thousand Oaks, CA
Contact:

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

Post by Audio1Man »

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
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

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

Post by mediatechnology »

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.
User avatar
terkio
Posts: 304
Joined: Thu Feb 07, 2019 3:17 am
Contact:

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

Post by terkio »

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
Posts: 18
Joined: Mon Feb 04, 2019 2:09 pm
Location: Thousand Oaks, CA
Contact:

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

Post by Audio1Man »

Wayne

What about placing the BIG TX into a 5 Gal steel paint can? This may give you another 10-20dB reduction.
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

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

Post by mediatechnology »

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.
brianroth
Posts: 91
Joined: Mon Jun 17, 2013 2:11 pm
Location: Salina, Kansas
Contact:

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

Post by brianroth »

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
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com
Post Reply