Go Back   Home > Forums > >

Pass Labs This forum is dedicated to Pass Labs discussion.

Amp Camp Pre+Headphone Amp - ACP+
Amp Camp Pre+Headphone Amp - ACP+
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools
Old Yesterday, 02:14 PM   #1621
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Amp Camp Pre+Headphone Amp - ACP+
Personally, I treat it as a matter of "mandatory good hygiene" to always, always include an electrical insulator between a power transistor and its heatsink. Mica+goop, or Keratherm, or SilPad: every time. I always do this, always always, even when the heatsink is electrically floating. Even when the heatsink is electrically connected to the same circuit node as the mounting tab of the transistor.

Why? Because I have met future-me and discovered he is forgetful. He cannot be relied upon to remember whether an insulator is required, or not. This is dangerous when repairing or modifying gear 6 months later (or 6 years later!). Future-me cannot be relied upon to remember WHY an insulator is or isn't required, leading to incorrect conclusions, leading to spectacular explosions after repair.

So I prevent future-me from screwing up, by always including an insulator on every power transistor. Always, always. Zero decisions need to be made, giving zero opportunities for mistakes.

This policy has accidentally resulted in significant cost savings too. When buying insulators and mounting hardware, it turns out there are TREMENDOUS savings to be had by purchasing in bulk. Many eBay sellers are happy to sell you a thousand pieces of TO-220 shoulder washers / mount bushings, for USD 5.00 per thousand. (They cost $0.45 at Mouser in qty=1). DigiKey's price for a hundred TO-220 insulating SilPads is quite low, have a look. And a tube of Aavid Thermalcote (or a jar of Wakefield Thermal Compound) is quite affordable.
  Reply With Quote
Old Yesterday, 02:18 PM   #1622
Chris In Milwaukee is offline Chris In Milwaukee  United States
Cheese Runner
diyAudio Member
 
Join Date: Dec 2020
Location: Milwaukee, WI
Amp Camp Pre+Headphone Amp - ACP+
Great advice.

Quote:
Originally Posted by Mark Johnson View Post
Personally, I treat it as a matter of "mandatory good hygiene" to always, always include an electrical insulator between a power transistor and its heatsink. Mica+goop, or Keratherm, or SilPad: every time. I always do this, always always, even when the heatsink is electrically floating. Even when the heatsink is electrically connected to the same circuit node as the mounting tab of the transistor.

Why? Because I have met future-me and discovered he is forgetful. He cannot be relied upon to remember whether an insulator is required, or not. This is dangerous when repairing or modifying gear 6 months later (or 6 years later!). Future-me cannot be relied upon to remember WHY an insulator is or isn't required, leading to incorrect conclusions, leading to spectacular explosions after repair.

So I prevent future-me from screwing up, by always including an insulator on every power transistor. Always, always. Zero decisions need to be made, giving zero opportunities for mistakes.

This policy has accidentally resulted in significant cost savings too. When buying insulators and mounting hardware, it turns out there are TREMENDOUS savings to be had by purchasing in bulk. Many eBay sellers are happy to sell you a thousand pieces of TO-220 shoulder washers / mount bushings, for USD 5.00 per thousand. (They cost $0.45 at Mouser in qty=1). DigiKey's price for a hundred TO-220 insulating SilPads is quite low, have a look. And a tube of Aavid Thermalcote (or a jar of Wakefield Thermal Compound) is quite affordable.
__________________
~Chris In Milwaukee
Aleph J | Muses v2 Volume Control | Aleph P v1.7 | WHAMMY
  Reply With Quote
Old Yesterday, 02:48 PM   #1623
poseidonsvoice is online now poseidonsvoice  United States
diyAudio Member
 
poseidonsvoice's Avatar
 
Join Date: Jul 2004
Location: NC
Amp Camp Pre+Headphone Amp - ACP+
Indeed. Wise words MJ. I follow the same philosophy.


A little off topic…
For large TO-247 Mosfets and the like, I now avoid the use of Keratherm and similar products especially in the situation where the heatsink is going to be reused for different amp modules. It’s very easy to tear/pierce the Keratherm when torquing it down. Suddenly you are wondering why your amp doesn’t work. Many of these large MOSFETS have the drain pin connected on back of the MOSFET as well. So the drain is now in contact with ground. Whoops!

