SX-Amp and NX-Amp

[PMI]

nx-Amp heatsink size

Looks like the heatsink required for one nx-Amp board will be a minimum of 5-inches tall, assuming a common-type heatsink w. vertical fins. The holes for the power transistors are fairly close to the edge of the board, and the leads on the transistors cannot be bent too close to the body of the part. So, the minimum space required is about 6 mm on either side, meaning beyond the outer edge of the circuit board.

 

[Bonsai]

Yes, the transistors do jut out beyond the edge of th PCB. Note also that the PCB edge must rest on the output transistor cases - they act as spacers.

You can also rotate the PCB on your heatsink if that gives you a better fit.

Check out the construction details In the write - up.

Good luck -I am really looking forward to seeing these amps built by you guys up and running and your listening impressions.

 

[PMI]

You can also rotate the PCB on your heatsink if that gives you a better fit...

Yes, perhaps better heat transfer to the heatsink that way from the power transistors. I will try that too, but in general I prefer the input connector to be close to the back of the chassis, with a short cable. Either way, five inches tall, or even six if one does not mind some empty space inside.

 

[pinnocchio]

Looks good! Yesssssssss!

 

[Junie]

Dear PMI,

Kindly include me in:

nx-Amp PCB +nx-Amp PSU+Protection PCB.

Thanks.
Junie

 

[Bonsai]

Further update/correction from my side

Q9 and Q11 are specified as BC547C and 557C which are 45V max Vceo rated, high hFE devices.

Please do not use these devices, but instead use BC546C and BC556C which have a Vceo rating of 65V for Q9 and Q11

For some reason, I had it in my head that the 547 and 557 were 50V Vceo devices - which would in any case be too close for comfort if your rails are running at the max specified value of +-50V.

This is another item I have added to the document correction list - if you see any others, let me know.

Thanks

(data sheet here: http://www.fairchildsemi.com/ds/BC/BC560.pdf)

 

[ivanlukic]

Could BC546B and BC556B used instead? Local shop does not have C rank.

 

[Idefixes]

Could BC546B and BC556B used instead? Local shop does not have C rank.

Not only local shop, "C" rank are obsolete fore 546/556 and difficult to find.

Marc

 

[Bonsai]

Yes, you can use B types if you cannot get C.

I just checked Digikey has them ( Fairchild) . But if you cannot get them where you are, the B will do. NXP does not do TO-92 bipolar small signal anymore so my recommendation is you go with Fairchild ( I have no checked ON).

 

[Project16]

SX Amp (single-sided PCB)

Hello all!

I fully intend to make this amplifier in the SX version, but in its entirety.
I have designed a single-sided pcb that n is not yet checked a hundred percent but I post my work anyway.
When everything is ok (I hope), I'll post the file. Pdf with the consent of the author.

Regards!

 

[PMI]

nx-Amp PCB list, now shipping:
---------------------------------------
$10/board, $20/stereo set, + shipping cost + paypal fee (if applicable)

PMI (2 nx-Amp) received
pinnocchio (2nx-Amp) shipped
fab (2 nx-Amp) shipped

ivanlukic (2)
evette (2)
potepuh (2)
JethroTull (2)
Cambe (2)
Junie (2)

nx-Amp PSU+Protection PCB, expected week of 22 July:
---------------------------------------------------------------------
(cost will the same $10/board, or very close)

PMI (1)
ivanlukic (1)
pinnocchio (2)
fab (2)
evette (0)
potepuh (1)
JethroTull (2)
Cambe (2)
Junie (1)

Please note that the PSU is designed to power BOTH channels, not just one, so there may not be enough PSU boards this round, but more can, and will, be ordered.

 

[PMI]

nx-Amp Silkscreen

@Bonsai: Can you take a look at the bottom layer silkscreen in this area please?
I think I can figure it out, but perhaps you should post a comment, so there is no confusion. Thanks.

 

[jorgovanko]

That place is for BC847C.

 

[PMI]

Corrected List:

nx-Amp PCB list, now shipping:
---------------------------------------
$10/board, $20/stereo set, + shipping cost + paypal fee (if applicable)

PMI (2 nx-Amp) received
pinnocchio (2nx-Amp) shipped
fab (2 nx-Amp) shipped

ivanlukic (2)
evette (2)
potepuh (2)
JethroTull (2)
Cambe (2)
Junie (2)

nx-Amp PSU+Protection PCB, expected week of 22 July:
---------------------------------------------------------------------
(cost will the same $10/board, or very close)

PMI (1)
ivanlukic (1)
pinnocchio (2)
fab (2)
evette (0)
potepuh (1)
JethroTull (2)
Cambe (2)
Junie (2)

Please note that the PSU is designed to power BOTH channels, not just one, so there may not be enough PSU boards this round, but more can, and will, be ordered.

 

[Bonsai]

That place is for BC847C.

Yes that is correct. I will add a picture to the documentation.

 

[Bonsai]

Project16,
Why don't you post this in a new thread, and then I will give you some feedback (and some of the other People can as well). If you keep it here, it will get lost/confused in the nx-Amp build.

 

[gannaji]

Dear Pmi,
Please let me know whether you can include all parts that has to go into the power supply and protection board. If so, I am interested in two sets. Thank you for your efforts.
--g annaji

 

[ivanlukic]

Further update/correction from my side

Q9 and Q11 are specified as BC547C and 557C which are 45V max Vceo rated, high hFE devices.

Please do not use these devices, but instead use BC546C and BC556C which have a Vceo rating of 65V for Q9 and Q11

For some reason, I had it in my head that the 547 and 557 were 50V Vceo devices - which would in any case be too close for comfort if your rails are running at the max specified value of +-50V.

This is another item I have added to the document correction list - if you see any others, let me know.

Thanks

(data sheet here: http://www.fairchildsemi.com/ds/BC/BC560.pdf)

Jorgovanko was also concerned about voltage rating of input transistors but I've seen in some thread that Sakis commented that input transistors can be used at voltage even higher than nominal and that then even sound better. Of course, there is some risk involved. Therefore, I shall use BC546 and BC556, as recommended, but for those who intend to build circuit at lower rail voltages, BC547 and BC557 are still easily available with C rank.

 

[Bonsai]

Ivanlukic,

There is always a risk if you use transistors over their rating. My suggestion is to use the 546 and 556 types. Digikey has Fairchild C types. 19c each for one off.

 

[PMI]

Ivanlukic,

There is always a risk if you use transistors over their rating. My suggestion is to use the 546 and 556 types. Digikey has Fairchild C types. 19c each for one off.

I don't see Fairchild BC556C in stock there (?) Mouser has them marked "obsolete". I believe they are still around, but not from the main distys.

edit: Btw, can you review the spec of the main filter caps in the power supply please?

Figure 10, C6 and C9 are 22 mf (22,000uF), on page 12, 47 mF 50V, and BOM, 667-ECO-S1HP223EA (Panasonic TS-UP series). At 50V nominal supply voltage, and assuming we want to design to the published specifications in the pdf document, a typical transformer rated at 34-35V secondary voltage @ full load, then at light load rail voltage will be around 52V DC. With some transformers even a bit more.