Heatsink for 8-DIP Opamp

[arupg]

Can someone help me find a heatsink for clipping on the 8-DIP opamp that I've biased to Class-A and now needs a suitable heatsink.

Thanks!

 

[Conrad Hoffman]

Thermalloy, now Aavid, used to have clip-ons for the longer DIPs, not sure about 8-pin though. They also had little finned extrusions the size of the top of the chip, that you'd just epoxy on. If I need to heat sink an IC, I just cut out a small piece of aluminum, bend it into a U shape, and epoxy it on. If there's space around the chip, sometimes just a simple flat plate will do the trick.

 

[hihopes]

I got some stick-on ones from Avnet (who seem to have offices all over the world, though some with slightly different names). They are actually for longer ic's - 14 pin, I think, but I just cut them in half and they fit an 8 pin dip beautifully.

 

[KP11520]

Hi arupg,

Was this done on an Amp, Preamp or CD Player?
Can you share the details of what op amp(s) and the method you used to bias the op amp(s). Any test measurements that you used and what impact on the difference of what you heard would also be interesting!

Thank you!

Regards//keith

 

[jacco vermeulen]

dip-8 is too small for a clip-on.
Fischer ICK-L is an adhesive type, used with thermal conducting tape.

 

[arupg]

Hi Conrad Hoffman & hihopes:

Thanks for the lead. Much appreciated!!

--------------------------

Hi Keith:

My Opamp that I biased into Class-A operation is in a Digital-to-Analog Processor; Audio Alchemy Dac-in-the-box (DITB).
Please read my post
http://www.diyaudio.com/forums/showthread.php?s=&threadid=106394

Most of your answers are there.

Cheers!

------------------
Arup

 

[arupg]

I did manage to locate the perfect item that I was looking for. Its a 8-DIP clip-on.

Please see this link:

http://www.aavidthermalloy.com/cgi-bin/stdisp.pl?Pnum=580100b00000g

Now, where do I find this??

 

[jacco vermeulen]

30 C/W, WOW !
I'd like me some of those too.
Mouser says non-stocked, 3000 number orders.

 

[peranders]

Can someone help me find a heatsink for clipping on the 8-DIP opamp that I've biased to Class-A and now needs a suitable heatsink.

Thanks!

Just wondering, but how much have you bias the opamp really? Do you know how to calculate minimum required current? Give me this data:

Supply voltage
Load
Max output voltage for REAL signals

 

[theAnonymous1]

They are available in single units at Arrow Electronics.....

http://www.arrownac.com/aws/pg_webc...neda=&start_index=0&search_type=click_through

There is a $10 international order fee on top of the normal shipping fees. If you two twist my arm enough maybe I will put in an order for some and ship them to you myself.

 

[arupg]

peranders:

The opamp in my circuit is in a digital-to-analog converter, the Audio Alchemy Dac-in-the-box (DITB).

The opamp is just before the final RCA outputs, so in essence, it behaves as a simple buffer for 2-ch since the AD 1860 dac chips does everything else.

Supply is +/- 12V via regulators for Analog Supply.

http://server3.uploadit.org/files/audioengr-Dac_1.jpg

http://server2.uploadit.org/files/audioengr-Dac_2.jpg

-------------------------

I used 18k resistors between Pins 4 & 7; Pins 4 & 1. Felt the sound was really lush but somewhat the highs & extreme highs were attenuated. Next was 22k resistors. Thats what I'm using now. They are 5% Tol purely for Trial.

Can you give any advice??

Thanks in advance!

---------------
Arup

 

[KP11520]

Hi arupg and P-A,

I saw that thread from carlosfm and decided to try the JFET Cascode for the new OPA627APs in my CD Player's analog output stage. I am about to solder it in and give it a listen. I have a thread going if you are interested in this approach rather than the resistor approach.

http://www.diyaudio.com/forums/showthread.php?threadid=106147&highlight=

Maybe you (arupg) can adapt this to your situation. I don't know how to measure the bias of the op amp before and after installing the little circuit I diagrammed there, but from some of the stuff I read, this is supposed to be the best way. I am not sure if this method can help lower the heat generated from the op amp.

P-A, I saw some threads where you and "ppl" have discussed this. I was hoping to get all of your opinions.

Thanks!

Regards//Keith

 

[arupg]

Thanks Keith for the suggestions. I did follow your Thread and am investigating on the possibility.

 

[peranders]

I used 18k resistors between Pins 4 & 7; Pins 4 & 1. Felt the sound was really lush but somewhat the highs & extreme highs were attenuated. Next was 22k resistors. Thats what I'm using now. They are 5% Tol purely for Trial.

That was a small class A bias I'd must say. Have you analyzed how much you ought to have? does the opamp really get hot of this?

 

[arupg]

I've just got hold of 2k resistors, i.e. 12v / 2000R = 6mA per ch of bias on the opamp. Will be inserting them very soon and will report if the chip get hot. By the way, I live in India where its a reasonably good summer going with average ambient room temp of 32-35 deg C. This itself could have an addt effect on the opamp's temp rising.

 

[arupg]

peranders:

What value resistors or how much mA bias current will you recommend me for the OPA2107 DiFET Opamp (dual)?

 

[KP11520]

arupg,

I believe this might be the formula that applies to this. The credit for this goes to "matjans" in carlosfm's thread "The OPA627 really sings". This is his quote:

basic stuff: v=i*r thus r = v/i

choose a bias current (say 7,5mA or 0,0075A) and fill in the formula:
r=12/0,0075 = 1600 or 1.6k ohms.

do check the datasheets for the different opamps for current capability, some opamps (like nicke said about the ad823) can't deliver too much.

I hope this helps and the JFET Cascode is still being explored!

Regards//Keith

 

[arupg]

Thanks for the suggestion. I did read the thread whereby you in your Rotel CDP went in for the 627s.

I reckon I need to measure the voltage across the pins to get a true picture of the supply conditions. Then apply the formula and choose the right value.

There's only 1 point here:

The 627 datasheet says Output Current +/- 45mA. Short Circuit Current is +/- 70mA.
I am using the 2107 whose datasheet says doesnt give the Output Current but Short Circuit Current is specified at +/- 40mA.

My load resistor is 100ohms. So I was playing safe by being conservative at 5.5 to 6mA of bias.

Do you think I can push this to 7.5mA?

 

[KP11520]

Honestly,

I am new at much of this and I am only a Parrot. Maybe P-A can answer this or maybe email "matjans" and ask!

Also, as Chris (Anatech) has suggested, read some of Walt Jung's writings about this.
I am just like you, trying to learn so much at the same time! It is overwhelming sometimes!

Regards//Keith

 

[arupg]

Thanks Keith. I am actually trying to find a way to reach/email CarlosFM. Hope someone can shed a light as to how I can manage that.

Still waiting for P-A to respond.