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Old 10th May 2013, 04:23 PM   #2911
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Quote:
Originally Posted by Joshua_G View Post
Can you please post the Eagle schematic?
How much is the kit and what does it include?
Schematic attached - please PM me for the details of the kit (which will include the ENIG-finish board as shown in post #2901, all actives except the matched input JFETs (I can provide unmatched JFETs right now), all passives, and the gold-plated pin set).

Edit: The schematic shows a dual PNP Q4 for the current mirror, but the final layout that was fabricated actually uses separate SOT23 PNPs.
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Last edited by linuxguru; 10th May 2013 at 04:26 PM. Reason: addendum
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Old 10th May 2013, 06:35 PM   #2912
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Linuxguru: nice! Do you think +-23v operation would be feasible? If so I would love some kits
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Old 11th May 2013, 03:57 AM   #2913
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Quote:
Originally Posted by luvdunhill View Post
Linuxguru: nice! Do you think +-23v operation would be feasible? If so I would love some kits
Thanks. As shown, +/-23v operation is outside the Vds max of the cascode FETs, the VAS current source, and possibly the VAS buffer (bc549c). You'll need 50V-rated JFETs (there are some Sanyo/OnSemi SMD parts that may fit the bill) for the cascode and VAS CCS, and bc560c or any PNP rated at 50V or higher for the VAS buffer. The output BJTs, the VAS and the current mirror are fine for +/- 23V operation.
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Old 13th June 2013, 12:09 AM   #2914
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I'm totally late, so can someone please summarize what design(s) have been chosen, and why?
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Old 13th June 2013, 09:08 AM   #2915
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Quote:
Originally Posted by keantoken View Post
I'm totally late, so can someone please summarize what design(s) have been chosen, and why?
There are several parallel prototyping efforts:

1. Dale (dchisholm) is focussed on Scott's SWOPA with API2520 or larger footprint.
2. I have built working FET990 prototypes as well as the folded-Kaneda/Constellation,
with focus on compact DIP8 plug-in replacements in SMD.
3. Richard (kgrlee) is also focussed on FET990.
4. Several other designs remain in simulation.

(Any others in various stages of prototyping/simulation may please be added to the list).

IMHO, SWOPA will be practical in larger formats including professional API2520 or similar form-factors, while DIP8 form-factors may require a simpler topology like FET990 or something else. SWOPA in a stacked DIP8 is possible in principle, but I don't know of any effort in that direction yet (except maybe Scott's initial prototypes).
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Old 13th June 2013, 06:25 PM   #2916
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Is the OP still around? It would be really nice if the first post could be edited with some of this info of who is doing what, and with relevant post #'s in the thread.
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Old 14th June 2013, 12:23 AM   #2917
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Alternatively, a new thread could be started for that purpose.
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Old 14th June 2013, 12:30 AM   #2918
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Quote:
Originally Posted by benb View Post
Is the OP still around?
Here's how I obtained the answer to that question: First, I went back to post #1 in this thread. Next, I clicked on the username of the member who made post #1 a/k/a, the Original Poster ("EUVL"). Finally, I clicked on "Find more posts by EUVL". The diyAudio software returned them chronologically, most recent post first.

I screen-grabbed the most recent post; after reading it, I think the answer to your question is: Yes.
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Old 14th June 2013, 07:12 AM   #2919
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Quote:
Originally Posted by benb View Post
Is the OP still around? . . .
He is active on the Forum, but his last post to THIS thread was Post #2625 on 25 Jan 2013

Dale
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Old 14th June 2013, 09:03 AM   #2920
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Quote:
Originally Posted by linuxguru View Post
3. Richard (kgrlee) is also focussed on FET990.
I don't think I'm so much 'focussed on FET990' as attempting to achieve Guru Wurcer's SWOPA performance with a much simpler circuit.

In SPICE world at least, the circuits in #2060, #2321 & #2323 achieve this and in most cases, the THD residual is less spiky; even with less Iq .. ie less xover. Guru Wurcer points out it is possible to Muntz these even further without losing performance.

#2062, #2083, #2183, #2306 have more and include comparisons with SWOPA.

The thread from #2324 - 2350 has some interesting discussions.

BTW, my main illustrative performance figures are at 10Vp @ 600R with 40dB gain ... and voltage follower 3.162Vp @ 15R.

In #2801, linuxguru demonstrates enhanced voltage follower performance up to near clipping. To match this, the i/p cascodes become u309.

keantoken also demonstrates elsewhere that bc550/560 are best at low Vce.

Hence, my present favourite circuit is as attached though I've not touched it for 3 mths and need to apply some of the tools I've learnt to use in the intervening period .. eg Tian probes & the THD Analyzer.
_______________

2 factors give this simple circuit performance rivalling even Guru Wurcer's SWOPA.
  • pure Cherry compensation
  • keeping the Holy HiZ VAS output clear of evil stuff like clamping diodes. The remaining distortion in the JE990 is almost all due to evil modulated C of the diode.
There was some talk about bootstrapping the evil clamp diode but no one has posted any results.
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