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Old 5th October 2013, 07:02 PM   #2981
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Are any of the constant current sources or sinks in the Wurcer op amp Wilsons and do the transistors need to be not only matched but thermally coupled to one another to prevent drift. I'm referring to the CCS above the FET cascode and the sink below. Thanks, Ray
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Old 6th October 2013, 08:45 AM   #2982
AndrewT is offline AndrewT  Scotland
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Originally Posted by gentlevoice View Post
........An oscillator would be interesting although I don't really know how to design one with low THD which would be my aim here..........
JLH and others have shown low distortion oscillators.
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Old 11th October 2013, 03:07 AM   #2983
RNMarsh is online now RNMarsh  United States
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You can buy an single fixed frequency oscillator on eBay from Victor. Single freq per small pcb and the lowest thd on the planet. Low cost- fully loaded and ready to run. You supply power and chassis to put it inside.

Thx-RNMarsh
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Old 31st October 2013, 03:47 PM   #2984
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Originally Posted by linuxguru View Post
Scott has built working SWOPAs, for sure - but I don't know about any others. I have built a 1st-gen FET990 variant with real parts and may build a 2nd-gen variant with a Diamond Cascode output stage later - it depends on the interest from the Gainwire/ODNF folks, who have some interest in using a discrete opamp for the error-correcting servo.
Linuxguru, RNMarsh has kindly offered to test your FET990 samples.

He's one of the few people in the known universe that can reliably measure THD20k below 1ppm.

I've sent you a message about how we should organise this.

It would be really nice to do this and establish an important bridge between the 'real world' and SPICE world.
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Old 31st October 2013, 04:09 PM   #2985
1audio is online now 1audio  United States
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I have similar capabilities and would be happy to make measurements. If you are in the bay area it would be easy to get together.
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Old 31st October 2013, 04:26 PM   #2986
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Originally Posted by kgrlee View Post
Linuxguru, RNMarsh has kindly offered to test your FET990 samples.
OK, I've built a few 1st-gen FET990 modules so far - I'm awaiting an EBay transistor tester which will allow Idss matching of SOT23 JFETs more easily. I'll make an additional pair of the 1st-gen modules with matched devices shortly.

Preliminary 2nd-gen layout (with the bootstrapped VAS clamp, Diamond Cascode O/P stage, etc.) is ready, just holding off on board fabrication to see if anything else can be incorporated.

At the moment, I have Toshiba 2sk209 FETs for the input LTP - will eventually go with BF862 (higher Yfs) once I can find a reliable local source. Are these EBay BF862s, claimed to be manufactured by Zetex, authentic?

http://www.ebay.com/itm/10PCS-BF862-...-/300880906571

Edit: Link above appears not to work, please search for BF862 in the EBay search box.

For the VAS, there seems to be no SOT23 PNP that's much better than the ubiquitous BC856B - any suggestions? The low Ccb alternatives are BF550 and BF821 - both possibly with much lower gain than the BC556B (not sure if the VAS beta is relevant - the VAS emitter-follower/buffer can be a high-beta device like BC859c).

Last edited by linuxguru; 31st October 2013 at 04:33 PM. Reason: addendum
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Old 31st October 2013, 04:46 PM   #2987
rsavas is offline rsavas  Canada
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Are these EBay BF862s, claimed to be manufactured by Zetex, authentic?
What? only NXP makes them. They are so cheap, buy them form Mouser/Digi-Key or any other NXP disti.
I'd like to see the link to the teester pls.
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there seems to be no SOT23 PNP that's much better than the ubiquitous BC856B - any suggestions?
According to the BC856 DS the complement is BC846
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Old 31st October 2013, 04:57 PM   #2988
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Originally Posted by linuxguru View Post
Preliminary 2nd-gen layout (with the bootstrapped VAS clamp, Diamond Cascode O/P stage, etc.) is ready, just holding off on board fabrication to see if anything else can be incorporated.
One candidate output-stage enhancement is a low-distortion buffer from Kenpeter and Elvee on this board, called Ken's Diamond (actually, not a diamond buffer - it has more in common with the Taylor source-follower):

four transistor emitter follower (diamond buffer) as power output stage?

It uses 6 BJTs (2 more than the Diamond Cascode) and a voltage reference, but gets rid of one CCS (typically a JFET). That also frees up the rail voltage limits (now limited to about +/-15V because the JFETs that are best suited for CCS duty are limited to 30V Vds). Board area is likely to be of the same order as (maybe a bit higher than) a Diamond Cascode because 6-pin duals can be used for 4 of the BJTs.

Let me run it through the sims for a while and see how it goes.
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Old 31st October 2013, 05:04 PM   #2989
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What? only NXP makes them. They are so cheap, buy them form Mouser/Digi-Key or any other NXP disti.
I'd like to see the link to the teester pls.
Shipping charges to India from Mouser/Digikey are steep - it would be great to have a reseller who can ship cheaply from North America by first-class mail or similar.

For the EBay tester, please search for "M328 Transistor Tester" in the EBay search box (deep links into EBay don't seem to work now).
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Old 31st October 2013, 05:28 PM   #2990
rsavas is offline rsavas  Canada
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Yup ebay is a total waste these days, it times out on me.
I can be a re-seller that will ship post to you. Make me an offer, you can probably use my paypal account to transfer funds. I have BF862 is my stock. Have you looked at KSC1845/KSA992 and the smt versions fjv992/1845?
I have a pending Mouser order. I wait til I get to $200 as shipping is free for me.
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