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Old 27th May 2009, 05:26 PM   #1361
AndrewT is offline AndrewT  Scotland
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Default Re: 6 transistor leach

Quote:
Originally posted by lgreen
(R26, R34, R68, R69 and R41,R42,R43,R60,R61,R62,R28,R30) are "to be defined".
these are the protection circuit resistors.
Their values are very dependent on:

The Vdc of the supply rails
The VA of the transformer
The value of smoothing capacitance fitted
The heat dissipation capability of the heatsink
The ambient temperature
The output devices fitted, both SOA and power
The Rth c-s of the isolation film used
The value of the load impedance
The value of emitter resistor fitted
The Vbe characteristic of the protection transistor

I suspect I have omitted a few, but you must include the builder's philosophy on what current is allowed to pass at full limiting, what should pass short term without any audible effect and what transient current should pass without triggering or activating the protection transistor. All of this is referred to in various posts in the clone threads.
There is no "one fits all " solution.
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Old 27th May 2009, 05:44 PM   #1362
duekfx is offline duekfx  Hungary
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Default Re: 6 transistor leach

Quote:
Originally posted by lgreen
I emailed Jens, but so far no reply.


I've got the 6 transistor Leach PCB, 7.4.6 (2005).

The parts are here-
6 transistor leach parts
(it does not look like the list was quite finished!)


But a number (R26, R34, R68, R69 and R41,R42,R43,R60,R61,R62,R28,R30) are "to be defined".

1. What are the values for these?

2. Also are MJL21195/96 suitable for output transistors? (I have many of these)

3. What voltage should I use for the DC rails to drive 4 ohm speakers?

- thanks
You can find info about those values on this page:
http://www.diyaudio.com/forums/showt...029#post686029
and this one for another rail voltage:
Smaller Leach Amp V1 (bottom of the page)

If you are still unsure, I'd suggest using the original construction from Dr. Leach.
PCB can be downloaded here (Protel files): http://www.sidesign.co.nz/downloads.htm

I hope this helps
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Old 27th May 2009, 05:55 PM   #1363
AndrewT is offline AndrewT  Scotland
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you cannot use Leach's values.
They are for a different protection circuit and ONLY applicable if the whole schematic is copied exactly. 3pair can never = 2pair.
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Old 27th May 2009, 06:01 PM   #1364
duekfx is offline duekfx  Hungary
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I didn't mean using those values. I meant constructing the original Leach with the plans of Dr. Leach and to forget about this Leach clone if he has problems calculating the values for the protection circuit. That's the reason I attached a link for the original PCB plans since you can't order those anymore.
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Old 27th May 2009, 09:13 PM   #1365
lgreen is offline lgreen  United States
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Default ahhh....

ahhh!!!! now i get it.

AndrewT is going to have me doing math!

Actually I'll try but maybe i'll ask for help when everything is ready? I hate to dissapoint cause he is such a nice person and has helped me a lot over the years.
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Old 27th May 2009, 10:27 PM   #1366
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There is a spreadsheet somewhere, might save you a second shipping/minimum order charge.
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Old 27th May 2009, 10:28 PM   #1367
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If you go to the Delta-audio.com site most of the information you need, including the protection circuit formula. Jens has a rather extensive detailed amount of helpful information. Pay attention the detailed spec dimensions for the parts. Believe me if I can build this amp from the available literature anyone can.
Remember the numbers are for the RAIL voltages not the transformer output voltage. Also pay VERY close attention to the PCM dimensions on the film capacitors or you will be placing another order. You will find that the Dale RN and RS resistors will be extremely tight in some of the pcb pads. Do not try to drill them out it is not worth it. Shoot for something more run of the mill and it will fit perfectly. Make sure the solder wicks to the front of the board.
Have fun.

Tad
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Old 28th May 2009, 05:19 AM   #1368
duekfx is offline duekfx  Hungary
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I wanted to do this project myself a few years ago, but the PCB is all about dimensions, and almost all quality components are larger.

Here is a bad example: http://img510.imageshack.us/img510/9...ndom072hs8.jpg
Some of the components didn't fit at all since the constructor didn't pay attention to dimensions.
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Old 28th May 2009, 11:17 AM   #1369
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duekfx,
That particular amp looks O.K. If you look through some of the threads on this forum you will see that some of the really experienced designers still stand the resistors vertical/semi-vertical out of choice not necessity.
The Leach clone is a large board as it is. To have designed it for large Rn resistors or some combination of other components would have made it so large it would have been prohibitive to have made.
I have two almost complete Leach 10 transitor boards stuffed with odd parts that I scrapped because I destroyed so many pads trying to get audiophile components on the board. I have since begun to acquire components that are just as good to my ears and much cheaper. They are also easier to work with. I learned this the hard way. If you look at some of Nelson Pass' commercial offerings you will not see any exotic components and he has one of the best reps out there.
One of the best places to spend money is on the pcb itself. If you choose a good job shop and spec heavy traces and board thickness I think the overall result is improved consisderably. I think we learn these things by trial and error. If you can not hear the difference with you own ears it does not make since to delve any deeper for components.
I have a small group of friends, none of which share my hobby interests, so I have no one to brag to about what items go in my projects. This is one reason I sold off all of my expensive gear and went DIY. If you can not boast to anyone about your expensive toys there value is lost. It is a man thing I guess. Just my rambling here.

Tad
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Old 28th May 2009, 12:05 PM   #1370
duekfx is offline duekfx  Hungary
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In my point of view of "quality" is a quite complex concept, it doesn't necessarily mean boutique stuff. A cap needs to have low noise, a good type of dielectric, long life and tight tolerance. Well, these parts are quite large and don't really fit on the PCB. Those "5mm pin spacing" types give you no other choice than polyester (or even worse: ceramic). As for resistors, if you need 0.25W for example, I prefer to use 1W instead for lower noise. Look at the feedback resistors, 4 in parallel on the PCB. You need to be quite tricky to fit such in that location. The list goes on, and it's quite long. I don't mean to offend anyone, in fact I like this design. It looks really professional, otherwise I wouldn't have tried getting proper parts, but I gave up. However it doesn't suit everyone's needs. There are basic rules for PCB designs. 1 is to avoid the parasitic effects which are generated when parts are insanely close to each other, the other 1 is to keep wires as short as possible. Vertical or semi-vertical means you will have longer wire on 1 side. The best way to go is to buy parts and design the PCB after you know the dimensions of your parts. I know, not everyone can do that, and the are a lot of careless people who don't bother with "quality" components, in fact there are quite a lot. I am not the type of guy (like our beloved Carlos ) to build 4700+ amplifiers. I prefer to build stuff that I'll use for decades, so "quality" means a lot to me.
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