Dual discrete opamp PCB in DIP8

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tiroth

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#1
Here is a potential layout for moamp's discrete opamp, designed to simulate a standard dual opamp. The idea is to use it with Jen's Active Filter 2 board. Of course, it could also be used in any other circuit as an opamp replacement.

There will likely be a group buy of these boards

You can see that the design will plug in Jen's board in DIP8, plus the two grounds into the bypass capactor pads. I have also laid it out to be used in a DIP12 pad for use in other designs. I'm not sure how critical the ground connections are as long as the host circuit has the appropriate components... 😕

Please let me know any comments on the layout so that it can be improved. Thanks!
 

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#2
Here is the corresponding schematic. It should match moamp's schematic . I included R10.

The other half merely has the resistor numbers + 10.

Warning! All of the 3-pin transistors are backwards in the schematic. This is because my schematic library had the pinouts backwards and I was too lazy to create new models. They should be correct on the PCB.
 

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#4
tiroth said:
Here is a potential layout for moamp's discrete opamp, designed to simulate a standard dual opamp. The idea is to use it with Jen's Active Filter 2 board.
Click to expand...



Hi,

If the discrete opamp is going to be used in Jens's board, some parts can be left out. R10 is necessary for DC stability and can be soldered directly onto the bottom side of the motherboard (from pins 1 and 7 to the ground), and an additional ground wire isn't necessary.

Regards
 

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#5
Tiroth,

Would it be a good idea to be able to adjust the output offset to zero volts? One of the drain resistors could have a footprint to accomodate an adjustable pot.

Moamps,

You obviously have board files for MOX and I dont remember anyone just asking if you would be willing to supply the files to someone so they could do a group run of your layout. I know we could make are own or do a perf. board, but a finished PCB is so neat and clean. PCB's give it that professional look!! Well, enough begging for now. I do thank you for all that you have contributed on this X-over.

BDP
 
#6
has anyone thought about making this thing pin-compatible with the standard dip8 dual opamps?

For example, you can break up the board into two pieces, each containing one opamps. On one side of the boards, you will have your input pins and output pin, and insirt each board into one bank of a dip8 socket so that they will be drop in replacement of typical dip8 opamps.

Wouldn't that make this thing more marketable?

and if you used smd parts, 🙂
 
#8
Now we're talking 😉

I suppose there will be a wiki / a prospective buyer list?

And, yes, it would be most useful as a pin compatible dual op amp replacement - I was thinking of building those with point to point wiring (would be a ball of components I guess) for easy drop in into legacy projects, or simply to compare with standard op amps. Also, it would fit any other PCB designed for dual op amps etc etc etc. That would definitely tickle many a fancy.

MBK
 
#9
millwood said:
has anyone thought about making this thing pin-compatible with the standard dip8 dual opamps?
Click to expand...

That's rather the point. 😉

For example, you can break up the board into two pieces, each containing one opamps.
Click to expand...

That's an interesting idea. You'd have to link the two halves though via wires in order to tap the bipolar supplies out of the opamps. It would probably make it compatible with more uses.

Thanks for the insight moamps. I will take it into consideration and simplify the layout further.

I'll also set up a wiki tomorrow and provide more details on a group order.
 
#11
Okay! This is much cleaner. Thanks again to moamps and millwood.

This can be used as a 6-pin SIP with ground, or two together can be linked by the pads on the left side and plug into a standard dual opamp pad.

For use as DIP8, the left half would use leads from 'O'ut through 'N'egative. The right half would use 'P'lus through -IN. Ground could be left unconnected if R10 were soldered to the PCB.

Any comments? BDP, where do you want the adjustable resistor?
 

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#12
tiroth said:
Any comments?
Click to expand...


it looks great.

One quick suggestion: you may want to drill a "hole" in the middle of the board. You can then tie the two modules togather using a screw through an insulation spacer (between the two modules). and the final module can be inserted into a dip8 socket directly.
 
#13
Tiroth

The pot. would be used in place of fixed resistor R3 or R4. Since they are in parallel it doesn't matter which one. In MOAMPS parts list the value is listed as 3.9K. The parallel value of 3.9K and 392 equals 357 ohms and I see MOAMPS has a 360 ohm value placed in the circuit previously posted.

BDP
 
#16
Tiroth,

the order of standard DIP 8 op amp pins is different from your PCB, it is "out, (-)in, (+)in", see pic.

I am not sure if it's a good idea to break up the board. As a drop in for dual op amps, it's unnecessarily complicated - better have just one board. And a drop in for a *single* op amp package would still have to be DIP 8, but with conflicting pin arrangements (dual DIP 8 op amps DIL's are not just two opposing single op amp SIL's).

So, I think it's most useful if it's either a drop in for dual op amps, pin compatible, therefore w/o the offset adjust *or* two additional pins, or as a drop in for single op amp (but still in DIP 8). Advantage of the single solution is the smaller board real estate (you don't get such big "wings" to the sides), and offset adjust capability in DIP 8. I wonder though how much offset you would get anyway with a FET input design...
 

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#18
MBK said:
the order of standard DIP 8 op amp pins is different from your PCB, it is "out, (-)in, (+)in", see pic.
Click to expand...
Ouch, that is what you get for rushing at night. 😉 An easy fix. Thanks!

I am not sure if it's a good idea to break up the board.
Click to expand...
Actually, I think it is simpler routing broken up. And it has a smaller footprint at the expense of vertical height...which means it is more likely to fit into pre-existing designs. 🙂

And a drop in for a *single* op amp package would still have to be DIP 8
Click to expand...
Well, it was never intended to be a DIP8 single opamp replacement. The idea was more that DIYers could feel free to, like moamps, design their boards around the SIP6 form factor if they wanted single discrete opamps.

I wonder though how much offset you would get anyway with a FET input design
Click to expand...
Virtually none, I think, with 2SK389. The offset adjust trimmer should come in handy for designs using standard (single) JFETs.

Thanks for your input.
 
#19
Updated PCB, with trimmer and screw pads.

The screw pads accommadate a 2-56 screw with 5/32" diameter spacer. R8 was moved to the back, and if you use the optional screw attachment R9 moves the back on the left half and must be soldered after the screw is attached on the right. Pretty easy. I didn't want to increase the board size (and cost) to those who don't need it.

If you are interested in these PCBs, please sign up! I am close to having enough commits to lower the price from 8 for $9 to 8 for $6.
http://www.diyaudio.com/wiki/index.php?page=Moxbuy
 

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