Size of output cap depends on next stage input impedance...F4 has input impedance of 47K. you would at at least a 5UF cap in order not to roll off the bass. 10UF is safer and will let you use amps down to 1K input.
Probably the best partner for the BA-3 is the F4 or BA-2 output stage since that is what it is designed for. You can lose the input jfets on the F4 if you are going to use the BA-3 exclusively (making it a BA-2). I've used the BA-3 with the F5 as well. Basically all the first watt amps are low gain so it will work well with all of them. But with an F4 with no gain you are still looking at only 20db of gain with the BA-3. That's not a lot by conventional standards. Really, the BA-3 is designed to be used with a buffer/follower amp like the F4 or BA-2 output AND a preamp in front of it if you want typical gain levels.
Keep in mind, a commercial system is typically designed for many different "mates".
The beauty of DIY is the ability to tune for your system. If the BA-3 pre is going to be used with a F4, then a smaller cap may work just as well. There are plenty of online high pass filter calculators such as this to use.
For a 47K input impedance, the fc of the 0.68uF cap is about 5hz. If you don't feel like lacking of low end, then IMHO, 2.2uF is probably all you need which is more than 1 decade below 20hz. Smaller cap also allows to afford a very decent coupling cap without breaking the bank.
There is no right or wrong, only whatever is suitable for you. Feel free to experience, it is DIY after all!!
Edit: corrected some typos.
The beauty of DIY is the ability to tune for your system. If the BA-3 pre is going to be used with a F4, then a smaller cap may work just as well. There are plenty of online high pass filter calculators such as this to use.
For a 47K input impedance, the fc of the 0.68uF cap is about 5hz. If you don't feel like lacking of low end, then IMHO, 2.2uF is probably all you need which is more than 1 decade below 20hz. Smaller cap also allows to afford a very decent coupling cap without breaking the bank.
There is no right or wrong, only whatever is suitable for you. Feel free to experience, it is DIY after all!!
Edit: corrected some typos.
even if you have Golden Ears , capable to tune one channel to your liking ....... no way that Ears are golden enough , to make second channel identical
so, leave it at 50% , and go back in few months , when you chew up how to use simple analyzing rig (pc, decent sound card and freeware prog)
so, leave it at 50% , and go back in few months , when you chew up how to use simple analyzing rig (pc, decent sound card and freeware prog)
That's where you read it. R12 is in series with the output and should have no dc across it.
I measure from the top of the big cap to GND.
Another BA-3 Preamp in the books! My second. I think the boards are ok 
Added switchs to adjust the gain between high (normal) and low.
Here it's driving the MoFo mono blocks, which need high gain to drive them.
The 10mm face plate is too thick for the pot and switch.
Needs to be milled out.
Thanks
Vince
Added switchs to adjust the gain between high (normal) and low.
Here it's driving the MoFo mono blocks, which need high gain to drive them.
The 10mm face plate is too thick for the pot and switch.
Needs to be milled out.
Thanks
Vince
Attachments
I said i would upload some pictures a while back, so here goes. I've had about a months time with it since finishing and i love it!
This was my first time doing some more serious casework, and that shows. Still, i am reasonably happy about it. As evident, the case is way to big, but it was pretty cheap and nice quality from Toroidy, and on the plus side it is absolutely hum free, no doubt owing to the massive separation between toroid and BA-3 board
Transformer is toroidal 2x22v from Toroidy also, PSU is Rod Elliotts preamp PSU set to 24V. I gather this is a bit more than it was intended for, and fitting the heatsinks to the LMs was a bit tricky since it is quite tight. Also, the wire holes were tiny so wiring it up got quite fiddly.
I used Salas I-select for input selector, together with his LED-selector solution (front pic below). I really like this board, i wish i had bought more than one! It gets power from the AUX section of the PSU, dropped to approx. 27V DC using 4 diodes in series.
