New Project at GGG - 6 Band EQ

[Dean Hazelwanter]

JD has posted one of the 3 projects I sent him in the last while, a 6 (or 5) band graphic equalizer using a pair of TL074s.

http://www.generalguitargadgets.com/index.php?%20option=content&task=view&id=216&Itemid=241

The next one should be up in a week or so.

Enjoy!

[Mark Hammer]

Excellent!!

Users will appreciate the inclusion of the table at the bottom on page 2 of the document that shows parts substitutions for different selected bands.  With that information a person could:
a) produce a 6-band unit with the PCB that could be adapted for bass, electric guitar, acoustic guitar, or even vocals
b) produce two cascaded units that cover the entire spectrum from 31.3hz to 16khz for EQ-ing  band or room.

I'm just guessing here, but I gather it will fit inside a 1590B?

[audioguy]

that looks easy enough... and since I play a 7 string... this might be my next build... but how do I wire it up to use pots rather than faders?

Thanks for the cool project!

[Zero the hero]

Nice project, Dean!

[Dave_B]

how do I wire it up to use pots rather than faders?

A fader is a pot, so they're wired up the same way.  The wiper (the arrow) connects to the middle terminal on your pot.  I plan to build one at some point, using pots to simplify the build.

[jrc4558]

Gorgeous! My bassist is getting one for his Bday!

[audioguy]

A fader is a pot, so they're wired up the same way.  The wiper (the arrow) connects to the middle terminal on your pot.  I plan to build one at some point, using pots to simplify the build.

I'll have to study the layout vs the schem to grasp it. Thanks for the response!

[Mark Hammer]

While linear slider pots are a nice way of visually representing emphasis and de-emphasis across the audio spectrum, you CAN build *any* equalizer using normal rotary pots.  If anything, they are more immune to invasion by dirt than slider pots.  Or rather, to get the same degree of dust immunity you find in a typical $1.50 rotary pot, you'd need to spend at least $5 on a slider pot.

[audioguy]

While linear slider pots are a nice way of visually representing emphasis and de-emphasis across the audio spectrum, you CAN build *any* equalizer using normal rotary pots.  If anything, they are more immune to invasion by dirt than slider pots.  Or rather, to get the same degree of dust immunity you find in a typical $1.50 rotary pot, you'd need to spend at least $5 on a slider pot.

Not to mention cutting the holes for the sliders.
Im sure I'll have a million questions when it comes time for me to wire this thing up!

[Dean Hazelwanter]

Thanks!

Yes Mark, it's designed to fit in a 1590B case. If you can afford to lose 2 mounting holes, notch out the rectangles around the 2 mounting holes. Then you can slide the board farther to one end of the case to gain some in-case space for stomp switch, jacks, pots etc. It also fits nicely in the bottom (lid?) of the case

As usual, I laid it out using the 0.1" center pins for all off-board wiring. The original version of this used the miniature Alpha (317-2091F-5K) pots from Mouser to minimize off-board wiring. In thinking about it for stompbox use, the vertical version of this pot (317-2090F-5K) would be handy, mounted on a little daughter board coming off of the 8 pin header.

[Toney]

Great!

[Noplasticrobots]

For info on pots as faders, check out "The Musical language of Tom Dowd" on DVD. There's either seom old photos or video of him using a mixer with pots. Looks hard as hell.

[dano12]

JD has posted one of the 3 projects I sent him in the last while, a 6 (or 5) band graphic equalizer using a pair of TL074s.

http://www.generalguitargadgets.com/index.php?%20option=content&task=view&id=216&Itemid=241

The next one should be up in a week or so.

Enjoy!

YES! I have been looking for a nice equalizer to add to some existing circuits for a while now. Thanks so much for the work!

(Can you tell I'm excited?)

[ncc]

JD has posted one of the 3 projects I sent him in the last while, a 6 (or 5) band graphic equalizer using a pair of TL074s.

http://www.generalguitargadgets.com/index.php?%20option=content&task=view&id=216&Itemid=241

The next one should be up in a week or so.

