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Old 2nd July 2013, 12:15 AM   #2931
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Default Bootstrapped Clamp diodes?

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Originally Posted by linuxguru View Post
Please post the Baxandall VAS when you think it's ready for scrutiny.

Meanwhile, I stumbled upon an output stage which simulates pretty good in Class-A or Class-AB. The preliminary sims are with an output stage current of 5 mA.
....
At 4V into 600R, THD20 is mostly H2, with everything else at ~ -170 dBr. I haven't exhaustively checked stability, but the unity-gain small-signal response looks smooth and continuous, so it shouldn't be a problem.
Siva, this looks good.

Is this also how you have implemented the Bootstrapped Clamp diodes?

Can you post a .ASC and also your SPICE models please.
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Old 2nd July 2013, 08:35 AM   #2932
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Yup, that's the bootstrapped-clamp (I tried several variations, including one with a diode in series with the emitter of the NPN, one without the NPN, etc., and they're mostly equivalent in performance - just slight differences in the DC leakage current through the clamp diode, etc.).

The models are 100% stock LTSpice models - here's the .asc file ( a few values may have changed from the schematic posted earlier, as I keep trying to fine-tune it).
Attached Files
File Type: asc lf06s_v1.4_diamond.asc (9.2 KB, 78 views)
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Old 18th July 2013, 09:21 AM   #2933
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OK, just finished the layout of the circuit (with the new output stage, which I'll call the Diamond Cascode) in the previous post - managed to squeeze it into 0.6" x 0.6 " (15.2 x 15.2 mm) as before. Had to use 2x Rohm PNP duals for the Wilson CM, substitute the output SOT89s by SOT23s, 5x 0603 resistors (all the rest are 0805 as before), double-sided SMD.

I'm still mulling over the output BJTs - having a slightly larger footprint and SOT89s may be a better option. I'll play with the layout for a while before committing it for fabrication.

The output stage can be biased into Class-A, AB or B just by adjusting one bias resistor, R12. It might be worth using an SMD preset for that resistor, need to find one which is small enough.
Attached Images
File Type: png lf06d_sch.png (8.6 KB, 609 views)
File Type: png lf06d_brd.png (75.8 KB, 594 views)

Last edited by linuxguru; 18th July 2013 at 09:26 AM. Reason: typo
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Old 19th July 2013, 11:47 PM   #2934
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hi linuxguru,

Great work !

Usually you need to use vector fonts on Eagle PCBs otherwise the text moves when you generate the gerbers.

Options -> User interface.. -> Persistent in this drawing

regards
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Old 20th July 2013, 08:06 AM   #2935
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Quote:
Originally Posted by Greg Erskine View Post
Usually you need to use vector fonts on Eagle PCBs otherwise the text moves when you generate the gerbers.

Options -> User interface.. -> Persistent in this drawing
Thanks, I'll try it out. I presently handle it manually by looking at the rendering on the generated gerbers with a viewer like Gerbv, and adjusting the anchor and/or size of each text string manually until it fits and is positioned correctly.
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Old 21st July 2013, 05:38 PM   #2936
dadod is offline dadod  Croatia
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Quote:
Originally Posted by linuxguru View Post
Yup, that's the bootstrapped-clamp (I tried several variations, including one with a diode in series with the emitter of the NPN, one without the NPN, etc., and they're mostly equivalent in performance - just slight differences in the DC leakage current through the clamp diode, etc.).

