Leach Super Amp Pcb Re-Design (LSAPRD)

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#382
JensRasmussen said:
Hello,

...maybe it’s time to pick up the work in this thread.

Hopefully we can now discuss flat pack type transistor layout without someone advocating to keep the TO-3 ones.

Everybody still interested, lets get it going again.

\Jens
Click to expand...

Jens, you do a great job with your layouts. I would be delighted if you just cut through the debate and lay it out, making your best judgement calls when needed. You will never please everyone, but you will have the only SuperLeach board available.
When you started this thread, you had 5 topics:

1)Overall component choice (I prefer standard non exotic parts)
2)Layout of the PCB
3)What should be included on the PCB other than the amp components
4)Technology (Double sided, single sided, Surface mount devises etc.)
5)Target price for the boards (to find out how many we need to order)

Generally, I would prefer this to actually be the Super Leach design, meaning ordinary, non exotic technology, bipolar transistors all the way. But more transistor modern packages will allow for a great simplification in wiring and reduced cost. Otherwise, I would prefer if you stay as close as possible to the well-debugged design of the Super Leach.

I suggest either TO-247 or TO-264 packaged outputs, which still alows wide options in choosing parts by the builder. Even though I have lots of TO-3s in my stock, I think this is a better choice for most builders. As for the drivers, I suggest using the MJE15030/31 pair in the TO-220 package. For the predrivers I would stay with the parts Dr. Leach designed it with (2N3440/5415), even though they are sole source from ST Microelectronics and in the TO-5 package, which is difficult to heatsink well. I am familiar with the Fairchild TN3440 and TN5415 but they are also sole source. I can bend the leads of the MJE340 and -350 to fit if needed later, but these are not as good parts. Label the pins BCE and we can deal with substitutions easily. I'll want the MPS8X99s for all the other transistors, but it is easy to sub in the higher voltage types if the designer so chooses. Through hole parts preferred, just because that is what I have on hand and know how to deal with.

Personally, I would prefer if you stay as close as possible to the well debugged design of the Super Leach, except for allowing the option of more output transistors in parallel. Perhaps a modular add-on board would be the right solution for those who want even more overkill there. I wonder if it is possible to put the input section in the center, and two groups of outputs on the right and left sides That may not be practical, but it has some system advantages. I like to spread the output transistors out physicaly too, just to spread the heat and placing the input section in the middle forces that. Standard 1.5mm thickness preferred (well, standard is 0.062 inch here and I converted that to 1.57mm and rounded down to an even dimension). Beefy copper is fine though (here we say 2 ounce, in our quant old fashioned measurents that's 2 ounce per square foot). I would prefer this were no more than a 2 layer board, even if a few jumpers are needed. Leach does in on 1 layer, so.......

Thank goodness you allow clearance between the board and outputs, that is much better than blocking all the airflow around the parts as is done down under.

Personally, I would prefer that the board have just the amp components, NOTHING additional. Specifically, leave out power supply and soft start functions. I prefer to design those myself. In particular, please don't mount monster capacitors on the board. The 100uF parts are sufficient local capacitance, I will overkill in the power supply, not here. The board needs to be just as designed by Leach, except for minmal changes to replace obsolete parts and allow mounting to a flat face heatsink with minimal hand wiring.

Cost? For a basic board with say triple output stacks (12 output transistors), aim for $30 in low quanity, $15 in volume. If there is an add-on for another triple of outputs or so, maybe 2/3 of those numbers. Just a guess, let me know if that is reasonable. Those seem like cost points where people would not blink. If you stay with standard thickness two layer boards this may be possible.


Well those are my suggestions. Don't let them bog you down. When in doubt, use your best judgement and GET 'ER DONE. Yay for you Jens, just do it.
 
#383
Thanks for the input,

I'm busy with a lot of other projects at the moment....

Status of the 6 Transistors leach:

An externally hosted image should be here but it was not working when we last tested it.


I'm working on the mechanical design right now and a PSU also with rectifiers caps and so on.

attachment.php


Oh yes then there is the low voltage regulator and active filter GB..... and only 24Hours in a day:bawling:

\Jens
 
#385
Howdy slowhands,
Silicon Valley eh?
The 2N3440/5415 part is readily available at most electronic parts outlets in your area. Anchor, Halted and so on.
One search to http://digikey.com/ uncovered hundreds available under
a buck and a quarter each. Proper heatsinks for them are also easily available at these same places for little money.
The Leach SuperAmp is not a cheap amp to build. The best scrounger will find it hard to keep under $300-$400.
The AVEL Y236905 800VA 60V+60V TOROIDAL TRANSFORMER $69.93
from www.partsexpress.com will not deliver the 85V needed to get 250 Watts from the design. Big value 100V power supply caps ain't cheap either. Be prepared for real sticker shock as the build progresses to the case and heatsink stage.
 
#387
Hello Mr. V.,
"$500 is a bargain" for this amp. Wishing thats all I put into the prototype. Just don't count the hours assembling it or collecting up the pieces in prep.

