UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 21st May 2020, 8:59 am   #1
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default PCB layout - rails to DIP 8 dual opamps.

I'm after making a PCB for this - https://sound-au.com/project97.htm but it won't be printed, I'll route out the traces with a Dremmel. This is just about do-able for dip 8 opamps. With this in mind I thought the best place to start is to figure out how to route the +/- supplies to the opamps and came up with this, see attached pic.

After reading a few application reports on the Texas site I got a few tips, like this one - https://e2e.ti.com/blogs_/archives/b...-for-an-op-amp , but all the relevant articles I could find used two sided boards and SMD's. Particular emphasis was with regards to the non inverting IP.

Another issue is where to put the ground plane, I usually lay out all traces and whats left becomes the ground plane but it would obviously help if this in the right places. Any tips would be welcome; for instance do you start with the OP and work backwards or the other way round? how to avoid crosstalk?

TFL, Andy.
Attached Thumbnails
Click image for larger version

Name:	DSC02580.JPG
Views:	177
Size:	156.2 KB
ID:	206362  
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 21st May 2020, 10:58 am   #2
lesmw0sec
Octode
 
Join Date: Jul 2009
Location: Carmel, Llannerchymedd, Anglesey, UK.
Posts: 1,498
Default Re: PCB layout - rails to DIP 8 dual opamps.

The only issues I have come across is in a mixer where various inputs fed in to a virtual earth mixing node. In this case a ground plane helps, but also if long tracks to the node are involved, it is worth including a ground run between each input line. If this is not done, some capacitive coupling can occur resulting in crostalk at the higher frequencies.
lesmw0sec is offline  
Old 21st May 2020, 2:55 pm   #3
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
Default Re: PCB layout - rails to DIP 8 dual opamps.

I don't do single sided boards any more. The slots to clear tracks disrupt the grounding and it doesn't function as a plane anyway. I use double sided layout.

Done by hand, you can leave the topside as the ground plane and countersink component leg holes for clearance, or don't countersink and solder those going to ground. With ICs or IC soclets, bend out the pin to be grounded and solder to the plane.

If anything, it makes layout easier.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 21st May 2020, 3:57 pm   #4
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: PCB layout - rails to DIP 8 dual opamps.

Thanks both. I keep meaning to try some double sided board and could have sworn i bought some, where it went is anyone's guess. So with double sided board one side is ground plane only? Also is there a better way to feed +/- to the op-amps. i considered jumpering to the pins.

For decoupling I was going to solder direct to the pins underneath, i often mount other components on the underneath too. doesn't look neat but is functional.

I find the hardest bit measuring the component distances, tricky to do with 2.5mm pin separation but using the sockets to make holes helps.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 21st May 2020, 6:56 pm   #5
buggies
Heptode
 
buggies's Avatar
 
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 760
Default Re: PCB layout - rails to DIP 8 dual opamps.

Quote:
Originally Posted by Diabolical Artificer View Post
I find the hardest bit measuring the component distances, tricky to do with 2.5mm pin separation but using the sockets to make holes helps.
I used to use 0.1 inch (no metric parts then) graph paper, taped to the board then a centre punch or pointed bradawl to mark through the paper for drilling.
Drawing the layout on graph paper is a good way to start - as a rubber is easier than a Dremel later.
__________________
George
buggies is offline  
Old 21st May 2020, 7:43 pm   #6
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
Default Re: PCB layout - rails to DIP 8 dual opamps.

Definitely a time when an automatic centre punch pays its way.

At work, someone asked to borrow a centre punch to mark where he was going to drill some holes. I fetched my personal toolbox in from the car and handed him an eclipse automatic centre punch. I thought no more about it until I heard the hammer blow. He'd never come across an automatic punch before. Fortunately it survived. I was helpless!

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 22nd May 2020, 5:56 am   #7
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: PCB layout - rails to DIP 8 dual opamps.

"I used to use 0.1 inch (no metric parts then) graph paper, taped to the board then a centre punch or pointed bradawl to mark through the paper for drilling." Now that's a good idea, thanks George.

"Definitely a time when an automatic centre punch pays its way." The first time I saw one was when Trevor used one to nick a car in Made in Britain. Been meaning to get one for years but have managed without. I guess it's one of those things where once you get one you realise that should never have been without one.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 22nd May 2020, 2:56 pm   #8
Guest
Guest
 
Posts: n/a
Default Re: PCB layout - rails to DIP 8 dual opamps.

I have an old "automatic" punch which is a closed coil spring with a heavy (ish) knob on it, place point on object, pull up knob and release. Works very well for light punches, better than the Eclipse one as it doesn't wander off.
 
Old 29th Jun 2020, 12:53 pm   #9
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: PCB layout - rails to DIP 8 dual opamps.

