Wow that is a nice build Junie!
Very neat!
You need still to do a few tests:-
Measure the volt drop across the VAS 15 Ohm resistors and also across the 1k resistors that feed the VAS transistors.
Be VERY careful though. My meter slipped when I was developing the board and I ended up popping a few resistors and transistors.
This is to check and see that VAS current is right.
Very neat!
You need still to do a few tests:-
Measure the volt drop across the VAS 15 Ohm resistors and also across the 1k resistors that feed the VAS transistors.
Be VERY careful though. My meter slipped when I was developing the board and I ended up popping a few resistors and transistors.
This is to check and see that VAS current is right.
Latest doc update list.
If there are any further comments about the PCB, let me know and I'll include them in the update.
1. Correct circuit –Q9 and Q11 – cannot use BC547 and BC557 devices – their max Vceo is 45V. Use BC546 and BC556 because their Vceo is 65V; OK to use ‘B’ devices
2. Also ok to use lower gain grade devices for TIS transistors KSC3503 and KSA1381 but must be the same gain grade
3. Comment on TIS current – sim’d and measured difference and why this is so - check TIS current – doc says 25mA, sims say 28mA measured is 43mA
5. Talk about option to increase TIS emitter resistors to say 22 or 27 Ohms
6. Check front end buffer load resistors – 4.7k or 10k? has big impact on TIS current
7. Add coil winding details: 8 turns of 2mm thick solid copper wire on 10mm former. Total outside diameter of coil is 14.25mm and total length is 17mm. Add photo as well.
8. Add transistor pin-out diagram page.
9. Correct supply voltage shown on circuit diagram – says +-20V - must say +-50 V maximum
10. Slew rate and small signal rise time numbers - you did not differentiate these two terms clearly in the doc.
11. Discuss Loop compensation - Add a section to cover this with original LTspice plots
12. Clean up main filter capacitor spec in document: 22mfd 50V (remove reference to 47mfd device)
13. Correct circuit diagram of protection circuit – R15 and R16 are 100k (shown as 22k on circuit. Note PCB is correct)
14. Tighten up description of transformer secondary voltage vs load spec. 34-0-34 at 5% regulation will give 49V
15. Check and correct BOM lists following on from above points.
16. Add points and plots to show that the nx-amp input stage does NOT go into class B
17. Change the output transistor holes to 1.6mm on the PCB’s
18. Move the 2.7k logos on the feedback resistors – they are need to be centralized within the resistor ouline
19. Check PSU main capacitor holes – make them a bit bigger
20. Cover capacitive coupling the input and how to do it.
21. Update PCB to remove 100k resistor on input - not needed
22. Check BOM list
23. Propose alternative transistors for the drivers
24. Add procedure to check VAS current.
If there are any further comments about the PCB, let me know and I'll include them in the update.
1. Correct circuit –Q9 and Q11 – cannot use BC547 and BC557 devices – their max Vceo is 45V. Use BC546 and BC556 because their Vceo is 65V; OK to use ‘B’ devices
2. Also ok to use lower gain grade devices for TIS transistors KSC3503 and KSA1381 but must be the same gain grade
3. Comment on TIS current – sim’d and measured difference and why this is so - check TIS current – doc says 25mA, sims say 28mA measured is 43mA
5. Talk about option to increase TIS emitter resistors to say 22 or 27 Ohms
6. Check front end buffer load resistors – 4.7k or 10k? has big impact on TIS current
7. Add coil winding details: 8 turns of 2mm thick solid copper wire on 10mm former. Total outside diameter of coil is 14.25mm and total length is 17mm. Add photo as well.
8. Add transistor pin-out diagram page.
9. Correct supply voltage shown on circuit diagram – says +-20V - must say +-50 V maximum
10. Slew rate and small signal rise time numbers - you did not differentiate these two terms clearly in the doc.
11. Discuss Loop compensation - Add a section to cover this with original LTspice plots
12. Clean up main filter capacitor spec in document: 22mfd 50V (remove reference to 47mfd device)
13. Correct circuit diagram of protection circuit – R15 and R16 are 100k (shown as 22k on circuit. Note PCB is correct)
14. Tighten up description of transformer secondary voltage vs load spec. 34-0-34 at 5% regulation will give 49V
15. Check and correct BOM lists following on from above points.
16. Add points and plots to show that the nx-amp input stage does NOT go into class B
17. Change the output transistor holes to 1.6mm on the PCB’s
18. Move the 2.7k logos on the feedback resistors – they are need to be centralized within the resistor ouline
19. Check PSU main capacitor holes – make them a bit bigger
20. Cover capacitive coupling the input and how to do it.
21. Update PCB to remove 100k resistor on input - not needed
22. Check BOM list
23. Propose alternative transistors for the drivers
24. Add procedure to check VAS current.
Well, SOME do...
