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B1 Buffer Preamp
B1 Buffer Preamp
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Old 8th March 2018, 05:11 PM   #4421
Mixi is offline Mixi  Europe
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Quote:
Originally Posted by tborzic View Post
Hi, Would it be possible to increase R1 a bit in order to lower PSU voltage?
I will be using 20V PSU, so I was aiming towards recommended voltage, especially if BF862 would be in question.

If possible, is there a need for changing C1 also, since R1 and C1 are working/acting as noise filter?

Thanks
Isn't the recommended voltage range 18-24V? So i guess 20V should be perfectly fine. On another forum people mentioned using it with power supply as low as 9V with good results.
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Old 4th April 2018, 03:25 PM   #4422
fgroen is offline fgroen  Netherlands
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I run my B1 off a symmetrical power supply with matched FETs, and did away with the input and output caps. Output offset is non-existent. Very pleased with the result.

I was wondering whether anyone has tried different JFETs, as the properties due to the buffer character may be a bit less critical compared to circuits with more than unity gain. I have procured some CPH3901's so will give them a try soon.
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Old 5th April 2018, 09:42 AM   #4423
Stanislav is offline Stanislav  Australia
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I have a B1 with 2sk369-GR.
It's been running for a good 3-4 years now. Magnificent!

Also ACA with 2sk369-BL (actually 5 channels). All good.

Soon will try it with the old 2N3819 (horror, horror!!!) cause I have hundreds of them.
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Old 5th April 2018, 10:54 AM   #4424
fgroen is offline fgroen  Netherlands
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The 2N3819 has an yfs between 3.0 and 6.5mS. Could that be the culprit?
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Old 5th April 2018, 11:06 AM   #4425
Stanislav is offline Stanislav  Australia
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It could be, but I guess if you parallel a few that can change.
Of course keep an eye on the Id and dissipation, maybe cascoding will help.

2n3819 is an exercise for the sake of it, as I said I have many of them and would prefer to use them one way or another than discard them.
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Old 12th August 2018, 03:28 PM   #4426
Skylar88 is offline Skylar88  South Africa
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I have this image in my archive for connecting a second output. I'm wondering why the negative line is not connected to the same point as the first output's? (shown in green in the second image)

In the first image, Output 1 has a 221K resistor to ground, but Output 2 doesn't.

Can someone shed some light, please?

B1 Buffer Preamp-output-schematic-png

B1 Buffer Preamp-output-schematic-question-png
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File Type: png Second Output Schematic.png (403.3 KB, 436 views)
File Type: png Second Output Schematic - Question.png (318.0 KB, 434 views)
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Old 12th August 2018, 03:35 PM   #4427
Itsmee is offline Itsmee  England
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Both are incorrect, duplicate R204 & R205 for the second output.
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Old 12th August 2018, 08:16 PM   #4428
Itsmee is offline Itsmee  England
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Quote:
Originally Posted by Itsmee View Post
Both are incorrect, duplicate R204 & R205 for the second output.
I was a little too quick, you can use the first one, it's just me, I would add R205.
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Old 12th August 2018, 09:35 PM   #4429
Skylar88 is offline Skylar88  South Africa
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Thanks Itsmee. I had confirmation from a different source that the first one is correct.

However, your suggestion to add R205 makes sense. Easy to check with and without, though.
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Old 30th August 2018, 02:32 PM   #4430
Niceonecyril is offline Niceonecyril  United Kingdom
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B1 Buffer Preamp
Default B1 Buffer, BF861B + Baffle step filter

If anyone's interested, I just completed this circuit, a baffle step filter sandwiched between two B1 type stages. Front and back of circuit same as B1. JFET's chosen for about 9mA Idss bottom, 10mA Idss top. For 20V, well within the maximum power and voltage specs for BF861B. Initial impressions sounding very good c/f existing LSK170-based B1. 4dB correction seems to be fattening the sound of my ACA/Coniston's 4-foot off rear walls nicely. Need to do much more listening now.
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File Type: jpg IMG_0774.JPG (962.1 KB, 64 views)
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