gar2520 build thread

[gar381]

Whoops..

The .25-watt ones will be fine for normal audio and will be fine for your testing.  I use the .5-watt guys because the .25-watt guys get a bit warm with the testing abuse I put the assembled gar2520s thru.

GARY

 

[Whoops]

Thanks Gary,
so I will leave the 0,25watts resistor

 

[Whoops]

Hi Gary,
I replaced the Diodes also, but unfortunately the Opamp is still not working.

There's no sound coming from the Mic Pre when I insert this Opamp.

I've replaced Bd140 , Bd139, the 5r6 resistors , Diode 1A and 1B.
(first time I tried it some weeks ago BD140, BD139 and r11 burned)

I took some pictures so you can see the unit,
please have a look at them if you have any time, maybe the solution is simpler than it looks.

There's any tests I could perform?
I have a DMM, a signal probe and I can have access to an Oscilloscope and signal generator.


http://twin-x.com/groupdiy/albums/userpics/10%7E2.jpg

http://twin-x.com/groupdiy/albums/userpics/8%7E3.jpg

http://twin-x.com/groupdiy/albums/userpics/5%7E4.jpg

http://twin-x.com/groupdiy/albums/userpics/7%7E4.jpg


Thanks a lot for your help

 

[SIXTYNINER]

bump

 

[emrr]

One of my friends saw a clear 990 for the first time, way back when. He stared at it for some time, shortly after smoking a big joint. Finally, he turned it upside down and right side up, then said "It would be great if it snowed inside".

John Hardy

F$&% yeah; damn right!

Let's roll out these snow-globe DOA's, you freakin' wizards!!!  NOW!!!!!

 

[d1pakula]

excellent thread.

I purchased a couple of these opamps and put the first one together in about an hour.  Great instructions!

However, I put into my poor man's 312 clone made with perfboard and the txfs that Jeff sells.  It's ment to be a two channel pre.  The first DOA offers mostly noise and oscillation. If I crank the gain, I can hear my voice over the top of the noise, but it's very distorted.  I tried all sorts of things to figure out what was going on and couldn't find the source of the noise.  Then I built the other OA, and it is super clean and quiet, at least until getting my 25K pot up about 3/4 of the way.  At higher gain there's some noise.  I take from this that the first opamp build is messed up somewhere.  I don't even know where to begin to look.  I have a small DMM, no o-scope.  I've checked for solder bridges under magnification, checked each solder joint and went over a couple that were questionable, but still no love from the first one.  The second one I'll check the dual diode (as recommended in an earlier posting).  If any one has other suggestions to diagnose the problem, I'd appreciate the help.

THX

Dave

 

[Stagefright13]

I had no problems assembling a few of these with the typical magnifying light...

Honestly if I failed on one somehow I would just build another. They are tiny. And very easy to bridge a joint etc.

Depends on what your time is worth to fix one. But I would fix one if I could. Like in my spare time... I would just make more.
They sound great! If ya made a beat one just buy a couple more.

Besides the transformers you decide on, the DOA gives it life and sound.  These DOA's sound great!!

They work great in a API circuit. And also in the real deal such as my outdated 512b's.

John

 

[d1pakula]

Thanks, John, for your post.  I've considered starting another, but I'd like to see if this one is salvageable.  If anyone has ideas, I'd welcome them.  Otherwise, I may order another kit from Jeff and see how it goes.....

D

 

[gar381]

Hi d1pakula
Check post:  http://www.groupdiy.com/index.php?topic=33970.msg425092#msg425092
This may help a bit.

As John (Stagefright13) says use a magnifying light for both assembly
and checking your work.  My old eyes are so blind I couldn't build
a gar without one. :-[

Most problems are solder bridges on the bottom side
or componet leads touching each other on the componet side.

Best of luck D and enjoy your gars

GARY

 

[d1pakula]

Thanks, Gary.

I've done that and will try it again.  I'm not sure how to determine if I've fried a transistor or a diode, though, by excessive heat from the iron.  My assumption is that, if going over the board with my magnifying glass for bridges, leads touching that shouldn't, etc., I've burned a transistor or diode and I won't know how to discover that.  Can you advise?

Thank you.

