Hi Guys, are there any Idss requirement for the input JFET? I have a few pair of matched J103 K246 @ 3.2mA IDss and I wonder if I can use them? Also can it be configure to drive headphone?
Check out post #111 in this thread. Papa shipped the initial kits with 6 mA Idss and recommended range is 6~8 mA from what I have read here.
Actually he did not recommend above 7 mA Idss as well but was not specific on the lower limit.
Idss has to be high enough to enable the mosfet to open with a 1k resistor. I just checked and there is around 4.6-4.7 volts between gate and rail. You would have to increase the trimmer to 2k with a 3.2 mA idss.
Hi strongbow60. Which 1k resistor are you referring to? R1, the input? Thanks!
I refer to the trimmers, P1 and P2. I think that Nelson hinted at that in an early post in this thread.
Ok Thanks, That makes sense now. And yes he did hit at that. I was puzzled by the 1k R reference rather than pot reference. Cheers!
If I ever do a rev.2 PCB layout of the Almost Clone board (link 1) , (link 2) ...
I'm thinking I might add a jumper wire in series between the power supply input barrel jack and the rest of the circuit. It's quite a small change and won't increase the PCB size at all.
This gives builders the option to connect a Murata 1433428C inductor (330 uH // series R=0.15 // S.R.F.=2.5 MHz // 2.8 amps // $2.49) in series between the SMPS brick and the Mini ACA Almost Clone board. The connection would use flying-leads (hookup wires) and the Murata inductor wouldn't be PCB mounted -- just glued or zip tied or otherwise affixed to the chassis. Notice that the flying leads actually increase the inductance and thus are Not Necessarily Bad.
Don't want the inductor? Solder in a jumper wire. Yes want the inductor? Omit the jumper wire, solder flywires to its pads, connect inductor to flywires. Easy either way. Also easy to conduct Before / After listening tests.
Mess around with the idea in simulation; check whether it has any effect upon high frequency SMPS noise and hash produced by the Mean Well PSU brick. Be sure to include some nonidealities when modeling real components -- these are what ultimately sets (limits) circuit performance. Equivalent Series Inductance ("ESL"), Equivalent Series Resistance ("ESR"), Self Resonant Frequency, and so on.
Or -- if you're ambitions -- do a brand new, ground up PCB layout including an on-PCB footprint for such an inductor. You might even make the PCB footprint flexible, to accept one or two or even three other inductor part-numbers from different manufacturers. Just in case DigiKey and Mouser sell out of the Murata inductor.
I'm thinking I might add a jumper wire in series between the power supply input barrel jack and the rest of the circuit. It's quite a small change and won't increase the PCB size at all.
This gives builders the option to connect a Murata 1433428C inductor (330 uH // series R=0.15 // S.R.F.=2.5 MHz // 2.8 amps // $2.49) in series between the SMPS brick and the Mini ACA Almost Clone board. The connection would use flying-leads (hookup wires) and the Murata inductor wouldn't be PCB mounted -- just glued or zip tied or otherwise affixed to the chassis. Notice that the flying leads actually increase the inductance and thus are Not Necessarily Bad.
Don't want the inductor? Solder in a jumper wire. Yes want the inductor? Omit the jumper wire, solder flywires to its pads, connect inductor to flywires. Easy either way. Also easy to conduct Before / After listening tests.
Mess around with the idea in simulation; check whether it has any effect upon high frequency SMPS noise and hash produced by the Mean Well PSU brick. Be sure to include some nonidealities when modeling real components -- these are what ultimately sets (limits) circuit performance. Equivalent Series Inductance ("ESL"), Equivalent Series Resistance ("ESR"), Self Resonant Frequency, and so on.
Or -- if you're ambitions -- do a brand new, ground up PCB layout including an on-PCB footprint for such an inductor. You might even make the PCB footprint flexible, to accept one or two or even three other inductor part-numbers from different manufacturers. Just in case DigiKey and Mouser sell out of the Murata inductor.
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If one was to design new artwork from the ground up, why not incorporate the PO89ZB circuit right into the new board? Jumper could be used to take it in and out of the circuit…even a switch for that matter (that would be fun)
My suggestions:
- three connection points per channel and jumpers to connect an optional input potentiometer (look my latest ACA mini)
- some more space and distance of the holes for 35VDC 15'000uF caps for the PSU part (C3) for people who dont want to use 25V caps
I have two questions, directed at our fearless leader, Professor Pass:
Dear Professor Pass,
Dear Professor Pass,
- Are the Harris MOSFETs still available anywhere else or do you have the last known stash of them? I could use enough for two more amps now under construction but imposing on you further does not feel right.
- Is there a meaningful audible difference between the Harris parts and others from, say, Vishay Siliconix? I bought four each from DigiKey. Are they suitable for use?
I have arranged for the ACA Mini to be in the store shortly. The essentials kit will consist of pcb and semis and will be quite inexpensive. There will also be a completion kit which has the other parts. At the moment I am testing a cheaper power supply for it.
The remaining Harris parts are to be found at Rochester Electronics. I see a few hundred Harris irf520 and 9520 so maybe someone would like to organize a group buy.
The remaining Harris parts are to be found at Rochester Electronics. I see a few hundred Harris irf520 and 9520 so maybe someone would like to organize a group buy.
Thank you, Papa! So do they need to be matched in any way or can any 520 be used with any 9520? And a cheaper PS would be marvelous! That's a big part of the BOM cost right now.
I like to provide them matched to each other and selected against the Idss of the Jfets. This is not strictly essential, but it provides for more consistent results and value added for finicky audiophiles...
It's nice to hear the parts and kits will be in the store soon. This amp should be enjoyed by a lot more people as it's a great amp. I was fortunate enough to get an almost clone board and really enjoy it. It's driving a set of 2 way horn speakers and it's a very good match.
Instead of going with a cheaper power supply mine is powered by the 5a power supply from the amp camp amp version 1.6. It sounds great and allows there to be one less power supply in the house.
Sometimes there are just too many parts around the house.
Use the DC filter on it, too.
Instead of going with a cheaper power supply mine is powered by the 5a power supply from the amp camp amp version 1.6. It sounds great and allows there to be one less power supply in the house.
Sometimes there are just too many parts around the house.
Use the DC filter on it, too.