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Old 23rd January 2010, 06:12 PM   #1
Bigun is online now Bigun  Canada
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Default Bigun's Botch Up amplifier

I've been thinking (and talking) about building something simple in Class A.

It's a junk box project, nothing fancy, trying to use whatever I can get my hands on. So I won't be making any pcb's.

From a pair of Acopian psu's I scavenged 4 Trafo's and 4 panel meters, so 1 Trafo and 1 meter per amplifier makes for 4 'experiments'.

A colleague gave me 4 metal boxes, used (cut outs) which are too small. In fact they can just fit in the Trafo. I've got some extruded heatsink that's not that beefy but I can cut it up and attach it to the sides of the boxes.

I'm thinking only low power, a few W for use with a single driver full range speaker.

With too little space in the box, inadequate heatsink it's going to be a real BOTCH UP

First up will be something JLH'ish. After 'borrowing proudly' from others who have gone before me the first circuit is looking like a simple JLH Follower. The output devices will be compound pairs to increase their input impedance. Unlike the original JLH I'm going to use only Sziklai pairs.

A couple of images, one of the parts I have on hand, the other showing the Follower. My CD player puts out a strong signal but I'm considering a preamp.
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File Type: jpg sch copy.jpg (55.2 KB, 1106 views)
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Old 23rd January 2010, 08:52 PM   #2
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Default This kind of amplifier sounds delicious and is easy to build

enjoy!

regards,

Carlos
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Old 24th January 2010, 02:55 AM   #3
AKSA is offline AKSA  Australia
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Gareth,

I believe 160uA flowing through Q5/Q3 is insufficient; you might consider ramping this up to a mA or so in order to strongly drive Q1 and Q2. You would then need to trim R3 down to a similar current; but even so, you still have two CCSs fighting each other. I think it would work well, however, and give you that lovely SE sound.

Innovative circuit!

Hugh

To do this, I believe you'd need only put in a resistor of 680R from base Q2 to ground, and
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Old 24th January 2010, 04:11 AM   #4
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Hi,
Quote:
I think it would work well, however, and give you that lovely SE sound.
Hardly.
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Old 24th January 2010, 05:21 AM   #5
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Cool, it has shades of JLH. (but also different)

CFP's decrease output impedance over the traditional Darlington, by dividing the masters' Gm.

Should be totally stable into any load.

If you just put a 680 ohm resistor across the Vbe of Q2, Q1 will work harder and take a little more of the power. So if you're worried about balance, you might add the same value resistor across Q1.

- keantoken
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Old 24th January 2010, 11:51 AM   #6
Bonsai is offline Bonsai  Taiwan
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Bigun, a few tweaks needed - AKSA has pointed the way. Looks very interesting. Looking forward to seeing the results.
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Old 24th January 2010, 12:10 PM   #7
Mooly is offline Mooly  United Kingdom
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I'm afraid Lumba is correct...
haven't we forgotten something
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Old 24th January 2010, 12:20 PM   #8
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Hi,
an example of single-ended input/output topology.
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Old 24th January 2010, 12:31 PM   #9
wahab is offline wahab  Algeria
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this circuit, as posted, will not work at all...
better to redefine the thing from scratch...
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Old 24th January 2010, 01:07 PM   #10
Bonsai is offline Bonsai  Taiwan
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It needs a few tweaks and a few corrections, but I like the simplicity.

For starters, Q3 needs a clearly defined load.

. . . . off you go Bigun.
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