More NVA Board Based Stuff

What people are working on at the moment
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Cressy Snr
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#1 More NVA Board Based Stuff

Post by Cressy Snr »

Started yesterday on this project by bending up a chassis and sorting out some kind of layout:
NVABoards.jpeg
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Heatsinks need trimming to fit but that's no great problem.
16000uF of capacitance per rail. The chassis will follow my current styling, with wooden side cheeks. Top will be perforated aluminium as in the valve amp.
This will be a single input, stereo power amp only. I'll be building a separate cathode follower buffer to act as a preamp. This'll be based on an ECC88, 5687, 6N6P or ECC99 (thanks Mr I for the latter 2 valves.) I haven't started to think about that bit yet.
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Nick
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#2 Re: More NVA Board Based Stuff

Post by Nick »

Just pay attention to the voltage on the output of the buffer when turning stuff on.
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Cressy Snr
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#3 Re: More NVA Board Based Stuff

Post by Cressy Snr »

Thanks for that warning Nick.
I’ll put a couple of back-to-back Zeners across the output
to clamp the voltage to a safe level. It’s just a matter of deciding the values to clamp it at, so that on the one hand I don’t introduce distortion and on the other I don’t burn out the input stages.
The BC182s have a max base to collector/emitter voltage of 50V so looks like I’ll have to clamp at 15 - 20V or so.
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Nick
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#4 Re: More NVA Board Based Stuff

Post by Nick »

Yep, and also, the NVA amp seem to have a history of failing if you squint at them, and driving the output to one of the rails may count as that.
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Cressy Snr
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#5 Re: More NVA Board Based Stuff

Post by Cressy Snr »

Spent the last few days trying various internal layouts and have decided on one that should be OK. I've ordered a selector switch and phono sockets for the buffer, if I can be arsed with it. If don’t do the buffer then the parts are still there for an integrated job.
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Cressy Snr
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#6 Re: More NVA Board Based Stuff

Post by Cressy Snr »

OK I’m on with the job. There are six inputs. The cathode follower buffer is MIA for now.
IMG_0415.jpeg
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IMG_0416.jpeg
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Mains toroid is in plus some of the mains wiring. Mains input socket is a filtered item with insulating boot.
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Ant
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#7 Re: More NVA Board Based Stuff

Post by Ant »

You could do a lot worse than the pass b1 buffer or the one ray built if you are in two minds about the cf buffer. Either should prevent the feedback going screwy when the volume pot is turned if you dont want to modify the boards, i presume thats why youre looking at the buffer in the first place, actually thinking on, eds headphone amp/buffer would be another alternative
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Ray P
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#8 Re: More NVA Board Based Stuff

Post by Ray P »

Steve, if you're in need of a buffer I can send you this FoC - i have a spare pair of BUF-03 devices I'll include too. Volume pot is an Alps Blue. It needs a +/-15V supply.

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Cressy Snr
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#9 Re: More NVA Board Based Stuff

Post by Cressy Snr »

Ray P wrote: Sat Apr 27, 2024 8:18 pm Steve, if you're in need of a buffer I can send you this FoC - i have a spare pair of BUF-03 devices I'll include too. Volume pot is an Alps Blue. It needs a +/-15V supply.
Yes please Ray. :)
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Ray P
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#10 Re: More NVA Board Based Stuff

Post by Ray P »

Steve, if you're in need of a buffer I can send you this FoC - i have a spare pair of BUF-03 devices I'll include too. Volume pot is an Alps Blue. It needs a +/-15V supply.

Image
Sorry, I couldn't resist!
simon
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#11 Re: More NVA Board Based Stuff

Post by simon »

I can also offer freebies! I use a DCB1 buffer with a PCB I drafted and I have spare boards. It needs LSK170s but Nick kindly sent me a few to match for a project and I'm sure he wouldn't mind me passing on the 4 needed. It's got a mute delay but needs a bipolar PS. I've probably got some SuperReg boards too you could have.

Edit - too late, I see you're sorted Steve.
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Ray P
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#12 Re: More NVA Board Based Stuff

Post by Ray P »

Cressy Snr wrote: Sat Apr 27, 2024 8:49 pm Yes please Ray. :)
No prob, I'll try to get it posted tomorrow.
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Cressy Snr
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#13 Re: More NVA Board Based Stuff

Post by Cressy Snr »

Progress so far:
IMG_0418.jpeg
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Cressy Snr
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#14 Re: More NVA Board Based Stuff

Post by Cressy Snr »

All wired up:
IMG_0421.jpeg
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Mains transformer is a 30-0-30V, 300VA job. These are bog standard NVA boards. However the input is cap-coupled with Nichicon ‘Muse’ bipolar electrolytics and the speaker outputs have the traditional 10R, 100nF Zobel network across them. Case is being used as the heat sink for the output transistors and is doing a grand job of keeping everything cool. Cap bank is a pair of 10000uF Supertech, slit-foil jobs.
Last edited by Cressy Snr on Mon May 06, 2024 5:52 pm, edited 5 times in total.
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Cressy Snr
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#15 Re: More NVA Board Based Stuff

Post by Cressy Snr »

Perforated top plate fitted:
IMG_0422.jpeg
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And playing in the system:
IMG_0423.jpeg
IMG_0423.jpeg (143.8 KiB) Viewed 279 times
This is the summer amp. :sunny:

Next project will be the buffer preamp courtesy of Ray.
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