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The BA-3 as preamp build guide
The BA-3 as preamp build guide
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Old 28th December 2018, 12:06 PM   #1331
McQuaide is offline McQuaide  United States
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cheer up

with mileage , I'm not smarter .... I'm just better in recognizing when short circuit between headphones is too dangerous to proceed


The problem was being off work and having too much time!

Signal chain is now all PassDIY (except when I swap the F5 with the Fisher 400). Having such simple circuits with so few caps in the chain makes for exceptional attack, dynamics, and clarity. I find I don't need as much volume to get a satisfying sound level.
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Old 12th January 2019, 08:30 PM   #1332
MEPER is online now MEPER  Denmark
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I have just adjusted bias on BA3-pre. Voltage is +-26.5 V. The temperature on heatsink of output transistors is 65 C. Is this considered OK or is it a bit on the high side? ….I assume that junction is well inside the limit. I could reduce voltage to 24V then I would probably get below 60 C on heatsinks.
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Old 13th January 2019, 02:32 AM   #1333
nashbap is offline nashbap  United States
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I have just adjusted bias on BA3-pre. Voltage is +-26.5 V. The temperature on heatsink of output transistors is 65 C. Is this considered OK or is it a bit on the high side? ….I assume that junction is well inside the limit. I could reduce voltage to 24V then I would probably get below 60 C on heatsinks.

I think 65 is too high. Is that with lid on or off?


What is the bias you are running at?


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Old 13th January 2019, 09:28 AM   #1334
MEPER is online now MEPER  Denmark
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What is lid?


Upps…….I just se my error now looking at the schematic again. I have adjusted bias by having 2V over the 22 ohm resistors (R10, R11) so I have double bias current. Backing off to 1V will solve all problems...…...or even 1.5 V.
Are there any advantages running higher bias that specified?
Now I know where the limit is using the small heatsinks……..by accident.. :-)
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Old 13th January 2019, 09:45 AM   #1335
MEPER is online now MEPER  Denmark
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Now I see…...lid = top cover?
No.....it was open.....so a couple of degrees more heat can be expected when lid is on. But I ordered top cover full vented so ventilation will be good.
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Old 13th January 2019, 02:08 PM   #1336
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The BA-3 as preamp build guide
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Are there any advantages running higher bias that specified?
Not really. Any advantage there might be in decreased distortion can be tuned much more easily and effectively with P3.
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Old 17th January 2019, 10:40 PM   #1337
MEPER is online now MEPER  Denmark
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I noticed using these Galaxy chassis that there is no galvanic connection from the bottom to the side panels so signal and safety ground is only the bottom. Is that a problem? …..I am more concerned about noise than the safety.
The way the bottom and top is connected to the side panels via the nuts in the rails does not make a galvanic connection when the small screws are in place. At least not in my Galaxy chassis. Something more "violent" has to be done to penetrate the black layer and aluminum oxide layer.
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Old 17th January 2019, 10:41 PM   #1338
6L6 is offline 6L6  United States
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The BA-3 as preamp build guide
Sandpaper or a file and rough up a spot on each touching panel.
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Old 18th January 2019, 07:24 AM   #1339
MEPER is online now MEPER  Denmark
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OK.....I "worked" the bottom and top screws a lot by loosen and fasten them a few times and it seems I succeeded in getting connection from top/bottom to side panels and also to front / back panels. Will recheck later to see if connection is persistent.
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Old 2nd February 2019, 01:15 AM   #1340
lae2 is online now lae2  United States
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My apologies for such a neophyte question. Is the volume control simply shunted across R1. I have not found a schematic for the build guide. If the volume control was implemented for the full blown BA3 push/pull, would the result simply be an integrated amplifier? Is there a DIY project for building BA3 push/pull as a integrated amplifier. Thank you for commenting.

Last edited by lae2; 2nd February 2019 at 01:18 AM.
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