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Old 12th June 2012, 12:12 PM   #51
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Hi Bonsai. Do you have this amp pcb set available for sale? Thanks.
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Old 12th June 2012, 02:11 PM   #52
Bonsai is offline Bonsai  Taiwan
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Hello Algar,
I am not planning to make his PCB available.

There are two other amplifiers in the works. A 15W Class A current feedback amplifier (the sx-Amp) and an 80 watt class AB current feedback design (the nx-Amp). These will be with full PCB layout and write-ups on my website for anyone to build. However, please note it will still be a few months. I like to build and test before publishing. Please be patient. Thanks for your interest.
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Old 12th June 2012, 02:53 PM   #53
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Tx for the info.
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Old 12th June 2012, 05:55 PM   #54
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Quote:
Originally Posted by Bonsai View Post
Hello Algar,
I like to build and test before publishing. Please be patient. Thanks for your interest.
Andrew, that is a novel idea, to build and test before publishing!!!
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Last edited by Nico Ras; 12th June 2012 at 05:59 PM.
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Old 13th June 2012, 01:08 AM   #55
Bonsai is offline Bonsai  Taiwan
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Ha ha.

I want to make sure i don't make an *** of myself.
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Old 26th June 2012, 09:28 AM   #56
wahab is offline wahab  Algeria
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Hi Bonsai

Here some sims of the original TEF step response as well as those
of a slightly modded version.

The idea of the latter is to reduce pre drivers agressive capacitive loading
by implementing a local miller loop , a solution find in many japanese amps.

The mod apparently reduce bandwith in small signal analysis , although
phase margin seems better by 15.

When checking the OPS in insulation , the modded version has in fact
better slew rate overall with more or less regular slope while due to
capacitive loading the original version exhibit a brutal reduction in slope.


The amplifier s step response with the two circuits , using only
two output pairs and 20R load :
Attached Images
File Type: gif BONSAI EA SR RISING HEDGE.gif (21.6 KB, 283 views)
File Type: gif BONSAI EA SR FALLING HEDGE.gif (23.1 KB, 281 views)
File Type: gif BONSAI EA.gif (18.9 KB, 288 views)
File Type: gif BONSAI EA MOD.gif (19.1 KB, 284 views)
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Old 26th June 2012, 02:25 PM   #57
Bonsai is offline Bonsai  Taiwan
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Wahab, looks like you put quite some effort into these sims. The networks between the bases of Q19 and Q28 and their associated rails in the diagrams above are not Miller compensation networks. They are damper networks, which along with the rail decoupling between Q19 and Q2 and Q11 and Q28 (not shown in your diagrams above) are designed to ensure that a Colpitts oscillator structure is not formed with the external circuit inductances. R1 and R9 (3.3 Ohm resistors) also aid in ensuring there is no parasitic oscillation in the output stage. I need to photograph the square wave response and post this up, but there is no overshoot on the final amp - note that the input filter is also part of the compensation network.

When looking at the compensation design, loop compensation has to be separated from parasitic prevention. The root causes of oscillation in these two areas are different.

I do measure slew rate with the filter disabled, but I don't think you can look at overshoot with part of the comp network (i.e. input filter) disabled.

In my write-up, note that when testing for squarewave response into an 8 ohm resistive load, this should be done by connecting the load before the output inductor - there should be no overshoot under those conditions. Again, when driving a normal load with expected capacitiance, then this is done with the load connected after the inductor and you can then expect to see ringing due to the tank circuit formed by the output inductor and the load capacititance.
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Old 26th June 2012, 08:14 PM   #58
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Hi Andrew,

What was the reason for your choice of input pair. Did you consider 2SC2240/2SA970 without the need of cascodes, or is there other advantages that I am missing perhaps.
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Old 26th June 2012, 11:29 PM   #59
Bonsai is offline Bonsai  Taiwan
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Hello Nico. I used 2N5550/5551 for the cascodes and 547/557 for the LTP's. I chose the 547/557"s because of their very high gain, but of course they are not rated for the 65V rail, and that's why I cascodes them.

You do get improved HF supply rejection with the cascodes as well.

Actually, the original proto used 5550/5551 without cascading, but I I struggled to select pairs near the upper part of the hfe range. There are no issues with this of course with the 547/557 pairs. I'll need to take a look at te types you mention - I have not used them before.
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Old 27th June 2012, 05:23 AM   #60
Bonsai is offline Bonsai  Taiwan
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Interesting Trannies Nico. Pd is 300mW so on 65V rails with 0.5 LTP current I am already dissipating 300mW, and on high output swing this will peak at over 600mW. (Another reason BTW for the cascodes was to limit the Pd in the diff amps)
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