homemade 2-band eq

jackson_bass · #1 11-29-2007, 10:44 AM

I am thinking of building this for a bass I built with passive "P" and Basslines "MM" pickups in it. Has anyone tried this circuit?

Attachment 74816

I am planning to use a TL082 FET opamp, but everything else should follow the circuit.

DavidRavenMoon · #2 11-29-2007, 10:58 AM

I made something very similar for my 8-string. It came out very nice.... I felt it had a very musical tone. I don't remember where the center frequencies were for the tone controls...

JackANSI · #3 11-29-2007, 11:00 AM

I wouldn't use a TL082... Using something that has better characteristics or make sure you socket the thing so you can swap later. The originals specified are sweet, stick with them if you can.

Try two AD797 even. You can even get them for free as samples directly from analog's website. http://www.analog.com/en/prod/0%2C28...D797%2C00.html

jackson_bass · #4 11-29-2007, 11:01 AM

Quote:

Originally Posted by DavidRavenMoon

I made something very similar for my 8-string. It came out very nice.... I felt it had a very musical tone. I don't remember where the center frequencies were for the tone controls...

Thanks. I think I will try it this w'end.

DavidRavenMoon · #5 11-29-2007, 11:09 AM

Quote:

Originally Posted by JackANSI

I wouldn't use a TL082... Using something that has better characteristics or make sure you socket the thing so you can swap later. The originals specified are sweet, stick with them if you can.

Try two AD797 even. You can even get them for free as samples directly from analog's website. http://www.analog.com/en/prod/0%2C28...D797%2C00.html

Ooh! Free samples! I'm designing a new preamp so this will come in handy.

I used a low noise dual bifet op amp, but I forget which one it was.

Passinwind · #6 11-29-2007, 11:17 AM

Quote:

Originally Posted by jackson_bass

I am thinking of building this for a bass I built with passive "P" and Basslines "MM" pickups in it. Has anyone tried this circuit?

Attachment 74816

I am planning to use a TL082 FET opamp, but everything else should follow the circuit.

I'd definitely go with the specified opamp. The OPA 2132 is the dual version, and it rocks. You can get free samples from TI if you ask nice.

The downside will be battery consumption, of course.

Is that an ESP design, or just a generic cookbook circuit? I have an ESP circuit board kicking around that includes two sections like that, plus some mixing capability.

jackson_bass · #7 11-29-2007, 03:31 PM

Just a circuit that I found through an I-net search. I am planning to socket this, but the OPA chip has a different pin-out. . . . I may rethink the TL . . . . . Oh! no- - - it does appear to have the same pin-out, the schematic that I found seems to be mislabeled.

A9X · #8 11-29-2007, 03:57 PM

Quote:

Originally Posted by jackson_bass

I am thinking of building this for a bass I built with passive "P" and Basslines "MM" pickups in it. Has anyone tried this circuit?

Attachment 74816

I am planning to use a TL082 FET opamp, but everything else should follow the circuit.

Change the first stage to a non-inverting. Otherwise it's pretty generic opamp based pre. You may need to tweak the gain of the first stage to taste.

Add a 1M resistor from Vin to ground. Keep R1 above 50k and adjust R2 to set the gain. Somewhere from 1-10 for gain is likely to be about right depending upon your pickups, system and desired output level.
EDIT: might be woth adding a 100u cap between R2 and ground to set DC gain at 1. You'll also need to bias the opamps to 1/2 battery V. I'll dig up a cct.

Most opamps, AD797 and OPA2123 included are a little current hungry for the average battery powered pre; power offboard and they would be good. The 797's superb noise characteristics are only valid with a low source impedance, ie, not a pickup.

12bass has been suggesting the LT1352. I haven't tried it yet but it looks like it has potential.

DavidRavenMoon · #9 11-29-2007, 04:22 PM

Good suggestion making the first stage non inverting.

Here's a cool thing for splitting the power rails:

The 'Rail Splitter' Precision Virtual Ground - TLE2426

I haven't tried one of these yet, but it looks real handy.

I also have a circuit for the voltage divider around here somewhere...

jackson_bass · #10 11-29-2007, 06:21 PM

thanks. I split the voltage to bias the amp at 1/2 battery with 2 100K's and 100uf caps. I also selected the feedback resistor in the schematic to give about a 2:1 gain through the first stage. I think I'll wire it up and see what happens. I also modeled this through a sim. . . . . (proteus), and generated a ckt bd,,,,,,,,, but this seems so simple that I am going to use perf. board for this one. I may tweak the ckt after I hear it.

A9X · #11 11-29-2007, 06:25 PM

I'd still suggest the first stage be inverting because it will work better with the huge impedance variations from the pickups and vol controls. Input Z should be 1M or so. Sims are useful, but they never give the detail needed.

jackson_bass · #12 11-29-2007, 07:49 PM

will do. thanks again.

Shoewreck · #13 11-30-2007, 05:46 AM

A pair of AD797's will consume about 20mA of current. That's a lot! You'll have to change your batteries approximately every 10 hours.

Quote:

Originally Posted by A9X

I'd still suggest the first stage be inverting because it will work better with the huge impedance variations from the pickups and vol controls. Input Z should be 1M or so.

Inverting stage with 1M input impedance will add some noise to the circuit. I'd suggest using a source follower with current load for low noise, THD and power consumption. A pair of 2SK170's is my usual choice.

A9X · #14 11-30-2007, 06:52 AM

Quote:

Originally Posted by Shoewreck

Inverting stage with 1M input impedance will add some noise to the circuit.

Ooops. Typo.

Should have read non-inverting first stage, but it should have been clear from earlier posts.

rumblinbass · #15 11-30-2007, 07:06 AM

A9X,
not that it is an issue, but the phase will be 180 degrees out.

jackson_bass,
have you decided on your power supply? sorry if you addressed this already but I haven't read every post. the configuration of you power supply could effect the signal path. In other words, if you are using one 9V battery you may need to bias the signal a bit because your op-amp will not be able to go below 0V (gnd).

edit: nevermind, I see that it has already been discussed. I am now reading up on rail splitters...you learn something new everyday.

A9X · #16 11-30-2007, 07:12 AM

Quote:

Originally Posted by rumblinbass

but the phase will be 180 degrees out.

So?

rumblinbass · #17 11-30-2007, 07:19 AM

Quote:

Originally Posted by A9X

So?

like I said...not that it's an issue.

jackson_bass · #18 11-30-2007, 10:41 AM

thanks for all of the input. I have been researching some other OpAmps, and I think the TL is not the best choice, but since it is socketed I can always experiment with some other brands somewhat. I am talking myself into making this one an external pre.. . . . . never tried that before, my other bass has an internal, but I think I may want to keep this one passive and still be able to use the pre. . . . I have a metal Altoids box that I will use.
Thanks again for all of the good information.

A9X · #19 11-30-2007, 12:08 PM

Quote:

Originally Posted by jackson_bass

I have been researching some other OpAmps, and I think the TL is not the best choice, but since it is socketed I can always experiment with some other brands somewhat.

Use a TL062 to test with, then sub something better. TL sounds awful.

rumblinbass · #20 11-30-2007, 12:39 PM

NE5532?

I have seen a lot of TL07X used in audio applications but I use mainly NE5532/5534. Just use a socket.