GEOFEX Simple Easy Graphic Equaliser PCB Layout

[frequencycentral]

From this schematic: http://www.geofex.com/article_folders/eqs/paramet.htm#graphic_eq
.......and this thread: http://www.diystompboxes.com/smfforum/index.php?topic=84017.0

I've used a TL072 dual opamp instead of a TL071, and used the extra opamp to provide a buffered vref. The resistor to ground at the output on the schematic (R27 on the layout) doesn't have a value - I'm guessing 100k? By my reckoning the PCB should be approx 26mm x 77mm.

[Ben N]

ut where's the glass? 

[StereoKills]

ut where's the glass? 

Yes, shouldn't it be done with all sub-minis? 

Seriously though, very nice job Rick!

[karter2000]

I'd really, really be interested in a couple pcbs for this, if anyone out there could make them for me.  Name your price!

[therecordingart]

I'd really, really be interested in a couple pcbs for this, if anyone out there could make them for me.  Name your price!

I think I may have finally got one to print at the right size. If you aren't in a hurry I may be able to help you out. I want to get one built before making any promises.

[Brymus]

Here is a pic of my first PCB for this tinned and ready to stuff,(note I did a quick and dirty job of drilling the holes)I will get it populated and hopefully verified tonight.
I should add that RG has kindly gave me permission to make some PCBs for sale (Thank You RG !!!!)
And Rick said I could use his layout (Thanks Rick !!)
So as soon as I verify this I will make a small run of PCBs and post them in the for sale board.
The ones for sale will be drilled much neater than my test piece...But they will all be tinned and the same size.

[Brymus]

I just realized I shouldnt have flipped the layout...
Oh well easy enough to make another one.
DOH !

[caspercody]

Bryan,
That is a nice pcb, what is your procedure for getting it that nice? I was using Staples, but no longer get that paper. Tries a transparent paper, did not work to good (maybe I had the iron to hot). What paper did you use?

Thanks
Rob

[Brymus]

Bryan,
That is a nice pcb, what is your procedure for getting it that nice? I was using Staples, but no longer get that paper. Tries a transparent paper, did not work to good (maybe I had the iron to hot). What paper did you use?

Thanks
Rob

Look here Rob > http://www.diystompboxes.com/smfforum/index.php?topic=84124.0
BTW those layouts you sent me look nice,I havent had a chance to try any of them yet but thank you all the same.
Bryan

[Brymus]

OK that didnt take too long.
Here is a new PCB flipped the right way,I even tinned it again.
I did make a couple of boo boos being in a hurry to get this done before the wife and kids get home.
But as a plus I figured out what makes my PCBs dark...
Its when I take the toner off with acetone some of it will soak into the FR4,I actually saw it happen this time.
I guess some FR4 is more porous in some places than others...
Now to populate it and get this layout verified for everyone else. >

[Brymus]

OK I just realized I dont have enough 6k8 resistors (14 needed) to populate this thing.
Could I use 5k6 or 10k  in place of the 6k8 ?
It looks like a simple voltage divider or would I have to adjust the 7 x 33k resistors too?

[Brymus]

OK I tried it with 5k6 resistors in place of the 6k8 x 14,all other components are the same as the schematic,I used a 100k for R27
And it sort of works...
Not any volume even with amp up all the way theres hardly any sound,just enought to hear it like it should sound almost all the way turned down,the EQ controls work as much as I can tell without more volume.

