mini-a pcb options -- pots and surface mount
mikew,
thanks again for the pcb and the effort to produce it. very nicely done.
some feedbak that may be of value, if you are still open to pcb options:
1. caddock makes a bunch of power film resistors, in both to-220 style for heat sink mounting, and a new style for surface mount. i've used the to-220 style, and they work real well.
i've never compared them to other options, but maybe they save additional board space:
they are at this link: http://www.caddock.com/Online_catalog/current_sense/current_sense.html
2. and marcello pellerano did a real nice job on a headphone amp, and included bias and balance pots to facilitate final setup. perhaps they might be a valuable add-on to your pcb design. the link is at headwize: http://headwize2.powerpill.org/projects/showproj.php?file=pellerano_prj.htm
anyway, thanks again for the board and for your hard work.
rono
mikew,
thanks again for the pcb and the effort to produce it. very nicely done.
some feedbak that may be of value, if you are still open to pcb options:
1. caddock makes a bunch of power film resistors, in both to-220 style for heat sink mounting, and a new style for surface mount. i've used the to-220 style, and they work real well.
i've never compared them to other options, but maybe they save additional board space:
they are at this link: http://www.caddock.com/Online_catalog/current_sense/current_sense.html
2. and marcello pellerano did a real nice job on a headphone amp, and included bias and balance pots to facilitate final setup. perhaps they might be a valuable add-on to your pcb design. the link is at headwize: http://headwize2.powerpill.org/projects/showproj.php?file=pellerano_prj.htm
anyway, thanks again for the board and for your hard work.
rono
I too would like to say what a great job Mike did on the PCB for the Mini. Mines been up and running now for about a week and sounds great. Wish I still had my digital camera...recently stolen!
Today I picked up a surplus E-I type transformer at Ra-Elco for the mini. I'm curoius about how hot a transfomer might get in this amp. This one is 24 vct secondary is rated at 10 amps. This thing gets really hot after a couple of hours of operation! I've ordered a custom fomr Victoria Magnetics but its a couple of weeks till delivery and I want to enjoy the Mini till it arrives. On the custom how large a transformer should I specify?
Mark Gulbrandsen
Today I picked up a surplus E-I type transformer at Ra-Elco for the mini. I'm curoius about how hot a transfomer might get in this amp. This one is 24 vct secondary is rated at 10 amps. This thing gets really hot after a couple of hours of operation! I've ordered a custom fomr Victoria Magnetics but its a couple of weeks till delivery and I want to enjoy the Mini till it arrives. On the custom how large a transformer should I specify?
Mark Gulbrandsen
size
I think a 250 to 300 VA, 12-0-12 AC to 15-0-15 AC should be OK. John made me some 300VA, 30-0-30 low profiles. Maybe he could use the same cores? They are very nice. For the next Mini-A there is a 480VA, 20-0-20 from Victoria Magnetics. It won't be so mini.
I think a 250 to 300 VA, 12-0-12 AC to 15-0-15 AC should be OK. John made me some 300VA, 30-0-30 low profiles. Maybe he could use the same cores? They are very nice. For the next Mini-A there is a 480VA, 20-0-20 from Victoria Magnetics. It won't be so mini.
Re: size
I was using a 300VA 2x12 toroidal transformer for a test
Mini-A and it worked fine.
Mike, with a 480VA 20-0-20 transformer, wouldn't your next
Mini-A grow up and become an Aleph3?
Dennis
MikeW said:I think a 250 to 300 VA, 12-0-12 AC to 15-0-15 AC should be OK. John made me some 300VA, 30-0-30 low profiles. Maybe he could use the same cores? They are very nice. For the next Mini-A there is a 480VA, 20-0-20 from Victoria Magnetics. It won't be so mini.
I was using a 300VA 2x12 toroidal transformer for a test
Mini-A and it worked fine.
Mike, with a 480VA 20-0-20 transformer, wouldn't your next
Mini-A grow up and become an Aleph3?
Dennis
Mine has been working great!!! Its been up and runnning since about a week after receiving your pcb. No problems at all and worked perfectly on first turn on. Put in an order for a VM toroid for it so shortly after it arrives and I install it some pictures will be posted. Have not done any measurements at all.....waiting for the VM to arrive. It'll be a 320 VA with a 13-0-13 secondary.
Mark
Mark
I had some time today and made some initial measurements on my Mini Aleph. Running plus and minus 16 volt DC rails the calculations showed 15.1 watts into 4 ohms @ 1% distortion, and 10.9 watts into 8 ohms again at 1% distortion.
I also noticed a bad spike on the leading edge of a just about any frequency square wave I pumped though the amp. I tacked a .0015 across the B-C of Q3 and Q10 and this brought it down to reasonable levels, it was literally off the top and bottom of the scope screen before the addition of the caps!. Adding a 5 to 10 pf cap across the feedback resistirs showed no other improvement so I've left them out for now.
