[sbelyo]

I have a question about insulating the opa541's and the LM338's. Do the opa541's have to be insulated from the heatsink itself? The same goes for the regulators.

Also if I use a heatsink pad is the white compound needed as well?

 

[Juergen]

Quote:

Originally Posted by sbelyo I have a question about insulating the opa541's and the LM338's. Do the opa541's have to be insulated from the heatsink itself? The same goes for the regulators. Also if I use a heatsink pad is the white compound needed as well?

Both need to be isolated from the heatsink. Thermal paste will help transfer the heat, just don't go crazy with it.

 

[amb]

Quote:

Originally Posted by sbelyo I have a question about insulating the opa541's and the LM338's. Do the opa541's have to be insulated from the heatsink itself? The same goes for the regulators.

Yes and yes.

Quote:

Also if I use a heatsink pad is the white compound needed as well?

If you use mica insulators, then yes. If you use something like the Bergquist SilPads, then no.

 

[sbelyo]

Thanks guys...
Quote:

Originally Posted by amb If you use mica insulators, then yes. If you use something like the Bergquist SilPads, then no.

I'll use the mica ones on the regulators and a pad on the op amps. I didn't see a mica insulator for the plastic power package.

What are some part #'s for mounting kits and pads for those op amps?

 

[amb]

Quote:

Originally Posted by sbelyo Thanks guys... I'll use the mica ones on the regulators and a pad on the op amps. I didn't see a mica insulator for the plastic power package. What are some part #'s for mounting kits and pads for those op amps?

I used Bergquist Silpads for the LM338T and the OPA541s. Digikey part numbers BER219-ND and BER107-ND. Both are slightly oversized and I trimmed them down with scissors.

For mounting the devices to the heatsink, you also need a nylon insulator collared washer and machine screw and nut. I used the washers from the TO-220 mounting kit from Radio Shack and socket cap screws and nuts from my bin, but it looks like you could also use parts from the Keystone TO-220 kit (Digikey 4724K-ND).

 

[sbelyo]

Quote:

Originally Posted by amb I used Bergquist Silpads for the LM338T and the OPA541s. Digikey part numbers BER219-ND and BER107-ND. Both are slightly oversized and I trimmed them down with scissors.

I'm going to use BER107-ND for the opa541's with the hardware from the Aavid mounting kits (mouser Part 532-4880SG). The aavid kit is a few cents cheaper and comes with a pad as well that doesn't need grease.


I'm going to work up an updated BOM today with this stuff in it.

 

[sbelyo]

Here's my BOM. It's missing the 10K pot that's on AMB's schematic. For those of you who have built this, is this right?

1eaXFMR - 100VA - 2 x 30VAC(RMS) @ 1.67A each3.4"D x 1.6"HAvel LindbergY236405Avel LindbergY236405

2eaIC - High Power Monolithic Op Amp11-pin Plastic PowerTI Burr-BrownOPA541APDigikeyOPA541AP-ND

2eaIC - 5A Adjustable RegulatorTO-220NationalLM338TDigikeyLM338T-ND

1eaIC - +5V Precision Voltage ReferenceDIP-8TI Burr-BrownREF02BPDigikeyREF02BP-ND

6eaCAP - Electrolytic, 4700uF, 63V, 105CD=25mm, L=50mmPanasonicECOS1JA472CA DigikeyP7485-ND

2eaSINK PAD - 11 Pin Plastic PowerBerquistDigikeyBER107-ND

8eaDIODE - Power Rectifier, Ultrafast, 600V 8ATO-220Mouser511-STTA806D

2eaDIODE - Silicon Rectifier0.500"Fairchild1N4004Mouser512-1N4004

2eaCONN - TERM BLOCK 3POS 5.08MM PCB5.08mmPhoenix Contact1729131Mouser651-1729131

1eaCONN - TERM BLOCK 4POS 5.08MM PCB5.08mmPhoenix Contact1729144Mouser651-1729144

8eaCAP - Monolithic Ceramic, 0.33uf, 50VAVXMouser581-SR215E334MAR

4eaCAP - Tantalum, 10uf, 50V, 10%, Radial0.150"KemetT350K106K050ASMouser80-T350K106K050

