advertisement


Naim clones on Ebay

I've got my boards working now. I didn't realise the signal ground had to be connected to the supply ground (D'oh!). DC offset on one board is 8mV but I didn't get any further. Importantly, they're alive any they play music!
 
Here's a couple of pictures of my clone power amp.

300VA transformer, dual rectifiers, 54mF total capacitance. It was a real challenge getting everything to fit. DC offset is approx 6mV on both boards, bias current is 20mA.

http://img139.imageshack.us/my.php?image=31102008177kp2.jpg
http://img112.imageshack.us/my.php?image=31102008178bg5.jpg

The Elna's on the boards have been bypassed, as have the resovoir caps. I will change Q5 and mount on the heatsinks in a few weeks time, I'm just happy they work for now.

The only issue is the transformer is supposed to be 33.5V AC out, but after rectification I get about 53V per rail....
 
colin Barron said:
Avondale cap6 boards would give an improvement.
Click to expand...
Thanks Colin, I'll bear that in mind as I get to know more about the many options discussed on this thread. Sorry, I'm editing this after having had a little look at the boards you mention. They fit completely with the philosophy of Dejan Veselinovic sometimes found contributing on TNT-audio, that I followed to learn the dual rectifier trick.

I'm very new to the Naim-sound, or whatever I need to call it, having been raised on Cyrus amps. Building kits and clones is a hobby. I need to get two transformers that have matching specs as a first priority on this build, but have been impressed enough to upgrade the source, leads and speakers to my best set-up to test the thing further (not that they're great shakes by the standards of most on this forum) - it sounds wonderful, by the way.

I've left pieces of speaker wire protruding at the points of measurement to get the 6-10mV recommended, which has made it a lot easier to adjust as its warmed-up (currently sitting at 7.9mV for both channels). The sound has altered a lot over the past week, so I've left it on to help settle it down. The effect of doing this is to fill out the bass a bit.
 
I ended up with 500va transformers, they have dual secondaries joined together which are supposed to be better. Les sells good transformers, canterbury and souter are other makes people rave about. Make sure upgrades are compatible with the amp you want to end up with.
 
Thanks again Colin for your kind advice. I can only imagine that the amps would benefit hugely from the improved current supply. A 500VA transformer would provide 5 times as much current as the amp's getting at the moment from my Antrim units, which also have dual secondaries joined through dual bridge rectifiers.

The amp is noticeably quieter than most of my other amps, and seems quite dynamic. It gets a little lost on busy rock but works brilliantly with Stevie Nicks' luscious tones. I guess the power supply recommendations would go a long way to address these issues.
 
A couple of useful improvements to this amp were to directly connect the speaker cable to the board and to smooth the mains.

No matter how good the connections, they can't beat direct connection, so to achieve this with the Kimber 4TC I used I first tightly wound 1 cm of the bare ends of this multi-strand cable together using needle nose pliers before soldering together with lots of lead solder. Once this was cool I filed the end to a fine tooth profile, which was just wide enough to fit in the PCB, and soldered it in place.

I noticed some improvement partly because we were on 'Sunday' power, the one day of the week when most any hi-fi sounds better in these parts. There's fairly lousy regulation of the power in NZ, as its mostly generated in hydro dams on the South Island and needs to be rectified over the Cook Straight on its way north. Listening today (Monday) the amp had lost some of its gloss. (I reckon the best power is in Norway - and this might be a nice topic for a thread)

The plaster over this broken leg was to use a transient voltage suppressor and VDR (mains rated) over the live to neutral input (Be careful! The mains needs to be respected at all times so make sure every-thing's powered down if you try this). This helped smooth the transformer buzz down a bit. I like the depth and pin-point focus this amp offers. It works well with Faithless too, I've noticed. The best you can hope from with any hi-fi is to allow you in to the recording without worrying about the components, which this set-up is certainly already getting close to.

My CD player is a Russ Andrews breathed on Yamaha CDX 670 with burr brown op-amps and output capacitors swapped-out for RATA supersound film caps. The speakers are ancient Mission monitors with tiny bass units which have similarly been modded and the caps replaced with Kimber caps with iron-dust core inductors attached to the bass units. I'm using Tara Labs link cables to connect between bass and treble units.
 
I like to define things in single words, like the hitch-hiker's guide. Kiwi's are nonchalant and this amp is stark! It bares open the recording and savages some of my older dodgy CDs. I swapped over to full Kimber cable, using 4PR for the interconnects and my home-brew extension cable made-up of MK wall-sockets and 10 metres of Russ Andrews earth wire. I switched the power leads for Yello and Reference powercords from Russ Andrews, and had to dig out my Sony CD player since this has an IEC socket on the back to allow me to use the MK plugged powercords. Finally, I dug out my old QED digit which hasn't seen daylight for about 3 years and plugged that in with 4PR cable. The Digit has been re-capped with Os-Cons throughout and uses a BB OPA 2604 in the analogue output stage (same as the Sony).
The sound has more beef - probably because the interconnects are only 20cm long and Russ Andrews always recommended short leads for passive pre-amps to maintain bass. My 'home-grown' 99.99% silver cords were trialled, but didn't sound much better than the Kimber interconnects.

The set-up is retrieving lots of detail, but stark audio is a new experience for me and contrasts with my normal coloured musical experience. I really wish I had my Kevlar bass, audax tweeter DIY speakers which are in someone's attic 14,000km away, because I'm sure they love the company and would likely pitch the system over the edge and into communication mode.

Good hi-fi, but I wonder if anyone has measured the distortion profile for this amp, and whether 2nd order harmonics dominate.

http://www.flickr.com/photos/75348731@N03/6774128429/in/photostream
 
Just to say thanks to Colin for putting me on to the power supply on this amp. A review of the power supply showed that the left channel was using just 2200uF of reservoir capacitance per side, as compared with 9400uF on the right channel. Digging around in my bit box for some spare caps and re-routing the wires, I was able to increase this to 8800uF per side.
Turning the amp back on, the effect was immediate with stronger bass and much better balance.
I'm not likely ever going to be able to justify 500VAC transformers and recommended capacitors Colin recommends, but am very happy with the improvement in sound and can fully see where he's coming from with this upgrade. One very happy camper. No longer stark, the sound has a newly discovered depth and solidity.
 
This site contains affiliate links for which pink fish media may be compensated.
kropo said:
I was wondering new power amp to replace my modded diy gainclone power amp.

Nap140 clone from ebay
http://item.mobileweb.ebay.com/viewitem?itemId=150490754451
or Neil McBride Nap135/250 clones
http://www.neilmcbride.co.uk/jknamps.html

I was wondering which one might be better?

Nap140 is kit, so it has almost everything and for Nap135 I need to find everyhing includin pcb.

Which one might be better? Meaning sound and possibilities to build one. :)
Click to expand...

You won't be able to find pcbs from Neil McB that was a long time ago. You can etch your own using the pdfs available...but the best bet is to look here at the latest HackerNap buy - I think it is still open...
 
This site contains affiliate links for which pink fish media may be compensated.
Really? Ok, then probably best to check those out. Still have some time untill group ordering ends. :) is there any topics about building hackernaps?
 
You must log in or register to reply here.


advertisement


Back
Top