I'm just building one BA-3 single-ended front end. No preamp. I think Nelson said that you want the bias between 6 and 12mA. That won't get very hot for a 288 box will it? I noticed your twisted pairs? This helps reject noise even though you don't have a two BA-3 boards wired as a diff amp for balanced stereo, which benefits from common mode noise rejection? Who makes your RCA jacks?[/QUOTE]
For a front end, you should be fine. This is like Tim barnes set up with his F4.
Russell, you use the BA3 preamp to drive the BA3 power amp?
Why the big transformer? Did you increase voltage or bias to get more power?
Why the big transformer? Did you increase voltage or bias to get more power?
I assume you mean the power amp! I had the transformer, 5U case, and power supply board from a group buy for the Turbo F-5. Decided the Turbo F-5 was a little "twitchy" for me and thought a Burning amp would be more to my uses.
While I am limited by the heatsinks, This transformer would allow me to bias the outputs into oblivion! But for my uses, its hardly stressed. Its a 24 + 24 volt transformer, instead of the called for 18 + 18 volt model. This results in 31 volt rails in my case, which is supposed to make more power, but in reality the difference between 25 watts and possibly 40 isnt really much of a big deal. I just had this transformer on hand, and when I saw 6L6 used a 24 + 24 volt model for his, decided to use it.
I also have a 18 + 18 at 500VA I could have used, but decided to save it for an Aleph J build, which I only need the case for. Boards are stuffed, everything ready except the case. Trying to sort out my F-5 right now, I rewired part of its power supply and messed up some grounding, may finish Aleph J once thats done.
Russellc
Oh, and yes right now I am using the BA-3 pre on the BA-3 power amp. Not that the gain is needed, it really drives the F-5 (fairly low gain amp) well, but it sounds so good I moved it the the BA-3 amp system, which is where I am using my turntable, and Pearl 2 phono pre. The combo is very nice sounding.
Russellc
I'm sure you would know, I've only tried it with the larger transformer. It is a very nice amp. I've wondered what the difference would be, whether the smaller transformer would result in a looser amp...being a tube guy previous to my Pass adventures, I've been partial to that sort of sound on the bass end of the scale. Not that the BA-3 is overly "tight" or anything. its bass has a nice power to it, very natural sounding. Not as "thin' as the F-5, and again, my F-5 is not "thin" sounding, but the BA-3 is less so, if that makes any sense.
The F-5 is a simple amp, ultra wide bandwidth, and its simplicity is makes for a nice open sound that is hard to complain about. BA-3 is a more "mature" amplifier and its sound, to me, reflects that. Just my opinion of course.
Russellc
The lower voltage transformer/amplifier will result in more clipping of the output signal.
That may be very audible, even if the extra power is not that audible.
That may be very audible, even if the extra power is not that audible.
I guess I made the right choice!😀 I hated just having that nice transformer and nothing to do with it!
Russellc
Congrats on this really great build! About the power supply, the basic design
looks similar to that in F4 amp; please see p. 14 here http://www.firstwatt.com/pdf/prod_f4_man.pdf. Would you recall the make and model of the 8 diodes that make up the two bridges?
I see the 0.0033uf AC line filter cap. Is that little white rectangular device on the primary side a fast blow fuse?
If yes, then assuming that the transformer has dual primaries, are those two black radial lead devices on that little pc board thermistors, like Nelson used in the F4 PSU?
If not, are they poly film caps to bypass the large electrolytics? One for each rail?
Did you find any need to add decoupling film caps to the solder side of the BA-3 board?
How long is that DC supply cable? About 3 feet?
I looked but can’t source those clear plastic multi wire clamps.
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I am building a step correction circuit to drop-in in between my BA-3 preamp and F-5's, and just want to confirm the output impedance of the BA-3 is about 100 ohm pretty much the value of R12, this this correct?
I am experimenting with my jordan92's and tuning up their match with the electronics and my listening room. And I will build an open baffle for my lowthers when i get this basic electronic approach sussed. from what I can tell at this point, - I really won't need a buffer stage to drive the F-5's, as I have enough gain and the impedences are well matched.
Has anyone done this, probably yes I just haven't found you yet?
I am experimenting with my jordan92's and tuning up their match with the electronics and my listening room. And I will build an open baffle for my lowthers when i get this basic electronic approach sussed. from what I can tell at this point, - I really won't need a buffer stage to drive the F-5's, as I have enough gain and the impedences are well matched.
Has anyone done this, probably yes I just haven't found you yet?
SS amplifiers have an output impedance. This can be very low to quite high and depends on the design and implementation.
This output impedance is not fixed, it varies with frequency. This variation with frequency also brings with it some reactive component, the output can appear as either a capacitor or as an inductor or as a pure resistance, but is more likely to be a combination of all three.
This output impedance can vary a lot over the audio bandwidth, expect the 1kHz value to vary by -50% and +100%.
The 100r output resistor is intended to swamp the variation in the inherent output impedance. The cable and the load see the 100r+output impedance. The main reason for the 100r is usually to isolate the cable capacitance/reactance from the NFB circuit of the transmitter
.
But for our purpose we can generally regard the source impedance as slightly higher than the added output resistance.
It could be equivalent to 110ohms or even 130ohms, but for the simple case the 100r resistor is a good guide to what the load sees.
This output impedance is not fixed, it varies with frequency. This variation with frequency also brings with it some reactive component, the output can appear as either a capacitor or as an inductor or as a pure resistance, but is more likely to be a combination of all three.
This output impedance can vary a lot over the audio bandwidth, expect the 1kHz value to vary by -50% and +100%.
The 100r output resistor is intended to swamp the variation in the inherent output impedance. The cable and the load see the 100r+output impedance. The main reason for the 100r is usually to isolate the cable capacitance/reactance from the NFB circuit of the transmitter
.
But for our purpose we can generally regard the source impedance as slightly higher than the added output resistance.
It could be equivalent to 110ohms or even 130ohms, but for the simple case the 100r resistor is a good guide to what the load sees.
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Okay guys, I'm new to the amp world. I just bought a set of boards to build a single-ended BA-3. This will be my first amp. Luckily I'm a mechanical engineer surrounded by a bunch of EE's 😉
Because this is single-ended, all I need is the N-channel. I wanted to know if anyone found a replacement for the IRFP240, or if people were trying to source them still? Of any that do exist, the prices are through the roof.
Because this is single-ended, all I need is the N-channel. I wanted to know if anyone found a replacement for the IRFP240, or if people were trying to source them still? Of any that do exist, the prices are through the roof.
IRFP240PBF Vishay Semiconductors | Mouser
$2.08 apiece are the ones I used. Lead free from my understanding is the difference. The one I built sounds great using these.
David
$2.08 apiece are the ones I used. Lead free from my understanding is the difference. The one I built sounds great using these.
David
Yes, buy at least 20 and get a better price $1.67 and match them. 30 would not be too many. I found that they are very close values but the better they match will keep one from getting hotter than the rest. You do not want one using more current than the rest. I just bought 10 more with an order and I do not need them now but I like having some around for other projects because they are used a lot.
David
David
It's single-ended, so n-channel only...as opposed to a complimentary which uses both N and P?
Ok, hang on a second. 🙂
The BA-3 consists of a BA-3 Front End driving a BA-complimentary (Push-Pull) output stage.
If using the SE output boards, it's probably better to use the BA-1 Gain Stage. I'm not sure if the BA-3 Gainstage can be used with the SE output boards... Has anybody actually done that yet? There's an extra connection or two that the -1 front end has that the -3 front end doesn't.
Yes, the SE output boards are N-channel only, so all you would need are IRFP240.