There are pages of troubleshooting threads posted by new builders regarding this.

So now I use Ceramic thermal interfaces and very scant amounts of thermal paste. I still use Keratherm for TO-247’s in secondary locations such as power supplies, etc…

For smaller TO-220 devices, I still use Keratherm or equivalents.

Just another perspective from yet another learner!

Eric did a very nice appraisal of different thermal interface materials. It’s a great read.

Best,
Anand.
__________________
Science is not a democracy - Earl Geddes
DIYAudio is a journey not a destination!
  Reply With Quote
Old Yesterday, 03:31 PM   #1624
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC (Virginia)
Amp Camp Pre+Headphone Amp - ACP+
Quote:
Originally Posted by BillEpstein View Post
Not sure what that entails but nothing should impede the job of the heat sinks to sink heat, no?

Also, doesn't the construction of the devices keep current out of the heat sinks?
Is there a risk of sayonara shock from any of the exposed devices? My cat would really like to know!

Completed board:
Quote:
Somewhere in the thousands of posts I read insulators weren't necessary for the J74s but some used conductive grease...
Sorry I thought you meant using keratherm to couple the two SJ74 JFETs together - that’s what I understood from your question. But you were referring to the keratherm or silicone insulators for the main MOSFETs. Sure, silicone insulators are fine. No need for keratherm.

For the thermal coupling between the output MOSFETs and the heatsinks, I use inexpensive silicone TO220 insulator sheets. Works fine - it’s not that much heat.

If you look at the space in between my MOSFETs and the heatsinks, you will see a thin grey insulator layer. That’s a standard TO220 silicone sheet (fiberglass reinforced) available for $4 for a bag of 100 from AliExpress.

For real hot high heat flux applications (like transferring 100w out of single MOSFET, I use alumina ceramic insulator pads and thermal grease).
__________________
XRKaudio Store // Manufacturer’s Forum

Last edited by xrk971; Yesterday at 03:35 PM.
  Reply With Quote
Old Yesterday, 03:34 PM   #1625
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Amp Camp Pre+Headphone Amp - ACP+
Quote:
Originally Posted by poseidonsvoice View Post
IIt’s very easy to tear/pierce the Keratherm when torquing it down. Suddenly you are wondering why your amp doesn’t work. Many of these large MOSFETS have the drain pin connected on back of the MOSFET as well. So the drain is now in contact with ground. Whoops!

So now I use Ceramic thermal interfaces and very scant amounts of thermal paste. I still use Keratherm for TO-247’s in secondary locations such as power supplies, etc…
Or you could spin it as a cost saving measure. OF COURSE you would replace the Keratherm pad every single time you removed a power transistor from the heatsink -- that's just common sense; the (reward vs risk) ratio when NOT replacing the pad is so unfavorable.

But Keratherm pads are kind of expensive, around USD 2.00 each. If you know in advance you're going to replace transistors on this heatsink, several times, then you save significant money when you buy the infinitely-reusable ceramic insulators instead of the one-time-use Keratherm.

edit- BTW, I smooth the backplate of power transistors before mounting them to Keratherm + heatsink, using eight or ten gentle swipes on a fine "6000 grit" sharpening stone. Specifically a "Japanese water stone" from the King brand, sold on Amazon.




_

Last edited by Mark Johnson; Yesterday at 03:42 PM.
  Reply With Quote
Old Yesterday, 09:07 PM   #1626
manniraj is offline manniraj  India
diyAudio Member
 
Join Date: Nov 2012
Quote:
Originally Posted by codyt View Post
I finally got around to trying the Toshiba 2SK2013 in the Q6 position of my ACP. Sounds and measures really nice. The only adjustment I made was to lower R15 to around 700R. I haven't done any tweaking to R12/13, as it sounds really nice with 2R2/6R8.
Hey codyt, did you change only the Q6 to the 2SK2013 mosfet along with the R15 changed from 1k to 700R? I presume you left the Q5 with IRF610 and no other changes. I am going to try the Q6 with 2013 as got a nice pair with me and for a change to see how the sound signature changes

Thanks
  Reply to this post

Reply


Amp Camp Pre+Headphone Amp - ACP+Hide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 11:52 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki