NAP-140 Clone Amp Kit on eBay

[Flappytango]

Ruwe, I was thinking if my power supply could be part of it but I thought if I was getting the right dc (+-40v) out it must be working. My transformer is an antek dual primary with dual secondary. Primaries are in series for 220V use and I have not connected their common connection. The rest is very much like attaced pic except I have a second capacitor bank connected to the rectifier circuit.

Greg, You are the first to comment on heatsinking. This was not my original heatsink setup but due to the space those darn capacitors are taking up I changed to this setup. Although the sinking is not finned there is a pretty good mass of aluminum and so far it only gets slightly warm. I planned to monitor this once I get my other problems worked out and playing at higher volumes. I will modify as necessary. This might include dumping my current capacitor setup to make space.

Thanks again

 

[barry.childs]

Hi Mate, I don't think you can improve much on that power supply. It has been said that if you lower the amount of smoothing capacitance you lose a bit of bass and gain a bit of treble. You could play with that by simply shorting out some of the caps on one channel and comparing. I don't think the circuit is designed to exceed about 20w RMS per channel which should blow your head off in an average room. I look forward to your pics. Did you build the Pass B1 yourself. I have heard one my friend built and I was very impressed. Regards Barry

 

[Dave S]

You could play with that by simply shorting out some of the caps on one channel and comparing.

Be prepared for the bang when you re-apply power.

I would recommend a C-R-C supply with 4,700uF - 0.1R - 4,700uF per rail. The small R removes most of the high harmonics and junk on the lines.

 

[Ruwe]

The rest is very much like attaced pic except I have a second capacitor bank connected to the rectifier circuit.

Hi, Flappytango.
This is a good circuit, I'm using it too. OK, no centre tap in this case, but then again, the line from the rectifiers going to ground should be connected directly to the star point and not through the zig-zagging wire on your capacitor bank.
I mention that just in case you have different wiring, I can't see on your pictures what you have connected to the star point.

By the way, guys, I've measured my amp, which is using +-30V DC rails and the output power before noticeable clipping on the scope is about 34W/8ohms and 51W/4ohms. With +-40V supply it should reach the 40W originally intended by Naim.
My heatsink is same or smaller than Flappytango's and even during these measurements at full power for several minutes, they never got above 40C.

 

[Flappytango]

Hi,
...What I am thinking is that the only common points between the two channels are the supply rails and the ground...

Good point…. This led me to do some experimenting with the power supply configuration and I have solved the bias issue.

First I hooked up both boards to one capacitor bank 1 (only moving the +- lead of second board and keeping the original grounding) . This did not work at first. It did work when I disconnected power to the capacitor bank 2.

Then i added an additional ground from rectifiers to the star ground, as suggested, and connected everything else as original. This ground line alone did not help.

So now I was wondering if there is a problem with capacitor bank 2 or filter circuit 2. So I connected +- supplies of both boards to bank 2. This worked but again only with power to the other capacitor bank disconnected.

To this point the only thing I haven’t changed was my ground T connection at the filter circuits connecting the two capacitor bank grounds where my star is located. I removed it and hooked everything else up. Eureka! Biasing adjusts as it should, channels behave independently, and no sensitivity to where I place my hands around the wiring.

The bad news is I couldn’t leave well enough alone… I wired it up without filter circuits to see If it would change the hum/buzz issue I have with no inputs connected. It didn’t.

It was getting late and when I final wired everything up an powered it up the fuses blew. I saw immediately but too late that I reversed polarity to one board. I killed at least 2 diodes, output and power transistors but teh autopsy is not done.

Ok, well no smoke or burns so I am pretty sure I can fix this without much proble. Still happy to have my mystery solved.


here is a couple of pics what the rectifier looks like now. The rectifiers are the point the two capaictor banks connect ground and this has a line running out to the star ground.
and the offending T ground

 

[Ruwe]

Grounding is major problem, glad you solved it!
... and sorry that you "overcooked" the amp.
Regards.

