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Old 30th December 2008, 03:12 PM   #1011
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Rob,
Would it look as neat as what Jens proposed? The idea was to use the copper on the bottom of the small board to help transfer the heat. If you grind the pads on the bottom off per Bob's recommendation and mount directly to the sink I think you will appreciate the results. Some thought was put into this design before it went out for us to build. I lot of people much smarter than I am contributed to this. I very much appreciate the input provided by the forum members on our projects. Also, remember that quite a few are up and running per design." If it ain't broke don't fix it. "

To all Happy New Year. And may we all have many new endeavors to play with in the coming year.

Tad
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Old 30th December 2008, 03:33 PM   #1012
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by rob3262
....why not just solder 1N4007's to the bottom of the PCB per the screening, add a dab of compound and mount the pcb with these diodes in direct contact to the heatsink. .............. and no thermal resistance.

Quote:
Originally posted by tryonziess
.......... grind the pads on the bottom off per Bob's recommendation and mount directly to the sink I think you will appreciate the results.
the SMD diodes are too thin to contact the heatsink.
The output To247/264 are far thicker and hold the PCB off the sink.

Grinding off the copper pads removes the main route for the VIAs to transfer heat from the sink side to the diode side. The PCB is too effective an insulator.
It was a serious doubt on the effectiveness of the VIA route that persuaded me to turn the PCB upside down and at the same time move it towards the output devices.
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Old 30th December 2008, 04:39 PM   #1013
rob3262 is offline rob3262  United States
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Quote:
Originally posted by tryonziess
Rob,
Would it look as neat as what Jens proposed?
Tad
Hi Tad
Yes, it would almost be identical. Using header pins, as Jens has, the standard diode pcb sits under the main pcb and utilizes the same access holes for mounting. The only difference I'm suggesting is the 1N4007's are under the diode pcb instead of on top, where the diode pcb can now sandwich the diodes against the heatsink directly. No need to transfer heat to the top side via plated mounting holes.

For the record, I have deep respect and admiration for the forum contributors, especially those whose projects I subscribe to. This Leach project is my first foray into DIY, I am simply thinking outside of the box, asking questions when I don't understand, and learning the hard way sometimes.

So I agree, it ain't broke. I don't need to fix it. Heck, I haven't even built it yet!

Quote:
Originally posted by Andrew T
Grinding off the copper pads removes the main route for the VIAs to transfer heat from the sink side to the diode side. The PCB is too effective an insulator.
Hi Andrew. The component thru-holes appear to be an issue, not the plated mount holes.

In looking at the SMD board, it appears that heat transfer through the single mounting hole would be effective as is, given the proximity of diodes around the mount. Also, the mounting screw would aid in that heat transfer. Like the standard diode pcb, I will still have to grind off the header pads from the bottom.

You have chosen something different by inverting and relocating. Will your amp be pushed to the limit, or do you simply seek a tweak that gets the best compensation performance?

- Rob
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Old 30th December 2008, 04:56 PM   #1014
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by rob3262
You have chosen something different by inverting and relocating.
I did what seemed simple and intuitive.
Look at Leach's solution. He embedded the diodes into the heatsink to ensure good temperature monitoring.
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Old 30th December 2008, 05:07 PM   #1015
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Although the conduction path is a bit longer, the vias on the mounting holes are pretty substantial, connecting the top and bottom ground planes.

There are many of theses amps out there working just fine. Perhaps we are over analyzing this issue.

It seems to me that as long as the thermal diode string does not short to the heat sink, it should be OK however you mount it in general home use (IMHO). If you are going to use it in a PA or other heavy duty application more attention to compensation diode mounting may be in order.

Geez, if Jens publishes a Thermal Track version, I'll have to build even more amps.

BTW, for those willing to use surplus parts, Apex Jr. has some 600 VA dual 45 V @ 6.6A/ 29V CT @ 22 VA / 17V @ 200 mA transformers available for $29.95, as well as 6,800 uF 80V snap in caps at $4.50
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Old 30th December 2008, 06:41 PM   #1016
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Jens,

A ThermalTrak version of the Leach would be very interesting!

I have experience with ThermalTrak devices. The convenience of having the tempco diodes embedded is overwhelming! I have thought about doing a Leach layout myself. However your work on the 6 output, 10 output and SuperAmp layouts has been exceptional. I'd be very interested in seeing what you have in mind when using ThermalTraks.

A few months ago there was a thread describing such a project. Did that go anywhere?
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Old 30th December 2008, 10:32 PM   #1017
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Jens,
I too would be interested in what you have done with the thermal trak devices. It would be nice to have a pot in the circuit in series with the diode to dial in the Vbe as needed-- if this is possible.
A great deal of discussion is going on at present concerning just how to implement the thermal traks and take full advantage of there design criteria.

Just a little note. Audio Express is no longer carrying the A-75 main boards. If anyone knows of a source for one please let me know.

Tad
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Old 31st December 2008, 12:07 AM   #1018
AudioG is offline AudioG  Italy
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Default best resistor 0,4-0,6 W

Hello, i'm always searching the components with the best performance/price rate, (because I have many time to waste?!).
What do you thingh about DALE CMF55 as low power metal film resistors? Their price at Mouser seems good and they have a good reputation for audio use.

Giuseppe.

P.S. 300 or 330 ohm is not very important.
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Old 31st December 2008, 01:31 AM   #1019
rob3262 is offline rob3262  United States
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Default Re: best resistor 0,4-0,6 W

Quote:
Originally posted by AudioG
P.S. 300 or 330 ohm is not very important.
Got it!
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Old 31st December 2008, 08:52 PM   #1020
clm811 is offline clm811  United States
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Default Use of current limiter vs delay relay...

Quote:
Try CL30 for current limiting. It's 2R5 cold and 0R34 at 2 amps. One per rail - driving both channels should work well.
OK, I got the CL-30's from Mouser.
I'm embarassed to admit I'm still confused.
There seems to be a lot of differing opinions as to where to put the thermistors(most posts relate to tube amps, Class-A amps, etc.); I did read that the constantly changing current demands of a Class AB amp may not be enough to keep the thermistor hot (and therefore its resistance low). Many recommend a delay relay (extra circuitry which I 'd like to avoid).

At the risk of sounding a bit daft , I'd like to ask:
where (exactly) should one locate these in a 100-200W Leach Class AB amp with a "basic" power supply(if at all)? Pros & cons?

I've attached a diagram of a typical "basic" power supply*, showing several possible installation points.

THANKS! And Happy New Year to all!

-Chas

*courtesy of TNT audio's website
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File Type: jpg psu1.jpg (21.8 KB, 411 views)
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