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I'm building my son his first amplifier and I'd be grateful for some advice

J

Jon Dennis

Bo Nydal
I'm a newbie here, though I have been lurking for a little while, and have rather limited knowledge and experience electronic engineering-wise. Nonetheless, I have decided to build my son an amplifier to go with the turntable he has recently acquired, for no better reason than my first amplifier was a self build (40-odd years ago) and I want to do the same for/to him. Although mine sounded pretty poor I'd like my son's to be rather better, though I'm not aiming for the stars.

I have recently replaced the amp boards in my NAP140 for a pair of Avondale Qudos boards and so I have a pair of Naim amp boards available around which I could build the new amplifier. I would not want to saddle the lad with an ongoing requirement for NACA5 speaker cable so I'd like to understand whether I can mod the amp boards to remove or sidestep the stability issue without excessive compromise to sound quality. If I can that's great, if not then I'll have to think again about the build approach. If possible I'd like to avoid simply buying and building a kit as I'd like to gain a little more from the experience than just some soldering practice.

I would be very grateful if anyone in the forum can answer this question and, should it be in the affirmative, offer help or advice about the mod itself. If anyone has any helpful suggestions about the wider project (other than "don't even try it, mate") they would also be very welcome. Ditto dire warnings and helpful, amusing or salutary anecdotes.

Thanks, in anticipation, for any help.

Bo
 
You need an inductor (coil) with a damping resistor in parallel at the amp's output. If you can find a circuit diagram for the Avondale NCC200 then you could copy that. I have two coils in a broken Cambridge audio amplifier (somewhere) that i could remove and send you , for free of course. You would need a 15R 2W resistor that you should solder in parallel with the coil (and actually locate it through the middle of the coil.
 
I DONT KNOW IF THE NAP140 BOARDS ARE THE SAME AS THOSE IN NAP 110 , BUT I`VE BEEN USING THE NAP110 AMP WITHOUT THE NACAS FOR MORE THAN 35 YEARS WITH NO STABILITY ISSUE WHATSOEVER . I´M FOND OF KIMBER CABLE ,THOUGH. I GUESS OTHER CABLES MAY ALSO BE SAFE AND MORE PLIABLE THAN THE OBTRUSIVE NACAS.
 
Have you considered something with glowing bottles instead? A stereo integrated amp with push-pull EL34s would be good for about 30-40 W/ch, and wouldn't be too terribly expensive or difficult to lash up.
 
Harthold said:
I DONT KNOW IF THE NAP140 BOARDS ARE THE SAME AS THOSE IN NAP 110 , BUT I`VE BEEN USING THE NAP110 AMP WITHOUT THE NACAS FOR MORE THAN 35 YEARS WITH NO STABILITY ISSUE WHATSOEVER . I´M FOND OF KIMBER CABLE ,THOUGH. I GUESS OTHER CABLES MAY ALSO BE SAFE AND MORE PLIABLE THAN THE OBTRUSIVE NACAS.
Click to expand...

Do you know the "Caps Lock" on you keyboard is stuck on?
 
mega lord said:
You need an inductor (coil) with a damping resistor in parallel at the amp's output. If you can find a circuit diagram for the Avondale NCC200 then you could copy that. I have two coils in a broken Cambridge audio amplifier (somewhere) that i could remove and send you , for free of course. You would need a 15R 2W resistor that you should solder in parallel with the coil (and actually locate it through the middle of the coil.
Click to expand...
That would be very kind, thank you. Can I just check, I assume that these components would be connected between the output +ve and -ve lines ?
Thanks again.
Bo
 
Harthold said:
I DONT KNOW IF THE NAP140 BOARDS ARE THE SAME AS THOSE IN NAP 110 , BUT I`VE BEEN USING THE NAP110 AMP WITHOUT THE NACAS FOR MORE THAN 35 YEARS WITH NO STABILITY ISSUE WHATSOEVER . I´M FOND OF KIMBER CABLE ,THOUGH. I GUESS OTHER CABLES MAY ALSO BE SAFE AND MORE PLIABLE THAN THE OBTRUSIVE NACAS.
Click to expand...
I have no personal experience of instability in these boards but have read warnings galore in Naim documentation and of HiFi fora over the years so I kind of assume that I should account for it as if it is true. That said, I did blow up a Nait a few years back, while using non-Naim speaker cable, and lazily attributed the event to cable related instability without a shred of evidence.
Cheers, Bo
 
Yank said:
Have you considered something with glowing bottles instead? A stereo integrated amp with push-pull EL34s would be good for about 30-40 W/ch, and wouldn't be too terribly expensive or difficult to lash up.
Click to expand...
Actually I have considered this and do find it quite an attractive idea. I'm sure the lad would find the glowing bottles rather cool, certainly at first, even his girlfriend might find them charming perhaps. Also thought that maybe a hybrid with valve pre and solid state power combination might be nice. Any idea where I might find a selection of valve designs to evaluate for my purposes ?
Thanks,
Bo
 
toprepairman said:
How old is your son? Perhaps he'd like to build his own amp.
I built a 2 valve radio when I was 9 (with dad's help, the soldering iron was a copper lump on the end of a metal stick heated on the gas cooker).
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He's 19, away at Uni. He's very bright but up to now hasn't really showed much interest in building stuff. He seems to have begun to take an interest recently, however, so this project might be a way into it for him. We'll see, I guess.
Cheers,
Bo
 
Jon Dennis said:
Actually I have considered this and do find it quite an attractive idea. I'm sure the lad would find the glowing bottles rather cool, certainly at first, even his girlfriend might find them charming perhaps. Also thought that maybe a hybrid with valve pre and solid state power combination might be nice. Any idea where I might find a selection of valve designs to evaluate for my purposes ?
Thanks,
Bo
Click to expand...

I think something like this might be a good starting point:

https://www.lundahltransformers.com/old-fasioned-30w-push-pull-amplifier/

It's essentially the Mullard 5-20, which many hobbyists built in the 1950s.

Unless you need a phono stage, it probably doesn't need further preamplification with line-level sources. Put two channels in one chassis, hang a volume control and selector switch on the front, and call it a day.
 
Jon Dennis said:
That would be very kind, thank you. Can I just check, I assume that these components would be connected between the output +ve and -ve lines ?
Thanks again.
Bo
Click to expand...

Hi Jon,

No they go in series with the +ve. The naim board will have a 0R22 resistor on the output. That will need removing. The zobel network is what goes to ground (resistor and cap in series). The naim board will already have that (from memory).

If you want the coils i have then PM me your address ( i assume you are in the uk) and i will remove them from the Cambridge audio amp and send you them. If you want to make your own then no worries. There is a certain satisfaction gained from making such things yourself. Enjoy.
 
I'd recommend keeping the original NAP140 boards so you can put them back someday if/when you sell it. It may be worth more in its original form than with aftermarkets mods. Or just give your son the NAP140 (returned to stock) and build the Avondale boards into a new amp for yourself.

Then I'd wait for the Nelson Pass ACA (Amp Camp Amp) to be in stock again and build that: https://diyaudiostore.com/products/amp-camp-amp-kit?variant=7072933085218
They are estimating it will be available again in April.

And for the Naim amps, just buy Linn K20 cable by the meter (£6/m) which is identical to NACA4 and much more flexible than NACA5.
 
This site contains affiliate links for which pink fish media may be compensated.
Enamelled Wire (shellac maybe). Maplins used to do it. I’ve probably got some but god knows where :) EBay might be your best bet.
 
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