Selector is cheap Valab one from Ebay, it's cropped up here and there in this thread before i believe (same as you vdi_nenna?). Mundorf caps, again if i ever build another one (i might) i will use something less wide, measuring the bias V was a pain with these!
jfets from store, matched toshiba mosfets from liubincalvin. I grounded connected a ground shunt on the output using a 100k resistor i believe (as per instructions from mr. ZM). It replaces the digital preamp mode of my audio streamer and punches way above it. It sounds gorgeous and has much more gain. For my 86db/W 4 ohm speakers (Dynaudio excite x16) i can now play much louder than i need I have actually not been above 3/4 of max volume yet since things start shaking by that time and i like my neighbours...
Thanks 6L6 for this great build guide, i studied it intensely while waiting for parts to arrive, and it allowed me to finish the build without major hickups. Such a great resource to us beginner DIY'ers! Thanks Mr. Pass for generously making this design available. Thanks to ZM for helpful answers along the way!
This was my first time doing some more serious casework, and that shows. Still, i am reasonably happy about it. As evident, the case is way to big, but it was pretty cheap and nice quality from Toroidy, and on the plus side it is absolutely hum free, no doubt owing to the massive separation between toroid and BA-3 board
Transformer is toroidal 2x22v from Toroidy also, PSU is Rod Elliotts preamp PSU set to 24V. I gather this is a bit more than it was intended for, and fitting the heatsinks to the LMs was a bit tricky since it is quite tight. Also, the wire holes were tiny so wiring it up got quite fiddly.
I used Salas I-select for input selector, together with his LED-selector solution (front pic below). I really like this board, i wish i had bought more than one! It gets power from the AUX section of the PSU, dropped to approx. 27V DC using 4 diodes in series.
Selector is cheap Valab one from Ebay, it's cropped up here and there in this thread before i believe (same as you vdi_nenna?). Mundorf caps, again if i ever build another one (i might) i will use something less wide, measuring the bias V was a pain with these!
jfets from store, matched toshiba mosfets from liubincalvin. I grounded connected a ground shunt on the output using a 100k resistor i believe (as per instructions from mr. ZM). It replaces the digital preamp mode of my audio streamer and punches way above it. It sounds gorgeous and has much more gain. For my 86db/W 4 ohm speakers (Dynaudio excite x16) i can now play much louder than i need
I have actually not been above 3/4 of max volume yet since things start shaking by that time and i like my neighbours...Thanks 6L6 for this great build guide, i studied it intensely while waiting for parts to arrive, and it allowed me to finish the build without major hickups. Such a great resource to us beginner DIY'ers! Thanks Mr. Pass for generously making this design available. Thanks to ZM for helpful answers along the way!
Attachments
Thanks! By the way, not sure what your plans for the front plate is, but i found it pretty easy with a counterbore bit like this:
M10 x 18mm HSS 3 FLUTED COUNTERBORE TOOL 1512011000 EUROPA tool / CLARKSON #P29 | eBay
on my 8mm faceplate.
M10 x 18mm HSS 3 FLUTED COUNTERBORE TOOL 1512011000 EUROPA tool / CLARKSON #P29 | eBay
on my 8mm faceplate.
I was going to route out the backside of the faceplate.
I have some mill ends, but no mill. Just a drill press
A friend of mine has a mill.
Take him 10 minutes and do a nicer job than me.
I know. Never use a drill press as a mill.
Can't handle the lateral stress. It's dangerous.
A mill is designed for the job.
I have some mill ends, but no mill. Just a drill press
A friend of mine has a mill.
Take him 10 minutes and do a nicer job than me.
I know. Never use a drill press as a mill.
Can't handle the lateral stress. It's dangerous.
A mill is designed for the job.
317/337 from parts-exprsss.com. $11US each.
I suppose I could use some better regs, but someone should tell the cheap regs they shouldn't sound this good first.
This preamp was supposed to be a "throw together quick" project to hear the Mofo power amp. The combination is excellent. Really engaging.
