Samuel, you can make the boards single sided. The sense transistor (BC847C) must be placed very close to the collector lead of one of the output devices. If its placed on the bottom side between the PCB and the heatsink (assuming you use the same construction as I do), that should work ok. I did not couple the sense transistor to the output transistor with thermal grease - you can also do that but I find it not necesary.
Bogdan, it's set to 300mA about 1 minute after start up( 125mA per pair plus 50mA for the front end) and it goes to c 350mA after the heatsinks get hot driving a 8 ohm load.
With no music, the bias setting is very stable after switch on.
Note in this design, the drivers and the power devices are on the same Heatsinks and the drivers are fullpack TO-220. This is the same construction technique used on the e-Amp.
I have impression that this project is not receiving attention it deserves. Considering my small listening room and high efficiency Tannoy dual concentric loudspeakers, I would probably have enough power even with 15W Ovation sx, but summer temperature in my listening room reaches 28C (no additional heating is required!) and I am not sure that I can provide good enough heatsinking for class A amp. Therefore I decided to build nx instead, some time soon.
What I like about this project:
1) Neither too complex to discourage average diy-er, nor too simple to let performance suffer
2) Practical. There are two pairs of output transistors if you need 100W, but you can probably use a single pair with lower supply rails if you need less power (I’m thinking about using a capacitance multiplier with 35-40V rails )
3) Project is well documented and we are here on the forum not only to get a good amp, but to learn something. It is not diy if you just buy the boards, discussion and knowledge is just as important.
4) Current feedback symmetrical circuit is almost guarantee that builder will have a good sounding amp
5) Overall cost is acceptable for a high quality amp of this level
Questions:
1) If one pair of output transistors is used, do we still need 4R7 stoppers, or we could use jumpers instead
2) Text (page 5) mentions MJL (TO264) output devices but schematic and pics show NJW (TO3P). Pin spacing is the same, but MJL devices have different pin width (max is 1,48mm compared to 1,2mm for NJW). Are the holes on gerber files big enough for both?
I think that fellow diy-er PMI, great gentleman of proven benevolence, has small quantity of surplus boards for a possible GB, so take a look in Commercial Sector/Group Buys some time in the future.
What I like about this project:
1) Neither too complex to discourage average diy-er, nor too simple to let performance suffer
2) Practical. There are two pairs of output transistors if you need 100W, but you can probably use a single pair with lower supply rails if you need less power (I’m thinking about using a capacitance multiplier with 35-40V rails )
3) Project is well documented and we are here on the forum not only to get a good amp, but to learn something. It is not diy if you just buy the boards, discussion and knowledge is just as important.
4) Current feedback symmetrical circuit is almost guarantee that builder will have a good sounding amp
5) Overall cost is acceptable for a high quality amp of this level
Questions:
1) If one pair of output transistors is used, do we still need 4R7 stoppers, or we could use jumpers instead
2) Text (page 5) mentions MJL (TO264) output devices but schematic and pics show NJW (TO3P). Pin spacing is the same, but MJL devices have different pin width (max is 1,48mm compared to 1,2mm for NJW). Are the holes on gerber files big enough for both?
I think that fellow diy-er PMI, great gentleman of proven benevolence, has small quantity of surplus boards for a possible GB, so take a look in Commercial Sector/Group Buys some time in the future.
Thanks for the kind words Ivanlukic.
You could try without the stoppers and use a different output device - if you have a problem put them back again.
Runnin with 1 pair for lower powers is also fine. I used 2 pairs to allow the amp to handle reactive loads, and also to ensure that bybcurrentbshsring like this, the devices were generally operated at higher hFE vs IC part of their characteristic.
Devices are TO3 - my error and thanks for pointing out. I will correct it in the next week or so ( travelling on business now). I will need to check the pin hole on the PCB. I will make this 1.5mm when correct the text if it is not already.
sx-Amp indeed runs hot. The latest one i assembled is at about 55 C with ambient at c 24.
You could try without the stoppers and use a different output device - if you have a problem put them back again.
Runnin with 1 pair for lower powers is also fine. I used 2 pairs to allow the amp to handle reactive loads, and also to ensure that bybcurrentbshsring like this, the devices were generally operated at higher hFE vs IC part of their characteristic.
Devices are TO3 - my error and thanks for pointing out. I will correct it in the next week or so ( travelling on business now). I will need to check the pin hole on the PCB. I will make this 1.5mm when correct the text if it is not already.
sx-Amp indeed runs hot. The latest one i assembled is at about 55 C with ambient at c 24.
Hi Bonsai
Thanks for the reply . I saw in another thread today (SKA amp) that PMI member could possibly run a few boards of your nx amp. I would be interested in buying 2 of them if he is willing to do a few more than for himself ... If he reads this post...
Fab
Correct. I have been posting in the other thread where Bonsai made the layout and documentation available. Very generous of Bonsai, and seemed too good to pass up (to me, anyway...Hi Bonsai
Thanks for the reply . I saw in another thread today (SKA amp) that PMI member could possibly run a few boards of your nx amp. I would be interested in buying 2 of them if he is willing to do a few more than for himself ... If he reads this post...
Fab
)This thread:
sx-Amp and nx-Amp
As far as I know, there are 3-4 people interested, including myself. I have ordered enough boards to have another 3-4 sets not yet spoken for.
I am passing them on at my cost, plus shipping etc., $10/board, or $20/set.
The boards are professionally made, with solder mask and silk screen top and bottom, plated holes, gold over tin. They come from a company in California which specializes in small prototype runs, and which I am using for my through-hole version of the VSSA pcb, which turned out very well, better quality than I expected at that price.
Downside is the leadtime - it takes over two weeks w. shipping to get a small quantity of boards in my hands.
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