Built a bugle and it doesn't work-need tshooting help

pmc999 · « **on:** 4 Sep 2005, 10:28 pm »

Hi,
I built a stock bugle using the recommened parts. Put in two fresh new 9v batteries and then tried to measure the dc offset before plugging it in. I got 0v on both channels so I figuerd I was set. I hooked the bugle up, but I didn't get any amplification.
To troublshoot the issue, I double checked the batteries with a voltmeter and they are fine. I grounded one probe of the voltmeter to the ground screw and checked the - supplies of the opamps and did get voltage. I connected one probe to the - battery terminal and checked the + supplies of the opamps. I looked at the solder joints for any cold solder joints, but I can't see any. What should I do next?
thanks,
Pat

hagtech · « **Reply #1 on:** 5 Sep 2005, 03:23 am »

Turn the opamps around. Maybe. Sometimes they get installed backwards. Pin 1 should be towards output.

I am confused as to what testing you did. Easiest to reference all voltages to ground. Not sure why you chose a battery terminal (which could have been -9V).

It is also possible to hook up backwards in a system. Hey, I've done it. Re-check supplies and outputs referenced to ground. Let us know what you get.

jh

pmc999 · « **Reply #2 on:** 5 Sep 2005, 07:52 pm »

Hi,
I think I got the opamps in right, I have the u shaped notch on the opamp pointed toward the outputs.
I screwed up measuring the voltages I found out after downloading the OPA2134 spec sheet. I didn't get a +9v on pin8 because I was measuring pin 5 intsead, sorry.
Right now this is what I've got. If I only have 1 battery in, I have voltage on the outputs and I also get the voltage to the opamp pin. If I plug both batteries in, I get the -9v to pin 4, but I don't get +9v to pin8. It seems like with both batteries plugged in, the +9v never makes it to the opamp. Any ideas? Sorry to be such a pain.
thanks,
Pat

hagtech · « **Reply #3 on:** 6 Sep 2005, 01:09 am »

Did you mount the batteries in the stock sockets? Can you post a pic? I'm guessing that the positive supply battery has it's "-" terminal tied to the negative battery.

jh

pmc999 · « **Reply #4 on:** 8 Sep 2005, 12:56 am »

Hi,
I think that my not getting +9v had more to do with my multimeter than anything. I pitched my old meter and got a new one. I know have the right voltages on the power pins of the opamps and some dc offset at the outputs, but still no gain.
Looking through this forum, I saw another person saying they were shipped incorrectly labeled resistors. I went back and checked with a meter and r3,r5,r21, and r23 are 80k instead of 1.3k(the resistor codes are for 80K, the package was labeled wrong). I'm not sure if that is causing my problem, but I plan to get some 1.3k resistors and see if that helps. Hopefully my next post will be that it is running great.
thanks,
Pat

hagtech · « **Reply #5 on:** 8 Sep 2005, 03:21 am »

Wow, I hardly ever come across wrongly labeled resistors, but it does happen. If you want, I can send you the 1.3k resistors, so you don't have to place an order. Let me know by email.

How much dc offset? Should be less than 20mV, usually averaging 5mV.

jh

pmc999 · « **Reply #6 on:** 10 Sep 2005, 01:39 am »

Hi,
Thanks for the offer of sending me 1.3k resistors, that goes above and beyond and just proves all of the good things I've heard about you.

I'm impatient so I went to Radio Shack and picked up 330R and 1k carbon film resistors and put them in series for 1.3k. Thank goodness for the 5% tolerance, I could match them and got between 1305 and 1309. I may pickup 1.3k metal films in the future to replace them.

After replacing the resistors, I got sweet music coming out. The sound is good with no hum and that is with my junk turntable, I can't wait to try it in my main system. My DC offsets are 2v and 6v so I think I should be all set. Thanks for all of the help.
Pat