gar2520 build thread

[technoteo]

Hallo everybody, I need some help

Yesterday one of my CAPI 312 almost went on fire!!!  :'( :'( I had 2 VP28 in the first slots, two 312 and a LC53 in the fifth slot. I had this pres up and running since march, so three months of great work. Suddenly, after one hour of work smoke start getting out one of the 312...as you can see in the pictures the GAR 2520 is gone  ........ the output transformer was really hot. I checked if something else was black or broken, but I can't see anything damaged or hot on the main board.

The 312 was cabled in a patch bay but I wasn't using it, I was using the VP28s and everything was ok. I turned off the PSU, get the damaged module out and then tested all the other ones. Everything was working as usual. The fuse on the PSU didn't blow. My question is : what the hell happened since I used it for three months and didn't move or changed anything?
Can anyone suggest me what to check before puttin' in another 2520 ? The modules is 24V version in a 51x rack+psu .

here are the other pictures:
http://s827.photobucket.com/user/technoteo/library/Gar2520%20Blown

Thanks

 

[gar381]

Hallo everybody, I need some help


.Can anyone suggest me what to check before puttin' in another 2520 ? The modules is 24V version in a 51x rack+psu .

here are the other pictures:
http://s827.photobucket.com/user/technoteo/library/Gar2520%20Blown

Thanks

Was the gar2520 running from the 24v rails?? ???

GARY

 

[technoteo]

Hi Gary, thanks for the reply
Yes it was running from the 24v rail. It worked well for three months..

 

[jstark]

It worked well for three months..

...until it didn't.

That doa is only rated for 20V rails.

http://classicapi.com/catalog/product_info.php?cPath=71_72&products_id=136



David

 

[technoteo]

Mmmmmm  ???
Yes jstark you 're right !
But What was I supposed to use since all the doa on the capi site are 20v max ?

 

[gar381]

Hi Gary, thanks for the reply
Yes it was running from the 24v rail. It worked well for three months..

Wow ! I am amazed it lasted that long.

While they will run fine up to 20v
If you run them at max 18v it will run a lot cooler than 20v
with only a fraction of a db less headroom. 

They hardly get warm at vpr spec 16v ... Recommended!!

Best

GARY

 

[technoteo]

Wow ! I am amazed it lasted that long.

While they will run fine up to 20v
If you run them at max 18v it will run a lot cooler than 20v
with only a fraction of a db less headroom. 

They hardly get warm at vpr spec 16v ... Recommended!!

Best

GARY

huh 
thanks gary ....
I must be lucky since the other one is still running... I will switch it to 16V

but ....  ???
I'm still wondering what should I use in the 24V version of CAPI 312...the Scott lieber's DOA?
sorry but I totally missed this information

 

[gar381]

but ....  ???
I'm still wondering what should I use in the 24V version of CAPI 312...the Scott lieber's DOA?
sorry but I totally missed this information

Just run them at 16v!!! Don't worry about 24v.
But if you must use 24v do a search for 24v DOA.  Hairball makes a nice 990c kit.
There are lots of others out there and most will work in Jeff's 312 just fine.
They all have different colors/flavors of sound.

Best.

GARY

 

[technoteo]

Thanks Gary for the info
I will switch them to 16v and.....order another gar2520 
Best
Teo

 

[Category 5]

GAR381, I though I read somewhere that matching q1 and q2 foe hfe on a small multimeter was good enough, right?  Why do we have to match for vbe on some devices but hfe is good enough here?  Also, anyone have any recommendation for a ready made vbe tester (or at least a decent PCB for it).  I can't find the ptp one I did and making a new one doesn't seem very fun.

I do have a meter that will measure hfe though.

 

[gabygab]

Hello,

So I destroyed C5, 10pf 50V, while I was unsoldering it. One of the leads fell out.  :-[

I was wondering if I could replace it with a capacitor from my local electronics shop

http://www.abra-electronics.com/products/CD1R0-Ceramic-Disc-Capacitor-1pf-50V.html


Should still work right?

Thanks for helping out a noob.

 

[gar381]

you need a 10pf not a 1pf cap. 

gaby.. look for a 10pf  5%  cog.

.1"(2.5mm) LS

GARY

 

[Category 5]

Gary,  any opinion on the differences between bc550s?  I had a bunch from when I got Baumans 2520s and they all test about 550-560.  They are tape reel variety and have the Fairchild F stamped on them.  The newer ones I got aren't a stamped with the F, they are loose not taped and all test well above 600.

Any ill effect of combining the two variants?  Will higher hfe give me higher gain? Lastly does rail voltage affect gain or just headroom?

 

[gar381]

Cat5..

To my ears.. (lots of experimenting and listening over the years)

No difference  between 500 and 800.  No difference between tape and bulk.
Rail Voltage effects headroom but be careful...  raising the voltage creates more
heat than headroom. ( Note Technoteo's pics above )

I use Fairchild BC550Cs  because of consistency and quality. (only use Cs)
I have found that sealed bags of 1000 transistors have over 90% that vary only  +/- 15 hfe
Mixing brands should not be a problem but have a close listen
to the finale product.

Hope this helps.

GARY

 

[Category 5]

Thanks Gary.  All of mine are Fairchild but the bagged ones are easier to fit than the taped.  Problem is I matched about 25 pairs of the taped ones perfectly (exact match) so even though they are older and test in the 500s I still want to use them rather than re-match.  Of course for the others I want to use the newer ones since they are easier to fit into the boards cleanly.

I have to say that these are probably the best sounding op-amps I have tried aside from my original Melville era 2520s.  Dare I say they are sweeter than the brand new API 2520s I have in my collection.  They seem to really like being run little into the red.  +/- 16V is no problem for me since the headroom is mostly wasted going into AD converters anyway.  Been testing them at +/1 18V too though, and they barely get warm to the touch.  Luckily, most of the parts I bought for Bauman's boards 10 years ago are still on the BOM.  Thanks for a great project!

BTW - I found that if you stagger the height of the resistors butted against each other you can get a cleaner fit on the whole board.  The fat ends fit into the center area of the adjacent resistor.

 

[gabygab]

Hi! Just wanted to thank every one in this thread. It was a lot of help! I got all my opamps working!

 

[belman2003]

Hey guys,

First post here 

I have recently assembled two CAPI VP26's but i am having trouble with one of the opamps. I have switched the opamps over and the problem followed to the other unit. My BAE power supply is switching to safety mode and not lighting the green light (which i am lead to believe is the positive indicator) I have visually inspected very thoroughly and cannot see any difference between the working one and the non working one.

Any ideas? Or am i just missing something very obvious in these photos?

Cheers.

 

[belman2003]

For above post

 

[belman2003]

and from the top

 

[gar381]

Hi belman

I don't see any unwanted solder  bridges on the bottom.
It's hard to tell for shure  in your pic but lots of joints
look suspect.  Try reflowing all your joints.

Best of luck..

GARY