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Old 12th April 2007, 12:15 AM   #41
GK is offline GK  Australia
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Quote:
Originally posted by bogdan_borko
MINI CLASS A?

good joke !

Well at 12W rms into 4 ohms, it isn't the Morris Major of class A amplifiers, isn't it?
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Old 12th April 2007, 01:54 AM   #42
fab is offline fab  Canada
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Quote:
Originally posted by G.Kleinschmidt
Finally.....just finished the amplifier PCB. There have been a few minor changes to the circuit. I'll update it over the next couple of days. Now I have to go and eat dinner.

Bye bye.
Wow that is really a STAR Ground !


Do you also isolate the input/feedback circuit ground from the high power ground?
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Old 12th April 2007, 09:35 AM   #43
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Quote:
Originally posted by fab


Wow that is really a STAR Ground !


Do you also isolate the input/feedback circuit ground from the high power ground?

Now even more starry (I got a little artistic while tidying up the component overlay – se attached picture). I also moved the NFB pick-off point to a more optimal position. That pretty much finishes it all off. Now I can move on to the regulator board

There is a separate ‘small signal’ ground on the amplifier PCB, isolated from the main power ground by R1. This isolated ‘small signal’ ground also connects to the GND terminal of the input RCA socket, which is isolated from both the amplifier chassis and the ‘small signal’ ground of the other channel.

Cheers,
Glen
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Old 28th January 2008, 12:21 AM   #44
m_buzzi is offline m_buzzi  Switzerland
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Hi,

Since I'm trying many vas stages I would like to see, if possible, the final schematic of your amp which seems to be available no more.

Could you link it here or mail me at michele.buzzi@[nospam]gmail.com? (cut off the [no spam])


Thanks,
Michele
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Old 28th January 2008, 11:11 PM   #45
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Quote:
Originally posted by m_buzzi
Hi,

Since I'm trying many vas stages I would like to see, if possible, the final schematic of your amp which seems to be available no more.

Could you link it here or mail me at michele.buzzi@[nospam]gmail.com? (cut off the [no spam])


Thanks,
Michele

Sorry that I don't have my webpage up anymore. I'll try to get the schematic out by the end of the week - the computer it is on / study stuff is currently upside down due to home renovations.

Cheers,
Glen
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Old 28th January 2008, 11:33 PM   #46
m_buzzi is offline m_buzzi  Switzerland
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Hi,

Many thanks, I will wait some notice for you!

Michele
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Old 29th January 2008, 05:20 AM   #47
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OK, I don't have access to the original schmatics ATM, but I just redrew the cct from memory in LTspice (had a little free time).

The schematic is a bit crappy (resolution / file size constraints) but it is readable.

THD-20kHz sims as follows:

1W / 4 ohm
0.000053%

12W / 4 ohm
0.000946%


OPS bias current is 1.5A

I have built a prototype unit and confirmed the ~10ppm THD-20.
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Old 29th January 2008, 05:22 AM   #48
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50kHz full power squarewave.
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Old 29th January 2008, 05:23 AM   #49
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Clipping
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Old 29th January 2008, 06:07 AM   #50
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The input filter (R39/C9) was a little heavy. Here is the 50kHz squarewave response with C9 reduced from 1n to 330pF
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