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Jens Rasmussen Leach clone group buy

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#242
Boards arrived!

Thanks Tad - my boards (and the MO) were waiting when I return to the country today.
These are the best DIY boards I ever bought.
All 10 boards arrived safely thanks to the great packing.
Many thanks again for your effort.
:cloud9:
 
#247
TO-3BPL / TO-264 Insulated?

So, I was looking at Jens' site, and I see this picture of his amp mounted on a heatsink. It didn't look like there were any insulators under the transistors.

I've never worked with this type package (first big amp project), but I'd assumed that the packages weren't insulated. At the same time, I don't see anything on OnSemi's data sheets or package drawings that say which pin the back is connected to, like you'd see on a TO-220 package.

I don't see any insulators on the parts list, even for the TO-220 MJE1503x parts

So can someone straighten me out on this?

--Greg

Here's the pic:
 
#248
mjl4281 insulator

If you look further on Jens and Peter's website you will see additional pictures of the heatsinks, pcb and parts with sil-pad insulators under the output power transistors.
I did notice with my mjl4281 units that the insulated bushing might not be needed. I will check the plastic inner hole liner with the DMM and see. Good luck with your amp Tad
 
#249
Re: mjl4281 insulator

gmikol said:
I was looking at Jens' site, and I see this picture of his amp mounted on a heatsink. It didn't look like there were any insulators under the transistors.
.....................OnSemi's data sheets or package drawings that say which pin the back is connected to
Click to expand...
The middle pin is connected to the metal back plate and must be insulated from the chassis.
tryonziess said:
mjl4281 units that the insulated bushing might not be needed. I will check the plastic inner hole liner with the DMM and see.
Click to expand...
Onsemi's To264 has an insulated hole that does not need an insulated bushing.
The hole is slightly tapered , the front face diameter is a close fit for a 3.5mm bolt but the rear face diameter is just too small to fit a 3.5mm screw/bolt.
It can be drilled to 3.5mm right through and still retain integrity of the insulation for a bolted fixing. The To247 sil-pads just fit if carefully centred on the hole and aligned to cover the whole of the metal backplate.
 
#250
Thanks!!!

Thanks Tad, Andrew...this is what I thought. I'm just curious as to why that pic is on Jens' main Leach page without insulators, unless he's got separate sinks for the PNP and NPN sides.

Thanks again for the clarification, and for the awesome boards, Jens and Tad...even though I probably won't be able to do anything with them until Summer...:bawling:

--Greg
 
#251
Hi,

I have one (of an old prototype) picture on the homepage where the insulation washer is so small that it does not show. The heat sink is non conductive on the surface.

I have other pictures where I have used the right size insulation washers that are clearly visible.

Always use washers, and 3mm screws to mount the transistors.

:att'n: Never:att'n: enlarge the holes in the output transistors to use bigger screws as this may damage the package of the transistor and cause long term failure.


\Jens
 
#252
Leach Amplifier Boards

Jens,

Do you still have both Leach Super Amp and Leach Low TIM boards available? Also do you have any thoughts regarding the sound quality of the Low Tim Amp vs the Super Amp with its cascoded stages? Normally, it seems the fewer output devices in series with the load, the better the sound quality. The availability of high voltage modern output transistors would seem to make the Super Amp topology unnecessary for anything but very high power output requirements.

Regards, Harold
 
#253
Harold

I had thought about making another board group buy after the New Year if there is enough interest in buying the boards. I will have to have about 100 boards sold to make the price acceptable.
There are some interesting white papers on the web concerning the cascode output stage. They are in favor of series op transistors in that they enhance the dynamics. One such paper can be found on the Pass site. Tad
 
#254
Hi,
I would like to get some boards. Will you organise some group buy in close future?

Can you tell me the price for each 10 transistor board?


My plan is to use two boards in bridge to drive one 4ohm Aliante 15 sub.
Can you sugest me output devices and supply voltage for 800W+?


Tnx
Zeljko M
 
#255
Bridging into a 4 ohm load the amp "sees" a 2 ohm load. I'll let the experts talk about SOA issues, but my gut feel is that you'd need more than 10 output devices per side to keep the amp alive. If you're OK with a risk that you might exceed the SOA if you push your sub and blow up the amp, around 45V rails ought to get you close to 1KW average.

Is that sub a dual voice coil model? You could run the rails up around 85V to get 400W into 8 ohms and have each amp drive a voice coil. I'd use MJL4281/4302 outputs for this option.
 
#258
To be realistic, for sub use at that power level, consider a pro sound amp. You can get something inexpensive and reliable for a lot less money and trouble than modding a DIY project.

The down side of most pro amps is the fan. For home use you can safely modify the fan to run slower (=less noise) The Behringer Euro Power series is pretty popular in another forum. You can also minimize noise with careful mounting and sound absorbtion near the amp.

Just because the manufacturer says use 500W minimum doesn't mean that you really need it though. Model the sub in something like unibox and see how much power you'll really need to get to your target SPL/extension. You may find that you can get away with less power, especially if you can use a bigger box.

Good luck with your project.
 
#260
Hi,

i am also very interested to buy leach amp PCBs in a group buy.

It depens on the price...I am interested in 2 pieces of PCB (but if the price is good....i will take more).

Do you need additional infos from me?

best regards

Alan & Ayk
Germany
 
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