JLH 10 Watt class A amplifier

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#1,747
paulb said:
I posted this before, many pages back, but here it is again: I put drawings and notes from Geoff on my personal webspace at:
http://members.shaw.ca/paul.r.brown/DIY/Geoff Moss JLH/
There are links to schematics and PCB layouts at the bottom. This is the version I built (MJ15003 output transistors) and I am very happy with it.
Click to expand...

Hi Paul

Thanks for posting the link. It realy looks very good.

😕 However I'm a little confused with regards to the PSU-schematics - the terminals J2 and J3.😕

How are the off-board reservoirs ment to be connected? In series with the rails or ??

Best regards

Knud
 
#1,749
canute said:
...I'm a little confused with regards to the PSU-schematics - the terminals J2 and J3.😕
How are the off-board reservoirs ment to be connected? In series with the rails or ??
Click to expand...
They're for capacitors or inductors. You would connect the J2/1 and J2/2 together, and the J3/1 and J3/2 together, for external parallel capacitors, or you could connect 2 inductors, on J2 and J3.

Stormrider said:
How much heatsinking does Q3/Q8 need with +/-20-22vdc rails and 1A to 1.5A bias? Are those TO220 heatsinks Paul B. used necessary? I will probably use MJE3X0 or MJE1503X devices.
Click to expand...
Probably not that big - I used that size because I got some cheap and they look cool. They don't even get warm (thus the coolness prevails). I think you will need some heatsinks, though.
 
#1,753
the power rating of any trimmer must be converted to current for the resistance of the specific trimmer.
That is the maximum current rating for that trimmer no matter what position the wiper is at.

As usual with all resistances, it's not wise to use the full current capacity, instead consider whether you want to use 50% or 25% or 10% of maximum rating.

A 400mW 1k0 trimmer has a maximum current rating of 20mA.
I would never pass more than 14mA through and probably try to ensure <=6mA (9%) for normal operational use and 10mA (25%) for transients.
 
#1,754
AndrewT,

Thank you, great stuff! I appreciate your comments and help.

Bruce


AndrewT said:
the power rating of any trimmer must be converted to current for the resistance of the specific trimmer.
That is the maximum current rating for that trimmer no matter what position the wiper is at.

As usual with all resistances, it's not wise to use the full current capacity, instead consider whether you want to use 50% or 25% or 10% of maximum rating.

A 400mW 1k0 trimmer has a maximum current rating of 20mA.
I would never pass more than 14mA through and probably try to ensure <=6mA (9%) for normal operational use and 10mA (25%) for transients.
Click to expand...
 
#1,755
Output transistors

I built this amp a couple of years ago when i had a electronic project at my school. back then I used the schools lab power supply's to power it on the presentation. After this it was stored away. I think i bulit it with BC560, 2N1711 and the 15003 at the output. I've built the power follower before I bulit this one. Had det BOZ as the preamp. Now I think I'll retire the power follower and steel it's Toroid trafo and use it in this amp. Planing on building the B1 bufffer as a replament for the BOZ preamp. I'm very interested in the sanken 2SC3264 to see if I could get a little bit more out of this amp and does anyone have a bether replasement for Q3 (2N1711) or will this do with the sanken? 🙂
 
#1,757
Re: Output transistors

kimarin said:
I built this amp a couple of years ago when i had a electronic project at my school. back then I used the schools lab power supply's to power it on the presentation. After this it was stored away. I think i bulit it with BC560, 2N1711 and the 15003 at the output. I've built the power follower before I bulit this one. Had det BOZ as the preamp. Now I think I'll retire the power follower and steel it's Toroid trafo and use it in this amp. Planing on building the B1 bufffer as a replament for the BOZ preamp. I'm very interested in the sanken 2SC3264 to see if I could get a little bit more out of this amp and does anyone have a bether replasement for Q3 (2N1711) or will this do with the sanken? 🙂
Click to expand...
Why not build the newer version at
http://www.btinternet.com/~tcaas/jlhupdate.htm
 
#1,758
Cool

I think I'll have a goo at this modification, but is it possible to build it without 4 15003 , only 2 15003 at the output? I dont know if my case cab handle 4 of them ( Bouth my case from lcaudio.dk for several years ago, it was made for housing a 50 w push-pull class a amp named The End I think). Anyone know where I can buy print boards for this amp in europe ? I can buy from the states allso if no one knows any dealer in europe. I really loocking forward to fire up my amp again. I've been using a 2x90 w klass ab commersial cheap onkyo for the last 4 years on my B&W 803 matrix 🙂
 
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