Another Desktop Capable NHB amp
Just got done building and testing this one for a customer in Texas. It has a 5.5mmx2.5mm barrel connector on the side to allow connection to a PSU when used as a desktop amp. The jack disconnects the batteries when plugged in. This particular unit measures really nice at only 0.013%THd for 1Vpp into 270ohm load. This particular PSU is from eBay and uses a transformer and LT voltage regulator. It has very low (almost non existent 60Hz and 130Hz peaks and a -115dB 240Hz peak. Inaudible at that level.
Just got done building and testing this one for a customer in Texas. It has a 5.5mmx2.5mm barrel connector on the side to allow connection to a PSU when used as a desktop amp. The jack disconnects the batteries when plugged in. This particular unit measures really nice at only 0.013%THd for 1Vpp into 270ohm load. This particular PSU is from eBay and uses a transformer and LT voltage regulator. It has very low (almost non existent 60Hz and 130Hz peaks and a -115dB 240Hz peak. Inaudible at that level.
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I recently got a pocket amp from the swap meet here on diyaudio. It sounds fantastic both for headphone and as a line stage. I replaced the Oscons with some Panny FC, and now I am even more impressed.
I am feeding it 14v with a lab supply and an Allo cap mx. I smoked two of the mt3608 boosters when I hooked them up to the Allo cap mx. Polarity and voltage levels were fine so it must be a load issue. I am wondering if I can hook up an mt3608 booster board directly to the amp to get the more optimal 16-18v. Would that work? I have 2x 1500uf on the board, and would unplug my headphones when switching on/off.
I am feeding it 14v with a lab supply and an Allo cap mx. I smoked two of the mt3608 boosters when I hooked them up to the Allo cap mx. Polarity and voltage levels were fine so it must be a load issue. I am wondering if I can hook up an mt3608 booster board directly to the amp to get the more optimal 16-18v. Would that work? I have 2x 1500uf on the board, and would unplug my headphones when switching on/off.
You can connect the MT3608 directly via a 2W 3.3R resistor in series. I would try the Juma cap Mx because perhaps the Allo does not have the gradula startup capability? It is a different topology altogether. Have the 14v lab supply feed the MT3608, then feed the Juma cap Mx, then feed the CRCRC then the amp. You could connect the MT3608 to the amp directly but the 2200uF caps on board will cause in-rush and the MT3608 will shutoff. Since you are using a lab supply, having lots of power is not an issue so use a 3.3R 2W resistor between the MT3608 and the amp. It will get warn but MT3608 won't shut off.
Glad you like the amp. Out of curiosity - who did you buy the amp from? I am wondering if it was a DIY one or one that I made?
Glad you like the amp. Out of curiosity - who did you buy the amp from? I am wondering if it was a DIY one or one that I made?
Yes it would! Dealing with three extra boards is fiddly.
And I still haven't figured out what I did wrong with my load sharing board, so I guess I'm especially interested in a different solution. I double checked all the resistor values with my multimeter. No problems there. I can make the LED light up with my multimeter but it does not light when the board is powered up.
xrk971 said:
I have been working on such a board for my own purposes. I expect it is currently a little large for Altoids tin use, but maybe I can rearrange the layout. I have planned for a micro-USB charger with load sharing, DC-DC conversion by a TI LMR62421, and smoothing with a capacitance multiplier. The design is yet untested, and testing will be a few weeks off since I will have to wait for boards, parts, and time... But, I may have something to offer as a solution in the not-too-distant future.
Hi everyone 
.
After a lengthy absence I'm back on the forums. I did the layout for X's excellent pocket amp. I'm absolutely thrilled to see so many people enjoying this amazing little amp!
Would anyone be interested in a layout designed specifically for a desktop version of this amp (with X's permission, of course)? It would be straightforward to include the cap multiplier and CRCRC filter on the same board, or I could do a separate amp and power supply.
.After a lengthy absence I'm back on the forums. I did the layout for X's excellent pocket amp. I'm absolutely thrilled to see so many people enjoying this amazing little amp!
Would anyone be interested in a layout designed specifically for a desktop version of this amp (with X's permission, of course)? It would be straightforward to include the cap multiplier and CRCRC filter on the same board, or I could do a separate amp and power supply.
BDHM,
Welcome back man! Where were you? Hope all is well.
Of course we would love to see a desktop version with DC step up cap Mx, and CRCRC! Actually folks are asking for a small PSU board that goes into the battery bag of the original board and has LiPo JST jack and USB charging battery management, cap Mx, and CRCRC. I have tested it all out as separate pieces and they fit in the bay. But would be nice on one board.
Did you ever get the amp I sent you? I fear SA mail thieves snatched it.
Cheers,
X
Welcome back man! Where were you? Hope all is well.
Of course we would love to see a desktop version with DC step up cap Mx, and CRCRC! Actually folks are asking for a small PSU board that goes into the battery bag of the original board and has LiPo JST jack and USB charging battery management, cap Mx, and CRCRC. I have tested it all out as separate pieces and they fit in the bay. But would be nice on one board.
Did you ever get the amp I sent you? I fear SA mail thieves snatched it.
Cheers,
X
Some rather nasty health issues forced me to focus on the basics of life and not much else. Things are looking much better now though
. I did indeed receive the amp! I thought I had emailed you expressing my thanks, but I see I did not
What were the final values you used for the cap multiplier? I'm sure it's buried in the thread somewhere, but I haven't found it yet. CRCRC is 2200uF / 0.47R right?
And would you guys prefer through-hole or SMD (or one of each)?
Some rather nasty health issues forced me to focus on the basics of life and not much else. Things are looking much better now though
I did indeed receive the amp! I thought I had emailed you expressing my thanks, but I see I did not
What were the final values you used for the cap multiplier? I'm sure it's buried in the thread somewhere, but I haven't found it yet. CRCRC is 2200uF / 0.47R right?
And would you guys prefer through-hole or SMD (or one of each)?
If you look at the main board JPS64 made for the Aksa Lender Preamp it has the cap Mx and CRCRC needed for a desktop amp. IRF610 works fine with 220uF cap and 10k resistor. The CRCRC provides the C needed so don’t need one right after cap Mx.
AKSA's Lender Preamp with 40Vpp Ouput GB
So glad you got the amp! Hope your health issues are behind you, and again, welcome back!
Alrighty, I've done a preliminary TH layout incorporating the cap multiplier and CRCRC from the Lender preamp. Will start the SMD version this weekend.
Next question: do you guys want board-mounted headphone jack / volume pot or just headers? I personally prefer the latter, which provides more flexibility.
Next question: do you guys want board-mounted headphone jack / volume pot or just headers? I personally prefer the latter, which provides more flexibility.
Welcome back, BDHM. Glad you are well. We have been getting a lot of enjoyment out of the excellent boards you designed. I'd like to try a desktop version, and I would agree that headers make it more flexible.
X, weren't you saying something a few pages back about a new trick you learned--adding inductors to reduce THD? Is that a feature worth exploring for a desktop board?
X, weren't you saying something a few pages back about a new trick you learned--adding inductors to reduce THD? Is that a feature worth exploring for a desktop board?
Yes, if you look at the MoFo amp, it uses a circa 60mH to 100mH (0.5ohm DCR) inductor to store energy and re-release it to basically double the output swing for a given DC rail voltage. This gives more headroom voltage and current capability so that the amp is more efficient and powerful. If you still play music at same SPL, it uses less of the full dynamic range of the power and distortion is lower. And it lets you play louder and into lower impedance loads with less distortion. It takes a pretty large choke even for a headphone amp though. About 20mH - air core is best but that’s a big choke.