JLH 10 Watt class A amplifier
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 26th October 2004, 08:00 AM #1011 numbernine   diyAudio Member   Join Date: Oct 2004 preset calculation Thanks all respondents! Mikelm: I will make straps first then I will try different values/dispositions. Merci beaucoup. I have however others four (stupid) question: First: Dutch Diy: "Do not forget to use a 0.1uF mkp in parallel". 1. Here where I'm living (south of France) I can buy only by mail. I will pay 4,30E for the expedition and 0.20E for capacitors. I have some recuperated ceramic (?) capacitors. Two pairs: first is marked: KC 104K and many others invisible things, the second: 0.47uF-MKT-250V. What happens if I don't put them? Second: Geoff: 2. U nderstood all about Q5 Q6. I will chose the simplest way, no C3, R=10-12K. 3. Now the other problem.Your answer about R8: "I would suggest making your R8 a preset ..............................the necessary resistance for R8 will depend on the gain of your output transistors and this can vary quite widely" I never found the detailed method of calculation, when the potentiometer is a small one 0,15 Watt - for example. I remember the JLH for the Quad ESL where I found an explanation but not the detailed way to calculate it. Please can you make the effort to explain in a linear way (hope this is the wright English word: I mean "step by step") how to calculate the preset, the R8 and the R5? I think I'm not the only one interested by. My hypothese is (but of course you could use anotherone): U= +-12 to 14 Volt I= 0,8 to 1,0 Ampère Hfe Q1, Q2: about 30-40 (Q3- if it matters: 100-120) Disponible power potentiometers: 0,15Watt Third: I don't know to whom: 4. You remember maybe that I want to mount the PCB inside the "channel" of a H-shaped heatsink on the other side than the MJ 15003. I saw this kind of assembling to a Marchand module. It's nice. But the PCB will be very hot, I suppose. Must I change this idea? Many thanks again, Numbernine
 3rd November 2004, 06:33 AM #1012 serosmaness   diyAudio Member   Join Date: Jan 2004 Location: Cortez Colo. I have a question. If I lose a rail on the JLH will I get the remaining rail voltage delivered to my speaker and how do I prevent this. Thanks. Steve
diyAudio Member

Join Date: Jul 2003
Location: Dona paula, Goa
Supply OK...

Quote:
 how do I prevent this.
Here is a simple circuit idea which can be adapted to protect the speakers on losing a supply rail.
There was an LED in the original ckt but I replaced it with an optocoupler. Select the convenient and change the Rs as needed. MCT2E is just a quick example.

This is a battery OK indicator, but is very easy to modify to suit the +/-rails of the Power amp. The supply to this ckt should be the Amp supply whereas the transistor in the optocoupler should be used in the speaker de-thump circuit to disable the relay, the contacts of which are connected in the leads of the speaker. When the rails are OK, the Optocoupler transistor will be ON

U can also use as standalone protection, but the relay should have its own separate supply and may be derived from the same transformer.

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 4th November 2004, 09:59 PM #1014 serosmaness   diyAudio Member   Join Date: Jan 2004 Location: Cortez Colo. Thanks. Do many DIY use DC protection with the JLH? serosmaness
chris ma
diyAudio Member

Join Date: Sep 2001
Quote:
 Originally posted by serosmaness Thanks. Do many DIY use DC protection with the JLH? serosmaness

I am using purchased kits in one set of my JLH amps. It did save my speakers once when one of the 4 output MJ15003 just died with no reason after almost two years in service..

Regards
Chris

 5th November 2004, 07:33 PM #1016 serosmaness   diyAudio Member   Join Date: Jan 2004 Location: Cortez Colo. Thanks Chris. So it is a good idea to use protection. Where did you get the kit ? Thanks serosmaness
 5th November 2004, 08:16 PM #1017 chris ma   diyAudio Member     Join Date: Sep 2001 Location: Pickering, Canada I am using the Velleman K4700 kit, although this is a stereo version I just connect one channel for my mono block.. that means you have to buy two kits if yours are like mine mono blocks. Regards, Chris
dutch diy
diyAudio Member

Join Date: May 2001
Location: NL, The Hague
Quote:
 Originally posted by serosmaness Thanks. Do many DIY use DC protection with the JLH? serosmaness
No, and no thumb suppresion either.

dutch diy
diyAudio Member

Join Date: May 2001
Location: NL, The Hague
Quote:
 Originally posted by chris ma I am using purchased kits in one set of my JLH amps. It did save my speakers once when one of the 4 output MJ15003 just died with no reason after almost two years in service.. Regards Chris
Chris,

At what rail voltage and bias current were you operating?
I'm running for over a year now on 29.5V and 2.2 A on 4 mj15003's.

During testing of my first J-amp set my Shack Speaker however survived several + an - 22 V DC-offset problems, and not for milli seconds i can tell.

dutch diy
diyAudio Member

Join Date: May 2001
Location: NL, The Hague
Re: preset calculation

Quote:
 First: Dutch Diy: "Do not forget to use a 0.1uF mkp in parallel". 1. Here where I'm living (south of France) I can buy only by mail. I will pay 4,30E for the expedition and 0.20E for capacitors. I have some recuperated ceramic (?) capacitors. Two pairs: first is marked: KC 104K and many others invisible things, the second: 0.47uF-MKT-250V. What happens if I don't put them? Many thanks again, Numbernine [/B]
Use the 0.47 MKT type.

We know that an electrolitic capacitor has a poor impedance at higher frequencies, so adding a small non elco capacitor in parallel cures this problem.

the actual value isn't quite as important as the fact that you use a non-polar (like MKT) type.

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