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A BA-1 FE as preamplfier build thread
A BA-1 FE as preamplfier build thread
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Old 20th January 2018, 05:13 PM   #1
delecoy is offline delecoy  United States
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Default A BA-1 FE as preamplfier build thread

There are plenty of threads on the burning amps, but none on just the BA-1 FE as a stand alone preamp that I was able to locate. Starting this in the hopes it is needed....if not, ohhhh welllll

I have spare Antek AS-1220 and AS-1228 transformers, as well as multiple unbuilt Salas BiB kits and a few original peter daniel PS boards.

Here's my questions, to start:

Lightly ( LM317 ) regulated or shunt regulated power supply? ( I haven't built a shunt regulated PS yet )

How much gain will the BA-1FE make?

Can the BA-1 FE gain be easily adjusted?

Would a certain value of volume pot would be preferred? I have alps blue velvet 20K and 100K on hand already.

If this thread doesn't get deleted I fully intend to use it to ask a large amount of stupid questions that other people will greatly benefit from.


Last edited by delecoy; 21st January 2018 at 10:20 PM. Reason: More clarity
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Old 20th January 2018, 08:14 PM   #2
Zen Mod is offline Zen Mod  Serbia
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A BA-1 FE as preamplfier build thread
-reg whichever you prefer ; I always prefer shunt
- find resistors around input gates, marked 10K and 47K ; their ratio si gain of stage
-yeah , easily
-say that 20K pot is better, having input impedance of BA1 stage in account ...... and it's dominated by value of 10K resistor , already mentioned
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Old 20th January 2018, 08:30 PM   #3
Zen Mod is offline Zen Mod  Serbia
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A BA-1 FE as preamplfier build thread
I presume you know which elements from BA1 FE you don't need , for preamp duty ?
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Old 21st January 2018, 12:21 PM   #4
Goffe is offline Goffe  Sweden
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Click the image to open in full size.
I made the FE once but never listened. BA-3 came in between. Jfets are removable!
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Old 21st January 2018, 05:33 PM   #5
delecoy is offline delecoy  United States
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I found this in the article, on gain, but I'm not sure which parts to omit for stand-alone preamp use:

R201 through 204 form the balanced inputs networks. R201 = R203 and R202 = R204, and
the gain is R203/R201. Compensation capacitors C201 and C202 form the high frequency
roll-off for the gain, and while C201 is not strictly essential, it helps to retain the balanced input
common mode rejection figure at high frequencies. If you are interested in higher gain
figures, adjusting the values of R201 and R202 is a good place, as it minimally disturbs the
frequency compensation.

Thank you for the help
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File Type: png BA-1_FE_Schem.PNG (127.5 KB, 232 views)
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Old 21st January 2018, 05:46 PM   #6
delecoy is offline delecoy  United States
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Default Schematic

There is another schematic for the BA-1 FE in the BA-3 article:
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File Type: png BA-1_FE_Schem_2.PNG (61.3 KB, 259 views)
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Old 21st January 2018, 06:02 PM   #7
Russellc is offline Russellc  United States
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A BA-1 FE as preamplfier build thread
Thought I had a BA1 board. Nope, it is a BA2 board....

Russellc
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Old 21st January 2018, 06:03 PM   #8
Zen Mod is offline Zen Mod  Serbia
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A BA-1 FE as preamplfier build thread
+D is your output

you don't need C207 (that;s node to connect out of amp , for bootstrapping ; if you don't know what bootstrapping is , just ignore it

also , put bleeder resistor from output side of C203 (where D is ) to GND , to ensure that cap is always discharged , important not to zap amp when fiddling with interconnection

10 to 100K will do the job
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Old 21st January 2018, 06:13 PM   #9
WalterW is offline WalterW  Netherlands
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A BA-1 FE as preamplfier build thread
Quote:
Originally Posted by Russellc View Post
Thought I had a BA1 board. Nope, it is a BA2 board....

Russellc
Hahaa, they are the same both front ends

I received a few weeks ago, two PCB's from the store. Wanting to explore this classic circuit better and maybe put a 2SK79 in it as the output stage instead of the 610.
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Old 22nd January 2018, 02:47 AM   #10
6L6 is offline 6L6  United States
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A BA-1 FE as preamplfier build thread
I had a conversation with Nelson a while ago seeing if he had any suggestions on making the BA-1 front-end PCB into a linestage. He did, and was so kind as to make a modified schematic for this very purpose --

A BA-1 FE as preamplfier build thread-ba1-line-stage-copy-jpg
Attached Images
File Type: jpg BA1 Line Stage copy.jpg (199.9 KB, 390 views)
Attached Files
File Type: pdf BA1 Line Stage.pdf (14.4 KB, 62 views)

Last edited by 6L6; 22nd January 2018 at 02:49 AM.
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