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Jens Rasmussen Leach clone group buy

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TonyTecson

TonyTecson

Member
Joined 2003
Junie said:
So is it safe for 2SC5200 and 2SA1943 to run on that supply voltage? so far my amp not smoking yet, it sounding good.
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these devices are best used at +-55volts, above that you will have to use many in parallel.....

if your standby rails are +-75 and they drop near the 55volt levels at full power, then you are safe....

the MJL21193/21194 are a better choice at high rails...
 
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spookydd

Member
Joined 2012
Hi all,

I thought I was among the few left who are interested in the leach amp, but I guess I was wrong.

I would be very interested myself as well for about 10 of the 10 transistor versions layed out by Jens.

However I was wondering if there were any newer versions of the gerbers for that 10 trans board, which would include the latest tweaks that were done to the 6 trans version.

I would gladly join the group buy.
 
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spookydd

Member
Joined 2012
BobEllis said:
Bias setting is done by adjusting the trim pots. Professor Leach discusses how in his article suggesting 100 - 120 mA for 2 output pairs. You can also use the ~0.025 V across the emitter resistor rule or just choose what sounds best without running too hot.
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I think a better way would be to use a scope and adjust it to make the crossover disappear. Perhaps make it disappear and add a tiny bit more, for good measure.

This may end up making the idle current different for different amps, depending on the parts used. But it's the best way instead of just guessing.
 
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spookydd

Member
Joined 2012
Earthquake said:
I'd also be interested in a GB for both the 10 & 6 transistor versions possibly 10 of each and possibly more depending on cost.
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Making more than on model costs more, so I think a good idea for those wanting to make the 6 trans version, would be to use the 10 trans version and just populate the board accordingly.

I have a stereo set of 4 ways speakers that I made long ago with the goal of doing active crossover and multi-amp, so that means I need a minimum of 8 amps, and the 2 amps for the lowest end would be best as bridges, so that means I would need 10 boards just for that.

btw: I was looking around for a thread about anyone playing around with the leach amp in a grounded bridge setup. But didn't find any. So perhaps this would be another thread to start, but I would definitely want to work on such a configuration if at all possible. I was thinking about making a small amp with a bunch of 2n3055 or 2n3773 (I have a bunch of those handy) in a quasi topo and bridge them as a grounded bridge to experiment. All this before trying to do a grounded bridge with a leach amp.

Is that of any interest to anyone?
 
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spookydd

Member
Joined 2012
still4given said:
I hope you can find some. Jen's boards are really nice.
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With a group buy, we CAN find some. It only takes a few who want at least 10 boards and we can reach 100 boards fairly easily.

Right you are about Jen's boards, he's a master!!

And I wanted to say you are a real amp freak!!! :):):) I've been following threads for some time and you've been making amps for some time, and not just the leach I assume. Man how many amps have you built in your life???

I wouldn't mind stopping by your house for a visit and have you show me all those beasts you have.

I would be a freak just like you if I had the finances. I've been making amps and other things for a very long time too, but I haven't been able to do what I want and for way too long, so now I am ACHING badly to make some amp right away, it's an itch I can't scratch!!! :D:D:D
 
BobEllis

BobEllis

Member
Joined 2003
Spooky, Of course if you have a scope available use it. But for those without the 0.025 V rule I believe is Self's. it takes into account different emitter resistors, and the basic characteristics of bipolar transistors. Leach said he didn't hear a benefit to going to higher bias. Coincidentally, with 2 devices sharing 110 mA with the specified 0R47 emitter resistors what is the voltage across them?
 
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spookydd

Member
Joined 2012
BobEllis said:
Spooky, Of course if you have a scope available use it. But for those without the 0.025 V rule I believe is Self's. it takes into account different emitter resistors, and the basic characteristics of bipolar transistors. Leach said he didn't hear a benefit to going to higher bias. Coincidentally, with 2 devices sharing 110 mA with the specified 0R47 emitter resistors what is the voltage across them?
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Are you referring to Douglas Self?

I've been looking around for his books, which I can't get from the local library and they are far too expensive for me to buy, even at amazon.

So basically, when we're adjusting bias on a 10 trans beast, we just look at the drop accros one of the emitter res and seek 55mA ?

What about the variation between transistors if they're not matched? I guess we can only be sure if we use an amp meter instead of the fuse on a power rail.

And then that includes all the currents from the previous stages as well. It's a difficult compromise.

A long time ago when I didn't have my own scope, I always found a way to either borrow one or take an amp to a teacher in a school where they have them and don't mind doing some extra teaching...

I haven't built a leach amp yet and I'm aching to do so. Let's do a group buy on Jen's pcbs.
 
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spookydd

Member
Joined 2012
Hi all,
After reflection, I think I would really like to have the 12 trans version. Since Jens had made it in a way that allows snapping off half of the output stage, then those who want a 6 trans version can also have it.

It seems we have a good potential for a group buy of a quantity at least 100 boards, so it's worth a shot. I guess I'm not the only one seeking 10 boards or more. Just a few such orders can get us close to a high enough quantity for a lower unit price.

Who has the latest files for the 12 trans version? Jens has more or less abandoned his web site and he hasn't kept all the files on it for download. It's nice that he still has a few there, but those are older versions without the latest tweaks.

One thing I would really like to have on the board is the protection and relay, with a temperature sensor judiciously positioned right off the board (TO-220 maybe) and on the heatsink without extra wiring.

A good protection would mute the amp when overheating occurs, command a fan and a DC protection would release the output relay. This would be a minimum.
 
JensRasmussen

JensRasmussen

Member
Joined 2002
Gerber files for group buy

Hi All,

I have been really busy with family and work for the last 2 years.... so time and energy for DIYaudio has be limited.

Let me know what version you want to use, and I will generate a set of gerbers to match...

I can even make the silkscreen so it reflects the group buy year - ?

If the DIYaudio shop wants to offer boards, I'm open to this also - let me know - thanks

Warm regards
Jens
 
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