4eaCAP - Monolithic Ceramic, 0.1uf, 50V, Z5U0.150"AVXMouser581-SR155E104MAR

2eaRES - Thick Film Power, 0.20ohm, 30W, 1%TO-220CaddockMP930-0.2-1%Mouser684-MP930-0.2

2eaRES - Metal Film, 121ohm, 1/4W, 1%0.400"Vishay-DaleRN60D1210FB14Mouser71-RN60D-F-121

2eaRES - Metal Film, 3.57Kohm, 1/4W, 1%0.400"Vishay-DaleRN60D3571FB14Mouser71-RN60D-F-3.57K

1eaRES - Metal Film, 49.9Kohm, 1/4W, 1%0.400"Vishay-DaleRN60D4992FB14Mouser71-RN60D-F-49.9K

3eaRES - Metal Film, 10Kohm, 1/4W, 1%0.400"Vishay-DaleRN60D1002FB14Mouser71-RN60D-F-10K

4eaMounting Hardware w/Sink Pad - TO-220Aavid Thermaloy4880SGMouser532-4880SG

 

[amb]

I would recommend a 3.32K resistor instead of the 3.57K given that you're using 30Vx2 transformers. This makes for a more balanced amount of heat dissipation between the LM338T and the OPA541s.

 

[Juergen]

Quote:

Originally Posted by sbelyo Here's my BOM. It's missing the 10K pot that's on AMB's schematic. ..

I used a Bourns 10K trimmer (Mouser #652-3296W-1-103LF)

 

[amb]

Quote:

Originally Posted by Juergen I used a Bourns 10K trimmer (Mouser #652-3296W-1-103LF)

That trimmer on the PSU board is optional. It gives you a small range of adjustment of the output voltage, but I built my dynahi without it and the output was +/-29.8V. There is no reason why it needs to be perfectly +/-30V.

 

[sbelyo]

Quote:

Originally Posted by amb I would recommend a 3.32K resistor instead of the 3.57K given that you're using 30Vx2 transformers. This makes for a more balanced amount of heat dissipation between the LM338T and the OPA541s.

I will change that... Thanks. I just got the Xformer tonight. Avel Lindberg definitely makes nice stuf and it's cheap too!

I have enough to do the layout in the case and start putting together the heatsink arrangement togther this weekend. I scored this huge heatsink off of ebay for 18 bucks. If I cut it up I can make 2 PSU heatsinks and maybe 4 amp board heatsinks

Quote:

Originally Posted by amb There is no reason why it needs to be perfectly +/-30V.

Someone would lay awake at night and think about it for sure. Then you'd see a thread where someone says they can hear the difference of 0.01 volts

 

[flecom]

Quote:

Originally Posted by sbelyo I will change that... Thanks. I just got the Xformer tonight. Avel Lindberg definitely makes nice stuf and it's cheap too! I have enough to do the layout in the case and start putting together the heatsink arrangement togther this weekend. I scored this huge heatsink off of ebay for 18 bucks. If I cut it up I can make 2 PSU heatsinks and maybe 4 amp board heatsinks Someone would lay awake at night and think about it for sure. Then you'd see a thread where someone says they can hear the difference of 0.01 volts

I doubt it makes any difference, I run my dynahi with my own PSUs at +/- 24v and it sounds awesome (as good as other dynahi's I have listened to with real "dynahi" PSU's)

 

[sbelyo]

This PSU cost is adding up....

$50.00 to mouser after adding the pot and IEC inlet

$30.00 for Xformer

$80.00 to Digikey

with shipping and some of the heatsink cost it's close to $190

 

[flecom]

crazy, thats as much as I paid for all the parts for my dynamite lol

yay overkill eh?

 

[sbelyo]

We'll see how it turns out. I haven't made the BOM for the amp boards yet, but at least I only have to buy the components. I've got a case, heatsinks, and boards already.

My case was around $50.00 I think (I bought it over a year ago and never used it). I have some audionote rca jacks that are on a tube amp that never materialized. I have plenty of 1/4" jacks and led's. So I'm about half way there for about $240.00 I don't use a volume pot, I just use passive pre-amp with a blue velvet pot.

I'm going to layout the empty boards w/heatsinks in the case and mount the toroid and rear iec inlet. Also drill the holes for mounting the boards. So I'll have enough to do this weekend until the parts come next week.