F5 power amplifier - Page 294 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 Search this Thread
Old 14th February 2009, 10:08 AM   #2931
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Quote:
Originally posted by EUVL
first
Patrick,

you're half mechanical engineer, half electronics engineer.
As a mechanical engineer you have had formal training in mechanics, thermodynamics, robotics, control systems, mechanical design, maybe even fluid dynamics.
You've had practical experience in at least three places in the UK, NL and D, have access to CNC milling and wire cute facilities.
You're also thoroughly skilled in electronics, at which occasion should you have been congratulated ?

The amps on these pics are more authentic successors of the ML20(.5) than the No33, claimed by Madrigal to be designed with the 20 in mind.
=> front
=> back

Though idling at less than 30% of the No33 number, these do have a regulated output stage.
The ML engineers who worked on the 33 and 33H are told to want to do mechanically expensive/impossible things, guess where they headed to and what they designed when they left Madrigal.

You are not an industrial designer, combining solid mechanical and electronic engineering experience into something that looks outstanding justifies a post that can indeed be interpreted as a compl(i)ement.
__________________
The buck stops Here
  Reply With Quote
Old 15th February 2009, 12:20 AM   #2932
diyAudio Member
 
Join Date: Dec 2005
Location: St. Louis, MO
Default Aavid flow calculator

Actually free convection velocity varies with sink to ambient temperature delta and sink geometry. Aavid publishes correction factors for natural convection, depending on the heat sink size. For natural convection with my heat sink geometry, the correction factor is equivalent to ~ 215 fpm forced convection vs. the default value of 500 fpm. When I plug this in with a comparable Conrad heat sink geometry, I get their published thermal resistance values for 80 degrees C, (the standard way these guys are spec'ed). Heat sink thermal resistance goes DOWN as temperature increases, so the value at 80 degrees C can be 65% of what it at 25 degrees C. (this is goodness, or the first law of thermo. would be in doubt).

When all is said and done, though, it is still all a guess unless you measure it on the case in the right environment, with a known heat load, (P=IV), per Jackinnj's earlier suggestion. My plan is to instrument my sink at the MOSFET locations and measure the temperatures as I increase the bias. When I get to 60 degrees C or 1.3 amps, I quit and put on Kind of Blue !!
  Reply With Quote
Old 15th February 2009, 12:44 AM   #2933
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
My heatsinks get to almost 50 deg C in a 22-23 degC room with reasonable but not completely free air circulation (in a rack). After running for >12hrs today the bias voltage gets to about 0.65 and is stable at that. That works out at nearly 1.4A. takes at least an hour for the amp to get up to temp. DC offset is minimal - about 5mV.


The F5 sounds great, really happy with it now. I'm putting the lid on tomorrow and will take a few pics when I have it out of the rack. While I had my fair share of troubles building this one (down to me of course) overall it has been well worth it and now I have an amp that really is first class.

******************************

For those of you with the knowledge.... what size of a chunk of steel would I need to use to act as a heatsink instead of finned alu? If I used say something like 1" plate with a copper spreader etc? (I'm only thinking of alternate builds is all). I know it might not be as efficient as the finned alu, but could it be done with a big enough chunk of steel? If i used a lump twice as big as the alu would that be good enough?



Fran
  Reply With Quote
Old 15th February 2009, 01:44 AM   #2934
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by woodturner-fran

For those of you with the knowledge.... what size of a chunk of steel would I need to use to act as a heatsink instead of finned alu? If I used say something like 1" plate with a copper spreader etc? (I'm only thinking of alternate builds is all). I know it might not be as efficient as the finned alu, but could it be done with a big enough chunk of steel? If i used a lump twice as big as the alu would that be good enough?



Fran
View a chunk of steel as a chunk of aluminum or copper -- or like a battery -- you can charge it up with energy but what you want to do is transfer the energy to the environment.
  Reply With Quote
Old 15th February 2009, 01:59 AM   #2935
Variac is offline Variac  United States
diyAudio Editor
 
Variac's Avatar
 
Join Date: Dec 2001
Location: San Francisco, USA
You probably need about the same number of square inches exposed as are exposed on a finned heatsink that works, if the steel is say about a half inch thick to make sure the heat willl flow..The thickness would be determined by the conduction of the material. That could be looked up. If it is half the conduction, then twice as thick?... but the heat spreader might be a good idea close to the mosfets.