I've had this preamp built now for a month, and it works well, apart from a few issue's where my work wasn't 100%, EG not quite soldered components, SC's where solder had blobbed over two traces etc all was well. See attached schematic.

Yesterday whilst correcting one such I noticed HF oscillation on the inverting IP's of the final OP stage, these are singing away at 357,142khz. When I did the layout I paid attention to the traces on the inverting IP's as advised in the Texas article linked in post #1. They are very short, about 1.5cm. The opamp is decoupled as advised by Rod Elliot, EG 100n multilayer ceramic caps bang on the +Vcc & -Vcc ins, there are also two 10u caps across the rails to ground where the supply connects to the board, as well as a 10u near to the said pins on the OP opamp. These work ok on the other two opamps, it's just this one that is giving me gyp.

I tried a 12p cap from one of the inverting IP's to ground, this being the first low value cap I pulled out the drawer, no go, I then tried a 100p ceramic in parallel with R113, which is a 15k, not the 33k as per the schematic, which I calculated would reduce gain at 100khz approx, this resulted in the OP oscillating, this turned out to be a short on the - IP. I then tried a 47p ceramic but finally settled on a 330p multilayer ceramic, this stops the HF on the - IP, but reduces the OP slightly at 20khz, only 25mV RMS, which I can live with.

So, have I done right here or is there a better way? Swapping the 5532 for a TL072CP solves the issue too, because AFAIK it's not such a fast opamp, I think.

Andy.
Attached Thumbnails
Click image for larger version

Name:	hifi preamp OP stage schematic.gif
Views:	81
Size:	5.2 KB
ID:	209799  
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 30th Jun 2020, 10:46 am   #10
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
Default Re: PCB layout - rails to DIP 8 dual opamps.

Bunging those 100R inside the loop (between output pin and FB resistor might help?
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 30th Jun 2020, 12:30 pm   #11
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Default Re: PCB layout - rails to DIP 8 dual opamps.

Your cct. diag. does not show any decoupling capacitors fitted adjacent to the PSU connections of the op-amp. Are those caps actually installed?

Al.
Skywave is offline  
Old 30th Jun 2020, 3:05 pm   #12
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: PCB layout - rails to DIP 8 dual opamps.

"Bunging those 100R inside the loop (between output pin and FB resistor might help? " You mean move the junction of R113/pin 7 to junction of R114/C103 Chris?

Re decoupling caps...."Are those caps actually installed?" Yes Al, see attached. Attached are also the other schematics so we know what were talking about. C1 is on across U1, C2 across U2 and C3 & C6 across U3 where the issue is. C1 & 2 are within spitting distance of the Vcc pins on U1 & 2, but on U3 I soldered the cap bang on the pins. C6 is across the rails adjacent to U3 as described in post #9.

Andy.
Attached Thumbnails
Click image for larger version

Name:	PSU decup.gif
Views:	63
Size:	3.0 KB
ID:	209907   Click image for larger version

Name:	hifi preamp schematic.gif
Views:	67
Size:	10.4 KB
ID:	209910   Click image for larger version

Name:	hifi preamp OP stage schematic.gif
Views:	50
Size:	5.2 KB
ID:	209911  
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 1st Jul 2020, 1:30 am   #13
Terry_VK5TM
Nonode
 
Terry_VK5TM's Avatar
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
Default Re: PCB layout - rails to DIP 8 dual opamps.

Your arrangement of the decoupling caps is not a common one that I have come across.

Normal practise for split rail supplies is to put the caps from each supply rail to ground, not across the + & - rails. Remember, they are two seperate supplies referenced to ground.

Most op-amp application notes only give the most minimum mention of decoupling of power rails and if you got that from the TI note I think you did, it was talking about single supply op-amps even though it is in the part of the app note that was dealing with split supply circuits.
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is offline  
Old 1st Jul 2020, 4:26 pm   #14
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Question Re: PCB layout - rails to DIP 8 dual opamps.

Quote:
Originally Posted by Diabolical Artificer View Post
Re decoupling caps...."Are those caps actually installed?" Yes Al, see attached.
Yes - but are they connected immediately to the PSU pins of the op-amps with very short leads and very short leads to 0v. / gnd.? , But connecting the decoupling caps across the PSU rails instead - as you have shown - is asking for trouble! The inductance of a few cm. of connecting wire can be significant.

Al.

Last edited by Skywave; 1st Jul 2020 at 4:29 pm. Reason: General re-write
Skywave is offline  
Old 2nd Jul 2020, 7:13 am   #15
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: PCB layout - rails to DIP 8 dual opamps.

Re coupling caps, see original article - https://sound-au.com/project97.htm . Davids mentioned coupling caps across the rails before, see this thread - https://www.vintage-radio.net/forum/...d.php?t=162698, post #12. The caps I used have very short leads, bang on the pins.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:30 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.