Go Back   Home > Forums > >

Group Buys Members group buys

PeeCeeBee V4H GB
PeeCeeBee V4H GB
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 15th January 2021, 04:41 PM   #1501
Norgaard is offline Norgaard  Denmark
diyAudio Member
 
Join Date: Sep 2007
Location: Viborg
This is just listed for information should others also experience issues with oscillation despite the update(s), you might want to take a closer look at the thermal pads that you are using and the capacitive coupling of these (DA). Maybe change to a different type will eliminate the problem.



Background:

Finally got to build-up two of the boards bought in the spring last year rev.1

Actually adjusting the boards went without any issues at all, stable and easy setup, everything as described.

Then on to the actual test with load - where I despite using the updated boards and proper grounding of the heat sinks, experienced the oscillation described in #583



Initially I thought it was an unstable SMPS, but that really just reacted to the high peak loads by entering protect mode.


After different attempts at tracking down the problem I finally decided to run common source on the heat sink - thus removing my ceramic(!) heat pads. The amplifier is now completely stable and I did measure just over 40v peak into the small Apogee's (3.5ohm) without hiccups.


The capacitive coupling to the Lateral Mosfet's is known to be critical, so it wasn't entirely surprising, when looking for something out of the normal in my build which could cause the instability.


Doing a common source direct mount configuration is NOT for the beginner and even the experienced might get caught out by old habit's, when chassis is "output" and each channels PSU's (incl GND) are to be kept separate.
I own active ATC monitors and they are a perfect example of a commercially available construction configured this way.


Thanks a lot for the design and for the support Shaan!
I am now happily moving on to finalize the four mono-blocks as soon as I receive the 4x 630G SMPS from Sami (Cresnet)... pictures to follow

Last edited by Norgaard; 15th January 2021 at 04:44 PM.
  Reply With Quote
Old 15th January 2021, 04:43 PM   #1502
Cresnet is offline Cresnet  Jordan
diyAudio Member
 
Cresnet's Avatar
 
Join Date: Nov 2012
Location: AMMAN - JORDAN
PeeCeeBee V4H GB
They are under assembly!

Shipping next week!
  Reply With Quote
Old 15th January 2021, 05:21 PM   #1503
Norgaard is offline Norgaard  Denmark
diyAudio Member
 
Join Date: Sep 2007
Location: Viborg
Great! That's faster than I had dared hope for- Thanks Sami!
  Reply With Quote
Old 15th January 2021, 06:09 PM   #1504
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Kolkata
Quote:
Originally Posted by Norgaard View Post
This is just listed for information should others also experience issues with oscillation despite the update(s), you might want to take a closer look at the thermal pads that you are using and the capacitive coupling of these (DA). Maybe change to a different type will eliminate the problem.



Background:

Finally got to build-up two of the boards bought in the spring last year rev.1

Actually adjusting the boards went without any issues at all, stable and easy setup, everything as described.

Then on to the actual test with load - where I despite using the updated boards and proper grounding of the heat sinks, experienced the oscillation described in #583



Initially I thought it was an unstable SMPS, but that really just reacted to the high peak loads by entering protect mode.


After different attempts at tracking down the problem I finally decided to run common source on the heat sink - thus removing my ceramic(!) heat pads. The amplifier is now completely stable and I did measure just over 40v peak into the small Apogee's (3.5ohm) without hiccups.


The capacitive coupling to the Lateral Mosfet's is known to be critical, so it wasn't entirely surprising, when looking for something out of the normal in my build which could cause the instability.


Doing a common source direct mount configuration is NOT for the beginner and even the experienced might get caught out by old habit's, when chassis is "output" and each channels PSU's (incl GND) are to be kept separate.
I own active ATC monitors and they are a perfect example of a commercially available construction configured this way.


Thanks a lot for the design and for the support Shaan!
I am now happily moving on to finalize the four mono-blocks as soon as I receive the 4x 630G SMPS from Sami (Cresnet)... pictures to follow
Hi Norgaard.

Thanks for sharing your findings and I hope it helps anyone dealing with the same problem.

If possible, see if you can try mica or silicone-glassfiber pads (which result in more capacitive coupling between mosfet back and heatsink ground). These mosfets really like some constant small capacitance (few tens of pF) to ground at their sources, as you can see that with them mounted directly on heatsink body which is insulated from chassis ground, the total surface area is much larger and results into some adequate value that loads the source nodes just enough so that no oscillation occurs. I measured the capacitance between two 300mm heatsinks separated 5cm with air in between to have 20-25pF, and the back of mosfet to heatsink body when using sil-pads to have almost 40-50pF, and with thermal paste soaked thin mica to have almost 100pF! Ceramic pads are of considerable thickness which cannot create a large enough parasitic capacitor between the mosfet backs and a grounded heatsink, compared to even heatsink body to chassis ground capacitance with air dielectric which solved the case for you.