Dave

 

[mitsos]

It's doubtful that you fried a transistor with your iron.  You would have lifted the solder pads at that point. Speaking of which, since you seem unsure of your solder "technique" I'll just mention that you may have a lifted pad not visible under a blob of solder.  Might be interesting to check continuity between any doubtful solder joints and the next ones over.

Check the link below to see how to test diodes and transistors with a simple ohm meter. Most digital meters have a specific diode test position which may be better to use. 

Check to make sure you have your diodes in the right way around, and make sure you have PNPs where PNPs go and NPNs where NPNs go. Take some good clean macro shots of the solder side, many times it's easier to check for shorts than with a magnifying glass.

http://www.electronics-radio.com/articles/test-methods/meters/multimeter-diode-transistor-test.php

 

[d1pakula]

Mitsos:

great link.  Thank you.  I've gone over and over this one DOA.  The second one is now working really well.  I can't figure out the first.  I'll try the diode/transistor testing, but I'm on the verge of just ordering another, assembling and hoping for a better outcome.

 

[Jarno]

Not a snow-globe, but I did a snap-on cover for these preamps in the 3d CAD program I use at work.
I think I'll order a few at Shapeways (online rapid prototyping), to see if they fit. Not dirt cheap, but it does add robustness.

I made ventilation holes where the output pair is located, and a recess to mount a label. Maybe I'll make wallthicknesses a bit thinner, as the price at shapeways is based on volume, the design looks sturdy enough.

Opinions?

 

[Jarno]

Soldered one of the kits I bought from Jeff, and also did a 325 board with onboard power to test it. It works fine, superb!
I do see some nastiness on the scope, but right now I have no OT mounted on the 325 board, just put in some resistors. Also, the thing is mounted on a piece of board, so no shielding or anything.
But squarewaves have a serious slant to them, and I see some HF "grass" on the curves. Maybe put a bigger cap in the feedback loop. There's no cap across the inputs, probably should mount that as well.

Assembling the kit was a breeze, but I'm glad I bought a kit, the choice of components is critical it seems (basically that's just the caps, there's not that much variation in resistors, diodes and transistors).

 

[Rybow]

Just built my first one. Went together nicely, and the build docs were a huge help! Everything looks good to me, but I won't know until I get my transformers and power up my 312 for the first time. Thanks for the project Gary! I am looking forward to powering this bad boy up.

 

[funkmuffin]

Gary -- don't know if you're still monitoring this thread, but I have a question.

Do you have any specs on how much current the the GAR2520s draw under load?  I'm building a 24 channel API-style mixer that has one 2520 per channel, plus 4 in one of Jeff's 2ACABOs.  I'm working on specs for a power supply, and it's easy enough to get a +/-16V supply together, but I need to make sure I'll have enough current for 28 2520s at load.

Any help you can offer?

Thanks!
Ryan 

 

[jsteiger]

Hey Ryan,

From tests with my preamps driving a 600 ohm load, the module draws approximately 51mA. You probably won't see that but I suppose it depends on your surrounding circuit.

Cheers, Jeff

 

[gar381]

Hi Ryan

Jeff's finding on draw is in the ballpark of what I've measured.

If I were designing a PSU for this project I would over design it a bit.
I probably would use an avellindburg Y236402
transformer. http://www.avellindberg.com/transformers/y23_range_specs.htm
and a pair of 338K TO3 case regulators.  You could get away with LM317K/LM337K
(also TO3 case regs) but they will run warmer than the 338Ks. 
Use some good size heat sinks at any rate and your PSU should run just fine.

Have fun !!

GARY

 

[ilfungo]

Hello Gary
I built 2 x API 312 (Bob PCB) with GAR2520
I have noise problems on both
I think my problem is on GAR2520
How can I test Them?
There are reference Voltages?
help!
thanks

 

[helterbelter]

I have build 2 of Gar's 2520. Excellent, and easy to do if you follow the build instructions. Both were working the first time I powered them up. Nice !


Ilfungo :
Both the same amount of noise ?!? Have you checked the wiring ? maybe you have done something wrong to both 312 boards. Maybe a groundjumper missing or something like that ? (I haven't built Bob's 312, so I don't know the details).

Anyway, I don't think the problem will be caused by the DOA.