NAP-140 Clone Amp Kit on eBay

Ok i have built my psu. Its a 500 va 0-25 x2 unit running into a seperate bridge rectifier per channel. the + on one tied to the negative of the other.I have 22,000 uf between each rail and 0v. My issue is that i get about 26 v rail to neg without caps and 36v (what i was expecting) with caps. Is this right, i am guessing it is cos obviously i should get 25v x 1.41.

Almost ready to fire em up!!
 
Current stage, progressed slowed a great deal my deadly man flu
 

Attachments

  • heatsinkjpg.jpg
    heatsinkjpg.jpg
    65.4 KB · Views: 7,195
Fill,

First things first, stop, turn all off and take a step back. Then without us influencing you draw us a diagram of exactly what you are doing, or link if you have one. Dont want to break anything, especially you, though it will cure your cold :D

Both yourself and Dave, nice looking work there ;)

Brian
 
Did just that, i was getting stressed which is always when things go wrong. So i sat and watched two ebisodes of 'The Long way down' which sort of chilled me out.

Well i am 99% sure my psu is cool, i have got twin secondary windings going into 2 bridge rectifers. The plus of one is tied to the minus of the other as per :-

http://www.tnt-audio.com/clinica/ssps2_e.html


I have got a 22,000 uf between each rail. This gives me a +37v and a -37v in comparison to the tied togther zero rail.

All this is working fine.

My issue is i have never measure current apart from using a clamp meter at work. From what i have read i have to put the meter effectively like a fuse in the +37v rail. It appears i blew the fuse in the metre on doing this i dont know why.

Any steps i should do or avoid whislt trying to measure the bias current?

Many thanks,

Fil
 
OK, it sounds like what you are doing is right, connecting all the amp up, remove the positive supply to the amp boards and then connect the meter in series.

A few gotchas here though!

1) have the meter on Amps
2) make sure the leads are plugged into the amp sockets on the meter and not voltage
3) nothing should be connected, no input or output form the amp

I have blown a fuse on one of those little yellow meters (200mA MAX) before (goes off nice and bright:D). If you are sure what you are doing is right there might be something wrong on the boards, ie a short of some sort, but if you are set to current on the meter and plugged in right it should be ok.

Get it plugged in and post up a photo or two of the meter and where the wires go before you turn on and we can look at it. Im being totally selfish ;) I want a review.
 
Its a little too high, but not stupidly so, but it is something Les reported having issues with on his boards he tried.

You cant have let it run for very long, leave it on for 20 minutes with the meter in series, my amp drifted for a while, had to keep tweaking the bias.
 
Haha i just logged on the other forum so know you did run for 20 minutes, but keep it to 38mA, perhaps lower. Do me a favour and keep to that forum, besides, no insults meant but for this the other place has the complete geeks ;)

Come back here and update when you are all happy an running.

See you there :)
 
burnt-in and on a friends system

I thought that I would return and give you an update on the amp after a few weeks of listening. Took it around to a friends house; he has an open mind and lots of expensive gear (huge tannoy boxes etc) and we all knew that it left his collection of expensive tube gear standing in every way aside from a slight soulfulness (distortion!!???). Detail was huge and accurate; timing was great as you would expect and imaging was exceptional (compared to valve amps - I normally use valve amps also). I have always thought that Naim was supposed to be a quite sterile sound, not in this incarnation but I have little experience with Naim gear so what do I know? Everybody that heard it, after it had warmed up, knew - including people that know a lot about audio. An ancient design, generic one might say but the knees were jiggling away and there was a recognition that it really sounded good. I thought it was pretty good but with my electrostatic midrange beauty I did not get the accuracy and speed of the base. After the session everybody wanted one, really wanted one!
I hope that this is enough to encourage you
PS I have no idea who tubehunter is if that thought had crossed your mind.
 
Member
Joined 2005
Paid Member
DaveS-

You seem to have been through the gamut of Amps I had my eyes on - the P3A, GB150, AKSA55 - fair to assume that you prefer the Naim Incarnate if you have donated its case?

I have the P101, UCD400, a number of Traipaths, Gainclones etc...

I prefer my P101 heavily biased with lower rails over all the above.


Have you compared your line of amps with higher bias? Make a bit of difference.

I have since built a Krell clone that is looking like it may unseat the P101. All class A and it rules the roost.

Bias at 38ma? I havemy Krell at 630ma, the P101 at just under 250ma...

I hear the P3A heavily biased is quite nice (need monster sinks), and that it is very close the the JLH Class A in design.