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Old 26th October 2004, 08:00 AM   #1011
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Default 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
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Old 3rd November 2004, 06:33 AM   #1012
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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
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Old 4th November 2004, 07:09 AM   #1013
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Default 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.

Gajanan Phadte
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Old 4th November 2004, 09:59 PM   #1014
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Thanks. Do many DIY use DC protection with the JLH?
serosmaness
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Old 5th November 2004, 04:55 PM   #1015
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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
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Old 5th November 2004, 07:33 PM   #1016
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Thanks Chris.
So it is a good idea to use protection.
Where did you get the kit ?
Thanks
serosmaness
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Old 5th November 2004, 08:16 PM   #1017
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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
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Old 7th November 2004, 12:03 AM   #1018
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Quote:
Originally posted by serosmaness
Thanks. Do many DIY use DC protection with the JLH?
serosmaness
No, and no thumb suppresion either.
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Old 7th November 2004, 12:10 AM   #1019
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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.
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Old 7th November 2004, 12:20 AM   #1020
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Default 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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