Enjoy!

Dean,
This is a great contribution.
Can you share what the other two projects are?

Thanks a bunch,

ncc

[Dean Hazelwanter]

The next one is a gene splice between my original 800mS delay (DHEcho) and Scott Swartz's vastly superior PT-80 (300mS) design. So, 800mS, with Scott's companding and filtering. And yes, Scott gave his blessing and input. 

Please, don't bug JD with any questions about the SHEcho (Swartz-Hazelwanter Echo) just yet. It will just delay getting the project posted, and many of the questions you have might be answered by what is posted. After it's posted, fire away! 

[audioguy]

So... looking at the schem... the center terminal of the pot goes into 1-6 on the board... but does terminal 1 and 3 connect to terminals 1 & 3 of the next pot and so on?

Thanks!

[Transmogrifox]

One thing I would like to see explained is the input buffer.  Just looking at it, it appears unstable--like it could get pinned to a rail and not get free in certain circumstances--or at least induce a certain degree of DC offset...it really looks prone to drift off into no-man's land.  Furthermore, electrolytic caps induce less distortion when they have a DC bias of at least a couple volts on them.  Whatever the case, it doesn't accomplish DC blocking very well, and doesn't block DC at all in the case of R1=R2...the capacitors cancel eachother out so you're better off not even having them in the circuit at all.

Also as a rule of thumb, the inverting op amp is a higher noise configuration.  This circuit probably isn't very noisey any way you do it so I doubt that's really an issue.

I comment somewhat "pussy-foot-like" because sometimes when I see something like that input stage that looks a little strange I find the designer had a good reason for it...and I'm making a fool of myself with every word.  If it is stable, I do see the immediate advanage of being able to adjust from -20dB to +8dB input gain with few additional parts--though again you could get rid of more parts by doing away with the capacitors since they aren't doing anything good (from anything I can determine from the equation).

Otherwise, it looks like an excellent circuit and straightforward build. I've been thinking about making a couple EQ's for general purpose stuff.  I may go for a little bit more "tried and true" input buffering + pre-emphasis / de-emphasis scheme like in Boss's 7-band EQ unless you present some reasoning that shows this is a "tried, true, and superior" input stage.   I really don't intend to be the "wet blanket man".  I am sincerely curious if there is a good explanation for the way it's done.  If there isn't, then I would recommend to anyone who builds it to just replace the capacitors with jumpers and make sure that anything plugged into the input is at ground potential to prevent DC drift.

[TELEFUNKON]

do I see problems coming up with people hooking up the battery negative wire to a stereo input jack ring for power switching on by plugging in the cable?

[Dean Hazelwanter]

I comment somewhat "pussy-foot-like" because sometimes when I see something like that input stage that looks a little strange I find the designer had a good reason for it...and I'm making a fool of myself with every word.

...And yet you continue...

But seriously, as it says in the project notes, this is based on an ETI project from 1977. While I didled with the component values and shaved it from 10 band to 6, I used the original topology because it worked. I can't say why the designer did it this way, and it looked strange to me also, but I've made a few of these and have never had problems, so I didn't give it anymore thought.

When you say

doing away with the capacitors

and

just replace the capacitors with jumpers

are you talking about the electrolytic in the feedback loop of the first stage, or are there others? This is the only one that looks 'goofy' to me.

[Mark Hammer]

The next one is a gene splice between my original 800mS delay (DHEcho) and Scott Swartz's vastly superior PT-80 (300mS) design. So, 800mS, with Scott's companding and filtering. And yes, Scott gave his blessing and input. 

Please, don't bug JD with any questions about the SHEcho (Swartz-Hazelwanter Echo) just yet. It will just delay getting the project posted, and many of the questions you have might be answered by what is posted. After it's posted, fire away! 

Looking forward to this.  I still have one more HT8955 left in my parts bin.