gar2520 build thread

[kante1603]

Please read this thread…..?

 

[Spino]

My first try at this build is not working
I've went through component checking (except the 2 innermost capacitors, I can't read those, everything else looks fine), retouched all the solder joints, went through visual and multimeter check for possible  shorts.

I noticed that Q9 gets really warm (not at all Q7 and Q8)

The preamp (I'm using the opamp in a VP26) passes a barely little HF. Another clue is that it emits loud noises when toggling polarity or pad.

Another thing that I discovered is that when I turn off the preamplifier,  it starts working while the remaining tension ramps down.

I'll be checking everything over some more, but if anybody has a better clue on where I could double check it would be great help.

Thanks!

 

[salomonander]

can anyone tell me what input impedance these are? cheers

 

[jsteiger]

can anyone tell me what input impedance these are? cheers

Greater than 10MΩ.

 

[gar381]

I built my first gar2520 and it did not work. So I built 2 more and these are not working either. I dont even know where to begin to try and trouble shoot . I have a magnifing Lamp and can see pretty well that there are no shorts/Bridges. all that I can think of is maybe I got a component to hot ? I have been soldering for years, not on things quite so small but it didn't seem like I got anything to hot. Anyway any suggestions on where to begin on trouble shooting would be helpful.

Thanks much,
Thomas Thew

Thomas..
Chances are you made the same error on all your builds
If nothing is getting hot,  2 things to check....

Make shure the the voltages are correct at the DOA socket
with the DOA removed.

Check for solder bridges on the input pins of the DOA.
(This is the number one cause of no output with nothing
getting hot.)


Spino..
Nothing  specific  that I can think of off hand that would cause your
problems. 

Both of you guys..
Read thru this thread as there are lots of trouble shoot tips here.

In general Check...

Parts are in the right holes especially that the correct transistors
are in the correct places

Transistors are turned the correct way

Diodes are in the correct holes and Black band on the diode
goes to the circle on the PCB

No solder bridges on solder side of PCB

No component leads touching each other on the top of the PCB

Best of luck guys

GARY

 

[Golgoth]

Hi!

A dirty 2520's habit made me twist'n'solder two 4148 together before I realize I'm working on a v4 pcb.  :
Can I solder between 1a and 1b with my diode's pair? I believe I have to solder from the 1a square to the 1b circle right?

Thanks a lot!
G

 

[gar381]

band to D1A circle  other end to D1B square

GARY

 

[geardude]

Hey fellow capi enthusiasts! I'm currently having an issue with my Gar2520's- they are humming upon output with no other mic signal getting through. I've started a thread and checked for bad bridges & joints but no luck. Here's a link to my thread with more specifics. Thanks and I appreciate anyone's help and feedback! This isn't my first rodeo so to speak as I've built a handful of these before, but this is indeed my first hiccup!

http://groupdiy.com/index.php?topic=63058.0

 

[Whoops]

Hey fellow capi enthusiasts! I'm currently having an issue with my Gar2520's- they are humming upon output with no other mic signal getting through. I've started a thread and checked for bad bridges & joints but no luck. Here's a link to my thread with more specifics. Thanks and I appreciate anyone's help and feedback! This isn't my first rodeo so to speak as I've built a handful of these before, but this is indeed my first hiccup!

http://groupdiy.com/index.php?topic=63058.0

I replied in your thread,
I solved my issues by soldering each component to bottom and also the Top of the pcb.

 

[geardude]

Thanks whoops! Appreciate the input unfortunately after hours of going over them and doing touch ups.... no luck.

 

[kevinkace]

Finished building 2 GAR2520s, second one went perfect and sounds normal (haven't done thorough testing).

But the first... Initially I had Q7 and Q8 swapped (BD13916, BD14016), which I then corrected. It now works, but there is distortion. Could those transistors have been damaged?

 

[Allecstatic]

I accidentally swapped q7 and q8 in one of my gar2520s. It caused the r11 and r12 resistors to brown.

I read this forum and did what was suggested when this happens - I replaced the r11 and r12 resistors and put the q7 and q8 transistors in their proper places. The resistors continue to burn.

What is likely the case? When the q7 and q8 were swapped was damage done to the transistors or maybe a capacitor or diode?

The unit is still passing audio.

Any help is grately appreciated

 

[gar381]

At this point I would try NEW pair of outputs (Q7,Q8) and R11,R12.

Double check... Make Shure they are in the right holes and facing
the right direction as shown in the assembly manual.

