BA-3 Amplifier illustrated build guide

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#1,482
^ Agreed, it is a challenge to find information, particularly for a specific use if you're not doing your build exactly as in 6L6's excellent guides.

What you need is probably best asked in the pre-amp thread and/or you may want to start your own thread, IMO.

i.e. "How could I adapt the BA-3 circuit to be used as a VAS for a DAC?" The rest of the BoM and how to bias it is fairly simple. The gain change is only one resistor... I think...
 
#1,483
NightFlight said:
Volunteers to assemble the discussed? Personally, I'm looking to potentially build it as a pre. However, the whole thread is a bit long in the tooth. I don't have the skill to identify what is good information and what is a good revision, etc. I'm just a cut and paste guy, merely dangerous with a soldering iron - more likely to set my house on fire than anything else.
Click to expand...
Ifyou want to build a BA3 then this is the correct link.
6L6

Thread 'The BA-3 as preamp build guide'

Using the BA-3 gain stage (“Front-end”) as a line stage preamp. A mini build guide. 🙂

PCB - P-BAGSN-1V20 - Burning Amplifier Gain Stage for BA-3 (Requires bias boards and output stage; Makes 2 channels; Rev 2.0) - Circuit Boards

BA-3 as preamp thread - http://www.diyaudio.com/forums/pass-labs/234641-ba-3-preamp.html

A club in Minnesota that used this preamp as their club-wide reference! https://sites.google.com/site/audiosocietyofminnesota/Home/diy-projects/pass-ba-3-preamplifier

The BA-3 front end is able to act as a wonderful preamp, with plenty of gain that is...
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The first few pages should give you all the information that you need but it is worth reading through.
There are a couple of mods that make biasing better. These are simpler to install as you build it rather than going back to modify things.
 
#1,485
^ If all you need is the BA-3 "front end" with a modification to 10X gain, then there is probably no need to move it around. That may be more confusing to you.

Attached is a BoM I used. Note that the "original" MOSFETs were Toshiba parts. The MOSFETs listed below are the Fairchild parts with the pots adjusted accordingly for the change in Vgs. Those Fairchild parts are also obsolete now, and are becoming harder to find. However, if you don't already have them, I know you can probably find some in the swap meet.

The existing gain is (I think) 15dB. To raise the gain to 10X (20dB) you will need to alter it slightly. I think it's R13, but I am not 100% sure.

So, what I would do is...

@Zen Mod or other skilled friends - would you please confirm that R13 in the BA-3 front end is the proper resistor to alter to change the gain? Is 20dB realistic for this without any other unintended consequences? If so, what value would get it close?

Thanks!!!

1742313835795.png



Edited to add - my quantities were for a balanced build. So, you can cut that in half. 🙂
 
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#1,489
^ Not everything will be in the first post of a thread, but IMO that should always be the first place that you look for anything. Second to that... search Firstwatt.com articles.

But... here ya go... from the first post of this thread.
6L6 said:
If you haven’t yet, please read this article before continuing. If you have read it, might as well skim over it again, it has lots of great information —

Nelson Pass BA-3 article - Burning Amplifier BA-3 - diyAudio
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