The BA-3 as preamp build guide

Jump to Latest
D

Dennis Hui

Member
Joined 2002
Paid Member
myleftear,

If you want to use the VRDN for +/-24V without the de-noiser you can leave
out all the parts after the J3 and J4 jumpers. Also you need to make small
adjustments to the LM317/337 programming resistors since the values in the
VRDN schematics limit things to about +/-20V. (For example, increasing
R7 and R10 in the VRDN schematics here
https://www.diyaudio.com/forums/att...level-ckts-11v-20v-1-5a-de-noiser-figure1-png )

Please see https://www.ti.com/lit/ds/symlink/lm317.pdf, section 9 for more details.
 
myleftear

myleftear

Member
Joined 2017
Paid Member
Dennis Hui said:
increasing R7 and R10 in the VRDN schematics.
Click to expand...



6L6 said:
220R from OUT to ADJ, 4K from ADJ to GND.
Click to expand...



Hi guys
Did I get it right this time?
Thank you!

PS: Is the denoiser restricted to 20 V too, so that it wouldn’t work on 24V (or not without further tweaks)?
There‘s a already populated VRDN laying around, which I could use (even though it’s blue :) ), and since the denoiser can be just disabled by that bridge...
 
myleftear

myleftear

Member
Joined 2017
Paid Member

Attachments

  • VRDN-scm.png
    VRDN-scm.png
    474.8 KB · Views: 452
D

Dennis Hui

Member
Joined 2002
Paid Member
You're interested in the resistance from the ADJ pin to ground. In this case,
this means the group R7/R8/VR1 (for the LM317) and
R10/R9/VR2 (for the LM337) As Jim wrote, when these groups are at 4K,
you have about +/-24V. How you achieve that is up to you, but changing
R7 and R10 to 4K will give you a min voltage of about +/-24V.

If you use 2.5K for R7 and R10 you should be able to adjust from
about +/-15.5V to +/-25V

You still need to set the J3 and J4 jumpers.
 
Mark Johnson

Mark Johnson

Member
Joined 2011
Paid Member
How can it hurt, other than economically? You test 50 parts, and pick out the four best-matched pairs. Then you discard (recycling preferred!) the other 42 parts. Assuredly your parts cost has increased by a factor of (50/8) = 6.25X. Test cost is zero because testing is enjoyable hobby-behavior; and hobby-behavior has zero cost, instead it has nonzero benefit.

But has the exercise done anything bad, electrically?
 
C

cal3713

Member
Joined 2014
myleftear said:
Here's the story:
I had the occasion to melt a little bit of solder, so I started to source parts for the BA-3. (My next excuse not to start my F4 which scares me don't know why...)
Stumbled on those PRP-resistors...
Hei, red resistors on a red PCB!
Checked the available values, which seem to be "strange" (there's a name for certain groups of values), some don't fit the BOM.
Piggybacking 2 resistors could be an option to come close.

But that's just stupid, I won't do it...

Finally, here's the question:

The BOM requires 10r, PRP has 11r... that's a 10% deviation. Would this work?
Click to expand...

I second 6L6. Build the f4. My first ever soldering project and my favorite amp (vs many much more expensive commercial offerings).
 
You must log in or register to reply here.
Top Bottom