BA-3 Amplifier illustrated build guide

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wdecho

Member
Joined 2014
grimberg said:
The build guide is just an additional help for absolute novices, and no substitute for the original articles written by Nelson Pass. When you read the articles, especially the one most relevant in this case, the "Burning Amplifier BA-3", the answer is in the very first paragraph.
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I understand this but novices as you say may not and try to build from the diyaudio schematic and Jim's build guide. The schematic on our site is obviously wrong to you and I but others may get confused. My hope is a person in charge of the diyaudio store sees this post and corrects it. The BOM for the BA-2 is correct in that the IRFP240 and IRFP9240 are listed as needed. Just something I noticed and needing correcting.

Both the BA-1 and BA-2 builds are outstanding amplifiers and I do hope they restock these boards.
 
T

tommydoan84

Member
Joined 2016
hi 6L6 and all,

Talking about novice, I have some novice questions :)
I am also collecting parts to build the exact same BA-3 configuration as 6L6 (Jim)
Using BA-3 preamp as front end feeding into Differential FE, Complimentary output (BA-2).

Here're my questions
1. Instead of using BA-3 preamp, can I use different tube preamp to feed into Complimentary output (BA-2) ? If yes, then what is the input impedance of just Complimentary output (BA-2) ?

2. If the answer is no, then can I feed the tube line-stage preamp to (BA-3 front end + BA-2 comp output) to add more gain and adding tube color to the overal sound ? What is the input impedance of BA-3 front end + BA2 complimentary output? is it 47 kohm ?

I know we can feed different preamp both SS or tube to F4 amp since F4 has the input impedance of 47kohm in front of the series of // nFet and pFet as long as the preamp output cap/resistor matches with 47kohm input Z of F4. Not sure if this can be done with BA-3 amp and how can we do it if all possible?

Many thanks in advance.
Tom
 
J

jswen

Member
Joined 2002
Hey All,

I finally finished assembling the BA3 preamp. Let in burn in for about 5 days and it sounded good. Last night one channel started sounding like a cracked paper woofer, kinda buzzing on top of the sound. I've checked all measurements (worst DC offset @ 15mV) and am lost. Any thoughts?

Thanks,
John
 
6L6

6L6

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Joined 2010
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dimkasta said:
Would you share some more details on how you did that matching and what levels did you end up using?
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My sincere apologies for answering this question many months after it being posted. I just saw it now...

Tools - HP 339A distortion analyzer and a load resistor. Adjustments made at 1K, 1W at Nelson always suggests.

Previously to this we had the distortion pot (P3) dialed down to minimum THD. This makes for the lowest measured distortion, and because you are nulling out the 2nd, the remainder has a dominant 3rd harmonic. Makes for a clean and fast sound, very nice.

As Tyson wanted to have more 'flesh and blood' in the playback, we though that making the distortion spectra 2nd harmonic dominant would be worth trying. The P3 pot was turned back so that the distortion went back up and at a certain point it didn't really rise much more with further turns. The first channel was set to that point, and a little less, to tighten up the readings a little.

At first I though I could just set the other channel to the same point and the same THD reading, but the numbers just didn't match L to R. (Much of the reason why is because this is a zero feedback amp and you'd have to match everything L to R very tightly get both to measure identically) Anyway, to get the same THD reading, the distortion residual shape was not insignificantly different. So that didn't seem the best approach.

So we decided that the numbers didn't really matter, and instead the shape of the distortion was important, so the first channel was hooked back up a quick phone photo of the scope was taken.

Comparing the phone photo to the scope connected to the 1st channel, we merely adjusted the 2nd channel so that the shape of the residual was as close as could be made to the shape of the first.

It sounded absolutely wonderful!! :D
 
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6L6

6L6

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Joined 2010
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No.

For there to be a voltage measurement or resistance that I could take and you apply to your amp, both your amp and my amp would have to have Jfet pairs of identical Idss, Front-end Mosfets (N and P) of identical Vgs, and output mosfets (N and P) of identical Vgs.

And even then it would be an approximation. :(
 
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KevinHeem

KevinHeem

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Joined 2007
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jswen said:
For those of us without any analyzers, is there a voltage(s) we can dial in on P3 to achieve your nirvana?
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You can try something like ARTA software (free for non commercial use) as a Spectrum Analyzer on your computer using an external USB interface (ie Focusrite Scarlet). This set up gives you the the ability to view the signal in the frequency domain. Now you can make adjustments by ear but have a reference to the ratio of second harmonic.
 
N

neno70

Member
Joined 2016
12 mosfet x channel

hello, but in the original scheme of pass, there are 12 mosfet x channel while in the pcb I think there are only 6 (3N / 3P), but when you put 2 sets of pcb and putting them in series, you can get the original? If ; what advantages would they have? thank you
 
W

wdecho

Member
Joined 2014
KevinHeem said:
You can try something like ARTA software (free for non commercial use) as a Spectrum Analyzer on your computer using an external USB interface (ie Focusrite Scarlet). This set up gives you the the ability to view the signal in the frequency domain. Now you can make adjustments by ear but have a reference to the ratio of second harmonic.
Click to expand...

Can be done with decent FFT function on oscilloscope as well as PC software, ARTA.
 
6L6

6L6

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Joined 2010
Paid Member
neno70 - Yes, the PCB are made to be linked together if you want to do that. Advantages are much more current capability into the load.

Disadvantages are significantly more heat, bigger chassis, bigger PSU, more cost, etc... and no real increase in power as the front-end can't swing any more voltage into the output stage.

If you want more power (about 4x) build a BA-3 balanced Burning Amp BA-3b (Balanced) I suggest monoblocks, which puts you right back at a more expensive project, but at least you get more power out of it.

If you've never had a real class-A amplifier before, build one. (The standard BA-3 as shown here is still my favorite) They really do sound better, and sound much, much more powerful than their output power would suggest.
 
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wdecho

Member
Joined 2014
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6L6

6L6

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Joined 2010
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Most digital scopes have 8-bit vertical resolution, nowhere near enough to FFT a fundamental signal and look at the distortion spectra of a low-distortion amp like a BA-3.

ARTA will do everything you could ever want. As for USB soundcard, all on the market will work beautifully. Focusrite, Tascam, Behringer, all wonderful.

For a very effective and easy cable between the device under test and the soundcard, I've made his and it works extremely well - Electronic Equiptment - DIY soundcard scope probe

Remember to turn it all the way down before attaching to DUT, then increase the pot until the card input sees 1v
 
N

neno70

Member
Joined 2016
6L6 said:
neno70 - Yes, the PCB are made to be linked together if you want to do that. Advantages are much more current capability into the load.

Disadvantages are significantly more heat, bigger chassis, bigger PSU, more cost, etc... and no real increase in power as the front-end can't swing any more voltage into the output stage.

If you want more power (about 4x) build a BA-3 balanced Burning Amp BA-3b (Balanced) I suggest monoblocks, which puts you right back at a more expensive project, but at least you get more power out of it.

If you've never had a real class-A amplifier before, build one. (The standard BA-3 as shown here is still my favorite) They really do sound better, and sound much, much more powerful than their output power would suggest.
Click to expand...
thank you , since I already have transformers and houses, plan to build bi-amping with Ba3 x medium high and a class ab x medium low (H: B.) x my new Ekta Grande ...:D:D
 
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