Voltages are in = 8.8V on the Qs (2n5088 x 7) are >Collector 8.8v, Base 4.4v ,Emiter 3.7v all 7 are the same.
IC (TL072) pin 1 = 1.4v ,pin2 = 1.7v, pin3 = 1.8v, pin4 = 0v, pin5 = 4.4v, pin6 = 4.4v ,pin7 = 4.4v , pin8 = 8.8v
I went over the schematic VS layout and it all appears right,I took my time soldering,no bridges or other errors I could find.
Im not sure but shouldnt there be a bigger difference between the base and emiter voltages ?
Im still new to this so IDK but why are R22 and R23  4k7  instead of 47K ?
And why are C15 and C16 10uf instead of the usual 100uf ?
I will try switching the 5k6 to 6k8 but I would appreciate some feedback on whats wrong here,and why ,thanks

[frequencycentral]

I do hope it's not my layout! The values of R22, R23, C15 and C16 shouldn't matter too much, and look to be fine as you're getting half the power rail at pins 6 and 7. What value did you use for R27? When I was first looking at the schematic my head was saying it needs a buffer at the input. Has anyone else built the circuit successfully using a different layout I wonder?

[therecordingart]

I do hope it's not my layout! The values of R22, R23, C15 and C16 shouldn't matter too much, and look to be fine as you're getting half the power rail at pins 6 and 7. What value did you use for R27? When I was first looking at the schematic my head was saying it needs a buffer at the input. Has anyone else built the circuit successfully using a different layout I wonder?

I thought R27 was 1M.

[frequencycentral]

I thought R27 was 1M.

It's not marked on the schematic, but looking at the whole page at GEOFEX again, it would appear that you may be correct, as all the other circuit snippets on that page show a 1M to ground at the output. It it ends up being 1M I'll amend the layout accordingly.

[Brymus]

OK I have been messing with this for a couple hours now,and can say for certainty its not R27 being 100K,I tried 1 meg and 2m2.
The EQ works fine if only one band is connected to its pot ,remove the other 6 pots and it works fine.It doesnt matter which band as long as its the only one with a pot hooked up.
I first changed out one band with 6k8 for the 5k6 and it worked fine (but I only had one band hooked up...)Note the voltage difference between base and emiter was even less than with the 5k6 resistors>So I thought cool thats the problem> but after swapping all the resistors it had the same problem,because I hooked up all the bands.
So I tried swapping out R27> still the same it only works with one pot connected,to any band,all of them work but only individually.
So that only leaves two things >one being the buffered Vref that isnt in the original circuit that RG drew up.
Also the original circuit that RG took and drew this from had a bi polar +/- 12V supply.
You can see the original circuit here >
http://www.4qdtec.com/graph.html
I am going to try bypassing the other half of the opamp and remove the buffered Vref to see what effect that has,I dont undrestand how that would make a difference but I have tried everything else.
If that doesnt work that would only leave switching to a bipolar supply

[slotbot]

oh ya nm.

[Brymus]

If I understand it right the op amp is biased through R25.
I just moved the op amp to the breadboard and connected everything w/o the buffered Vref and it seems to work just fine.
I will post back in a little while some more definetive results...

[slotbot]

Voltages are in = 8.8V on the Qs (2n5088 x 7) are >Collector 8.8v, Base 4.4v ,Emiter 3.7v all 7 are the same.
IC (TL072) pin 1 = 1.4v ,pin2 = 1.7v, pin3 = 1.8v, pin4 = 0v, pin5 = 4.4v, pin6 = 4.4v ,pin7 = 4.4v , pin8 = 8.8v

I *think* this is showing some sort of problem. Pin 3 should show Vcc/2 and so should Pin 1 if there is no input.

EDIT

also

maybe the connection of LUGS 1 shoudl go to Vb instead of the + input of the opamp. I know this is not the samne as teh schematic but i woudl suggest trying it to see what happens.

[Brymus]

I will give that a try.
Its not the buffered Vref,what I discovered is that if you turn it on then unplug lugs 1 or 3,then plug them back in it works until you cut power> turn the power on and you have to unhook lugs 1 or 3 and reconnect it for it to work again,wierd...
Luckiliy I have both lugs 1 and 3 hooked to busses and the pots hooked to that for testing.
what is locking it up causing it not to work until one of lugs 1 or 3 are disconnected and then reconnected for it to work ?
I will try your suggestion slotbot and report back...