PCB Layout check

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Well I took a PCB I found posted on this board and attempted to modify it to better suit my components. Can somebody please take a look at this layout and see if I have missed anything. I build the original circuit and the PCB came out fair, hey it was my first time, but it was just too cramped. The Riken resistors are pretty big.


Thanks in advance.

Eric

BTW the my first PCB gainclone worked and sounded good, but after a few minutes would start to distort at low volume, turn it up and it sounded decent again.

An externally hosted image should be here but it was not working when we last tested it.
 
Retired diyAudio Moderator
Joined 2002
supereri said:
Well I took a PCB I found posted on this board and attempted to modify it to better suit my components. Can somebody please take a look at this layout and see if I have missed anything.

With a quick look, the routing looks correct for the inverting gainclone (thorsten) schematic.

As for the routing, I would make the traces thinner under the chipamp, as it looks like you have clearance issues. A better option might be to move the .22 ohm resistor, crossing over the V+ trace, and run the output down, instead of running under the chip. This would avoid the clearance issues and still allow you to use your current trace thickness.

What program did you use to make the layout? ExpressPCB?

--
Brian
 
Hi,
How about this one? any comments welcomed.
 

Attachments

  • 3875pcb1.jpg
    3875pcb1.jpg
    56.3 KB · Views: 1,017
Hi Supereri,

being the author of the original version of this pcb I felt somewhat responsible for your troubles... :bigeyes: on the other side, I couldn't find the time to build the circuit, yet, so please consider my suggestions just as an anthology of other people's posts and not first-hand experience. Keep also in mind that I'm not an EE. Hope it helps.

A question: did you measure the quiescent current drawn by the amp immediately after power on and when the problem arises? According to the datasheet, normal values should be between 30 e 70 ma. A larger current draw could be a sign of oscillation.

If this is the case, you could do various things.

1. implement the clever suggestions from Brian;
2. streamline the traces from the chip to the decoupling 1uF capacitor, or at least remove the weird "elbow";
3. considering that you're not using a power supply connector (the big square box), you might make components closer, shorten quite a bit the traces and make a smaller pcb;
4. you could replace the 1uF electrolytic capacitor (see #2) with the Siemens stacked cap recommended by Saint Thorsten. Don't know where to find it in Arizona, but Newark stocks a similar cap "manufatured" from Farnell (yes, www.farnell.com).
You might check if this is in fact a Siemens cap with the Newark people before buying it.
This is the real thing: www.rswww.com (search for product code 191-3452)
This is the "mysteryous cap": http://www.newark.com/NewarkWebCommerce/newark/en_US/support/catalog/productDetail.jsp?id=25H9503
5. According to Joe Rasmussen, the resistor values you choosed could help the amp oscillating when the pot is in the intermediate position. If you look at my thread, there is an Excel file listing some combination of values that should hopefully not "help" the amp to oscillate.
6. Don't trust too much my suggestions. There is something against nature in giving advice about an amp not yet built... :D

Ciao,
Massimo
 
Antomas,

First of all thanks a bunch for posting the pcb files, they provided a great place for me to start. I really liked your grounding layout.

Second I have modified the circuit as sugested by Brian as I think he suggested.

Also I had forgotten the 22k resistor to Signal ground, which I have added below.

A question: did you measure the quiescent current drawn by the amp immediately after power on and when the problem arises?

I am not sure how to do this. I am a complete newcommer and I am trying to learn by doing.

All in all before distortion set in I was quite impressed by the sound. I had heard reports of lack of bass, but I was pleasantly surprissed by the amount.

Thanks for all of the great replies!!!

An externally hosted image should be here but it was not working when we last tested it.
 
Nearly,

keep the star-point where it was originally on the previous pcb layout at the power 0V input.

The connection for the PSU caps is now correct.

The 0V for the LS output should connect directly to the star point and should not be shared with the input 0V.

The input 0V should first connect to the bottom of the 22k resistor (this is the feedback 0V) and then a single track should take it to the star-point (this track can be quite thin if necessary).

It is tempting when using star-earthing to connect everything to the centre using seperate tracks and if the star-point had zero impedance this would be ok, but it doesn't and currents flowing across it will cause small changes in potential.

If your input 0V was connected to one side of the star and feedback 0V to the other then small potential differences between these points due to charging currents or loudspeaker currents would be amplified just like any other input signal.
 
The earthing seems ok but I've just noticed the rest of the circuit looks a bit strange. Something strange has happened since post#1 and a 22k resistor has become connected to 0V and the feedback point.

Delete the 22k it isn't required connect the 0V end of the 18k to the same point on 0V that the 22k was connected previously. This will bring it back to the electrically correct original and also correct earthing.

Sorry, I didn't notice this earlier. I think there was confusion between inverting or non-inverting modes. I take it you intend inverting?
 
Ok here is the zip file.

http://members.cox.net/turboz/gainclone.zip

I don't expect people to just do this for me as I want to learn, but I am not grasping this as well as I had hoped. This schematic I had originally used showed a 22k resistor to signal ground , which is why I had included. I saw that it was left out on the first layout I posted.

Wait, I think it just sunk in what Richard C was talking about when he advised to delete the 22k and connect its connection to the 18K. How is this?

An externally hosted image should be here but it was not working when we last tested it.
 
quote:
A question: did you measure the quiescent current drawn by the amp immediately after power on and when the problem arises?
I am not sure how to do this. I am a complete newcommer and I am trying to learn by doing.

Hi, you should:

1. put a current meter between V+ of rectifiers and V+ rail of your amp. Set it to 1 amp maximum value;
2. connect your amp to your source (cd) and to the speaker (or to a dummy load);
3. turn on your source and amp; don't play a cd;
4. measure the current drawn of your amp with the pot at the minimum, intermediate and maximum position (volume); write the values down;
5. repeat step 4 after waiting the time "needed" by the amp to distort.

Report your figures on the forum; you shall probably find better advice about that than mine... ;)

Massimo
 
Just had a look at the schematic, not sure why the 22k resistor is there, the amp should work ok without it. Perhaps it helps improve stability? but it's inclusion is not common.

Refering to the latest layout: just move the 18k to the right so that its lower end connects to the input ground before the star-point. Then every thing will be ok.
 
Yes, that's a better arrangement because the charging current pulses no longer pass through the star and both input grounds will now be at the same potential.

The connection from the between the main caps and the star-point could be shortened by about 2/3 reducing its resistance by the same factor.:)
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.