"You invested anymore time in that pcb designing package"
Ahhhh....hours and hours of cursing, mumbling. It looks sooo easy. NOT. Fortunate to have a high WAF.

Kicad is free open source software so one should expect some learning curve problems. It isn't very pretty, but extremely functional. No size limitations for board or components and multilayer is possible. Got to (get to) make your own library/footprint for some parts. One caution, accurate printing from the menu is still fubar and requires an add on program like PDFCreator to preview/print your new component footprint or the final board creation for inspection. The postscript printing function is all that works correctly.
The entire program with all your work can be burned to a cd and just copied onto another computer and run from the .exe files. Can be run from a remote computer on a network. Now that's cool.

All the board designs are now complete as single side. Etched and ready for drilling, stuffing and final test.

Regards, be well.
 
#389
Hi infinia,
"a used Adcom 555" is not a Leach SuperAmp. "it just sounds better" because it is a Leach SuperAmp which will expose all your speakers deficiencies. Now you can "work on speakers where the design work really pays off". However the 555 might be a good parts source for a transformer as part of the SuperAmp power supply.

Regards
 
#391
The Leach SuperAmp would make a good reference amp from which to evaluate your speaker design and active crossover. It takes all the parts in the chain to achieve great sound. My wife takes it for granted that the music sounds like it does thru our Leach amps.
 
#392
acenovelty said:
Howdy slowhands, Silicon Valley eh? The 2N3440/5415 part is readily available at most electronic parts outlets in your area. Anchor, Halted and so on.
]
Click to expand...

ST Microelectronics is the only vendor of new parts of those types. This is not about what is easy for me to buy. I already have literally thousands of those transistors, for service I do. It is my judgement as an experienced engineer that it is unwise to invest in a new design that has sole source parts Voice of experience.
acenovelty said:
One search to http://digikey.com/ uncovered hundreds available under a buck and a quarter each. Proper heatsinks for them are also easily available at these same places for little money.
]
Click to expand...
I paid much less than that for my stock, but thank you for sharing. I don't like most of the heatsinks for TO-5s, especially the loosy-goosy flag types that Dynaco and Hafler used. The best ones are the two piece screw together ones from Thermalloy, which cost too much and I seldom find anymore in surplus. The TO-126 package is much easier to heatsink well. That is my main reason to prefer an alternate like the MJE3X0 in that package. But the silicon is not as good. So I would prefer a design that could accept either type easily.
acenovelty said:
The Leach SuperAmp is not a cheap amp to build. The best scrounger will find it hard to keep under $300-$400.
The AVEL Y236905 800VA 60V+60V TOROIDAL TRANSFORMER $69.93
from www.partsexpress.com will not deliver the 85V needed to get 250 Watts from the design. Big value 100V power supply caps ain't cheap either. Be prepared for real sticker shock as the build progresses to the case and heatsink stage.
Click to expand...
Those are good points. You are correct, it is expensive.

I attach a Super Leach Amp BOM in text format so that you can plug in your own costs and put hard numbers on costs. Feel free to use this as a tool or modify it as needed. I converted it to text from excel format, just to make distribution easier, but you will want to import it into excel, widen columns, and add the multiplication formulas where obvious. I guess i could zip the excel file if there is interest.

This worksheet is a summary sheet, which allows you to plug in the number of boards, your unit costs and get total units to procure and total costs.
 

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#394
Excel works for me. It would be good to add baseline item cost if applicable and source ie digikey, mouser, parts express, etc. this would be good to pinpoint cost savers if a lot of eyes are focused.
The PCB I missed on the GB any chance to get that price again?
 
#395
infinia said:
Excel works for me. It would be good to add baseline item cost if applicable and source ie digikey, mouser, parts express, etc. this would be good to pinpoint cost savers if a lot of eyes are focused.
The PCB I missed on the GB any chance to get that price again?
Click to expand...

I will attach the BOM in excel format, zipped. You add your costs. I can put in Pro forma costs from distributors possibly, but I meant this as a tool for you to put in your costs, not use mine. Mine are low because I am a long time surplus scrounger. For new parts, I go to the ON Semiconductor or Fairchild websites for costing, and order from a distributor in large quantities (Avnet is local for me and they have supplied me for many years).

If you want the board, we will have to do another group buy. The last one closed in July 2005, but it was for the standard Leach Amp, not the Super. I believe the new Super Leach layout is close to ready but Jens needs someone else to manage the Group Buy. And before that, to check out the prototype and make a Bill of Materials (the attached BOM refers to the Leach design, and Jens may have made minor changes not reflected in this, so beware). Frankly, you could also buy the board from Dr. Leach for $12.50 each, but then you have to hand wire the outputs (builds character).

This BOM is for cost estimate purposes only, but I could easily update it to use the reference designators that Jens uses (or he could change his to the Leach numbers, maybe that would be better for those who prefer the Leach documentation).

