Building a DIY amp with NVA amplifier boards

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Starting to plan this music centre built in to a sideboard like enclosure. I will be using better quality wiring between psu and amp board - that orange stuff was found in a 50 metre reel in an old caravan :lol: It is 2.5mm stranded 3 core but is donkeys years old and probably starting to oxidise. I soldered some male spade connectors on to the nva amp boards for ease of connection.

When adding local decoupling (big smoothing cap) at the amp board I can actually solder one of the legs to the amp board. The other leg obviously must go to ground but not on the board itself. Don't want to mix power ground into signal ground. In a NVA system with multiple power amps the 0V all connect up in the preamp at the sockets along the back panel. I thought about copying that but what I have now seems to work. I have soldered the 0V wire from each psu to the 0V bus bar I have linking up each amplifier board. The two 0V wires from the mid bass psu join each other half way along the bus bar between the amp boards they are powering. Same for the tweeter amp psu's. It works and there is absolutely no hum.

Doc wasn't a fan of star earthing so I have tried to avoid that which is hard when you've been doing it that way for so long. Doc would probably have joined all the various psu 0V wires in the psu and then sent one 0V wire from the remote psu to the head section. Choices choices. I remember in an interview Doc said screw up the earth at your peril.
DIY inspired by Richard "The Doc" Dunn RIP

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

I have got the latest version of my amplifier wired up and tested. Now have all six NVA boards in use and six remote PSU's. wiring still all over the place and the two 0V wires from the two added PSU's are joined on the bus bar half way between the two boards they power. Still absolutely zero hum :dance: :dance: :dance: so I must be doing ok but still wonder if the six psu grounds should be joined together in the remote psu and one taken to the head unit and joined to the bus bar between the back panel sockets and the first amp board in the chain :think:

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The psu's aren't arranged tidily but you get the idea, nothing is attached to the chipboard. I am now using all EI frame transformers with twin centre tapped secondary windings. Three transformers and one winding per amplifier board. These transformers are smaller in voltage and VA than my big Canterbury Windings transformers but you wouldn't know it.

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I prefer the presentation with EI transformers it seems. Never tried C cores or R cocers but I can't be bothered. Less hash let through from the mains is bringing out low detail I could not quite resolve before. I don't play loud and the speakers are a very easy load as there are NO components between any of the amps and the drivers, just wire :dance: :dance: The four mid bass amps see the 7.5 ohm impedance of the mid bass driver only and the tweeter amps see the 20 ohm impedance of the four tweeters wired in series and nothing else.

Well, the concept works so time to try adding some psu caps at the load. Then I need an input selector switch and a volume control to sit between all the power amp boards. I can then move on to the phono amp - the head unit is going in the integrated and the psu's are going down at the bottom next to the power amp psu,s. Eventually my CDP psu's will go down there as well and possibly the Turntable psu as well.
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Some observations.

When you change the impedance seen by the amp from 16 ohms to 4 ohms by changing two mid bass wired in series to wired in parallel the volume of the mid bass goes up which wrecks the balance of the speaker (unless you have two tweeters which you can do similar with).

When taking two mid bass wired in series and giving them an amp each instead of sharing the same one the two amps see half the impedance that the sole amplifier did. But the overall volume doesn't go up. So what's the point in doing it ? Well there us an increase in SQ but I am not sure why. Maybe the 16 ohm impedance effects the drivers qes like when you put a resistor in front of a mid bass to increase qts.

When checking the dc offset of the six amps I noticed the tweeter amps had a slightly higher amount. Nothing major but interesting none the less. Must be to do with the high pass filter I have put on the input. :think:

Edit: I removed some bollox that I wrote :roll:
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

After adding local smoothing caps at the amplifier boards my next job is to remove the 10uf coupling caps in my cdp. I then need to put some Wima 3.3uf film coupling caps at the input of the four mid bass power amp boards. The tweeter amps already have 560pf polystyrene coupling caps which together with the 47K resistor to ground already on the nva amp board make up the line level high pass filter for the tweeters. They also do the job of blocking DC ofc which is essential when I have removed the coupling caps from the source.

The coupling caps that I need to put on the input of the four mid bass amp boards are for blocking DC only. A 3.3uf capacitor together with the 47k resistor to ground will form a high pass at 1Hz. This will not roll off the audible bass as even 40hz is over five octaves above 1hz and first order filters roll off at 6dB per octave.

Doing all this will mean that I won't have two high pass filters in the signal chain before the tweeters, only one. In effect that will amount to the removal of one filter (less evil) as everything else is the same (the coupling caps in the mid bass circuit have just being moved from source to amplifier.

The only fly in the ointment MAY be that any DC going through a volume control MIGHT make it noisy in operation. But I won't know that for sure until I get a volume control. Suck it and see as Doc would say.

