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NCC300 Dual-Mono in a big Case

New transformers in place, which brings me to the same point as yesterday afternoon. My mains are currently reading 123VA, resulting in supplies of ±54VDC. My mains shouldn't rise enough to hit the 60VDC maximum.

FYI, both types of transformer are spec'ed to have an input voltage of 115VAC, which explains why a 40VAC secondary was pushing it so high when the mains rose to 125VAC.

NewTransformers.jpg


Remaining steps:
  • Add female spades to the wires going to the NCC300 boards
  • Adjust input stage voltage (must be 5V lower than the supply voltage, to provide a buffer for the regulators)
  • Adjust bias current
  • Wire up RCA input
  • Listening tests!
 
So strange, even with 10% variation in the AC (which I believe must be the globally accepted, at least that's the case in my country), your voltage rating, i.e. 40VAC should be enough for 63V caps.. Normally, it should give something like 56-57 VDC so there is enough headroom. I don't know why with a variation below 5%, like yours, you have such high voltage output.
With 40VAC transformer, 150 watt output is normal but I've read somewhere that Les wanted the output to be something like 130 watts with 37VAC transformers.
If they weren't from Plitron I'd have modified them, unwinding some turns of the wiring till 37VAC was achieved. I'd also do it if I know I'm gonna keep the amps for sure.
Plitron are probably the best toroids out there, the only other alternative for me would be EI cores, professionally made ones.
 
40V transformer with high mains:
40V X 125/115= 43.5V AC

Convert to DC
43.5 X 1.41 = 61.3V DC

Add 5% for transformer regulation (with no load) = 64.4V DC

Knock 0.6V off for the bridge rect diode drop (at almost no load), and you are still around 64V.
 
The amp is done! I decided to adjust each side for 115mA bias, to give it a bit of breathing room. One channel's DC offset is 8.5mV, while the other is just 1mV.

I've hooked it up to a pair of crash test speakers, and I'm utterly gobsmacked! Even with crappy little speakers, I could probably live with it myself. My friend is going to be very, very happy. Thanks for all of your insights along the way, chaps. Here's another shot of the inside, in its completed form:

Complete%20Internal.jpg
 
Mike Hanson said:
The amp is done! I decided to adjust each side for 115mA bias, to give it a bit of breathing room. One channel's DC offset is 8.5mV, while the other is just 1mV.

I've hooked it up to a pair of crash test speakers, and I'm utterly gobsmacked! Even with crappy little speakers, I could probably live with it myself. My friend is going to be very, very happy. Thanks for all of your insights along the way, chaps. Here's another shot of the inside, in its completed form:

Complete%20Internal.jpg
Click to expand...
Nice job Mike looks great
Nice layout and flow to the wiring :cool:

Alan
 
Mike Hanson said:
The amp is done! I decided to adjust each side for 115mA bias, to give it a bit of breathing room. One channel's DC offset is 8.5mV, while the other is just 1mV.

I've hooked it up to a pair of crash test speakers, and I'm utterly gobsmacked! Even with crappy little speakers, I could probably live with it myself. My friend is going to be very, very happy. Thanks for all of your insights along the way, chaps. Here's another shot of the inside, in its completed form:

Complete%20Internal.jpg
Click to expand...
I wanna be your friend ! Nice work.
 
Finally got the 300 rebuilt...

Previously my NCC300 amp had had (quite a few) moments of brilliance but didn't quite pass the "Long Listening Session Get on Tits Test". IMO this was caused by a touch of ss mid forwardness. I did quite a bit of experimenting with the regs to try to ameliorate this, even running without front end regs. The edge was coming from somewhere else.

Therefore I decided to rebuild it with the following "features":
- Swap out a pair of Yamaha EIs for the Les monster EI + his smaller front end EI
- Swap to BHC caps due to some suspicions about the "sound" of the previously used Vishays
- Reinstate the regs but with my mods (approved by Les)
- Keep the modded driver arrangement for the reasons mentioned up thread
- Revised grounding arrangement

I had to change the layout and the grounding scheme so that I could use Les'EI core transformers as the front end transformer only has 2 secondaries i.e. not suitable for a dual mono build. Therefore I decided to had to adopt a grounding scheme like a NAP200 i.e. a single signal star point for both channels and a power star point for each channel (the giant Les EI has two sets of 35-0-35V secondaries). The signal star dictates that the signal 0V connections on the PCBs must be very close together, which means keeping the rather inconvenient double decker arrangement.

Initial listening results are very pleasing indeed and I'm hopeful it will go on to pass the LLSGoT Test in due course :).
At least I now know that this is how Les indended the NCC to be used (excepting my minor mods).
 
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I'm trying hard not get too excited about the latest configuration of my NCC300. Just had a long and loud session and I'm stunned by how good this amp is.
It's incredible how much better it sounds that in its previous configurations.
 
If it isn’t too rude a question, how much are the bits needed to build one of these including a typical stereo chassis, £1500?

Nice tidy build there Mike btw :)
 
Johnjo said:
If it isn’t too rude a question, how much are the bits needed to build one of these including a typical stereo chassis, £1500?

Nice tidy build there Mike btw :)
Click to expand...
To be honest, I have no idea. I ordered the pieces for it in amongst a bunch of other stuff, and I've never asked for an itemized breakdown.
 
Oh yeah, and this particular build (at least the NCC300 and smoothing caps) were purchased from a friend, not directly from Avondale. My own NCC300s had been purchased from Les at couple of years ago. I'm hoping that build wraps up (mostly) this weekend, so I'll finally have my own NCC300 amps to enjoy.
 
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