 

[Flappytango]

So while i was ordering some new parts i started thinking about changing my current setup or buliding a second stereo NAP140...

I have this Denon PMA-925 (i plucked it out of a recycle bin), see pic. Only 1 channel works. I determined it is something to do with one channel of the internal preamp but on top of that the speaker relays dont always behave. so i think i use it for parts.

Interesting power supply. Two transformers that parallel into a single rectifier to give +-49V. This feeds two 12000uf caps.

I was thinking about using these tranformers and turning then into dual mono. I could set them up in with thier own rectifers and caps. I could use the caps i have (100VDC) in my current amp but i dont think there is room in the case. So investigating options.

So i have some capacitor questions.

For the nap140 what is the minimum capacitance i would want to use? and what is the max (the uf value where going larger makes no difference)?

Also cap voltage rating. For example for my +-38VDC supply it is safe to use 40VDC rated caps right? like these, the spec sheet says peak voltage of 1.15xrated.
Digi-Key - 495-4222-ND (Manufacturer - B41456B7229M)

thanks

 

[Ruwe]

For the nap140 what is the minimum capacitance i would want to use? and what is the max (the uf value where going larger makes no difference)?

Also cap voltage rating. For example for my +-38VDC supply it is safe to use 40VDC rated caps right? like these, the spec sheet says peak voltage of 1.15xrated.
thanks

To my knowledge 10000uF per rail is the standard for this amp, but more capacitance will not hurt. For dual mono you'll need 4 pieces, and if you buy those 22000uF ones, you'll have 4 times more than the usual. Considering the quality and the good price of the Epcos I would go for them.

The voltage is borderline, but is still below 40V, so why not. The only problem - if the voltage in the electric grid in your area changes ... then you may exceed the rating for these caps during peaks (your secondaries will follow). From 220V to 240V is almost 10% difference, and that's not unusual fluctuation. If you always measure below +-40V, especially in late evenings, then you're OK. "1.15xrated" is the manufacturer fool proof practice, IMO if they are rated for 40V they'll work reliably at 40V.

 

[Mr_Dave]

Well I've finally got my kit assembled and working! Pretty good these things by all accounts. Mine came with the Sanken 2SC3858 output transistors. Its running with a 30mA bias current @ 42v with 60,000uF per channel.

Somehow I was bagged a pair of the long blue boards from ebay for £10!

Its got really deep bass, more than my Linn LK85, and I think maybe a bit too heavy on the bass really! Are there any recommendations for component values to peg it back a tad? I'm running it through a little valve pre-amp I got from the same seller: Buffer 6N3 Tube Preamplifier AMP +220V/110V Transformer on eBay (end time 15-Mar-11 10:42:36 GMT)

Its been a good 15 years since I last built an amp.... ohh it takes me back!

Dave

 

[Ruwe]

Its got really deep bass, more than my Linn LK85, and I think maybe a bit too heavy on the bass really! Are there any recommendations for component values to peg it back a tad?

Hi Dave,
I had the same findings and what worked for me was changing a little bit the values of the input resistors. It gave some noticeable boost in the higher frequencies for better balance. IMO, Naim amps are slightly on the darker side anyways, being (perhaps) designed with the idea to compensate for the player and the speakers in an all-Naim system.

You probably have input resistors like 4.7k to 22k, or 2.7k to 24k depending on your board version. My suggestion is to change them to 1.5k to 25.5k (you can make 25.5k by paralleling 47k with 56k). The series resistor is working as a low pass filter with the 330pF (220pF) input capacitor to ground, generally speaking.

The change will allow wider bandwidth. The amp sounds more refreshing, especially if it's additionally choked with higher output impedance from the source (probably in your system with a tube preamp)

If you decide that it's still not enough, you may want to change the input pair transistors and the VAS transistor with some higher gain devices. I found ZTX692A/ZTX792A to be expensive but very suitable. That will reduce the remaining distortion and will remove most of the loading of the differential pair and your source (preamp). So, more detail will be added to the sound, and the lower notes will be cleaner and leaner.

