MEP-250 Bridged-T equalizer

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
billshurv
Posts: 396
Joined: Thu Feb 01, 2018 7:07 am

Re: MEP-250 Bridged-T equalizer

Post by billshurv » Mon Mar 25, 2019 7:33 pm

Suddenly I remember why I am using a PC for parametric duties. I'd never find time to build that.

Gold
Posts: 590
Joined: Sat Dec 01, 2007 6:20 pm

Re: MEP-250 Bridged-T equalizer

Post by Gold » Tue Mar 26, 2019 2:02 pm

billshurv wrote:
Mon Mar 25, 2019 7:33 pm
Suddenly I remember why I am using a PC for parametric duties. I'd never find time to build that.
It took about 100 hours to build. The second unit I expect to come in at half that or less. These EQ’s are for a console that will be used daily to generate billing. I certainly wouldn’t do it just for fun. These cost a fortune to build. The second one is well in its way.
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Gold
Posts: 590
Joined: Sat Dec 01, 2007 6:20 pm

Re: MEP-250 Bridged-T equalizer

Post by Gold » Wed Apr 03, 2019 11:17 am

Some notes on a real Sontec. They use polystyrene caps for the smaller value in the tuning circuit. I guessed right on that. This one used Evox (Kemet) polypropylene film caps for the larger value. This one had a noise floor of -82dBu unweighted. The one I built has a noise floor of -86dBu.

The one I built doesn’t sound exactly the same but it’s in the same ball park. Mine is a two opamp 250 style. This Sontec is a 4xx and is a three opamp version. On the three opamp version sum and output use separate opamps.

Bill Wilson
Posts: 18
Joined: Wed Dec 08, 2010 11:45 am

Re: MEP-250 Bridged-T equalizer

Post by Bill Wilson » Tue Dec 10, 2019 6:12 pm

In the Sontec circuit C25's value is 33mfd, 6vdc. The values for all 5 filter frequencies are listed ln the lower right hand corner of the schematic.

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