Hi all,
I've reverse engineered early Naim XS2 schematics (attached). I've got a burned amp and trying to fix it. It was always interesting what's inside, so now I have a chance to check.
I'm sure there are mistakes in the schematics as I don't want to completely disassembly the amp still. Also some parts of the schematics looks a bit strange to me. And it's interesting that influence of the good old NAP140 is really visible here.
Can you please take a look with fresh eyes on the schematics, any thoughts?
I've reverse engineered early Naim XS2 schematics (attached). I've got a burned amp and trying to fix it. It was always interesting what's inside, so now I have a chance to check.
I'm sure there are mistakes in the schematics as I don't want to completely disassembly the amp still. Also some parts of the schematics looks a bit strange to me. And it's interesting that influence of the good old NAP140 is really visible here.
Can you please take a look with fresh eyes on the schematics, any thoughts?
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I'm pretty sure Q608 should be a current source (sink), and R601 wiring looks wrong. R715 / U701 should also connect somewhere.
Other than this section, it looks reasonable though.
Other than this section, it looks reasonable though.
Thank you! I've updated the schematics, new connections are in red:
- R601 is corrected
- Q702/R715 - connection to +
Still not sure that all is fine with Q608, but I don't see any missing links on the pcb..
Interesting story with U701, this is a part of CNY74-4 optocoupler, and diodes are connected with the logic section of the amp. Any idea what's happening there and whats the idea?
- R601 is corrected
- Q702/R715 - connection to +
Still not sure that all is fine with Q608, but I don't see any missing links on the pcb..
Interesting story with U701, this is a part of CNY74-4 optocoupler, and diodes are connected with the logic section of the amp. Any idea what's happening there and whats the idea?
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It's something strange with XS and XS2 amps. The one what I have has XS2 on the box but XS on the amp's back, serial# is the same on the box and on the amp. I've seen the same situations before and people consider such amps as "early xs2", but looks like schematics absolutely the same as for XS. So it's more XS actually.
The pic you posted is for "real" XS2. Attaching a pic of my amp.
Comparing XS and XS2 pics this is what I can say:
1. I don't see a headphones amp in XS, 3.5mm jack is connected directly to pre-out. In XS2 there is a separated phone amp (two tall black caps + 4 transistors with small heatsinks at the middle of the amp), Looks like this is the main difference
2. Ceramic capacitors in the power amp changed to films in XS2. Plus there some additional minor changes but looks like the topology is the same.
3. Different output transistors.. both Sankens, more of less equivalents
4. Preamp is the same
RCA inputs are connected to the PCB with super thin wires so it's true that it's better to use DINs but this setup looks really artificial. In Supernait DIN and RCAs use are connected similarly.
And the transformer in XS is really beautiful )
The pic you posted is for "real" XS2. Attaching a pic of my amp.
Comparing XS and XS2 pics this is what I can say:
1. I don't see a headphones amp in XS, 3.5mm jack is connected directly to pre-out. In XS2 there is a separated phone amp (two tall black caps + 4 transistors with small heatsinks at the middle of the amp), Looks like this is the main difference
2. Ceramic capacitors in the power amp changed to films in XS2. Plus there some additional minor changes but looks like the topology is the same.
3. Different output transistors.. both Sankens, more of less equivalents
4. Preamp is the same
RCA inputs are connected to the PCB with super thin wires so it's true that it's better to use DINs but this setup looks really artificial. In Supernait DIN and RCAs use are connected similarly.
And the transformer in XS is really beautiful )
Attachments
Highly interesting!
Can you find out some of the component values? It seems to me that the basic circuit is not too different to the original Naim amplifier schematic.
Can you find out some of the component values? It seems to me that the basic circuit is not too different to the original Naim amplifier schematic.
Few more small updates, looks like the schematic is fully correct now.
U701 opto is used for a kind of a switch on delay / mute.
And I found a amp with very similar schematic - Apex 45w a/b (second attachment), not much info on it, only that it was published in Everyday Electronics May 87 and got a good reviews. And no part list available for it.
Ok, ready to back this baby to life, smd fan has arrived ).
U701 opto is used for a kind of a switch on delay / mute.
And I found a amp with very similar schematic - Apex 45w a/b (second attachment), not much info on it, only that it was published in Everyday Electronics May 87 and got a good reviews. And no part list available for it.
Ok, ready to back this baby to life, smd fan has arrived ).
Attachments
the topology is not that unusual... the VAS has a cascode, and Q701/702 is a bit wierd, but thats about it
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