Ahh Richard, you are observant - thank you for raising that question.
If the front end buffer transistor emitter load resistors are 10 k ( the correct value) and the current summing and level shifter stand off resistors all 15 Ohms, the TIS standing current is nominally 20 mA +- 5 mA.
The reason for all the confusion the in some of the earlier prototyping, I used 4k7 buffer load resistors, then 10 k then changed the level shifter stand off resistors to 33 ohms.
The latest circuit version has the correct resistor values.
For the total standing current of the amplifier, I just set it to 300mA. This is higher than the 0.026/Re(tot) that Oliver's analysis suggests, but it sounded better to my ears so that's why it's biased high.
Note, the voltage drop across the 15 Ohm rail filter resistors should be about 0.45V and not 0.75V. I will correct this in the doc next week, along with Bill_P's points above.
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Not observant. Just the result of trying to sim it.
Thanks Andrew. Everything makes sense now.
Here's another item: on page 23 the large power supply capacitors are listed as 47000uF but the build actually uses 22000uF.
On page 37 the third bullet says to match Q7 to Q7, should be Q6 to Q7. Two paragraphs below that is a sentence for matching Q7 to Q8 that should also be Q7 to Q6.
Hi Bonsaï
Maybe is too late or too much work given the small size of the pcb but here some items to consider if you happen to modify the Gerber files for the layout of the amp pcb:
1) include an optional series resistor footprint with the VBE multiplier for those who wants to experiment with MOSFET outputs.... And if so footprint for Zener diode for MOSFET gate....
2) more room to fit a 1000uf (63v) filter cap for the output transistors.
But I realize that it is out of the scope of your original project...
Fab
Maybe is too late or too much work given the small size of the pcb but here some items to consider if you happen to modify the Gerber files for the layout of the amp pcb:
1) include an optional series resistor footprint with the VBE multiplier for those who wants to experiment with MOSFET outputs.... And if so footprint for Zener diode for MOSFET gate....
2) more room to fit a 1000uf (63v) filter cap for the output transistors.
But I realize that it is out of the scope of your original project...
Fab
I have updated the write up and made the changes to the layout files based on all the feedback received over the last few months.
On my website is the write-up, along with the Gerbers Ovation nx-Amplifier: A 100 W class AB Current Feedback Amplifier
I'd like to take this opportunity to thank PMI, Bill_P, fab, Esperado, Junie and the other contributors for their comments and feedback.
(mods, how do I put the links into the first post of this thread?)
On my website is the write-up, along with the Gerbers Ovation nx-Amplifier: A 100 W class AB Current Feedback Amplifier
I'd like to take this opportunity to thank PMI, Bill_P, fab, Esperado, Junie and the other contributors for their comments and feedback.
(mods, how do I put the links into the first post of this thread?)
Hi Bonsai,
the edit button always there in post #1(on the left Quote button)
The thread starter can edit first post at anytime
now I'm downloading the updated write up
How to open gerbers files? what software must be used?
I know this was answered but no software is recommended yet.
Regards
the edit button always there in post #1(on the left Quote button)
The thread starter can edit first post at anytime
now I'm downloading the updated write up
How to open gerbers files? what software must be used?
I know this was answered but no software is recommended yet.
Regards
How much has changed on the layout?
Has the BOM changed?
There are several people who never finished building the last revision of the boards, probably around 8~9 out of the 10~11 or so who received the last board, I would say.
If the new directions refer to a new layout, that may be a problem.
Should the old boards be assembled according to the new write-up, or the old?
Hi Bonsai,
the edit button always there in post #1(on the left Quote button)
The thread starter can edit first post at anytime
now I'm downloading the updated write up
How to open gerbers files? what software must be used?
I know this was answered but no software is recommended yet.
Regards
John,
You can down load Gerber viewers from the web - just google it - there are quite a few out there.
Thanks it works (the one that need free registration with email) now I can see or print the boards
but some parts are not available here, but I think PMI can help me
Regards
I will probably want a spare set for the future. Even if not that many people sign up, I can just add a few boards to another order.2 additional stereo sets ( amp only) for me since it sounds so good
Fab
Has the BOM in the new document been updated? I have not had a chance to compare the old and new documents.
There were quite a few component availability issues, especially outside the US. Even some of the resistors were hard to get, the FODM3012, at least one or two other parts.
Unless we put what we know on one list in one place, new people could easily pay more for shipping parts from 3 sources than the cost of parts (!).
I have plenty of the KSC3503E, and the BC556C, if those are still on the BOM, and some PDTA115ET,215, which were not available in the US except by the reel.
The power transistors NJW3281/NJW1302, last I checked, were least expensive from the ON Semiconductor online store, and after that, on "promotional" sale at Newark/Farnell.
I have not found any easily available 22,000uFd caps for a power supply rated at a nominal 50V, because I would prefer the cap rating to be over 50V, to allow for line and load regulation. 18,000uFd/63V was the closest that fit, and in stock at Mouser or Newark.
... and I am sure I am forgetting a few things,
The latest BOM shows KSC3503D and KSA1381E, a mismatch that is advised against in a note at the bottom of the BOM chart. The lack of general availability for the KSC3503E is the single biggest component sourcing headache in the project. Were it not for your kindness in providing some KSC3503E's, I would not be able to build the amplifier, at least not with matching parts.
BC556C transistors are no longer in the BOM. This is just as well since they are hard to find and the ones you have seem to have extremely low gain for a 'C' version and as such they can't be easily matched.
I am using a substitute for the PDTA115ET,215 - Rohm DTA115EKA.
For the capacitors, I would rather see the board changed to accept some of the taller 4 or 5 pin capacitors. This would allow the use of 63 volt parts without a reduction in capacitance. In fact the capacitance could be raised above 22,000uF if desired.
My boards are built and the chassis is partially drilled. I am waiting for the power transformer from Antek. It should be in stock in two or three weeks and then I can finish up the build.
Bill, I'll correct that KSC/KSA in about an hour and reload it up.
I've just loaded up the ( 10 mins ago) doc with lots of small errors corrected. I guess I missed that one - thanks for pointing it out.
The Rohm parts make good substitutes and there should be no issues as long as they are pin for pin compatible and the resistor values are the same.
I've just loaded up the ( 10 mins ago) doc with lots of small errors corrected. I guess I missed that one - thanks for pointing it out.
The Rohm parts make good substitutes and there should be no issues as long as they are pin for pin compatible and the resistor values are the same.