Hello! a few questions on the JLH 1969 - diyAudio
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Old 30th November 2011, 03:55 PM   #1
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Default Hello! a few questions on the JLH 1969

Hi,


I've bought a jlh 1969 kit from e bay
2pcs JLH 1969 A CLASS A amplifier kit sc | eBay


I've built a few class d amps from 41Hz Audio - Main page which are quite nice, but can become a little tiring to listen too after a while. I hope that a super simple class a will take some of the edge off.

If I may, I'd like to ask a few questions?
1. would I be better off changing any of the kit component before I start? ie caps, resistors etc. (i dont want to change the output transistors, not yet anyway)

2. I need to set Iq, which I can do with an ammeter in series with the + rail input yes? A value of about 1a seems common.

3. I have a 2x18v 300va torroid, will this be enough to power both amps? I am thinking it will be close but should be ok.

4. I am confused as to what needs to be grounded to the case? Do I ground - signal input, - power out, are the transistors needing to be grounded?


Thanks in advance for any help given on the subject

matt

5.
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Old 30th November 2011, 04:09 PM   #2
sreten is offline sreten  United Kingdom
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Hi, The Class-A Amplifier Site , rgds, sreten.

A 300VA transformer is plenty more
than you need for two 10W amplifiers.

Also see : http://sound.westhost.com/project15.htm

And read up on class A heatsinking ......
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Last edited by sreten; 30th November 2011 at 04:31 PM.
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Old 30th November 2011, 04:15 PM   #3
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Thanks for the reply! I have seen and read through that site having found it via google, but much of it is beyond me I'm afraid so I thought I'd ask here


added...
Thanks for adding the extra information, I will also look into heatsinks.

Last edited by webleylongbow; 30th November 2011 at 04:34 PM.
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Old 30th November 2011, 04:57 PM   #4
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18-0-18 is fine for the JLH.

It can take 20-0-20VAC which would give you the +/-27VDC.

Reducing the voltage by a couple of volts will just mean that the maximum output power is slightly reduced.
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Old 30th November 2011, 04:58 PM   #5
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Are you happy with the Power Supply Design. It requires DC not AC supplies.
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Old 30th November 2011, 05:16 PM   #6
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Quote:
Originally Posted by KatieandDad View Post
Are you happy with the Power Supply Design. It requires DC not AC supplies.

Hello, I plan on buying an unregulated board with big smoothing caps rather than make my own. They seem quite cheap.
Thanks for the help!
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Old 1st December 2011, 02:02 PM   #7
ljm_ljm is offline ljm_ljm  China
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The transformer is AC18V. Only need a group.

Through the rectifier filtering into DC24V-0.

The transistor need to unscrew connected in PCB above. Because of the transistor iron shell is the collector.

Through to unscrew conduction.

But pay attention to the transistor's shell. Can't the heat conduction. This must be a test of security.
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