Make Shure there are NO shorts between R11 and the 2 Millmax pins
next to R11s pads on the foil side of the PCB.

Best of luck 

GARY

 

[Allecstatic]

At this point I would try NEW pair of outputs (Q7,Q8) and R11,R12.

Double check... Make Shure they are in the right holes and facing
the right direction as shown in the assembly manual.

Make Shure there are NO shorts between R11 and the 2 Millmax pins
next to R11s pads on the foil side of the PCB.

Best of luck 

GARY

Thanks, Gary!  I'll give that a shot!  Are the output transistors and the r11/r12 resistors the last components in the circuit on the 2520? Just wondering if there is anything else down the stream that could have been damaged that I should just replace to be safe. Thanks again for your time. These opamp builds have been a treat!

 

[gar381]

Thanks, Gary!  I'll give that a shot!  Are the output transistors and the r11/r12 resistors the last components in the circuit on the 2520? Just wondering if there is anything else down the stream that could have been damaged that I should just replace to be safe. Thanks again for your time. These opamp builds have been a treat!

Thats correct R11 and R12 are the output emitter resistors and
their junction feeds the output Millmax pin. 
Do double check .... No shorts between R11 and the 2 close
Millmax pins.

GARY

 

[Allecstatic]

Thats correct R11 and R12 are the output emitter resistors and
their junction feeds the output Millmax pin. 
Do double check .... No shorts between R11 and the 2 close
Millmax pins.

GARY

I will double check. Much appreciated!

 

[Allecstatic]

Thats correct R11 and R12 are the output emitter resistors and
their junction feeds the output Millmax pin. 
Do double check .... No shorts between R11 and the 2 close
Millmax pins.

GARY

I double checked that there were no shorts, including between r11 and the millmax pins. I have also replaced the q7 and q8 transistors as well as the r11 and r12 resistors. The r11 and r12 resistors still burn up quickly even though it passes audio during that time. Is it possible that one of the components provided in the kit is a dud? Not sure what else to do at this point.

 

[gar381]

Most unlikely that there was a bad part shipped in the Kit.  There has to be a part in the
wrong position or a solder bridge somewhere.  Check the diode string to make sure
they are in the correct holes and polarized correctly also make sure one of them is not
shorted from your original bad reverse of Q7&Q8.  Make sure all the TO92 case
transistors are in the right holes and facing the correct way.  Make sure all the resistors
are in the correct holes.  Make sure none of the component leads on the top are touching.
Make sure that there are no solder bridges.  Check out all of these thing with a magnifying light.
Are you feeding the DOA with the correct voltages and polarity ?
If all else fails,  get a new kit and start over.

Best of luck

GARY

 

[Allecstatic]

Most unlikely that there was a bad part shipped in the Kit.  There has to be a part in the
wrong position or a solder bridge somewhere.  Check the diode string to make sure
they are in the correct holes and polarized correctly also make sure one of them is not
shorted from your original bad reverse of Q7&Q8.  Make sure all the TO92 case
transistors are in the right holes and facing the correct way.  Make sure all the resistors
are in the correct holes.  Make sure none of the component leads on the top are touching.
Make sure that there are no solder bridges.  Check out all of these thing with a magnifying light.
Are you feeding the DOA with the correct voltages and polarity ?
If all else fails,  get a new kit and start over.

Best of luck

GARY

Hey Gary,

Thanks for getting back to me. There are no solder bridges, the diodes and transistors are in the correct positions as well as facing the right way. The resistors are in the right positions and no leads on the underside, nor on the top side, are touching.

I didn't know the diodes could have been damaged when the q7 and q8 were reversed as they come before those components (clearly I do not know enough).  I thought I asked it above as well.

I am running the DOA in a CAPI pre that is working with other DOA, housed in an API lunchbox. So I do not think voltage or polarity is the issue.

I will either replace it or replace the diodes, q7 and q8 transistors, as well as the output resistors (r11 and r12).

Thanks again, Gary!

 

[Allecstatic]

Would the following work as substitutes:

For BD13916
BD139g
bd139-16
2SD669

For BD14016
BD140
BD140g
BD140s
2SB649

Also, when I test the q7 and q8 transistors in the gar2520s circuit that are working I connect the prongs of a multimeter to the base and emitter and get a reading of about 650. When i connect the prongs to the base and collector I get a reading of about double. Also, when I connect the prongs to the emitter and collector I get a reading of 650, but when I switch the prongs on the emitter and collector there is no reading. Is this what should be happening?