He advised me that doing a tweeter high pass at line level was no better than doing it at speaker level. I don't know what his motive was there - maybe he thought I was talking about opamp based active line level filters or the fact that the tweeters have no protection anymore. Anyway, I will never know. What I do know is that the music is better doing the high pass filter passively at line level and all it required was adding a cap at the amplifier input. Because of the much larger resistor to ground (47k compared to the speaker's 8 ohms impedance) I get to use a much smaller capacitor. In this range there are polystyrene caps available which are said to be the ultimate for passing signal :dance:

It's a win win for the music, a total no brainer :guiness; :guiness; :guiness;
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

More faffing about with amplifiers and CD players. I decided to remove the two 10 uf Wima caps (one per channel) from my cd player which together with 100K resistors to ground perform the role of blocking DC from the signal before it is passed through the volume control to the power amps.

My CD player before removal :shock:

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Still not finished :roll: . Anyway I removed the two big red caps in the pic below and soldered the silver signal wiring to a leg of the dac chip polystyrene filter caps. There is a single order filter after the dac - I bypassed the rest of the anologue stage coz basically it was not doing the music any good what so ever.

Before

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After

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Signal then goes via some silver wire to my volume control. Here it is in all it's glory :dance: It's that octopus of wires and black resistors just before the bodged in output sockets and lovely TIS cables.

Image
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

So we get to the other end of those TIS cables - the power amps.

No DC blocking in the Naim CD3.5 now so it is now performed on the NVA power amp boards. But instead of two caps in the cdp (one per channel) I now have a cap for each of the six power amp boards and can chose different ones were diffrent amp boards. The tweeter amps already have a polystyrene cap in series with the signal at the input of the power amp board as seen here flying in the air.

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But now the four amp boards for the two mid bass need a capacitor added. I chose some little red wima 3.3uf which in conjunction with the 47k resistor already on the input of the amp board makes a high pass filter from 1Hz therefore blocking DC. See here

Image
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

So why did i do this ? I was bored :lol: No only joking.

Originally the tweeters had a high pass capacitor at the speaker which in conjunction with the drivers impedance makes the filter. I removed that and put the filter at line level before the power amp using the amp boards existing 47k resistor to ground. So I just moved the filter so all the amps having nothing between them and their drivers.

But I still have one more filter in the chain between source and tweeter than I do between source and mid bass (because they have always been run without speaker level low pass filter). Tweeter had 10uf in the CDP and 560pf on the input of the power amp board. Mid bass just had the 10uf in the CDP.

In order to have just one filter between source and the tweeters (like the mid bass) I had to move the shared ones in the cdp to the amp boards. reduced the capacitance as well (3.3uf instead of 10uf).

So what effect has it had ? Moving the cap from the tweeter to line level was really good. More detail and all that. Removing one filter from before the tweeter so it has the same number as the mid bass is even better :dance: More detail but with the added improvement of the frequencies being timed better between mid bass and tweeter.

I have been sat here for hours in awe of what is coming out of my 5" bipole speakers. Simply magnificent :guiness; People always go on about how much better active is than passive ( not Richard though). Well I reckon this is even better coz there are no active filters (opamps and all the associated bollox plus a psu or two to power it) just a capacitor at line level .

Winner winner chicken dinner
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Something I don't understand.

My NVA AP20 has a switch on thump - not as severe as some amps but noticeable non the less. My 6 channel integrated with nva amp boards and remote psu's don't have an audible switch on thump at all. :think:
DIY inspired by Richard "The Doc" Dunn RIP

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Re: Building a DIY amp with NVA amplifier boards

Unread post by savvypaul »

karatestu wrote: Mon Mar 01, 2021 10:02 am Something I don't understand.

My NVA AP20 has a switch on thump - not as severe as some amps but noticeable non the less. My 6 channel integrated with nva amp boards and remote psu's don't have an audible switch on thump at all. :think:
Your AP20 won't have any switch on thump if you follow the NVA user instructions: https://nvahifi.co.uk/pages/user-instructions
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karatestu (Mon Mar 01, 2021 10:19 am)
I am in the hi-fi trade
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Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Thank you Paul. Very wise instructions. I have copied a section from it below;

Powering Back On

Switch off music source (failure to do this may damage your equipment), lower the volume control(s) to minimum on pre-amplifier / integrated amplifier, then power the amplifier on from the switch on the rear panel. You may notice a small 'bump' type noise through the speakers when you power back on. This is normal and will not damage your speakers.


On power up I always switch on the source first - with no music playing obviously. I then turn on the AP20 and I always get the small 'bump' noise through the speakers that you refer to above. It doesn't worry me at all and is quite normal for most amps. My Naim's used to give a much bigger thump at switch on even when switching on in the correct sequence and they had a time delay relay in the preamp.

What I don't understand is my diy "creation" with nva amp boards doesn't do a 'bump' noise at all. Nothing, zilch, nada. Nothing on power down also.
DIY inspired by Richard "The Doc" Dunn RIP

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