There is a fair amount of difference between the PNP and NPN complementary pairs, so that is not even the whole story. Especially the BC546C/BC556C, which may be of most immediate concern.
BC556C ~ 430-450, sample of 5
BC546C ~ 500-520, sample of 6
I plan to run this over, since it may matter the most. Any suggestion about what collector current I should test at?
The BC546B/556B did not even come from the same country, one envelope was labeled Korea, the other one, China. Definitely not the Fairchild that was...
Hi Junie
Have you tested electrically only or listened to it also?
Mine is playing in my living room since last Thursday! I wanted to do some serious listenings before posting here. The main reason for that is that I am using an electrolytic cap for input coupling and I wanted some burn-in ...(even though it is bypassed by a film cap...). Also, I am also performing burn-in at the same time on new DIY speakers so I have lost some references for comparison purpose...
However I can say at this moment that the NX amp:
1) has a great soundstage. From memory in the same level as my Hiraga super class A and my VSSA type amps where it is very good. These 3 amps are all current feedback type.
2) has great dynamics and a solid bass.
3) very clean sound with no exaggerated sibilance.
When I have the chance to compare with my other amps I will keep you posted.
But in general, I personally like this amp so far
Thanks Bonsai and PMI
Nice heatsink by the way Junie ... it seems to be perfect for the bees....
Fab
Hi Fab,
Good morning!
I played music, "Spencer Day" Mystery of You played beautifully
.What you described about the NX amp is the same I have in my mind.
Heatsinks are from Surplus shop, you know in this part of the world where limited materials are available you need to be resourceful
. BR,
Junie
Thanks Andrew and good morning to you.
I'll take note on that and do some measurements later, now I'm preparing to go to office.
I adjusted the DC offset to 0mv and set Iq at around 22mv (across the Re). The lightbulb started to glow at 22mv and heatsink started to get warm so I reckon I will stop there momentarily until I get the right OP (pulled the Sanken's from scrap DENON AVR).
Cheers,
Junie
Well, SOME do...
There is a fair amount of difference between the PNP and NPN complementary pairs, so that is not even the whole story. Especially the BC546C/BC556C, which may be of most immediate concern.
BC556C ~ 430-450, sample of 5
BC546C ~ 500-520, sample of 6
I plan to run this over, since it may matter the most. Any suggestion about what collector current I should test at?
The BC546B/556B did not even come from the same country, one envelope was labeled Korea, the other one, China. Definitely not the Fairchild that was...
My experience for matching with complementary parts is that it is a difficult process based on either luck ...
or acces to a great quantity of parts having multiple manufacturing lots with big HFE variation where you select the ones you need.
In my case I was very lucky with my bc547c/557c with several of them having HFE match within 3 - 5% range. However, they have vce of 45vdc so perfect for the 2 input transistors but not ok for the next voltage shifter stage if you are using more than 45vdc. In my case I use 42vdc supply so close to spec max....
Probably the HFE matching is more critical for the 2 inputs Q compared to the voltage shifter stage...
Fab
for now I am doing it manually, so I can control the current using the adjustable bench supply. Can't do many parts that way, and for now it looks like the BC546C/556C are too far apart. I am going to try to redo the test at the lower current Andrew suggested. Might have better luck with the samples from Dominic...
I set my Iq at 125mA - so a little bit higher than you have there at 22mV across Re.
However, at 100mA like you have now, you should be able to get a good idea on the sound of this amp.
Last edited:
So Junie have used 0,22 RE instead of indicated 0,33 ohms in the doc..
I have used 0,30 ohms and run a little bit higher IQ at about 160ma per transistor for more class A....
Fab
Fab,
The ideal bias current is .026/( total emitter resistance) where the total emitter resistance is Re+re+rbb.
