The BA-3 as preamp build guide

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#1,024
Finished building a balanced BA-3 a few weeks ago. It's a simple balanced in-blanced out. It feeds a pair of balanced f4 monoblocks which have served me very well for several years with a variety of pre-amps.

Some pictures are attached not so much to show off, just as proof!

I am very happy with the sound. Amazed actually.

I set P3 at the midpoints. But just for the challenge I tried to set up a computer/sound card to adjust them. Understand, I am way too much of a paint-by-numbers builder with no measuring expertise beyond DMMs.

I didn't get very far.

I tried to use half of one balanced channel, e.g. the + to ground, to the sound card but that doesn't seem right and has little output. But at least there would be a single P3 to adjust this way.

I then tried feeding the sound card with a single, full balanced channel. This gives a nice signal.

But I am wondering if this is the correct approach as I will have to adjust two P3s at the same time. And I already have repetitive stress from all the bias, offset adjusting.

I really can't thank everyone in this community enough. You are all just amazing.
 

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#1,025
it would be simple , with sound card having bal output and bal input

without that , you need something to jump few times between SE and Bal realms

so:
- card SE out - xformer for SE-Bal conversion - preamp in
-preamp out - xformer for Bal-SE conversion - card SE in

considering prices of decent xformers .... it's clever to think of cheapest external card with bal in/outs
 
#1,026
I was checking my ba3 for bias offset. It was working fine. But i got strange readings..I got 0.4v dc after the output cap. Before cap offset dancing between 0-80mV. After cap there is 0.4v dc. Other channel also have similar readings. Around 0.1vdc. What is wrong?

Thanks
 
#1,027
starbender said:
I was checking my ba3 for bias offset. It was working fine. But i got strange readings..I got 0.4v dc after the output cap. Before cap offset dancing between 0-80mV. After cap there is 0.4v dc. Other channel also have similar readings. Around 0.1vdc. What is wrong?

Thanks
Click to expand...


Is the cap output connected to the input of another component, i.e. an amplifier?

The cap needs a load, after the cap connect a 100k resistor to ground for measurement.
 
#1,029
Gain of "Gain" Stage

Hi
I'm thinking of building an F6 (ordered the boards) and looking at using the BA-3 gain stage as the preamp. However, I have a Hagerman Cornet 2 as the phono preamp and based on the 44 dB gain of this unit and the output of my current cart, the phono only puts out about 0.9V, which I think is a bit low for the F-6. So I was wondering if anyone could tell me what the gain of the BA-3 gain stage is? Ideally a gain of at least 4-5 would cater for future carts with lower output and allow me to attenuate the input into the F-6 with a volume control.
Thanks in advance - these threads have been a great help.
 
#1,031
vcec said:
Hi
I'm thinking of building an F6 (ordered the boards) and looking at using the BA-3 gain stage as the preamp. However, I have a Hagerman Cornet 2 as the phono preamp and based on the 44 dB gain of this unit and the output of my current cart, the phono only puts out about 0.9V, which I think is a bit low for the F-6. So I was wondering if anyone could tell me what the gain of the BA-3 gain stage is? Ideally a gain of at least 4-5 would cater for future carts with lower output and allow me to attenuate the input into the F-6 with a volume control.
Thanks in advance - these threads have been a great help.
Click to expand...

full analysis of circuit is in article , few Papa's re-type mistakes corrected later in comments
 
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