Audio Nirvana,Nap 140 clones.

[phf36guzzi]

I have read several threads concerning the Audio Nirvana drive units and Nap140 clone amplifiers. I would like to share my experience. I have built a pair of Audio Nirvana 15 inch ferrites and a pair of Mono Naim Nap 140 clones and this combination is fantastic! this coming from someone who has been listening to an Audio note Oto with type E speakers for the past 20 years. I think some people are concerned with the Audio Nirvanas frequency response of 23 hz-14khz, I am 52 and did an online hearing test before I bought the Nirvana`s and could only hear 12khz if I turned my ear towards the source! Unless you are lucky enough to be a horny adoelesant who can pinpoint the click of a high heal from a 100 yards its unlikely you will miss much above 14 kHz. I have made speakers before but am a novice at amplifier building. The amplifiers work first time by using diagrams I found online. ( I used a dual symmetrical power supply and 22,000 uf 50 volt Keindel Capacitors).
Now I hope someone can help me. ! When I plug a source into the clone amplifiers they work fine, but when I go via the passive preamplifier I just get mains hum (which varies in volume using the volume control) I assume I have an earth loop, The 0v on the clone amps is not connected to earth, but on the passive preamp it is. Any advice would be appreaciated. I am happy to give information to members regarding what I did.

 

[Ian Finch]

The subject of safety and grounding for DIY projects connecting to mains power is a long topic and a serious one. It's not a matter of just a few lines of advice helping to clean up the grounding problem but you must ensure you are working within your national safety guidelines for amateur built appliances - presumably called class 1, meaning fully earthed enclosures and 3-wire mains connections. I realize there are still many 2-wire unearthed mains supplies around the world but you don't show your flag to tell us where you live or local regulations.

First, I suggest you read this site carefully, particularly this amplifier earthing guide and become familiar with the issues and the general idea behind earthing.
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
There is much, much more to study and learn about wiring amplifiers and almost anything about audio for DIY enthusiasts on this site too. Good reading

 

[phf36guzzi]

Thank you, For your reply Ian, One of my priorities was staying alive! both the passive pre amp and the clones have their chassis earthed with 3 core cable back to rcd breakers, and on to a ground spike in the garden!

 

[Ian Finch]

OK, by definition, a passive preamp has no more than a variable resistance in circuit but probably includes a selector and signal routing switches as below, from Goldpoint.

Many commercial music players, laptops etc. are class 2, double insulated and their connectors cannot be grounded until their output cables are fitted to the to the amplifier, so they won't pose a hum problem but if the passive preamplifier is wired independently to the mains supply for some reason, that will probably introduce an earth loop and hum. Is the passive preamp not really passive and powered for some reason?

I'm curious why, as you say, you have not connected the amplifier 0V to earth because the power supply and hence the amplifier itself is then unearthed in your amplifier.

...The 0v on the clone amps is not connected to earth, but on the passive preamp it is....

Is this right? Class 1 equipment must also have all external connectors (the RCA sockets) grounded to mains earth. That's one reason why I posted the ESP article link which includes an earth wiring arrangement (fig.4) for a power amplifier. It also incorporates a massive "loop breaker" diode, resistor and capacitor but these should be omitted for the purpose of locating any earth loop. It may be that the amplifier then hums with whatever you connect to it but that would probably mean your earth wiring in the amplifier is not arranged correctly to a single "star" earth point.

 

[phf36guzzi]

Thank you again Ian .Ok , I think I see the problem, the passive is connected as above, BUT there is a mains connected transformer with dual secondaries that powers each speaker protection circuit in the power amps mounted on the passive amps chassis, the mains power is earthed on the same chassis as RCA cables. So Should I use a diode between these cables and the chassis. The power amplifiers have a star earth point but it is not connected to the chassis, should I use a diode here also to connect this point to earth?.

 

[Ian Finch]

The diode+ parallel cap. and resistor are a last resort if your equipment is poorly wired such that that you have to break direct earth connections in even a simple audio system to avoid hum loops. Ordinarily, it doesn't happen if your equipment earthing is correctly done. Retail audio gear seems to get along just fine without loop breaking, so you don't need to fudge it if you study how it is done. You will need to search and read a bit more though: Douglas Self's book "Audio Power Amplifier Design Handbook" covers earthing well, as should any decent textbook on amplifier design - money well spent.

The NAP140 clone boards follow a slightly different method according to original amplifier wiring where amplifier star earth is on board, at the signal input earth connector and then connected to power supply earth, as is the speaker return. Often, it is actually better to connect signal earth direct from the input socket to star earth and run a twisted pair of signal leads from the socket to the amplifier input terminals. Either way, only earth the power amplifier 0V once at each amplifier's star ground, along with the power supply filter caps.

Make certain the input sockets are fully insulated from the chassis - even if solid metal sockets look cool, the extra earth connection to chassis there definitely isn't. Because there are now 2 supplies, the same goes - earth them and their amplifiers together once only, making a star of both power supply star earth connections and mains protective earth to the chassis protective earth connection bolt - the only point of earth connection to chassis. By ensuring that all earths connect at the same location and potential, very low hum levels are possible - better than older, distributed earthing ideas that you find for example, on NAP140 kits which date back to the original design in the 1980s. Note, original NAP140 was never intended for dual mono and Naim did not make dual mono amplifiers until more recently, from around 2000 and even these were still powered from the one transformer.

"Dual mono" can be an absolute PITA to debug, even if you know what you are doing. If you aren't sure, wire it as a conventional stereo amplifier first and get it hum-free by conventional wiring - then investigate the dual mono arrangement after you have some positive experience.

 

[phf36guzzi]

Ok, Thanks a lot for your help Ian , I will see what I can do now I have some idea, keeping safety my priority.