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★★ Free PCB for JLH 2005 Class-A Amplifier
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Old 2nd June 2016, 07:54 AM   #281
polsol is offline polsol  South Africa
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If the positive rail is disconnected out increases to 0.5V.
Negative rail disconnected output goes to V+ (18V)

Removing one of the secondary fuses blows the other one.

So I'll leave the secondary fuses where they are and put 5 Amp fuses in both and I'll see what happens.

Thanks for your help Andrew.

Now I need to order a new box of fuses to replace the multiple 4 amp ones I've used up
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Old 2nd June 2016, 08:17 AM   #282
AndrewT is offline AndrewT  Scotland
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Remove the secondary fuses.
Rely on a close rated primary fuse.
Decide whether a DC detect and speaker protect is desirable.
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Old 26th July 2016, 05:00 PM   #283
ferret is offline ferret  South Africa
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Hi Tony M,

Have you had success with your JLH amps yet?

KevinH
Pretoria
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Old 9th August 2016, 09:34 AM   #284
polsol is offline polsol  South Africa
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Hi Ferret,

Yes, finished it about a month or so ago. It's not the 'finished' article I'd like at the moment but it's up and running.
Hopefully the image will come through ...
JLH 15W.jpg
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Old 9th August 2016, 03:24 PM   #285
e_fortier is offline e_fortier  Canada
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★★ Free PCB for JLH 2005 Class-A Amplifier
Hi Tony,

Amazing work, congrats !!

Can I please have a link of your red power supply pcb, look sturdy with good terminal strips.

Thanks,
Eric
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Old 10th August 2016, 07:40 AM   #286
polsol is offline polsol  South Africa
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Hi Eric,

For the records and completeness (in case anyone is interested) from top left:
1) Soft power supply
This one has a number of problems. The 'push to make' contact didn't work reliably so I had to modify. There's also some problem with 'leakage' to the output terminals - i.e. when 'off' there's still some current flow to the capacitor bank. Soft start not necessary but I had it lying around and it had 2 by 75C temperature 'cut outs' (connected to centres of heat sinks).
2) 15-0-15 160 VA transformer (Farnell)
3) Copper bus bar: Ground lift circuit ex ESP (can't find reference at the moment). 5 Amp AC fuses either side.
4) Jim's Audio 'MUR3020' rectifier/cap bank. Works well and construction is pretty good:
Bridge Rectification PSU PCB Using 4 Ultrafast Diodes Partial Kit | eBay
5) Alps log pot bought ex EBay. Needs replacing as the accuracy between the stereo tracks is very poor (suspect a 'knock-off')
6) Case ex Modushop:
Dissipante 02/300B 2U 10mm ARGENTO
Too small at 2U and 300mm depth - i.e. a little 'tight' to fit everything in.
I had someone drill the front panel for me. Think he held a rat and got it to gnaw the power switch and pot holes - will replace when next I order anything from Modushop.
Current set at 1.6 Amps per channel (otherwise the driver transistors get too hot - for my liking anyway - around 70C or so). I fitted LED heat sinks to them (limited space for anything else). Not sure if these drivers should be attached to the main heat sinks?

The main heat sinks run at around 30 to 35C above ambient when the amp is run for around an hour (without case top panel off).

Still to do:
1) Replace front panel.
2) Remove Alps pot and use external volume control. As the pot is too cramped and the lead wires too close to the cap banks (there is some hum pick up on the right channel).
The PCBs are placed for use of an integrated volume control. If I had known from the start I'd end up using an external volume control I'd have done the layout differently (Amps closer to the back).

Anyway, this is my first attempt at my own Amp. Been meaning to build the JLH since the original article came out. Probably find others might have a better idea of the layout.

Next in line is the Hiraga 30W Class A using a 4U Case ....

Hope this helps.

Cheers
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Last edited by polsol; 10th August 2016 at 07:42 AM.
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Old 10th August 2016, 03:54 PM   #287
e_fortier is offline e_fortier  Canada
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★★ Free PCB for JLH 2005 Class-A Amplifier
Perfect, thanks Tony.
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Old 10th August 2016, 05:07 PM   #288
balle123 is offline balle123  Norway
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Quote:
Originally Posted by polsol View Post
Hi Ferret,

Yes, finished it about a month or so ago. It's not the 'finished' article I'd like at the moment but it's up and running.
Hopefully the image will come through ...
Attachment 564046
Nice amplifier..
Noe chassis grounding
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Old 10th August 2016, 05:22 PM   #289
balle123 is offline balle123  Norway
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Quote:
Originally Posted by polsol View Post
Hi Ferret,

Yes, finished it about a month or so ago. It's not the 'finished' article I'd like at the moment but it's up and running.
Hopefully the image will come through ...
Attachment 564046
Nice amplifier..
No chassis grounding
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Old 10th August 2016, 09:33 PM   #290
polsol is offline polsol  South Africa
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Quote:
Originally Posted by e_fortier View Post
Perfect, thanks Tony.
Only a pleasure Eric.

T
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