There is a lot of work in bringing up a proto and shaking the bugs out of the documentation, and it is painstaking detailed work that must be done before you have a product.
 

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#396
Howdy slowhands,
Seein' as how you already have thousands of the 2N3440/5415
on hand, this is not a problem for you. Also paid lots less than new retail for my stock, but that helps others not at all to find the original part to build the amp as described by the Prof. These particular parts have been rumored to be unavailable for most of the past ten years.
Even still on the web site, Prof. Leach notes that they are difficult to find. Yet I continue to find them easily from many sources. This design is certainly not new by any means, but rather a tried and tested build.
You can use "the MJE3X0" . But the silicon is not as good." Dificult to have it both ways. Good part or easy heat sink. Hmmm.
Maybe a little advice from the source is appropriate to lessen folks worries on this issue.

Prof. Leach says these transistors , "can run a little warm. I have never had problems with these running too hot. Although I don't think they are needed, you can put TO-5 clip-on heat sinks on them. There is not much room on the circuit board for the heat sinks, so they must have small fins. Another type of heat sink which will fit is in the shape of a flag (about 1 inch high by 3/4 inch wide) with rounded clips on one end that clip around the transistor. If you can't find them, they are easy to make from sheet metal flashing. The clips should make good mechanical contact to the transistor for good heat conduction."

Let's not sweat the small stuff when this great design will give so much satisfaction.

Regards, be well.
 
#397
Hi infinia,
Before you gut the 555, check out the transformer output voltage and find if it will make at least 80-85VDC so you can get 250 watts from the boards. Are the power supply caps in good shape and at least 100WVDC?
And then it would be a really good idea to read all the documentation on Prof. Leach's site. Both http://users.ece.gatech.edu/~mleach/lowtim/
and
http://users.ece.gatech.edu/~mleach/superamp/
to get an idea just what you're about to get into.

Regards
 
#398
If there is interest, I can add pro forma distributor (Avnet) costs to this BOM, say 100 piece prices that a group buy might get. I get pretty close to these numbers when I buy new, so they will be fairly accurate. It would be the previous spreadsheet with the cost and quantities updated.

Folks, we have to make some decisions about the type of output devices and how many. My choice would be the MJL4281A/4302A set, simply because they have the best safe operating area of any plastic packaged devices we have considered. It's time to decide, and this is my pick.

How many? Jens went with 16 (4 each in 4 push pull cascode stacks). That's overkill, you can stuff less, but the spreadsheet allows you to decide and plug in the numbers. I will add the additional parts in a way that they can be zeroed out easily, for cost purposes. As I said, this is a tool for you to use or modify as needed.

Regarding the 2N5415/3440, they are available new from ST Microelectronics at about $0.45 and $0.62 in qty. 100, sole source. That's the old SGS Thomson combine, a huge producer in Europe, so I'm not too worried about a near term outage. But like I said, we have a fall back to the MJE3X0 parts, so no real worry.

So, should I go ahead and plug in some costs, with 16 outputs?
 
#399
Thanks for the excel SS! I'll start scrounging for prices, any tips for sources will be appreciated. It sure would be good to get mini group buys going for Nor/SoCal people to go direct to distributors and XFMR houses.

Adcom is around +/-70 Vrails 75V caps if memory serves me (200W 8 ohm). My woofers are 4ohm so cannot bridge them with the Adcom. (so i'll keep it stock)

I'm interested in the improvments that are offered for this board, mainly the non-totem pole outputs and non-flying leads. What is the rating for super Leach at 4ohms? Cannot bridge this one at 4 ohms either?
 
#400
infinia said:
... It sure would be good to get mini group buys going for Nor/SoCal people to go direct to distributors and XFMR houses.
Click to expand...
Here is an ebay listing for a transformer that seems to fit the bill for a 2 channel Leach Super Amp running on +-89 volts nominal. He has 25 available as of now, and charges $75 plus $10 fixed shipping in the USA. He has others for different voltages.

http://cgi.ebay.com/63-63V-800VA-To...7540255500QQcategoryZ4660QQrdZ1QQcmdZViewItem

infinia said:
...
I'm interested in the improvments that are offered for this board, mainly the non-totem pole outputs and non-flying leads. What is the rating for super Leach at 4ohms? Cannot bridge this one at 4 ohms either? [/B]
Click to expand...
If you want to drive low impedance loads, I would suggest you build the regular Leach amp, but with the 10 output transistors, that Jens has a beautiful board for ($45) on his website here:
http://www.delta-audio.com/Leach-Clone.htm

I say this because for low impedance (2 ohm) loads, which is what you effectively have if you bridge these on a 4 ohm load, you need more output devices in parallel to handle all the current and not trip the protection circuit (or burn up!). The 10 transistor output will put out 2.5 times more current with the same protection circuit resistors, so it's closer to what you want. You don't want more voltage, which is what the Leach Super Amp delivers into an 8 ohm load. The cascoded output does not meet your needs, but the original Leach may with the extra parallel outputs. Make sense?
 
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