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Burning Amp BA-3
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Old 24th April 2019, 03:24 PM   #2321
albapa is offline albapa
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I am trying to understand how the voltage gain is calculated in BA-3. The original article says "The voltage appearing at the Gate of Q3 is amplified by something less than the ratio of R10 divided by R8". I don't quite understand how the value of R8 influences the voltage, as I thought the gate resistance is so high that anything in series won't affect it. Thanks in advance.
I've found the corrected text in another topic, now it's a bit clearer.
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Old 15th May 2019, 03:49 PM   #2322
rafapb is offline rafapb  Brazil
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Hi! I am interested in building the complementary version of BA-3, but the PCBs are sold out at DIYaudio store. Does anyone have an idea of when those boards will be back on stock? Thanks!
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Old 15th May 2019, 05:45 PM   #2323
Itsmee is offline Itsmee  England
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Burning Amp BA-3
Alternativly, use some pucks with 0R1 ~ 0R22 source resistors
No need to use insulators (just goo) or to match up a bunch of FETs
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Old 15th May 2019, 06:39 PM   #2324
Itsmee is offline Itsmee  England
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Burning Amp BA-3
If you don't fancy the above (you would have to build the bias generators), use the F4 boards (see ZM's crippled F4 schematic)
Attached Images
File Type: gif F4-crippled-1.gif (20.3 KB, 303 views)
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Old 16th May 2019, 02:31 PM   #2325
rafapb is offline rafapb  Brazil
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So, the F4 boards are a direct replacement to the complementary BA-3 boards? Are there any adaptations to be made? I really don't know enough to do this if there is some engineering to be made to make this work...
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Old 17th May 2019, 10:41 AM   #2326
woofertester is online now woofertester  United States
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Originally Posted by rafapb View Post
So, the F4 boards are a direct replacement to the complementary BA-3 boards? Are there any adaptations to be made? I really don't know enough to do this if there is some engineering to be made to make this work...
Have you already acquired the transistors and boards for the front end of the BA3?

The complete BA3 is a 3-stage amplifier while the F4 is a 2-stage amplifier.

In addition, the BA3 has 6 pairs of output devices per channel while the F4 has 3 pairs of output devices per channel.

Do you just want an amplifier or do you really want exactly the BA3?

Answer the two questions above and it will be more clear what help you actually require.
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Old 17th May 2019, 01:13 PM   #2327
Russellc is offline Russellc  United States
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Burning Amp BA-3
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Originally Posted by woofertester View Post
Have you already acquired the transistors and boards for the front end of the BA3?

The complete BA3 is a 3-stage amplifier while the F4 is a 2-stage amplifier.

In addition, the BA3 has 6 pairs of output devices per channel while the F4 has 3 pairs of output devices per channel.

Do you just want an amplifier or do you really want exactly the BA3?

Answer the two questions above and it will be more clear what help you actually require.
No, BA3 has same output stage as F4, 3 pairs...would have to be mono blocks for 6 pairs.

Scroll down to pic of output boards:

BA-3 Amplifier illustrated build guide

You are correct about the front end. You probably got the idea of six pairs from various schematics of BA3, which do show six pairs. ( schematic with 6 pairs appears in same link above, just before pic of output stage.

I don't know if the complementary bias cards are the same for BA3 as F4, somehow the spare BA3 complementary output boards I bought some time ago for BBA3 monoblocks don't have bias boards with them....

Russellc
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Old 17th May 2019, 01:23 PM   #2328
6L6 is offline 6L6  United States
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Burning Amp BA-3
The standard BA-3 output stage is shown here with the bias board. The schematic shows 6 pairs, the PCB has 3 pairs, and the ability to daisy-chain additional PCB if you happen to have a large enclosure.

Click the image to open in full size.

As to the question of can a F4 pcb be used in lieu of the BA-3 output stage, (with the F4’s input buffer removed) the answer is yes, with very little modification. Being a simple mosfet follower stage with a clever bias circuit, the amp circuit is the same in theory and almost identical in details.
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Old 17th May 2019, 02:27 PM   #2329
Russellc is offline Russellc  United States
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Quote:
Originally Posted by 6L6 View Post
The standard BA-3 output stage is shown here with the bias board. The schematic shows 6 pairs, the PCB has 3 pairs, and the ability to daisy-chain additional PCB if you happen to have a large enclosure.

Click the image to open in full size.

As to the question of can a F4 pcb be used in lieu of the BA-3 output stage, (with the F4’s input buffer removed) the answer is yes, with very little modification. Being a simple mosfet follower stage with a clever bias circuit, the amp circuit is the same in theory and almost identical in details.
Just occurred to me the F4 is all in one so to speak, without separate bias cards like the BA3. I have complementary output boards I got for future BBA3 build, but when organizing things the other day, I don't have the bias cards. I guess When again available, I can rebuy them for the BBA3, and daisy chain these extra boards for a behemoth 12 output pair BBA3. Now to find 2 behemoth cases with requisite heatsinks.

Russellc
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Old 14th June 2019, 05:28 PM   #2330
escucalin is offline escucalin
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Quote:
Originally Posted by Russellc View Post
Just occurred to me the F4 is all in one so to speak, without separate bias cards like the BA3. I have complementary output boards I got for future BBA3 build, but when organizing things the other day, I don't have the bias cards. I guess When again available, I can rebuy them for the BBA3, and daisy chain these extra boards for a behemoth 12 output pair BBA3. Now to find 2 behemoth cases with requisite heatsinks.

Russellc
What chassis have you considered for such dissipation?
I still have to power up my balanced BA3 which accounts for the same 12 pairs and contrary to what i calculated i fear grose overheating in Dissipantes 500mm deep
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