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Old 15th August 2011, 02:15 PM   #231
Salas is online now Salas  Greece
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I see 35V 10mF filters on board 1.4. Isn't meant to be 50V? Because ~35VDC is the rails spec, no?
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Old 15th August 2011, 03:03 PM   #232
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Salas, I used a 22-022V transformer so I only needed 35V caps. You can run this design to 55V if you please and then 63V caps is the obvious choice. My calculation (22VAC - 1.4V)x1.414 plus 10% mains variation = 32V then 35V caps are fine.
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Old 15th August 2011, 03:09 PM   #233
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Alex's board is nicer looking than mine so uses Alex's board. I just showed what I use for interest sake. My track are fairly narrow and pads are small which is not so great if you are going to etch at home, my PCBs are commercially made.

Alex what Salas said regarding 50/63V caps makes good sense if there are people who want to push the power envelope a little, all I wanted to do was confirm that the amp sounds as good as it is simple. It does.

Nico
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Old 15th August 2011, 03:16 PM   #234
Salas is online now Salas  Greece
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Did you measure the amp's power on some dummy when using the 2x22VAC Tx?
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Old 15th August 2011, 03:39 PM   #235
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Today I made some measurements with the SSA BIGBT exact sch post #217

As you can see from the Tex scope plots, CH1 input signal, CH2 output signal:

- first plot, fs = 1 kHz, Av = +21,44 dB, phase shift = 0
- second plot, fs = 2 MHz, Av = +21,68 dB, phase shift = -24

I also measured/calculated the output impedance at 1, 10 and 100 kHz, 4 ohm load and it is 180 mohm in all cases, which will also be improved with higher voltage gain in the second stage, later in the process.

So I intend to prepare SSA sch, mosfet driver/BJT output, soon.

P.S. Input signal at 2 MHz is a little bit more rounded than at 1 kHz because of the signal generator upper limit distortion. As you can clearly see on the plots, output signal corectly followed this anomaly.
In the whole SSA amp there were no compensating capacitors whatsoever, only three electrolytic caps for DC potentials smoothing.
Attached Images
File Type: jpg SSA 1kHz.JPG (552.7 KB, 1553 views)
File Type: jpg SSA 2MHz.JPG (563.1 KB, 1400 views)

Last edited by Lazy Cat; 15th August 2011 at 03:59 PM.
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Old 15th August 2011, 08:34 PM   #236
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Quote:
Originally Posted by Salas View Post
Did you measure the amp's power on some dummy when using the 2x22VAC Tx?
18.1V(RMS) into 8,2 Ohms
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Old 15th August 2011, 08:47 PM   #237
Salas is online now Salas  Greece
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Thanks. That's 40W. Not bad. At what DC bias? The sensitivity is on the low side. Something like 16dB? Would it go much more THD if fixed at say 28dB? Is there enough OLG?
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Old 16th August 2011, 06:42 AM   #238
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Salas, I adjusted the gain to work with my pre-amp out which is 2V p-p. I have not checked OLG, but the BW is huge so I cannot see a problem increasing gain a tad.

I have not decided what final bias should be, it sounds nice as it is. On the week-end I will set up the spectrum analyser and see what bias offers the best harmonic distribution. Just by listening it is hard/impossible to tell.
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Old 16th August 2011, 09:00 AM   #239
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For the full power measurements I will prepare some 200VA transformer/60mF caps bank running on +/-35V, as specified as Safe Operating Area for one output pair in SSA.

Until now I have used 1,5A limited power supply for the safety reasons, like always at the begining of any new power amp's life.

I also calculated the propagation delay in the 2 MHz Tek plot from input to output waveform which is exactly 33ns, I suppose due to parasitic capacitances sumed from all semiconductor parts together and current layout (spider network). This figure maybe improved or not with the use of a neat PCB like Alex or Nico made, will find out later.

P.S. The propagation delay in 1kHz plot is of course the same 33ns, only that it is not visible in 500us/DIV time domain sweep.

Last edited by Lazy Cat; 16th August 2011 at 09:13 AM.
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Old 16th August 2011, 03:41 PM   #240
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In simulation it is actually 29nS. I doubt if one can do much better than 33nS, Lazy Cat that is excellent!!

Nico
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