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Old 2nd March 2014, 02:50 PM   #3941
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Quote:
Originally Posted by cwtim01 View Post
Thanks both. LSK170 is indeed an option, but the cost of 8 pieces of LSK + shipment is probably enough to get 50 pieces of BF862 locally so I'll try the latter. Hopefully I can find a few matched pair towards the 10mA side, otherwise will try lowering the DC voltage as suggested by Andrew.
If you going to use BF862, try Juma version
BF862 Preamp

Didiet
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Old 2nd March 2014, 03:11 PM   #3942
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Quote:
Originally Posted by AndrewT View Post
bf862 is smd.
The parameters are a good substitute for the k170.
They run @ Idss with 10Vds so will be warm. Might be good to add a copper or aluminium flag to the case and keep big trace areas to cool the lead outs.

two channels of the B1 needs 4 off k170 (either lsk170 or 2sk170)
two channels of the DCB1 needs 6 off k170 (either lsk170 or 2sk170)
The other transistors in the DCB1 are BJT, or do not need to be low Vp, high gm, devices.

I wonder if the DCB1 would be better at +-8Vdc, when using the SMD BF862 to help reduce temperatures?
If so, the BF862 version could run on 12+12Vac transformer.
I've never noticed the JFETs having a temperature problem.
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Old 2nd March 2014, 03:26 PM   #3943
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cwtim01,

You should still be able to get some matched jfets from Spencer (FET Audio | Hi-End Audio Projects) and I think he's local to you.

Cheers,
Dennis
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Old 2nd March 2014, 04:07 PM   #3944
cwtim01 is offline cwtim01  Hong Kong
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Quote:
Originally Posted by Dennis Hui View Post
cwtim01,

You should still be able to get some matched jfets from Spencer (FET Audio | Hi-End Audio Projects) and I think he's local to you.

Cheers,
Dennis
Thanks Dennis, from the FET Audio site it seems Spencer is now in Singapore, though I'm not sure.

Anyway, for around the same price of 1 matched pair of 2SK170BL from Spencer, I just order 100 pieces of BF862 (plus adapters below).

Click the image to open in full size.
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Old 2nd March 2014, 04:17 PM   #3945
cwtim01 is offline cwtim01  Hong Kong
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Quote:
Originally Posted by didiet78 View Post
If you going to use BF862, try Juma version
BF862 Preamp

Didiet
Thanks Didier for the link, for the past 3 weeks I've been making quite some effort to understand how the B1 and DCB1 works, so will try to build them first.

The Juma version also seems very interesting, and the thread even contains the Gerber files so it's pretty easy to print a PCB (it quite cheap to print a PCB in China and ship to HK), so I might try that out later.
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Old 2nd March 2014, 04:43 PM   #3946
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Quote:
Originally Posted by cwtim01 View Post
Thanks Dennis, from the FET Audio site it seems Spencer is now in Singapore, though I'm not sure.

Anyway, for around the same price of 1 matched pair of 2SK170BL from Spencer, I just order 100 pieces of BF862 (plus adapters below).

Click the image to open in full size.
Wow...where you are you getting these adapters?

Dennis
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Old 2nd March 2014, 10:28 PM   #3947
cwtim01 is offline cwtim01  Hong Kong
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Search for "SOT23 adapter" in ebay and you'll find them. I order from electronic stores in China directly which is much cheaper, but it's not possible to deal with them in English.
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Old 4th March 2014, 12:55 PM   #3948
massimo is offline massimo  Italy
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Thank you for spotting those adaptors cwtim! Look great.
@ less than .20 USD ea. shipped from HK they aren't expensive.... did you pay less?
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Old 4th March 2014, 02:59 PM   #3949
cwtim01 is offline cwtim01  Hong Kong
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I paid 8 USD for 200 pieces (including 600 number of angled pins below), plus 5 USD for shipment - averaging .065 USD per piece include shipment, from the Chinese online market called TaoBao.

Anyway, they're cheap enough so eBay is fine

Click the image to open in full size.
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Old 11th March 2014, 03:41 PM   #3950
cwtim01 is offline cwtim01  Hong Kong
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First time to solder SMD parts, it turns out to be easier than I thought. I have a question about idss matching though.

I've measured the Idss (@12V, as I have no 10V source around) of 40 pieces of BF862, and got some matched pairs. I would like to know if it's better to use a loosely quad-matched for the 2 channels of B1, or 2 closely matched pairs.

Idss of Quad matched: 14.89,14.93,14.98,14.99mA
Idss of 2 matched pairs: 15.81,15.81 and 15.90,15.91mA
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File Type: jpg BF862.jpg (182.2 KB, 264 views)
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