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Old 9th September 2011, 01:31 AM   #721
Bigun is online now Bigun  Canada
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Hi Hugh,

The trouble is I don't really have space for power supply on-board with 3 channels on one heatsink. I'm not too concerned about it - if I like what I hear I can always scale up to build a no-compromise stereo but for my HT system this isn't warranted. I do like your pcb's though so I'll see if this flat-on-metal approach is feasible.

My version of Eagle doesn't have any blasted library items for a TO-264 package though.

What do you mean by the 'complementary approach' ? (sorry if I'm being thick !)
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Old 9th September 2011, 02:12 AM   #722
AKSA is offline AKSA  Australia
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Ah, complementary pairs means transistors identically placed but opposite gender supported from positive and negative rails......

Hugh
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Old 9th September 2011, 04:07 AM   #723
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by AKSA View Post
Ah, complementary pairs means transistors identically placed but opposite gender supported from positive and negative rails......Hugh
doh !


I've started the process of drawing a schematic into Eagle, the general concept is attached. The pcb will be around 75mm x 75mm for each channel. Ignore parts choices, those are just convenient to get the right physical package shape and size - it's the toplogy I need to get right at first.

Output stage is 'standard' AKSA / TGM1 / double EF. Any reason to use something different (all BJT) ?

What am I missing ? do I need to make provision for compensation caps ?
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Last edited by Bigun; 9th September 2011 at 04:09 AM.
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Old 10th September 2011, 05:15 AM   #724
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It is not a good practice to bypass electrolytic caps with film ones. Not only it do not reduce the impedance in the 10MHz bandwidth, but it increase-it, because the self of the electrolytic (around 15nh) makes a resonant circuit with the film cap. Better to use low ESR (ESL) electrolytics.or use some serial resistance to damp if we want to parallel with films ones.
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Old 10th September 2011, 05:43 AM   #725
Sheldon is offline Sheldon  United States
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Nico,

I infer that your BJT version is identical to the FET output version, except for the the output devices themselves. Is that correct, or were there other small changes?

Sheldon
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Old 10th September 2011, 10:36 AM   #726
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Quote:
Originally Posted by AKSA View Post
Gareth,

I can recommend the FetZilla mounting style. It saves space, confers very good cooling, and simultaneously mounts the pcb along with the output devices saving brackets, standoffs, and other messy options. And if you incorporate the power supplies too, you can minimise power supply lead inductance and make it easier to get going.
I couldn't agree more, not only that, I recommend you to do it in that manner. First Alex's PCB was like that.


Quote:
Originally Posted by AKSA View Post
I really like Andrej's complementary approach here, it sims extremely well with almost an evenly descending train of artefacts. My only concern is that you invariably need to set up tight balance between upper and lower halves with consequences for offset control, but aside from that, his approach to avoid AC coupling is inspired and innovative.

Cheers,

Hugh
DC offset is not even an issue in SSA amp, it is in range of +/-10mV no matter what, of course if the input pair is matched and thermally coupled.
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Old 10th September 2011, 10:40 AM   #727
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Originally Posted by Nico Ras View Post
This amplifier is capable to operate in VHF band depending on the transistors you choose.

Nico
Linear gain in VHF band, antenna load impedance and still stable as a rock.
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Old 10th September 2011, 10:44 AM   #728
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Originally Posted by Idefixes View Post
For Lazy Cat

Marc
Super, go for it !
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Old 10th September 2011, 10:48 AM   #729
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Quote:
Originally Posted by Nico Ras View Post
Hi Esperado

The praise should go to Lazy Cat, I merely contributed a small portion. I suggested a thread with each design complete with schematics simulation PCB layout and measurements, BOMs, etc. but it never took off.

To be honest my interest in the thread was that the design was just so refreshingly different that I was compelled to add my preferred output devices, the lateral mosfets.

Kindest regards

Nico
Very kind of you Nico. Thank you.

P.S. Some pics pls.
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Old 10th September 2011, 10:52 AM   #730
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Quote:
Originally Posted by Bigun View Post
Hi Hugh,

The trouble is I don't really have space for power supply on-board with 3 channels on one heatsink. I'm not too concerned about it - if I like what I hear I can always scale up to build a no-compromise stereo but for my HT system this isn't warranted. I do like your pcb's though so I'll see if this flat-on-metal approach is feasible.
After feeling a taste of the SSA a no-compromise stereo will come too, no doubt about it.
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