Durability of Leach Amp (how mean can I be) - diyAudio
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Old 21st April 2002, 02:17 AM   #1
swede is offline swede  Switzerland
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Default Durability of Leach Amp (how mean can I be)

Hi all!

I've blown a hand full of output transistors (and others as well) in my attempts to get a Leach Amp up and running. The first ones went away with a big pop when I powercycled the amp really fast. (off, wait one second, then on again)

The transistors I had was of the type earlier discussed in a recent thread about counterfeit (fake) Motorola MJ15003/MJ15004, so after a couple of tries I just gave up on my local supplier and ordered some from a more reliable source. My new ones are branded with the "ON" logo instead of "Motorola", which I believe is a good thing.

Since my last attempt was so _unsuccessful_, I'm not sure if the new amp (new PCB's, new circuits) will be just as fragile, or will I be able to put my amp out in my living room? In my workshop nobody else have access to it, but if I have it somewhere else, my family will most likely be tampering with it.

Is the Leach Amp in general really that sensitive and break for sure if I powercycle it too quickly, or was it just my last one with the "fake" transistors?

Regards,
//magnus
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Old 21st April 2002, 03:18 AM   #2
BrianGT is offline BrianGT  United States
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Just an observation on the leach amp... (assuming you have real parts)

Dr. Leach has had his first leach amp running every day for the last 30 years with no problems. It is a solid circuit. I see it everytime that I go to his office. He turns it off each night at 9pm and on each morning at 11am. It is the same as the one in the original article. See the picture in the article:

Build a low tim amplifier ('76)

I have talked to others who have used theirs daily since the 80s with no problems.

I do not think that the circuit has stability. I have ran mine constantly for over 2 months with no problems.

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Old 21st April 2002, 09:52 AM   #3
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Probaly is true,circuit is nice designed and shoud work OK.Problems come with your mistakes.My amp runned with no center tapped transformer and survive.Now i'm in the process buying new one.
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Old 21st April 2002, 10:10 AM   #4
swede is offline swede  Switzerland
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Well, I agree with you, that the amp (if built with proper parts) should last long (for decades), but my question is on how mean I can be, turning it on and off a couple of times.

I don't see a problem with the powercycle if the filtering caps are fully uncharged, but since my last amp didn't make it very well, I'm just curious on what will happen if a four year old kid starts to fiddle around with the power switch.

I've got a whole bunch of the output transistors (including the 2n21193 and 2n21194 (that someone said to be more durable) laying around now. After the last disaster I ordered some fifty devices.

Hughs,
//magnus
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Old 21st April 2002, 01:01 PM   #5
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Switching power probaly cant cause any problems.Maybe some damage to switch and transformer.Depends on transformer power imself,i dont recommend above 500VA.
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Old 21st April 2002, 01:19 PM   #6
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If the power supply is large with alot of capacitance and you cycle the power repeatedly, the inrush current could blow some fuses, diodes and perhaps damage the transformer .... if these problems are dealt with promptly, no damage should be done outside of the power supply and maybe the mains fuse which would probably blow.
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Old 21st April 2002, 01:39 PM   #7
nar is offline nar
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I think you should try some inrush suppressor on the AC line





I sugest you to try with a power thermistor as seen in the DIGIKEY catalog under the reference CL 60



If a kid plays with the main AC switch it shouldn't be a problem after implementing it
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Old 21st April 2002, 02:12 PM   #8
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surge suppressors may not be terribly effective if the power is cycled repeatedly because the thermistor will not have time to cool and thus return to it's high resistance state.
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Old 21st April 2002, 05:11 PM   #9
swede is offline swede  Switzerland
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OK,

Thanks a lot!

I have already installed the inrush limiter that was published in one issue of Elektor some years ago, so that would probably do fine.

What happened to me last time is probably due to the low quality transistors I used.

Hughs,
//magnus
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