 

[Flappytango]

parts source

Hi,

I just thought i would tell you guys about this ebay seller..

Thaishopetc items - Get great deals on Electronic Parts, ICs items on eBay Stores!

I have ordered from them twice to buy Toshiba 2SC5200 output transistors.
They have great prices on them and crazy fast shipping considering they are in thailand.

for example: i ordered two 2SC5200 for $4.90 including shipping on the 2nd and they arrived on the 7th to sweden! the same fast shiping on my first order also.they have other components as well.

cheers

 

[Mr_Dave]

Hi Ruwe, fantastic info, thanks! I've got 4.7k, 22k and 330pF, quite right. I'm going to leave it for a few days and do some more listening (I've hardly used the thing yet!) and see if I still think the same.

I'm pretty sure I will, and I know my speakers aren't known for their bass and I've always wanted more....... but perhaps not this much.

With regards to the input pair/VAS, the ones that came with the kit were BC546/2N5551. Its been a while since I did ANYTHING with electronics.... but we're talking input Q1/Q2 and Q3 for the VAS aren't we...? Its been 15 years since my electronics degree!! I think I've forgotten absolutely everything!

An externally hosted image should be here but it was not working when we last tested it.

Thats the same layout as my amp, a few different transistors here and there, but its the same design

I'm amazed how detailed its able to sound. I've got some Led Zep on at the moment, and I just paused it wondering what the funny squeek was.... its his fingers running up the strings on the frets...

All the best,
Dave

 

[Ruwe]

Hi Dave,
That's right - Q1, Q2, and Q3.
About the sound, after I built this amp I never tried another one (3rd year already) ... and I'm very fussy about sonics. Before I used to build every working schematic that I could find, to compare, upgrade etc... total "audiophilia nervosa". Not anymore, this one I like a lot.
Enjoy!
Regards

 

[gaborbela]

These is a great amp nice mids and solid bass.
I built (tested) several version, now I want to test the Chrome Bumper with Sanken power transistors.
To me the NCC sounded the best until now, but I want to test the modified version.
That was modified by Greg Ball (SKA designer)
Greetings gabor

 

[Flappytango]

gaborela,

where did you find first that schematic? was there a thread with it? i didnt find it looking for chrome bumper...

 

[gaborbela]

Hello
Those are not the Chrome bumper circuit.
I will look at for you!
Greetings

 

[gaborbela]

Chrome Bumper

Hello

Here is the website.
http://www.acoustica.org.uk/t/naim/power_amps.html
Picture of the Chrome Bumper (one of the best Naim amp at that time)
I will test it that to.
I like the NCC200 great amp, all do I just built the clone not the orig kit.
I tested the driver transistor what the CB use , I can say that is a very good sounding driver transistor,
Only problem the big hFE difference between the PNP & NPN.
I have to play with the signal transistors to get read of the offset.

Greetings

 

[gaborbela]

Hello
Please not be fooled by the look of the amplifier !
Those are Welwyn high quality resistors! Surly the capacitors can be upgraded Elna Silmic or so.
I have the Sanken (original) and those driver, I want to give a try.
My NCC200 sound far better than the Ebay kit.
Actually still have that kit, need some capacitors at the protection, I took the out.
I can sell it $15 plus shipping a pair if someone interested. I paid $65 on that time plus shipping.
I can provide picture upon interest.
Greetings Gabor

 

[GruZZ]

Good day! I am the owner of the clone nap 140. voltage after the rectifier bridge 56v + - Can I use my nap140 stable? What should you do to expose the bias in 5mv? Help! Thanks in

 

[Bengali]

Hi,

is there much of a difference betweenthe avondale pcb's and the gigaworks kit?

does the gigaworks np140 kit stock kit sound good or requires lot of component replacement or modification. are they using fake transistors(?)

thanks.