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The BA-3 as preamp build guide
The BA-3 as preamp build guide
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Old 23rd June 2014, 11:14 PM   #11
bcmbob is offline bcmbob  United States
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Originally Posted by 6L6 View Post
None.
The power amp would have a few sets of input jacks, a selector switch and a pot. It doesn't need to be any more complicated.

Thanks. After thinking of the BA-3 Pre as a line stage (as stated in your post) I see attenuation only from the pot. Wasn't sure if any DC blocking needed to be added to the input of the output section/chassis in case a non-well adjusted Pass FE might be connected. Sounds like making the output stage independent/self-contained would be an interesting project on it's own. There are probably several examples of such somewhere around the forum.
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Old 23rd June 2014, 11:28 PM   #12
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
Quote:
Originally Posted by bcmbob View Post
Sounds like making the output stage independent/self-contained would be an interesting project on it's own. There are probably several examples of such somewhere around the forum.

Yes. You can find it here -

FIRST WATT F4

A guide to building the Pass F4 amplifier.
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Old 23rd June 2014, 11:43 PM   #13
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Old 27th July 2014, 10:17 AM   #14
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The BA-3 as preamp build guide
Any PCB available anywhere?

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Old 27th July 2014, 10:58 AM   #15
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
Yes - P-BAGSN-1V20 - Burning Amplifier Gain Stage for BA-3 (Requires bias boards and output stage; Makes 2 channels; Rev 2.0) - Circuit Boards

(Currently out of stock, there should be a reorder soon.)
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Old 27th July 2014, 06:33 PM   #16
delecoy is offline delecoy  United States
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Have my BA-3 FE up and running, and biased to about 45mv. But, I've observed no DC offset on R11 for either channel. Is this possible?
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Old 27th July 2014, 06:39 PM   #17
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The BA-3 as preamp build guide
R11 ?
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Old 27th July 2014, 06:45 PM   #18
delecoy is offline delecoy  United States
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Thank you for the quick response!. 0 at r12 too. So 45mv at R10, 0 and 0 at R11 and R12. Circuit is built exactly according to the original article, Toshibas all the way around, 9.6 ma for the matched jfets. Q3 and Q4 are not matched. I just set up my F4 last weekend and had to play with the bias and offset to get it right. So I was very surprised to see no offset on the BA3-FE. I have to have missed something somewhere. Set the bias the first time around with the input shorted, Then tried again without it shorted. Still no offset.
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Old 27th July 2014, 06:48 PM   #19
delecoy is offline delecoy  United States
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PSU is reading 24.0 and -24.2. Is the Peter Daniel universal board with LM317/337 regulators.
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Old 27th July 2014, 07:07 PM   #20
delecoy is offline delecoy  United States
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I see now. Sheesh...45ma...1 volt across R10, not 45mv.
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