So, the bias current actually goes down as your emitter resistance goes up.
For my build, I used 0.33 Ohms and I over biased at 125 mA per pair where the theoretical number would be something well below 78 mA.
I prefer the high bias - I have the feeling the amp sounds smoother and 'warmer' but I have no proof - just my feeling. Same story with my Ovation 250 - it's also biased quite high and I really like the sound. The e-Amp is biased closer to the ideal. I did not experiment yet with high bias on that one.
Junie, my only concern with 0.22 Re is the thermal stability. I would say you need to check that carefully. With 0.33 Ohms on my heatsinks and 125mA per pair, the bias stability is very good.
The ideal bias current is .026/( total emitter resistance) where the total emitter resistance is Re+re+rbb.
So, the bias current actually goes down as your emitter resistance goes up.
For my build, I used 0.33 Ohms and I over biased at 125 mA per pair where the theoretical number would be something well below 78 mA.
I prefer the high bias - I have the feeling the amp sounds smoother and 'warmer' but I have no proof - just my feeling. Same story with my Ovation 250 - it's also biased quite high and I really like the sound. The e-Amp is biased closer to the ideal. I did not experiment yet with high bias on that one.
Junie, my only concern with 0.22 Re is the thermal stability. I would say you need to check that carefully. With 0.33 Ohms on my heatsinks and 125mA per pair, the bias stability is very good.
Last edited:
PCB Status, FINAL
All board sets have been paid for and shipped. There are 4 Power Supply pcb's left from the second order ( just in case of a power supply "emergency"... well, not really, but some kind of use will emerge, I am sure... ).
The FODM3012 Optocouplers were included for everyone outside of US and Canada.
Partial component sets have shipped this week to Europe, including the PDTA115ET. (I have close to 100 of those, at a cost of a few cents, so hopefully this will not be an issue in the future.)
Anything shipped this week includes a set of KSA3503E transistors and BC546C/BC556C, with spares.
The documentation for the nx-Amplifier is available from Bonsai's web site in a PDF document, including BOM and build instructions, here:
The Ovation nx-Amplifier V2.0
and a list of changes and errata, posted by Bonsai, here:
Documentation Changes
Anyone who received boards earlier and needs a set of KSA3503E and/or BC546C/556C for their build, should send me a pm.
Note that the BC546C/BC556C are old stock, and they will not make closely matched pairs, no matter how many you test. At the 1 mA test current suggested above, the hfe for NPN and PNP is 15-20% apart. I have sampled the parts twice, and results are very consistent, there is no overlap, and they are all on tape and from the same date codes. However, they do test with gains about double the "B" version, so that is a small plus...
Matching the KSA3503E is a lot easier, if you have a few KSA1381E on hand (the latter are still in production, and available from Mouser).
All board sets have been paid for and shipped. There are 4 Power Supply pcb's left from the second order ( just in case of a power supply "emergency"... well, not really, but some kind of use will emerge, I am sure...
).The FODM3012 Optocouplers were included for everyone outside of US and Canada.
Partial component sets have shipped this week to Europe, including the PDTA115ET. (I have close to 100 of those, at a cost of a few cents, so hopefully this will not be an issue in the future.)
Anything shipped this week includes a set of KSA3503E transistors and BC546C/BC556C, with spares.
The documentation for the nx-Amplifier is available from Bonsai's web site in a PDF document, including BOM and build instructions, here:
The Ovation nx-Amplifier V2.0
and a list of changes and errata, posted by Bonsai, here:
Documentation Changes
Anyone who received boards earlier and needs a set of KSA3503E and/or BC546C/556C for their build, should send me a pm.
Note that the BC546C/BC556C are old stock, and they will not make closely matched pairs, no matter how many you test. At the 1 mA test current suggested above, the hfe for NPN and PNP is 15-20% apart. I have sampled the parts twice, and results are very consistent, there is no overlap, and they are all on tape and from the same date codes. However, they do test with gains about double the "B" version, so that is a small plus...
Matching the KSA3503E is a lot easier, if you have a few KSA1381E on hand (the latter are still in production, and available from Mouser).
Don't try to set the bias with the bulb tester in line.
When you remove the bulb tester the bias usually changes and usually it rises when the supply voltage increases.
I always recommend that the bulb tester be removed for bias setting.