The models are 100% stock LTSpice models - here's the .asc file ( a few values may have changed from the schematic posted earlier, as I keep trying to fine-tune it).
Hi linuxguru,
When I saw this yours opamp I thought that it will be good to use it in my ODNF power amp as ODNF helper opamp. More about here: ODNF or no GNFB power amp
I have a problem to have it working, it ascilate. Attached is LTspice zip file, and if you have suggestion what could be the problem, .ac looks OK to me, but .tran oscilate.
Thanks Damir
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File Type: zip GainWire-diamond-HEC-ODNF-power-linuxguru.zip (9.3 KB, 42 views)
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Old 21st July 2013, 07:26 PM   #2937
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Quote:
Originally Posted by dadod View Post
I have a problem to have it working, it ascilate. Attached is LTspice zip file, and if you have suggestion what could be the problem, .ac looks OK to me, but .tran oscilate.
I'm not sure what a servo opamp for ODNF or Error-Correction applications should be optimized for, but I'm guessing that you'll need a fast opamp (high GBW) and suitable compensation/stability mods. The cascoded VAS variant of the FET990 that Richard (kgrlee) posted earlier has (or can be made to have) higher GBW - you may want to look at that.

The component to play around with to improve stability of my variant is C1 on the ltspice simulation schematic, the Cherry compensation cap - try increasing it from 47pF to 100..150pF. Beyond that, THD20 will be adversely impacted, but it may or may not be an issue for an ODNF servo - I don't know.

(Monolithic fast opamps that could possibly be used for the ODNF servo include the LT1361 and 1364, apart from the LT1468 suggested earlier.)

Edit: I spotted a mistake in the way you've wired the Cherry compensation network - it needs to be connected to the output node of the opamp, not the inverting input (the mistake probably arose because I posted unity-gain buffer simulation schematics, where the output is also connected to the inverting input). Here's the corrected .asc file, and it works without oscillation in transient analysis, even with the original 47pF Cherry C1.
Attached Files
File Type: asc GainWire-diamond-HEC-ODNF-power-linuxguru-mod1.asc (21.2 KB, 47 views)

Last edited by linuxguru; 21st July 2013 at 07:44 PM. Reason: addendum
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Old 21st July 2013, 08:41 PM   #2938
dadod is offline dadod  Croatia
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Quote:
Originally Posted by linuxguru View Post
I'm not sure what a servo opamp for ODNF or Error-Correction applications should be optimized for, but I'm guessing that you'll need a fast opamp (high GBW) and suitable compensation/stability mods. The cascoded VAS variant of the FET990 that Richard (kgrlee) posted earlier has (or can be made to have) higher GBW - you may want to look at that.

The component to play around with to improve stability of my variant is C1 on the ltspice simulation schematic, the Cherry compensation cap - try increasing it from 47pF to 100..150pF. Beyond that, THD20 will be adversely impacted, but it may or may not be an issue for an ODNF servo - I don't know.

(Monolithic fast opamps that could possibly be used for the ODNF servo include the LT1361 and 1364, apart from the LT1468 suggested earlier.)

Edit: I spotted a mistake in the way you've wired the Cherry compensation network - it needs to be connected to the output node of the opamp, not the inverting input (the mistake probably arose because I posted unity-gain buffer simulation schematics, where the output is also connected to the inverting input). Here's the corrected .asc file, and it works without oscillation in transient analysis, even with the original 47pF Cherry C1.
Thanks linuxguru, I'll try that.
P.S. It's working now, how stupid of me not to see where the Cherry compenstion has to go.
Look the original thread for result.
BR Damir

Last edited by dadod; 21st July 2013 at 09:04 PM.
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Old 23rd July 2013, 09:21 PM   #2939
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Originally Posted by scott wurcer View Post
Once bottled spirits tend not to age. I once bought a bottle of Burbon bonded in 1916 and stored to avoid prohibition, lost and found in a warehouse in the 1980's. One taste and Scarface, the Godfather, and Al Capone all make sense.
Read the reviews on this one....
http://www.amazon.co.uk/Barrettine-M.../dp/B002ATI4VG


but my real favourites are Dalwhinnie, Caol Isla, Bowmore and a few others.
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Old 6th August 2013, 03:53 PM   #2940
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Has anyone assembled a working Wurcer opamp with real parts or are we still simulating? Thanks, Ray
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