Op amp no work

[dogears]

Hi guys,

I did a homebrew op amp based on a quad eight AM10 schematic I found in the technical documents section.

I also found a layout by PeterC that I based my transistor swaps on.

However, they don't work. Low output level, high distortion.

I've checked and double checked and triple checked my schematic, transistor orientation, and pcb traces.

I'm running it at +/- 20V. Can anyone give me some troubleshooting advice here? I feel like I must be missing something simple.

 

[rackmonkey]

What Power Supply are you using? Is it truly bipolar? If you run an opamp that was designed for a bipolar supply with a single supply (Vs & ground) it will clip the signal severely and output will be low.

BT

 

[JohnRoberts]

Keep checking...

JR

 

[dogears]

Homebrew, but it's truly bipolar. +20 and -20 on each DC rail. Also tested it with another PSU that is +/-15 to make sure. The PSU works with other op amps.

 

[PRR]

> Can anyone give me some troubleshooting advice here?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

That's for 9V pedals; adapt as needed.

 

[gar381]

Hope this helps..

GARY

 

[iprovlek]

I have same problem here dogears!!!

But I bought PeterC AM10 opamp....

Schematics is the same like Gar381 put!!!


So I contact to PeterC and he told me that I must use bc550b and bc560b transistors instaed bc550c and bc560c and no use ST 2n4036 and ST 2n2102!!!

I didnt try this cause I didnt have time....

Here is pic of it...

 

[iprovlek]

Here is pic of opamp....

 

[peterc]

Some interesting stuff here......

So I contact to PeterC and he told me that I must use bc550b and bc560b transistors instaed bc550c and bc560c and no use ST 2n4036 and ST 2n2102!!!

Not me, I only use the 'c' versions.

There was no commercial version made of my layout (as far as I know....) and the PCB you have shown is DEFINITELY not my layout. For example, it is double sided and has curved tracks, not something I have ever done. Seems to have been done by someone called KLONTZ.

Sorry I cant help further, but it was 13 years ago, and I dont have any of those left. I only built 2 as far as I can remember.

Dogears, can you post some DC voltages at the transistor pins, I can try and do a simulation, or you can try one yourself as well.

Do you have a pic of the opamp?

Peter

 

[iprovlek]

Sorry Peter my fault....
You are right, that is Simon Klontz opamp!!!

 

[iprovlek]

But found this....where is my Simon Am10 to ,so I mixed you up with Simon!

Here is your layout Peter....

 

[dogears]

Here's my voltages. The + and - rail offsets are from the circuit I'm using, there are 10 ohm resistors on the supply, some variance there. PSU is sending +/-20.

 

[peterc]

Something serious;y wrong there.

Check the 19.3v on both sides of the 10R resistor in the +ve line. Check the 10R resistor.

 

[PRR]

This part clearly can not be right.

 

[abbey road d enfer]

This 20.5 voltage is also Q5's Vbe!

 

[gyraf]

                                                              ....I love this forum....  ;D

 

[PRR]

> This 20.5 voltage is also Q5's Vbe!

Why my mark-up says "Q5 must be blown".

Much more likely: his "19.3V" really isn't. Someone mentioned 10r resistors, but there's other places that could be bad.

 

[dogears]

Work's been nuts, I'll go over it today.

Thank you for the help, I was working quickly on my lunch break when I took those so I may well have written or probed the wrong locations . Didn't even look at the values... 



:-[

 

[dogears]

I'm almost too embarrassed to admit it, but there was only one problem.

In the EDA program I use the pins aren't part of the schematic, only a package on the PCB side. So you have to manually add the trace from the net to the corresponding pin. If you forget, the design rule check doesn't catch it, because it's an extra package not on the net list in the schematic.

I forgot to connect the +V pin to the +V net.

Add the small jumper of shame, and everything works great.

 

[PRR]

> Add the small jumper of shame

Everybody needs an ample supply of those jumpers. EVERYBODY has "done a dumb thing". Few of us are brave enough to admit it.

BTW, the take-away is that pros make as many mistakes as beginners, but with experience pros are faster to detect and fix/hide their mistakes. (Not saying you are a beginner; but maybe in this detail of your EDA program.)