Multitone 7 Band EQ - built

[RickL]

This one: http://www.freewebs.com/nassetronics/vintagecircuit.htm

I finally finished this one and, with some limitations, it works.

I built it on perfboard and used trims for the pots. I also had to sub a couple of the capacitor values (27pf for the 25pf, 470pf for the 500pf, that sort of thing).

I tested it using a Vulcan that I haven't boxed yet that I have set up with a switch to select only the first stage for clean sounds or the full effect for hard distortion.

The bands are pretty broad but all have a noticable effect on the sound especially with a distorted signal that has lots of harmonic content. The top band was less noticable with a clean signal but was useful for trimming off some edge on distorted sounds. With all the pots turned down the signal was almost completely cut out.

It needs a pretty hot signal (that's why I tested it with the Vulcan) because it robs a lot of volume. I took it out of the circuit without changing the settings on the Vulcan and the sound went from bedroom volume with the EQ to loud squealing feedback without.

It would probably be a usable eq with some sort of booster in front of it like the first stage of the Vulcan but you'd probably get a better eq for less money by buying a used Dano mini graphic. Now that I've built it I may tack it permanently on the end of my Vulcan when I finally box it.

[Nasse]

Thanx for reporting. I should really update or delete those pages...

It might not be the most clever passive EQ circuit there, does not save pots and parts but I am happy if it works

I should really try this Vulcan circuit and that diode compression

[RDV]

That circuit would function much better with a dual OA providing buffering(1st stage) and some volume recovery(2nd stage).

A truly great article on EQs: http://www.geofex.com/Article_Folders/EQs/paramet.htm

Regards

RDV

[John Lyons]

Hey RDV or anyone else. I built the Parametric Eq (linked above, with resonance/Q, boost/cut and frequency controls). I used two 5532 opamps.
I can only get minimal boost or cut. The entire effect is very subtle. Everything seems to do its function but it's barely doing anything as far as changing the tone. The only thing I did is change from the schematic are  the cap values to allow for more of a mid and high band instead of low to mid. Do the cap values have to be close to perfect to make this circuit work or did I get something else wrong? I tried to aproximate with standard availible values. C1 .03, C2 .008, C3.008, C4 .004

Just looking for someone who might have built this and had experience with it.

Thanks in advance.

John

[RDV]

If you have the Resonance or Q control wired up(10K pot), you should first try it at full minimum or near 0 ohms resistance. Set like this you should get a substantial sweep(almost wah-wah like) as you sweep the Frequency knob with the Boost/Cut knob at either extreme. As you bring up(or increase resistance) the Q control you widen the bandwidth that you are affecting making the control very subtle indeed. I would highly suggest socketing the caps used in the 2 tone sections and try values till you get what you want. R.G.'s values are a great place to start, but experimentation will prove to be effective in acheiving what you want.

Regards

RDV

[RDV]

I tried to aproximate with standard availible values. C1 .03, C2 .008, C3.008, C4 .004

I would at least switch C3 & C4. I've tried to use a 10 to 1 ratio in the caps, like C1 = .1, C2 = .01 etc.

Regards

RDV

[John Lyons]

RDV

Played a bit with the para eq today. Seems that the High Q settings are the only way to get much out of the circuit. Otherwise it's not enough boost for get a radical change in tone. I would think that the 15db or 12...cant remember what it's suppossed to boost/cut, would be enough to get more of a wild eq shift.

I searched for some posts on the subject and one by R.G. was saying to add at least 10uf to bybass the power and add a .1uf cap across the +9volt supply. Did you add these caps to you circuit? Does the 0.1 go across the battery leads? How exactly does the 10uf get added?

John

[RDV]

RDV

Played a bit with the para eq today. Seems that the High Q settings are the only way to get much out of the circuit. Otherwise it's not enough boost for get a radical change in tone. I would think that the 15db or 12...cant remember what it's suppossed to boost/cut, would be enough to get more of a wild eq shift.

I searched for some posts on the subject and one by R.G. was saying to add at least 10uf to bybass the power and add a .1uf cap across the +9volt supply. Did you add these caps to you circuit? Does the 0.1 go across the battery leads? How exactly does the 10uf get added?

John

I now know why your circuit is not working. Photobucket is down right now, or I'd post a solution for you.

I know you'll need a voltage divider network with the apprpriate caps and resistors in order to make your opamps work. I guess I assumed that you'd worked with opamps before.

Here's an example from the DIY FAQ:

Power Supply - What is V.R., V.B, VREF, 1/2V+ etc....?

Well, V.R. is voltage reference and 1/2V+ is 1/2 of your most positive voltage (usually 9 volts). Usually they are one and the same and you can typically see V.R. connected to a resistor that connects to the input of an op amp as in the Shaka Braddah 3, The Rat and many others. Basically if you see 4.5V or V.R. or 1/2V+ ( all the same), you find all the places on the schematic that reference the label and connect them together. So all of the places that reference V.R. would connect together; one of the connections actually creates V.R. or 1/2V+. The connection that usually creates V.R. or 1/2V+ aka 4.5V (for a 9V battery) usually is a voltage divider. Typically two identical resistors, one to V+ (such as 9V), the other to ground. The place where they connect is V.R. or 1/2V+.

Vr & Vb mean the same thing and the 47uF cap in the picture could be a 10uF. Hook the Vr to the points on R.G.'s schem that say Vb. Try this and see if your circuit works a bit better. I just got home from driving 500 miles and I'm kinda burned out, so I hope I helped out in this condition.

Regards

RDV

[Apokas]

Im a complete newb at this things, but I want to make a 7 band equilizer.
Just a question from reading these posts....the difference between active and passive equilizers is that passive just cut down where as active cut down then amplify with a booster to bring back to original volume?..so in a way amplify the selected frequencies and at the same time cut down the unwanted ones?

[John Lyons]

RDV

I have the voltage bias section in my Paa eq circuit already actually. I used the schematic just as it is on the GEO site with the exception of Caps 1 through 4 in the frequency selection.  Also mentioned by RG in an old post was putting a 0.1 cap across the +9v. Would this be across the possitive and ground? or?

Right now the first band works ok, when the Q is more towards  a bell than a peak there isn't too much boost available, er enough for what I want to do with it. Is there any way to squeeze more boost gain out of the circuit, Other than tacking on a booster etc. I like the High Q settings for a wild effect but I would usually use the bell type settings of Q and there isn't enough boost this way.

Also, I believe the opamps used will effect the higer freqs, or that some opamps just don't have enough bandwidth or push to deal with the higher frequencies. Which op amps did you use?

Thanks for the help. I appreciate it.

John

[RDV]

You could put a pot in the place of the feed back resistor(the2.7K), maybe 10K and try to add gain there. If you could post a link to the thread that R.G. made his statement in, I could perhaps figure out what he meant, but as it is I be guessing. Perhaps he meant a bypass cap in the FB loop to Vr? I'd have to see it. I've got a NE5532 in the EQ section of the HMP, but a JRC4558 was about the same.

Edit:

I went back and found that post myself and I think he was simply refering to the Vb power section that I suppose he added later(perhaps right after that posting).

I still think making the buffer opamp boost instead of buffer will probably give you more of what you want. It may want to howl a bit though(especially during full moon). :wink:

RDV