__________________
V4 | V4H | PSU | PREAMP | ALPS 50Kohm Log Pots

Last edited by shaan; 15th January 2021 at 06:17 PM.
  Reply With Quote
Old 16th January 2021, 07:27 PM   #1505
Norgaard is offline Norgaard  Denmark
diyAudio Member
 
Join Date: Sep 2007
Location: Viborg
Hi Shaan,


That is very helpful info, but it also had me recheck why I had success . Since I actually didn't mount it that way

In my POC I have no ground connection to chassis and heatsink at all - entire housing is all connected to common source for the 4 Exicon's

The problem behind the problem, is that the devices are very sensitive to source inductance when running multiple set's, so even the short pcb traces between the mosfets are problematic.

Key is to shunt out the inductance, with the thermal pads and isolation it is shunted by series connections of basically: small inductor->capacitor->small inductor

But when mounted directly w.o. isolation it's shunted by the heatsink, 10mm alu slab with ribs, which is a very poor inductor (good shunt).

In the final build-up I will mount the V4H directly on it's own block of aluminium, which is then mounted electrically isolated from the chassis and main heatsink.


N.B: I have sent you an email.

Last edited by Norgaard; 16th January 2021 at 07:53 PM. Reason: poor grammar & typos
  Reply With Quote
Old 17th January 2021, 09:25 AM   #1506
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Kolkata
Hi Per.

I agree, you either get inter-source inductance lower, or increase capacitive loading and get it shunned. Both ways work, but I asked you to try the second way very much because you didn't, as mentioned in post 1501, and that is okay since you are already aware of its effects. What matters is whether your current setup works without hiccups or not, and I'm happy to know it does.

If I'm not wrong, in case of mounting on a grounded heatsink via thin thermal pads it would be small capacitor (mosfet parasitics) -> inductor (mosfet source and PCB trace) -> small capacitor (mosfet source to heatsink ground, pads acting as dielectric). I have never tried the thick ceramic insulators, so thank you for letting us know with experiments why those might not be a good idea for this amp and how a stable setup can be done without using any thermal insulation for the mosfets at all.

I have checked your email. Thank you for the much valuable information!
Can't wait to see your final build!
__________________
V4 | V4H | PSU | PREAMP | ALPS 50Kohm Log Pots
  Reply With Quote
Old 19th January 2021, 09:57 PM   #1507
robodo is offline robodo  Czech Republic
diyAudio Member
 
Join Date: Jan 2016
I was ready to use 1.5 mm wide ceramic thermal pads. Now, after reading your experience, I will have to use something else.
The heatsink is grounded with case. What pads do you recommend for optimal capacity?
Thank you for the advice

Robert
  Reply With Quote
Old 20th January 2021, 08:48 AM   #1508
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Kolkata
Hi Robert.

Thin mica, or silpads, with a thin coat of heatsink paste.
Attached Images
File Type: jpg images.jpg (9.0 KB, 67 views)
File Type: jpg images1.jpg (9.0 KB, 67 views)
__________________
V4 | V4H | PSU | PREAMP | ALPS 50Kohm Log Pots
  Reply With Quote
Old 20th January 2021, 09:43 AM   #1509
Bassivus is offline Bassivus  Serbia
diyAudio Member
 
Bassivus's Avatar
 
Join Date: Aug 2004
Location: Novi Sad, Vojvodina
I have used this kind with success:
Silikonisolatoren
Attached Images
File Type: jpg s-l1600.jpg (29.4 KB, 56 views)
  Reply to this post

Reply


PeeCeeBee V4H GBHide 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
PeeCeeBee V4 GB! shaan Group Buys 1058 13th December 2020 07:07 AM
PeeCeeBee shaan Solid State 2814 25th March 2020 03:50 PM
FS :PeeCeeBee V4 meanman1964 Swap Meet 0 1st December 2017 04:54 AM
Retro PeeCeeBee inspired by Juma. gannaji Solid State 20 21st November 2017 02:41 AM
FS: PeeCeeBee PauloPT Swap Meet 10 2nd September 2016 04:48 PM


New To Site? Need Help?

All times are GMT. The time now is 09:45 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki