ADA8000 power supply and heat

[AntonZ]

I know the sheer mentioning of the B brand can stir things up around here, with mixed and mostly strong emotions. Now I'm not depending on this for a living, nor does my rig get used in situations where other people's bread and butter depend on it. Also, I can currently not spend much on pre's of higher esteem. Perhaps I can afford an ADA8200 when they become available http://sactalk.com/images/smilies/icon_e_wink.gif . So, I'm not saying everyone should do as I do, nor do I want to start a B debate, but I'm stuck with mine. With that out of the way, here goes.

There are two ADA8000 in my little rig. A while ago one of them started giving occasional static ticks on the outputs. So I have that one on input duty only. It seems the likely cause for this is overheating of voltage regulators in the power supply. This weekend I popped the lid off and looked at ways to get rid of some heat. I am in the process of taking the voltage regulators (all 6 of them) off the main circuit board and mount them on the case sides. That seems to me like the best position to get the heat out of the case instead of from the regulators into other parts. No problem getting 3 on the far side, the others are more of a challenge. I believe I have now found room for all. Still working on it.

Two regulators were sitting very close to two capacitors that are hardly up to their task anyway without being overheated by nearby regulators. So now that I've got the circuit board out of the box, I have replaced these capacitors with new higher capacity, higher temp rated models (1000uF, 105°C).

If anyone is interested, I can make a few pictures before I put the lid back on. Fingers crossed I don't short circuit anything before that :D

[dbarrow]

It's a common problem. I have lost at least four units to that heat issue. I helped another band I work with solve that problem by powering the four ADA-8000 units in their rack with a Japanese step down transformer that lowers the voltage from 120 to 100. Those units run cooler and have lasted for several years. The ART TubeOpto-8 units run very hot, too. I had some of those go bad with the same symptoms. ART repired them for free. I currently use the Focusrite Optopre Dynamic units. They work great and run cool without issue.

[janneman]

hey anton

I'm interested in some pictures.

by the way, Alkmaar last saterday was a succes and great gig, you definity
missed something.

greetings
janneman

[TomyN]

Hi,

they only caps that fit in size I've found were panasonic 680uF.
Which 1000uF caps do you use?

Tomy

[Mattseymour]

I've seen a few mods where the caps are moved onto a separate board to deal with the size issue.

[TomyN]

Yes, I,ve seen such things, too.

If you move the regulators, make sure that you place caps near to their legs in order to avoid oscilation.

Tomy

[AntonZ]

The rack ears are aluminium, which is a good heat conductor. Also, they connect to the rack rails for further distribution of heat away from the inside of the units. Heat conducting grease on all. And insulation (!), since the mounting surface is not to be connected to ground on most of the regulators.

Regulators 7815 and 7915 on the left side rack ear.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS1.jpg

From the outside.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS2-1.jpg

The other side gets the LM317 regulator (which regulates phantom power)
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS5-1.jpg

Piece of aluminium prepared for mounting three 7805 regulators. These do not have heat sinks originally, run quite hot to the touch though.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS3.jpg

Mounted inside the case.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS4.jpg


Only one pair of 7815/7915 remains in place. These do not run very hot. After removal of the original 680uF caps I could add small heatsinks to these regulators, then install the 1000uF caps. No room for these caps with all regulators in place, after removal the fatter caps fit fine.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS6.jpg

Overview.
http://i295.photobucket.com/albums/mm124/antonz_bfm/SAC/ADA8K/ADA8K_PS7.jpg



If you move the regulators, make sure that you place caps near to their legs in order to avoid oscilation.
Thanks for bringing that up Tomy. I forgot about that. I should have installed small caps near the regulators indeed, shame on me. I believe those can be smaller values. Would you happen to know what values I should have put there?

[AntonZ]

by the way, Alkmaar last saterday was a succes and great gig, you definity
missed something.

I'm sorry that I couldn't be there Jan, I was at a party in Utrecht - dear friends celebrating their birthdays and wedding anniversary, would not miss that either. I hope to be at the Parkhof gig again next year. Do get in touch whenever you have other work in the area!

[Phil]

It's a common problem. I have lost at least four units to that heat issue. I helped another band I work with solve that problem by powering the four ADA-8000 units in their rack with a Japanese step down transformer that lowers the voltage from 120 to 100. Those units run cooler and have lasted for several years. The ART TubeOpto-8 units run very hot, too. I had some of those go bad with the same symptoms. ART repired them for free. I currently use the Focusrite Optopre Dynamic units. They work great and run cool without issue.

I have 8 ada8000 units on the stepdown transformers (4 per) since dec 2009. They are also spaced a bit. 3 units per 4u. No issues.

[TomyN]

From an old datasheet of the LM7815:

"Cin is needed if regulator is located an appreciable distance from power supply filter"

Cin is a 0u33 (330nF) cap.

Tomy

[cgrafx]

I know you've now gone through the trouble of modifying your ADA's, but you might want to consider an alternative that will actually accomplish more than what you have done with the internal mod. As your mod helps dissipate heat, but does nothing to correct for the added stress on the voltage regulators caused by too high a primary voltage.

Drop the external voltage to the unit as suggested with a step-down transformer. Dropping the mains voltage will significantly reduce the heat generated by the regulators and can be used with any stock ADA8000.

if you want to, build your own step down system as I did into a furman power strip and you get all the benefits without having to mod your ADA's.

see the instructions here.

http://www.sawstudiouser.com/forums/showpost.php?p=133266&postcount=1

[AntonZ]

Thanks for the suggestion Phillip. I'm in Europe, we have different line voltages here (240V 50Hz) and hence different transformers in the ADA's. It seems the stress on the regulators is a bit less in our models. I'm not sure a step down transformer would help over here.

[Mattseymour]

The regulators still get a higher voltage than they need over here. The big issue with the us voltage models is a more stressed transformer that can saturate in some circumstances. Reducing the input voltage will reduce the amount of heat generated by the regulators. Which is fine until you have a voltage sag and then there isn't enough for the regulators to regulate and it dies. The main reason the Psu has this problem is the range of voltage government (in our case the eu) require an appliance to work with.