Then here is the question as to whether fins are possibly less efficient because unless they are very widely spaced there might be some resistance to air flowing between them . On the other hand maybe the fins create a "stack effect" that increases flow.

Putting a big resistor on it and pumping power into the resistor is of course what would really answer your question, once ywere willing to buy some material. But by then I guess yo ucould just bolt the amp into it!

You thinnking of those 4'x8' plates the street repair guys use to cover excavating?
  Reply With Quote
Old 15th February 2009, 08:23 AM   #2936
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Quote:
You thinnking of those 4'x8' plates the street repair guys use to cover excavating?


Well, yes I was thinking of that kind of thing. Well, its just that I can lay hands pretty cheaply on all sorts of scrap steel in all sorts of shapes and sizes. Walk into a scrap yard and pick something heavy enough to do the job. However, heatsinks, well you'd have to pay for those!

Theres also a good source in older cast iron equipment, stuff thats scrapped.

Next time I'm in a scrap yard I might just pick up some stuff and see how it works out. At least I have a benchmark here now and know with the proper heatsinks the temps the mosfets themselves get to (60-70degC at the moment)

Fran
  Reply With Quote
Old 15th February 2009, 10:54 AM   #2937
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Variac must be getting close.

Try double the surface area cf. aluminium heatsink.
Will both sides dissipate heat or just one side?
Keep the radius to thickness ratio @ ~10:1

A typical aluminium heatsink with Rth s-a of 0.3C/W will have a surface area around 300,000 sq mm.

A steel plate of twice this area will be about 770mm sq.
Radius from centre to corner ~540mm.
Thickness required ~54mm.
Weight ~224kg (~500lbs).
That's as good a guess as I can make for 0.3C/W as a steel plate.

But it would take all day and night to reach operating temperature. Maybe that's a plus rather than a negative.
__________________
regards Andrew T.
  Reply With Quote
Old 15th February 2009, 11:35 AM   #2938
h_a is offline h_a  Europe
diyAudio Member
 
h_a's Avatar
 
Join Date: Sep 2006
Location: Graz, Austria
Quote:
If it is half the conduction, then twice as thick?
No that is not a linear relationship - in simple words: that won't work well

Steel has poor thermal conductivity and thermal conductivity dictates how large a heatsink may become before it's efficiency breaks down. No use for a large sink if the fets are cooking and the outter fins are barely warm.

Don't forget that the force behind thermal conductivity is difference in temperature, so poor thermal cond. leads to high local temperature elevation of the fets. Also the average distance is larger for thicker baseplates, so efficiency is further reduced. Not to mention the weight of that beast

Avoid steel if possible or use at the least an alu heat spreader.

Have fun, Hannes

Quote:
But it would take all day and night to reach operating temperature. Maybe that's a plus rather than a negative.
No the heat (energy) has to be dissipated - the fets +local part would be cooking.
  Reply With Quote
Old 15th February 2009, 01:44 PM   #2939
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Ah well, it was just a thought. I mean, I'm sure that if it woulda worked, I wouldn't have been the first to come up with the idea!

Anyways, if I see something that looks like it might do the job sometime I'll pick it up. Otherwise its on to alu only.

Fran
  Reply With Quote
Old 15th February 2009, 03:52 PM   #2940
rhysh is offline rhysh  United Kingdom
diyAudio Member
 
rhysh's Avatar
 
Join Date: Sep 2008
Location: Southampton
Send a message via MSN to rhysh
Just confirm its okay to use wirewound 3w's for R7 & R12?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Rockford Fosgate Power 20001 bd amplifier power rating?? pachoorion Car Audio 8 8th May 2011 10:49 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 05:23 PM
McIntosh Power Amplifier Power Guard johnnyrt Solid State 2 23rd August 2007 10:22 PM
Output power for a power amplifier Progg70 Solid State 33 10th September 2006 08:44 AM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 04:06 PM


New To Site? Need Help?

All times are GMT. The time now is 04:37 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2