New Discrete Opamp Format Discussion

[tk@halmi]

Here we go again... I am about to create a larger DOA format to make construction easier and enable opamps with larger part counts. The 1"x1" format restricts the number of transistors you can cramp on there to about 10 plus the supporting resistors and capacitors. I am not ready to go to surface mount expecially after the horror stories posted here about SMD resistors.
Also, the pins are difficult to source for many and they are not so easy to line up well unless you have a jig.
Here is what I have in mind:
1. Make the board stand on its edge as opposed to laying down. This configuration has been used successfully in commercial products already.
2. Use a 10 (2x5) pin double row headers with used commonly in computers. I also thought about the 9 pin RS232 type plugs that are extremely common. I am opne to suggestions.
3. Make the board 2" long and 1" tall or if space allows 2" tall. It is usually easier to grow verically once you have an existing host PCB you are plugging this into.
4. Besides the old convention of +in, -in, out, gnd, +v, -v, and offset adjust add a -out and a feedback point pin. The feedback point pin is useful if you need to add a inductor or resistor between it and the output. The -out would come handy for balanced devices.

Cooling could be done with off the shelf heatsinks so there would be no need for potting. You could still smother your components with that epoxy to obscure them if necessary. :roll:
I will post a drawing if there is enough interest although I would prefer to get some input on it first.

Cheers,
Tamas

 

[AnalogPackrat]

Interesting idea, Tamas. One thought about using a single 2x5 header is that it's pretty small which means ins near outs and not a lot of physical strength to hold a vertical board in place (especially one 2" long). What about using a 2x2 nearer one end and a 2x3 near the other to better support the board and separate ins and outs. This would also prevent the old "plugging it in backwards" smoking DOA.

Are board mounted sockets for those square pin headers common? I have had a lot of trouble finding them, but maybe I've been looking in the wrong places. Seems like most female parts are made for cable connections.

It might also be useful to consider the possibility of an adapter to allow new DOAs to plug into old format sockets. I'm glad you're sticking with through-hole! I can't stand the thought of DIY with surface mount. Call me an old fogey.

Analog Packrat

 

[tk@halmi]

You are right the sockets are more difficult to find than the headers. I will continue the search for a better pin/socket solution.
That is an excellent idea of separate heades for input and output pin clusters. They help with stability, both mechanically and electronically, and if they are dissimilar it is easy to see what way the board should be plugged in.

Thanks,
Tamas

 

[VacuumVoodoo]

A two board sandwich could work. Same cost as for 1"x2" pcb. Would use same real estate on main board, just higher. Could still have same pinout.

 

[KingKai]

Tamas,

The 9-pin DB connector has some attractiveness as it would provide for screws to secure it to the mating connector. This would be of use particularly with equipment that is intended to be mobile. The end of the card could then have through holes for stand-off use to support the board.

On my DIY mixing board, I used 37 pin DB's for all buss connections, 9-pin DB's for power and a second 9-pin for the Fader connections on each channel. This worked very well.

Peace - out
Irv

eddited for clarity (whatever that is)

 

[Kev]

IDC10 connector or similar
not the DB9 for internal connections

 

[Samuel Groner]

Great! Personally I once decided to introduce a 5040-footprint (twice the area of a 2520, same pinout just spreaded to fit the 1.1"x2.2" board), but didn't have the time to build one opamp so far.

I'd be interested to include the new format for my opamp test jig (see www.groupdiy.com/index.php?topic=12509). I just started with the board design yesterday, so if I don't have to wait another month till we settled for the details I'll change the boards.

What about two compensation pins? I still have the mic pre in mind which changes the compensation with gain.

I'd suggest grouping the pins in three rows:
first row: + in, - in
middle row: offset, 2x compensation
last row: VCC, VEE, GND, Out, Feedback

I think that's what would make board design most easy.

As for the pin/sockets, I'd go for the SPL solution: sssssupra.jpg

These are pretty easy to source, no?

Samuel

 

[TomWaterman]

Hey Tamas,

sounds cool, the spl block with 0.1" headers is exactly what I've done for the calrec1061....with a 2x1" board ala the original. The nice thing about that is the amount of space between the pins to run tracks on the main board.

Vertically mounting seems ideal to save host board space but bear in mind that a vertical 2x2" block would only mount in a 2U case or bigger. Might prove a disadvantage overall, saving motherboard space only to have to use a bigger rack case to house it....

I'd stick with 2x1" and 90 degree header blocks.

Tom

 

[Gus]

Some things to think about

If vertical and if it has any mass vibration it WILL move the pins in a socket.

What is the leakage current between contacts of a a DB9? This would be for Fet high z input amps. I don't like the db9 idea

I have worked on a lot of different stuff over the years

I don't like connectors they all can cause problems.

I think a better way for modules could be a board 1x1 1x2 etc mounted with two screws and standoffs with the board soldered in the leads would be soldered to the main board and come up and connect to pads on top of the board kind of like SMD. There are not many wires maybe two inputs an out and + and - FIVE fast to make/desolder solder joints. The trim(s) could/should be on the module. Also if screws and standoffs are used you can still mount resistors etc. under the module.

You would make the two screw spacing and solder pads the standard

I don't like connectors

 

[tk@halmi]

Yes, I know what you mean. None of us like connectors, but soldering it directly onto the host board is not an option. Input Z should be limited to 1 megaohm even with FET inputs, there is no good reason to go higher in most audio gear. Microphones are the exception (it is unlikely that someone would want to use these in a mic). On the other hand adding support with posts and screws is an outstanding idea. It takes the responsibility off the connectors to keep the board from tilting,vibrating, etc.
Ok, I have thrown the DB9 out of the hat mainly because of the real estate it would take up.

Wow, we have 10 pins assigned already!

Thank You All,
Tamas

 

[Kev]

so IDC 10 ... or did someone already say that ? :green:

IDC??
room for expansion or use of double pins for current, spread the ground within and between the conductors of the the ribbon
err
that so didn't make sense

 

[tk@halmi]

Hi Kev,

Forgive me, I did not ignore your suggestion, but I am still searching around for PCB mount IDC10 sockets. Can you point me to a source? (perhaps I am just a retard and they are easy to locate). Actually, I was thinking using two of them for input and output clusters. Do they come keyed so doofies don't plug them in backwards?

Thank You,
Tamas

 

[Kev]

That's cool Tamas

I guess I was feeling lonely.

I think we buy our IDC's from Farnell ... I'll check.
Should also check with Joe Malone as he too like the IDC ... must be the ex Telecom thing.

He is away for a couple of days but one of us should ask him where he buys cos I'm sure he will have found a good price.
I just buy frokm Farnell cos it's easy and it's not my money (works money)

Jaycar may have these things too.
http://www.jaycar.com.au/index.asp
search
use the pull downs
PLUGS AND SOCKETS
IDC

Altronics Aust has them for 47cents without the wings and $1.00 for the cable unit.
http://www.altronics.com.au/index.asp?area=prod&grp=167

I can't make the Farnell site work right now ??

 

[Samuel Groner]

Some further inspiration:
apex_open_frame.pdf
APEXMP108MP111PRESSPHOTO.jpg

Samuel

 

[tk@halmi]

Hi Samuel,

Those are neat ideas for boards. Maybe a horizontal board is easier to deal with. A row of pins on each side would provide very good stability.
I have located 0.1" sockets and plugs at futurlec.com where they have nice little pics of them.

Thank You,
Tamas

 

[Samuel Groner]

Maybe a horizontal board is easier to deal with.

Probably. And the space saving for vertical boards isn't that big and probably rather unimportant for DIY.

I have located 0.1" sockets and plugs at futurlec.com where they have nice little pics of them.

Those?
http://futurlec.com/Connectors/HEADS2.shtml
http://futurlec.com/Connectors/FHEADS2.shtml

Samuel

 

[clintrubber]

[quote author="tk@halmi"]Maybe a horizontal board is easier to deal with. A row of pins on each side would provide very good stability.[/quote]

If not already brought up - a vertical board could more easily give problems with 1HE boxes... Another reason for horizontal.

 

[Bauman]

I really like the vertical one... but a horizontal with pins in 2 sides ( the smaller ones) is what I was working on some time ago.... It was like 1" x 2" if I recall correctly.

cheers!
Fabio

 

[Samuel Groner]

After some thoughts I opted for my needs for a board with the same pinout as the 2520 but larger area, mainly for easy backwards compatibility. See solid_state_amplifier_catalog_23.gif, top right with three pins removed.

Three board sizes (1.1"x1.1", 1.1"x1.65" and 1.1"x2.2") should cover most needs.

Samuel

 

[clintrubber]

http://www.philbrickarchive.org/solid_state_amplifier_catalog_dateien/solid_state_amplifier_catalog_23.gif not working...