The amps sound a wee bit cleaner than they did with the the caps added, and I suspect it lowered distortion a bit. My O.P. devices were IRFP240's.
On future boards it would be nice if there was a position for these caps so a tack job doesn't have to be performed in this tight spot. I also noticed very slight unbalanced clipping and a position for a 10 turn pot at R10 and R31 would be nice as well for adjusting for symetrical clipping. Having it perfectly symetrical might help squeek another few milliwatts out of the mini.
Feedback (pun intended!) and suggestions would be appreciated here!!
Mark
I also noticed a bad spike on the leading edge of a just about any frequency square wave I pumped though the amp. I tacked a .0015 across the B-C of Q3 and Q10 and this brought it down to reasonable levels, it was literally off the top and bottom of the scope screen before the addition of the caps!. Adding a 5 to 10 pf cap across the feedback resistirs showed no other improvement so I've left them out for now.
The amps sound a wee bit cleaner than they did with the the caps added, and I suspect it lowered distortion a bit. My O.P. devices were IRFP240's.
On future boards it would be nice if there was a position for these caps so a tack job doesn't have to be performed in this tight spot. I also noticed very slight unbalanced clipping and a position for a 10 turn pot at R10 and R31 would be nice as well for adjusting for symetrical clipping. Having it perfectly symetrical might help squeek another few milliwatts out of the mini.
Feedback (pun intended!) and suggestions would be appreciated here!!
Mark
feedback
The caps and pot can be added. It may be easier to attach the cap between E3,E17 and R9, R30. Should the pot be in parallel with R10 and 31? What color for the next silkscreen? Thanks for the input. I will order some more boards in January.
PS. I changed the feedback R15 and R36 to 22K in both of my amps.
The caps and pot can be added. It may be easier to attach the cap between E3,E17 and R9, R30. Should the pot be in parallel with R10 and 31? What color for the next silkscreen? Thanks for the input. I will order some more boards in January.
PS. I changed the feedback R15 and R36 to 22K in both of my amps.
A little more gain. I also had an oscillation with the 10k. The first MINI was built with Fairchild output MOSFETs. They had much higher transconductance and capacitance. It sounded good. So I built the second one with the same values.
The Aleph 5 has a .047 from C-E for the current source.😀
The Aleph 5 has a .047 from C-E for the current source.😀
Just back from a lengthy service run and my Victoria Magnetics toroid was waiting for me. Installed it in place of the E/I tranny I had bought surplus and WOW, what a difference! Particulularly in the bottom end. This thing actually has serious bottom end now. The 320 VA toroid has dual 13 volt secondarys giving me plus and minus 16.7 volts per rail, just a few tenths more than it was before with the E/I. Kept the PS simple with just one 120,000 mfd Panasonic THA cap per rail.
My next years project is going to be a small portable biamped system consisting of a mini Aleph and an Aleph 30 built with Mike W's pcb's, along with x-over and Aleph P in one case set up to bi-amp a pair of small Dynaudios. I'll have Victoria wind me a tranny with multiple secondaries to keep the whole package to a reasonable size. Gotta have music while I travel!
BTW, This toroid cost me 54.00. Quite reasonable and the quality is excellent.
Mark
My next years project is going to be a small portable biamped system consisting of a mini Aleph and an Aleph 30 built with Mike W's pcb's, along with x-over and Aleph P in one case set up to bi-amp a pair of small Dynaudios. I'll have Victoria wind me a tranny with multiple secondaries to keep the whole package to a reasonable size. Gotta have music while I travel!
BTW, This toroid cost me 54.00. Quite reasonable and the quality is excellent.
Mark
New Mini-A
The updated mini-A is almost ready. It will be very close to the Aleph board, but same size as the last mini-A. I will order some boards in January after vacation. I have checked the board and it looks good. I am still waiting for Mark to check it before it is ordered. If you would like a board let me know.
The updated mini-A is almost ready. It will be very close to the Aleph board, but same size as the last mini-A. I will order some boards in January after vacation. I have checked the board and it looks good. I am still waiting for Mark to check it before it is ordered. If you would like a board let me know.
Member
Joined 2002
The boards come in pairs, but you can cut the in half if you want to make mono blocks. The price will depend on how many. Hopefully under $10.
Member
Joined 2002
JasonL said:
Jason,
The regular Aleph boards can also be used to build a Mini A, since it is the same circuit, just with lower powered rails, and without parallel output devices. Just thought I would mention it, since you probably have a few sets of those boards left.
--
Brian
Member
Joined 2002
Mike,
Since others have expressed interest I would suggest we start a WIKI for the Mini boards if you are up to it. Let me know what you think. I'd start it off with 10 boards. I have several friends that with some guidance would love to build a Mini A.
Mark
Since others have expressed interest I would suggest we start a WIKI for the Mini boards if you are up to it. Let me know what you think. I'd start it off with 10 boards. I have several friends that with some guidance would love to build a Mini A.
Mark
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